Studies and reports in hydrology 41

Recent titles in this senes:

20. 21.* 22. 23. 24.

25. 26. 27. 28. 29. 30. 31.

32. 33. 34.

35. 36. 37. 38. 39. 40. 41.

Hydrological maps. Co-edition Unesco- WMO. World catalogue o f very large floods/Répertoire mondial des très fortes crues. Floodflow computation. Methods compiled from world experience. Water quality surveys. Effects o f urbanization and industrialization on the hydrological regime and on water quality. Proceedings o f the Amsterdam Symposium. October 1977/Effets de l’urbanisation et de l’industrialisation sur le régime hydrologique et sur la qualité de l’eau. Actes du Colloque d’Amsterdam. Octobre 1977. Co-edition IAHS-Unesco - Coédition AISH-Unesco. World water balance and water resources o f the earth. (English edition). Impact o f urbanization and industrialization on water resources planning and management. Socio-economic aspects o f urban hydrology. Casebook of methods of computation of quantitative changes in the hydrological regime o f river basins due to human activities. Surface water and ground-water interaction. Aquifer contamination and protection. Methods of computation of the water balance of large lakes and reservoirs.

Vol. I Methodology Vol. II Case studies (in preparation)

Application of results from representative and experimental basins. Groundwater in hard rocks. (In preparation). Groundwater Models.

Sedimentation Problems in River Basins. Methods of computation of low stream flow. Proceedings o f the Leningrad Symposium on specific aspects of hydrological computations for water projects (Russian). Methods of hydrological computations for water projects. Hydrological aspects of drought. (In preparation). Guidebook t o studies of land subsidence due t o groundwater withdrawal. Guide t o the hydrology o f carbonate rocks.

Vol. I Concepts, problems and methods o f analysis with examples o f their application.

- * Quadrilingual publication: English-French-Spanish-Russian.

For details o f the complete series please see the l i s t printed at the end o f this work.

Guide to the hydrology of carbonate rocks

Begun originally by a Working Group during the International Hydrological Decade, with the technical secretariat provided by the Food and Agriculture Organization. Updating and editorial responsibility for the final version provided by : Philip E. L a Moreaux Betty Morere Wilson Beshir A. Memon

Unesco

The designations employed and the presentation o f material throughout this publication do not imply the expression o f any opinion whatsoever on the part o f Unesco concerning the legal status o f any country, territory, city or area or of its authorities, or concerning the delimitation of i t s frontiers or boundaries.

Published in 1984 by the United Nations Educational, Scientific and Cultural Organization 7, place de Fontenoy, 75700 Paris Printed by Imprimerie de la Manutention, Mayenne

ISBN 92-3-102206-7

@ Unesco 1984

Printed in France

Preface

Although the total amount o f water on earth is generally assumed to have remained virtually constant, the rapid growth of population, together wi th the extension of irrigated agriculture anâ industrial development, are stressing the quantity and quality aspects o f the natural system. Because o f the increasing problems, man has begun to realize that he can no longer follow a “use and discard” philosophy - either wi th water resources or any other natural resources. As a result, the need for a consistent policy o f rational management o f water resources has become evident.

Rational water management, however, should be founded upon a thorough understanding of water availability and movement. Thus, as a contribution to the solution o f the world’s water problems, Unesco, in 1965, began the f irst world-wide programme o f studies o f the hydrological cycle - the International Hydrological Decade (IHD). The research programme was complemented by a major effort in the field o f hydrological education and training. The activities undertaken during the Decade proved to be o f great interest and value to Member States. By the end o f that period, a majority o f Unesco’s Member States had formed IHD National Committees to carry out relevant national activities and to participate in regional and international co-operation within the IHD programme. The knowledge o f the world’s water resources had substantially improved. Hydrology became widely recognized as an independent professional option and facilities for the training o f hydrologists had been developed.

Conscious o f the need to expand upon the efforts initiated during the International Hydrological Decade and, following the recommendations o f Member States, Unesco, in 1975, launched a new long-term intergovernmental programme, the International Hydrological Programme (IHP), to follow the Decade.

Although the IHP is basically a scientific and educational programme, Unesco has been aware from the beginning o f a need to direct i t s activities toward the practical solutions o f the world’s very real water resources problems. Accordingly, and in l ine wi th the recommendations o f the 1977 United Nations Water Conference, the objectives o f the International Hydrological Programme have been gradually expanded in order t o cover not only hydrological processes considered in interrelationship wi th the environment and human activities, but also the scientific aspects o f multi- purpose utilization and conservation o f water resources t o meet the needs of economic and social development. Thus, while maintaining IHP’s scientific concept, the objectives have shifted perceptibly towards a multidisciplinary approach t o the assessment, planning, and rational management o f water resources.

As part o f Unesco’s contribution‘ t o the objectives o f the IHP, two publication series are issued: “Studies and Reports in Hydrology” and “Technical Papers in Hydrology.” In addition to these publications, and in order t o ex- pedite exchange o f information in the areas in which i t i s most needed, works o f a preliminary nature are issued in the fonn o f Technical Documents.

The purpose o f the continuing series “Studies and Reports in Hydrology” to which this volume belongs, i s t o pre- sent data collected and the main results o f hydrological studies, as well as to provide information o n hydrological research techniques. The proceedings o f symposia are also sometimes included. I t i s hoped that these volumes wi l l furnish material o f both practical and theoretical interest t o water resources scientists and also t o those involved in water resources assessments and the planning for rational water resources management.

Contents

PREFACE FOREWORD INTRODUCTION (P.E. LaMoreaux)

PART I - FACTORS DETERMINING THE WATER REGIME I N CARBONATE ROCKS

1. CARBONATE ROCKS AND GEOLOGICAL PROCESSES 1.1 I n t r o d u c t i o n (L.A. He ind l ) 1.2 L i t h o l o g y (D.J. Benson) 1 . 2 . 1 Mineralogy 1.3 Sedimentation and s t r a t i g r a p h y (D.J. Burdon) 1 . 3 . 1 Facies 1.3.2 Size and shape o f beds 1.3.3 I n f l u e n c e o f s t r a t i f i c a t i o n 1.3.4 E f fec ts o f p a l e o h i ç t o r y 1 . 4 S t r u c t u r e ( T r a v i s H. Hughes) '

1 . 4 . 1 P e r m e a b i l i t y and s t r u c t u r e 1.4.2 F r a c t u r e systems 1.4.3 T i l t e d and f o l d e d carbonate a q u i f e r s 1.5 M i c r o t e x t u r e - v o i d s (D.J. Burdon) 1 .5 .1 I n t e r s t i c e s 1.5.2 M i c r o f i s s u r e s

11 13

2 1

2 1 2 1 2 1

3 1

36

45

2. HYDROGEOLOGICAL FEATURES OF CARBONATE ROCKS ( G i l b e r t Castany) 47 2 . 1 P o r o s i t y - Water s to rage i n k a r s t 47 2 .1 .1 Types o f e f f e c t i v e p o r o s i t y 2.1.2 Storage c o e f f i c i e n t 2.1.3 Storage capac i t y o f k a r s t i c carbonate rocks

2.2.1 Pe rmeab i l i t y types 2.2.2 Ca lcu la t i o n s 2.2.3 An iso t ropy and he te rogene i t y o f t h e r e s e r v o i r rocks 2.3 P o r o s i t y and p e r m e a b i l i t y s p a t i a l d i s t r i b u t i o n 60 2 . 3 . 1 Heterogenei ty o r homogeneity, and transformed s p a c i a l sca le o f t h e

2.3.2 Heterogenei ty and geometry o f t h e medium 2.3.3 Average c h a r a c t e r i s t i c s o f a r o c k mass (massi f ) 2.3.4 V a r i a t i o n o f t h e hyd rogeo log ica l c h a r a c t e r i s t i c s w i t h depth 2.4 Ground-water c i r c u l a t i o n (Harry E. LeGrand) 64

3. PHYSICAL AND CHEMICAL CHARACTERISTICS OF CARBONATE WATER (D. Langmuir) 69 3 .1 I n t r o d u c t i o n 69

3 .2 .1 A c t i v i t i e s and i o n i c s t r e n g t h 3.2.2 The r e a c t i o n s and thermodynamic data 3.2.3 S o l u b i l i t i e s o f c a l c i t e an.d do lomi te i n pu re water

2.2 Pe rmeab i l i t y 53

da ta f o r mean va lue c a l c u l a t i o n

3.2 Carbonate s o l u t i o n - m i n e r a l e q u i l i b r i a concepts 69

3.2.4 3.2.5 3.2.6

3.3 3 .3 .1 3.3.2 3.4 3.5 3 . 5 . 1 3.5.2 3.5.3

3.6

3 . 6 . 1 3.6.2 3.6.3 3.7 3 . 7 . 1 3.7.2

4 . 4 . 1 4.2 4 . 2 . 1 4.2.2 4 .2 .3 4 .3 4 . 3 . 1 4 .3.2

4 . 4 4 . 4 . 1 4 .4 .2 4 .4 .3 4.4.4 4 .4.5

5. 5 . 1 5.2 5 . 2 . 1 5.2.2 5.3 5.4 5 .5 5.6 5 . 6 . 1 5.6.2 5.7 5 . 7 . 1 5.7.2 5.7.3 5.7.4 5.7.5

E f f e c t o f i o n i c s t r e n g t h on c a l c i t e s o l u b i l i t y The ca lc ium t o magnesium r a t i o The s a t u r a t i o n s t a t e o f groundwaters w i t h respec t t o c a l c i t e and

S o l u b i l i t y o f h a l i t e and gypsum 92 H a l i t e s o l u b i l i t y Gypsum (and anhydr i t e ) s o l u b i l i t y

do l o m i t e

M i x i n g o f carbonate groundwaters 94 D iscuss ion o f some carbonate groundwater analyses 99 Table o f water analyses Impor tan t c o n t r o l l i n g processes V a r i a t i o n i n some major chemical c h a r a c t e r i s t i c s (Donald Langmuir,

I s o t o p i c v a r i a t i o n s i n t h e water c y c l e and t h e i r h y d r o l o g i c a l

S tab le i so topes o f hydrogen and oxygen i n t h e h y d r o l o g i c a l c y c l e T r i t i u m i n t h e h y d r o l o g i c a l c y c l e Carbon i so topes i n t h e h y d r o l o g i c a l c y c l e Appendices 116 Concent ra t ion u n i t s and conversion f a c t o r s Table o f water analyses

H e n r i Schoel ler , e t a l . )

s i g n i f i c a n c e (R.M. Brown, e t a i . ) 104

HYDROLOGY OF CARBONATE AREAS , I n t r o d u c t i o n (Harry E. LeGrand)

Runoff and discharge ( B . I . Kudel in) Runoff and discharge c h a r a c t e r i s t i c s i n k a r s t i c areas R e l a t i o n between r u n o f f and p r e c i p i t a t i o n Roles o f o t h e r f a c t o r s I n f i l t r a t i o n (Habib Zeb id i ) I n f i l t r a t i o n c h a r a c t e r i s t i c s o f k a r s t t e r r a i n R e l a t i o n s h i p o f p r e c i p i t a t i o n t o i n f i l t r a t i o n and r a t e o f

i n f i l t r a t i o n O u t l e t s (M. Herak and D.J. Burdon) D i f f u s e o u t l e t s Concentrated o u t l e t s Spr ing discharge i n t o ponds and lakes Surface discharge t o a l l u v i a l a q u i f e r s Submarine s p r i n g discharge

GEOMORPHOLOGY I n t r o d u c t i o n (L.A. He ind l ) K a r s t land form fea tu res and c l a s s i f i c a t i o n s C l a s s i f i c a t i o n based on landform C l a s s i f i c a t i o n system proposed by Q u i n l a n Pseudokarst Thermomineral k a r s t ( A r i e I s s a r ) Pa leokars ts (D.J. Burdon) Ana lys i s o f geomorphic processes Q u a n t i t a t i v e a n a l y s i s Q u a l i t a t i v e a n a l y s i s E f f e c t s o f k a r s t types on stream f l o w regimes (M i lan Herak) Tabular sha l low k a r s t Basin k a r s t F l u v i o k a r s t Folded sha l low k a r s t Deep k a r s t

1 3 1 1 3 1 1 3 1

134

138

1 4 3 143 143

147 147 148 149

152

PART II - PRACTICES 157

6 . METHODS OF INVESTIGATION 157 6 . 1 I n t r o d u c t i o n (L.A. He ind l ) 157 6 .2 Geo log ica l s tud ies (L.A. Heindl , H.E. LeGrand and V.T. S t r i n g f i e l d ) 158 6 . 2 . 1 F i e l d s t u d i e s

6 ..2.2 6.2.3 6.2.4 6.3 6 . 3 . 1 6.3.2 6.3.3 6.3.4 6.3.5 6 .3 .6 6 .4 6 . 4 . 1 6.4.2 6 .4 .3 6.5 6.5.1 6.5.2 6.5.3

6.5.5 6.6 6 . 6 . 1 6.6.2 6.6.3 6.7 6 . 7 . 1 6.7.2 6.7.3 6.7.4 6.7.5 6.7.6 6.7.7 6.7.8 6 .8 6 .8.1 6.8.2 6.8.3 6 .8 .4 6.9 6 .9 .1 6.9.2 6.9.3

6.5 .,4

7. 7 . 1 7.2 7.2.1 7.2.2 7.2.3 7.3 7 . 3 . 1 7.3.2 7.3.3 7.3.4 7.4 7 . 4 . 1 7.4.2

I n t e r p r e t a t i o n o f r e s u l t s P resen ta t i on o f r e s u l t s F i e l d i d e n t i f i c a t i o n o f m ine ra l s (D.J. Burdon) Remote sensing (P.E. LaMoreaux and B.M. Wi lson) Examples o f uses A e r i a l photographs S a t e l l i t e imagery Thermal i n f r a r e d imagery Radar Data sources Geophysical p rospec t i ng Surface methods (J.L. A s t i e r ) Borehole methods A i rborne methods Geochemical methods D isso lved s o l i d s and gases i n v e s t i g a t i o n s Neutron a c t i v a t i o n a n a l y s i s Environmental is*otope hydrogeology ( IAEA s t a f f ) A r t i f i c i a l i so tope hydro logy Combined use o f environmental i so topes and a r t i f i c i a l t r a c e r s

Labora tory de terminat ions o f p o r o s i t y Labora tory measurement o f p e r m e a b i l i t y F i e l d t e s t s Hydro log ic observa t ions and t h e i r i n t e r p r e t a t i o n s (B . I . Kude l i n ) 237 Observa t iona l networks P r e c i p i t a t i o n Runoff Evapora t ion and r e l a t e d me teo ro log i ca l observa t ions I n f i l t r a t i o n and i n f l o w Springs Groundwater observa t ions I n t e r p r e t a t i o n and p r e s e n t a t i o n o f r e s u l t s Water balance c a l c u l a t i o n s (Habib Zeb id i and H. Schoe l l e r ) General case o f o v e r a l l water balance Recession curve Spec ia l case o f obse rva t i on w e l l s o r piezometers Conclusion Hydro log ic mapping (Bashi r A. Memon and B e t t y M. Wilson) Hydrogeo log ica l mapping I n t e r p r e t i v e maps Water resources maps

Determinat ion o f a q u i f e r c h a r a c t e r i s t i c s ( G i l b e r t Castany) 210

166

1 7 1

186

247

259

DEVELOPMENT AND MANAGEMENT OF KARST GROUNDWATER RESOURCES I n t r o d u c t i o n (Stanley W. Posey) Resource e v a l u a t i o n Q u a n t i t a t i v e e v a l u a t i o n (Stanley W. Posey) Q u a l i t a t i v e e v a l u a t i o n (Stanley W. Posey) System a n a l y s i s (Stanley W. Posey) Development ( A r i e I s s a r and Stan ley W. Posey) P r e l i m i n a r y s t u d i e s Development techniques D i s t r i b u t i o n systems (Stanley W. Poçey) Consequences o f development (Stanley W. Posey) Management (Stanley W. Posey) General cons ide ra t i ons Ground-water management f u n c t i o n s

261 261 261

267

274

8. METHODS OF COST ESTIMATION (D.J. Burdon) 279 8 . 1 I n t r o d u c t i o n 279 8.2 Cost o f surveys and i n v e s t i g a t i o n s 2 80 8.2.1 General f a c t o r s de termin ing c o s t o f surveys and i n v e s t i g a t i o n s 8.2.2 Est imates o f c o s t i n u n i t s o f area i n v e s t i g a t e d 8.2.3 Est imates o f c o s t by p r o j e c t approach

8.3 8 .3 .1 8.3.2 8.3.3 8.3.4 8 .3 .5 8.3.6 8.3.7 8 .3 .8 8.4 8 . 4 . 1 8.4.2 8.4.3 8 .4 .4 8.5 8 .5 .1 8.5.2 8.5.3 8.5.4 8 . 6 8 . 6 . 1 8.6.2 8.7 8.8

Cost o f groundwater development General case - c o s t o f boreholes and pumps Cost o f d r i l l i n g Cost o f c leaning, a c i d i z i n g and b l a s t i n g boreholes Cost o f t e s t p u m p i n g Cost o f cas ing and screens Cost o f pumps and motors Cost o f sur face f i t t i n g s and access Cost o f s h a f t s and g a l l e r i e s Cost o f groundwater e x t r a c t i o n The groundwater development and p r o t e c t i o n s i t u a t i o n F i xed cos ts Opera t ing cos ts Cost o f water Cost o f groundwater recharge and management Recharge o f k a r s t a q u i f e r s Example o f c o s t c a l c u l a t i o n f o r groundwater recharge Cost o f recove r ing recharged groundwater Ideas on cos ts o f groundwater management Cost o f groundwater f o r i r r i g a t i o n A c t u a l c o s t o f i r r i g a t i o n water ob ta ined from underground P r i c e p a i d f o r i r r i g a t i o n water Comparative cos ts o f sur face and underground water F e a s i b i l i t y study f o r p lann ing and investment purposes

282

291

297

300

303 303

SELECTED BIBLIOGRAPHY

CONTRIBUTING AUTHORS

307

345

Foreword

Th is Guide was prepared as p a r t o f t h e program o f t h e I n t e r n a t i o n a l H y d r o l o g i c a l Decade (IHD). I t was o r i g i n a l l y o rgan ized by t h e Working Group on t h e Hydrology o f Carbonate Rocks i n the Mediterranean Basin, which was c o n s t i t u t e d hy the IHD Coord ina t i ng Counc i l i n t h e f i r s t year o f t h e Decade, 1965. The t e c h n i c a l s e c r e t a r i a t was p rov ided by t h e Food and A g r i c u l t u r e Organizat ion, s p e c i f i c a l l y through i t s Water Resources and Development Serv ice i n t h e Land a n d Water Development D i v i s i o n o f t h e A g r i c u l t u r e Department.

The Working Group was under t h e Chairmanship o f P r o f . M i l a n Herak o f t he U n i v e r s i t y o f Zagreb, Yugoslavia. I t s members were: D r . E. Karageorgiou (Greece) , P r o f . E. T o n g i o r g i ( I t a l y ) , M r . A. Hernanz (Spain) , D r . H. Z e b i d i (Tun is ia ) , D r . El. Herak (Yugoslavia) , D r . G. Castany ( IAH) , Prof . H. Schoe l l e r (IASH) , and M r . J. A. Da Costa (UNESCO). Observers were: M r . J. R. Pelaez Pruneda (Spain) , D r . L. A. H e i n d l (USA) , and D r . Y. B. Osipov (USSR). Members o f t he Techn ica l S e c r e t a r i a t p rov ided by FAO were: D r . D. J. Burdon, Consul.t ing Hydrogeo log is t , Land and Water Development D i v i s i o n ; M r . C. E. Houston , Ch ie f , Water Resources and Development Serv ice , Land and Water Development D i v i s i o n ; M r . R. G. Thomas, Hydrogeo log is t , Water Resources and Development Service, Land and Water Development D i v i s i o n .

A t i t s t h i rd meeting, h e l d i n 1971 i n Tunis, t h e Working Group asked Drs. L. A. H e i n d l , G. Castany and H. Schoe l l e r t o a c t as e d i t o r s , w i t h D r . H e i n d l assuminçr chairmanship.

P a r t i c u l a r thanks are due t o t h e U n i t e d Sta tes N a t i o n a l Committee f o r t h e I H D and i t s Work Group on Hydrology o f Carbonate T e r r a i n s f o r c o n t r i b u t i o n s o f m a t e r i a l and f o r making D r . H e i n d l a v a i l a b l e f o r h i s task. The USI IHD Work Group was c h a i r e d s u c c e s s f u l l y by M r . V. T. S t r i n g f i e l d o f t h e U. S. Geo log ica l Survey (1967-72) and D r . P. E. LaMoreaux, D i r e c t o r o f t h e Geo log ica l Survey o f Alabama (1972-75) , and composed o f D r . W i l l i a m Back, D r . Heind l , M r . H. E. LeGrand, and D r . G. B. Maxey.

The p resen t E d i t o r s recogn ize t h a t many comp i la t i ons such as t h i s Guide which i s t h e produc t o f many au thors from many c o u n t r i e s , w i l l be marked by unevenness o f con ten t , s t y l e , and emphasis. T h i s manuscr ipt has rece ived t h e s incere rev iew and r e v i s i o n o f a g r e a t many k a r s t s p e c i a l i s t s as a l a b o r o f love. The o r i q i n a l manuscr ipt was a ve ry l a r g e c o l l e c t i o n o f i n d i v i d u a l papers w r i t t e n i n d i f f e r e n t format, s t y l e s , and Eng l i sh . These o r i g i n a l manuscr ipts con ta in a g r e a t d e a l o f va luab le theory, thought, and da ta but as m i g h t be expected i n d i v i d u a l chapter c o n t r i b u t i o n s developed much d u p l i c a t i o n and omission o f m a t e r i a l f o r c o n t i n u i t y .

The Guidebook o r i g i n a l l y evolved through work o f D r . L. A. Heindl , D r . G. Castany, and P r o f . H. Schoel- ler. The manuscr ipt l a t e r was reviewed by D r . David Burdon and M r . Jose da Costa. When the manuscr ipt was r e f e r r e d b y Jose d a c o s t a t o P. E. LaMoreaux i n 1979 d u r i n g a v i s i t t o Unesco i n P a r i s , i t was w i t h complete a u t h o r i t y t o e d i t , r e v i s e , de le te , and update as needed.

Beginning i n 1 9 8 0 Robert Fambrouqh, hyd rogeo log is t and Jan ice Fehlmann, g e o l o g i s t - e d i t o r , o f P. E. LaMoreaux and Associates, I n c . (PELA) , attempted t o con tac t a l l c o n t r i b u t i n g au thors and o b t a i n any r e v i s i o n o r upda t ing o f m a t e r i a l . Some responded and t h e i r comments were i n t e g r a t e d . Subsequently, Greg Powers and Doyle B. Knowles o f PELA worked on t h e manuscr ipt and f i n a l l y environmental g e o l o g i s t B e t t y Wi lson brought toge the r and e d i t e d t h e f i n a l manuscr ipt t r a n s m i t t e d f o r p u b l i c a t i o n w i t h t e c h n i c a l ass is tance from D r . Bash i r A. Memon. Other sen io r s t a f f members w i t h PELA p r o v i d i n g geologist . Wi lson w i t h support i nc luded M r . W i l l i a m J. Powel l , D r . T r a v i s H. Hughes, M r . Stan Posey, and M r . Jon Dow.

11

Every at tempt was made t o r e t a i n t h e s c i e n t i f i c i n t e g r i t y o f t-he o r i g i n a l manuscr ip t a n d t o i d e n t i f y t h e o r i g i n a l authors. However, t o prov ide ' a manuscr ip t w i t h c o n t i n u i t y and w i t h a minimum o f r e p e t i t i o n , i t was necessary t o d e l e t e many sentences, paragraphs and even sect ions. Some sec t ions were combined o r re-organized w i t h o the rs and some supplemental m a t e r i a l added f o r c o n t i n u i t y . A few sec t i ons were t o t a l l y r e w r i t t e n by new authors; they i nc lude s e c t i o n 1 .4 which was r e w r i t t e n by T r a v i s Hughes. The o r i g i n a l manuscr ipt was never completed by t h e l a t e L. A. He ind l . Donald Langmuir rewro te Chapter 3 u s i n g the prev ious manuscr ip t and p ioneer ing work o f H e n r i Schoe l le r as the foundat ion f o r much o f t he work. I n p laces the e d i t o r s p rov ided a d d i t i o n a l re fe rences t o more recen t o r supplemental l i t e r a t u r e as an a i d t o t h e reader.

Sect ions and subsect ions which c a r r y au thors ' names are those which were used w i t h minor review. Some sec t ions f o r which no a.uthor i s l i s t e d con ta in major r e v i s i o n s by t h e e d i t o r s . The major p o r t i o n o f some chapters was w r i t t e n by one author o r a committee o f authors. I n these cases, t h e pr imary authors a re l i s t e d w i t h t h e chapter t i t l e w h i l e t h e authors o f any supplemental sec t i ons are l i s t e d a t t h e headings o f t he subsect ions which they prepared.

The e d i t o r s would g r a t e f u l l y acknowledge t h e many hours o f t h e p a t i e n t and knowledgeable c l e r i c a l ass is tance g i ven t o them by Marsha M a r t i n (PELA) , the b i b l i o g r a p h y research by Jackye Lan ie r (PELA, and the r e d r a f t i n g o f a l l o f t he f i g u r e s by the Graphics Department o f PELA.

The E d i t o r s

P h i l - i p E. LaMoreaux, Pres ident B e t t y Morere Wilson, Environmental Geo log is t Bash i r A. Memon, Hydrogeologis t

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Introduction (P. E. LaMoreaux)

The purpose o f t h i s Guide t o t h e Hydrology o f Carbonate Rocks i s t o a s s i s t hydrogeo log is ts and o the rs work ing toward the s o l u t i o n o f p r a c t i c a l water problems i n carbonate t e r r a i n s . I t presents p r i n c i p l e s , p r a c t i c e s and experiences i n t h e f i e l d s o f geology, chemist ry , hydro logy a n d eng ineer ing which are used i n the study o f water i n and on carbonate rocks.

The main d i f f e r e n c e bet.ween carbonate and most o t h e r rocks i s t h e i r comparat ive ly h i g h degree o f s o l u b i l i t y , which r e s u l t s i n t h e development o f t he sur face and subsurface c h a r a c t e r i s t i c s c a l l e d k a r s t . More s p e c i f i c a l l y , t he ou ts tand ing fea tu res o f k a r s t s a r e t h e enlarged f i s s u r e s and v o i d s which pe rm i t f a s t i n f i l t r a t i o n r a t e s and l a r g e p r e f e r e n t i a l p e r m e a b i l i t i e s and which channel t h e . w a t e r i n t o a complex d i s t r i b u t i o n p a t t e r n . These c h a r a c t e r i s t i c s a re SO d i s t i n c t e i v e t h a t t h e hydro logy o f carbonate rocks forms a s p e c i a l f a c e t o f hydro logy and hydrogeology t h a t r e q u i r e s unusual a t t e n t i o n t o t h e chemist ry o f b o t h t h e water and t h e rock and s p e c i a l concepts and techniques which must be mod i f i ed o r ad jus ted when a p p l i e d t o f r a c t u r e d and channel led rocks o f carbonate ter ranes.

The word, hydro logy i s used i n t h e Guide as i t i s de f i ned by t h e I n t e r n a t i o n a l Hydro log i ca l Decade: "The science t h a t dea ls w i t h t he waters o f t h e Ear th, t h e i r occurrence, c i r c u l a t i o n and d i s t r i b u t i o n , t h e i r chemical and p h y s i c a l p r o p e r t i e s and t h e i r r e a c t i o n w i t h t h e i r environment, i n c l u d i n g t h e i r r e l a t i o n t o l i v i n g beings" . Thus t h e Guide dea ls w i t h a l l aspects o f t h e water and p r e c i p i t a t i o n a s w e l l as w i t h groundwater, which i n many ins tances i s t h e p r i n c i p a l focus o f i n t e r e s t .

The term "carbonate rocks" i s used i n t h e t i t l e i n pre ference t o such terms as carbonate te r ranes o r k a r s t f o r two reasons. F i r s t , i t p laces t h e emphasis on a s p e c i f i c type o f rock-carbonate, whereas t h e term k a r s t and i t s d e r i v a t i o n s may a l s o r e f e r t o rocks con ta in ing so lub le m ine ra l s such as gypsum and h a l i t e o r i c e . I t migh t even i n c l u d e such non-solub le rocks as b a s a l t . And second, i t emphasizes t h e f a c t t h e Guide i s concerned w i t h t h e m a t e r i a l - carbonate r o c k - and n o t w i t h e i t h e r i t s exposure a t t h e sur face o r i t s s t r a t i g r a p h i c p o s i t i o n . Thus t h e Guide dea ls w i t h carbonate rocks whether o r n o t they are k a r s t i f i e d , exposed a t t he sur face, o r bu r ied . Th is i nc ludes those s i t u a t i o n s where k a r s t i f i e d carbonate rocks a re b u r i e d beneath l a y e r s o f non-carhona.te m a t e r i a l s o r a re u n d e r l y i n g non-kars t i c t e r r a i n s .

Much o f t.he Guide dea ls w i t h carbonate k a r s t phenomena. The s i n g u l a r e f f e c t s associ.ated w i t h carbonate rocks a re b e s t expressed i n t h e c l a s s i c k a r s t ter ranes, p a r t i c u l a r l y i n t h e Mediterranean b a s i n where they have been w i d e l y studied. Moreover, t h e c l a s s i c k a r s t phenomena p rov ide i n s i g h t n o t o n l y i n t o t h e i r own processes and fea tures , but al.so i n t o those o f i n c i p i e n t , l e s s w e l l developed, and hidden (bur ied) stages o f k a r s t i f i c a t i o n . These occur i n t h e t r a n s i t i o n zones between c l a s s i c k a r s t s and non-ka.rst ic t e r r a i n s and between r e l a t i v e l y pu re carbonate rocks and those w i t h i nc reas ing p r o p o r t i o n s o f sand, c l a y and o t h e r ma te r ia l s .

Water i n carbonate t e r r a i n s occurs under so many unusual and s u r p r i s i n g cond i t i ons t h a t i t has been g i ven a v e i l o f mystery by some. Water i n some k a r s t i c areas appears t o de fy na.t.ural forces and t o obey myster ious laws. However, i n carbonate rocks and k a r s t i c t e r r a i n s water cont inues t o f l o w downhil l . and seeks i t s own l e v e l . These apparent ly unna tu ra l phenomena a re due t o measurable d i f fe rences i n pressure, dens i t y , s a l i n i t y , tempera.ture, o r o t h e r p h v s i c a l c h a r a c t e r i s t i c s e x i s t i n g under cond i t i ons somewhat more comp1.e~ than those o r d i n a r i l y found i n na ture .

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The Guidebook assumes t h a t t h e user has a b a s i c acquaintance w i t h h y d r o l o g i c a l p r i n c i p l e s and p r a c t i c e s , w i t h p e r t i n e n t elements o f geology, chemist ry , and phys ics, and eng ineer ing methods used i n sur face water and groundwater analyses and w i t h t h e mathematical, s t a t i s t i c a l , and computer-based techniques app l i cab le t o water s tud ies .

The Guide avoids l eng thy d iscuss ions o f concepts and i n f o r m a t i o n contained i n t e x t s and references, except t o show t h e i r a p p l i c a t i o n t o carbonate hydrology.

I n sho r t , t h i s Guide does n o t presume t o p resent a l l b a s i c h y d r o l o g i c a l theory and technique; r a t h e r i t concentrates on t h e i r use i n t h e study o f carbonate rocks under p r a c t i c a l f i e l d and o f f i c e cond i t ions .

The Guide i s d i v i d e d i n t o two p a r t s - p r i n c i p l e s and p r a c t i c e s . The p a r t on " p r i n c i p l e s " has f i v e chapters , d e a l i n g success ive ly w i t h t h e na ture and s i t u a t i o n o f carbonate rocks, and p h y s i c a l and chemical c h a r a c t e r i s t i c s o f t he water w i t h which t h e r o c k i n t e r a c t s , t he consequent p o r o s i t y and permeab i l i t y , and t h e i r dynamic i n t e r r e l a t i o n s h i p s o r hydro logy a n d t h e i r geomorphology. The second p a r t , p r a c t i c e s , dea ls w i t h techniques and app l i ca t i ons . These are d i v i d e d i n t o two broad ca tegor ies - those t h a t a re i n v o l v e d i n a c t u a l f i e l d work, and those i n v o l v e d i n t h e decision-making process, such as p lanning, programming, and f inanc ing .

Carbonate rocks, p r i m a r i l y l imestones and dolomites, comprise roughly 1 5 percent o f a l l sedimentary rocks and u n d e r l i e 75 percent o f t h e e a r t h ' s surface. Besides t h e i r g r e a t economic va lue as a m i n e r a l resource, carbonate rocks conta in , i n p laces, l a r g e amounts o f ground water, an impor tan t q u a n t i t y o f t he w o r l d ' s supply 04 petro leum and n a t u r a l gas, and va luab le reserves o f t h e w o r l d ' s metals. Because o f t h e i r unique and complex c h a r a c t e r i s t i c s , a g r e a t d e a l o f research has been ded ica ted t o the study o f carbonate rocks.

There has been an increased i n t e r e s t i n carbonate rocks and t h e i r hyd ro log i c c h a r a c t e r i s t i c s , as i n d i c a t e d by the a t t e n t i o n g i ven t o the sub jec t a t many meetings and by the establ ishment o f work groups t o study the hydrology o f carbonate ( o r k a r s t i c } t e r r a i n s as a p a r t o f t he I n t e r n a t i o n a l Hydro log i ca l Decade and t h e Assoc ia t i on o f I n t e r n a t i o n a l Hydrogeologists. A l i s t o f some o f t h e more impor tan t meetings i s g i ven i n Table 1, which updates t h e l i s t by La - Moreaux, LeGrand and S t r i n g f i e l d (1975) . Recent books on k a r s t hydro loqy

A number o f books on k a r s t and k a r s t hydro logy have been pub l ished i n the l a s t f i f t e e n years as a r e s u l t o f i nc reas ing i n t e r e s t i n t h i s f i e l d . Sone o f t h e more im.portant t e x t s are:

1.

2.

3.

4 .

5.

6 .

7 .

8.

9 .

10.

11.

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Rack and LaMoreaux (eds.) ( 1 9 8 3 ) , V. T. S t r i n g f i e l d Symposium.

F o g l i ( 1 9 8 0 ) , K a r s t Hydrology and Phys ica l Speleology.

Burger and Dubet re t (eds.) (19751, Hydrology o f K a r s t i c Ter ra ins .

D i l amar te r and Csal lany (eds. ) ( 1 9 7 7 ) Hydro log ic Problems i n K a r s t Regions.

Jacus ( 1 9 7 7 ) Morphogenetics o f K a r s t Regions.

Jennings (1971.) Kars t .

Herak and S t r i n g f i e l d (eds.) ( 1 9 7 2 ) Karst ; Impor tan t K a r s t Regions o f t he Nor thern Hemisphere.

Fi i lanoviC ( 1 9 8 1 ) K a r s t Hydrogeology.

P e t r i k and Herak (eds.) ( 1 9 6 9 ) KrsJugoçlav ie (Carsus 1ugoslavi.ae) . Sweeting ( 1 9 7 3 ) K a r s t Landforms.

Tolson and Doyle (eds.) ( 1 9 7 7 ) K a r s t Hydrogeology.

Table 1. Symposia and conferences on hydro logy o f carbonate rocks.

Locat ion T i t l e Sponsor ( s ) Date

Havana , Cuba I n t e r n a t i o n a l Workshop on K a r s t Hydrology o f t h e Caribbean Region

Unesco D i v i s i o n 1983 o f Water Sciences

A t lan ta , Georgia U.S.A.

Washington , D. C . U.S.A.

Oymapinar, Turkey

Budapest, Hungary

V. T. S t r i n g f i e l d Symposium- Processes i n K a r s t Hydroloçy

Research Needs i n Hydrology and Water Resources o f K a r s t i f i e d Carbonate T e r r a i n s

I n t e r n a t i o n a l Symposium on K a r s t Hydrogeology

I n t e r n a t i o n a l Symposium on K a r s t Hydrology

Bowl ing Gkeen, I n t e r n a t i o n a l Symposium on Kentucky, U.S.A. Hydro log ic Problems i n

K a r s t Regions

Budapest, Hungary Hydrogeology o f Great Sedimentary Basins

L j ubl j ana , Yugoslavia

Dubrovnik, Yugoslavia

H u n t s v i l l e , Alabama , U. S. A.

T h i r d I n t e r n a t i o n a l Symposium o f Underground Water T rac ing

U.S.-Yugoslavian Symposium on K a r s t Hydrology and Water Resources

T w e l f t h I n t e r n a t i o n a l Congress of t h e I n t e r n a t i o n a l Associa- t i o n o f Hydrogeologis ts - K a r s t Hydrogeology

Geo log ica l Soc ie ty 1 9 8 0 America

The N a t i o n a l Science Foundat ion

S t a t e Hydrau l i c Works , Un i ted Nat ions Develop- ment Programme

Hungarian S pe 1 e O 1. og i c a 1 Soc ie ty , Hungarian Geo log ica l Soc ie ty , and Hungarian Me teo ro log i ca l Soc ie ty

Western Kentucky U n i v e r s i t y

Hungarian Geo log ica l I n s t i t u t e , I n t e r n a t i o n a l Assoc ia t i on o f Hydro log i ca l Sciences , -and Unesco

Yugoslav Committee f o r I n t e r n a t i o n a l Hydro log i ca l Program

B i l a t e r a l U.S.- Yugoslavia Re- search P r o j e c t on K a r s t Hydro l ogy a n d Water Re sources

i n t e r n a t i o n a l Assoc ia t i on o f Hydrogeologis ts

1 9 8 0

1 9 7 9

1 9 7 8

1 9 7 6

1 9 7 6

1 9 7 6

1 9 7 5

1 9 7 5

15

1 2 . Yev jev ich (ed.) (1981) K a r s t Water Research Needs.

1 3 . Yev jev ich (ea.) ( 1 9 7 6 ) K a r s t Hydrology and Water Resources.

1 4 . 2 8 t l ( 1 9 7 4 ) Kars thydro log ie .

B i b 1 i og raph ie s

L i t e r a t u r e d e s c r i b i n g the i n f l u e n c e o f carbonate rocks on man appears i n p u b l i c a t i o n s o f a l l types, rang ing from s p e c i a l o r f e a t u r e s t o r i e s i n newspapers and magazines t o t e c h n i c a l j ou rna ls , textbooks and t r e a t i s e s . The sources o f t h e l i t e r a t u r e a re worldwide, i l l u s t r a t i n g t h e wide d i s t r i b u t i o n o f carbonate rocks and t h e i r importance t o man. H i s t o r i c a l re ferences on carbonate hydro logy have been reviewed by LaMoreaux and o the rs ( 1 9 7 5 ) .

As the volume o f l i t e r a t u r e on carbonate rocks grows, the p r o f e s s i o n a l work ing on l imestone hydro logy s tud ies may over look impor tan t p e r t i n e n t l i t e r a t u r e . To h e l p so lve t h i s problem, b i b l i o g r a p h i e s have been prepared. The Union I n t e r n a t i o n a l e de Speleolog ie has been p u b l i s h i n g spe leog ica l abs t rac ts s ince 1968, and Tony Oldham, 0f theU.K. has been p u b l i s h i n g "Current T i t l e s i n Speleology" s ince 1 9 6 9 . Un fo r tuna te l y , €or the hydrogeologis t , these c o l l e c t i o n s a re o r i e n t e d toward the s p e l e o l o g i s t and o f t e n do n o t cover o the r areas.

"An Annotated B ib l i og raphy o f Limestone T e r r a i n s " was prepared and pub l ished a s B u l l e t i n 94-A o f t he Geo log ica l Survey o f Alabama ( 1 9 7 0 ) . Th is b i b l i o g r a p h y i s composed o f re ferences t o t h e geology, hydrology, geochemistry, and geophysics o f carbonate rocks and t o se lected, c l o s e l y r e l a t e d subjects . The b i b l i o g r a p h i c m a t e r i a l i s s to red on d i s k s o f an IBM 360 Model 50 computer and i s a v a i l a b l e i n p r i n t o u t form f o r each category o f indexed in fo rmat ion . A second e d i t i o n o f t h e b ib l i og raphy , B u l l e t i n 94-GI con ta ins more than 1,500 e n t r i e s .

The b i b l i o g r a p h y was prepared by the Geo log ica l Survey o f Alabama as p a r t o f a p r o j e c t on t h e hydro logy o f l imestone t e r r a i n s sponsored by t h e O f f i c e o f Water Resources o f t he U. S. Department of I n t e r i o r ; t he Department o f Geology and Geoqraphy o f t he U n i v e r s i t y o f Alabama; t h e Water Resources I n s t i t u t e o f Auburn U n i v e r s i t y ; and the U. S. N a t i o n a l Committee f o r t h e I n t e r n a t i o n a l Hydro log i ca l Decade of t h e U. S. N a t i o n a l Academy o f Sciences - N a t i o n a l Research Counci l ; and t h e I n t e r n a t i o n a l Assoc ia t ion o f Hydrogeologists.

Con t r i bu to rs t o t h e b i b l i o g r a p h y i nc lude members o f t h e Commission o f Hydrogeology o f K a r s t o f t he I n t e r n a t i o n a l Assoc ia t ion o f Hydrogeologists; members o f t h e s t a f f s o f seve ra l S ta te Geo log ica l Surveys i n the U. S.; members o f t he d i s t r i c t s t a f f s o f t he Water Resources D i v i s i o n o f t he U. S. Geologica l Survey; t he Tun is ian Committee o f t he I n t e r n a t i o n a l Hydro log i ca l Decade; D r . A. B. A. B r ink , Department o f Geology, U n i v e r s i t y o f Witwatersrand; J. Ens l i n , D i r e c t o r , Geo log ica l Survey o f South A f r i c a ; and D r . David J. Burdon, Food and A g r i c u l t u r e Organ iza t ion o f t he IJni ted Nat ions.

Progress i n t h e Development o f Methods a n d Techniques f o r t h e Study o f K a r s t Areas

The word k a r s t denotes any t e r r a i n u n d e r l a i n by compact carbonate rocks i n which c i r c u l a t i n g water has d i sso l ved t h e rock , c r e a t i n g such p h y s i c a l fea tures as enclosed depressions, s inkholes, swallow ho les , l o n g d r y v a l l e y s , s c a r c i t y o f sur face streams, and subterranean drainage through s o l u t i o n openings. As mentioned e a r l i e r , k a r s t t e r r a i n s a re much more predominant i n Europe, where t.he i n i t i a l s tud ies were made; however, o the r k a r s t areas o f t he wor ld have been s tud ied i n the more recen t past .

E a r l y i n t h e 1960's a need was r e a l i z e d f o r c l a r i f y i n g the numerous terms used i n d i scuss ing t h e hydro losv and qeomorphology of carbonate t e r r a i n s . I n 1 9 6 5 , "Vocabula i re Franca is des Phénomènes Kars t iques" appeared and presented French equ iva len ts o f k a r s t terms. Monroe compi led "A Glossary o f K a r s t Terminology" i n 1 9 7 0 , and i n 1 9 7 3 , a m u l t i l i n g u a l g lossarv was pub l ished by UNESCO. Un fo r tuna te l y , Gams' "Slovenska Kraska Termino log i ja " ( 1 9 7 3 ) has not been t r a n s l a t e d from t h e o r i g i n a l Slovenian t o Engl ish. Less comprehensive

1 6

g lossa r ies have appeared a t t h e conc lus ion o f seve ra l books on k a r s t (Sweeting, 1 9 7 3 ) Burger and Duber t re t (1975) and elsewhere.

I n t h e USSR k a r s t terminology was pub l i shed i n geographica l (Kalesnik , 1 9 6 8 ) and i n hydrogeo log ica l (Makaveev, 1971) d i c t i o n a r i e s as w e l l as i n books by Gvozdetsky ( 1 9 5 4 1 , D. S. Sokolov ( 1 9 6 2 ) and Maksimovich (1963, 1 9 6 9 ) .

European c o n t r i b u t i o n s t o t h e understanding o f ground-water c i r c u l a t i o n i n k a r s t t e r r a i n s have come from many i n v e s t i g a t o r s . An e a r l y w r i t e r on pr in- c i p l e s of movement, occurrence, and dynamics o f f l o w o f water i n k a r s t was A. G r u n d (1903, 1 9 1 0 ) . He and Lehmann ( 1 9 3 2 ) emphasized t h e complex movement o f k a r s t water and the dynamics o f ground water i n k a r s t , p a r t i c u l a r l y as r e l a t e d t o l a r g e s o l u t i o n openings. R o g l i c ( 1 9 6 5 ) has a p p l i e d some o f Lehmann's ideas t o the c i r c u l a t i o n o f water i n t h e k a r s t o f Yugoslavia. I n recen t years, t r a c e r s have been used by many workers t o determine ground-water c i r c u l a t i o n pa t te rns , i n c l u d i n g Z o t l ( 1 9 6 1 ) , Dub i tansk i (1971) , Mi lanov ic ( 1 9 7 2 ) , Atk inson and o the rs ( 1 9 7 3 ) The (Yugoslavian) I n s t i t u t e o f K a r s t Research (Gospodaric and Habic, 1976). Geologic and phys iographic i n f l uences on kars t -water c i r c u l a t i o n have been s tud ied by Wi l l i ams ( 1 9 7 0 ) i n western I r e l a n d ; Pa t te rson ( 1 9 7 1 ) and Atk inson ( 1 9 7 7 ) i n England; and Za j t sev ( 1 9 4 0 ) , Sokolov ( 1 9 6 2 ) , Maksimovich (1969), and Babushkin and o the rs ( 1 9 7 2 ) i n t h e Sov ie t Union. Work sponsored by the Food and A g r i c u l t u r e Organ iza t ion i n k a r s t areas has a l s o c o n t r i b u t e d va luab le in format ion; a r e p o r t by Burdon and Papakis ( 1 9 6 3 ) examines water resources and methods o f s tudy ing t h e k a r s t hydro logy o f circum-mediterranean count r ies ; a work by Wozab and Wi l l i ams ( 1 9 6 7 ) dea ls w i t h qround-water f l o w problems i n Jamaica , West Ind ies .

S t r i n g f i e l d ( 1 9 6 6 ) compl.eted an ex tens ive syn thes is o f t h e k a r s t a r t e s i a n system i n t h e southeastern U.S.A. Th is r e p o r t b rought together va luab le in fo rmat ion from many d e t a i l e d l o c a l s tud ies and descr ibed t h a t hyd ro log i c system, which i s one o f t he most p r o l i f i c k a r s t a q u i f e r s known. S t r i n g f i e l d and LeGrand prepared a rev iew on carbonate-rock hydro logy, w i t h s p e c i a l r e f e r - ence t o t h e U n i t e d Sta tes (1969a), a n d b rought together many concepts on which i n d i v i d u a l workers g e n e r a l l y agree. They s tud ied t h e f resh-water and s a l t - water r e l a t i o n s h i p s i n f o u r c o a s t a l k a r s t areas, and showed t h a t uneven d i s t r i b u t i o n o f p e r m e a b i l i t y i n c o a s t a l k a r s t s causes m o d i f i c a t i o n o f t h e normal balance between f r e s h and s a l t water t h a t has been conven t iona l l y descr ibed i n c o a s t a l sand a q u i f e r s (1969a, 1 9 7 1 ) . A comparison o f t h e a r i d k a r s t s o f western Egypt, t h e N u l l a r b o r P l a i n o f A u s t r a l i a , t h e Kaibab P la teau o f Ar izona, and t h e Yucatan Peninsula o f Mexico w i t h h u m i d k a r s t reg ions was made by S t r i n g f i e l d , LeGrand, and LaMoreaux (1974) i n o rde r t o understand dynamic hyd ro log i c processes i n k a r s t reg ions. To f u r t h e r descr ibe some p r i n c i p l e s , they pub l ished a r e p o r t ( 1 9 7 7 ) on the development o f k a r s t and i t s e f f e c t s on p e r m e a b i l i t y and c i r c u l a t i o n o f water i n carbonate rocks, w i t h s p e c i a l re fe rence t o t h e southeastern s t a t e s o f t h e U.S.A.

Burdon and Papakis (1963) demonstrated t h e need f o r understanding t h e r e g i o n a l movement o f k a r s t ground water i n t h e i r s tudy o f areas i n Greece. T h r a i l k i l l e t a l . ( 1 9 8 2 ) produced an ex tens ive study on t h e groundwater i n the In te r -B luegrass k a r s t reg ion o f Kentucky, U.S.A. S t r i n g f i e l d and LeGrand ( 1 9 6 6 ) descr ibe i n d e t a i l t h e occurrence o f groundwater i n t h e l imestones i n t h e southeastern U n i t e d States. Much work has a l s o been done on the Edwards Aqu i fe r , Texas (Macclay and Small, 1976 and 1 9 8 3 ) . I n t h e USSR t h e r e l a t i o n o f k a r s t t o streamflow has been s tud ied by Kolodyazshnaya (1961) , M o l i t v i n (1962), Sokolov (19701, Balkov (1970) and Vladimirow ( 1 9 7 0 ) .

The t e c t o n i c c o n t r o l on movement o f water i n k a r s t reg ions i s shown i n a l l coun t r i es descr ibed i n the volume by Herak and S t r i n g f i e l d , e d i t o r s ( 1 9 7 2 ) , i n Turkey by Eroskay and Gunay (1980) and i n t h e Mediterranean area by Avias ( 1 9 7 7 ) . Ivanov (1974) s t a t e d t h a t major f a u l t s i n t h e mountain Crimea a re t h e main d r a i n s o f f i s s u r e - k a r s t i c waters t h a t serve as t h e b a s i s o f k a r s t i f i - ca t ion . The t ime o f f a u l t i n g enables us t o determine t h e t ime when ground-water f l o w and t h e process o f k a r s t i f i c a t i o n o f morpho log ica l s t r u c t u r e s s ta r ted . The e f f e c t o f t e c t o n i c s on ground-water dynamics i n t h e USSR was i n v e s t i g a t e d by P l o t n i k o v and o t h e r s ( 1 9 6 1 ) , D. S. Sokolov ( 1 9 6 2 ) , N. V. Rodionov (1963) , Golvtsyn and o the rs (1966) , Lykoshin (1968) , and M a r u a s h v i l i (1974).

Regional maps showing k a r s t hydrogeologic fea tu res a re p r o v i n g t o be ve ry u s e f u l i n Yugoslavia ( M i j a t o v i c , 19711, France (Paloc, 1972; K i r a l y , 1973) , and I t a l y (Boni and Paratoo, 1 9 6 9 ) , and i n t h e USSR (Rodionov, 1969; V lad imi rov ,

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1 9 7 0 ) . Ground-water l e v e l s i n k a r s t reg ions va ry g r e a t l y i n l o c a l areas and a re d i f f i c u l t t o measure; t he re fo re , w i t h t he except ion o f t he wa te r - l eve l map o f t h e T e r t i a r y l imestone system o f t h e southern Un i ted Sta tes ( S t r i n g f i e l d , 1 9 6 6 ) , and t h e groundwater b a s i n map o f t he Mammoth Cave Region, Kentucky (Qu in lan and Ray, 1 9 8 1 ) a lmost a l l r e g i o n a l k a r s t s tud ies show water movement by arrows on maps r a t h e r than by wa te r - l eve l contours. Both the r e g i o n a l and l o c a l approaches t o k a r s t water must be considered, as has been done i n the Transvaal , Republ ic o f South A f r i c a (Ens l in , 1 9 6 7 ) , i n t h e c o a s t a l areas o f Yugoslavia (Komatina, 1 9 6 5 ) , and i n France (Avias, 1 9 6 3 ) .

I n t h e USSR, subd iv i s ion o f major areas accord ing t o k a r s t man i fes ta t i on cond i t i ons as a form o f k a r s t mapping has been w ide ly used. These are the maps o f Maksimovich ( 1 9 6 2 ) on t h e whole t e r r i t o r y o f t he USSR, Gvozdetsky ( 1 9 5 2 ) on the Caucasus, and Rodionov ( 1 9 6 3 ) on t h e European p a r t o f t he USSR, the U r a l s and Caucasus.

A. G. Chik ishev ( 1 9 7 3 ) has produced a genera l i zed map combining recen t s p e l e o l o g i c a l i n v e s t i g a t i o n s .

A r e l a t i v e l y new group o f techniques u s i n g s p e c i a l i z e d inst ruments - sonar, geo-bombs, down-hole t e l e v i s i o n cameras, deep-well c u r r e n t meters, down-hole pH samples, c o n d u c t i v i t y ( p r o f i l e ) t raverses , and c a l i p e r l ogg ing dev ices - i s now i n use. Studies u s i n g some o f these techniaues are be ing made a t Pennsylvania S ta te U n i v e r s i t y , t h e Geo log ica l Survey o f Alabama, and t h e U.S. Geo log ica l Survey; t h e Geo log ica l Survey o f South A f r i c a ; t he U n i v e r s i t y o f M o n t p e l l i e r , France; t h e H. E. T r e b i s n j i c a , Yugoslavia; and a t Ploscow S ta te Un i .vers i ty and t h e USSR I n s t i t u t e o f hydrogeology and eng ineer ing geology.

A complex o f geophysica l methods in tended f o r i n v e s t i g a t i o n o f k a r s t te r ra ins , e s p e c i a l l y f o r covered o r b u r i e d k a r s t , i s b e i n g w ide ly app l i ed i n the USSR (Og i lvy , 1957, and 1 9 4 8 , Golovtsyn and o thers , 1 9 5 7 ) . These i n v e s t i - ga t i ons a re in tended t o c l a r i f y g e o l o g i c a l - s t r u c t u r a l p e c u l i a r i t i e s o f k a r s t i c massi fs ; t o eva lua te t h e degree and the t r e n d o f j o i n t i n q ; t o l o c a t e and determine t h e e x t e n t o f k a r s t c a v i t i e s ; t o d iscover concealed discharge areas; and t o study t h e d i r e c t i o n s and r a t e s o f f l o w o f k a r s t waters w i t h depth, changes i n temperature and chemical composi t ion o f k a r s t waters. The main methods used f o r these i n v e s t i g a t i o n s are seismic and g rav ime t r i c surveys, radiowave prob ing , high-frequency prospect ing, gamma-ray neutron logg ing , r e s i s t i v i t y s tud ies , micro-magnetic survey, he l ium survey, charged-body method, and t h e r e f r a c t e d waves method. Geophysical s tud ies are combined w i t h hydrogeo log ica l i n v e s t i g a t i o n s .

A t t h e U n i v e r s i t y o f M o n t p e l l i e r , Jacques Avias has c a r r i e d o u t research u s i n g sur face g r a v i t y , r e s i s t i v i t y , and seismic methods t o de l i nea te s o l u t i o n systems i n l imestone, and a down-hole T.V. camera t o de l i nea te s i z e and shape o f s o l u t i o n - c a v i t y development. M u l t i s p e c t r a l photography i s be ing used t o study d ischarge from submarine spr ings . Th is technique has a l s o been used by the FAO and U.S. Geo log ica l Survey f o r t he same purpose i n Jamaica (Kohout and o the rs , 1 9 8 1 ) , S i c i l y , and Hawaii . Considerable a d d i t i o n a l use o f remote sensing can be made i n more r e f i n e d s tud ies o f water i n l imestone and dolomite. For example, t h e Marine Oceanographic Research I n s t i t u t e i n S p l i t , Yugoslavia, has used a sonic-depth f i n d e r t o map s inkholes i n t h e l imestone on t h e sea f l o o r t h a t d ischarge water i n t o t h e open sea. Cur ren t meters used by scuba d i v e r s o f f t h e coas t o f F l o r i d a a re be ing used f o r d ischarge measurement o f subterranean s p r i n g f low. Concentrated submarine d ischarge o f k a r s t i c water was s tud ied by means o f va r ious geophysica l methods by Dakknov ( 1 9 5 1 ) , Brashnina ( 1 9 6 3 ) , Buachidze and Mei ivova, ( 1 9 6 7 ) , and Lvova and Popov (1971). Moore and Stewart ( 1 9 8 3 ) have used geophysica l methods t o de l i nea te f r a c t u r e t races whose genera l l o c a t i o n s were mapped u s i n g a e r i a l photographs.

During t h e p a s t f i f t e e n ( 1 5 ) years a g r e a t d e a l o f work i n k a r s t hydro logy has been done w i t h geochemical methods. O f p a r t i c u l a r i n t e r e s t i s t he work o f Back and Hanshaw ( 1 9 7 0 ) i n t h e Yucatan and FI -or ida, where they found c o n t r a s t i n g ‘ground-water geochemist r ies due t o presence o r l a c k o i a q u i f e r confinement. Hanshaw and Back ( 1 9 7 9 ) l a t e r pub l i shed a h i g h l y i n s t r u c t i v e paper on t h e major geochemical processes which c o n t r i b u t e t o the e v o l u t i o n o f carbonate-aqui fer systems. Much recen t work i n carbonate geochemistry such as White ( 1 9 7 7 1 , Plummer, e t a l . ( 1 9 7 8 1 , and Nadler e t a l . ( 1 3 8 0 ) has concentrated on t h e k i n e t i c s o f chemical processes i n carbonate aqu i fe rs . Drake ( 1 9 8 2 ) has repo r ted on t h e e f f e c t s o f geomorphology and seasona l i t y on the chemist ry o f

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carbonate groundwater. P l u m e r and Busenberg ( 1 9 8 2 ) have reeva lua ted va lues f o r severa l o f t he s o l u t i o n constants used i n carbonate hydro logy.

Spec ia l a t t e n t i o n should be p a i d t o t h e i n v e s t i g a t i o n s devoted t o s tudy ing the r a t e s o f k a r s t development. K a r s t denudation, accord ing t o Maksimovich ( 1 9 6 2 ) , i s c o n d i t i o n a l l y determined by t h e l a y e r o f k a r s t i f y i n g rocks expressed i n microns, removed during one year f rom t h e whole t e r r i t o r y o f t h e mass i f ( f o r example, t h e r a t e i s 35.3 microns p e r year f o r t h e Crimea). Accord ing t o Rodionov ( 1 9 4 9 ) , t h e index o f modern k a r s t development i s t h e r a t i o o f t he amount o f so lub le rock c a r r i e d o u t f o r one thousand years t o t h e volume o f t he k a r s t massi f expressed i n percent (0.008 pe rcen t f o r t h e Crimea and 0.007 percent f o r t h e Caucasus).

Harmon's work i n n o r t h - c e n t r a l Mexico ( 1 9 7 1 ) on s o l u t i o n r a t e s , denudat ion r a t e s i n N o r t h America ( 1 9 7 2 ) and a p p l i c a t i o n o f s t a b l e carbon i so tope s tud ies ( 1 9 7 1 ) t o k a r s t research i s a l s o encouraging. Impor tan t i so tope s tud ies have a l s o bee done i n t h e Edwards Aqu i fe r , Texas, U.S.A. , by Pearson and Rettman ( 1 9 7 6 ) . Back and Z o e t l !1975) d i d a genera l survey o f t h e use o f geochemistry, t race rs , and iso topes i n k a r s t hydrology.

The i n f l u e n c e o f aggressiveness o f n a t u r a l water upon the process o f k a r s t development was discussed by Laptev (1939), who o f f e r e d some formulas f o r q u a n t i t a t i v e e v a l u a t i o n o f n a t u r a l water i n f l uence upon s o l u t i o n o f k a r s t i f y i n g rocks as w e l l as t h e schedules o f fo rmat ion o f aggress ive m ix tu res f rom any two nonaggressive components o f n a t u r a l waters, such as carbonic , su lphu r i c , ace t i c , and m u r i a t i c acids; o rgan ic ac ids ( o x a l i c , formic, s u c c i n i c ) connected w i t h t he development o f microorganisms; and humic a c i d and fu l voac id , which appear i n s o i l c o n t a i n i n g organ ic p a r t i c l e s .

Studies on carbonate depos i t i on ( 1 9 7 1 ) a t Car lsbad Caverns, c a l c i t e under -sa tura t ion o f waters i n Kentucky, and d i g i t a l computer model ing o f t h e s inkho le p l a i n a q u i f e r o f wes t -cent ra l Kentucky ( 1 9 7 2 ) have been c a r r i e d o u t by T r a i l k i l l . Par izek and White ( 1 9 7 1 ) have r e l a t e d t h e major types o f pe rmeab i l i t y t o geo log ic format ions i n Pennsylvania, U.S.A., u s i n g calcium/magnesium r a t i o s and o the r geochemical parameters. Bray ( 1 9 6 9 ) d iscussed some o f t h e problems encountered w i t h s tandard methods o f hardness es t imat ion . D e t a i l e d work by Drew ( 1 9 7 0 ) in theU.K. revea led d isc repanc ies i.n ca lc ium carbonate contents , which are exp la ined by Laptev ( 1 9 3 9 ) a n d B o g l i ' s ( 1 9 7 1 ) theory o f co r ros ion by m i x i n g waters. Auber t ( 1 9 6 7 ) , work ing i n the Jura Pountains, es t imated the occurrence o f s o l u t i o n on the bedrock sur face, i n f i s s u r e s and i n deep caverns. Other impor tan t workers i n s o l u t i o n r a t e s i nc lude Corbe l ( 1 9 5 9 ) , who developed a formula f o r r a t e o f s o l u t i o n ; W i l l i ams ( 1 9 6 3 ) , who m o d i f i e d Corbe l ' s formula; P i t t y ( 1 9 6 6 ) and Gams ( 1 9 6 2 ) . The Frenchman Roques ( 1 9 6 9 ) rev iews present-day problems i n t h e p h y s i c a l chemist ry o f carbonates i n so lu t i on . W i t t k e ( 1 9 6 8 ) and K i r a l y ( 1 9 6 9 ) have s tud ied theo r ies o f f l o w i n f i s s u r e d rocks i n k a r s t . Models o f carbonate rocks exp la in ing hyd ro log i c charac ter and water movement have been made by J. P. T r i p e t ( 1 9 7 1 ) and White ( 1 9 6 9 ) .

The r e s u l t s o f t h e o r e t i c a l exper imenta l i n v e s t i g a t i o n s ob ta ined i n work ing o u t t he methods o f hydrogeologic research and fo recas t i ng i n t h e r e g i o n o f development o f f i s s u r e d k a r s t i c water-bear ing rocks are f u l l y s t a t e d by Babushkin and o the rs (1972) . They descr ibe methods o f mathematical mode l l i ng and p r o b a b i l i s t i c - s t a t i s t i c a l es t ima t ions and a p p l i c a t i o n o f these methods f o r f o recas t i ng ground-water regime under d i s t u r b e d cond i t i ons .

Desc r ip t i ons o f topographic fea tu res o f major k a r s t reg ions o f t h e w o r l d were a v a i l a b l e many years ago, and much o f t h e e a r l y work l e d t o d e s c r i p t i o n o f k a r s t sur face fea tu res by geographers and geomorphologists. Fo r example, t h e work o f C v i j i c 11893) gave c l e a r s imple d e f i n i t i o n s o f k a r s t landforms, such as do l ines , karren, and p o l j e s . Some o f t h e most d e t a i l e d geomorphic analyses o f k a r s t areas are b e i n g done by t h e Federa t ion o f Spe leou is ts o f L j u b l j a n a , Yugo- s lav ia . Comprehensive works t h a t g i v e e x c e l l e n t o v e r a l l d e s c r i p t i o n s o f k a r s t forms found throughout t h e w o r l d i n c l u d e Maksimovich ( 1 9 6 3 , 1969) ; J. N. Jennings (1971) ; Herak and S t r i n g f i e l d (1972) ; Sweeting ( 1 9 7 3 ) and Jacus ( 1 9 7 7 ) . A number o f works on t r o p i c a l k a r s t have a l s o been pub l ished, i n c l u d i n g r e p o r t s by B i r o t and o t h e r s ( 1 9 6 8 1 , Corbel and Muxart (1970), Gvozdetski ( 1 9 7 0 ) , Isphord ing (19771, and Watson Monroe's t r a n s l a t i o n o f M io tke ' s r e p o r t ( 1 3 7 3 ) on Puer to Rican k a r s t . Reports on a l p i n e k a r s t i n c l u d e those by Ford ( 1 9 7 9 and 1 9 8 0 ) , Campbell (19791, and Maslyn ( 1 9 7 9 ) . The e f f e c t s

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o f g l a c i a t i o n on k a r s t have been s tud ied by Ford ( 1 9 8 3 ) and Smart and Ford (1983).

A newlo ld f r o n t i e r i n k a r s t hydro logy has reopened i n recen t years w i t h t h e resumption o f s c i e n t i f i c communication between China and the West. Carsolog ica S in i ca , a j o u r n a l pub l i shed by t h e I n s t i t u t e o f K a r s t Geology, G u i k i n , Guangxi, The People 's Republ ic o f China i nc ludes an E n g l i s h a b s t r a c t o f each paper as do t h e p u b l i c a t i o n s o f t he I n s t i t u t e o f Geology, Academia S in ica . Research o f China K a r s t (Ka rs t Research Group, 1979) i s a comprehensive book t h a t i nc ludes a summary i n Engl ish. Other accounts o f k a r s t i n China i n c l u d e Song L inhua and o the rs ( 1 9 8 3 ) , Sch ind le r ( 1 9 8 2 1 , Back (19821, and S i l a r ( 1 9 6 5 ) .

The use o f a e r i a l remote-sensing methods has g r e a t l y expanded s ince R ich f i r s t r e p o r t e d on j o i n t i n g o f l imestone mesas i n no r the rn Oklahoma, U.S.A. Perhaps t h e work o f Lattman and Par izek ( 1 9 6 4 ) and T r a i n e r and E l l i s o n (1967) may be considered the most thorough t reatments o f e a r l y photogeologic i n t e r p r e t a t i o n and t h e occurrence o f ground water. Sonderegger ( 1 9 7 0 ) put e a r l i e r photogeologic techniques t o use i n one o f a s e r i e s o f r e p o r t s on t h e hydro logy o f l imestone te r ranes i n n o r t h Alabama, U.S.A. Remote sensing ( i n f r a r e d and thermal i n f r a r e d ) has a l s o been success fu l l y used by Coker ( 1 9 6 9 ) , Newton and o the rs ( 1 9 7 3 1 , Newton ( 1 9 7 6 ) , and Warren and Wielchowsky ( 1 9 7 3 ) f o r t he study o f s inkhole-prone areas o f t he southeastern U.S. Brown ( 1 9 7 2 ) used thermal i n f r a r e d imagery t o l o c a t e k a r s t spr ings i n Canada. Remote sensing shows g r e a t promise i n t h e study of env i ronmenta l problems i n carbonate te r ranes , such as r e s e r v o i r - s i t e s tud ies (Powel l and o thers , 1970; Sowers, 1 9 7 3 ) and mon i to r i ng and management o f ground-water recharge areas t o p revent contaminat ion (Jamier, 1 9 7 6 and Burger, 1 9 7 9 ) .

I n t h e U n i t e d States, seve ra l geo log i s t s and h y d r o l o g i s t s a re work ing on env i ronmenta l problems p e c u l i a r t o carbonate t e r r a i n s . As p o i n t e d o u t by Par izek a n d White (1971) , t h e p r i n c i p a l land-use problems are: foundat ions, water-supply development, min ing, a g r i c u l t u r a l a c t i v i t y , highway c o n s t r u c t i o n and maintenance, d i sposa l o f s o l i d and l i q u i d wastes, and land-use i n ground-water d ischarge areas. S inkhole fo rmat ion i n areas o f extreme dewater ing o r improper water -we l l development have been s tud ied ex tens i ve l y i n South A f r i c a (Jennings, 1 9 6 6 1 , Pennsylvania, U.S.A. (Foose, 1 9 5 3 ) , and Alabama (Powel l and LaMoreaux, 1 9 6 9 ) , (Newton and others, 19731, (Newton, 1 9 7 6 ) . As a r e s u l t o f these s tud ies , s inkho le a c t i v i t y may be recognized o r p r e d i c t e d p r i o r t o damage t o s t r u c t u r e s o r p roper t y , o r persona l i n ju ry . Calembert ( 1 9 7 5 ) c o l l e c t e d repo r t s , notes and comments by s c i e n t i s t s i n many coun t r i es t o produce an ex tens ive r e p o r t on g e o l o g i c a l eng ineer ing problems i n k a r s t i c reg ions. Environmental s tud ies (Moser and o thers , 1971) o f carbonate t e r r a i n s a re becoming more impor tan t as popu la t ions expand i n t o carbonate t e r r a i n s f o r m r l y devoted t o f o r e s t s , a g r i c u l t u r e and mining. C a r e f u l land-use p lans should be a t o p p r i o r i t y f o r f u t u r e s tud ies.

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Part I: Factors determining the water regime in carbonate rocks

1. Carbonate rocks and geological processes

1.1 I n t r o d u c t i o n (L. A. He ind l )

The hydrogeology o f carbonate rocks can o n l y he understood by c a r e f u l observat ion o f t h e p h y s i c a l c h a r a c t e r i s t i c s and d i s t r i b u t i o n o f t h e rocks. The fundamental g e o l o g i c a l approach t o t h e exp lo ra t i on , use, and conserva t ion o f water i s through cons ide ra t i on of t h e cornpositism o f t h e rocks, t h e shape o f t h e i r u n i t s , how the composi t ion o f t h e un i t v a r i e s throughout i t s ex ten t , t h e sequence o f u n i t s and how i t v a r i e s , how the sequence has been deformed and t h e i n f l u e n c e o f t h e deformat ion on t h e c h a r a c t e r i s t i c s o f t h e rocks, t h e u n i t s , t he sequence, and t h e topographic and phys iograph ic s i t u a t i o n . These c h a r a c t e r i s t i c s a re discussed i n the f o l l o w i n g sec t ions on l i t h o l o g y , sedimentat ion and s t r a t i g r a p h y , s t ruc tu re , and m ic ro tex tu re .

1 .2 L i t h o l o g y (D. J. Benson)

1 .2 .1 Mineralogy. Carbonate rocks a re r e l a t i v e l y uncompl icated m ine ra log i ca l l y . They a re composed p r i m a r i l y o f carbonate m ine ra l s which combine main ly b i v a l e n t c a t i o n s w i t h t he carbonate r a d i c a l . The, t h r e e most common rock forming carbonate m ine ra l s a re a ragon i te , c a l c i t e , and dolomi te.

Aragoni te i s an orthorhomhic ca lc ium carbonate which i s cha rac te r i zed by n i n e - f o l d coo rd ina t i on ( 3 c a t i o n s f o r each oxygen). I t i s r e l a t i v e l y pu re ca lc ium carbonate c o n t a i n i n g o n l y sma l l amounts ( l e s s than 2 mole percent ) o f Mg. Because o f t h e n i n e - f o l d coord ina t ion , t h e s u b s t i t u t i o n o f l a r g e r c a t i o n s i s favored and aragon i te commonly conta ins t r a c e amounts o f S r , Ba, Pb, and K. Aragoni te i s a high temperature polymorph o f ca lc ium carbonate (Jamieson, 1953; Crawford and Fy fe , 1 9 6 4 ) and, as such, i s metastable under sur face cond i t i ons .

C a l c i t e i s a rhombohedral ca lc ium carbonate which i s cha rac te r i zed by s i x - f o l d coo rd ina t i on ( 2 c a t i o n s f o r each oxygen). I o n i c s u b s t i t u t i o n i s much more common i n c a l c i t e than i n aragoni te . Cat ions such a.s Fe, Mn, Z n , and C u a re favored i n t h e rhombohedral s t r u c t u r e and a re common t r a c e elements s u b s t i t u t i n g f o r calcium. C a l c i t e a l s o shows widespread s u b s t i t u t i o n o f Mg f o r Ca. The Mg conten t i n c a l c i t e s can range f rom t r a c e amounts t o 20 mole percent. Th i s v a r i a t i o n i n magnesium conten t a l l ows t h e d i f f e r e n t i a t i o n o f c a l c i t e i n t o low-magnesium c a l c i t e which con ta ins l e s s than 4 mole pe rcen t MgC03, and high-magnesium c a l c i t e which conta ins f rom 4 t o 20 mole percent MgC03.

The mineralogy o f t h e ca lc ium carbonates i s c o n t r o l l e d by t h r e e major f ac to rs : (1) na ture o f t h e carbonate producing organisms, (2) water tempera- tu re , and ( 3 ) pos t -depos i t i ona l a l t e r a t i o n . Since the m a j o r i t y o f ca l c ium carbonate sediment i s produced o r g a n i c a l l y , t he major c o n t r o l on minera logy i s t h e na ture o f t h e producing organism. C e r t a i n organisms, such as Codiacean and Dasycladacean algae and S c l e r a c t i n i a n coe len tera tes secre te s t r i c t l y a r a g o n i t i c s k e l e t a l m a t e r i a l . Others such as brachiopods secre te low-magnesium c a l c i t e w h i l e echinoderms secrete skeletons composed o n l y o f high-magnesium c a l c i t e .

Some -organisms a re a l s o capable of s e c r e t i n g skeletons o f d i f f e r e n t composi t ion under d i f f e r i n g temperature and s a l i n i t y c o n d i t i o n s (Lowenstam, 1 9 6 4 ; Chave, 1 9 5 4 ) . A ragon i te p r e c i p i t a t i o n i s favored under c o n d i t i o n s o f h i g h water temperature and h i g h pH, whereas c a l c i t e i s favored w i t h lower water temperatures, low pH, and t h e presence o f s u l f a t e i o n s i n the s o l u t i o n .

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Diagenet ic a l t e r a t i o n a l s o has s i g n i f i c a n t c o n t r o l on t h e minera logy o f aDcient ca lc ium carbonates. Both aragon i te and high-magnesium c a l c i t e a re metas*able under sur face cond i t ions , a l t e r i n g t o low-magnesium c a l c i t e . Whi le T e r t i a r y carbonates commonly con ta in mix tu res o f aragoni te , low-Mg c a l c i t e , and high-Mg c a l c i t e , Paleozoic carbonates are composed almost e x c l u s i v e l y o f low-Mg c a l c i t e . Though the t rans fo rma t ion o f a ragon i te and high-Mg c a l c i t e t o low-Mg c a l c i t e through t ime has been documented ( S t e l h i and Hower, 1 9 6 1 ) , i t s importance i s p r e s e n t l y be ing debated. Some f e e l d iagene t i c a l t e r a t i o n i s respons ib le f o r t h e l a c k o f a ragon i te and high-Mg c a l c i t e i n o l d e r carbonates, w h i l e o the rs (Folk , 1 9 7 4 ) i n t e r p r e t t he change t o r e f l e c t a change i n t h e na tu re o f t h e carbonate produc ing system through t ime w i t h changes i n t h e chemist ry o f t he w o r l d oceans t h e most w ide ly evoked cause.

The .third major m ine ra log i c component o f carbonate rocks i s dolomite. Dolomi te i s a ca lc ium magnesium carbonate CaMg(CO312. I d e a l l y i t cons is t s o f an a l t e r n a t i o n o f c a t i o n l a y e r s composed e n t i r e l y o f Ca w i t h l a y e r s composed e n t i r e l y of Mg. I n na ture , however, Ca commonly s u b s t i t u t e s f o r Mg i n the Mg I.ayers, r e s u l t i n g i n an excess o f Ca i n the s t ruc tu re . Because o f t h i s s u b s t i t u t i o n dolomi tes range i n Ca content f rom 5 8 mole percent CaC03 t o 50 mole percent CaC03 ( i d e a l do lomi te ) . Fe a l s o commonly s u b s t i t u t e s i n the l a t t i c e producing anke r i t e , an i r o n - r i c h dolomi te. Z n and Mg are o the r ca t i ons which s u b s t i t u t e i n t r a c e amounts.

Whi le some do lomi te has been shown t o be a p r imarv p r e c i p i t a t e , most do lomi te i s formed through replacement o f o r i g i . n a l a ragon i te o r c a l c i t e . Severa l processes have been proposed f o r t h i s " d o l o m i t i z a t i o n " i n c l u d i n g seepage r e f l u x (Adams and Rhodes, 1 9 6 9 1 , evapora t ive pumping (Hsu and Siegenthaler , 1 9 6 9 ) , c a p i l l a r y concent ra t ion (Friedman and Sanders, 1 9 6 7 ) , and freshwater-seawater m i x i n g (Hanshaw e t a l . , 1 9 7 1 ; Badiozamani, 1 9 7 3 ; F o l k and Land, 1 9 7 5 ) but a consensus o f op in ion on the a c t u a l mechanism ( o r mechanisms) o f d o l o m i t i z a t i o n has n o t v e t been reached (See Zenger e t a l . , 1 9 8 0 ) .

1 .2.1.1 Carbonate cons t i t uen ts . Carbonate rocks are c h a r a c t e r i s t i c a l l y very pure be ing composed o n l y o f carbonate minera ls . Th i s i s a r e f l e c t i o n o f t he orqan ic o r i g i n o f most carhonate sediment. Most carbonate producing organisms are f i l t e r feeders o r depend upon photosynthes is . The presence o f s i g n i f i c a n t amounts o f t e r r i genous m a t e r i a l i n the water column hampers carbonate produc t ion , and i f g r e a t enough, w i l l e f f e c t i v e l y e l i m i n a t e it. Thus most carbonate rocks c o n t a i n o n l y minor amounts o f te r r igenous m a t e r i a l . The carbonate components can be d i v i d e d i n t o t h r e e separate groups; a l l ochemica l cons t i t uen ts , m i c r i t e , and cement.

1.2.1.1.1 A l lochemica l cons t i t uen ts . The te rm a l l ochemica l c o n s t i t u e n t was in t roduced hy F o l k (1959) t o descr ibe the framework cons t i t uen ts o f carbonates. There are s i x a l l ochemica l cons t i t uen ts which are common i n carbonates: s k e l e t a l g ra ins , oo ids, oncoids, pe lo ids , i n t r a c l a s t s , an6 aggregate gra ins .

S k e l e t a l g ra ins , commonly termed b i o c l a s t s , a re perhaps the most common a l l ochemica l c o n s t i t u e n t s o f carbonates. They represent whole o r fragmented hard p a r t s o f carbonate sec re t i ng organisms which i n h a b i t e d the environment o f depos i t ion . S k e l e t a l q r a i n s occur i n a wide v a r i e t y o f s izes r e f l e c t i n g the morphology o f t h e organism which produced them. Recause o f t h e i r o rqan ic o r i g i n they p rov ide considerable i n fo rma t ion on t h e ecology o f t h e environment o f depos i t ion .

Ooids a re s p h e r i c a l g r a i n s which c o n s i s t o f a c e n t r a l core o r nucleus (commonly a s k e l e t a l g r a i n o r o the r al lochem) surrounded by a number o f concen t r i c l aye rs . These l a y e r s a re composed o f aragoni t e o r c a l c i t e c r y s t a l s which are o r i e n t e d e i t h e r normal ( r a d i a l oo ids) o r t a n g e n t i a l ( t a n g e n t i a l oo ids) t o the sur face o f t he u n t l e r l y i n g l aye r . The l a y e r s o r coa t ings are formed through chemical p r e c i p i t a t i o n as t h e g r a i n i s moved back and f o r t h i n warm, saturated, h i g h l y a g i t a t e d waters. As such, oo ids are one o f t he few carbonate p a r t i c l e s which are de r i ved i n o r g a n i c a l l y , though t h e r e i s recent evidence t h a t o rqan ic a c t i v i t y may p l a y an i n d i r e c t r o l e i n the fo rmat ion o f a t !.east some oo ids (Davies e t a l . , 1 9 Ï F ) . The term o o i d i s t y p i c a l l y r e s t r i c t e d t o g r a i n s l e s s than 2 mm in diameter. Grains g rea te r than 2 mm i n diameter are

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terms p i s o i d s . Many p i s o i d s form through processes d i f f e r e n t f rom t h a t descr ibed above.

Oncoids a re a l g a l l y coated g r a i n s g e n e r a l l y l a r g e r than 2 mm i n diameter. L i k e p i s o i d s they c o n s i s t o f a nucleus which i s surrounded by concen t r i c layers . They d i f f e r f rom p i s o i d s i n t h a t t h e coat ings a re t y p i c a l l y i r r e g u l a r i n th ickness and c o n s i s t o f f i l amen ts de r i ved from a l g a l e n c r u s t a t i o n o f g r a i n s which are p e r i o d i c a l l y moved on t h e sea f l o o r .

Pe lo ids a re s p h e r i c a l t o subspher ica l aggregates o f m i c r o c r y s t a l l i n e ca lc ium carbonate commonly l e s s than 2 mm i n diameter. Many p e l o i d s a re generated as f e c a l p a r t i c l e s by sediment i n g e s t i n g organisms and are commonly termed p e l l e t s . Other p e l o i d s a re produced through t h e b i o l o g i c a l degradat ion o f smal l al lochems by e n d o l i t h i c ( b o r i n g ) algae o r through t h e mechanical breakdown o f l a r g e r m i c r o c r y s t a l l i n e p a r t i c l e s .

ï n t r a c l a s t s a re l a r g e (g rea te r than 2 mm) p a r t i c l e s o f penecontemporaneous sediment which has been s e m i - l i t h i f i e d , eroded, t ranspor ted , and redepos i ted w i t h i n t he b a s i n o f depos i t ion . The p a r t i c l e s a re t y p i c a l l y composed o f l i m e mud but. may a l s o c o n t a i n o the r al lochems i n c l u d i n g b i o c l a s t s , p e l o i d s , and ooids.

Aggregate g r a i n s a re composite g r a i n s formed by t h e a g g l u t i n a t i o n o f a number o f i n d i v i d u a l al loche mi cal^ p a r t i c l e s (pe lo ids , oo ids, o r s k e l e t a l g r a i n s ) . Th is a g g l u t i n a t i o n i s produced by e a r l y cementat ion (grapestones) o r by a l g a l o r o rgan ic enc rus ta t i on ( lumps). Aggrega-te g r a i n s a re c h a r a c t e r i s t i c o f low energy environments w i t h slow sedimentat ion r a t e s , good water c i r c u l a t i o n , and v a r i a b l e l e v e l s o f a g i t a t i o n (F luge l , 1 9 8 2 ) .

1.2.1.1.3. M i c r i t e . The term m i c r i t e was proposed'hy F o l k ( 1 9 5 9 ) t o descr ibe the m i c r o c r y s t a l l i n e l ime mud common i n low energy carbonate depos i ts . Th i s m i c r i t e i s t he carbonate equ iva len t o f d e t e r i t a l m a t r i x i n te r r i genous deposi ts. I t occurs between al lochems and i t s presence and abundance i s an impor tan t c h a r a c t e r i s t i c i n the c l a s s i f i c a t i o n o f carbonate rocks. Whi le i t was once thought t h a t most o f t h i s m i c r i t e was t h e produc t o f i no rgan ic p r e c i p i t a t i o n , i t has been shown t h a t almost a l l m i c r i t e i s produced through d i s a r t i c u l a t i o n o f calcareous a lgae (Stockman e t a l . , 1967).

1.2.1.1.3 Cement. The t h i r d major component o f carbonate rocks i s cement. Cement i s ve ry common i n h i g h energy carbonate depos i ts where i t occurs as a pass ive pore f i l l i n g p r e c i p i t a t e d from sa tura ted so lu t i ons . These s o l u t i o n s c o n t r o l t he composi t ion o f t h e cements and a r a g o n i t i c , c a l c i t i c (bo th high-Mg and low-Mg), and d o l o m i t i c cements a re a l l found i n carbonate. U n l i k e allochems and m i c r i t e which a re d e t r i t a l c o n s t i t u e n t s o f carbonate rocks, cements a re d iagene t i c i n o r i g i n and en te r t h e sediment a f t e r depos i t ion . A v a r i e t y o f cement types have been recognized based on t h e i r c r y s t a l s i z e a n d morphology i n c l u d i n g m i c r i t i c , f i b r o u s , drusy, bl-ocky, and s y n t a x i a l r i m cements. Many o f these cements can be recognized by t h e i r coarse c r y s t a l s i z e and c l e a r appearance and have been termed spar ry cements.

1 .2 .1 .2 Non-carbonate cons t i t uen ts . Whi le carbonate rocks a re composed p r i m a r i l y o f carbonate c o n s t i t u e n t s (al lochems, m i c r i t e , and cement) , they do con ta in minor amounts o f non-carbonate m a t e r i a l . T h i s non-carbonate m a t e r i a l f a l l s i n t o two classes; d e t r i t a l components and d iagene t i c components. Non-carbonate d e t r i t a l components c o n s i s t p r i m a r i l y o f t e r r i genous c lays , s i l t s , and sand.s. These p a r t i c l e s seldom comprise more than a few percent o f most carbonate rocks s ince t h e i n t r o d u c t i o n o f s i g n i f i c a n t amounts o f te r r igenous m a t e r i a l i n t o a carbonate b a s i n w i l l h a l t carbonate produc t ion .

D iagenet ic non-carbonate components o f carbonate rocks are those cons t i t uen ts which have been added a f t e r depos i t ion . These i n c l u d e m a t e r i a l s which f i l l p r imary pores i n t h e sediment and m a t e r i a l s which rep lace t h e o r i g i n a l carbonate components. Cher t and anhyr i te lgypsum a re t h e major d iagenet ic components. Cher t i s a common component i n carbonates, p a r t i c u l a r l y s l i g h t l y a r g i l l a c o u s carbonates, and may make up apprec iab le p o r t i o n s o f c e r t a i n u n i t s . I t e x h i b i t s a l l stages o f replacement f rom d i s c r e t e nodules t o

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complete replacement o f e n t i r e beds o f carbonate. The replacement o r i g i n f o r t he c h e r t i s revea led by t h e i n c l u s i o n w i t h i n t he c h e r t o f ghosts o f al lochems o r remnants o f unreplaced m a t e r i a l .

1.2.2 C l a s s i f i c a t i o n o f carbonate rocks. The l i t e r a t u r e conta ins a l a r g e number o f c l a s s i f i c a t i o n s o f carbonate rocks. These c l a s s i f i c a t i o n s va ry f rom ve ry genera l c l a s s i f i c a t i o n s o f carbonate rocks a.s a whole t o very s p e c i f i c c l a s s i f i c a t i o n s o f l imestones. I n some cases a genera l c l a s s i f i c a t i o n based on t h e r e l a t i v e p ropor t i ons o f carbonate and non-carbonate c o n s t i t u e n t s i s a l l t h a t i s requ i red . I n o thers , a ve ry s p e c i f i c c l a s s i f i c a t i o n , perhaps r e q u i r i n g microscopic examinat ion o f t h e l i t h o l o g y i s necessary.

1.2.2.1 General c l a s s i f i c a t i o n o f carbonates. Carbonate rocks are commonly de f i ned as sedimentary rocks which con ta in g rea te r than 5 0 percent carbonate minera ls . Though most carbonate rocks are composed o n l y o f carbonate minera ls , mixed ter r igenous-carbonate l i t h o l o g i e s do occur. These mixed l i t h o l o g i e s occur as th in in te rbeds w i t h i n carbonate u n i t s o r near the boundar ies between carbqnate and c l a s t i c u n i t s . Quar tz sands and c l a y m ine ra l s represent t h e most common te r r i genous components and t h e mixed carbonate-c las t i c l i t h o l o g i e s can be adequately c l a s s i f i e d u s i n g a s imple te rna ry d.iagram (See f i g u r e 1 . 2 - 1 ) .

The te rm l imestone i s r e s t r i c t e d t o those rocks which con ta in g rea te r than 90 percent ca lc ium carbonate. I f t h e rock conta ins more than 50 percent but l e s s than 90 percent ca lc ium ca rbomte , i t i s termed an arenaceous l i n e s t o n e o r an a r g i l l a c e o u s l imestone depending upon the r e l a t . i v e amounts o f qua r t z sand and c l a y m ine ra l s present .

Dolomi te i s a l s o a common m ine ra log i ca l component o f carbonate rocks. Some o f t h i s do lomi te i s a p r imary p r e c i p i t a t e , but most forms as a d iagene t i c replacement o f c a l c i t e o r aragoni te . Carbonates show a l l stages o f replacement f rom complete ly pure l imestones which conta in no do lomi te t o dolostones i n which a l l t h e c a l c i t e and/or a ragon i te has heen rep laced by dolomite. I t i s convenient t o subdiv ide t h e spectrum i n t o fou r c lasses based on t h e percent age o f do lomi te (See f i g u r e 1 . 2 - 2 ) .

1 .2.2.2 C l a s s i f i c a t i o n o f l imestones. The l i t e r a t u r e conta ins a s u b s t a n t i a l number o f l imestone c l a s s i f i c a t i o n s (Folk, 1959, 1 9 6 2 ; Dunham, 1962 ; Embry and Klovan, 1 9 7 2 , Le igh ton and Pendexter, 1 9 6 2 ; Plumley, e t a l . , 1 9 6 2 ; and Todd, 1966). These c l a s s i f i c a t i o n s range from p u r e l y d e s c r i p t i v e c l a s s i f i c a t i o n s t o ext remely gene t i c c l a s s i f i c a t i o n s and are based on a v a r i e t y o f a t t r i b u t e s o f l imestones i nc lud ing , type o f a l l ochemica l cons t i t uen ts , r a t i o o f a l l ochemica l c o n s t i t u e n t s t o m i c r i t e and cement, rounding and s o r t i n g o f allochems, d e p o s i t i o n a l t e x t u r e , and energy o f t he environment O € depos i t ion . Two o f t he most w i d e l y used c l a s s i f i c a t i o n s a re the c l a s s i f i c a t i o n s o f F o l k ( 1 9 6 2 ) and Dunhan ( 1 9 6 2 ) .

1 .2 .2.2.1 C l a s s i f i c a t i o n o f F o l k (1.962) . The c l a s s i f i c a t . i o n o f F o l k i s an at tempt t o subdiv ide carbonate rocks I n t o a number o f c lasses which approximate the energy o f t h e environment o f depos i t ion . Th is c l a s s i f i c a t i o n i s based on the types o f a l l ochemica l c o n s t i t u e n t s p resent and t h e i r r e l a t i v e p ropor t i ons , t he r a t i o o f a l l ochemica l c o n s t i t u e n t s t o m i c r i t e o r cement, and t h e s o r t i n g and rounding O € t he allochems.

I n i t i a l l y t he c l a s s i f i c a t i o n subdiv ides l imestones i n t o th ree major types; a l l ochemica l rocks, or thochemical rocks, a n d autochtonous r e e f rocks (See f i g u r e 1 . 2 - 3 ) . The a l l ochemica l rocks are those rocks which con ta in a l l ochemica l c o n s t i t u e n t s ( i n t r a c l a s t s , ooids, s k e l e t a l g ra ins , p e l o i d s ) . The or thochemical rocks are those rocks which are l a c k i n g (<l percent ) i n allochems and which a re composed e n t i r e l y o f m i c r i t e . These rocks are termed m i c r i t e s or,, i f t h e d e p o s i t i o n a l t e x t u r e has been - dis tu rbed by the burrowing a c t i v i t y o f organisms o r by dess i ca t i on d i s m i c r i t e s . The autochtonous r e e f rocks are those depos i ts which have been formed by the -- i n s i t u growth o f organisms (co ra l s ,

2 4

Carbonate taco,)

Ca I careous Sandstone

Argillaceous

F igu re 1.2-

Calcareous Shale

\ Arenaceous 1

Limestone

L i m esto ne

General c l a s s i f i c a t i o n o f mixed terr igenous-carbonate rocks (mod i f i ed from Krumbein and S loss f 1 9 6 3 ) .

PERCENT CALCITE 100 90 50 10 O

a, c O v) c

.- ?! A

O 10

Dolomitic Limestone

Calcitic

Dolostone

50 90 100

PERCENT DOLOMITE

F igu re 1.2-2 C l a s s i f i c a t . i o n o f c a l c i t e - d o l o m i t e m i x t u r e s (mod i f i ed f rom P e t t i j o h n , 1 9 5 7 ) .

25

ALLOCHEMICAL ROCKS

I II

CEMENT MICRITE

INTRACL ASTS

INTRASPARITE

OOIDS

OOSPARITE

SKELETAL GRAINS

BIOSPARITE

PELOIDS

PELS PA RITE

a CEMENT

INTRAMICRITE

OOMlCRlTE

BlOMlCRlTE

PELMICRITE

ORTHOCHEMICAL ROCKS

m MICRITE

LACKING ALLOCHEMS

MICRITE

DISMICRITE

AUTOCHTHONOUS REEF ROCKS

E

BlOLlTHlTE

F igu re 1.2-3 M o d i f i c a t i o n of F o l k ' s ( 1 9 6 2 ) c l a s s i f i c a t i o n o f l imestones.

2 6

algae, mol luscs) i n t o a r i g i d , wave-res is tant framework. The depos i ts a re termed b i o l i t h i t e s .

The a l l ochemica l rocks can be subdiv ided i n t o two c lasses based on t h e na ture o f t h e i n t e r p a r t i c u l a t e m a t e r i a l (See f i g u r e 1 . 2 - 3 ) . I n c l a s s I rocks the allochems a re i nc luded w i t h i n cement, whereas i n c l a s s II rocks t h e allochems are surrounded by m i c r i t e . The c lasses a re then subdiv ided based on the na ture and r e l a t i v e p r o p o r t i o n s o f t h e i nc luded allochems. The al lochems are ranked and considered i n a h i e r a r c h i c a l sequence based on t h e r e l a t i v e amount o f energy needed f o r t h e i r format ion. I n t r a c l a s t s , because they t y p i c a l l y r e f l e c t t h e h i g h e s t energy o f format ion, a re considered f i r s t fo l lowed by ooids, s k e l e t a l g ra ins , and pe lo ids . I f i n t r a c l a s t s comprise g rea te r than 25 percent o f t h e al lochems, regard less o f t h e p r o p e r t i e s o f t h e o the r components, i t i s considered an i n t r a s p a r i t e i f t h e i n t e r p a r t i c u l a t e m a t e r i a l i s cement o r an ~ i n t r a m i c r i t e i f the i n t e r p a r t i c u l a t e m a t e r i a l i s m i c r i t e . I f l e s s than 25 percent o f t h e al lochems a re i n t r a c l a s t s , t h e percentage o f oo ids i s examined. I f g r e a t e r than 25 percent o f t he al lochems are ooids, t h e rock i s e i t h e r an oospar i t e o r an o o m i c r i t e depending upon t h e na ture o f t h e i n t e r p a r t i c u l a t e m a t e r i a l . I f t h e rock conta ins l e s s than 25 percent i n t r a c l a s t s and l e s s than 25 percent oo ids, then t h e r a t i o o f s k e l e t a l g ra ins ( b i o c l a s t s ) t o p e l o i d s i s examined. I f t h e r a t i o o f s k e l e t a l g r a i n s t o p e l o i d s . i s g rea te r than 3 : l , t h e rock i s termed a b i o s p a r i t e o r a b i o m i c r i t e . I f the r a t i o l i e s between 3 : l and 1:3 then the rock i s e i t h e r a b i o p e l s p a r i t e o r a b i o p e l m i c r i t e . I f t h e r a t i o i s l e s s than 1 : 3 t h e rock i s e i t h e r a p e l s p a r i t e o r a p e l m i c r i t e . T h i s i n i t i a l c l a s s i f i c a t i o n prov ides a broad c o r r e l a t i o n between rock type and energy o f t h e environment o f depos i t ion . Orthochemical rocks ( m i c r i t e s and d i s m i c r i t e s ) and t h e m i c r i t i c a l l ochemica l rocks ( p e l m i c r i t e s , B i o m i c r i t e s , e tc . ) i n d i c a t e a low energy environment o f d e p o s i t i o n as evidenced by t h e presence o f abundant m i c r i t e . The cement-r ich a l l ochemica l rocks ( i n t r a s p a r i t e s , oospar i tes , e tc . ) , on t h e o t h e r hand, suggest a h i g h energy environment o f depos i t i on based on t h e l a c k o f m i c r i t e and t h e high i n i t i a l p o r o s i t y which was subsequently f i l l e d by cement..

To f u r t h e r r e f i n e the c o r r e l a t i o n between the c l a s s i f i c a t i o n and energy l e v e l s i n t h e environment o f depos i t ion , F o l k ( 1 9 6 2 ) proposed a t e x t u r a l m o d i f i c a t i o n o f t h e i n i t i a l c l a s s i f i c a t i o n (See f i g u r e 1 . 2 - 4 ) . The t e x t u r a l c l a s s i f i c a t i o n mod i f i es t h e c l a s s i f i c a t i o n o f a l l ochemica l and or thochemical rocks. I t i s based upon t h e amount o f m i c r i t e p resent , t h e percentage o f allochems present , and t h e rounding and s o r t i n g o f t h e al lochems. The i n i t i a l subd iv i s ion i s based on the r a t i o o f m i c r i t e t o cement i n t h e rock. I f g r e a t e r than 2 / 3 o f t h e i n t e r p a r t i c u l a t e m a t e r i a l i s m i c r i t e , t h e rock i s termed a m i c r i t e . I f g rea te r than 2 / 3 o f t h e i n t e r p a r t i c u l a t e m a t e r i a l i s cement, t h e rock i s a s p a r i t e . I f t h e rock con ta ins subequal amounts o f m i c r i t e and cement, t h e rock i s considered a p o o r l y washed s p a r i t e .

The m i c r i t i c rocks are subdiv ided based upon t h e percentage o f a l lcchems present. Rocks which con ta in l e s s than 1 percent al lochems are or thochemical rocks and a re termed m i c r i t e s o r d i s m i c r i t e s f o l l o w i n g the i n i t i a l c l a s s i f i c a t i o n . I f the rock con ta ins 1 t o 1 0 percent al lochems, i t i s termed a f o s s i l i f e r o u s m i c r i t e . (For i l l u s t r a t i v e purposes s k e l e t a l g r a i n s a r e considered the dominant al lochems i n t h e examples o f t e x t u r a l nomenclature. The terms must be mod i f i ed t o r e f l e c t t h e dominance o f o t h e r allocherns.) I f i t conta ins 10 t o 50 percent allochems, i t i s termed a sparse b i o m i c r i t e , and i f i t conta ins g rea te r than 50 pe rcen t allochems, i t i s termed a packed b i o m i c r i t e . Whi le the re a re except ions t o the r u l e , t h e o v e r a l l inc rease i n a l lochemica l c o n s t i t u e n t s i n a m i c r i t i c rock i s g e n e r a l l y a r e f l e c t i o n o f p rogress ive winnowing o f t h e m i c r i t e from t h e sediment. Thus, t h e t r a n s i t i o n f rom f o s s i l i f e r o u s m i c r i t e t o packed b i o m i c r i t e represents a genera l inc rease i n energy.

W i t h an inc rease i n energy more and more m i c r i t e w i l l be removed and w i t h t he subsequent f i l l i n g of t h e pores by cement, p o o r l y washed b i o s p a r i t e w i l l be formed con ta in ing subequal amounts o f m i c r i t e and spar.

With cont inued removal of m i c r i t e , cement becomes t h e dominant i n t e r p a r t i c u l a t e c o n s t i t u e n t and we move i n t o t h e s p a r i t e p o r t i o n o f t h e c l a s s i f i c a t i o n . Subd iv is ion o f t h e s p a r i t e s i s based on t h e s o r t i n g and roundness o f t h e allochems. Studies have shown t h a t as t h e energy o f an

27

s

d

I O

aJ

c

.-

W

c

O

- ul

1.

m

-

O

28

environment i s increased t h e sediment w i l l f i r s t be winnowed, then sor ted, and f i n a l l y rounded (Folk , 1 9 6 2 ) . I f t h e s o r t i n g i s poor t h e rock i s termed an unsor ted b i o s p a r i t e . If t h e s o r t i n g i s good but the g r a i n s a re s t i l l angular , t he rock i s termed a so r ted b i o s p a r i t e . I f t h e rock con ta ins we l l - so r ted allochems which a re highly abra ided and w e l l rounded, t h e rock i s termed a rounded b i o s p a r i t e .

I n a l l , t h e t e x t u r a l c l a s s i f i c a t i o n de f i nes e i g h t c lasses which represent an energy continuum from extremely h i g h energy l e v e l s represented by m i c r i t e s and d i s m i c r i t e s t o ext remely low energy l e v e l s represented by t h e rounded spa r i t es . Whi le t h e r e a re except ions, t h e c l a s s i f i c a t i o n does p rov ide a good c o r r e l a t i o n between rock types and energy.

The F o l k c l a s s i f i c a t i o n prov ides an e x c e l l e n t v e h i c l e f o r s u b d i v i s i o n o f carbonate rocks but i t does have one major drawback. Use o f t h e c l a s s i f i c a t i o n i s dependent upon t h e u s e r ' s a b i l i t y t o determine n o t o n l y t h e components which make up the l i t h o l o g y , but a l s o t o accu ra te l y determine t h e i r q u a n t i t a t i v e importance i n t h e rock. I n most cases, t h i s can o n l y be done through examination o f t h in -sec t i ons o r ace ta te pee ls . The c l a s s i f i c a t i o n i s thus u s e f u l i n microscopic a n a l y s i s o f l imestones but has severe l i m i t a t i o n s as a f i e l d c l a s s i f i c a t i o n .

1.2.2.2.2. C l a s s i f i c a t i o n o f Dunham ( 1 9 6 2 ) . L i k e the c l a s s i f i c a t i o n o f F o l k ( 1 9 6 2 ) , t he Dunham c l a s s i f i c a t i o n i s an at tempt t o determine energy c f t h e environment o f d e p o s i t i o n through observa t ion o f p h y s i c a l c h a r a c t e r i s t i c s o f a carbonate rock. U n l i k e the F o l k c l a s s i f i c a t i o n , ' however, t h e Dunham c l a s s i f i c a t i o n i s based on megascopic a t t r i b u t e s o f t he rock and i s thus a ve ry u s e f u l f i e l d c l a s s i f i c a t i o n .

The c l a s s i f i c a t i o n i s based on t h r e e major c h a r a c t e r i s t i c s o f carbonate rocks: (I) t h e presence o r absence o f m i c r i t e , ( 2 ) t h e pack ing o f t h e a l lochemica l c o n s t i t u e n t s i n t h e rock , and ( 3 ) t h e p resen t o f i n d i c a t i o n s o f o rgan ic b i n d i n g i n t h e rock (See t a b l e 1 . 2 - 1 ) . The i n i t i a l s u b d i v i s i o n o f t h e c l a s s i f i c a t i o n i s based on the a b i l i t y t o recognize o r i g i n a l d e p o s i t i o n a l t ex tu res i n t h e rock. I f d e p o s i t i o n a l t e x t u r e s have been obscured by diagenesis, t h e rock i s termed a c r y s t a l l i n e carbonate and must be f u r t h e r descr ibed u s i n g genera l m o d i f i e r s . I f t h e d e p o s i t i o n a l t e x t u r e i s v i s i b l e , t h e rock i s examined f o r i n d i c a t i o n s o f o rgan ic binding during d e p o s i t i o n such as s k e l e t a l i n te rg rowth , s k e l e t a l encrus ta t ions , l am ina t ion c o n t r a r y t o g r a v i t y , o r over-s ized c a v i t i e s roo fed by s k e l e t a l components. I f i n d i c a t i o n s o f organic b i n d i n g d u r i n g d e p o s i t i o n a re found, t h e rock i s termed a boundstone.

I f t h e r e i s no i n d i c a t i o n o f b i n d i n g a t t h e t ime o f depos i t i on , t h e presence o r absence o f m i c r i t e i s observed. I f m i c r i t e i s absent, t h e c o n s t i t u e n t g r a i n s w i l l be i.n g r a i n t o g r a i n con tac t ( g r a i n suppor t ) and t h e rock i s termed a gra instone. I f t h e r o c k con ta ins m i c r i t e , t h e na tu re o f t h e g r a i n t o q r a i n r e l a t i o n s a re observed. I f t h e rock i s g r a i n supported, t he rock i s termed a packstone. I f t h e g r a i n s a r e f l o a t i n g i n t h e m i c r i t e (mud supported), t h e percentage o f al lochems a r e est imated. I f al lochems comprise more than 1 0 percent o f t h e rock, i t i s termed a wackestone. I f al lochems comprise l e s s than 10 percent o f t h e rock, i t i s termed a mudstone.

The b a s i c premise o f t h e Dunham c l a s s i f i c a t i o n i s t h a t t h e presence o r absence an-d amount o f m i c r i t e p resent i n a l imestone i s a r e f l e c t i o n o f t h e a b i l i t y o r i n a b i l i t y o f t he environment o f d e p o s i t i o n t o remove (winnow) t h e m i c r i t e from t h e sediment. As m i c r i t e i s removed, a p rog ress i ve inc rease i n t h e amount o f a l l ochemica l c o n s t i t u e n t s r e l a t i v e t o m i c r i t e occurs and, w i t h s u f f i c i e n t winnowing, t h e t r a n s i t i o n from m u d supported t o g r a i n supported tex tu res takes p lace. The t r a n s i t i o n from mudstone through wackestone and packstone t o gra ins tone corresponds t o t h i s p rogress ive inc rease i n energy.

The Dunham c l a s s i f i c a t i o n i s an ext remely a t t r a c t i v e f i e l d c l a s s i f i c a t i o n , l a r g e l y because of i t s s i m p l i c i t y and because i t i s based on a t t r i b u t e s which are v i s i b l e w i t h t h e naked e y e , o r w i t h a hand lens. I n a c t u a l i t y , t h e s i m p l i c i t y o f t h e c l a s s i f i c a t i o n i s somewhat o f a drawback s ince i t does n o t d i f f e r e n t i a t e among a l l ochemica l cons t i t uen ts . T h i s can be remedied by mod i fy ing t h e b a s i c rock name w i t h an a d j e c t i v e i n d i c a t i n g t h e na tu re o f t h e dominant allochems, i .e. o o l i t i c gra instone, b i o c l a s t i c gra instone, p e l o i d a l gra instone.

29

Table 1.2-1. Dunham's ( 1 9 6 2 ) c l a s s i f i c a t i o n o f l imestones.

DEPOSITIONAL TEXTURE RECOGNIZABLE DEPOSITIONAL TEXTURE NOT RECOGNIZABLE

O r i g i n a l Components Not Bound Together O r i g i n a l components Dur ing Depos i t ion were bound together C r y s t a l l i n e

d u r i n g depos i t i on ... Carbonate as shown by i n t e r -

Contains mud Lacks mud grown skeleta l . ( p a r t i c l e s o f c l a y and and i s mat te r , l am ina t ion (Subdiv ide f i n e s i l t s i z e ) g ra in - c o n t r a r y t o g r a v i t y , accord ing t o

supported o r sediment- f loored c l a s s ï f i c a - c a v i t i e s t h a t a re t i o n s de- roo fed over by o r - s igned t o ganic o r quest ion- bear on ab le o rgan ic mat te r p h y s i c a l

Mud-supported Grain- sup- p o r t e d

Pack- Grain-

Less than More than and are t o o l a r g e t e x t u r e o r 10 pe rcen t 1 0 percent t o be i n t e r s t i c e s . d iagenesis. 1

Mudstone Wackestone stone stone Boundstone -

30

1.3 Sedimentation and s t r a t i g r a p h y (D. J. Burdon)

Studies o f t h e i n t e r n a l s t r u c t u r e s o f i n d i v i d u a l beds o f deposi ted m a t e r i a l s , t h e i r sequence and succession i n c l u d i n g t h e t ime changes represented by t h e e ros iona l hor izons, and t h e i r geographic e x t e n t p rov ide an i n s i g h t i n t o t h e environments i n which the sediments were deposi ted, and the sources o f t h e ma te r ia l . Th i s understanding i s needed i n assessing a q u i f e r c h a r a c t e r i s t i c s and t h e i r v a r i a t i o n s , b o t h l a t e r a l l y and v e r t i c a l l y , on a r e g i o n a l bas is .

The b a s i c p r i n c i p l e s o f sedimentat ion and s t r a t i g r a p h y apply as much t o carbonate rocks as they do t o o t h e r sedimentary fa-cies. The main a t t e n t i o n o f t h i s sec t ion , however, w i l l con t inue t o be focused on t h e e f f e c t s o f sedimentary and S t r a t i g r a p h i c processes on t h e p o r o s i t y and p e r m e a b i l i t y o f rocks and t o the movement and s torage o f water, b o t h as p a r t o f t h e i r e v o l u t i o n and as a p resent day c h a r a c t e r i s t i c .

1.3.1 Facies. Sedimentary rocks which have recogn izab le assoc ia t i ons o f l i t h o l o g i c and b i o l o g i c c h a r a c t e r i s t i c s a re commonly r e f e r r e d t o a.s f ac ies . Fac ies a re depos i ts whose charac ter i s determined by p a r t i c u l a r s e t s o f cond i t ions . Thus b iohermal depos i t s w i t h i n a l a r g e r l imestone un i t may be r e f e r r e d t o as a b iohermal f ac ies . I t i s a l s o u s e f u l t o i n v e s t i g a t e and d iscuss s i m i l a r f a c i e s deposi ted i n d i f f e r e n t p laces a t d i f f e r e n t t imes. Thus, b iohermal f a c i e s may be discussed as a category o f depos i ts t h a t represents depos i t i on under s i m i l a r c o n d i t i o n s throughout t h e h i s t o r y and i n a l l p a r t s o f the' globe. Since f a c i e s descr ibes t h e rock l a i d down i n a p a r t i c u l a r environment and because a l l sedimentary rocks were l a i d down i n some environment, i t f o l l o w s t h a t every sedimentary rock i s some s o r t o f f ac ies . Furthermore, because every s t r a t i g r a p h i c un i t has b o t h v e r t i c a l and h o r i z o n t a l v a r i a t i o n s i n l i t h o l o g y , each recogn izab le s e t o f v a r i a t i o n s may be considered as a fac ies . [EDITOR'S NOTE: For read ing on m ic ro fac ies a n a l y s i s see E r i k F l u g e l ( 1 9 8 2 ) ; t h i s t e x t i nc ludes an ex tens ive annotated b ib l iography, . ]

The f a c i e s concept i s p a r t i c u l a r l y impor tan t i n hydrogeologic s tud ies because i t he lps t o understand many v e r t i c a l and h o r i z o n t a l changes i n pe rmeab i l i t y .

Carbonate rocks commonly a re l a i d down on t h e s t a b l e s h e l f . I t i s most impor tan t t o recognize t h a t each carbonate environment grades i n t ime and space i n t o noncarbonate environments. For example, t he depos i t s outward f rom a beach i n some p laces have the f o l l o w i n g sequence: beach deposi ts , lagoona l evapor i tes a l t e r n a t i n g w i t h mudstones, b iohermal r e e f depos i ts i n t e r f i n g e r i n g seaward w i t h b ios t roma l l imestone, t h a t i n turn i n t e r f i n g e r s w i t h and grades i n t o l imey mudstone and e v e n t u a l l y c laystone. [EDITOR'S NOTE: For a d e t a i l e d study o f carbonate f a c i e s throughout geo log ic h i s t o r y , t h e reader i s r e f e r r e d t o Wi lson ( 1 9 7 5 ) .I

V e r t i c a l successions o f f a c i e s a.nd l a r g e r s t r a t i g r a p h i c u n i t s s t r o n g l y a f f e c t t he development o f t h e h y d r o l o g i c c h a r a c t e r i s t i c s , because successive u n i t s seldom have i d e n t i c a l l i t h o l o g i c c h a r a c t e r i s t i c s and p e r m e a b i l i t i e s . Moreover, t h e h i a t u s between two successive p e r i o d o f depos i t s c rea tes a sur face o r unconformi ty t h a t has i t s own hydrogeologic p r o p e r t i e s . Thus, t h e s implest p o s s i b l e succession o f u n i t s immediately poses a hyd ro log i c problem o f p o t e n t i a l l y immense complex i ty . I f t h e l i t h o l o g i c and h y d r o l o g i c c h a r a c t e r i s t i c s o f t h e two u n i t s and t h e unconformi ty zone a re s i m i l a r , regard less o f whether t h e p e r m e a b i l i t i e s a re high o r low, they may a c t as a hyd ro log i c unit . Th is w i l l occur w i t h o u t respec t t o t h e age d i f f e r e n c e s o f t h e u n i t s . I f t h e l i t h o l o g i e s a re d i f f e r e n t , t h e r e may be t h r e e hyd ro log i c u n i t s invo lved. The d e t a i l t o which such d i f fe rences must be considered depends on the na ture o f t he problem under study.

I n carbonate sequences, t h e development o f a k a r s t i c topography on a l imestone u-nit be fo re t h e subsequent depos i t i on o f a l e s s permeable un i t i s common. Examples a re descr ibed elsewhere i n t h i s guidebook.

Carbonate f a c i e s g e n e r a l l y o r i g i n a t e i n marine environments. Sediments deposi ted on t h e s h e l f i n shal low seas a re u s u a l l y w e l l so r ted and commonly have pr imary sedimentary s t r u c t u r e s such as cross-bedding and r i p p l e marks. Bedding i s good, i n d i c a t i n g many breaks i n sedimentat ion. The waters i n which the sediments were deposi ted were w e l l supp l i ed w i t h oxygen, e s s e n t i a l f o r

3 1

l i f e , and thus zoogenic rocks were formed (Gignous, 1 9 5 5 ) . W i t h i n t h i s genera l environment, two d i f f e r e n t groups o f l imestone were deposi ted. A t g rea te r depths a re t h e e x o g e n i t i c l imestone t h a t cons i s t s o f t ranspor ted calcareous granu lar m a t e r i a l , which behaves l i k e s i m i l a r quar tz g ranu la r m a t e r i a l . H igher up i n t h e f o r e l a n d f a c i e s a re the endogenetic l imestones t h a t r e s u l t e d f rom b o t h b iochemica l and chemical depos i t ion . These l imestones a re formed i n s i t u , under calm cond i t i ons , and are e s s e n t i a l l y t h e equ iva len t o f t h e shale beds where predominant ly c l a s t i c sediments were l a i d down i n the fo re land environment.

W i t h i n t h e main s h e l f f ac ies , t he re are c e r t a i n unusual subgroups. Limestone does n o t occur i n t h e e u x i n i c (b lack shale) f ac ies , but dolomi tes a r e genera l i n t h e s a l i n e f a c i e s i n assoc ia t i on w i t h gypsum and even h a l i t e .

W i t h i n t h e oceanic environment , carbonate f a c i e s occur a t t he l e s s e r depth; g l o b i g e r i n a ooze, p teropod ooze, and c o r a l mud and sand a l l con ta in more than 65 percent ca lc ium carbonate (CaC03). Whi le p resent day deep-sea depos i ts o f t h i s C l a s s i f i c a t i o n cover more than 25 percent o f t h e area o f t h e ear th , they a re n o t o f g r e a t importance i n a study o f k a r s t l imestone. Chemical l imestone or p e l a g i c l imestone a l s o occurs i n t h e geosync l i na l f a c i e s where they a re g e n e r a l l y assoc iated w i t h che r t . Lacus t r i ne l imestone and t h e t r a v e r t i n e and t u f a o f spr ings a re found i n t e r r e s t r i a l environments; but q u a n t i t a t i v e l y they a re o f l i t t l e importance. [EDITOR'S NOTE: The reader i s r e f e r r e d t o Wi lson (1975) f o r a d e t a i l e d d iscuss ion o f carbonate depos i t ion . ]

1.3.2 S ize and shape o f beds. The s i z e o f carbonate rock beds inc ludes t h e h o r i z o n t a l e x t e n t ( leng th , w i d t h , a rea) , th ickness a n d volume. The beds may he c l a s s i f i e d as t h i c k , medium, o r th in (See t a b l e 1.3-1. ) .

The shape o f sedimentary bodies may be descr ibed by a v a r i e t y o f terms. Some terms descr ibe what may be c a l l e d t h e i r genet ic shapes. Such terms i n c l u d e bars , bioherm, channel deposi ts , lenses, fans, and d e l t a s . Other terms r e l a t e area t o volume and i n c l u d e terms such as b l a n k e t bodies, t a b u l a r bodies, pr isms, and shoes t r ings (See f i g u r e 1 .3-1) . Bioherms and b l a n k e t bodies are shapes t y p i c a l o f carbonate-rock bodies.

The s tudy o f t h e shape o f l imestone depos i ts has l e a d t o a spec ia l i zed c l a s s i f i c a t i o n and nomenclature accord ing t o t h e i r bulk form. Among such terms a re bioherms and b iohermal masses, and b ios t roma l depos i ts . Bioherms are mound-like, g e n e r a l l y l e n t i c u l a r masses b u i l t ma in ly by sedentary organisms such as c o r a l s and a re enclosed i n rock o f d i f f e r e n t charac ter ( l i t h o l o g y ) . Bioherms a re o f t e n c a l l e d r e e f s , but t h i s use i s anomalous because t h e term r e e f i s a l s o a p p l i e d t o many wave-res is tant s t ruc tu res , o f which bioherms are j u s t one type. Bioherms commonly a re h i g h l y permeable. B ios t romal masses, o r biostroms, a re a l s o formed by sedentary organisms but i n t h i s ins tance the depos i ts a re r e l a t i v e l y well-bedded, and are pr isms- t i c t o t a b u l a r i n shape r a t h e r than mound-l ike as a re bioherms. Some b iost roms a re a l g a l , o thers a re coquina (masses o r s h e l l s ) , and some show few f o s s i l s t ruc tu res . The p e r m e a b i l i t i e s o f b ios t roma l masses va ry g r e a t l y . They a re o f t e n in terbedded w i t h shale u n i t s .

1.3.3 I n f l u e n c e o f s t r a t i f i c a t i o n . The i n f l u e n c e o f s t r a t i f i c a t i o n on t h e hydrageology o f t h e carbonate rocks i s expressed i n a number o f ways, some d i r e c t and some i n d i r e c t . The main in f luences a re l i s t e d under f o u r main ca tegor ies , as fo l l ows :

V e r t i c a l sequences - The d i f f e r e n t superposed beds t h a t form a sedimentary sequence w i l l d i f f e r i n l i t h o l o g y , th ickness, compaction, p l a s t i c i t y , hardness, r i g i d i t y and r e l a t e d Charac te r i s t i cs . Such a sequence may repeat r h y t h m i c a l l y o r i n a complex manner. The in te rbedd ing o f hard l imestone between p l a s t i c c l a y o r m a r l i s common, l a r g e th icknesses of carbonate rock w i t h no v e r t i c a l changes a re ra re .

H o r i z o n t a l changes - L i tho logy , th ickness and o t h e r c h a r a c t e r i s t i c s may change l a t e r a l l y i n any bed o r sequence of beds. A l though such a change i s commonly gradual , i t a l s o can be abrupt and s t r i k i n g , as i n the case o f r e e f l imestone.

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Table 1.3-1. A c l a s s i f i c a t i o n o f sedimentary bodies accord ing t o s i z e (Krynine, 1 9 4 8 ) .

Length W i d t h (a long (across Area Volume s t r i k e s t r i k e (square Thicknes s ( cub ic

D e f i n i t i o n m i l es) m i l e s ) m i les ) ( f e e t ) m i l e s )

Large (or t h i c k ) >200 >50 10 ,000 >500 >500

Medium 20-100 5-50 100-10,000 100-500 1 -500

Small ( o r th in) <20 <5 < l o o < l o o < 1

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BLANKET OR SHEET

thickness 1 unit

r---2 \a' width over 1000 units

!/

PRISM

TABULAR

~~

SHOESTRING

F igu re 1 .3 -1 E x t e r n a l morphology of sedimentary bodies showing scheme o f s i m p l i f i e d geometr ic r e l a t i o n s h i p s between b lanket , t a b u l a r body, prism, and s h o s t r i n g (Krynine, 1 9 4 8 ) .

34

Bedding p lanes and j o i n t s - The d i v i s i o n s (bedding p lanes) between successive beds may be well-marked (by e r o s i o n a l sur faces, accumulat ions o f f o s s i l s , and by sandy o r c layey p a r t i n g s ) , o r they may be almost i n v i s i b l e (because o f r e c r y s t a l l i z a t i o n o f carbonate m a t e r i a l s o r o n l y s l i g h t o r i g i n a l l i t h o l o g i c a l d i f f e r e n c e s ) . The j o in t i ng p r o p e r t i e s o f successive beds i n a sequence may a l s o be g r e a t l y d i f f e r e n t . The bedding p lanes and j o i n t s may o r may n o t have adequate openings f o r t he movement o f water.

React ion o f e x t e r n a l f o rces - E x t e r n a l forces, i n p a r t i c u l a r metasomatic changes, metamorphism ( thermal o r dynamic) and t e c t o n i c movements, t end t o a f f e c t d i f f e r e n t beds, sequences and f a c i e s i n d i f f e r e n t ways. As a r e s u l t , such e x t e r n a l f o rces can a l t e r successive beds i n d i f f e r e n t ways, i n c l u d i n g t h e i r a b i l i t y t o t r a n s m i t o r r e t a r d t h e movement o f water.

Thus, t h e changes i n v e r t i c a l and h o r i z o n t a l p o r o s i t y and p e r m e a b i l i t y r e f l e c t b o t h d i f f e r e n c e s i n the o r i g i n a l environment o f d e p o s i t i o n and d i f f e r e n c e s i n t h e pos t -depos i t i ona l h i s t o r y . The c h a r a c t e r i s t i c s o f a s i n g l e bed may n o t o n l y va ry g r e a t l y over i t s e x t e n t due t o d e p o s i t i o n a l v a r i a t i o n s , but a l s o may have been subjected t o v a s t l y d i f f e r e n t s t r u c t u r a l , e ros iona l , and s t r a t i g r a p h i c fo rces and events s ince i t was deposi ted.

The study o f sequences i n sediments i s a complex mat te r , and i s now genera l l y subjected t o mathematical a n a l y s i s t o make t h e i n t e r p r e t a t i o n as o b j e c t i v e as poss ib le . A good example o f t h e use o f s imple mathematical devices i n s t r a t i g r a p h i c a n a l y s i s i s g i ven by S e l l e y ( 1 9 7 0 ) i n h i s s tudy o f Miocene l i t t o r a l depos i ts o f t h e S i r e t e G u l f i n L ibya. Rauch and White ( 1 9 7 0 ) used s i m i l a r s t r a t i g r a p h i c and l i t h o l o g i c methods i n ana lyz ing s o l u t i o n p o r o s i t y under l y ing the N i t t a n y V a l l e y area o f Pennsylvania.

The hydrogeologic importance o f impermeable and p l a s t i c beds o f c l a y o r m a r l may be e s p e c i a l l y c r i t i c a l i n a genera l Limestone-dolomite sequence. Such beds n o t o n l y r e s t r i c t (and thereby concentrate) groundwater c i r c u l a t i o n t o s p e c i f i c beds o f zones i n a sequence, but a l s o by t h e i r p l a s t i c y i e l d o r f l o w under t e c t o n i c fo rces can g r e a t l y i n f l u e n c e t h e way l imestone w i l l behave under pressure. Even a smal l amount o f c l a y o r m a r l i n a l imestone means t h a t a coa t ing o f nonsoluble c l a y m ine ra l s may q u i c k l y cover and p r o t e c t f rom f u r t h e r s o l u t i o n the carbonate m ine ra l s composing t h e bulk o f t h e rock o r p r o v i d e a p l a s t i c f i l m which w i l l p e r m i t t he carbonate m ine ra l s t o g l i d e over each o t h e r under s t ress .

A b r u p t h o r i z o n t a l changes i n l imestone a re o f major importance i n the hydro logy and hydrogeology o f carbonate te r ranes . O f these changes, t h e abrupt expansion o f a l imestone bed i n t o a l imestone r e e f i s t h e most s t r i k i n g . Such a r e e f w i l l c o n s i s t o f a fo re- ree f , on t h e s i d e once open t o t h e sea, a ree f -core where the main rock- forming organisms l i v e d , and t h e back-reef, on the s ide p ro tec ted from t h e open sea. The r e l a t i v e importance, s i z e and composi t ion o f these t h r e e u n i t s w i l l va ry i n genera l , and t h e ree f -core w i l l be t h e most open and permeable i n t e x t u r e . A study o f Devonian r e e f l imestones around Kassel, Germany, by Krebs, ( 1 9 6 9 ) , i s an example o f a s tudy i n v o l v i n g abrupt h o r i z o n t a l changes.

There i s a major r e l a t i o n s h i p between t h e degree o f k a r s t i f i c a t i o n and the 1ithol.ogy o f t h e s t r a t i g r a p h i c u n i t s under study. The o r d i n a r y geo log ic map showing t i m e - s t r a t i g r a p h i c u n i t s can i n i t s e l f p rov ide suggest ions rega rd ing the water-bear ing c h a r a c t e r i s t i c s o f an area. However, once a r e l a t i o n s h i p between k a r s t i f i c a t i o n and s t r a t i g r a p h y has been es tab l i shed, and t h e p o r o s i t y and p e r m e a b i l i t y c h a r a c t e r i s t i c s a re added t o t h e i n f o r m a t i o n shown by t h e map, i t may y i e l d va luab le c lues and hypotheses rega rd ing t h e a r e a l e x t e n t o f k a r s t i f i c a t i o n and water-bear ing c a p a b i l i t i e s .

I n t h i s connect ion i t i s appropr ia te t o s t r e s s here a s imple but impor tan t rule-of-thumb: t h e t h i c k e r t h e l imestone sequence, t h e more impor tan t and dominant w i l l be t h e e f f e c t o f k a r s t i f i c a t i o n on t h e hyd ro log i c regime o f t he reg ion. If t h e carbonate rocks a re th in, then o n l y a s u p e r f i c i a l k a r s t w i l l develop. The appearance of extreme k a r s t o r hol.okarst immediately i n d i c a t e s a reg ion o f t h i c k l imestone sequences.

Carbonate rocks l o c a l l y reach cumulat ive th icknesses o f as much as 10,000 meters. However, no ma t te r how t h i c k they are, these sequences a re almost

emergence, o r e l e v a t i o n t o t h e genera l l e v e l o f t h e water t a b l e , subaer ia l , subaqueous, and subsurface e ros ion k a r s t i f i e d t h e access ib le carbonate rocks.

never cont inuous. Where d e p o s i t i o n was i n t e r r u p t e d by

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1.3.4 Ef fec ts o f p a l e o h i s t o r y . The c a p a b i l i t y o f a body o f l imestone t o t r a n s m i t water i s determined by i t s pos t -depos i t i ona l h i s t o r y , i n a d d i t i o n t o i t s smal l -scale c h a r a c t e r i s t i c s , i t s s i z e and shape, and i t s r e l a t i o n s h i p t o a d j o i n i n g deposi ts . The e x i s t i n g hydrogeo log ica l s i t u a t i o n i n any area represents p resen t h y d r o l o g i c c o n d i t i o n s and t h e c h a r a c t e r i s t i c s t h a t have developed or have been imposed s ince depos i t ion .

I n a c o n s i d e r a t i o n o f t h e f a c i e s o f most carbonate rocks t h a t occur i n t h e s t a b l e s h e l f t e c t o n i c environment (see s e c t i o n 1 .3 .1 ) , i t i s t o be expected t h a t t h e paleogeography w i l l be compl icated but d e f i n i t e l y re t raceab le . Limestone i s a rock o f t he sha l low seas, and i s t h e r e f o r e depos i ted n o t t o o f a r from t h e coast, commonly w i t h i n t h e zone of wave ac t i on . As a l ready noted, l imestones are commonly a f f e c t e d by emergence and submergence. I n general , l imestone may be considered as t y p i c a l of t h e b e l t where marine and c o n t i n e n t a l sediments occur.

Most paleogeographic d e s c r i p t i o n s focus on s p e c i a l i z e d g e o l o g i c a l problems such as t h e h i s t o r y o f sea- leve l changes. I t then becomes necessary t o r e i n t e r p r e t t h e i n f o r m a t i o n t o determine t h e hydrogeologic i m p l i c a t i o n s .

From t h e p o i n t o f v iew o f carbonate hydrogeology, t h e most s i g n i f i c a n t deduct ions a re those r e l a t i n g t o t h e e x t e n t of emergence, t h e l e n g t h o f t ime an emergence las ted , t h e degree o f e ros ion t h a t occur red and t h e c o n d i t i o n s o f b u r i a l a f t e r submergence. Examples of g e o l o g i c a l l y - o r i e n t e d paleogeography d e s c r i p t i o n s are g i ven by Gignous (19551, Hunt and o t h e r (1953) and Wilson ( 1 9 7 5 ) . E x c e l l e n t d i scuss ion o f t h e hydrogeologic o r i e n t e d analyses a r e g i ven by S t r i n g f i e l d and LeGrand ( 1 9 6 6 and 1971).

1.4 S t r u c t u r e ( T r a v i s H. Hughes)

The s t r u c t u r a l and t e c t o n i c h i s t o r y o f a r e g i o n p l a y s a s i g n i f i c a n t r o l e i n de termin ing t h e behav io r o f carbonate aqu i fe rs . Authors o f t h e v a r i o u s sec t i ons o f t h i s guidebook have discussed many f a c t o r s t h a t c o n t r i b u t e t o development o f carbonate aqu i fe rs . The range o f v a r i a t i o n among these many interdependent and independent f a c t o r s i s so wide that. no two carbonate a q u i f e r s have i d e n t i c a l c h a r a c t e r i s t i c s . The i n f l u e n c e o f geo log i c s t r u c t u r e on a q u i f e r c h a r a c t e r i s t i c s i s a l s o v a r i a b l e so t h a t i t i s n o t p o s s i b l e t o p rov ide a s e t o f s imple r u l e s governing t h e i n f l u e n c e o f j o i n t s , f a u l t s and f o l d s on groundwater movement o r a v a i l a b i l i t y . Th i s s e c t i o n i s designed t o p r o v i d e a conceptual framework and g u i d e l i n e s f o r thought which may a i d i n d i v i d u a . l s who a t tempt t o unraire1 s t r u c t u r a l c o n t r o l s o f groundwater movement i n t h e i r p a r t i c u l a r study areas.

The t e c t o n i c a l l y induced p o s i t i o n o f a body of carbonate rocks determines p o t e n t i a l recharge/discharge r e l a t i o n s h i p s . Fo ld ing , f a u l t i n g , and f r a c t u r i n g o f t h e rocks o f t e n determine t h e p o r o s i t y and p e r m e a b i l i t y o f t h e a q u i f e r as w e l l as s p e c i f i c d i r e c t i o n s o f groundwater f low through t h e carbonate system. A f t e r a recharge/discharge system i s es tab l i shed, p e r m e a b i l i t y o f t h e carbonate rocks must inc rease w i t h t ime i f t h e t r a n s m i t t e d groundwater i s unsatura ted w i t h respec t t o ca l c ium and/or magnesium carbonate. Therefore, k a r s t development i s a p rog ress i ve process alt.hough i t ’ s p robab ly n o t c y c l i c i n t h e sense descr ibed by Penck ( 1 9 0 0 ) o r Davis ( 1 9 0 1 ) . However, carbonate a q u i f e r s should have c o n t i n u a l l y changing c h a r a c t e r i s t i c s as l ong as a n open groundwater system e x i s t s .

1 . 4 . 1 Pe rmeab i l i t y and s t r u c t u r e . Primary p o r o s i t y o f carbonate rocks i s t he r e s u l t o f open spaces i n t h e rocks t h a t have p e r s i s t e d throughout t h e p e r i o d o f depos i t i on , d iagenesis and l i t h i f i c a t i o n . T e x t u r a l p o r o s i t y and i n t e r g r a n u l a r p o r o s i t y a re common terms used as synonyms f o r p r imary p o r o s i t y . Secondary p o r o s i t y i s a term used t o express the amount o f open space i n a rock t h a t has been c rea ted by p o s t - l i t h i f i c a t i o n processes such a s f r a c t u r e s ( j o i n t s , f a u l t s , p a r t i n g ) o r s o l u t i o n c a v i t i e s .

Jakucs (1977) has demonstrated t h a t t e x t u r a l p o r o s i t y and p e r m e a b i l i t y o f ca l c ium carbonate rocks i s g r e a t e s t f o r those rocks of T e r t i a r y o r Quaternary age (see F i g u r e 1 . 4 - 1 ) . The h i g h e s t p e r m e a b i l i t i e s measured were from l imestones o f Recent age. I n ca lc ium carbonate rocks o f Cambrian t o Recent

36

l I I I I I 1 I I I I I I I I

m 3 O

U Q) V m

.- m m

3

V m m m

.- CI

2 P .- O I= 1

I I

I I I I I I I I

I 1 I I I I L

Mesozoic -

Tertiary Quaternary

F igure 1 .4 -1 Geo log ica l age p l o t t e d a g a i n s t p e r m e a b i l i t y and open o r obs t ruc ted s t r u c t u r a l f i s s u r a t i o n i n ca lc ium carbonate rocks ( f rom Jakucs, 1977) .

37

age, Jakucs' work demonstrates t h a t dens i t y o f f r a c t u r e s increases w i t h age. However, i n Paleozoic l imestone, Jakucs found t h a t many m ic ro f i ssu res had been f i l l e d w i t h secondary c a l c i t e o r healed by r e c r y s t a l l i z a t i o n so t h a t t he g r e a t e s t d e n s i t y o f open f i s s u r e s occurred i n l imestones o f Mesozoic age. The p e r m e a b i l i t y o f Paleozoic and Mesozoic l imestones appears t o be d i r e c t l y r e l a t e d t o t h e d e n s i t y o f open f i s s u r e s r a t h e r than t h e t o t a l number o f f i s s u r e s i n t h e l imestone.

One would expect t o f i nd a f a i r l y un i fo rm p e r m e a b i l i t y d i s t r i b u t i o n associated w i t h undeformed, permeable T e r t i a r y and Quaternary l imestones. However, groundwater movement i n l imestones o f Paleozoic and Mesozoic rocks should be o r i e n t e d a long s t r u c t u r a l features such as f a u l t s and j o i n t s , o r c o n t r o l l e d accord ing t o the d i s t r i b u t i o n o f f o l d s i n t h e rocks.

Whi te (1969) presented a c l a s s i f i c a t i o n scheme f o r types o f carbonate a q u i f e r systems i n reg ions o f low t o moderate r e l i e f . He l a t e r updated the c l a s s i f i c a t i o n t o i nc lude f a c t o r s o f r e l i e f , s t r u c t u r e and a r e a l ex ten t o f t he a q u i f e r (White, 1 9 7 7 ) . A m o d i f i e d ve rs ion o f Whi te 's c l a s s i f i c a t i o n i s presented i n Table 1.4-1. The t h r e e pr imary types o f carbonate a q u i f e r systems de f ined by White are: (1) d i f f u s e - f l o w , ( 2 ) f ree- f low, and ( 3 ) con f ined- f low carbonate aqu i fe rs .

According t o White, " d i f f u s e - f l o w a q u i f e r s occur where s o l u t i o n a l a c t i v i t y o f t he moving ground water has been re ta rded by l i t h o l o g i c f a c t o r s " ( 1 9 6 9 , page 1 6 ) . White would a l s o i n c l u d e l imestones w i t h high pr imary p o r o s i t y ' i n t h i s category. Aqu i fe rs showing " f i ne - tex tu red pe rmeab i l i t y " (LeGrand and S t r i n g - f i e l d , 1971; LeGrand, S t r i n g f i e l d and LaMoreaux, 1 9 7 6 ) a re ve ry s i m i l a x t o the d i f f u s e - f l o w a q u i f e r s o f White. However, LeGrand, e t a l . recognized t h a t f i n e - t e x t u r e d p e r m e a b i l i t y may be a r e s u l t o f uni formly-spaced but poor l y - developed f r a c t u r e systems.

Free- f low and conf ined- f low a q u i f e r s as de f i ned by White have been sub- d i v i d e d i n t o seve ra l se l f -exp lanatory ca tegor ies (see Table 1 . 4 - 1 ) .

Free- f low a q u i f e r systems commonly e x h i b i t a "coarse- textured permeabi l - i t y " (LeGrand, e t a l 1 9 7 1 and 1 9 7 6 ) . The term "coarse- textured pe rmeab i l i t y " s t resses t h e uneven d i s t r i b u t i o n o f p e r m e a b i l i t y i n carbonate aqu i fe rs , t h a t i s , p o r t i o n s o f t h e a q u i f e r may have h i g h p e r m e a b i l i t i e s whereas i n t e r v e n i n g p o r t i o n s o f t h e a q u i f e r may have p e r m e a b i l i t i e s t h a t a re r e l a t i v e l y low. Pe rmeab i l i t y i n such a q u i f e r s has been developed because o f t he non-uniform d i s t r i b u t i o n o f f r a c t u r e systems t h a t i n t e r s e c t t h e carbonate body.

Table 1 . 4 - 1 has been presented as a means o f i l l u s t r a t i n g severa l r e l a t i o n s h i p s commonly assoc ia ted w i t h carbonate a q u i f e r s thus p r o v i d i n g a re fe rence frame f o r v i s u a l i z i n g p o s s i b l e c o n f i g u r a t i o n s r e s u l t i n g from f o l d i n g and f r a c t u r i n g t h e carbonate aqu i fe rs .

1 .4 .2 F rac tu re systems. I n carbonate rocks t h a t do n o t have a pr imary i n t e r g r a n u l a r pe rmeab i l i t y , j o i n t s o r f r a c t u r e s a re e s s e n t i a l f o r i n i t i a t i o n o f downward p e r c o l a t i o n o f water ( S t r i n g f i e l d , Rapp and Anders, 1.979). The l a t e r a l , as w e l l as v e r t i c a l , rou tes a long which groundwater f l o w i s channeled p r i o r t o s o l u t i o n m o d i f i c a t i o n may a l s o be cont ro l led . by f r a c t u r e p a t t e r n s (K ie rsch and Hughes, 1 9 5 2 ) . Research performed by numerous authors throughout. t he w o r l d has documented t h e c r i t i c a l importance o f f r a c t u r e s i n c o n t r o l l i n g groundwater movement i n carbonate a q u i f e r s o f Paleozoic and Mesozoic age. I n f a c t , t h e r e l a t i o n s h i p between f r a c t u r e s and s o l u t i o n a l l y developed p e r m e a b i l i t y i n carbonate rocks i s so w e l l documented t h a t one almost presumes the presence o f f r a c t u r e s i f s o l u t i o n c a v i t i e s e x i s t i n Paleozoic o r Mesozoic l imestones.

Bedding p lanes may a l s o p rov ide avenues f o r groundwater movement (Palmer, 1 9 7 7 ) . However, i n such cases movement o f ground water between bedding p lanes i s o f t e n f r a c t u r e c o n t r o l l e d .

T e r t i a r y and Quaternary l imestones f r e q u e n t l y have p e r m e a b i l i t y due t o s o l u t i o n development o f t h e i r p r imary t e x t u r a l p o r o s i t y ( S t r i n g f i e l d , 1 9 6 6 ) . Research by Vernon ( 1 9 5 1 ) and Love (1.983) has demonstrated t h a t even i n the F l o r i d a n a q u i f e r groundwater movement i s l o c a l l y i n f l uenced and mod i f i ed by the presence o f f a u l t s .

I f a favorab le recharge/discharge r e l a t i o n s h i p e x i s t s f o r a carbonate unit , then water can g a i n access t o t h a t un i t a n d move through it. The

38

Table 1 .4-1 . Types o f carbonate a q u i f e r systems i n reg ions o f low t o moderate r e l i e f , mod i f i ed f rom White ( 1 9 6 9 and 1 9 7 7 ) w i t h a d d i t i o n s f rom LeGrand and S t r i n g f i e l d ( 1 9 7 1 ) and 'LeGrand, S t r i n g f i e l d and LaMoreaux ( 1 9 7 6 ) .

Flow type Hydro log i ca l c o n t r o l Associated cave t ype

I.

II.

DIFFUSE FLOW ( f i n e - tex tu red permeabi 1 i t y )

SHALEY LIMESTONE; CRYSTALLINE DOLOMITES

Caves r a r e , smal l , have i r r e g u l a r pa t te rns .

High pr imary p o r o s i t y o r u n i f o r m l y d i s t r i - bu ted f r a c t u r e s

THICK, MASSIVE SOLUBLE ROCKS I n t e g r a t e d condu i t cave systems.

FREE FJJOW (coarse- tex tu red permeab il i t y )

Condui ts develop a long bedding, j o i n t s , f r a c t u r e s , o r f o l d axes.

A. PERCHED

1. Open

2. Capped

K a r s t system u n d e r l a i n by impervious rocks near o r above base l e v e l .

Cave streams perched - o f t e n have f r e e a i r s u r f ace.

So lub le rocks extend upward t o l a n d sur face.

S inkhole inputs ; heavy sediment load: s h o r t channel morphology caves.

Aqu i fe r o v e r l a i n by imper- v ious rock.

V e r t i c a l s h a f t i npu ts ; l a t e r a l f l o w under cap- p i n g beds; l o n g i n t e g r a t e d caves.

B. DEEP

1. Open

2. Capped

III. CONFINED FLOW

K a r s t system extends t o considerable depth below base l e v e l .

Flow i s through submerged condu i ts .

Solub le rocks extend t o l a n d surface.

Shor t t u b u l a r abandoned caves l i k e l y t o be sediment-choked.

A q u i f e r o v e r l a i n by imper- v ious rocks.

Long, i n t e g r a t e d condu i ts under caprock. A c t i v e l e v e l o f system inundated.

DIFFUSE FLOW OR FREE FLOW SYSTEMS STRATIGRAPHICALLY BOUND BETWEEN BEDS OF LOW PEFNEABI L I TY

A. ARTESIAN Impervious beds which f o r c e f lows below r e g i o n a l base l e v e l .

Rare, sma l l i r r e g u l a r caves ( d i f f u s e f l o w ) .

I n c l i n e d 3-D network caves ( f r e e f l o w ) .

Rare, smal l i r r e g u l a r caves ( d i f f u s e f l o w ) . H o r i z o n t a l 2-D network caves ( f r e e f l o w ) .

B. SANDWICH Th in beds o f so lub le rock between impervious beds.

39

groundwater movement w i l l g r a d u a l l y enlarge t h e f r a c t u r e s through which i t moves by s o l u t i o n and p e r m e a b i l i t y o f t he un i t w i l l increase w i t h t ime.

Moore ( 1 9 6 6 ) has p o s t u l a t e d t h a t pumping o s c i l l a t i o n s from e a r t h t i d e s and d i s t a n t earthquakes may move water through j o i n t s and p a r t i n g s t o o narrow t o move much water under normal h y d r a u l i c gradients . However, because f r a c t u r e s commonly have an uneven d i s t r i b u t i o n i n carbonate rocks, groundwater movement o f t e n develops secondary p e r m e a b i l i t y i n s e l e c t i v e areas o f c losely-spaced f r a c t u r e s o r a long open f r a c t u r e systems. Therefore, according t o LeGrand and S t r i n g f i e l d ( 1 9 7 1 ) , moderately l a r g e openings tend t o en la rge by s o l u t i o n a c t i o n w h i l e smal l openings n o t i n t h e p a t h o f water f l o w g e n e r a l l y en la rge o n l y s l i g h t l y . The n e t r e s u l t i s a t y p i c a l l y uneven d i s t r i b u t i o n o f p e r m e a b i l i t y i n a q u i f e r s where p e r m e a b i l i t y i s c o n t r o l l e d by f r a c t u r e s .

1.4.2.1 Jo in t s . J o i n t s a re t h e most f r e q u e n t l y o c c u r r i n g f r a c t u r e s found i n carbonate aqu i fe rs . T y p i c a l l y , j o i n t s are n e a r l y perpend icu la r t o bedding. However, depending on c o n d i t i o n s o f format ion, j o i n t s may have any o r i e n t a t i o n w i t h respec t t o bedding. Fo r example, Gr i ce ( 1 9 6 8 ) found t h a t j o i n t s near Grand Rapids, Manatoba, Canada, were e s s e n t i a l l y p a r a l l e l t o bedding planes.

J o i n t s may e x e r t p r imary c o n t r o l over t h e d i r e c t i o n o f groundwater f l o w p r i o r t o development of s o l u t i o n c a v i t i e s i n a carbonate a q u i f e r . Therefore, n o n - v e r t i c a l j o i n t s may e x e r t a considerable l a t e r a l i n f l u e n c e on the movement o f ground water. Therefore, use o f rose diagrams o r histograms t o represent the o r i e n t a t i o n o f j o i n t s may r e s u l t i n cons iderab le e r r o r i f these data a re used t o es t imate groundwater f l o w d i r e c t i o n s when j o i n t s are n o t v e r t i c a l .

I f recharge/discharge r e l a t i o n s h i p s a l l o w groundwater t o move through an open carbonate a q u i f e r (see Table 1 .4 -11 , then j o i n t s can become en la rged by s o l u t i o n o f t h e l imestone. The r e s u l t may l e a d t o development o f : (1) a ve ry permeable and cavernous, unsatura ted zone; ( 2 ) a zone of an e x c e p t i o n a l l y high p e r m e a b i l i t y i n v a l l e y s ; and ( 3 ) a r a p i d l y decreasing p e r m e a b i l i t y w i t h i n c r e a s i n g depth below t h e water t a b l e as p o s t u l a t e d by LeGrand, S t r i n g f i e l d and LaMoreaux ( 1 9 7 6 ) .

F i g u r e 1.4-2 f rom W i l l i a m s ( 1 9 8 3 1 , con ta ins t h r e e e x c e l l e n t examples o f j o i n t enlargement by s o l u t i o n . I t a l s o i l l u s t r a t e s movement o f water along bedding p lanes and an apparent r a p i d decrease i n p e r m e a b i l i t y w i t h depth. Stearns ( 1 9 7 7 ) has demonstrated t h a t t he openings i n the midd le Ordov ic ian l imestones o f t he Percy P r i e s t Dam area i n c e n t r a l Tennessee are a box-work o f bedding p lanes and j o i n t s . The p o r o s i t y o f t h e l imestones i s approximately 1 5 pe rcen t i n t h e upper 1 0 f e e t but decreases r a p i d l y t o about 1.5 percent a t a depth o f 30 f e e t .

S u r f i c i a l k a r s t f ea tu res developed as a r e s u l t o f s o l u t i o n a l enlargement o f j o i n t s should have a p r e d i c t a b l e d i s t r i b u t i o n based on the o r i e n t a t i o n o f j o i n t se ts i n t h e carbonate rocks. For example, a r e l a t i v e l y un i fo rm d i s t r i b u t i o n o f s inkho les t h a t extend t o the depth o f the water t a b l e would be expected i n a f i n e - t e x t u r e d carbonate rock exposed t o t h e sur face o f t h e ear th . However, f o r coarse- tex tu red carbonate rocks s inkho les should have p r e f e r e n t i a l o r i e n t a t i o n i n elongate zones and should be concentrated i n areas t h a t o r i g i n a l l y con ta ined closely-spaced j o i n t s . The occurrence o f s i n k i n g creeks o r r i s e p i t s i s more frequent in. those areas w i t h a coarse-textured p e r m e a b i l i t y than f o r carbonate rocks t h a t have a f i n e - t e x t u r e d pe rmeab i l i t y .

Powel l ( 1 9 7 7 ) has demonstrated t h a t i n p o r t i o n s o f I nd iana two se ts o f j o i n t s a re present. H i s "master j o i n t s " are j o i n t s t h a t cross more than one s t r a t i g r a p h i c o r l i t h o l o g i c unit . "Cross j o i n t s , " on the o t h e r hand, a re n e a r l y perpend icu la r t o the master j o i n t s , are s h o r t e r than master j o i n t s , and te rm ina te aga ins t master j o i n t s . The cross j o i n t s are g e n e r a l l y r e s t r i c t e d t o a s i n g l e stratum. F i g u r e 1.4-3, taken from Powe l l ' s work, i l l u s t r a t e s the r e l a t i o n s h i p of master j o i n t s and cross j o i n t s . S o l u t i o n channels developed along t h i s j o i n t system are non-uniform and may even be sinuous. O n t he o t h e r hand, Bocker ( 1 9 7 2 ) d iscusses k a r s t f ea tu res developed i n the Transdinubian c e n t r a l mountain range o f Hungary where again two se ts o f f r a c t u r e s a re present t h a t a re almost perpend icu la r , but i n t h i s case, t h e f r a c t u r e s a re s i m i l a r i n every dimension, even on the microscopic scale. As a r e s u l t , t h e p a t t e r n o f s o l u t i o n c a v i t i e s i s a box-work t h a t mimics t h e f r a c t u r e p a t t e r n .

QUARRY, COUNTY CLARE, IRELAND

QUARRY, VENETIAN PREALPS , ITALY

ROAD CUTTING, MAMMOTH CAVE, KENTUCKY

:m

Figure 1.4-2 V e r t i c a l s e c t i o n through l imestone outcrops showing d i m i n u t i o n o f f i s s u r e w id ths w i t h depth ( f rom Wi l l iams, 1 9 8 3 ) -

4 1

F i g u r e 1 .4-3 Block diagram showing i d e a l i z e d se ts o f master and cross j o i n t s i n t h r e e beds of rock ( f rom Powell , 1 9 7 7 ) .

Water

F i g u r e 1 . 4 - 4 Geo log ica l s e c t i o n o f t h e Malham, U.K., area showing s t r u c t u r e and an i n t e r p r e t a t i o n o f t h e underground drainage system ( f rom S m i t h and Atkinson, 1 9 7 7 ) .

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1.4.2.2 Fau l t s . F a u l t s a re considered t o be f r a c t u r e p lanes o r f r a c t u r e sur faces a long which the re has been apprec iab le movement. F a u l t zones may be charac ter ized as a se r ies o f c l o s e l y spaced f r a c t u r e s arranged i n bands, which may be seve ra l cen t imeters t o seve ra l k i l o m e t e r s i n w i d t h . The displacement o f rocks i n a f a u l t zone may be a r e s u l t o f c o l l e c t i v e o r d i f f e r e n t i a l movement a long the many f r a c t u r e s conta ined i n t h e f a u l t zone. Because o f t h e i r n e a r l y p lana r nature, f a u l t s and f a u l t zones p r o v i d e an inhomogeneous secondary p o r o s i t y i n carbonate aqu i fe rs .

Kas tn ing ( 1 9 7 7 ) has demonstrated t h a t w i t h respec t t o t h e i r i n f l u e n c e on groundwater f l o w and condu i t enlargement, f a u l t s may have: (1) a p o s i t i v e e f f e c t , ( 2 ) a negat ive e f f e c t , o r ( 3 ) a n e u t r a l e f f e c t as discussed below. I f the presence o f f a u l t s increases p e r m e a b i l i t y o f t he a q u i f e r o r o therw ise enhances f l o w c h a r a c t e r i s t i c s o f t h e a q u i f e r , Kas tn ing c l a s s i f i e s t h e e f f e c t o f t he f a u l t as p o s i t i v e . Examples used by Kastn ing t o represent t h e p o s i t i v e i n f l uences o f f a u l t s on groundwater movement i n c l u d e c h a r a c t e r i s t i c a l l y open f r a c t u r e systems r e s u l t i n g f rom t e n s i o n a l (ex tens iona l ) f o rces and increased r a t e breakdown o f cavern r o o f s i n areas where reverse f a u l t s o r t h r u s t f a u l t s i n t e r s e c t t h e caverns. Other examples o f p o s i t i v e e f f e c t s m i g h t i nc lude t h e c o n t r o l by r e g i o n a l f r a c t u r e s p a t t e r n s o f t h e l o c a t i o n and d i s t r i b u t i o n o f s inkho les by f a u l t s o r f a u l t zones (Medv i l l e and Werner, 1 9 7 7 ) ; f r a c t u r e c o n t r o l o f p o l j e development i n Yugoslavia (Mi lanov ic , 1 9 7 6 ) ; the upward movement o f water f rom deep a r t e s i a n a q u i f e r s (Love, 1 9 8 3 ) ; and f r a c t u r e s may p rov ide a h y d r a u l i c connect ion between a q u i f e r l a y e r s t h a t were o therw ise iso la ted . (Maclay and Small, 1 9 8 3 ) .

According t o Kas tn ing f a u l t s a re considered t o have a negat ive i n f l u e n c e on groundwater f l o w i f groundwater movement i s impeded o r d i v e r t e d upon i n t e r s e c t i n g t h e f a u l t p lane o r f a u l t zone. R e c r y s t a l l i z a t i o n o r m y l o n i t i z a - t i o n o f t he carbonate m a t e r i a l i n the f a u l t p lane during compressional f a u l t i n g may l o c a l l y impede groundwater c i r c u l a t i o n . Kas tn ing has shown t h a t condu i t s developed a long impermeable f a u l t p lanes may m ig ra te downdip as l o c a l ' b a s e l e v e l s drop.

The emergence o f seve ra l major spr ings f rom t h e Edwards Limestone a long f a u l t s i n t h e Balcones f a u l t zone o f c e n t r a l Texas (Green, 1 9 6 7 ) i l l u s t r a t e s negat ive i n f l u e n c e o f f a u l t s on groundwater f low. Maclay and Smal l ( 1 9 8 3 ) s t a t e t h a t f a u l t i n g i n t h e Balcones f a u l t zone has emplaced high p e r m e a b i l i t y rocks o f t h e Edwards Aqu i fe r aga ins t low p e r m e a b i l i t y rocks and thus c rea ted a l a t e r a l d i s c o n t i n u i t y caus ing p a r t i a l t o complete blockage o f groundwater f low. P i c a r d ( 1 9 5 2 ) o u t l i n e s seve ra l d i f f e r e n t s t r u c t u r a l t r a p s t h a t a l l o w ground water t o accumulate i n underground r e s e r v o i r s i n a r i d zones. Frangopoulos and Zervoannis ( 1 9 6 1 ) have presented diagrams o f ground water h e l d i n s t r u c t u r a l t r a p s i n l imestone o f Greece as a r e s u l t o f f a u l t i n g .

F a u l t s t h a t e x e r t no i n f l u e n c e over groundwater movement i n carbonate a q u i f e r s ( n e u t r a l e f f e c t ) a r e ra re . Kas tn ing (1977) c i t e s one example f rom Gregg ( 1 9 7 4 ) i l l u s t r a t i n g t h a t a low angle t h r u s t t r a n s e c t i n g Howe Caverns has n o t i n f l uenced development o f t h e cave. Demonstrat ion t h a t a f a u l t remains n e u t r a l i n i t s i n f l u e n c e o f groundwater movement would n e c e s s a r i l y i n v o l v e documentation t h a t t he f a u l t d id n o t i n f l u e n c e o r change t h e p e r m e a b i l i t y o f t he carbonate r e s e r v o i r .

The p l a n a r na tu re o f f a u l t s and f a u l t zones and t h e r e s u l t i n g l i n e a r express ion o f these fea tu res on t h e e a r t h ' s sur face a l l ows use o f a e r i a l photographs and s a t e l l i t e images as a means f o r mapping l ineaments and f r a c t u r e t races f o r t h e purpose o f groundwater exp lo ra t i on . I n many areas h i g h y i e l d w e l l s and spr ings occur a long such l ineaments ( f o r example see Moore, H ink le , and Moravec, 1 9 7 7 ) . Par izek ( 1 9 7 6 ) has p rov ided an e x c e l l e n t summary a r t i c l e on t h e na tu re and s i g n i f i c a n c e o f f r a c t u r e t races and l ineaments i n carbonate and o t h e r t e r r a i n s .

Wermund and Eepeda (1977) performed a r a t h e r comprehensive r e g i o n a l s tudy o f f r a c t u r e zones assoc ia ted w i t h t h e Edwards Limestone A q u i f e r o f Texas. The i r work demonstrates b o t h p o s i t i v e and negat ive i n f l u e n c e s o f t h e Balcones F a u l t zone on groundwater movement. The authors have a l s o demonstrated t h a t f r a c t u r e o r i e n t a t i o n i n t h e r e g i o n n o r t h o f t h e Balcones F a u l t zone a re d i s t i n c t l y d i f f e r e n t than f r a c t u r e o r i e n t a t i o n s w i t h i n t h e zone and may be r e l a t e d t o f r a c t u r e s i n t h e basement rocks.

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1.4.3 T i l t e d and f o l d e d carbonate aqu i fe rs . For t h e purposes o f d iscuss ion , f o l d e d and t i l t e d carbonate a q u i f e r s w i l l be subd iv ided i n t o f o u r ca tegor ies ' s i m i l a r t o those presented by LeGrand and LaMoreaux (1975) .

1. Near l y h o r i z o n t a l s t r a t a 2. Homoc l ina l l y t i l t e d s t r a t a

3. Folded s t r a t a

Gen t l y i n c l i n e d Moderately t o s t e e p l y i n c l i n e d

A n t i c l i n e s Domes Sync l ines and bas ins

4. Complex f o l d e d and f a u l t e d s t r u c t u r e s . Groundwater f l o w i n n e a r l y h o r i z o n t a l s t r a t a i s c o n t r o l l e d by t h e p o i n t s

o f d ischarge and whether t h e system i s cha rac te r i zed by d i f f u s e f l o w o r f r e e f low. I n f r e e f l o w systems, groundwater f l o w may be d i r e c t i o n a l l y o r i e n t e d along, o r d i v e r t e d by, f r a c t u r e systems. Groundwater f l o w i n h o r i z o n t a l , d i f f u s e f l o w a q u i f e r s may be d i r e c t i o n a l i f c o n t r o l l e d by t h e c o n f i g u r a t i o n o f t h e water tab le , t h e l o c a t i o n o f d ischarge p o i n t s , o r presence o f impermeable s t r a t a .

T i l t i n g o f s t r a t a induces a d d i t i o n a l c o n s t r a i n t s on groundwater f l o w d i r e c t i o n s . I n t i l t e d open a q u i f e r s o r open p o r t i o n s o f con f i ned a q u i f e r s groundwater should i n i t i a l l y f l o w i n a downdip d i r e c t i o n . A c t u a l groundwater movement may c o n s i s t o f movement p a r a l l e l t o bedding as w e l l as movement a long f r a c t u r e s t h a t c ross t h e beds. I f j o i n t s o r f a u l t s a re n o t p a r a l l e l t o the d i p o f s t r a t a , as i s commonly t h e case, d i v e r s i o n o f f l o w along t h e f r a c t u r e s may p r o v i d e a s i g n i f i c a n t d e v i a t i o n from t h e d i r e c t i o n o f d ip o f t h e beds. I n f o l d e d carbonate a q u i f e r s t h e plunge o f t h e f o l d a x i s may a l s o i n f l u e n c e the d i r e c t i o n o f ground-water f low.

A f t e r groundwater reaches t h e water t a b l e o r i f t h e carbonate a q u i f e r i s perched o r conf ined, t h e most impor tan t f a c t o r t h a t c o n t r o l s d i r e c t i o n o f groundwater movement i n f o l d e d o r t i l t e d a q u i f e r s i s l o c a t i o n o f t he p o i n t o r p o i n t s o f discharge.

Al though t h e d i r e c t i o n of dip, d i r e c t i o n o f p lunge o r t h e o r i e n t a t i o n o f f a u l t s o r f r a c t u r e systems may c o n t r o l d i r e c t i o n s of groundwater movement, i t i s obvious t h a t a t some reasonable depth beneath the e a r t h ' s sur face groundwater f l o w must be d i v e r t e d toward a v a i l a b l e p o i n t s o f discharge. Thus, groundwater may move i n a d i r e c t i o n t h a t i s o b l i q u e t o t h e d i r e c t i o n s o f s t r i k e and dip o r groundwater may move p a r a l l e l t o s t r i k e i n o rde r t o reach a discharge p o i n t . S t r i n g f i e l d ( 1 9 6 6 ) has demonstrated t h a t t h e T e r t i a r y l imestones o f t h e southeastern U n i t e d Sta tes o f t e n have major p o i n t s o f d ischarge near t h e lowest e l e v a t i o n where streams i n t e r s e c t these carbonate a q u i f e r s and t h a t groundwater must have a s t r i k e - p a r a l l e l f l o w component i n o rde r f o r d ischarge t o occur.

A few examples w i l l i l l u s t r a t e t h e above concepts. Palmer ( 1 9 7 7 ) demonstrated t h a t groundwater f l o w i n the Mammoth Cave area o f Kentucky was e s s e n t i a l l y concordant w i t h bedding and t h a t cave passages va ry w i t h d i p o f t he beds. S t r i n g f i e l d and LeGrand ( 1 9 6 9 ) s t a t e t h a t groundwater movement a long t h e f l a n k s o f t h e Sequatchie A n t i c l i n e i n Tennessee occurs a t some angle t o d ip and i n many areas groundwater f l o w i s p a r a l l e l t o s t r i k e . Subsurface drainage i n rocks o f t h e Greenbr ia r Group i n West V i r g i n i a o f t e n i n v o l v e s p i r a c y o f sur face waters. Subsurface f l ows may move downdip a long enlarged bedding planes o r movement may occur i n condu i t s p a r a l l e l t o t h e s t r i k e o f t he carbonate rocks.

I n f o l d e d o r t i l t e d , f ree- f low carbonate a q u i f e r s , t h e o r i e n t a t i o n of f r a c t u r e systems may p r o v i d e c o n t r o l o f groundwater f l o w d i r e c t i o n s r a t h e r than t h e d i r e c t i o n o f dip o r plunge of t h e s t r a t a . A n t i c l i n e s and sync l i nes c h a r a c t e r i s t i c a l l y have a zone of i n tense f r a c t u r i n g assoc ia ted w i t h t h e i r a x i a l reg ions. LaMoreaux and Powel l ( 1 9 6 3 ) have demonstrated t h a t abundant groundwater i s assoc ia ted w i t h t h e a x i s o f a s y n c l i n a l l y fo lded, perched carbonate a q u i f e r near H u n t s v i l l e , Alabama. The most i n t e n s e l y k a r s t i f i e d p o r t i o n o f t h e Basso Carso a n t i c l i n e of I t a l y i s assoc ia ted w i t h normal f a u l t s p a r a l l e l t o t h e a x i s o f t h e a n t i c l i n e ( B e l l o n i , M a r t i n i s , and Orombel l i , 1972).

Complex f o l d i n g and f a u l t i n g i n carbonate rocks o f Yugoslavia i s respons ib le f o r t h e c r e a t i o n of many of t he l a r g e p o l j e s f o r which Yugoslavia i s so famous (Herak, 1 9 7 2 ) . B e l l o n i , M a r t i n i s and Orombel l i ( 1 9 7 2 ) have

4 4

i l l u s t r a t e d some o f t h e complex s t r u c t u r a l r e l a t i o n s h i p s respons ib le f o r k a r s t p rov inces o f I t a l y , i n c l u d i n g areas o f i m b r i c a t e f a u l t i n g , nappe s t r u c t u r e s and p o l j e development.

Groundwater movement i n such complexly f o l d e d and f a u l t e d areas may be d i f f i c u l t t o decipher but d e t a i l e d e f f o r t s o f t e n p r o v i d e s u f f i c i e n t i n f o r m a t i o n f o r a t l e a s t a genera l understanding o f t h e system. Spigner and Graves (1977) were able t o s u c c e s s f u l l y l o c a t e m u n i c i p a l water w e l l s i n a f o l d e d and f a u l t e d carbonate a q u i f e r near I ronda le , Alabama, a f t e r mapping t h r u s t f a u l t s , wrench f a u l t s , and subordinate f o l d s .

F igeh Spring p rov ides a wa.ter supply f o r t h e c i t y o f Damascus and emerges from Turonian l imestones near the lowest e l e v a t i o n where these f o l d e d l imestones i n t e r s e c t t h e Barada R ive r . The recharge area f o r F igeh Spring i s the Anti-Lebanon range immediately n o r t h o f t h e sp r ings and c o n s i s t s o f a n t i c l i n a l l y f o l d e d sequence o f Cenomanian and Turonian l imestones. Water e n t e r i n g t h e l imestones moves o b l i q u e l y down t h e f l a n k s o f t h e a n t i c l i n e a long bedding p lanes and f r a c t u r e s ; becomes con f ined under o v e r l y i n g C o n i a t i o n mar l s and moves p a r a l l e l t o s t r i k e . The water c i r c u l a t e s below t h e l e v e l o f t h e Barada R i v e r and then r i s e s up-plunge, p a r a l l e l t o t h e a x i s o f a c ross - fo ld , t o emerge a t F igeh Springs.

A f t e r expending cons iderab le e f f o r t t o demonstrate t h a t s t r u c t u r a l i n f l uences on groundwater f l o w a re p r e d i c t a b l e , I s h a l l c l o s e w i t h one a d d i t i o n a l example. F i g u r e 1 .4-4 f rom S m i t h and Atk inson (1977) i l l u s t r a t e s t h a t groundwater i n t h e Malham area o f Great B r i t a i n moves oppos i te t o t h e d i r e c t i o n o f dipping l imestones, crosses t h e M i d Craven f a u l t and a s y n c l i n a l a x i s t o emerge a t Airehead Spring.

1.5 M ic ro tex tu re -vo ids - (D. J . Burdon)

The v a r i a b l e o r i g i n o f carbonate rocks (organic , chemical, d e t r i t a l and metasomatic) produces a v a r i e t y o f t e x t u r e s and s t r u c t u r e s probab ly unequaled by any o t h e r group o f rocks. I n t h i s s e c t i o n t h e emphasis i s on t h e t e x t u r e o f t h e vo ids (pores, m i c r o f i s s u r e s , i n t e r s t i c e s ) and o t h e r openings and t h e i r r e s u l t a n t p o r o s i t y and p e r m e a b i l i t y , r a t h e r than on t h e s o l i d body o f t h e rock.

I n s tud ies o f k a r s t hydrogeology and hydrology, t h e s i z e and number o f v o i d s and t h e manner i n which they are i n te rconnec ted are o f p r imary importance as they determine t h e p e r m e a b i l i t y o f t h e rock. Knowledge o f t h e g e o l o g i c a l h i s t o r y of an area w i l l h e l p i n understanding t h e development o f p o r o s i t y and pe rmeab i l i t y . The f i e l d study o f l imestone sequences w i l l show t h e i r l a t e r a l f a c i e s changes and genera l c o n d i t i o n s o f sedimentat ion. Examination o f a specimen w i l l g i v e d e t a i l e d i n f o r m a t i o n on t h e o rgan ic o r i n o r g a n i c n a t u r e o f t he depos i t and t h e gross s t r u c t u r e o f t h e vo ids. I t i s o n l y w i t h t h e pe t rog raph ic and e l e c t r o n microscopes, however, t h a t one 'sees t h e f u l l d e t a i l s o f t h e i n t e r s t i t i a l s t r u c t u r e s . [EDITOR'S NOTE: These techniques a re d e t a i l e d by F l u g e l (19821.1

Brown's study (1963) o f a bedded d e t r i t a l l imestone i n Dorse t and New- b e r r y ' s study (1968) o f t h e Upper C o r a l l i n e Limestone o f M a l t a a re i n t e r e s t i n g examples o f what can be learned from s tudy ing m ic ro tex tu re .

1.5.1 I n t e r s t i c e s . " I n t e r s t i c e s " o r "vo ids" r e f e r s t o a l l open spaces, i n c l u d i n g m i c r o f i s s u r e s , i n a rock. I n t e r s t i c e s o r pore spaces i n rocks may be e i t h e r p r imary o r secondary. As d e f i n e d by Meinzer ( 1 9 4 2 1 , "The p o r o s i t y o f a rock i s i t s p r o p e r t y o f c o n t a i n i n g i n t e r s t i c e s . I t i s expressed q u a n t i t a t . i v e l y as t h e percentage o f t h e t o t a l volume o f t h e r o c k t h a t i s occup ied by i n t e r - s t i ces . " Most emphasis i s p laced on t h e i n t e r g r a n u l a r spaces. However, because o f t h e i r importance t o carbonate rocks, m i c r o f i s s u r e s a re discussed separa te ly i n s e c t i o n 1.5.2.

The presence o f pores o r i n t e r s t i c e s i m p l i e s p o r o s i t y . However, t h e rock w i l l be s u f f i c i e n t l y permeable t o p e r n i t t h e movement o f f l u i d th rough i t s po re spaces and i n t e r s t i c e s o n l y i f t h e i n t e r s t i c e s a re i n te rconnec ted and a re o f adequate s i z e t o p e r m i t t h e i n c l u d e d f l u i d t o overcome molecu la r adhesion forces. Al though many aspects of open spaces i n t h e rock a r e discussed i n

-

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terms o f t h e i r p o r o s i t y , i t i s t h e i r p e r m e a b i l i t y t h a t i s o f p r imary s ign i f i cance .

1.5.1.1 Pr imary i n t e r s t i c e s . Rocks formed o f g ranu la r m a t e r i a l a re porous, t he degree o f p o r o s i t y and p e r m e a b i l i t y depend on the shape o f t he vo ids, t h e i r r e g u l a r i t y o f void shapes and t h e genera l arrangement o f t h e c o n s t i t u e n t g r a i n s o r o rgan ic debr is , i n c l u d i n g the amount and composi t ion o f such i n t e r g r a n u l a r cement as may be present . Limestone composed o f organic debr is , e s p e c i a l l y coquina and the b iohermal deposi ts , but a l s o some b ios t romal , and p e l a g i c l imestone, and some c a l c i r u d i t e s , ca l ca ren i tes , calcareous sandstone and o o l i t e s , tend t o have a high o r i g i n a l o r p r imary p o r o s i t y and pe rmeab i l i t y . The p o r o s i t y and p e r m e a b i l i t y may be reduced by f i l l i n g w i t h f ine-gra ined calcareous mud and c lay . C i r c u l a t i n g marine o r t e r r e s t r i a l l i q u i d s tend t o d i s s o l v e and r e p r e c i p i t a t e carbonates, r e s u l t i n g i n t h e enlargement o r f u r t h e r f i l l i n g o f t he pore spaces.

i n c o n t r a s t t o carbonate rocks formed o f o rgan ic d e t r i t u s , l imestones (o rgan ic o r i no rgan ic ) formed by p r e c i p i t a t i o n tend t o be f i ne -g ra ined and l a c k i n pr imary pore i n t e r s t i c e s , a l though some t u f a s are v i r t u a l l y l i k e sponge.

1.5.1.2 Secondary i n t e r s t i c e s . Pore openings which a re due t o l i t h i f i c a t i o n processes and n o t due t o e x t e r n a l fo rces such as t e c t o n i c o r metamorphic ac t i on , a re considered secondary i n t e r s t i c e s . O f these processes, t he chemical changes owing ' t o t h e d i s s o l u t i o n o f uns tab le p r imary a ragon i te and t h e metasomatic replacement o f p r imary ca lc ium by secondary magnesium i n t h e c r y s t a l l a t t i c e a re the most impor tant . These processes are b a s i c a l l y caused by c i r c u l a t i n g s o l u t i o n s e i t h e r i n t h e sea o r i n l imestone exposed t o the movement o f f r e s h groundwater.

1.5.2 M ic ro f i ssu res . M i c r o f i s s u r e s may be de f i ned as smal l i n t e r s t i c e s o f a p lana r nature, d i s t r i b u t e d u n i f o r m l y o r i r r e g u l a r l y throughout a rock, which a re n o t induced by e x t e r n a l t e c t o n i c o r metamorphic ac t i on . They are e s s e n t i a l l y d iagene t i c phenomena a n d occur as the o r i g i n a l p l a s t i c sediment s o l i d i f i e s . They are comprised o f :

1. S t r a t i f i c a t i o n o r bedding planes: 2. D e p o s i t i o n a l p lanes ( fo rm o f bedding p lane) : 3. Cross-bedding; 4 . S l u m p planes: 5. Compaction s l i p s , i n c l u d i n g d i f f e r e n t i a l compaction s l i p s ; 6 . J o i n t s , due main ly t o loading: 7. Dess ica t ion cracks and j o i n t s due t o exposure t o a i r . Openings a long s t r a t i f i c a t i o n p lanes and j o i n t s (main ly load ing) a re the

most common and most impor tan t o f t he mic ro f i ssures . S t r a t i f i c a t i o n o r bedding j o i n t s a re n o t t r u l y "m ic ro f i ssu res " s ince they can have g r e a t a r e a l ex ten t , but they a r e r e l a t e d t o the depos i t i on o f t he l imestone afid n o t t o subsequent ou ts ide forces: t h i s a l s o a p p l i e s t o j o i n t s which tend t o be perpend icu la r t o the bedding. I t must be recognized t h a t when carbonate rocks are exposed t o t e c t o n i c forces, then movement and r e l i e f o f s t r e s s w i l l tend t o take p lace a long e x i s t i n g p lanes, i n p a r t i c u l a r a long t h e bedding planes. A t t he same t ime i r r e g u l a r j o i n t s w i l l tend t o be reformed and have p r e f e r r e d o r i e n t a t i o n .

46

2. Hydrogeological features of carbonate rocks ( G i l b e r t Castany)

Hydrogeologica l parameters such as p o r o s i t y , storage c o e f f i c i e n t , p e r m e a b i l i t y , and leakance must be determined i n carbonate a q u i f e r s and r e l a t e d t o t h e s t r u c t u r e o f t h e vo ids and f i s s u r e s t h a t predominate t o assess the water resources o f an area. To accomplish t h i s complex task , t h e process o f eva lua t i on must use a v a r i e t y o f qeo log i ca l , chemical, eng ineer ing and mathematical d i s c i p l i n e s .

The p r i n c i p a l c h a r a c t e r i s t i c s of carbonate rocks, namely t h e i r heteroge- n e i t y and an iso t ropy , determine t h e p o r o s i t y and p e r m e a b i l i t y parameters on t h e s p a t i a l sca le w i t h i n which these parameters a re s tud ied. Resu l ts o f l a b o r a t o r y and f i e l d t e s t s represent o n l y c e r t a i n l o c a l va lues and cannot be genera l i zed t o t h e e n t i r e a q u i f e r w i t h o u t cons ide r ing t h e g e o l o g i c a l c h a r a c t e r i s t i c s such as l i t h o s t r a t i g r a p h y , s t r u c t u r e , and geomorphology.

2 . 1 Porosity--Water s torage i n k a r s t

P o r o s i t y i s t he p roper t y o f a r o c k hav ing i n t e r s t i c e s .

2 .1 .1 Types o f e f f e c t i v e p o r o s i t y . The types o f p o r o s i t y o f unconf ined o r conf ined a q u i f e r s can be c l a s s i f i e d on t h e b a s i s o f t he na tu re and p r o p o r t i o n o f vo ids, i n t e r s t i c e s , m ic ro f i ssu res and channels i n t h e rock and i n terms o f t he amount o f groundwater re leased g r a v i t a t i o n a l l y o r re ta ined .

2.1.1.1 P o r o s i t y c l a s s i f i c a t i o n on t h e b a s i s o f v o i d types. The cha rac te r i s - t i c s o f t he vo ids, t h e i r shape, s ize , d i s t r i b u t i o n , and volume, compared t o t h e o v e r a l l r ock volume a re t h e e s s e n t i a l f ea tu res necessary f o r d e f i n i n g t h e p o r o s i t y types. O n t h e b a s i s o f v o i d types, p o r o s i t y may be microscopic o r macroscopic (see Table 2 . 1 - 1 ) .

Microscopic vo ids between t h e m i n e r a l c r y s t a l s p r o v i d e t h e i n t e r c r y s t a l - l i n e p o r o s i t y which u s u a l l y accounts f o r 0 .1 t o 1 pe rcen t o f t h e t o t a l poros- i t y . Most o f these vo ids a re r a r e l y de tec ted even by microscope. I n t e r s t i t i a l p o r o s i t y de f i nes the vo ids between loose o r p o o r l y cemented g ranu la r ma te r ia l s . For example, an o o l i t i c l imestone o r a l imestone composed o f c a l c i t e p a r t i c l e s , such as chalk , has an i n t e r s t i t i a l p o r o s i t y comparable t o t h a t o f cemented sand o r porous sandstone. The de f ines t h e v o i d spaces formed by m i c r o j o i n t s , m ic ro f i ssu res , and beddins and s c h i s t o s i t y Planes.

c Depending upon t h e s p a t i a l sca le under cons idera t ion , some authors d i s t i n -

gu i sh between rock p o r o s i t y ( p o r o s i t y o f u n f i s s u r e d b locks) and massive o r f o rma t iona l p o r o s i t y ( p o r o s i t y o f l a r g e volumes inc ludes b o t h rock p o r o s i t y and f i s s u r e s ) (see F i g u r e 2.1.1) .

M i c r o f i s s u r e and macro f issure o r channel p o r o s i t y a re d i f f e r e n t i a t e d by means o f t he f l o w r a t e hydrographs o f k a r s i t i c a q u i f e r s (see F i g u r e 2 .1 .2 ) .

2.1.1.2 P o r o s i t y and groundwater types. Groundwater may be d i s t i n g u i s h e d ( i n r e l a t i o n s h i p t o i t s drainage c h a r a c t e r i s t i c s ) as:

G r a v i t a t i o n a l water (volume V ) o r water t h a t i s c o n t r i b u t e d t o the groundwater f l o w system under t h e i n f l u e n c e o f g r a v i t y ; and

4 7

Table

I I

2.1-1. C l a s s i f i c a t i o n o f vo ids and p o r o s i t y .

I n t e r c r y s t a l l i n e

Reference Scale

I n t e r c r y s t a l l i n e p o r o s i t y

Mic roscop ic

Macroscopic

vo ids Types I P o r o s i t y Types

Pores o r

I n t e r s t i c e s I n t e r g r a n u l a r I n t e r s t i t i a l

p o r o s i t y 1 I

Micro- f i s s u r e s

J o i n t s M i c r o f i s s u r e s

M i c r o f i s s u r e p o r o s i t y

Channe 1 s C a v i t i e s

~~~~~ ~ ~~

Channel p o r o s i t y

F i g u r e 2 . 1 - 1 P o r o s i t y types i n carbonate f i s s u r e p o r o s i t y .

a

Enlargement = x 100

rocks: (a) Rock p o r o s i t y , (b) Micro-

4 8

I\

A Water in storage in channels

Hydrograph of flow from tissures

Water in storage in fissures x, E O

\ /

t (days)

F igure 2.1-2 Hydrographs o f f low from both f issures and channels.

49

Retained water (volume Vr) , o r water t h a t i s r e t a i n e d w i t h i n t h e vo ids by sur face tens ion o r molecular a t t r a c t i o n . S p e c i f i c r e t e n t i o n i s t he r a t i o o f t he volume o f water which a rock w i l l r e t a i n aga ins t g r a v i t y t o i t s own volume.

The r e l a t i v e p r o p o r t i o n s o f these two ca tegor ies o f water depend e n t i r e l y on t h e v o i d s i zes and t h e m i n e r a l o g i c a l c h a r a c t e r i s t i c s o f rock ma te r ia l s . When f i s s u r e s are smal le r than 4 t o 5 microns i n s ize , water re leased under the i n f l u e n c e o f q r a v i t y wproaches zero and hence the groundwater movement ceases. For p r a c t i c a l purposes, sa tu ra ted rocks w i t h microscopic p o r o s i t y are complete ly sa tura ted w i t h r e t a i n e d water. That i s , water o c c u r r i n g i n these

. rocks doesn ' t d r a i n under t h e i n f l u e n c e o f g r a v i t y alone. The t o t a l p o r o s i t y , n i s t h e r a t i o o f t h e volume o f vo ids (Vv) t o the

t o t a l volume (V) o f a rep resen ta t i ve sample of t h e rock un i t expressed i n percent (see F igu re 2 .1 .3 ) :

i n percent vV n = - V

(2.1-1)

I n a sa tu ra ted rock, Vv i s t h e sum o f t h e volumes o f g r a v i t a t i o n a l and r e t a i n e d waters (Ve + Vr) : accord ing ly :

ve + vr i n percent V n = (2.1-2)

Some t o t a l p o r o s i t y va lues f o r carbonate rocks are g iven i n Table 2.1-2. E f f e c t i v e p o r o s i t y , ne, r e f e r s t o the amount of in te rconnected pore

space; t h a t i s , t h e space a v a i l a b l e f o r f l u i d t ransmiss ions. I t i s expressed as a percentage o f t h e t o t a l volume occupied by in te rconnec t ing i n t e r s t i c e s .

'e n = - i n percent e

(2.1-3)

E f f e c t i v e p o r o s i t v sometimes i s equated w i t h s p e c i f i c y i e l d but t h i s p r a c t i c e i s discouraged. E f f e c t i v e p o r o s i t y i s an index o f a v a i l a b l e i n t e r - connected pore space, whereas s p e c i f i c y i e l d i s t h e r a t i o o f t h e amount o f water t h e rock , a f t e r be ing saturated, w i l l y i e l d by g r a v i t y (V ) t o the volume o f t h e rock i t s e l f ( V ) (see F igu re 2 .1 -3 ) . The d e f i n i t i o n imE l ies t h a t g r a v i t y drainage i s complete and, i n e f fec t , t h a t t he va lue o f s p e c i f i c y i e l d increases w i t h t ime (see F i g u r e 2 . 1 - 4 ) . S p e c i f i c y i e l d may be considered as p o r o s i t y minus s p e c i f i c r e t e n t i o n .

Thus t h e d i f f e r e n c e between e f f e c t i v e p o r o s i t y and s p e c i f i c y i e l d i s a measure o f t h e completeness o f drainage, o r o f t he drainage w i t h i n a s e t p e r i o d o f t ime.

E f f e c t i v e p o r o s i t y o f carbonate rocks has an ex tens ive range o f va lues which a re approx imate ly p r o p o r t i o n a l t o t h e s i zes o f t h e f i s s u r e s (see Table 2.1-2) . These va lues , b e i n g ve ry low f o r i n t e r s t i c e s and m ic ro f i ssu res , p r a c t i c a l l y represent t h e t o t a l p o r o s i t y o f open f i s s u r e s and channels.

2.1.1.3 Fac tors a f f e c t i n g p o r o s i t y o f carbonate rocks. The p r i n c i p a l f a c t o r s a f f e c t i n g t h e p o r o s i t y o f carbonate rocks are:

1. F issu re openings measured i n m i l l i m e t e r s (major f a c t o r i n groundwater f l o w ) . These openings genera l l y a re en larged by e i t h e r s o l u t i o n o r mechanical a c t i o n o f movement o f water. A d i s t i n c t i o n , there fore , can be made between t h e pr imary p o r o s i t y due t o the conso l i da t i on o f sediments and t h e secondary p o r o s i t y r e s u l t i n g f rom s o l u t i o n and f r a c t u r i n g .

2. F i ssu re f i l l i n g . 3 . F i ssu re d e n s i t y measured i n l i n e a l meters. 4 . Rock petrography, e.g., t he dolomi tes are genera l l y 20 t o 30 percent

more porous than adjacent l imestone due t o t h e i r angular mode o f c r y s t a l l i z a t i o n and t o shr inkage d u r i n g do lomi t i za t i on .

50

altotal porosity n

b, effective porosity ne

V

I

volume t h l

I I

I I V I I

/

/'

F i g u r e 2.1-3 Diagramat ic exp lana t ion o f t o t a l and e f f e c t i v e p o r o s i t y .

5 1

Table 2.1-2. Some t o t a l p o r o s i t y va lues o f carbonate rocks. (From: V. C h i l i n g a r and H. Schoe l le r )

L i t h o l o g y

compact l imestone

f i s s u r e d l imestone

p o o r l y f i s s u r e d l imestone

p o o r l y f i s s u r e d l imestone

saccharoid l imestone

o o l i t i c l imestone

cha lk

do lomi te

marble

c a r r a r a marble

calareous tu f f

ca lareous sandstone dune

panchina

x v)

Y - 2' O

Q

a, > U Q)

e,

.- Y

.c .l-

Cretaceous

Carboni ferous

S i l u r i a n

Loca t ion

I t a l y

Buxton (1J.K.)

Dundee (USA)

England

Monk's Park (USA)

France

Micheldeau (U.K. 1

I t a l y

I t a l y

Ca lab r ia ( I t a l y )

I approaches retained approaches retained water volume total wrositv I n 1

M C v, m ?!

. -

-I I I l

O 1 2 3 4 8 time of drainage in months

T o t a l P o r o s i t y %

0.2 t o 1 4

1 4

2.2 t o 9.4

1 . 4 t o 1.6

27

20

30 t o 4 5

9 t o 22

0.4 t o 2.1

0 . 1 t o 0.2

20 t o 32

1 0 t o 66

15 t o 33

F i g u r e 2.1-4 E f f e c t i v e p o r o s i t y versus t ime ( l a b o r a t o r y da ta ) .

52

2.1.2 Storage c o e f f i c i e n t . The s torage c o e f f i c i e n t , S I i s d e f i n e d as the volume o f water re leased from a p r i s m w i t h i n t h e un i t c ross s e c t i o n a l area and a h e i g h t equa l t o t h e t o t a l th ickness o f t h e a q u i f e r , due t o one un i t meter change i n t h e p iezomet r i c l e v e l . I n conf ined aqu i fe rs , t h e c o e f f i c i e n t o f s torage genera l l y ranges from t o (see F i g u r e 2.1-5).

I n unconf ined aqu i fe rs , t h e s torage c o e f f i c i e n t corresponds t o t h e volume o f t h e f r e e water i n one cub ic meter o f t h e aqu i fe r ; and i s approx imate ly equa l t o the s p e c i f i c y i e l d . S p e c i f i c y i e l d g e n e r a l l y i s g i ven as t h e change i n the amount o f water i n s torage p e r un i t area o f unconf ined a q u i f e r t h a t occurs i n response t o a un i t change i n head. Such change i n storage i s dependent upon p a r t i c l e s ize , r a t e o f change o f t h e water t a b l e , t ime, and o t h e r va r iab les . The c o e f f i c i e n t o f s torage i s determined by means of p u m p i n g t e s t s o r f rom t h e records o f t h e drawdown o f water t a b l e (as, f o r instance, by d i v i d i n g t h e discharge by t h e corresponding d ra ined volume o f an unconf ined a q u i f e r ) . I t should be emphasized t h a t s p e c i f i c y i e l d and s torage c o e f f i c i e n t a re b o t h func t i ons o f t ime; t h e i r va lues inc rease as t ime increases.

2.1.3 Storage capac i t y o f k a r s t i c carbonate rocks. The s p e c i f i c y i e l d and storage c o e f f i c i e n t , determined from l a b o r a t o r y samples o r f rom f i e l d t e s t s , p rov ide an es t imate o f t h e amount o f water t h a t can be tapped f rom a c e r t a i n reg ion o f an aqu i fe r . For l a r g e unconf ined reservo i rs , . t h e s torage capac i t y i s approximately t h e volume o f f r e e water. The s torage capac i t y f o r some carbon- a t e t e r r a i n s i s g i ven i n Table 2.1-3.

2.2 Pe rmeab i l i t y Pe rmeab i l i t y i s t h e p r o p e r t y o f a r e s e r v o i r rock t h a t a l l ows a l i qu id t o f l o w under a pressure g r a d i e n t w i t h an apprec iab le v e l o c i t y . [EDITOR'S NOTE: The reader i s r e f e r r e d t o LeGrand and S t r i n g f i e l d , 1971, and S t r i n g f i e l d , LeGrand, and LaMoraeux, 1977, f o r f u r t h e r read ing on the development and d i s t r i b u t i o n o f pe rmeab i l i t y i n carbonate a q u i f e r s and t o Choquette and Pray f o r read ing on t h e c l a s s i f i c a t i o n o f p o r o s i t y i n carbonate rocks. ]

2.2.1 Pe rmeab i l i t y types. L i k e p o r o s i t y , p e r m e a b i l i t y depends upon t h e v o i d c h a r a c t e r i s t i c s , ma in l y t h e i r shapes and opening s izes. Some authors d i s t i n - gu i sh between seve ra l types: I n t r i n s i c pe rmeab i l i t y , f i s s u r e p e r m e a b i l i t y , and channel pe rmeab i l i t y . I n a l l cases, however, t h e hydrodynamic phenomena are the same. However, i t i s convenient t o d i s t i n g u i s h t h e r o c k o r i n t r i n s i c p e r m e a b i l i t y (microscopic) o f t h e rock mass and t h e r e g i o n a l o r f o rma t iona l

e r m e a b i l i t y (macroscopic) , which i nc ludes t h e added p e r m e a b i l i t y supp l i ed by ;oints, f i s s u r e s , and channels. Rock's i n t r i n s i c p e r m e a b i l i t y i s ve ry smal l compared t o t h a t o f r e g i o n a l f o r f o rma t iona l pe rmeab i l i t y .

S i m i l a r t o t h e p o r o s i t y , t h e p e r m e a b i l i t y v a r i e s w i t h t ime, and i t u s u a l l y increases w i t h t h e inc rease of t h e s i z e o f openii iqs o f t h e f i ssu res . Therefore , an i n i t i a l p e r m e a b i l i t y and a t r a n s i e n t p e r m e a b i l i t y r e s u l t i n g from the widening o f t h e vo ids , may be recognized.

2.2.2 Ca lcu la t i ons . Pe rmeab i l i t y and v e l o c i t y have t h e same dimensions; there fore , t h e most commonly used un i t i s t he meter p e r second (m/sec).

The p e r m e a b i l i t y uni t K may a l s o be de f i ned w i t h re fe rence t o Darcy 's Law:

Q = K * A * I (2 .2 -1 )

where Q i s t he volume o f water f l o w i n g (d ischarge) f o r a p e r i o d o f one second across a un i t c ross s e c t i o n a l area A under a un i t h y d r a u l i c g r a d i e n t I a t 2 O O C .

The Meinzer p e r m e a b i l i t y un i t , which has been used i n t h e Un i ted States, i s de f ined as t h e volume o f water i n ga l l ons , f l ow ing f o r one day across a un i t cross sect ion, one f o o t square, under a uni t h y d r a u l i c g r a d i e n t (1 f o o t p e r 1 f o o t ) a t 60°F (see openins A i n Ficrure 2.2-1) (Eleinzer, 1 9 2 3 ) .

C o e f f i c i e n t o f c T r a n s m i s s i v i t i (T) i s expressed' as t h e r a t e o f f l o w o f water a t t h e p r e v a i l i n q water temperature i n q a l l o n s o r cub ic meters p e r day, through a ve;tical s t k i p o f the- a q u i f e r one un i t wide ex tend ing t h e f u l l

5 3

I

impervious substrat urn

a

impervious substratum I' v e released =S A =?m2

b

F igu re 2.1-5 Diagrams of c o e f f i c i e n t o f storage, (at) c o e f f i c i e n t o f storage ( s p e c i f i c y i e l d ) i n a unconf ined aqu i fe r , (b) c o e f f i c i e n t o f storage i n a con f ined aqu i fe r .

5 4

Table 2.1-3. Storage capac i t y f o r some k a r s t i c carbonate t e r r a i n s .

s

I T e r r a i n

Zaghouan l imestones

Bent Saidane l imestones

Chennata l imestones

Bou Merzoug l imestones

Parnassos and d o l o m i t i c l imestones

Salon l imestones

Yarkow l i r ies tones

Maaman l imestones

Far West Rand d o l o m i t i c l imestones

Mesaoria l imestones

Country

T u n i s i a

II

II

A l g e r i a

Greece

France

I s r a e l

I s r a e l

South A f r i c a

Cyprus

Thickness (m)

1 0 0 0

800

100

20 O

3000

700

1 5 0

1 2 0 0

1 5 t o 30

Surface (km2)

20

1 7

1.8

140

1 7 7 4

1 2 0 0

250

1 2 5 0

500

OBSERVATION WELLS

OPENING E. 1 K)OT WlDE AND AWiFER THICKNESS l e i

' OPENING A , 1 FOOT SQUARE

Storage Capaci ty (106m3)

3.2

1.45

O .6

20

700

1

9 0 0

240

600

600

F igu re 2.2-1 Diagram o f c o e f f i c i e n t s o f p e r m e a b i l i t y and t r a n s m i s s i v i t y (mod i f ied f r o m Knowles, 1962) .

5 5

sa tu ra ted h e i g h t o f t h e a q u i f e r under a h y d r a u l i c g rad ien t o f 100 percent . ( I n F igu re 2.2-1, t h e f l o w i s measured through opening B, which has a w i d t h o f .1 f o o t and a h e i g h t ' e ' equa l t o the th ickness o f t h e aqu i fe r . A hydrau1j.c g r a d i e n t o f 1 0 0 percent means a 1 f o o t drop i n head i n 1 f o o t o f f l o w d is tance as shown by the p a i r o f observa t ion we l ls . )

T (L2 /T) = Ke (2.2-2)

I t i s an impor tan t parameter because i t def ines , more accu ra te l y than the pe rmeab i l i t y , t h e c h a r a c t e r i s t i c s o f ground water and i s e s p e c i a l l y u s e f u l i n e v a l u a t i n g the y i e l d o f an aqu i fe r . Table 2 .2 -1 g i ves c o e f f i c i e n t o f s torage and t r a n s m i s s i v i t y o f se lec ted carbonace t e r r a i n s .

The d i f f u s i v i t y , TIS, i s t h e r a t i o o f t h e t r a n s m i s s i v i t y t o t h e storage c o e f f i c i e n t . I t charac te r i zes t h e a b i l i t y o f t he a q u i f e r t o t r a n s m i t water and pressure. I n k a r s t i c aqu i fe rs , i t i s genera l l y high due t o the low h y d r a u l i c g rad ien ts and the r a p i d e f f e c t s o f propagat ion. That i s t o say, recharge a t a p o i n t i n an a q u i f e r o f t e n produces, a t remote d is tances, a r i s e i n t h e p iezo- m e t r i c sur face due t o pressure wave propagat ion. Th is p roper t y sometimes decreases t h e e f f i c i e n c y o f a r t i f i c i a l recharge.

2.2.3 Anisot ropy and he terogene i ty o f t he r e s e r v o i r rocks. As a consequence o f t h e f i s s u r a t i o n , t he r e g i o n a l l imestone i s genera l l y a n i s o t r o p i c and hetero- geneous, but t h e s p a t i a l d i s t r i b u t i o n o f t h e f i s s u r e s i s n o t e r r a t i c . I t f o l l o w s s t r u c t u r a l geology p a t t e r n s such as f o l d i n g , f a u l t i n g , j o i n t i n g , s c h i s t o s i t y , l i n e a r f o l i a t i o n s , bedding, d i a c l a s i s d i s t r i b u t i o n p a r a l l e l t o f o l d axes, etc.. . . The f i s s u r a t i o n occurs i n a form o f one o r severa l systems o f p a r a l l e l p lane f i s s u r e s (see F igure 2.2-2a). The number o f systems i s seldom more than th ree . They are f requen t l y d i s t r i b u t e d i n t h r e e d i s t i n c t d i r e c t i o n s : bedding j o i n t s , t e c t o n i c a l f i s s u r e s perpend icu la r t o the bedding i n two s t a t i s t i c a l l y d i s t i n c t d i r e c t i o n s (as, f o r instance, i n the k a r s t i f i e d cha lk o f t he Vanne R i v e r b a s i n southeast o f P a r i s ) . A s t a t i s t i c a l study o f t he f i s s u r a t i o n , p a r t i c u l a r l y on t h e outcropping d iac lases and on underground works, i n d i c a t e s two networks o f d i f f e r e n t ages. One presents v e r t i c a l f i s - sures w i t h major axes corresponding t o t h e average d ip hav ing no incoming waters; t h e o the r p resents i n c l i n e d d iac lases t h a t have a ma-jor r o l e i n the groundwater c i r c u l a t i o n (see F igu re 2.2-233).

I t i s poss ib le , t he re fo re , t o conclude t h a t s t a t i s t i c a l l y t h e r e g i o n a l rock may be d iv ided, as a f i r s t approximation, i n t o 1, 2 o r 3 systems o f p a r a l l e l and p lana r f i ssu res .

F i e l d observat ions have revea led two types o f f i s s u r a t i o n systems w i t h d i f f e r e n t h y d r a u l i c behaviors : p r imary water bea r ing systems and i n a c t i v e secondary systems (e.g. Vanne R i v e r bas in, see F igu re 2.2-233).

The main f a c t o r s o f f i s s u r a t i o n t h a t determine the pe rmeab i l i t y are: t he o r i e n t a t i o n and l o c a t i o n o f f i s s u r e s , t h e i r spacing i n each system, e x t e n t o f d i s t r i b u t i o n i n each system, the openinq of t he f i ssu res , t he f r a c t u r e sur face (roughness and form), and even tua l l y t he f i l l i n g o f t he f i s s u r e s ( r e s i d u a l c lays , o r sand). Table 2.2-2 g i ves the comparison o f p e r m e a b i l i t i e s o f rocks and f i s s u r e d r e g i o n a l rocks.

The da ta i n Table 2.2-2. show t h a t t he g e r m e a b i l i t y o f t he rock s t r u c t u r e i s ve ry small. and g e n e r a l l y l e s s than 10-l m/sec. However, f o r a r e g i o n a l f i s s u r e d rock, even w i t h ve ry f i n e f i s s u r e s o f , f o r example, 0 . 1 mm p e r meter, t he p e r m e a b i l i t y i s much l a r q e r (0 .7 x m/sec.).

The an iso t ropy o f t he rock mass i s produced from the f i s s u r e systems, o f t e n i n perpend icu la r planes. As a consequence, d i f f e rences between the v e r t i c a l and h o r i z o n t a l f l o w v e l o c i t y components e x i s t . Therefore, t he re should be a d i s t i n c t i o n between a v e r t i c a l pe rmeab i l i t y , Kv and a h o r i z o n t a l e r m e a b i l i t y , Kh (see F igu re 2 . 2 - 3 ) . The former i s o f i n t e r e s t p r i m a r i l y i n

t h e recharge o f a q u i f e r s ar.d the l a t t e r t o groundwater f low. The pumping t e s t s a re used t o determine the h o r i z o n t a l permeab i l i t y . I n geo-hydrodynamics, an a n i s o t r o p i c medium can be transformed i n t o an i s o t r o p i c medium on the bas i s o f t he degree o f an iso t ropy . Thus, t he t rans format ion f a c t o r s JKV/Kh f o r t he v e l o c i t i e s , and instance:

K 9 K i f o r t he discharges are def ined. For V

56

Table 2.2-1. Storage c o e f f i c i e n t and t r a n s m i s s i v i t y €o r some k a r s t i c carbonate t e r r a i n s .

f i s s u r e d l imes tone

------------ k a r s t i c f i s s u r e d 1 ime s tone

Carbonate Rock

Category

----------- f i s s u r e d do l om i t e I f r a c t u r e d marble

f i s s u r e d do l om i t e

mar ly 1 ime s tone

-----------

- - - - - - - - - - -

Upper Ju rass i c

Turonian- Cenomanian

Upper Cretaceous

Miocene

Ju rass i c

Upper Ju rass i c

Urgonian

Ju rass i c

II

II

L i a s

Juras s i c

Locat ion

Mout ie r (Switzer land)

I s r a e l

Tun i s i a

Murcie (Spain)

Lebanon

T u n i s i a

Salon (France)

Parnassos (Greece)

Vaucluse (France)

Grandes Causses (France)

Grandes Causses (France)

-------------------

Morocco

Parnassos (Greece

Almera (Spain)

Murcie I Spain)

Grandes Causses (France)

-------------------

1 t o 1.5

1

1.5 t o 1

1.7 t o 1

1.1 t o 2.4

.---------- 4 t o 5

5 t o 7

1 t o 5

5

1 t o 5

l o t o 1 2

T (mz/s)

0 . 1 x 1 0 - t o

1.3 x 1 0 -

1

0 . 1 x 10-

6 x 10 - t o

-----------

i o -3

1 t o 2 x 1 0 -

10-2

10-2 t o i o +

3 x 1 0 - ,-----------

5 7

Fissure planes .. Monolithic blocks

10 m

F igu re 2 .2 -2 F i s s i re s’

a

b stems i n calcareous t e r r a i n s , (a) calcareous t e r r a .ns

showing th ree systems K K ,K3 of p lane f i ssu res , d i v i d i n g the t e r r a i n i n mono l i t h i c bIoc$s, (b) chalk t e r r a i n i n the Vanne R iver Basin, southeast o f Par is , d i v i d e d by two systems o f f i s s u r e s ( a f t e r C. Megnien) .

5 8

Table 2.2-2. Comparison between some p e r m e a b i l i t i e s o f rocks and f i s s u r e d r e g i o n a l rocks. ( a f t e r C. Lou is )

1 imes tone

do lom i t e

s c h i s t

Rock

Rock Permeab i l i t y

(m/ sec)

0.36 t o 23 x

0.7 t o 120 x

0.5 t o 1.2 x 1 0 - l '

0.7 t o 1.6 x

Opening (mm)

Regional F i ssu red Rock W i t h One

F issu re p e r Meter

Pe rmeab i l i t y Along t h e F issures

(m/ sec 1

I

0 .1

4

6

2

0.7 x

0.5 x 10-1

1 .6 x 10 -1

0.6 x

F igu re 2.2-3 Systems o f f i s s u r e s producing anisot ropy, h o r i z o n t a l p e r m e a b i l i t y Kh, and v e r t i c a l p e r m e a b i l i t y Kv.

59

Qi = A I (2.2-3)

K i =/- (2.2-4)

V

where QI and K1 a r e r e s p e c t i v e l y t h e d ischarge and p e r m e a b i l i t y o f t he t ransformed i s o t r o p i c medium.

2.3 P o r o s i t y and p e r m e a b i l i t y s p a t i a l d i s t r i b u t i o n The s p a t i a l d i s t r i b u t i o n of t h e hydrogeo log ica l c h a r a c t e r i s t i c s , p o r o s i t y and p e r m e a b i l i t y , v a r i e s w i t h t h e geometry o f t h e rock mass, and i s d i f f i c u l t t o determine p r e c i s e l y . However, measurable mean va lues can be obtained.

The determined va lues o f t h e p o r o s i t y , storage c o e f f i c i e n t and the perme- a b i l i t y correspond t o e i t h e r a l i m i t e d volume o f a l a b o r a t o r y rep resen ta t i ve sample o r t o a l a r g e p o r t i o n o f t h e a q u i f e r through f i e l d t e s t s . I n the c l a s s i f i c a t i o n o f a groundwater r e s e r v o i r , t h e s t a t i s t i c a l a n a l y s i s o f these da ta c rea tes a problem o f s p a t i a l scale. The calcareous a q u i f e r s a re u s u a l l y heterogeneous, and the g e n e r a l i z a t i o n o f p o i n t da ta t o t h e e n t i r e reg ion i s in- accurate.

2.3.1 Heterogenei ty o r homogeneity, and transformed s p a t i a l sca le o f t he data f o r mean va lue c a l c u l a t i o n . A h y p o t h e t i c a l example would h e l p t o understand the r e l a t i o n between t h e t ransformed spa t ia l - sca le o f t he da ta and the homoge- n e i t y o r he terogene i ty (see F i g u r e 2 . 3 - 1 ) . A t t h e l abo ra toy sample scale, r a d i u s RI, t h e medium i s homogeneous. I t become heterogeneous a t a smal ler sca le ( p o r o s i t y = zero when P l i e s i n a s o l i d g ra in , and equals one when P l i e s i n a pore space), and a t a l a r g e r one ( rad ius R 2 ) . I t become homogeneous again, f o r a l a r g e fo rmat ion sca le ( rad ius R J ) .

The t o t a l p o r o s i t y measurement o f a l a b o r a t o r y rep resen ta t i ve sample i s r e l e v a n t t o a rock mass volume formed o f a porous m a t r i x w i t h an i n t r i n s i c p o r o s i t y . I f t h i s mass i s then subdiv ided i n t o smal l b locks by m ic ro f i ssu res w i t h m i c r o f i s s u r e p o r o s i t y , a t t h e sample scale, t h e medium may be considered homogeneous w i t h , f o r example, a measured average t o t a l p o r o s i t y o f 1 0 percent. Assuming t h e sample i s s p h e r i c a l w i t h a center a t P and a r a d i u s R ( 5 t o 1 0 cm), and has a f i n i t e volume AV, a l a r g e s i z e as compared t o the dimensions o f t he m ic roporos i t y (see F igu re 2 3 1 a ) , then:

The average t o t a l p o r o s i t y o f AV i s :

n (AV) = Bv

I f I? q r a d u a l l y decreases accord ing t o the func t ion :

AVV e x t r a p l i m

f ( n ) R = AV + O AV

(2.3-1)

( 2 . 3 - 2 )

a w ide ly v a r y i n g seri .es n i s ob ta ined such t h a t : i

(2.3 -3 )

The f l u c t u a t i o n s increase more and more, as R approaches O. When R i s very smal l (dimension o f t he p a r t i c l e o r t he molecule o f wa te r ) , and has a l i m i t R=O c o i n c i d i n g w i t h p o i n t P, n would reach an extreme va lue whether P l i e s i n s i d e a po re space, n=O, o r l i e s i n a g r a i n , n= l . The va lue o f t h e p o i n t p o r o s i t y a t P, r e f l e c t s t h e average t o t a l p o r o s i t y ,

n (AV) = n ( P )

60

(2 .3 -4 )

% AVA AVA

micro -scale meso-scale macro- scale R i R2 R3

F igu re 2 .3-1 I n f l u e n c e o f t h e s p a c i a l sca le upon t h e heterogeniety : (a) degrees of heterogenei ty , versus t h e volume of t h e r e s e r v o i r rock, (b) curve of t h e v a r i a t i o n s o f the t o t a l p o r o s i t y w i t h t h e volume o f t h e r e s e r v o i r r o c k (sphere o f r a d i u s R) .

6 1

around P a t t h e o r i g i n ; i .e . , i n t h e rep resen ta t i ve elementary volume AV i t i s determined by e x t r a p o l a t i o n a t t h e o r i g i n (see F i g u r e 2.3-lb) . As !?'in- creases, t h e volume o f t h e r e s e r v o i r rock, should i nc lude vo ids, m ic ro f i ssu res and e s p e c i a l l y macrof issures, and thus t h e average t o t a l p o r o s i t y f l u c t u a t i o n s ve ry much r e l a t i v e t o t h e encountered v o i d volumes. I n a heterogeneous rock mass a ve ry l a r g e enough r a d i u s R = b ( 5 0 - 1 0 0 m) , corresponds t o a l a r g e volume B o f t h e heterogeneous rock and the va lues o f n remain almost constant. Thus t h e medium can be considered homogeneous.

AvV e x t r a p l i m

AV + AVb AV f ( n ) R = (2.3-5)

Thus t h e degree o f he terogene i ty depends on t h e s i z e o f t h e considered p o r t i o n of t h e r e s e r v o i r rock. I n t h e above example, t h e t o t a l p o r o s i t y i s homogeneous when t h e sca le o f t he sample i s considered, then heterogeneous f o r some tens o f m3, then f i n a l l y homogeneous f o r t h e e n t i r e ca lcareous rock mass. As a p r a c t i c a l example, t h e Por t l and ian k a r s t i c l imestone f o r m a t i o n o f lower Burgundy (France) cover ing 600 km2 wide w i t h a th ickness o f 100 m, can be con- s ide red homogeneous a t t h e r e g i o n a l scale. Bu t i t was observed during t h e d r i l l i n g opera t ions t h a t , l a r g e f i s s u r e d l a y e r s o f k a r s t i c l imestones a l t e r n a t e w i t h semi-permeable beddings o f mar ly l imestones, thus forming a heterogeneous l i t h o s t r a t i g r a p h i c a l ser ies . A sample f rom a calcareous l a y e r would be con- s ide red homogeneous and t h e same would be t r u e f o r a semi-permeable stratum. Bu t a t t he sca le o f some tens of m3, t h e two samples are n o t geomet r i ca l l y i d e n t i c a l . A t t h i s scale, t h e r e s e r v o i r rock should then be considered hetero- geneous (see F i g u r e 2.3- la) .

The average t o t a l p o r o s i t y i s an e r r a t i c f unc t i on o f t he re fe rence volume (see F i g u r e 2 . 3 - l b ) .

2.3.2 Heterogenei ty and geometry o f t h e medium. A medium i s s t a t i s t i c a l l y homogeneous when i t s average i n t e r n a l c o n f i g u r a t i o n i n an elementary volume i s i d e n t i c a l i n a l l elementary volumes of ve ry smal l dimensions. Three orders o f maqnitude can t h e r e f o r e be de f i ned €o r the he terosene i tv . i n increasincr order.

- - -Th i rd o rde r he terogene i ty ( o r microscopic) ; i s a t t h e sample &ale. i t represents t h e pe t rog raph ic s t ruc tu re , when s tud ied w i t h a microscope: form . -

and s t r u c t u r e o f t h e g r a i n s o r t he c r v s t a l s and t h e i r cementation. -Example: m i c r o j o i n t s between the c r y s t a l s :

--Second o rde r he terogene i ty ( o r mesoscopic), i s a t t h e pumping t e s t sca le, f o r instance, o r a t t h e sca le o f l i t h o s t r a t i g r a p h i c a l s e r i e s determined by d r i l l i n g . Under t h i s c lass , t he he terogene i ty i s due t o a l t e r n a t i n g f a c i e s w i t h va r ious degrees o f compaction, bedding, j o i n t s , and d iac lases.

- - F i r s t o rde r he terogene i ty ( o r macroscopic) , i s a t t h e r e g i o n a l l imestone scale, such as l a t e r a l c ross ing o f f ac ies , f a u l t s , f o lds . I t i s i n the order o f r e g i o n a l geology.

2.3.3 Average C h a r a c t e r i s t i c s o f a r o c k mass (mass i f ) . The a n a l y s i s o f p o i n t da ta a l lows t h e de terminat ion o f t h e average c h a r a c t e r i s t i c s o f a rock mass (mass i f ) , on t h e b a s i s o f s t a t i s t i c a l ana lys is . These da ta a re based on geomorphological, l i t h o s t r a t i g r a p h i c a l and s t r u c t u r a l c h a r a c t e r i s t i c s . I f the number o f records i s s u f f i c i e n t , t h e use o f analog and mathematical models g i ves s a t i s f a c t o r y so lu t i ons .

2.3.4 V a r i a t i o n o f t h e hydrogeo log ica l c h a r a c t e r i s t i c s w i t h depth. The p e r m e a b i l i t y a n d s torage c o e f f i c i e n t genera l l y increase g radua l l y but non- un i fo rm ly w i t h t h e c i r c u l a t i o n o f water. Genera l ly , they reach a maximum value c lose t o the lowest p iezomet r i c sur face (see F igu re 2 .3 -2 ) . Th i s i s due t o the f l u c t u a t i o n s o f t h i s sur face, f a c i l i t a t i n g the dynamic and chemical ac t i ons o f t he groundwaters, and thus a l l o w i n g a l t e r n a t i n g cond i t i ons o f s o i l a e r a t i o n and sa tu ra t i on . Then the p e r m e a b i l i t y and storage c o e f f i c i e n t va lues decrease w i t h depth. As an example, t he 1 2 0 0 m t h i c k l imestone fo rmat ion o f t h e Far West Rand (South A f r i c a ) i s c i t e d : E f f e c t i v e p o r o s i t y o f 9 percent a t 60 m, 5.5

62

Land surface,

High seasonal stage /- , of water table

LOW seasonal stage /-- of water table

Increasing opportunity for circulation f and solution. [Resulting from increasing

ne, S and K.

F igu re 2 . 3 - 2 R e l a t i o n s h i p between hyd rogeo lbg ica l c h a r a c t e r i s t i c s and depth. S o l i d l i n e represents a common c o n d i t i o n and dashed and d o t t e d l i n e s represent l e s s common but not unusual c o n d i t i o n s (adapted f r o m LeGrand and S t r i n g f i e l d , 1 9 6 6 ) .

6 3

percen t a t 75 m, 2.6 pe rcen t a t 100 m, 2 pe rcen t a t 1 2 5 m and 1.3 percent a t 150 m.

Below a c e r t a i n depth o f 100 m t o seve ra l hundreds, t h e f i s s u r e s are sealed and t h e p e r m e a b i l i t y i s ve ry low. T h i s lower geo-dynamical l i m i t , c o n s t i t u t i n g t h e t r u e substratum o f t h e a q u i f e r v a r i e s as a f u n c t i o n o f t he g e o l o g i c a l and geomorphological r e g i o n a l e v o l u t i o n . The most impor tan t f a c t o r i s t h e hyd rogeo log ica l base l e v e l and i t s f l u c t u a t i o n s .

2.4 Ground-water c i r c u l a t i o n (Harry E. LeGrand) Inves(derab1e progress i n understanding t h e hydrology of carbonate rocks s ince the e a r l y p a r t o f t h e p resen t century. However, some i n v e s t i g a t o r s s t i l l d isagree on t h e na tu re o f t h e occurrence and movement o f water i n carbonate rocks. Many i n v e s t i g a t o r s o f ground water i n carbonate rocks now recogn ize a zone o f s a t u r a t i o n ( p h r e a t i c water) w i t h e i t h e r a water t a b l e under nonar tes ian c o n d i t i o n s o r a p iezomet r i c sur face under a r t e s i a n cond i t i ons . The wa te r - tab le concept i s use fu l , even where the p e r m e a b i l i t y i s so low t h a t t h e water t a b l e i s d iscont inuous o r so g r e a t t h a t water moves th rough l a r g e a r t e r y - t y p e openings.

Spec ia l emphasis i s p laced on carbonate rocks as condu i ts f o r t h e t rans - m iss ion o f water because o n l y where a c t i n g as condu i t s are they i n con'tact w i t h moving water, and, t he re fo re , vu lne rab le t o s o l u t i o n . I n a c t i n g as a condui t , a carbonate t e r r a i n may be under e i t h e r water- t a b l e o r a r t e s i a n cond i t i ons ; i n h o t h cases, t h r e e t h i n g s a r e e s s e n t i a l . I t must have (1) an area o f i n t a k e , i t must (2) t r a n s m i t , and ( 3 ) d ischarge water. If any one of these t h r e e r e q u i r e - ments i s n o t met, t h e l imestone body i s h y d r o l o g i c a l l y i n e r t and cannot a c t as a condu i t f o r water (LeGrand and S t r i n g f i e l d , 1 9 6 6 , p. 6 5 ) .

T h e o r e t i c a l l y , ground water moves i n arcuate pa ths f o l l o w i n g l i n e s o f f l o w t h a t have t h e i r o r i g i n a t t h e t o p o f t he zone o f s a t u r a t i o n i n recharge areas (Swinnerton, 1949, p. 6 6 5 ) . The f l o w l i n e s curve downward f o r sdme d i s tance and then r i s e t o an o u t l e t o r p o i n t o f discharge. Diagrammatical ly, these l i n e s can be represented by a f a m i l y o f curves, t h e spacing o f which i s c l o s e s t near t h e area o f t h e o u t l e t and becomes w ider along t h e t o p o f the zone o f s a t u r a t i o n as t h e d i s tance from the o u t l e t increases. I n u n i f o r m l y permeable m a t e r i a l where geo log ic s t r u c t u r e has o n l y subordinate i n f l u e n c e on i t s d i r e c - t i o n o f movement, t h e water may be expected t o have t h i s a rcuate p a t t e r n o f f low. However, even i n t h e i n i t i a l stages o f ground-water c i r c u l a t i o n i n l imestone and o t h e r carbonate rocks, l i n e s o f f l o w are modi f ied. C i r c u l a t i o n i n t h e discharge area, hav ing g r e a t e r v e l o c i t i e s , may r e s u l t i n an enlargement o f t h e o u t l e t and a consequent sha l low ing of t h e more arcuate paths. S o l u t i o n openings a long t h e more d i r e c t pa ths w i l l become l a r g e r than those a long t h e l e s s d i r e c t pa ths and w i l l p e r m i t p r o g r e s s i v e l y l a r g e r f lows a t t he expense o f o t h e r passageways.

As s t a t e d by Rhoades and S i n a c o r i (1941, p. 7 9 4 ) and demonstrated by Bedinger (1967), t h e i n i t i a l f l o w o c c u r r i n g b o t h a t g r e a t and shal low depths causes s o l u t i o n which i s q u a n t i t a t i v e l y more pronounced i n t h e upper zone because o f g r e a t e r c i r c u l a t i o n i n t h a t zone. Progressive concen t ra t i on o f f l o w i n t h e upper p a r t o f t h e zone o f s a t u r a t i o n produces master condu i t s and l i m i t s f l o w and s o l u t i o n a t deeper l e v e l s .

Where any semblance o f p e r m e a b i l i t y e x i s t s , t h e rock where a c t i n g as a condui t , may be considered schemat ica l l y as a hyd ro log i c continuum: t h i s continuum i s composed of areas where recharge predominates, areas where d i s - charge predominates, and i n t e r v e n i n g t ransmiss ion areas t h a t may a c t subordi- n a t e l y as recharge o r discharge areas. Cons idera t ion of t he carbonate system as a continuum i s acceptable whether t h e p e r m e a b i l i t y i s u n i f o r m o r non- un i form. Non-uniform c o n d i t i o n s are common, and p r e f e r e n t i a l channel ways th rough which water moves a re c h a r a c t e r i s t i c . The f a c t t h a t carbonate rocks between channel openings may be e s s e n t i a l l y impermeable does n o t reduce the va lue o f t h e continuum scheme ( B o r e l i and P a v l i n , 1967, p. 3 4 ) .

S o l u t i o n channels are formed and widened i n t h e v i c i n i t y o f sp r ings where concen t ra t i on o f f l o w occurs. The s o l u t i o n channels g r a d u a l l y develop u n t i l one g i a n t s p r i n g "captures" t h e ground water o f a l a r g e area (Mandel, 1967, p. 662). Thus, l a r g e r openings tend t o inc rease i n s i z e a t t h e expense of smal ler ones as l o n g as t h e l a r g e r openings a r e a c t i v e condui ts. Spring discharge may increase u n t i l p i r a c y occurs. P i r a c y i s c h i e f l y subsurface and occurs when and

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where avenues a re developed and used a t lower p o s i t i o n s than those p r e v i o u s l y used--always tend ing toward lower discharge p o i n t s o r steepest o v e r a l l grad ients . As t h e l a r g e r openings inc rease i n s i z e t h e d i s t r i b u t i o n o f pe r - m e a b i l i t y i n space becomes d i s p r o p o r t i o n a t e , t end ing toward t h e development o f i n c r e a s i n g l y a n i s o t r o p i c aqu i fe rs .

Lack o f u n i f o r m p e r m e a b i l i t y may be a t t r i b u t e d t o some combinat ion o f t h e f o l l o w i n g cond i t i ons . Separate p a r t s o f carbonate fo rmat ions may (1) have had d i f f e r e n t o r i g i n a l p o r o s i t y - p e r m e a b i l i t y c h a r a c t e r i s t i c s , ( 2 ) have had d i f f e r - e n t o p p o r t u n i t i e s f o r ground water t o c i r c u l a t e i n them, ( 3 ) have had d i f f e r e n t degrees o f access t o water undersa tura ted w i t h respec t t o ca l c ium carbonate and ( 4 ) have had d i f f e r e n t o p p o r t u n i t i e s f o r e ros ion o r , conversely, f o r preserva- t i o n ( S t r i n g f i e l d and LeGrand, 1 9 6 6 , p. 4 1 ) .

Al though b o t h t h e occurrence and movement o f ground water i n carbonate rocks are r e l a t e d t o geo log ic s t r u c t u r e s , t h e r e l a t i o n s h i p s a re n o t d i r e c t and exc lus ive. We can n o t r i g h t f u l l y p l a c e such geo log ic s t r u c t u r e s as sync l ines, a n t i c l i n e s , monoclines, and f a u l t s i n t o separate ca tegor ies f o r an a p p r a i s a l o f t h e i r r e l a t i o n t o t h e occurrence and movement o f ground water. I n some areas f a u l t s may serve as avenues f o r movement o f water, and i n o t h e r s they may serve as b a r r i e r s . A n acceptable technique c a l l s f o r v iew ing t h e geo log ic framework i n r e l a t i o n t o t h e superinduced h y d r o l o g i c continuum. I s t h e h y d r o l o g i c continuum r e a l and s i g n i f i c a n t f o r a p a r t i c u l a r s e t t i n g ? The answer may be negat ive i f one o f t h e f o l l o w i n g i tems app l i es : (1) i n s i g n i f i c a n t recharge f a c i l i t i e s , ( 2 ) i n s i g n i f i c a n t d ischarge f a c i l i t i e s , ( 3 ) i n s i g n i f i c a n t perme- a b i l i t y i n t h e system, and ( 4 ) i n s i g n i f i c a n t h y d r a u l i c head i n t h e system.

The n a t u r e o f underground c i r c u l a t i o n depends l a r g e l y upon t h e geo log ic s t r u c t u r e and t h e r e l a t i o n o f permeable rocks t o groundwater discharge areas. I n s o f a r as c i r c u l a t i o n i s concerned, a carbonate fo rma t ion o r body a t any one p lace possesses a t l e a s t one o f t h e f o l l o w i n g four types o f h y d r o l o g i c zones (LeGrand and S t r i n g f i e l d , 1 9 6 6 , p. 66). ZONE 1. Carbonates a t o r near t h e surface: The water t a b l e occurs i n t h e

k a r s t rock. Water f rom p r e c i p i t a t i o n moves v e r t i c a l l y downward t o the water t a b l e and then l a t e r a l l y toward a sur face stream.

ZONE 2. Carbonates b u r i e d beneath an impermeable bed, forming a homoc l i na l a r t e s i a n system: Water moves under a r t e s i a n pressure f rom an e l e - va ted i n t a k e area, through t h e rock, toward a lower discharge area.

ZONE 3. Carbonates w i t h no s i g n i f i c a n t discharge f a c i l i t i e s : I t may be (a) a homoc l ina l a r t e s i a n system SO deeply b u r i e d beneath impermeable beds t h a t almost no water can escape. I t may a l s o be (b) carbonates l y i n g below t h e stream c o n t r o l l i n g the base l e v e l o f e ros ion and perhaps so f a u l t e d o r f o l d e d as t o n e a r l y p rec lude the discharge o f water.

ZONE 4 . Carbonates denuded and e leva ted above subjacent v a l l e y s and s u f f i - c i e n t l y impervious l o c a l l y t o p rec lude a cont inuous zone o f sa tura- t i o n : No subsurface discharge o f water occurs. T h i s zone i s absent i n many areas.

The c l a s s i f i c a t i o n above i s n o t concerned p r i m a r i l y w i t h t h i ckness and a r e a l d i s t r i b u t i o n o f format ions. Rather i t i s based on un i t volumes o f carbonates i n which t h e c i r c u l a t i o n o f water i s c o n t r o l l e d b y s p e c i f i c geo log i c frameworks i n r e l a t i o n t o t h e ease o r d i f f i c u l t y w i t h which water can c i r c u l a t e i n t h e carbonate system and d ischarge from it. Genera l i za t i ons about t h e hydro logy o f carbonate fo rmat ions should be tempered by t h e r e a l i z a t i o n t h a t most fo rmat ions cross a t l e a s t two o f t h e f o u r s t r u c t u r a l zones on which t h e c l a s s i f i c a t i o n i s based. O n l y Zone 1 i s i n v o l v e d i n t h e development o f k a r s t topography. Zone 3 (b) i s subjacent t o Zone 1 i n areas where t h e carbonates extend t o apprec iab le depths below t h e bottom o f t h e l a r g e s t stream. The t o p o f Zone 3 (b) rep re - sents the h i g h e s t l e v e l o f t h e zone i n which c i r c u l a t i o n i s n e g l i g i b l e and may range from about 50 f e e t t o a few hundred f e e t below t h e l a r g e s t stream, depending upon l o c a l geo log i c c o n t r o l s . Where s l i g h t l y i n c l i n e d homoc l ina l a r t e s i a n systems occur, as i n t h e case i n c o a s t a l areas o f t h e T e r t i a r y l ime- stone i n southeastern U n i t e d States, t h e zones l i e i n tandem, ex tend ing from Zone 1 a t t h e surface, which passes i n t o Zone 2, where p o t a b l e water i s n o t an accurate c r i t e r i o n f o r separa t i ng Zones 2 and 3 ( a ) . A c t u a l l y , d ischarge c a p a b i l i t i e s , which c o n t r o l c i r c u l a t i o n o f water, i n Zone 2 are o n l y s l i g h t l y b e t t e r than i n Zone 3 ( a ) . Consequently, t h e l i n e between these zones i s a r b i t r a r y .

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Under water - tab le c o n d i t i o n s t h e zone o f g r e a t e s t p e r m e a b i l i t y tends t o develop i n t h e zone o f g r e a t e s t c i r c u l a t i o n and s o l u t i o n , which i s commonly j u s t below t h e water t a b l e . Topography and p o s i t i o n o f carbonates below ground a re impor tant ; carbonate rocks t h a t a l l o w a t l e a s t moderate c i r c u l a t i o n and are entrenched by p e r e n n i a l streams tend t o develop s o l u t i o n openings and t o inc rease c i r c u l a t i o n . Deep- ly ing carbonate rocks t h a t have impeded c i r c u l a t i o n a r e almost h y d r o l o g i c a l l y i n e r t ; ye t , t h e c i r c u l a t i o n i n and t h e d ischarge from such rocks as deep as a few hundred meters may be adequate t o cause a gradua l inc rease i n p e r m e a b i l i t y i n an a r t e s i a n system i f t h e water i s n o t complete ly sa tu ra ted w i t h ca lc ium carbonate. S t r u c t u r a l geology i s ve ry impor tant , n o t as a separate e n t i t y , but i n r e l a t i o n t o topography and recharge-discharge circum- stances (LeGrand and S t r i n g f i e l d , 1 9 6 6 , p. 6 7 ) .

Where carbonate bod ies a re th in and are compartmented by o the r rocks i n complex s t r u c t u r a l s e t t i n g s , t h e hydro logy commonly i s s i m i l a r t o t h a t o f t he enc los ing rocks. Under these cond i t i ons some aspect o f (a) d ischarge, (b) movement through t h e rock , o r ( c ) recharge i s l i k e l y t o be so r e s t r i c t e d t h a t a carbonate rock does n o t a c t as a separate hyd ro log i c system. Such microcom- partments, i n which c i r c u l a t i o n of water i s so s l i g h t as t o r e s t r i c t k a r s t development, should be d i s t i n g u i s h e d from macrocompartments i n which the b read th o f carbonates i n a water - tab le c i r c u l a t i o n system may be seve ra l m i les . Where carbonates occur as macrocompartments, many fea tures o f k a r s t hydro logy may develop; ye t , t he hydro logy w i l l be in f luenced by the hyd ro log i c and topo- g raph ic fea tu res o f t h e enc los ing f o r e i g n beds.

I n a d d i t i o n t o compartments o f ground water i n carbonate rocks r e s u l t i n g f rom the i n t e r c e p t i o n o f a q u i f e r s by impermeable o r i n s o l u b l e m a t e r i a l s , such as those i n f o l d e d systems, some elements of compartments occur i n broad carbonate a q u i f e r systems t h a t a re c lose enough t o l a n d sur face t o be i n t h e meteor ic water c i r c u l a t i o n system. I n such a system a drainage network w i t h a major l i n e o f f l o w l i e s on the p iezomet r ic sur face and depresses it. These drainage l i n e s may be p e r e n n i a l sur face streams i n t o which water f rom the Carbonates discharges, o r i n the case o f mature k a r s t areas where no p e r e n n i a l sur face drainage occurs, they may be l i n e s o f concentrated ground-water d ra in - age t h a t l i e a t t h e base o f a i r - f i l l e d openings, depressing the water t a b l e and l e a d i n g t o p o i n t s o f ground- water discharge. These compartments a re separated l a t e r a l l y by ground-water d i v i d e s , which do n o t necessa r i l y co inc ide w i t h land-sur face topographic d i v ides . V e r t i c a l l y below they merge i n t o t h e o v e r a l l carbonate system.

The theory o f ground-water mot ion i n smal l drainage bas ins has been descr ibed by Toth ( 1 9 6 2 , 1 9 6 3 ) , and t h e theory has a p p l i c a t i o n t o broad carbon- a t e reg ions where t h e r e are l o c a l d ischarge areas superimposed on them. Where these compartments occur i t i s wise t o evaluate the most l i k e l y d i r e c t i o n s o f f l o w o f water. Jn many cases more than 90 percent o f recharge i s shunted o u t i n t o one o f t he compartments, l e a v i n g l i t t l e water t o reach the lower and major carbonate system. R e l a t i v e l y poor f a c i l i t i e s f o r water t o move o u t o f t he lower p a r t o f t he carbonates a l l ows t h i s p a r t t o s tay f u l l o f water and t o r e j e c t most o f a v a i l a b l e recharge. A conceptual model t h a t cons iders compart- ments o f carbonate hydro logy he lps t o evaluate the d i s t r i b u t i o n o f f l o w o f water and o f contaminants t h a t may be i n it.

Where an a r t e s i a n c i r c u l a t i o n system occurs, base- level cons idera t ions may be l e s s s i g n i f i c a n t because the p iezomet r ic sur face i s above the aqu i fe r . Zones o f g rea te r c i r c u l a t i o n and s o l u t i o n may develop, perhaps near the top o f t he conf ined carbonate aqu i fe r , but these zones a re n o t c l o s e l y r e l a t e d t o base l e v e l . Development o f secondary p e r m e a b i l i t y i n an a r t e s i a n carbonate system may have considerable o v e r a l l importance but i s slower and l e s s dynamic than t h e development o f secondary p e r m e a b i l i t y i n a wa te r tab le carbonate aqu i fe r . I t should be noted, however, t h a t some carbonates i n the a r t e s i a n system were a t some e a r l i e r t ime i n a water - tab le c i r c u l a t i o n system.

Under a r t e s i a n cond i t i ons i n i n c l i n e d aqu i fe rs , water may move downdip where: (1) t h e a q u i f e r i s o v e r l a i n by r e l a t i v e l y impervious beds, ( 2 ) t he r e l a t i v e p o s i t i o n s o f t h e recharge and discharge areas are favorable, and ( 3 ) t h e h y d r a u l i c g r a d i e n t i s i n t h e same d i r e c t i o n as the d ip ( S t r i n g f i e l d and LeGrand, 1 9 6 6 , p. 1 9 ) . Such cond i t i ons genera l l y a re n o t widespread because much water takes arcuate courses t o concentrated d ischarge areas, and the d i r e c t i o n o f t h i s water movement l o c a l l y cannot co inc ide w i t h t h e dip. Where t h e permeable zones connect ing recharge and d ischarge areas are n o t homocl ina l ,

6 6

as i n f o l d e d a q u i f e r systems t y p i c a l o f carbonates o f t h e southern Appalachi- ans, water may move downdip on one l i m b o f t h e s t r u c t u r e and undip t o some degree on t h e o t h e r l i m b .

Land sur face topography has an everpresent i n f l u e n c e on t h e p o s i t i o n o f t he water tab le . Combinations o f topographic and permeable cond i t i ons c o n t r o l t he p o s i t i o n i n g o f t h e water t a b l e i n impor tan t p r a c t i c a l ways. The f o l l o w i n g genera l statement forms a b a s i s f o r u s e f u l genera l i za t i ons : A water t a b l e deep below l a n d sur face occurs where high topographic r e l i e f and ve ry permeable l imestone are combined. L o c a l v a r i a t i o n s o f cons iderable magnitude i n perme- a b i l i t y a re common i n carbonate t e r r a i n s , these v a r i a t i o n s c o n t r i b u t i n g t o t h e disappearance o f sur face streams i n t o underground courses and t o t h e i r reap- pearance a t o t h e r p laces.

Discharge o f water f rom carbonate a q u i f e r s i s commonly l e s s d i f f u s e d than t h a t f rom o t h e r types o f aqu i fe rs . Development o f l a r g e s o l u t i o n openings through which the re i s p r e f e r e n t i a l movement o f water g i ves r i s e t o l a r g e spr ings i n many low p laces i n carbonate t e r r a i n s ; t h e spr ings may be obscure o r somewhat i n d i s t i n c t where they occur i n r i v e r channels and i n shal low seas. Discharge may be d i f f u s e d where water passes from carbonates i n t o sands o r c l a y s i n low areas. Discharge above p e r e n n i a l streams o r the sea may occur where r e l a t i v e l y impermeable rocks u n d e r l i e t h e a q u i f e r above t h e low areas (Burdon and Papakis, 1 9 6 3 , p. 1 5 1 ) .

I n summary, k a r s t i f i c a t i o n occurs where c i r c u l a t i o n o f water i s n o t impeded. The c i r c u l a t i o n o f water i s n o t evenly d i s t r i b u t e d i n carbonate rocks; t he re fo re , t h e so lut ion-developed openings, rep resen t ing major perme- a b i l i t y f ea tu res o f k a r s t rocks, a re a l s o unevenly d i s t r i b u t e d .

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3. Physical and chemical characteristics of carbonate water (Donald Langmuir)

3 . 1 I n t r o d u c t i o n

The chemical behav io r o f water must be considered i n r e l a t i o n t o t h e m a t e r i a l through which i t c i r c u l a t e s , p a r t i c u l a r l y when t h a t m a t e r i a l i nc ludes carbonates, because o f t h e many v a r i e d r e a c t i o n s and i n t e r a c t i o n s between t h e water and an e a s i l y so lub le media.

3.2 Carbonate s o l u t i o n - m i n e r a l e q u i l i b r i a concepts

3.2.1 A c t i v i t i e s and i o n i c s t reng th . The e x t e n t o f r e a c t i o n among species i n s o l u t i o n o r between so lutes, gases o r m ine ra l s i s a f u n c t i o n o f t h e a c t i v i t i e s of the species o r substances i nvo l ved , and n o t t h e i r t o t a l concent ra t ions . The a c t i v i t y o f s o l v e n t water i s approximately equa l t o i t s mole f r a c t i o n (see equat ion 3.2-1, Gar re l s and C h r i s t , 1 9 6 5 ) . The a c t i v i t y o f gases such as carbon d i o x i d e CO2 o r oxyqen O 2 equals t h e gas p a r t i a l p ressure i n atmo- spheres a t low t o t a l pressures, and by convent ion t h e a c t i v i t y o f pure s o l i d s p resent throughout a r e a c t i o n i s taken as u n i t y . The a c t i v i t y o f s o l i d s o f v a r i a b l e composi t ion i s discussed by Gar re l s and C h r i s t ( 1 9 6 5 ) . The a c t i v i t y and s o l u b i l i t y o f ca l c ium- r i ch do lomi te i s discussed by Lerman ( 1 9 6 5 ) and Langmuir (1971), and o f magnesium c a l c i t e s by P l u m e r and Mackenzie (1974) and Lahann and S i e b e r t ( 1 9 8 3 ) among o the rs . The magnesium i n c a l c i t e and excess ca lc ium i n do lomi te make these m ine ra l s more so lub le than t h e pu re phases. Most o f t h e c a l c i t e and do lomi te i n Pa leozo ic and o l d e r rocks i s c lose enough t o s to i ch iomet ry , however, so t h a t assuming t h e m ine ra l s a r e pure i s a f a i r approximat ion i n most ground water s tud ies.

The a c t i v i t y (ai) o f a species i i n s o l u t i o n , i s r e l a t e d t o i t s m o l a l concen t ra t i on (mi) by the expression

a = yimi (3.2-1)

where y, t h e a c t i v i t y c o e f f i c i e n t i s u s u a l l y l e s s t h a n unity. The a c t i v i t y o f so lu tes changes w i t h t h e i o n i c s t r e n g t h (I) o f t h e s o l u t i o n . By d e f i n i t i o n

i

I = i / 2 c mizi2 (3 .2-2)

where m. and z . a r e t h e m o l a l i t y and valence o f i o n i c species i and C denotes \he s u d a t i o n o f m.zi2 f o q a l l d i s s o l v e d i o n i c species. I n a pure carbonate ground water where H , o r OH-, and C 0 3 2 a r e n e g l i g i b l e , charge balance i n s o l u t i o n r e q u i r e s

(3.2-3) -

2mCa2+ + 2mMg2+ = mHC03

S u b s t i t u t i o n i n t o expression (3.2-2) then g i v e s t h e r e l a t i o n s + -

I = 3(mCa2+ + mMg2 ) = 1.5 mHC03 (3.2-4)

Because b o t h s p e c i f i c conductance ( U ) and i o n i c s t r e n g t h (I) are a r e f l e c t i o n o n l y of charqed species, t h e conductance may be used t o es t ima te i o n i c s t r e n t h . The e m p i r i c a l equat ion

69

I = 1.88 x 10-5 (3.2-5)

i s based on s p e c i f i c conductance (ii) and t o t a l chemical analyses o f 5 6 carbonate ground waters w i t h i o n i c s t reng ths (I) up t o 0.018 (Langmuir, 1971). Es t imated and computed va lues of I were w i t h i n + l o pe rcen t f o r 5 1 o f these ground waters. Lind (1970) descr ibes i n d e t a i l r e l a t i o n s between s p e c i f i c conductance (ii) and i o n i c s t r e n g t h (I) f o r a v a r i e t y o f waters o f v a r i a b l e p r e v a l e n t chemical character .

I n general , t h e a c t i v i t y o f water,

[H20] = pH20/p0H20 (3 .2 -6 )

H 2 0 i s t h e vapor p ressure o f pure water, and 'H20 the vapor where pressure over the s o l u t i o n o f i n t e r e s t a t t he same temperature. Based on t h i s expressions [H20] = 0.98 i n sea water, and 0.75 i n a water sa tu ra ted w i t h sodium c h l o r i d e (NaCl) a t 25OC. Because few carbonate groundwaters exceed t h e s a l i n i t y o f sea water, depar tu re o f [H201 from u n i t y may g e n e r a l l y be ignored.

A c t i v i t y c o e f f i c i e n t s o f d i s s o l v e d gases such as carbon d i o x i d e [C02(aq ) ] and oxygen [ 0 2 ( a q ) ] inc rease w i t h i o n i c s t r e n g t h (I) according t o the e m p i r i c a l Setchenow expression

P O

l o g yi = K m I (3.2-7)

a t cons tan t temperature and pressure, where K i s t h e m o l a l s a l t i n g c o e f f i c i e n t (Gar re l s and C h r i s t , 1 9 6 5 ) . Up t o I = " 1 5 , Km = 0.09 f o r carbon d i o x i d e [CO2(aq)] i n sodium c h l o r i d e (NaCl) s o l u t i o n s a t 25OC and 1 atmosphere (atm) t o t a l pressure. Because, by convent ion a l l carbon d i o x i d e [C02(aq ) ] i s assumed t o be H2C03° i then

(3.2-8)

A c t i v i t y c o e f f i c i e n t s o f n e u t r a l i o n p a i r s decrease w i t h i n c r e a s i n g i o n i c s t r e n g t h (Reardon, 1 9 7 4 ) accord ing t o t h e e m p i r i c a l equat ion

l o g yi = - B I (3.2-9)

The cons tan t B rough ly equals 0.5 f o r d i v a l e n t - d i v a l e n t i o n p a i r s such as ca l c ium carbonate (CaC03') , magnesium carbonate (MgC03') , and ca lc ium s u l f a t e ( C ~ S O L , ~ ) , and 0 .1 € o r monovalent-monovalent i o n p a i r s such as sodium b icarbonate (P?aEIC030) a t 25OC f o r i o n i c st.rengths below u n i t y (Reardon and Langmuir, 1974).

The extended Debye-Hückel equat ion may be used t o compute the a c t i v i t y c o e f f i c i e n t s o f monovalent i o n s when i o n i c s t r e n t h (I) i s 1-ess than 0.1, and d i v a l e n t i o n s when t h e i o n i c s t r e n g t h (I) i s l e s s than 0.01. The equat ion i s

(3.2-10) + f -109 Yi = A Zi2 I / ( 1 + Bai I )

where A. and B a re cons tan ts a t 1 atm pressure and a p a r t i c u l a r temperature. A t 2 5 " C , A = 0.5108 a n d B = 0 .3287 (Hamer, 1970). Values o f A and B a t o t h e r temperatures a re g i ven by Gar re l s and C h r i s t ( 1 9 6 5 ) and Hamer ( 1 9 7 0 ) . I n equat ion (3.2-10) a . i s a cons tan t r e l a t e d t o t h e diameter o f t he aqueous i o n i n Angstroms. Valdes o f ai a re l i s t e d by Gar re l s and C h r i s t ( 1 9 6 5 ) , S t u r m and Morgan (1981), and Hem (1970). Table 3 . 2 - 1 g i v e s yi and ai values f o r some i o n s o f p a r t i c u l a r i n t e r e s t i n s tud ies o f carbonate ground waters. The y . va lues l i s t e d inc rease o n l y a few percent from 25 t o O O C . I n the absence O $ a computer, t h e most convenient method t o o b t a i n v . values from I, i s t o read these va lues o f f a p l o t o f y . versus I based on t h e da ta i n t a b l e 3.2-1 ( o r computed a t some o t h e r temperature) p l o t t i n g vi as t h e o rd inan t , and I as the abscissa on a l o g sca le (see F i g u r e 3 .2-1) .

A t i o n i c s t reng ths from 0.01-0.1 m, up t o 1-5 m, a c t i v i t y c o e f f i c i e n t s o f many monovalent and some d i v a l e n t i o n s may be computed from mean s a l t data g i ven by Robinson and Stokes (1970) u s i n g methods descr ibed by Gar re l s and C h r i s t ( 1 9 6 5 ) . Such va lues a re under l i ned i n t a b l e 3.2-1.

70

Table 3.2-1. Values O € ai, and o f yi a t 25OC €o r some i o n s computed from t h e

extended Debye-HUckel equation, except € o r under l i ned yi values

which a re based on e x t r a p o l a t i o n s t o mean s a l t measurements.

Y a t l i s t e d I values i

a.x108 0 . 0 0 0 1 0.0005 0 . 0 0 1 0 .0025 0.005 0.010 0.025 0.05 0 .1 1

I o n

H+ 9 .989 .975 .967 .950 .933 -

HC03 I

CaHC03+ , MgHCO 3 + 4.5 .989 .975 . .964 .947 .928

OH- 3.5 .989 .975 .964 .946 .926

Mg2+ 6.5 j .955 .904 .870 .809 . 7 4 9

Ca2+ 6 .955 .904 .869 ..807 .747

CO 3 2' 4.5 .955 .903 .867 .803 .740

so42- 4.5 .955 .903 .867 .803 .740

.914 .88 .86 .83

.904 .866 . 8 3 1 .790

.900 .855 .815 .76

- ---

.679 .572 .492 .412

.675 --- .565 .484 .407

.667 .562 .476 .389

.664 --- .556 .484 .413

---

- ---

7 1

d

I rJ

Fr)

al k

9

P

-4

h

72

I n sa l i ne g r o u n d w a t e r s o r b r i nes having i o n i c strengths above t h a t of sea w a t e r (0.7 m) , t h e m o s t accurate approach t o t h e ca l cu la t i on o f m i n e r a l s o l u b i l i t i e s i s due t o P i t z e r and h i s c o - w o r k e r s ( s e e P i t z e r , 1 9 7 3 ; P i t z e r and M a y o r g a , 1 9 7 4 ; and P i t z e r and K i m , 1 9 7 4 ) . The m o d e l , w h i c h p e r m i t s c o m p u t a t i o n of i o n a c t i v i t i e s and t h e s o l u b i l i t y o f m i n e r a l s such as g y p s u m and h a l i t e i n t h e s y s t e m Na-K-Mg-Ca-Cl-S04-H20 a t 25OC, has been success fu l l y used a t i o n i c s t r e n t h s as high as 2 0 m ( H a r v i e and Weare, 1 9 8 0 ) . P r e l i m i n a r y w o r k has been done t o a l l o w m o d e l i n g the s o l u b i l i t y o f carbonate m i n e r a l s i n sea w a t e r ( M i l l e r o , 1 9 8 3 ) , a.nd a t higher i o n i c s t rengths (karv ie , 1 9 8 1 ) .

3.2.2 T h e r e a c t i o n s and t h e r m o d y n a m i c data. T h e f o l l o w i n g r e a c t i o n s and corresponding e q u i l i b r i u m expressions a re i m p o r t a n t i n s tud ies o f the c h e m i s t r y o f ground w a t e r i n carbonate rocks. The s o l u t i o n o f carbon d iox ide (C02) gas i n w a t e r may be w r i t t e n

For t h e f i r s t d i s s o c i a t i o n step o f carbonic ac id

H2CO3' = H + HCO3

K i = [H+l [HC03- ] / [H2C03'1

- +

For t h e second step -

H C O ~ = H+ + ~ 0 3 2 -

K 2 = [H+l [ C 0 3 2 - l / [HC03- I

For t h e d i s s o c i a t i o n o f the f o l l o w i n g i on p a i r s -

CaHC03' = Ca2+ + HCO3

K (CaHC03+) = [Ca2+ ] [HC03-] / [CaHC03+1

MgHC03' = Mg2+ + HCO3

K(MgHC03') = [Mg2+] [HC03- ] / [MgHC03+1

-

C ~ C O ~ O = Ca2+ + ~ 0 3 2 -

K(CaC03' ) = [Ca2+] [C032-3 / [CaC03'1

M.gC03' = Mg2+ + C032'

K(MgC03') = [Mg2+] [C032- ] / [MgC03'1

cas040 = Ca2+ + ~ 0 4 2 -

K(CaS04' ) = [Ca2+] CSOI+~- I / [CaS04'1

MgS04' = Mg2+ + S 0 4 2 -

K(MgS04') = [Mg2+] [Soh2- ] / [MgS01+'1

For t h e s o l u t i o n o f c a l c i t e and d o l o m i t e , r e s p e c t i v e l y

C ~ C O ~ = Ca2+ ~ 0 3 2 -

K~ = [ ~ a 2 + 1 [ C O ~ Z - I

( 3 . 2 - l l a )

( 3 . 2 - l l b )

(3 .2-12a)

(3 .2 -12b)

(3 .2 -13a)

(3 .2 -13b)

(3 .2-14a)

(3 .2-14b)

(3 .2-15a)

(3 .2 -15b)

(3 .2 -16a)

(3 .2 -16b)

(3 .2 -17a)

(3 .2-17b)

(3 .2-18a)

(3 .2 -18b)

(3 .2-19a)

(3 .2-19b)

(3 .2 -20a)

(3 .2-20b)

73

CaMg(CO3) 2 = Ca2+ + Mg2+ + 2c032- (3.2-21a)

(3.2-2133)

Table 3.2-2 l i s t s va lues which, when s u b s t i t u t e d i n t o a genera l equat ion, descr ibe changes i n these e q u i l i b r i u m constants f rom O t o 5 0 ° C a t 1 atm pressure. Values o f t h e e q u i l i b r i u m constants f o r r e a c t i o n s 3 .2 -11 through 3.2-19 a t 25°C a re g i ven i n Table 3.2-3. D i s s o c i a t i o n constants f o r c a l c i t e and. do lomi te and o t h e r m ine ra l s i n the system Ca0-Mg0-C02-S02-H20 a t 25°C a re g i ven i n Table 3.2-4. The magnesium carbonates and h u n t i t e a re ra re , a n d except f o r magnesite u s u a l l y occur o n l y as secondary m ine ra l s p r e c i p i t a t e d a t t h e e a r t h ' s sur face o r i n caves by evaporat ion and/or carbon d iox id f (CO2) degassing. Evaporat ion i s u s u a l l y r e q u i r e d t o concentrate t h e Mg2 s ince m ine ra l s such as hydromagnesite and nesquehonite a re 1 0 and 2 4 t imes as so lub le as c a l c i t e a t 2 5 " C , r espec t i ve l y . The - l og K (pK) va lues i n t a b l e 3.2-4 are g e n e r a l l y based on measured s o l u b i l i t i e s i n water a t low temperatures (Langmuir, 1 9 6 5 ) . Such evidence i s genera l l y p r e f e r a b l e f o r d iscuss ions o f low temperature s o l u t i o n behavior , t o pK da ta computed from heat capac i ty and heat o f s o l u t i o n measurements (Robie and Hemingway, 1973; Hemingway and Robie, 1 9 7 3 ) o r f rom r e a c t i o n s a t high temperatures. Thermal decomposit ion da ta has been used t o compute pK = 8 .12 f o r magnesite a t 2 5 O C (S tou t and Robie, 1963). Th is valGe would make a l l t h e magnesium carbonates except magnesite metastable, a n d the oceans 8.5 t imes supersaturated w i t h magnesite (Reardon and Langmuir, 1 9 7 4 ) . The absence o f magnesite i n marine sediments and i t s r a r i t y i n low temperature environments suggests magnesite i s n o t as s t a b l e as t h i s va lue o f pK i n d i c a t e s (Langmuir, 1 9 6 5 ) .

The probable appearance o f s t a b i l i t y r e l a t i o n s among the magnesium carbonates below 1 0 0 ° C i n the presence o f l i q u i d water ([H20] = 1) ' a t 1 atm t o t a l pressure a re shown i n f i g u r e 3.2-2. The i n f o r m a t i o n i n t h i s f i g u r e i s based on pK da ta i n t a b l e 3.2-4 and evidence presented elsewhere (Langmuir, 1 9 6 5 ) . F i g u r e 3.2-3 shows how phase r e l a t i o n s change w i t h H20 = 0.2 a t temperatures between O and 100°C. Th i s i s equ iva len t t o a r e l a t i v e humidi ty o f 20 percent . A t lower water a c t i v i t y magnesite i s s t a b l e a t a l l temperatures r e l a t i v e t o nesquehonite and l a n s f o r d i t e , and t h e s t a b i l i t y o f hydromaanesite i s s h i f t e d t o lower CO2 pressures. The same genera l r e l a t i o n s e x i s t a l s o a t a r e l a t i v e humid i ty o f 3 0 percent , except t h a t t h e magnesi te-hydromagnesi te boundary i s then near CO2 = l o - ' atm. Thus, f o r example, i n dry caves o r sur face environments a t moderate CO2 pressures, t h e hydrated magnesium carbonates tend t o a l t e r t o magnesite i n the absence o f l i q u i d water. Because o f t h e r e c a l c i t r a n c e o f magnesite once formed, t h i s r e a c t i o n i s e s s e n t i a l l y i r r e v e r s i b l e .

3.2.3 S o l u b i l i t i e s o f c a l c i t e and dolomi te i n pure water. I t i s i n s t r u c t i v e t o consider the t h e o r e t i c a l s o l u b i l i t i e s o f c a l c i t e and dolomi te i n pure water t o show r e l a t i o n s among m o l a l i t i e s pf t h e d i sso l ved species present as a f u n c t i o n o f such v a r i a b l e s as C 0 2 , pH, s p e c i f i c conductance, and teypera ture . AlLhough carbon-ate groundwaters o f t e n con ta in such species as Na , S o b 2 , C 1 , and NO3 among others, t h e pure water d iscuss ion s t i l l p rov ides a genera l gu ide t o the water chemistry. The s o l u b i l i t y o f c a l c i t e i n pu re water a t 25°C i s shown i n F igu re 3.2-4 which i n d i c a t e s the m v l a l i t i e s of r e l a t e d species as a f u n c t i o n o f C 0 2 . The graph shows t h a t H and CaOH never- approach 1 percent o f t he concent ra t ion l e v e l o f t he major ions . C 0 3 2 becoyes s i g n i f i c a n t at. CO2 pressures below about 10 atm, whe_reas CaHC03 i s o n l y impor tan t a t h ighe r CO2 pressures. CaCO3" and 'OH a re s i g n i f i c a n t o n l y a t CO2 pressures below about atm.

T h e o r e t i c a l equat ions which descr ibe the s o l u b i l i t y o f c a l c i t e and. do lo- m i t e i n pure water a t CO2 pressures between 10 ' and atm a t 25°C are, f o r c a l c i t e

0.354 Ca2+ (mmol/il) = 8.73 Pco 2

(3 .2 -22 )

and f o r do lomi te

74

Table 3.2-2. Values o f a, b, cI d, and e, i n t h e genera l equat ion logloK = a + bT + c /T + d log1oT + e/T2, which descr ibes the v a r i a t i o n o f d i s s o c i a t i o n constants f rom O t o 50'C. P e r t i n e n t e q u i l i b r i u m express ions a re g i ven i n t h e t e x t and Table 3.2-3. Sources o f t he da ta a re l i s t e d i n the foo tno tes .

K a b C d e

KW

KCO * K1

KC

KA

Kd

-6 .O875

108.3865

-356.3094

-107 .8871

1228 .732

-1209.120

-21.39

14 .217

-1 .O0

1 . 2 3 1

-171.9065

-171.9773

-23.694

O .O1706 4470.99

O .O1985076 -6919.53

-0 .06091964 21834.37

-0 .03252849 5151 .79

O .299444 -35512.75

-0 .31294 3 4 7 6 5 .O5

O .O4467 3 2 6 5

-0 .O1987 -2184

-0.0044 O

-0 .O1173 O

-0 .O77993 2839.319

-0 .O77993 2903.293

O .O7965 5052 .9

O

-40 .45154

126 .8339

3 8 . 9 2 5 6 1

-485.818

478.782

O

O

O

O

71 .595

71 .595

O

O

669365 .

-1684915 .

-563713.

O

O

O

O

O

O

O

O

O

Data Sources:

- Harned and Owen ( 1 9 5 8 ) . KW

+ KCOZ, KI, K2, Kc, KAl K(CaHC03 1 , K(CaC03') - P l u m e r and Rusenberg ( 1 9 8 2 ) .

K(MgC03') - Reardon and Langmuir ( 1 9 7 4 ) .

K (MgHCO3+) - R.eardon ( 1 9 7 4 ) . K(CaS04') - Based on B e l l and George ( 1 9 5 3 ) .

K(MgS04') - Na. i r and Nancol las ( 1 9 5 8 ) .

Kd - Langmuir ( 1 9 7 1 ) .

75

Tab le 3.2-3. Some e q u i l i b r i u m constants i n t h e s y s t e m Ca0-Mg0-C02-S02-H20 a t 25OC and 1 a t m t o t a l pressure.

~~ ~

E q u i l i b r i u m constant express ion -1ogK (pK) S o u r c e

14 .00

KCO = [H2C03'1 /Pco i a t m ) 1.47

K 1 = [H'] [HC03-] / [H2C03'] 6.35

K p = [H+l [ C 0 3 2 - l / [HC03-I 10 .33

K (CaC03 O 1 = [Ca2+] [CO3 2-1 / [CaC03 O I 3.22

1 .ll

2.88

O .97

2 .31

2.27

2 2

K (CaHC03+) = [Ca2+] [HC03-1/ ICaHC03'1

+ K(MgC03') = [Mg2 1 [C032- ] / [MgC03'1

K (PlgHCO3') = [Mg2+ l [HC03+1/ [MgHC03+1

K(CaS04 ' ) = [Ca2+] [Soh2- ] / [CaS04'1

K (MgSO4 ) = [Mg2+] [SOI , 2 - ] / [PlgS04 ' 1

H a r n e d and Owen ( 1 9 5 8 )

P l u m m e r and B u s e n b e r g ( 1 9 8 2 )

P l u m m e r and B u s e n b e r g (19823

P l u m m e r and B u s e n b e r g ( 1 9 8 2 )

P l u m m e r and B u s e n b e r g (19823

P lummer and B u s e n b e r g (1 9 8 2 )

R e a r d o n arid L a n g m u i r (1974)

R e a r d o n ( 1 9 7 4 )

B a s e d on B e l l and G e o r g e ( 1 9 5 3 )

N a i r and Nancollns ( 1 9 5 8 )

76

T a b l e 3.2-4. D i s s o c i a t i o n constants o f some m i n e r a l s i n t h e s y s t e m Ca0-Mg0-C02-S02-H20 a t 25OC and 1 a t m t o t a l pressure. S o u r c e s o f t h e data a re l i s t e d i n t h e f o o t n o t e s .

M i n e r a l Fo r m u 1 a K e x p r e s s i o n -1ogK (pK)

p o r t l a n d i t e

b r u c i t e

c a l c i t e

a r a g o n i t e

m a g n e s i t e

nesquehonite

l ans fo rd i te

a r t i n i t e

h y d m m a g n e s i t e

huntite

d o l o m i t e

gypsum

5.23

10 .88

8.48

8.34

4 .9

5.42

5.29

15 .4

35 . O

30.3

17 .0

4.59

portkandite - L a n g m u i r 1 1 9 6 8 ) .

bruci te - McGee and H o s t e t l e r ( 1 9 7 3 ) .

c a l c i t e - P l u m e r and B u s e n b e r g ( 1 9 8 2 ) .

aragonite - P l u m m e r and B u s e n b e r g ( 1 9 8 2 ) .

m a g n e s i t e - Based on pK298 f o r nesquehonite, t h i s tab le, and da ta f r o m L a n g m u i r ( 1 9 6 5 ) .

nesquehonite - H o s t e t l e r , c i t e d by R o b i e and Hemingway ( 1 9 7 3 ) , and R e a r d o n ( o r a l commun., 1 9 7 4 ) .

l a n s f o r d i t e - B a s e d on t h e nesquehonite-lansfordite e q u i l i b r i u m ( L a n g m u i r , 1 9 6 5 ) , and pK298 f o r nesquehonite, t h i s t a b l e .

a r t i n i t e - R e c o m p u t e d f r o m L a n g m u i r ( 1 9 6 5 ) . pK298 = 18.3 c o m p u t e d f r o m da ta o f Hemingway and R o b i e ( 1 9 7 3 ) m a k e s a r t i n i t e s t a b l e re - l a t i v e t o b r u c i t e p lus h y d r o m a g n e s i t e , w h i c h seems doubtful.

f r o m data given by L a n g m u i r f 1 9 6 5 ) .

and R o b i e ( $ 9 7 3 ) and o the r AGf' da ta f r o m L a n g m u i r ( 1 9 6 5 ) .

h y d r o m a g n e s i t e - F o r m u l a f r o m R o b i e and Hemingway ( 1 9 7 3 ) . pK298 r e c o m p u t e d

hunt i te - B a s e d on AG O = -1004 .71 K c a l / m o l f o r hunti te f r o m Hemingway

do l o m i t e - L a n g m u i r ( 1 9 7 1 ) .

g y p s u m - R e a r d o n and L a n g m u i r ( 1 9 7 4 ) .

77

100

75

100

75

1 5 0

25

O

“1

50

-

-

Brucite -

-

I I

- 7 -6 -

25

Brucite

L -7 -6 -

Hydro mag nesite -.

Mag nesite

Lansford i te - 4 -3 -2 -1 O 1 2

Log Pco, (atm)

F igu re 3.2-2 Probable appearance o f s t a b i l i t y r e l a t i o n s among b r u c i t e and the Mg carbonates below ~ O O O C i n water a t 1 atm t o t a l pressure, based on thermodynamic da ta i n Table 5 and presented by Langmuir ( 1 9 6 5 ) .

T(’C Hydro-

nagnesite

4 -4 -. Log P (atm)

2

Magnesite

- - 2 -1 O

F igu re 3.2-3 Probable appearance o f s t a b i l i t y r e l a t i o n s among b r u c i t e and the Mg carbonates below 100°C a t an a c t i v i t y o f water o f 0 . 2 , and 1 atm t o t a l pressure, based on thermo- dynamic da ta i n Table 5 and presented by Langmuir, ( 1 9 6 5 ) .

7 8

4

c\I

m

e

ln

I I

I I

I O

4

I I

I I

I O

d

I

c\J

I

h

E

-r m

U

79

(3 .2 -23 ) O. 354 Ca2+ + Mg2+ (mmol/k) = 10.38 Pco 2

For c a l c i t e p l u s do lomi te

(3.2-24) 0 .356 Ca2+ + Mg2+ (mmoi/k) = 10.9 pc0 2

where i n a l l t h e expressions t h e i o n concent ra t ions are t o t a l values. These equat ions are p l o t t e d i n F i g u r e 3.2-5.

There i s evidence t h a t f o r any p a r t i c u l a r CO2 pressure, c a l c i t e s o l u b i l i t y a t temperatures between O and 5OoC i s r e l a t e d t o i t s s o l u b i l i t y a t 25OC by a cons tan t f a c t o r f o r each temperature (Frear+and Johnston, 1929). The r a t i o o f c a l c i t e s o l u b i l i t y as t o t a l dhssolved Ca2 a t t h a t temperature, t o t h e s o l u b i l i t y a t 25OC f o r a cons tan t CO2 equals r. Values o f r based on s o l u b i l i t i e s g i ven i n t h i s chapter a re l i s t e d i n Table 3.2-5.

The s o l u b i l i t i e s o f c a l c i t e and do lomi te i n pure water a t 25OC and 12OC a re g i ven f o r seve ra l CO2 pressured i n Table 3.2-6. The cons iderab le e f f e c t o f CO2 p ressure on carbonate s o l u b i l i t y i s c l e a r from t h i s t a b l e and F igu re 3.2-5. The f i g u r e a l s o shows t h a t do lomi te, and c a l c i t e p l u s do lomi te are more s o l u b l e then c a l c i t e .

3.2.4 E f f e c t o f i o n i c s t r e n g t h on c a l c i t e s o l u b i l i t y . The form o f equat ion (3.2-22) (arguments f o r equat ions (3.2-23) and (3 .2 -24 ) a re s i m i l a r ) i s based on w r i t i n g t h e s o l u t i o n expression f o r c a l c i t e as

- CaC03 + COz(g) + H20 = Ca2+ + 2HCO3 (3.2-25)

The e q u i l i b r i u m cons tan t expression may be w r i t t e n

K = ecl

(3.2-26) -

Where Ca2+ and HCO3 a r e - o n l y de r i ved from c a l c i t e d i s s o l u t i o n and pH < 8.3, then 2mCa2+ = mHC03 ( i g n o r i n q i o n p a i r s ! . Expression (3 .2 -26 ) may then be s i m p l i f i e d and so lved f o r mCa2 , e l i m i n a t i n g Keq t o g i v e

where y f , t h e mean a . c t i v i t y c o e f f i c i e n t o f Ca(HC03) 2 equals [ (yCa) (yHC03) 2l l / 3 . I n t r o d u c i n g e q u i l i b r i u m cons tan t valu.es f o r 25OC from Tables 3.2-3 and 3.2-4, t h i s reduces t o

( 3 . 2 - 2 8 )

Equat ion (3.2-28) i n d i c a t e s t h a t f o r a g iven temperature and CO2 pressure the s o l u b i l i t y o f ' c a l c i t e i s d i r e c t l y p r o p o r t i o n a l t o l / y I .

Values o f y f up t o i o n i c s t r e n g t h (I) o f 0 .1 m o l a l may be determined from t h e da ta i n Table 3.2-1 o r equat ion (3 .2 -10 ) , and a t h i g h e r i o n i c s t renghts f rom mean sa. l t data g i ven by Robinson and Stokes (1970) u s i n g methods descr ibed by Gar re l s and C h r i s t ( 1 9 6 5 ) . F i g u r e 3.2-6 i s a p l o t o f l / y + versus I (see a l s o Gar re l s and C h r i s t , 1 9 6 5 ) . Values o f y f above rough ly L = 0.5 are ques t ionab le because o f p o s s i b l e i o n p a i r f o rma t ion i n the s a l t s o l u t i o n s used t o c a l c u l a t e y+ .

I I mNaCl i n a s o l u t i o n where Na and C1+ a re t h e predominant ions. F i g u r e 3.2-6 shows t h e e f f e c t o f i n c r e a s i n g concent ra t ions o f NaCl on c a l c i t e s o l u b i l i t y up t o s a t u r a t i o n w i t h NaCl ( h a l i t e ) a t I = 4.54. The p l o t i n d i c a t e s a doub l i ng o f c a l c i t e s o l u b i l i t y by a c t i v i t y c o e f f i c i e n t (I) e f f e c t s i n sea water (I 0.7) . S i m i l a r behav io r f o r do lomi te and. t he o t h e r carbonates can be expected.

+

80

5

4

3

h - - \ * O E E v +

N WI 2 + +

N

'F O. 5

- 3.0 2.0 1.0 Log P (atm)

c02

F igu re 3.2-5 The s o l u b i l i t i e s o f c a l c i t e , do lomi te, and c a l c i t e p l u s do lomi te i n pure water a t 250C and 1 atm t o t a l p ressure i n terms o f CO2 pressure and t h e t o t a l concen t ra t i ons o f ca l c ium p l u s magnesium i n s o l u t i o n .

8 1

Table 3.2-5. Values o f r a t va r ious temperatures, wher? r i s t h e r a t i o o f c a l c i t e s o l u b i l i t y as t o t a l d i sso l ved Ca2 temperature, t o c a l c i t e s o l u b i l i t y a t 25' f o r a constant P

a t t h e g i ven

cog

T'(OC) r T(OC) r

O 1 .62 25 1.00

1 0 1 .34 30 O . 9 1

2 0 1.11 50 0 . 6 1

Table 3.2-6. S o l u b i l i t y o f c a l c i t e and dolomi te i n pure water a t 25OC ( t o p t a b l e ) and 12OC (bottom t a b l e ) and seve ra l CO2 pressures. S p e c i f i c conductance ( p ) i s i n micromhos a t 25OC.

C a l c i t e Do l o m i t e

l o g Pcog (atm) -3.5 -2.2 -1.6 -3.5 -2.2 -. 1 6

Ca2+ (ppm) 20 5 8 95 1 2 35 57

Mg2+ (ppm) - - - 7 2 1 34

HC03 (ppm) 6 1 1 7 7 288 7 3 212 3 4 4 -

PH 8.30 7.45 7 .06 8.38 7 . 5 3 7.13

96 278 454 1 1 0 323 5 1 7

C a l c i t e Do l o m i t e

l o g Pcog (atm) -3.5 -2.2 -1.6 -3.5 -2.2 -1.6

Ca2+ (ppm) 2 7 8 0 1 2 9 1 6 46 7 7

filg2+ (ppm) - - - 1 0 28 47

HC03 (æpm) 82 243 394 9 7 282 46? -

PH 8.33 7.49 7 .O9 8.40 7.55 7 .16

IJ 1 2 9 3 8 2 6 1 7 1 4 8 429 7 1 4

I \

\ \

\

Ck

-d

a,

a,&

h

i7

cia

U

) c U

-d

W I

cv

m

a, k

-ri F

83

- The fo rmat ion o f i o n p a i r s and complexes o f Ca2+, Mg2+, HCO3 , and

C 0 3 2 - tends t o f u r t h e r inc rease carbonate s o l u b i l i t i e s i n waters where I exceegs about 0 .01 mo la l . Thus i n sea water w i t h I 1 0.7 t h e t o t a l i o n produc t (mCa2 ) (mC032-) = 2.81 x (Berner, 1 9 7 1 ) , whereas i n pure water t h i s p roduc t i s 5.87 x o r 480 t imes less . Accord ing ly , i o n i c s t r e n g t h e f f e c t s c o n t r i b u t e a 2 - f o l d increase, and i o n p a i r fo rmat ion a 240- fo ld inc rease i n c a l c i t e s o l u b i l i t y f rom pure water t o sea water.

3.2.5 The ca lc ium t o magnesium r a t i o . The r a t i o mCa2+/mMg2+ i n a carbonate groundwater i s a u s e f u l index t o whether t h e predominant r o c k type i s l imestone ( c h i e f l y c a l c i t e ) o r do lomi te. (See f o r example M e i s l e r and Becher, 1967). The r a t i o i s g e n e r a l l y c lose t o u n i t y as expected f o r groundwaters f rom dolomi te, and ranges f rom about 2 t o 10 i n most groundwaters f rom l imestone (Langmuir, 1 9 7 1 ) . H igher r a t i o s a re poss ib le i n waters f rom pure 1-imestone, o r when gypsum o r anhydr i t e a re present . Ra t ios below uni ty g e n e r a l l y do n o t occur except when evaporat ion o r CO2 degassing o f groundwater f rom dolornit? rocks causes c a l c i t e o r a ragon i te p r e c i p i t a t i o n , thus concent ra t ing t h e Mg2 present .

E q u i l i b r i u m between c a l c i t e and do lomi te may be w r i t t e n

2CaC03 + Mg2+ = CaMg(CO3) 2 + Ca2+ (3.2-29)

f o r which K = [Ca2+] /CMg2+l. Now K = Kc 2 /Kd = [Ca2+] / [Mg2+l. I n most eq eq

waters yCa2+ E yMg2+ so t h a t i g n o r i n g i o n p a i r i n g we can w r i t e

(3.2-30)

t o a good approximat ion. Th is equat ion has been used $0 est imat? Kd from groundwater analyses, g i ven K and an a n a l y s i s o f C a 2 and Mg2 conten t (€?su+ 1964+; Barnes and Back, '1964; see a l s o Hanshaw e t a l . , 1 9 7 1 ) . The mCa2 /mMg2 r a t i o f o r t h e o r e t i c a l ca l c i t e -do lomi te e q u i l i b r i u m as a f u n c t i o n o f temperature may be computed from K and Kd va lues i n Table 3.2-2. Such c a l c u l a t i o n s i n d i c a t e t h a t do lomi te s h h l d d i s s o l v e incon t o p r e c i p i t a t e c a l c i t e a t temperatures below about 20°C, g i v i n g mCa /mMg r a t i o s below uni ty. There i s l i t t l e evidence f o r t h i s behavior , however, i n carbonate groundwaters f rom Pennsylvania (Jacobson, 1 9 7 3 ) .

The ca l c i t e -do lomi te e q u i l i b r i u m , and o the r e q u i l i b r i u m reac t i ons i n v o l v i n g t h e carbonate m i n e j a i s i r$ Table 3 . 2 - 5 and 3.2-4 can be w r i t t e n i n terms o f t h e r a t i o [Ca2 1/[Mg2 I and/or C 0 2 . Th i s pe rm i t s us t o c o n s t r u c t a diagram d e p i c t i n g t h e i r s t a b i l i t y r e l a t i o n s i n water ([H20] = 1) a t 25OC (see F igu re 3 . 2 - 7 ) . The crosshatched rec tang le encompasses the composi t ion o f n e a r l y a l l carbonate groundwaters and sur face waters, t h e l a t t e r o c c u r r i n g a t t h e l o y e r CO+ p ressur s. I f do lomi te p r e c i p i t a t e d r e a d i l y f rom waters hav ing [Ca2 3/[Mg2 3 and 'CO2 va lues w i t h i n i t s s t a b i l i t y f i e l d , then n e i t h e r c a l c i t e ( o r a raaon i te ) cou ld p r e c i p i t a t e f rom sea water, nor cou ld these carbonates c o e x i s t w i t h nesquehonite o r hydromagnesite i n cave depos i ts o r sur face sediments. Such p r e c i p i t a t i o n does occur because f o r k i n e t i c reasons do lomi te does n o t r e a d i l y p r e c i p i t a t e under these cond i t ions .

3.2.6 The s a t u r a t i o n s t a t e o f groundwaters with respec t t o c a l c i t e and dolomi te. Whether t h e e q u i l i b r j urn constants g i ven i n Tables 3.2-2 , 3.2-3 and 3.2-4 accu ra te l y p r e d i c t t he chemist ry o f a groundwater, depends (1) on the r a t e o f t h e r e a c t i o n be ing considered, and ( 2 ) on the res idence t ime o f t he groundwater i n a p h y s i c a l l y and chemica l l y homogeneous groundwater environment. I n o t h e r words, be fo re we can apply e q u i l i b r i u m concepts t o a r e a l water we must know whether e q u i l i b r i u m i s l i k e l y t o have been a t ta ined . The answer i s always yes f o r r e a c t i o n s which a re amone o n l y d i sso l ved species. i on - ion r e a c t i o n s g e n e r a l l y e q u i l i b r a t e i n 1 0 t o seconds o r f a s t e r . I o n - n u e t r a l species r e a c t i o n s may be somewhat slower, but a re s t i l l p r a c t i c a l l y instantaneous. The h y d r a t i o n r e a c t i o n H20 + C02(aq) = H2CO3' i s complete i n about 0 . 1 seconds ( B u t l e r , 1 9 6 4 ) . Gas-so lut ion o r m ine ra l - so lu t i on reac t i ons , however, cannot always be assumed a t e q u i l i b r i u m i n r e a l groundwater systems. Gas-so lut ion r e a c t i o n s r e q u i r e from minutes t o hours t o e q u i l i b r a t e .

04

p e n t ; y

2 ' - Calcite

R' I I g - 4 U

\ +- N -5 U

v

M O -J -6

- 7

O -2 -4

Brucite

- 6 - 8

'7 I

F igu re 3.2-7 S t a b i l i t y r e l a t i o n s among t h e calcium-magnesium carbonates a t 25OC and 1 atm t o t a l pressure, as a f u n c t i o n o f t h e calcium- magesium molar r a t i o and CO2 pressure. The s t i p p l e d f i e l d i s t h a t o f c r y s t a l l i n e do lomi te . The p l o t shows t h a t when do lomi te i s k i n e t i c a l l y i n h i b i t e d from p r e c i p i t a t i n g , nesquehonite, hydromagnesite o r b r u c i t e can Co-exist w i t h c a l c i t e under metastable c o n d i t i o n s .

85

CO2 gas d i sso l ves f a s t e r t h a n i t exsolves f rom water. Thus, a stream e n t e r i n g a subsurface environment can e q u i l i b r a t e w i t h t he normal ly h ighe r CO2 l e v e l s p resent i n t h e subsurface i n perhaps tens o f minutes, whereas CO2 e x s o l u t i o n f rom a d i scha rg ing sp r ing water may n o t be complete i n 10 hours (See Schmalz and Swanson, 1 9 6 9 ) .

Labora tory and f i e l d s tud ies i n d i c a t e t h a t c a l c i t e d i sso l ves more r a p i d l y than dolomi te, but t h a t e q u i l i b r i u m w i t h these minera ls s t a r t i n g w i t h f resh , undersaturated waters takes f rom weeks t o months.

I n f o r m a t i o n on t h e degree o f s a t u r a t i o n o f groundwater w i t h respec t t o c a l c i t e o r do lomi te has seve ra l va luab le app l i ca t i ons . Because s o l u t i o n o f t he carbonates by undersaturated water takes t ime, r e l a t i v e degrees o f s a t u r a t i o n p r o v i d e i n f o r m a t i o n on r e l a t i v e subsurface res idence t imes o f groundwater? i n $ common o r s i m i l a r hydrogeologic te r rane. Along w i t h t he molar Ca2 /Mg2 r a t i o , r e l a t i v e degrees o f c a l c i t e and dolomi te s a t u r a t i o n can i n d i c a t e whether t h e groundwater comes c h i e f l y f rom a c a l c i t e ( l imestone) o r do lomi te aqu i fe r . Marked supersa tura t ion o f groundwater w i t h c a l c i t e o r do lomi te probably occurs c h i e f l y i n caves and open condu i ts where impor tan t CO2 e x s o l u t i o n can occur (Hol land, e t a l . , 1 9 6 4 ) , o r where m ix ing o f two d i f f e r e n t groundwaters takes p l a c e (Langmuir, 1971). The l e v e l o f groundwater s a t u r a t i o n w i t h c a l c i t e i s a l s o impor tan t t o the water t reatment p l a n t opera tor i n t e r e s t e d i n removing the hardness by l i m e a d d i t i o n f o r example. Such problems a l s o concern t h e water w e l l manager whose w e l l s may d e c l i n e i n y i e l d because o f CaC03 encrus ta t ion .

Whether a water i s undersaturated, saturated, o r supersaturated w i t h c a l c i t e o r do lomi te can be determined by comparing the e q u i l i b r i u m constant o f t he m i n e r a l o f i n t e r e s t t o t h e i o n a c t i v i t y p roduc t ( I A P ) o f t h a t m i n e r a l i n the water. Thus f o r c a l c i t e one computes IAP from the s o l u t i o n ana lys is :

IAP~ = [ ~ a 2 + 1 ic032-1 ( 3 -2 -31)

Log ( I A P c / K c ) i s de f i ned as t h e s a t u r a t i o n index, S I c , o f c a l c i t e . For do lomi te, t h e s a t u r a t i o n index:

(3 .2 -32 ) S I d = l o g ( IAPd/Kd) f

where I A P i s based on t h e s o l u t i o n ana lys i s us ing:

IAP~ = [ ~ a 2 + 1 [ ~ g 2 + 1 [co32-l'2 (3 .2 -33 )

Negat ive S I o r S I d va lues i n d i c a t e undersaturat ion. A water i s sa tura ted w i t h c a l c i t g i f S I = O, and w i t h do lomi te i f S I = O . P o s i t i v e va lues o f t he i n d i c e s ind ica5e water supersaturated w i t h &e carbonate i n quest ion. Tak ing i n t o pccount probable u n c e r t a i n t i e s i n the f i e l d measured pH , l a b analyzed Ca2 , Mg2+, and HCO3 values, i o n i c s t rength , and e q u i l i b r i u m constants invo lved, t h e s a t u r a t i o n i n d i c e s are probably known t o + O .1 u n i t s a t

Because pH and mHC03 a re the usua l measurements i n a water r a t h e r than mHC032-I i t i s convenient t o recas t t h e s a t u r a t i o n index express ion i n terms o f these two parameters. For c a l c i t e the s o l u t i o n r e a c t i o n may be w r i t t e n

C ~ C O ~ + H = Ca2+ + H C O ~ ( 3 . 2 - 3 4 )

bes t . -

+ -

f o r which

K = [Ca2+] [HC03-]/ [H'] ( 3 . 2 - 3 5 )

+ - eq Expression (3.2-13b) may be w r i t t e n [HCOq+l/ [H 1 -= [C032-l /K2. i n t o express ion (3 .2 -351 gives-K = JCa 1[C032 1/K2, o r Kc = K * K 2 ' I A P c

S u b s t i t u t i o n

accord ing ly equals [Ca2 3 [HC03 I@/ [ H 3 . Therefore eq

= l o g ( [Ca2+] IHC03-lK2/1H+lKc) (3.2-36

A s i m i l a r t reatment f o r do lomi te, based on the s o l u t i o n r e a c t i o n -

CaMg(C03)2 + 2H+ = Ca2+ + ng2+ + 2HC03 (3 .2 -37

86

g ives

S I d = l o g ( [Ca2+] [Mg2+] [HC03-] 2K22/ [H+] 2*Kd) 4 (3 .2 -38 )

Carbonate groundwaters a re n o t always i n con tac t w i t h a gas phase. Even when a gas phase i s p resent i n the subsurface, i t s CO2 p ressure may n o t be i n e q u i l i b r i u m w i t h CO2 l e v e l s d i s s o l v e d i n t h e groundwater. However, a i s e q u i l i b r i u m between gaseous and d i sso l ved CO2 l e v e l s i s p robab ly r a r e i n the subsurface, except i n w e l l v e n t i l a t e d caves, o r p a r t i a l l y g a s - f i l l e d condu i t systems, s ince s u f f i c i e n t t ime t o a t t a i n e q u i l i b i u m u s u a l l y e x i s t s . I n any case, i t i s u s e f u l t o compare the computed 'C02's o f d i f f e r e n t waters even though they a rephypo the t i ca l i n t h e absence o f a gas phase.

The computat ion o f C O 2 r e q u i r e s f i e l d measured temperature and pH values, an a n a l y s i s o f HCO3 and a measure o f i o n i c s t rength . Combining e x p r v s i o n s f o r K 1 c z d e n k C 0 2 so as t o e l i m i n a t e [H2C03'] , and s o l v i n g f o r CO2 g i ves

- PC02- K I (3 .2-39)

The f i e l d temperature measurement pe rm i t s s e l e c t i o n o f p roper K va lues from Table 3.2-2 I o n i c s t r e n g t h i s needed t o compute yECO3 u s i n g equat ion - 3.2-10, o r+ t o read i t o f f F igu re 3.2-1. Then [HCO3 ] = yHC03.mHC03 . W i t h [H 1 = express ion (3.2-29) may be so lved f o r t h e h y p o t h e t i c a l e q u i l i b r i u m CO2 pressure.

3.2.6.1 I o n p a i r i n g . C a l c u l a t i o n o f i n d i v i d u a l i o n a c t i v i t i e s , s a t u r a t i o n i n d i c e s o f c a l c i t e o r do lomi te, i s compara t ivy ly s imple -when t h e t o t a l concent ra t ions o f analyzed species such as Ca2 o r HCO3 a r e i n f ree , uncomplexed form. However, when impor tan t amounts o f i o n p a i r s a re present , as i n carbonate waters hav ing conductances above 500-1000 micromhos (I > 0.01-0.02), these p a i r s reduce amounts o f f r e e i o n s by t h e i r amounts i nvo l ved i n the p a i r i n g . Because i o n p a i r i n g produces species o f lower n e t charge than the c o n s t i t u e n t ions , i o n i c s t r e n g t h i s a l s o reduced. Thus i o n p a i r i n g reduces concent ra t ions o f f r e e i o n s below t h e i r t o t a l concent ra t ions , and leads t o an e f f e c t i v e i o n i c s t r e n g t h (I) which i s l e s s than i t s t o t a l o r uncorrected va lue ( C I). Such e f f e c t s become h i g h l y s i g n i f i c a q t i n sea water , where C I = 0.70, and I = 0.67. Format ion o f MgHCO3 , MgC$', and MgS04' i o n p a i r s , f o r example reduces t h e concen t ra t i on o f f r e e Mg i n sea water by 17.5 percent . MgCO3', CaC03', and NaC03 i o n p a i r s reduce t h e f r e e C 0 3 2 - concen t ra t i on by 85.5 pe rcen t (Reardon and L a n g m u i r , 1 9 7 4 ) .

The e f f e c t o f i o n p a i r i n g on s p e c i a t i o n and I i n most carbonate groundwaters i s f a r l e s s than i t i s i n sea water. I n carbonate groundwaters w i t h s p e c i f i c conductances up t o 1000 micromhos s tud ied by Langmuir ( 1 9 7 1 ) , t h e maximum e f f e c t o f i o n p a i r s on S I o r S I was l e s s than -0.05 u n i t s . Thus f o r approximate c a l c l a t i o n s t h e 9 may f?e ignored i n t h e computat ion o f s a t u r a t i o n i n d i c e s o r 'C02.

o r 'CO2

3.2.6.2 Computation o f S I S I d , and 'C02. A genera l d e s c r i p t i o n o f procedure € o r c a l c u l a t i n g ' I P C 0 2 and t h e s a t u r a t i o n s t a t e o f water w i t h respec t t o c a l c i t e and do lomi te has a l ready been prov ided. Such c a l c u l a t i o n s are most e f f i c i e n t l y performed on a high-speed d i g i t a l computer. The computer can a l s o be r e a d i l y programmed t o compute concent ra t ions o f i o n p a i r s and t h e i o n i c s t r e n g t h (3ee Nordstrom, e t a l . , 1 9 7 9 ) . A sample manual c a l c u l a t i o n o f S I S I d , and CO2 f o r a moderately p o l l u t e d carbonate w e l l water which has s i g n i f i c a n t i o n p a i r i n g i s g i ven i n Table 3.2-7.

F i r s t , a t e s t o f t h e accuracy and completeness o f t h e a n a l y s i s i n Table 3.2-7 may be made bv comparing t h e t o t a l epm o f c a t i o n s t o t h a t o f t he anions. The balance i s computed from

C '

- - (3 .2 -40 )

+ 2mCa2+ + 2mMg2+ + mNa + mK+ = mHC03 + mSOb2- + mC1- + mN03

87

T a b l e 3.2-7. C h e m i c a l a n a l y s i s o f g r o u n d w a t e r f r o m w e l l 336 ( L a n g m u i r , 1 9 7 1 ) . T o t a l i on concentrat ions a r e i n mmo1/9,. S p e c i f i c conductance ( U ) i s i n m i c r o m h o ç at. 25OC.

- TOC Ca2+ Mg2+ Na K+ ECO 3

+ Fi

9.8 1.70 2.30 .O48 .O23 7 .18 .30 . O90 .124 7 20

F i e l d p H D i s s o l v e 6 O x y g e n % sa t . W e l l depth ( m e t e r s ) R o c k T y p e

7.17 65 53.3 do l o m i t e

88

and g ives C epm c a t i o n s = 8.07, C epm anions = 7 .69 . The p e r c e r t d i f f e r e n c e i s 5 percent , i n d i c a t i n g a f a i r epm $alance. The excess o f Mg2 over Ca2+ may r e f l e c t a n a l y t i c a l e r r o r i n t h e Mg2 ana lys ' (Jacobson, 1 9 7 4 ) .

We w i l l c a l c u l a t e S I c , SId., and 'C02, f i r s t i g n o r i n g i o n p a i r s , and then cons ide r ing them. The i o n i 5 s t r e n g t h est imated from LI and equat ion (3.2-5) i s 0 .0135. Based on t h e Ca2 and Mg2+ conten t ( 3 . 2 - 4 ) , I = 0 . 0 1 2 . From t h e t o t a l i o n i c a n a l y s i s and t h e d e f i n i t i o n o f I i n equat ion ( 3 . 2 - 2 ) I = 0.0123 , t h e number we w i l l use. For s i m p l i c i t y , we w i l l s e l e c t yi va lues from F igu re 3.2-1 i n a l l f o l l o w i n g c a l c u l a t i o n s . y va lues f o r i o n s o f i n t e r e s t a re thus: yCa = 0 ,650, yMg = 0.656, yHC03 i= 0.897.. M u l t i p l y i n g these va lue? by t h e i o n m o l a l i t i e s g i ves the a c t i v i t i e s [Ca2 I = 1.105 x

[Mg2 ] = 1 .51 x [ H C O ~ I = 6.44 x 1 0 - 3 I n l o g a r i t h m i c terms these become [Ca;'; = 1 0 2 .96r [Mg2 3 = 10-2*82', and [HC03-] = 10-2.'9.

The approp r ia te e q u i l i b r i u m constants must n e x t be com u t e d from the func t i ons i n Table 3.2-2 f o r 9.8'C. These are:

Now Pco bssed on equat2:/?3.2-26) i s

- - 1o-T.27 E ( ~ = 1 0 - 6 . 4 7 , KCO 2 K~ = 10-10 .49 , K = 10'8.41, - - 10-16 .71 .

2 - - 10'7.17 10-2.19/10-1.27 10-6.47 = 10-1.62 atm

pco 2

From equat ion (3.2-23)

= log(10-2.96 x 10-2.19 x 1 0 - 1 0 . 4 9 / 1 0 - 7 . 1 7 x 10-8.41) = -0.06

A s i m i l a r s o l u t i o n o f equat ion (3 .2 -251 , g i ves S I = -0.05. These c a l c u l a t i o n s p rov ide t h e b a s i s f o r a more r i q o r o u s approach which

inc ludes t h e e f f e c t o f i o n p a i r i n g . As a f i r s t approx imat ion we w i l l assume C I = I. This pe rm i t s an i n i t i a l es t imate o f y . va lues, i n t h i s case the same as used above. A s a genera l r u l e i f t h e complexed o r i o n p a i r e d form o f an i o n i s l e s s than one percent o f i t s f r e e form, t h e i o n p a i r o r complex may be ignored.

Rearranging and expanding i o n p a i r e q u i l i b r i u m express ion (14b) g i ves

d

We must n e x t decide which i o n h a i r s a re s i g n i f i c a n t .

- ( 3 . 2 - 4 1 ) +

yCa*mCa2+/yCaHC03*mCaHC03 = K (CaHC03+) /yHC03 *mHC03

which, because yCaHC03 = yHC03, s i m p l i f i e s t o -

mCa2+/mCaHC03+ = K (CaHC03+) /yCa-mHC03 (3 .2 -42 )

S u b s t i t u t i n g f o r t h e r i qh t -hand s i d e w i t h yCa and mHC03 va lues computed i g n o r i n g i o n p a i r i n g g i ves

-

mCa2+/mCaHC03+ = i O - 0 * 9 7 / i O - 2 . 3 = 22.9 ( 3 . 2 - 4 3 ) +

Thus CaHC03 i s about four percent o f t h e f ree calc ium, and must be considered.

A s i m i l a r c a l c u l a t i o n shows

mMg2+/mMgHC03+ = 28.2 ( 3 . 2 - 4 4 ) +

so t h a t MgHC03 i s about 3.5 pe rcen t o f t h e f r e e magnesium. Expression (3.2-16b) may be r e w r i t t e n

yCa*mCa2+ /yCaC030*mCaC030 = K(CaC03') [C032-l (3 .2 -45 )

S u b s t i t u t i n g f o r [C032-l u s i n g express ion (3.2-1313) , and rea r rang ing g i ves -

mCa2+/mCaC03' = yCaC03' [H+]K(CaC03') /yCa*yHCOg*mHCO3 * K 2 (3 .2 -46 )

From equat ion (3.2-91, yCaC03' = 0.983. S u b s t i t u t i o n and s i m p l i f i c a t i o n g ives :

mCa2+/mCaC03' = 363 (3 .2 -47 )

so the i o n p a i r may be ignored. S i m i l a r t rea tment shows

89

mMg2+/mMgC03' = 77.6

so MgC03' i s a l s o n e g l i g i b l e . R e w r i t i n g t h e expression f o r K(CaS04') g ives

(3.2-48)

mCa2+/mCaS04' = yCaS04 ' -K(CaS04 ' ) / y C a * y S 0 4 * m S 0 4 2 - (3 .2 -49 )

F r o m equat ion (3.2-9) yCaS04' = 0.983. F igure 3 .2-1 g ives ySO4 = 0.640. S u b s t i t u t i o n , and s i m p l i f i c a t i o n o f t h e above expression gives

m ~ a 2 + / m ~ a ~ 0 4 0 = 43.7 13.2-50)

so CaSO,' i s s i g n i f i c a n t . S i m i l a r l y we f i n d

+ mMg2 /mMgSO4" = 63 .1 (3 .2 -51)

and MgS04' cannot be ignored.

concentrat ions i n t a b l e 3.2-7. Thus : Next we s e t up mass balance equations i n t e r m s o f t h e a n a l y z e d t o t a l i on

+ E mCa2+ = mCa2+ + mCaHC03 + mCaS04' (3 .2 -52 )

E mMg2+ = mMg2+ + mMgHCO3' + mMgSO4' (3 .2 -53)

E mHCO3 = mHC03 + mCaHC03 + mMgHCO3 (3 .2 -54)

E m ~ 0 4 2 - = m ~ 0 4 2 ' + m ~ a ~ 0 4 ' + m~gs040 (3 .2-55)

+ + - -

T h e e igh t equat ions (3.2-43, 4 4 , 50 -55 ) i n e i g h t u n k n o w n s may now be solved s i m u l t a n e o u s l y i n a f i r s t a p p r o x i m a t i o n . S u b s t i t u t i n g equat ions (3.2-43) and (3 .2-50) i n t o (3 .2 -52 ) t o e l i m i n a t e t h e i o n p a i r s g ives

EmCa2+ = 1 .70 x = 1 .067 mCa2+

a n d

mCa2+ = 1 .593 x

S i m i l a r l y , mMg2+ = 2.188 x S u b s t i t u t i n g these va lues i n t o expreçsfons (3 .2 -43 ) , (3 .2 -44 ) , (3.2-50) and (3 .2-51) g ives, r e s p e c t i v e l y , mCaHCO3 = 6.96 x mMgHg:,3 = 7.76 x l o - ' , mCaS04' = 3.65 x l o - ' , and mMgSO4' = 3.47 x 10 - . Now expreszions (3 .2-54) and (3 .2-55) may be solved t o g i v e mHC03 = 7.07 x 1 0 3 , and mSOb2' = 2.29 x l o b 4 . H a v i n g c o m p l e t e d t h e f i r s t a p p r o x i m a t i o n , we now c o m p u t e i o n i c strength, using t h e i o n concentrat ions j u s t obtained, and f i n d I = 0.01163.

T h e second a p p r o x i m a t i o n i s begun by s e l e c t i n g a new s e t o f yi va lues f o r I = 0.01163 w i t h w h i c h t o r e c o m p u t e t h e r a t i o s i n equations (3.2-43, 44 , 50 , 5 1 ) , and then t h e o v e r a l l spec ia t i on i n so lu t i on using equat ions (3 .2 -43 -55 ) . T h e s e y . vciues are: yCa = 0 .654, yMg = 0 .661, yHC03 = 0 .899 ( t h e same f o r t h e &O3 i o n p a i r s ) , yS04 = 0.646, yCaS04' = yMgS04' = 0 .987. Us ing t h e same approach as be fore , but w i t h t h e i o n concentrat ions f r o m t h e f i r s t a p p r o x i m a t i o n g i ves

+ +

mCa2+/mCaHC03 = 22.9 (3 .2 -56)

mMg2+/mMgHC03 = 28.2 (I,. 2-57)

mCa2+/mCaS04 = 43.6 (3 .2 -58)

mMg2+/mMgS0~' = 77.6 (3 .2 -59)

E l i m i n a t i n g i o n p a i r concentrat ions f r o m equatioTs (3 .2-52) a n d - ( 3 . 2 - 5 3 ) as before, y i e l d s mCa2+ = 1 .594 x and mMg2 = 2.194 x 1 0 3 . S u b S t i - tu t ing these va lues in$o express ions (3 .2 -56) - (3 .2-59) g i ves mCaHC03 = 6.96 x l o - ' , mMgHCO3 = 7 .78 x mCaS04' = 3.66 x l o - ' , and

90

- ~M~SOL,~= 2.83 x Now from equat ions (3.2-54) and (3 .2 -55 ) mHC03 = 7.03 x and mSOb2- = 2.35 x I o n i c s t r e n g t h c a l c u l a t e d from the r e v i s e d i o n concen t ra t i ons i s I = 0.01164. Because I i s w i t h i n +1 percen t o f i t s p rev ious va lue, we may assume t h a t t h i s second approximat ion adequately d e f i n e s t h e d i s t r i b u t i o n o f major i o n i c species. A t h i rd c y c l e changes major i o n concen t ra t i ons by l e s s than 1 pe rcen t and e i o n p a i r s by l e s s than 2 percent . Acco rd ing l y we may now c a l c u l a t e 'CO,, S I c , and

Thus, w i t h t h e l a s t s e t o f concen t ra t i ons and y . va lues we compute 'Ed; = 1 0 - 1 6 3 atm, S I c = -0.09, and S I = -0.'08. Log 'CO2 i s 0.01 u n i t s l e s s , and S I c and S I d 0.03 u n i t s qess than computed i n i t i a l l y i g n o r i n g i o n p a i r i n g . Based on a probable u n c e r t a i n t y o f I O . l u n i t s i n S I c and S I t h e water i s sa tu ra ted w i t h b o t h c a l c i t e and dolomite.

T te u n c e r t a i n t y o f 20 .1 u n i t s i s based on a p o s s i b l e e r r o r vf kO.05 un i ts i n t h e f i e l d measured pH, and u n c e r t a i n t i e s i n Ca2+, Mg2 , and HCO3 analyses and i n t h e e q u i l i b r i u m cons tan ts used i n t h e computation o f t h e s a t u r a t i o n i n d i c e s (Langmuir, 1 9 7 1 ) . Because any pH e r r o r i n t roduces a n equa l e r r o r i n S I o r S I d , i t i s most impor tan t t h a t t h e pH measurement be made i n the f i e l $ a t t h e t ime o f sample c o l l e c t i o n . Based on pub l i shed analyses, H o s t e t l e r ( 1 9 6 4 ) computes t h e s a t u r a t i o n s t a t e w i t h respec t t o t h e Ca-Mg carbonates o f 6 3 sur face and groundwaters f rom A f r i c a , A u s t r i a , Canada, t h e Un i ted States, and the USSR, t a k i n g i n t o account b o t h i o n i c s t r e n g t h and i o n p a i r i n g . However, most o f t h e pH's pub l i shed f o r these analyses a re l a b o r a t o r y values, which f o r t h e groundwater p a r t i c u l a r l y , a re o f t e n t o o h i g h because o f CO2 degassinq. Such e r r o r s can i n d i c a t e waters a re super-saturated w i t h carbonates, whereas they may be more n e a r l y a t s a t u r a t i o n . Supersa tura t ion o f F l o r i d a n carbonate w e l l waters w i t h respec t t o c a l c i t e and do lomi te repo r ted b y Back and Hanshaw (1.970) a re p robab ly caused by m i x i n g o f groundwater f rom d i f f e r e n t carbonate a q u i f e r s d u r i n g the pumping process. The bedrock p o r t i o n o f many F l o r i d a n w e l l s i s uncased, and connects a q u i f e r s o therw ise separated by r e l a t i v e l y impermeable c l a s t i c sediments. Supersa tura t ion o f cave waters w i t h c a l c i t e and do lomi te i s caused b y evapora t ion and/or CO2 degassing (Ho l l and e t al., 1 9 6 4 ) .

Langmuir ( 1 9 7 1 ) , Jacobson (19741, and Shuster and White (1971) , found no carbonate s p r i n g o r w e l l waters s i g n i f i c a n t l y supersa tura ted w i t h c a l c i t e o r do lomi te i n c e n t r a l Pennsvlvania, U.S.A., except f o r sp r ings d i scha rg ing i n caves. Supersa tura t ions no ted i n Kentucky, U.S.A., k a r s t groundwaters, which f l o w i n highly-developed c o n d u i t systems, occur c h i e f l y during low f l o w c o n d i t i o n s (Hess, 1974). A t t h i s t ime t h e condu i t s a re n o t f i l l e d w i t h groundwater, and CO2 degassing probab ly occurs as i n caves. The n e a r l y h o r i z o n t a l bedding o f t h e carbonate rocks f a c i l i t a t e s such degassing. A s i m i l a r expa lna t i on may account f o r supersa tura t ions no ted by Feder (1973) i n M issour i , U.S.A., carbonate groundwaters. M i x i n g and o t h e r exp lanat ions f o r computed supersa tu ra t i on o f groundwaters w i t h carbonate m ine ra l s a re descr ibed i n more d e t a i l i n s e c t i o n 3.4. I n any case r e c e n t s t u d i e s suggest t h a t t h e chemistry o f groundwaters i n carbonate rocks i s more e f f e c t i v e l y c o n t r o l l e d by the t h e o r e t i c a l s o l u b i l i t i e s o f c a l c i t e and do lomi te than has been p r e v i o u s l y supposed.

3.2.6.3 Graphic methods. As t h e fo rego ing s e c t i o n showed, r i g o r o u s a p p r a i s a l o f t h e degree o f s a t u r F t i o n o f - c a l c i t e o r do lomi te i n water r e q u i r e analyses o f temperature, Ca2 , HC03 , gnd f i e l d measured pH ( o r 'CO2) t o compute S I c , and a d d i t i o n a l l y Mg2 t o computed S I A lso needed a re t h e concent ra t ions o f o t h e r i o n s t h a t i n f l u e n c e i o n i c d ' s t r e n g t h and cause i o n p a i r i n g . Fc$r pure wa$er a t cons tan t temperasure graphs may be cons t ruc ted , because Ca2 and Mg2 a re r e l a t e d t o HCO3 th rough a s imple e q u i v a l e n t s p e r m i l l i o n ca t ion-an ion balance. I n carbonate w*ers, however, these i o n s va ry somewhat independent ly o f each o t h e r and of CO2 o r pH because o f t h e presence o f o t h e r d i s s o l v e d species. Thus, except i n pu re water, most g rahp ic methods can g i v e o n l y approximate answers. I n a d d i t i o n t h e m a j o r i t y o f pub l i shed graph ic r e l a t i o n s a re e i t h e r based on i n c o r r e c t e q u i l i b r i u m cons tan ts f o r carbonic a c i d and t h e carbonate minera ls , o r do n o t i n c l u d e c o r r e c t i o n s f o r i o n i c s t r e n g t h o r i o n p a i r i n g (see T i l lmans, 1932; Trombe, 1 9 5 1 ) . Jacobsqn and Langmuir (1972) showed t h a t Trombe's graph of Ph versus t o t a l Ca2 f o r c a l c i t e s a t u r a t i o n suggests t h a t waters are l e s s sa tu ra ted w i t h c a l c i t e than i s

9 1

a c t u a l l y t h e case by from 0 .1 t o 0.5 pH ( o r S I ) u n i t s a t 10°C. More soph is t i ca ted graph ic techniques which consiqer tempegature - and s a l i n i t y ( i o n i c s t reng th ) e f f e c t s , a long w i t h pH, Ca2 and HCO3 (Lange l ie r , 1946 ; Schoe l le r , 1 9 6 9 ) can g i v e a more accurate a p p r a i s a l o f a wa te r ' s c a l c i t e s a t u r a t i o n s ta te . However, t h i s same a n a l y t i c a l data makes p o s s i b l e a simple, and more accurate and p r e c i s e computation o f S I c ( i g n o r i n g i o n p a i r s ) as o u t l i n e d he re in . Such graph ic methods are p e n l e s s s u i t a b l e f o r dolomite, because o f t h e necess i t y o f hav ing an Mg2 ana lys i s as w e l l as the data r e q u i r e d t o compute c a l c i t e sa tu ra t i on .

3.2.6.4 Saturometry. Weyl ( 1 9 6 1 ) has shown how the s a t u r a t i o n s t a t e o f a water may be determine d i r e c t l y w i t h a pH e lec t rode measurement. S o l u t i o n pH i s measured b e f o r e and a f t e r a d d i t i o n o f t he carbonate m i n e r a l o f i n t e r e s t . I f pH r i s e s , t h e i n i t i a l s o l u t i o n was undersaturated. I f pH drops, t h e s o l u t i o n was supersaturated. F h i s response i s based on the f a c t t h a t s o l u t i o n o f carbonates consumes H ions , whereas carbonate p r e c i p i t a t i o n generates them (see equat ions 3.2-34 a n d 3 7 ) . I n p r i n c i p a l t h e technique i s v a l i d , however, o p e r a t i o n a l problems make r e s u l t s based on i t l e s s c e r t a i n . For exanp1.e the g rea te r s o l u b i l i t y o f t he f i n e carbonate p a r t i c l e s added i n the powdered carbonate normal ly used, enhance i t s s o l u b i l i t y r e l a t i v e t o w e l l c r y s t a l l i z e d c a l c i t e o r do lomi te (Chave and Schmalz, 1 9 6 6 1 , and suggest t h a t a sa tura ted water i s undersaturated. Saturometry i s b e s t used w i t h sur face waters, where CO2 degassing and temperature changes du r ing the experiment a re minimized. Changes i n groundwater pH upon c o l l e c t i o n due t o temperature changes o r CO2 degassing may mask t h e pH changes caused by adding the carbonate minera ls .

3.3 S o l u b i l i t y o f h a l i t e and gyp sum

Carbonate rocks, p a r t i c u l a r l y those o f post-Paleozoic age, may be associated w i t h evapor i t e minera ls , p resent as i n c l u s i o n s o r as d i s c r e t e lenses o r beds. These minera ls a re predominant ly h a l i t e and gypsum o r anhydr i te . Because o f t h e i r g r e a t s o l u b i l i t y , a percent o r more o f such minera ls assoc iated w i t h t he carbonates has a major e f f e c t on t h e groundwater q u a l i t y .

3.3.1 H a l i t e s o l u b i l i t y . The m o l a l sq lub i l - i t y p roduc t o f h a l i t e (NaCl) a t 25OC i s ve ry l a rge , i .e . Ksp = [Na ] [ C l I = 38. I n pure water NaCl s o l u b i l i t y a t O , 2 5 , and 5 O o C i s 263 .1 , 265.5, and 267 .9 gms/kg o f so lu t i on , r e s p e c t i v e l y . The 25OC s o l u b i l i t y corresponds t o a TDS va lue o f 365,600 mg/R as NaCl. Such ext remely h i g h concent ra t ions are r a r e j.n groundwater, and are approached o n l y i n some stagnant a r t e s i a n a q u i f e r s !usua l ly noncarbonate) assoc iated w i t h pet ro leum depos i ts (see Schoel ler , 1 9 6 2 ) , bedded o r dome s a l t format ions, and i n evapora t ion-cont ro l led c losed bas in lakes. The e f f e c t o f i nc reas ing NaCl concent ra t ions on t h e s o l u b i l i t y o f c a l c i t e i s shown i n F igure 3.2-6 and discussed i n sec t i on 3.2-4.

3.3.2 Gypsum (and anhydr i te ) s o l u b i l i t y . Both gypsum (CaS04-2H20) and anhydr i t e (CaS04) a re found i n sedimentary rocks. Anhydr i te i s favored r e l a t i v e t o gypsum by i nc reas ing temperature and inc reas ing s a l i n i t y (reduced a c t i v i t y o f w a t e r ) . Berner ( 1 9 7 1 ) examines gypsum-anhydrite s t a b i l i t y r e l a t i o n s i n . d e t a i l . Gypsum i s more abundant than anhydr i t e i n sedimentary rocks. Because gypsum i s l e s s so lub le t h a n anh d r i t e i n most groundwater, gypsum s o l u b i l i t y tends t o i.n these waters.

The s o l u b i l i t y p roduc t o f gypsum i s g iven i n Table 3.2-4. Gyps~~?! s o l u b i l i t y i s enhanced by the presence o f CaS04' o r o the r i o n p a i r s o f Ca o r Sob2- . A t 25OC pu re water sa tured w i t h gypsum conta ins 6 1 7 mg/R Ca2+ ( t o t a l ) and 1 4 7 8 mg/R S O k 2 - ( t o t a l ) . About one t h i r d o f t he Ca2+ and sob2- are present as C ~ S O ~ O .

Gypsum s o l u b i l i t y i s a l s o enhanced by i o n i c s t r e n g t h e f f e c t s . F igure 3 .3 -1 shows t h e inc rease i n gypsum s o l u b i l i t y w i t h i nc reas ing NaCl

l i m i t Ca2+ and Sohy- concent ra t ions

9 2

3000

2 500

w -l k

6 2000 a m P

0 1500 =! I z O 1000

2 -l

+ z IT

500

O 2100 2200 2300 2400 2500 2600

CacSO, IN MILLIGRAMS PER LITER

F igu re 3.3-1 S o l u b i l i t y o f gypsum i n NaCl s o l u t i o n s a t 25OC and 1 atm t o t a l pressure, m o d i f i e d a f t e r Hem ( 1 9 7 0 ) .

9 3

concen t ra t i on a t 25OC computed by Hem (1970) f rom the da ta o f T a n j i and Donneen (1966).

Solut ion- o f t h e gypsum o r anhydr i t e assoc iated w i t h carbonate rocks can reduce HCO3 (and C 0 3 2 - ) concent ra t ions and pH by causing c a l c i t e p r e c i p i t a t i o n . The o v e r a l l r e a c t i o n i s

- CaS04-2H20 + HCO3 = CaC03 + H+ + Soh2- + 2H20 (3 .3 -1 )

f o r which, a t 25OC

(3.3-2)

hus, based i n p a r t on Frear and Johnston ( 1 9 2 9 ) , i n pure water a t 25OC and 'CO4 = 0 . 1 atm ths composi t ion o f c a l c i t e - s a t u r a t e d water i s 1 5 8 mg/R Ca2 , 4 8 1 mg/ HCO3 , and pH = 6.7. I n c o n t r a s t a water sa tu ra ted w i t h b o t 9 c a l c i t e and gypsum- f o r t h e same cond i t i ons has a composi t ion o f 639 m [ R

and pH = 6.2. Ca2 , 1 7 1 mg/R HCO3 ( a n e a r l y 3 - f o l d r e d u c t i o n ) , 1 3 9 0 mg/R SOI, Y ,

3.4 M i x i n g o f carbonate groundwaters

Except i n some con f ined i s o t r o p i c carbonate aqu i fe rs , m i x i n g o f carbonate groundwaters o f d i f f e r e n t o r i g i n s and h i s t o r i e s during t h e i r f l o w i s t h e r u l e r a t h e r than t h e except ion. M i x i n g a l s o occurs between groundwater recharge and groundwater i n t h e c a p i l l a r y zone o r a t t h e water tab le . Because such processes a re p r a c t i c a l l y ub iqu i t .ous, a summary o f t h e e f f e c t s o f m i x i n g on groundwater q u a l i t y i s warranted.

When species i n v o l v e d i n m i x i n g a re conserved ( n o t p r e c i p i t a t e d , adsorbed, o r f u r t h e r d i sso l ved f o r example) , the concent ra t ion , CI o f a f i n a l m ix tu re i s r e l a t e d t o concent ra t ions o f t h e same species, Cif i n t h e waters i nvo l ved p r i o r t o m i x i n g through t h e r e l a t i o n

i CQ = C C . 0 i-i

based on conservat ion o f mass. Q denotes the f l o w r a t e o r volume o f t he m ix tu re , and Qi t h a t o f each m i x i n g water. Any u n i t s o f concent ra t ion and f l o w o r volume may be used i n t h i s l a s t expression. When o n l y two waters a re mixed, and the pe rcen t (P) o f each i n t h e f i n a l m i x t u r e i s be ing considered, then t h e p rev ious express ion reduces t o

c = (CiPi+C.P.)/lOO 3 3

Such equat ions have been used t o es t imate the base f l o w 'component o f stream f low (Pinder and Jones, 1 9 6 9 ) , t he percent o f r i v e r water versus groundwater reach ing some we1l.s (Larson, 1 9 5 0 ) , and most f r e q u e n t l y t o compute the percent o f f resh o r s a l t water i n m ix tu res o f f r e s h groundwater w i t h ocean water (Back and Hanshaw, 1 9 7 0 ) o r s a l i n e water.

M i x t u r e c a l c u l a t i o n s a re b e s t performed u s i n g species l e a s t l i k e l y t o be i n v o l v e d i n removal processes. A common choice i s c h l o r i d e , al though any ( u s u a l l y d isso lved) species may be used i f one can be con f iden t t h a t i t w i l l be conserved i n t h e system o f i n t e r e s t .

The b e s t species € o r c a l c u l a t i o n o f m ix ing e f f e c t s a re a l s o the b e s t f o r use as groundwater t r a c e r s . I n e i t h e r case the species o f i n t e r e s t may be n a t u r a l t o the water o r added as a spike. The s e l e c t i o n and use o f t r a c e r s t o cha rac te r i ze groundwater f l o w p a t t e r n s i n k a r s t a q u i f e r s has been d e t a i l e d by Schoe l l e r ( 1 9 5 9 ) , and more r e c e n t l y by Atk inson e t a l . ( 1 9 7 3 ) , and Back and Zoetl. ( 1 9 7 5 ) , and Gospodaric a n d Habic ( 1 9 7 6 ) and w i l l . n o t be considered here. The impor tan t po in t . i s t h a t by j u d i c i o u s s e l e c t i o n o f t r a c e r s , such as spikes o f f luorecene dyes and v a r i - c o l o r e d lycopodium spores, and u s i n g m ix ing equat ions, i t i s sometimes p o s s i b l e t o l e a r n t r a v e l t imes and r a t e s o f groundwater f low, a n d volumes and s torage c h a r a c t e r i s t i c s o f k a r s t aqu i fe rs . Such methods a re r e s t r i c t e d i n use t o unconf ined o r water t a b l e carbonate

94

system, and work b e s t where groundwater m i x i n g i s complete, and t r a v e l t imes a re a few days o r l e s s as i n some s o l u t i o n en la rged f i s s u r e s o r condui ts .

An impor tan t consequence o f m i x i n g o f carbonate groundwaters i s t h a t mix tu res u s u a l l y d i f f e r f rom component waters i n t h e i r s a t u r a t i o n s t a t e o r c o r r o s i v i t y w i t h respec t t o c a l c i t e and do lomi te (see Howard, 1966: T h r a i l k i l l , 1968; and Runnel is, 1 9 6 9 ) . I n f a c t B b g l i ( 1 9 6 4 ) has argued t h a t most o f t h e s o l u t i o n i n g o f carbonate rocks by groundwater i s a consequence o f i t s inc reased c o r r o s i v i t y caused by m i x i n g o f d i s s i m i l a r waters.

Equat ion 3.2-22 dqscr ibes t h e s o l u b i l i t y o f c a l c i t e i n pure water a t 25OC. A l i n e a r p l o t o f Ca2 versus C02(aq) f o r c a l c i t e s a t u r a t i o n based on t h i s equat ion i s g i ven i n F i g u r e 3.4-1. Th i s p l o t , which i s s i m i l a r t o F i g u r e 1 o f B b g l i ( 1 9 6 4 1 , shows t h a t m ix tu res o f waters w i t h composi t ions a t p o i n t s 2 and b have composi t ions a long l i n e amb, a l l undersa tur3 ted w i t h c a l c i t e . Fo r t h e example g i ven i n F i g u r e 3 . 4 - T w a t e r a has Ca2 = 1.00 mmol/R and CO2 = 0.076 mmol/R, and b, Ca2+ = 2.49 mmol/R-and CO2 = 1.0 mmol/II. A r n i x t y e o f 6 2 percent o f 2 and 3 8 pe rcen t o f b g i ves water m w i t h 1.57 mmol/II Ca2 and 0.43 mmo1/11 CO2. Th i s water i s undersa tura ted aKd so capable o f d i s s o l v i n g a d d i t i o n a l c a l c i t e . As l o n g as CO2 (aq) i s conserved, equat ion ( 3 . 2 - 2 5 ) shows t h a t every mole o f CO2 consumed produces a mole o f Ca2 u n t i l s a t u r a t i o n i s r e a t t a i n e d a t p o i n t s. L i n e sm then always has a s lope o f -1.

B b g l i ' s arguments a re v a E d , but w i t h a number o f q u a l i f i c a t i o n s . (1) The shape . o f t he c a l c i t e s a t u r a t i o n curve shows t h a t m i x i n g co r ros ion depends on major d i f f e r e n c e s i n the composi t ion of t h e component waters, and on r e l a t i v e l y s i m i l a r volumes o f these waters. ( 2 ) The model assumes CO2-closed system cond i t ions , t h a t i s CO2 i s conserved i n t h e mix ing. S tab le carbon i so tope s tud ies o f Pennsylvania carbonate ground waters by Deines e t a l . 1 1 9 7 4 ) show t h a t i n unconf ined carbonate a q u i f e r s t h e carbonate rock does i n f a c t d i s s o l v e l a r g e l y under c lpsed system conditions-. ( 3 ) B b g l i ' s model ignores sources o r s inks o f Ca2 , H , C 0 2 , HCO3 and C032 ' o t h e r than c a l c i t e s o l u t i o n o r p r e c i p i t a t i o n . ( 4 ) A l so i gno red a re i o n i c s t r e n g t h and complexat ion e f f e c t s on t h e water c$emistryl The l a s t two o b j e c t i o n s a re probably t h e most ser ious. If Ca2 , HCO3 , and C02(aq) a re a l lowed t o va ry independent ly, which i s n o t uncommon, p a r t i c u l a r l y i n more s a l i n e carbonate groundwaters, then s a t u r a t i o n w i t h c a l c i t e must be represented by a sur face i n three-dimensional space. The s a t u r a t i o n sur face f o r c a l c i t e i n pu re water i s shown schemat ica l l y i n F i g u r e 3.4-2 f o r 25OC based on equat ion ( 3 . 2 - 2 6 ) . (1) a t constant Ca , t h e m i x t u r e w i l l be undersaturated: ( 2 ) a t cons tan t HCO3 the m ix tu re w i l l remain saturated: w h i l e (3) a t cons tan t CO2 t h e m i x t u r e ecomes supersaturated. The l a t t e r p o s s i b i l i t y corresponds t o cons tan t

'CO,, and would be expected f o r m i x i n g i n many cave and s o i l environments, t h a t i s f o r systems open t o a l a r g e CO2 gas r e s e r v o i r o f cons tan t composit ion.

Because o f t h e i r complex i ty and t h e o v e r s i m p l i f i c a t i o n s necessary t o handle m ix ing systems g r a p h i c a l l y , most m i x i n g c a l c u l a t i o n s today a re b e i n g done by d i g i t a l computer (Plummer, 1 9 7 5 ) . The computer can so lve t h e m i x i n g equat ion f o r major i o n s and CO,(aq), assuming a c losed system (CO2 conserved) o r open system (CO;! f i x e d ) , w i t h pH then computed f rom t h e r a t i o s o f carbonate species u s i n g t h e d i s s o c i a t i o n constants f o r H2CO3. The degree o f s a t u r a t i o n o f t h e water w i t h respec t t o c a l c i t e o r do lomi te may then be c a l c u l a t e d by computer as p r e v i o u s l y descr ibed.

A p l o t o f t h e r e s u l t s o f such a c a l c u l a t i o n i s shown i n F i g u r e 3.4-3 mod i f i ed a f t e r Badiozamani (1973) f o r va r ious m ix tu res o f sea water ( a n a l y s i s 2 4 ) and carbonate groundwater f rom X-Can, Yucatan (ana lys i s 9 ) . Badiozamani assumes a c losed system w i t h respec t t o C 0 2 . T h i s approach i s p e r t i n e n t i n t h a t Yucatan groundwaters a re l a r g e l y m ix tu res o f f r e s h groundwater w i t h under l y ing sea water (Back and Hanshaw, 1970). The p l o t shows t h a t a groundwater w i t h up t o 5 pe rcen t sea water mixed can d i s s o l v e dolomi te, whereas mix tu res of up t o 50 pe rcen t sea water and f resh groundwater can d i s s o l v e c a l c i t e . Fo r sea water concent ra t ions rang ing from 5 t o 50 percent , c a l c i t e may be rep laced by do lomi te i n t h e aqu i fe r . Such c a l c u l a t i o n s a re o f i n t e r e s t t o b o t h sedimentary geochemists and hydrochemists (see Plummer e t a l , 1976).

T2%e f i g u r e shows t h a t i f m i x i n g o f sa tu ra ted waters occurs:

95

3

2

1

- E E Y

+ N

m O

1

O O

I I I O. 5 1.0

( rnrnol /P 1 1.5 2.0

F igu re 3 . 4 - 1 S o l u b i l i t y o f c a l c i t e i n pure water a t 25OC and 1

2 atm t o t a l pressure as a f u n c t i o n o f ca lc ium and CO concent ra t ions . Waters w i t h cornpositions below the curve a re undersaturated and those above t h e curve supersaturated w i t h respec t t o c a l c i t e . The l i n e a-b i s t h e locus o f composi t ions o f m ix tu res o f waters a and b. (See t e x t ) .

96

4. \ O - E E v

+ N

(TI O

\

F i g u r e 3.4-2 The s a t u r a t i o n sur face o f c a l c i t e i n pure water a t 25OC and 1 atm t o t a l pressure.

97

- 0.2

- 0.4

O 10 20 30 40 561 60 70 80 90 100

% Sea Water

F i g u r e 3.4-3 The s a t u r a t i o n i ndex o f mix tu res o f a ground water f rom X-Can, Yucatan ( a n a l y s i s 9 ) and sea water (ana lys i s 2 4 ) m o d i f i e d a f t e r Badiozamani ( 1 9 7 3 ) . The system i s assumed c losed w i t h respec t t o carbon d iox ide .

9 8

3.5 Discuss ion o f some carbonate groundwater analyses

3 .5 .1 Table o f water analyses. A c o l l e c t i o n o f r e l a t i v e l y complete analyses o f carbonate groundwater o f d i f f e r e n t types f rom t h e Un i ted States, Yucatan, Mexico, Nor th A f r i c a , Sy r ia , and T u n i s i a a re g i ven i n Appendix II. Also inc luded are analyses o f groundwater f rom gypsum rocks (analyses 2 1 and 22) and sea water (ana lys i s 2 4 ) f o r purposes o f comparison. O n l y analyses complete enough t o p e r m i t an equ iva len ts p e r m i l l i o n check were se lected. Un fo r tuna te l y few pub l ished analyses i nc lude a f i e l d measured pH, which i s necessary i f meaningfu l c a l c u l a t i o n s o f t h e CO2 con ten t o r degree o f s a t u r a t i o n o f t he water w i t h c a l c i t e o r do lomi te a re sought. Where t h e pH r e p o r t e d i n Appendix II i s probably a l a b o r a t o r y measured va lue, de r i ved CO2, S I c , and Sa va lues are l i s t e d p a r e n t h e t i c a l l y .

3.5.2 Impor tan t c o n t r o l l i n g processes. Numerous processes i n f l u e n c e the chemical q u a l i t y o f a groundwater be fo re i t reaches a s p r i n g o r i f i c e o r w e l l head. Among the most impor tan t o f these are:

1. The composi t ion o f t h e atmospheric p r e c i p i t a t i o n which becomes

2 . Evapo t ransp i ra t i on losses from groundwater recharge and shal low

3. The a c i d i t y and degree o f undersa tu ra t i on o f groundwater recharge and

4 . The a v a i l a b i l i t y and s o l u b i l i t y o f carbonate and assoc ia ted rocks , 5 . Rates o f s o l u t i o n o f these rocks and con tac t t ime o f t h e groundwater

6 . Hydro log ic processes such as d i l u t i o n by f r e s h groundwater recharge

7 . Anthropogenic processes, i n c l u d i n g groundwater p o l l u t i o n by l i qu id

Chemical analyses o f atmospheric p r e c i p i t a t i o n are g i ven by Schoe l le r ( 1 9 6 2 ) , C a r r o l l ( 1 9 6 2 ) , Hem ( 1 9 7 0 ) , and Pearson and F i s h e r ( 1 9 7 1 1 , among o thers . The s a l t con ten t o f r a i n o r snow g e n e r a l l y increases towards c o a s t a l areas because o f w i n d blown s a l t spray. Except d u r i n g major storms, however, t h i s i s a minor e f f e c t . Thus, C l l e v e l s i n r a i n , f o r example, average 3-6 mg/R c o a s t a l areas, and l e s s than 1 mg/R 1 6 0 km i n land . Wind blown dus t can add impor tan t amounts o f s a l t s t o r a i n i n mid-cont inent areas (Junge and Werby, 1 9 5 8 ) , as can a i r p o l l u t a n t s (see a l s o Pearson and F i she r , 1 9 7 1 ) .

The capac i t y o f r a i n t o dissol.ve carbonate rocks i s l i m i t e d because o f i t s low average CO2 conten t o f 0.03 percent ( 0 . 0 0 0 3 a t m P 1 . The s o l u b i l i t y o f c a l c i t e and do lomi te a t t h i s CO2 pressure i s g i ven $4' Table 3.2-6. O n l y when r a i n f a l l en te rs t h e subsurface d i r e c t l y v i a s inkholes, f r a c t u r e s , o r sandy s o i l , poor i n humus f o r example (see a n a l y s i s 2) can groundwater n e a r l y sa tura ted w i t h c a l c i t e o r do lomi te have such a low s o l u t e content . When groundwater recharge passes through an average s o i l zone carbonate rock s o l u b i l i t i e s a re g rea y increased by t h e a s s i m i l a t i o n o f s o i l CO2 i n amounts up t o about

Where s o i l s a re s i l t o r c l a y r i c h , and evapo t ransp i ra t i on r a t e s exceed p r e c i p i t a t i o n r a t e s , t he s a l t con ten t o f groundwater recharge may become subs tan t i a l . Such c o n d i t i o n s can occur d u r i n g summer months i n temperate c l imates , o r con t inuous ly i n a r i d e q u a t o r i a l areas. As a r e s u l t t h e s a l t con ten t o f groundwater recharge ma17 be r e l a t i v e l y h igh , and i t s aggressiveness t o carbonate rocks low. I t may be near o r a t Sa tu ra t i on w i t h c q l c i t e and do lomi te evEn be fo re i t reaches the groundwater tab le . The N , S042-- , C l and NO3 conten t o f Thompson Spr ing ( a n a l y s i s 4 ) de r i ves c h i e f l y f rom leach ing o f s a l t s concentrated i n s o i l near t h e s p r i n g by evapo t ransp i ra t i on (Jacobson and Langmuir, 1974).

The a c i d i t y o r capac i t y o f a groundwater t o d i s s o l v e carbonate rocks may come from processes opera t i ng on groundwater recharge i n t h e s o i l zone ( i g n o r i n g the u s u a l l y minor c o n t r i b u t i o n o f atmospheric C O 2 ) , o r f rom processes o c c u r r i n g w i t h i n t he groundwater aqu i fe r . The 1-a t te r source has u s u a l l y been ignored, but i s o f t e n o f cons iderab le importance. S o i l a c i d i t e s

99

groundwater recharge;

groundwaters ;

groundwater w i t h respec t t o t h e carbonate rocks;

i n c l u d i n g h a l i t e , gypsum, and anhydr i te ;

w i t h them;

and m i x i n g o f d i s s i m i l a r groundwaters;

wastes, o r leachates f rom s o l i d wastes.

atm%.,, ( 7 5 m g l R C02(aq) a t 1 0 ° C ) (see Table 3 . 2 - 6 ) .

a r e generated c h i e f l y by t h e CO2 f rom decay and p l a n t r o o t r e s p i r a t i o n . Shor t cha in f a t t y ac ids a re a l s o impor tan t i n some s o i l s , as a re t h e f u l v i c and h u m i c a c i d groups. A d d i t i o n a l a c i d i t i e s i n t h e sa tura ted zone r e s u l t f rom such processes as o x i d a t i o n of o rgan ic ma t te r i n t h e rock o r in t roduced i n t h e water as po l lu t ion (analyses 10 , 11, 1 9 , and 2 2 ) i o x i d a t i o n o f p y r i t e i n c l u s i o n s i n t h e rock; b a c t e r i a l r e d u c t i o n of n i t r a t e o r s u l f a t e (ana lys i s 1 4 ) ; and p r e c i p i t a t i o n of c a l c i t e ( o r a ragon i te ) because o f Ca2+ a d d i t i o n f rom the s o l u t i o n o f gypsum o r anhydr i t e (analyses 1 6 , 17 , 1 8 , and 2 0 ) .

I n genera l , t h e more s o l u b l e a m i n e r a l t he more r a p i d l y i t d isso lves . Impor tan t a re t h e c r y s t a l l i n i t y , t ex tu re , and pu r i t y o f t he rock. Such f a c t o r s a re discussed by Schoe l le r (1962). Contact t ime o f t he water w i t h rock can be es t imated by t r a c e r methods i n some carbonate a q u i f e r s (see Back and Zoet l , 1975 and Jacobson and Langmuir, 1 9 7 0 ) .

U s u a l l y carbonate groundwaters a re more sa tura ted w i t h c a l c i t e and do lomi te i n a r t e s i a n than i n water t a b l e systems. Th is r e f l e c t s sho r te r groundwater rock con tac t t imes i n t h e water t a b l e systems, but a l s o p e r i o d i c m i x i n g o f t h e groundwater w i t h r e l a t i v e l y f r e s h unsaturated groundwater recharge i n these systems. M i x i n g o f f resh , shal low carbonate groundwaters w i t h deeper s a l i n e waters i n c l u d i n g sea water i s common , p a r t i c u l a r l y i n c o a s t a l areas (Plummer e t a l . , 1 9 7 6 ) . Ana lys is 23 i s an example o f such a water (Back and Hanshaw, 1 9 7 0 ) .

Where carbonate rocks a re exposed w i t h o u t s o i l cover, and groundwater f l o w i s v i a secondary fea tu res such as s inkholes, s o l u t i o n enlarged f r a c t u r e s and condu i ts , t h e p o t e n t i a l f o r groundwater p o l l u t i o n i s g rea t . S o l i d waste d i s p o s a l (see a n a l y s i s 1 0 ) , sewage t i l e f i e l d s (ana lys i s i l ) , improper ly f u n c t i o n i n g s e p t i c tank systems (ana lys i s 1 9 ) , and a g r i c u l t u r a l and urban r u n o f f a re common sources o f groundwater p o l l u t i o n i n carbonate aqu i fe rs .

3.5.3 V a r i a t i o n i n some major chemical c h a r a c t e r i s t i c s .

3.5.3.1 Temperature (Donald Langmuir and H e n r i Schoe l le r ) . Determinat ion o f s p r i n g and w e l l water temperatures y i e l d s impor tan t i n f o r m a t i o n on the c i r c u l a t i o n p a t t e r n o f ground water i n carbonate rocks. The temperature o f carbonate qround water depends on the i n i t i a l temperature o f t he p r e c i p i t a t i o n , and t h a t o f t h e d i f f e r e n t environments through which i t t h e r e a f t e r passes, and t o a l e s s e r e x t e n t on chemical reac t i ons i n t h e subsurface which may add o r s u b t r a c t heat f rom t h e water (Rack a n d Hanshaw, 1 9 7 1 ) . Schoe l le r ( 1 9 4 9 ) has reviewed i n d e t a i l v a r i a t i o n s i n and c o n t r o l s on t h e temperature o f ground water.

The temperature o f ra inwa te r o r i g i n a t i n g i n c louds a t e l e v a t i o n s 6 0 0 t o 1600 m above t h e l a n d sur face i s l e s s than t h a t o f a i r i n con tac t w i t h t he s o i l s by 2 t o 7OC. Rain may be warmer o r coo le r than near-surface s o i l , depending on a v a r i e t y o f f ac to rs . E a r t h m a t e r i a l s below about 10 m depth seldom va ry more than l 0 C i n temperature d u r i n g t h e year. From about 1 0 m depth t o severa l tens o f meters depth, t h i s temperature i s u s u a l l y w i t h i n a degree o r so o f t he mean annual temperature o f the area. A t g rea te r depths, depending on t h e thermal a c t i v i t y present , t h e temperature o f b o t h rock and assoc ia ted water a re warmed by t e r r e s t r i a l heat f l o w (average 1.5 x ca l /cm2/sec) . Resu l tan t temperature g rad ien ts t y p i c a l l y range f rom 8 - 4 0 ° C / k n depth increase.

I n unconf ined o r water - tab le carbonate systems recharg ing water may be c o o l e r than the rock, a n d d i scha rg ing water warmer, d u r i n g w i n t e r months. The converse i s t r u e d u r i n g summer months. Whether the water i n t h e unsaturated zone (zone o f ae ra t i on ) o r sa tura ted zone approaches the temperature o f assoc ia ted e a r t h ma te r ia l s , depends on the charac ter o f i t s f low. The number o f c a l o r i e s (amount o f heat) gained o r l o s t , and hence the temperature o f t he water, depends on t h e c i r c u l a t i o n r a t e and on the area o f con tac t o f t he water w i t h t h e rock. I f movement i s slow and i f t h e r a t i o o f rock sur face area t o water volume i s l a r g e , as i n smal l openings o r pore spaces, t h e water and water-bear ing format ions reach thermal e q u i l i b r i u m a f t e r a s h o r t passage, and throughout the c i r c u l a t i o n network, t h e temperature o f t he water i s e s s e n t a i l l y equa l t o t h a t o f t he enc los ing s o i l and rock. I n such systems, shal low subsur- face waters approach t h e average temperature o f t he s o i l . However, i f movement

100

i s f a s t and i f the s p e c i f i c sur face i s smal l , then the i n i t i a i thermal d i s e q u i l i b r i u m between water and rock w i l l p e r s i s t , a l though decreasing d u r i n g underground c i r c u l a t i o n .

When k a r s t i c subsurface waters a r e f e d c h i e f l y b y water movement over seve ra l m i l e s v i a sma l l openings , annual temperature v a r i a t i o n s o f t h e water may be l e s s than 1'C. Such f l o w has been c a l l e d d i f f u s e (Schuster and White, 1971) and u s u a l l y occurs under semiconfined o r a r t e s i a n cond i t i ons . When t h e r a t e o f movement i s high and t h e f i s s u r e s and channels a re l a rge , as w i t h condu i t - type f l o w (Schuster and White, 1971) , which i s most common i n unconf ined f l o w systems, then t h e temperature o f s p r i n g o r w e l l waters w i l l d i f f e r from t h e mean annual temperature by +1-3'C.

Temperature v a r i a t i o n i n s p r i n g o r w e l l waters measured during o r f o l l o w i n g storm events, o r over longer pe r iods , may be used t o d i s t i n g u i s h condu i t (water t a b l e ) and d i f f u s e - t y p e (semi-conf ined o r a r t e s i a n ) groundwater f lows (Shuster and White, 1971; Jacobson and Langmuir, 1 9 7 4 ) . Such v a r i a t i o n s may be descr ibed i n terms o f t h e c o e f f i c i e n t o f temperature v a r i a t i o n VI which equals 100 t imes t h e standard d e v i a t i o n d i v i d e d by t h e mean water temperature. Jacobson and Langmuir ( 1 9 7 4 ) found t h a t V equa l l ed 26.9 and 1 .4 f o r a condu i t and a d i f f u s e s p r i n g water r e s p e c t i v e l y . These au thors no ted t h a t temperature v a r i a t i o n was a b e t t e r means of d i s t i n g u i s h i n g c o n d u i t and d i f f u s e - t y p e f l ows than were v a r i a t i o n s i n any o f t h e d i s s o l v e d species.

. P i t t y ( 1 9 6 8 ) used v a r i a t i o n s i n s p r i n g water temperature and hardness t o e s t a b l i s h groundwater res idence t imes o f a month o r longer i n some c o n d u i t systems.

Groundwater temperatures depend on e l e v a t i o n o f l a n d sur face and may be 1 t o 0.7OC c o o l e r f o r every 100 m inc rease i n a l t i t u d e . Hence, where i n f i l t r a t i o n occurs a t h i g h a l t i t u d e s , r e l a t i v e l y low ground water temperatures may occur; f o r example, 6.2' i n s t e a d o f 12'C f o r t h e Source du Loup near Laruns i n t h e Pyrenees, and 6.8' versus l 0 ' C f o r t he Source du Pont de l a Nor t , i n t h e G u i 1 V a l l e y o f t h e French Alps, where t h e l a t t e r temperatures i n each case a re mean annual l a n d sur face va lues a t t h e s p r i n g d ischarge p o i n t s (Schoe l l e r , 19491.

I n unconf ined o r water t a b l e carbonate groundwater f l o w systems i n temperate zones, seasonal temperature v a r i a t i o n s a re pronounced. Thus over t h e year v a r i a t i o n s o f as much as 5'C a r e u s u a l a t t h e Fonta ine de Vaucluse, near Avignon, Franch (Schoel ler , 1 9 4 9 ) and o f 6'C f o r Rock Spring i n c e n t r a l Pennsylvania, U.S.A. (Jacobson and Langmuir, 1974). The temperature o f such waters u s u a l l y reaches a maximum towards the end o f t h e summer and a m i n i m u m i n l a t e w i n t e r . Seasonal temperature v a r i a t i o n s i n a r t e s i a n carbonate groundwaters, as i n the F l o r i d a n A q u i f e r (Hanshaw, Back, and Rubin, 1 9 6 5 ) , a re u s u a l l y minor o r absent.

3.5.3.2 D isso lved s o l i d s . General r e l a t i o n s between s p e c i f i c conductance and t o t a l d i s s o l v e d s o l i d s (TDS) f o r waters o f d i f f e r e n t p r e v a l e n t chemical charac ter a re g i ven i n s e c t i o n 6.5. Because most d i s s o l v e d species are i o n i z e d and so c o n t r i b u t e t o the s p e c i f i c conductance, c o n s i d e r a t i o n o f conductance and TDS separa te ly i s redundant. F o l l o w i n g d i scuss ion i s t h e r e f o r e l i m i t e d t o TDS v a r i a t i o n s only .

The s o l u t e s present i n carbonate groundwaters a r e d e r i v e d from atmospheric p r e c i p i t a t i o n , concentraton i n groundwater recharge o r sha l low groundwater by evapo t ransp i ra t i on , weather ing and s o l u t i o n o f s o i l and r o c k m a t e r i a l s , m i x i n g w i t h s a l i n e waters, and p o l l u t i o n .

The m g o r d i sso l ved species i n f r e s h carbonate groundwaters a r e g e n e r a l l y Ca2+, Mg2 I . HÇ03 and- H~COJ ( l a r g e l y d i s s o l v e d CO21 , w i t h smal le r amounts of Na , S o b 2 , C 1 , s f l i c a _(present c h i e f l y as H4Si04') , d isso lved oxygen and n i t r o g e n , K , NO3 and C032- . Other d i s s o l v e d species r a r e l y exceed 1 mg/R.

A t t h e h i g h e s t CO2 pressures no rma l l y found i n carbonate groundwaters (about 1 O - l ' atm) and a t 10°C, s o l u t i o n o f pu re carbonate rocks can y i e l d a maximum TDS ( res idue ) of about 450 mg/P.. Higher TDS va lues g e n e r a l l y r e f l e c t : (1) increased Ca2+ and S o b 2 - from s o l u t i o n o f gypsum i n t h e rock (analyses 1 5 , 1 6 , 1 7 ( ? ) , 1 8 , 21 , and 2 2 ) ; ( 2 ) g r e a t e r carbonate s o l u b i l i t y because of unusua l l y high CO2 pressures found i n some thermal, a r t e s i a n waters ( a n a l y s i s 17); (3) s o l u t e s added i n groundwater p o l l u t i o n (analyses 10,

1 0 1

11, and 19); ( 4 ) m i x i n g w i t h s a l i n e waters o r s o l u t i o n o f h a l i t e as w e l l as gypsum (analyses 20 and 2 3 ) .

The d i s s o l v e d s o l i d s conten t o f groundwater genera l l y increases w i t h t ime and f l o w because o f s o l u t i o n o f carbonate rocks and associated non-carbonate minera ls . T h i s i s p a r t i c u l a r l y t r u e o f con f ined carbonate groundwaters moving away from sources o f f r e s h recharge (see Back and Hanshaw, 1 9 7 0 ) . Shallow water t a b l e carbonate groundwaters may n o t increase i n d i sso l ved s o l i d s content w i t h f l o w because o f l o c a l m i x i n g w i t h more d i l u t e f r e s h recharge.

W e l l waters o f t e n have a h ighe r TDS conten t than adjacent s p r i n g waters i n the same carbonate aqu i fe r . Th i s i s because sp r ing waters g e n e r a l l y discharge from zones o f s o l u t i o n enlarged p o r o s i t y and pe rmeab i l i t y , whereas randomly s i t e d w e l l s most o f t e n draw water f rom l e s s permeable zones. A l so groundwater recharge t o spr ings i s o f t e n r a p i d and low i n CO2 when i t en te rs t h e a q u i f e r v i a s inkho les and s i m i l a r fea tures . I n con t ras t , un less w e l l s a re i n t e n t i o n a l l y s i t e d t o draw water f rom zones o f s i m i l a r l y high pe rmeab i l i t y , most o f t h e i r groundwater recharge i s l o c a l i n o r i g i n , pe rco la tes downward through s o i l s where i t p i c k s up a d d i t i o n a l CO2, and may a l s o inc rease i n s a l t con ten t because o f evapot ransp i ra t ion .

An example o f t he e v o l u t i o n o f TDS conten t i n a carbonate sp r ing water, Rock Spr ing ( a n a l y s i s 1 1 , i s g i ven i n F igu re 3 . 5 - 1 a f t e r Jacobson and Langmuir ( 1 9 7 0 ) . The p l o t shows changes i n TDS o f t he water as i t moves down a mountain s lope on sha le i n t o a carbonate a q u i f e r a t t he base o f t he slope, and discharges as a s p r i n g a f t e r 1700 m o f subsurface f low. Dye t r a c i n g ,shows the subsurface f l o w takes 2-6 days. Groundwater sampling a t a d is tance o f 1 4 0 0 m i s i n a cave. Because o f t h e low s o l u b i l i t y o f t h e sha.le and associated mountain s o i l s , TDS E 20 mg/R i n t h e mountain stream. TDS values increase r a p i d l y t o about 1 7 0 mg/R once t h e stream disappears i n t o i t s channel bot tom and en te rs carbonate rocks i n t h e subsurface. Th is increase i s caused by the g rea te r con tac t t ime o f t h e groundwater and rock than stream and i t s channel sediments , and g rea te r s o l u b i l i - t y o f t he carbonates than t h e shale. CO, losses t o t h e atmosphere a t t he s p r i n g (d is tance 2700 m) cause t h e r e s u l t a n t stream t o become supersaturated w i t h c a l c i t e a . t about 300 m, so t h a t i t cannot f u r t h e r d i s s o l v e carbonate rocks.

Most carbonate groundwater systems are t o o complex t o p e r m i t t he k ind o f sur face water-groundwater chemist ry study j u s t descr ibed, however, t he processes considered here t h a t c o n t r o l TDS l e v e l s commonly operate elsewhere.

3.5.3.3 Preva len t chemical charac ter . The p reva len t chemical charac ter (PCC) o f a water i n d i c a t e s the r e l a t i v e abundance o f t he major c a t i o n s and anions, and thus p rov ides a means o f d i s t i n g u i s h i n g d i f f e r e n t waters by type and o r i g i n . PCC i s determined by conver t i ng p a r t s p e r m i l l i o n concent ra t ions t o equ iva len ts p e r m i l l i o n , o r m i l l i g r a n s p e r l i t e r concent ra t ions t o m . i l l i e q u i v a l e n t s p e r l i t e r (see Appendix I). The major ca t i ons and anions are then l i s t e d i n order o f abundance.

Severa l methods a re used t o express PCC from ion-abundance l i s t s . Assume f o r example t h a t t h e order o f abundance i s Ca, Na, K I Mg, and HCO3, C 1 , SOL,, and CO3. Sometimes t h e most abundant c a t i o n and anion are given; a Ca-HC03 water. Sometimes the two most abundant ca t i ons and anions are given; a Ca,Na - HCO3,C l water. More f r e q u e n t l y t h e epm o f seve ra l species are lumped together . Thus (Ca + Mg) , (Na + K I , and (CO3 + HCO3) , and (SO4 + C i ) a re o f t e n combined. Th is l a s t approach obv ious lv s i m p l i f i e s th ings , but a t t h e same t ime provid-es much l e s s i n fo rma t ion w i t h regard t o d e t a i l e d geochemistry than t h e f i r s t two approaches, and i n f a c t may be mis leading, as i n t h i s case: a Ca, Mg - CO3, HCO3 water. L u m p i n q i s t o be discouraged a l s o because i t i n f e r s a s i m i l a r behav io r and o r i g i n f o r t he lumped species, which i.s o f t e n i n c o r r e c t .

As i n f e r r e d i n t h e fo rego ing sec t i on on TDS , r e l a t i v e l y f r e s h carbonate groundwaters a re g e n e r a l l y of t h e Ca, Mg, -HCO3 type. TDS above 450 mg/R most o f t e n i n d i c a t e s t h e i nc reas ing presence o f i ons such as SO4, C 1 , and Na, a long w i t h i n c r e a s i n g amounts o f Ca. T y p i c a l l y such waters a re o f t he Ca-S04 (analyses 1 5 , 1 6 , and 1 8 ) o r Na-Cl types (analyses 1 9 , 20 , and 2 3 ) w i t h NaCl waters g e n e r a l l y hav ing the h ighe r TDS content .

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F igu re 3.5-1 The chemical e v o l u t i o n o f su r face and ground waters i n t h e Rock Spr ings system, near S ta te Col lege, Pennsylvania, USA a f t e r Jacobson and Langmuir ( 1 9 7 0 ) . S o l i d l i n e s denote the chemistry o f sur face water f lows, dashed l i n e s t h a t o f t h e ground water. The two arrows i n d i c a t e t h e l o c a t i o n o f a d d i t i o n a l ground water i n p u t s t o t h e system. (See t e x t ) .

1 0 3

3.5.3.4 D isso lved oxygen and redox p o t e n t i a l . The 3 o l u b i l i t y o f t he oxygen i n a i r increases w i t h oxygen gas p a r t i a l pressure ( 0 2 ) and t o t a l baromet r ic pressure, and decreases w i t h i n c r e a s i n g temperature. A t 25OC and sea l e v e l ,

O 2 i n atmospheres equals

= K x D O (3.5-1) 2

where K I t h e Henry 's Law cons tan t equals 0 2 4 6 atm/mg/ll, and DO i s i n m i l l i g r a m s p e r l i t e r . ' r va lue o f 0.203 atm (290 m g / i O 2 i n a i r ) a t 25"C , DO = 8.25 mg/ll, andv02 = 0.002 atm f o r DO = 0 .01 mg/&, which i s near t h e l i m i t s o f d e t e c t i o n f o r DO by convent iona l means.

DO l e v e l s i n unconf ined carbonate groundwaters a re genera l l y near s a t u r a t i o n (see a n a l y s i s 2) . P o l l u t i o n o f these groundwaters by organ ic wastes such as sewage can, however, reduce o r dep le te t h e i r DO content (see analyses 10 and 11). Such DO reduc t ions are u s u a l l y accompanied by an inc rease i n t h e w a t e r ' s CO2 content , i n p a r t because o f o x i d a t i o n o f t h e wastes.

O n l y when DO i s below d e t e c t i o n should Eh measurements be considered t o e s t a b l i q h t h e o x i d a t i o n s t a t e o f a water. However, such e l e c t r o a c t i v e species as Fe2 and Mn2+ are u s u a l l y a t t r a c e (pg l l l ) l e v e l s i n carbonate groundwaters making thermodynamical ly meaningfu l Eh measurements d i f f i c u l t (Langmuir, 1 9 7 1 ) . Never the less t h e o r e t i c a l r e l a t i o n s among redox responsive species o f oxygen, hydrogen, n i t rogen , manganese, i r o n , s u l f u r , and carbon are wor th d iscuss ing .

The Eh va lues a t pH = 7 and 25OC f o r severa l impor tan t redox reac t i ons are shown i n F igu re 3.5-2. T h e o r e t i c a l l y a l l waters con ta in ing more than 0 . 0 1 m g / l l DO have Eh's w i t h i n t h e cross-hatched area ( 7 6 3 t o 808 mv). T h i s i nc ludes e s s e n t i a l l y a l l carbonate streams and unconf ined groundwaters un less they are g r o s s l y p o l l u t e d . I n conf ined carbonate groundwaters, however, e s p e c i a l l y where organ ic m a t e r i a l i s p resen t which has a redox s t a t e a t o r below methane (CH4) , a l l r e d u c t i o n r e a c t i o n s shown f o r h igher Eh 's can occur. Usua l l y microorganisms a re r e q u i r e d f o r these reac t i ons (Baas Becking e t a l . , 1 9 6 0 ) . Un fo r tuna te l y pub l i shed Eh measurements o f carbonate groundwaters a re extremely r a r e , and more are needed, p a r t i c u l a r l y o f con f ined carbonate groundwaters. I n any case t h e occurrence o f these reac t i ons can o f t e n be i n f e r r e d from a chemical a n a l y s i s and f i e l d observat ions. For example, t h e H2S odor and p r e c i p i t a t e d e lementa l s u l f u r ( S o ) i n A i n K b r i t Spr ing (ana lys i s 1 4 ) i n d i c a t e s t h a t o x i d a t i o n o f H2S t o S o o c c u r i y , and so the Eh i s near -200 mv.

Where i r o n i s p resent as Fe2 , the Eh should be l e s s than about 50 mv. When Eh va lue2 are too h igh , i n c o n s i s t e n t w i t h t he presence o f reduced species such as Fe2 (see ana lys i s 1 2 ) , they may be assumed thermodynamical ly meaningless, o r t he water i s b e i n g oxidi_zed by m ix ing o r a e r a t i o n near the d ischarge p o i n t . The l a t t e r i s most l i k e l y f o r Heal in?+Spring (ana lys i s 1 2 ) which has 2 m g / l l DO, an amount t o o h i g h f o r t he E h o r Fe present.

Thus, f o r a normal '62 i n

3.6 I s o t o p i c v a r i a t i o n s i n t h e water c y c l e and t h e i r h y d r o l o g i c a l s i g n i f - icance. (R. M. Brown, R. G. G o n f i a n t i n i , B. R. Payne, Kaz ik Przewlocki , and Yucel Yur tsever)

The i so tope r a t i o s o f n a t u r a l compounds may change as a consequence o f t he env i ronmenta l processes t o which such compounds have been subjected. Study o f i s o t o p i c v a r i a t i o n s o c c u r r i n g i n n a t u r a l waters can y i e l d va luab le h y d r o l o g i c a l i n fo rma t ion . [EDITOR'S NOTE: The reader i s r e f e r r e d t o Harmon ( 1 9 7 7 ) f o r a d i scuss ion o f t h e i s o t o p i c composi t ion o f carbonate groundwaters, t o M i lanov ic (1981) and Howard and Howard (1972) f o r d iscuss ions o f t h e a p p l i c a t i o n o f i so tope s tud ies t o k a r s t hydro logy s tud ies and t o Gaspar and Oncescu f o r ex tens ive read ing on the use o f r a d i o a c t i v e t r a c e r s i n hydrology.]

The s t a b l e env i ronmenta l isotopes, hydrogen-1 and 2 (deuterium) ( D ) , oxygen-16 and 1 8 , and carbon-12 and 1 3 , are n a t u r a l l y occur r ing . The r a d i o - a c t i v e env i ronmenta l i so topes o f i n t e r e s t , t r i t i u m (hydrogen-3) and carbon-14, occur n a t u r a l l y as a r e s u l t o f t h e i n t e r a c t i o n o f cosmic r a d i a t i o n w i t h t he atmosphere and a re man-made i n t h e exp los ion o f nuc lear devices. The man-made iso topes have been d ispersed throughout the e a r t h ' s atmosphere and t h e i r p a r t i c i p a t i o n i n t h e h y d r o l o g i c a l c y c l e i s now regu la ted by n a t u r a l processes. 104

800

NO;

N,(aq) -

600

400

200

O

- 200 So

- 400

Mn O,

Mn"

N 0; NO;

NO,-

-

-

- NH:

Fe (OH l3

Eh imv 1

Fe '*

so:- FeS, so:

H, S (aq) H CO;

CH,(aq 1

" 2 0

F igu re 3.5-2 The Eh ( o x i d a t i o n s t a t e ) o f some impor tan t o x i d a t i o n - r e d u c t i o n r e a c t i o n p a i r s a t pH=7 and 25OC. Crosshatched area g ives Eh 's €or 02(aq)/H20, where 02(aq) ranges from 8.25 t o 0.01 mg/l. Other c o n d i t i o n s are: NOSN2(aq) a t N (aq)=14mg/l ( s a t u r a t i o n w i t h N (9) i g a i r ) , d t o t a l

Fe(4;) /Fe SO /$es a t Fe = 1 mg/l and SO = 96 mg/l? and S / i 2 S (aqf a t H2S(aq) = 108 mg/l ( fO-1 .5 mo la r ) .

N f a q ) = 1 0 - 3 2 ~ o l a r ; n O (pyrolusiSe)/Mn + a t Mn 4f = 1 m /is

a t f;$!y+=21 mg/l and Ksg- fo r Fe(0H) = 10- 38.5;

1 0 5

The mean abundances and r a d i a t i o n c h a r a c t e r i s t i c s o f env i ronmenta l i so topes o f h y d r o l o g i c a l i n t e r e s t a re presented i n t a b l e 3.6-1.

I so topes o f oxygen and hydrogen, elements which c o n s t i t u t e the water molecule, a re i d e a l geochemical t r a c e r s o f water because t h e i r concent ra t ions a re n o t sub jec t t o changes by i n t e r a c t i o n w i t h t he a q u i f e r ma te r ia l . I n con t ras t , carbon compounds i n groundwater may i n t e r a c t w i t h t he a q u i f e r mate- r i a l , comp l i ca t i ng the i n t e r p r e t a t i o n o f 14C data.

A few o t h e r env i ronmenta l i so topes such as s i l i con -32 , 32~i, ( L a i e t a i . , 1 9 7 0 1 , su l fu r -34 , 3 4 S , (Rightmire e t a l , 1 9 7 4 1 , and the uranium-238 t o uranium-234 r a t i o , 2 3 8 U / 2 3 4 U , (Kaufman e t a l . , 1 9 6 9 ) have been proposed f o r h y d r o l o g i c a l purposes.

3 . 6 . 1 S tab le i so topes o f hydrogen and oxygen i n the h y d r o l o g i c a l cyc le . Among a l l s t a b l e i s o t o i c species o f water poss ib le , o n l y these a re o f p r a c t i c a l i n t e r e s t s : The v a r i a t i o n s o f t he i s o t o p i c r a t i o s D/H and l 8 0 / l 6 O i n water samples a re expressed i n terms o f pe r m i l l e d i f f e r e n c e (6'/,,) w i t h respec t t o the i s o t o p i c r a t i o s o f mean ocean water (which c o n s t i t u t e s t h e re fe rence standard SMOW) (Craig, 1 9 6 9 b ) :

H2180, HD160 and H 2 l 8 O .

6 O / , , = - 1 x 1 0 0 0 (3.6-1)

RSMOW

where R i s t he i so tope r a t i o D/H o r l 8 0 / l 6 O . Thus a sample which has 6 l 8 0 = +5 ( o r -5 ) has an l 8 0 conten t 5 O / , , h i ghe r ( o r lower) than t h a t o f t he mean ocean water. The same app l i es t o the 6D f o r t he deuter ium content .

Us ing s tandard techniques o f sample p repara t i on (Friedman, 1 9 5 3 ; Eps te in and Mayeda, 1 9 5 3 ) and one o f t he i so tope r a t i o mass spectrometers now commer- c i a l l y a v a i l a b l e , standard d e v i a t i o n s of l . O o / , , f o r 6D and 0. io / , , f o r 6 l 8 0 can be achieved. These dev ia t i ons , f o r p r a c t i c a l purposes, a re comparable because the D / H v a r i a t i o n s i n n a t u r a l waters are, i n most cases, 5 t o 8 t imes l a r g e r than those o f l 8 0 / l 6 O . Th i s measurement accuracy i s s u f f i c i e n t f o r h y d r o l o g i c a l s tud ies .

3.6.1.1 I s o t o p i c v a r i a t i o n s i n p r e c i p i t a t i o n . Many n a t u r a l processes cause v a r i a t i o n s of t he i s o t o p i c composi t ion o f n a t u r a l waters. Among them, the most impor tan t a re evapora t ion and condensation. During t h e evaporat ion process, t he l i g h t molecules o f water ( H 2 l 6 O ) a re more v o l a t i l e than those con ta in ing a heavy i so tope (HDl60 o r H 2 l 8 0 ) . Therefore, water vapour which evaporates from t h e ocean conta ins about 1 2 - 1 5 percent l e s s l 8 0 and 80-120 percent l e s s deuter ium than does ocean water. When t h i s atmospheric water vapour undergoes successive c o o l i n g and condensation du r ing the produc t ion o f c louds a n d p rec ip - i t a t i o n , t h e l e s s v o l a t i l e heavy molecules condense p r e f e r e n t i a l l y , l eav ing a r e s i d u a l vapour more and more dep le ted i n D and l80. As a r e s u l t , successive p r e c i p i t a t i o n s de r i ved from the same i n i t i a l vapour mass w i l l be more and more dep le ted i n heavy isotopes. Because t h e degree o f condensation o f a vapour mass depends on t h e temperature, a r e l a t i o n s h i p between i s o t o p i c composi t ion o f p r e c i p i t a t i o n and i t s temperature o f fo rmat ion should be expected; as the foremat ion temperature decreases, t he 6-values o f p r e c i p i t a t i o n decrease (Dansgaard, 1 9 5 4 ) . Th i s has been observed d i r e c t l y i n A n t a r c t i c p r e c i p i t a t i o n ( P i c c i o t t o e t a l . , 1 9 6 0 ) and a wor ldwide r e l a t i o n s h i p between 6 l 8 0 o f p r e c i p i - t a t i o n and mean annual a i r temperature has been repo r ted (See f i g u r e 3 . 6 - 1 ) .

Th is dependency on temperature produces seasonal v a r i a t j - o n s i n isotopes caused o f p r e c i p i t a t i o n ( w i n t e r p r e c i p i t a t i o n i s dep le ted i n heavy isotopes w i t h respec t t o summer p r e c i p i t a t i o n ) , l a t i t u d e v a r i a t i o n s ( h i g h l a t i t u d e p r e c i p i t a t i o n i s dep le ted w i t h respec t t o low l a t i t u d e p r e c i p i t a t i o n ) and a l t i t u d e v a r i a t i o n s ( t h e heavy i so tope content o f p r e c i p i t a t i o n decreases w i t h i nc reas ing a l t i t u d e ) , (Friedman e t a l . , 1 9 6 4 ; Moser a n d S t i c h l e r , 1 9 7 0 ) . The l a s t e f f e c t i s e s p e c i a l l y impor tan t i n r e g i o n a l h y d r o l o g i c a l s tud ies i n which, f o r instance, groundwaters d e r i v i n g from recharge areas a t d i f f e r e n t e leva t i ons may be d i f f e r e n t i a t e d . The a l t i t u d e e f f e c t may chan e from r e g i o n t o reg ion but, i n genera l , i t i s about 0.3"/,, decrease i n " 0 - content and 2.5'/,, decreased f o r D conten t pe r 100 metres increase i n e leva t i on .

1 0 6

Table 3.6-1. Main env i ronmenta l i so topes used i n hydrology.

R e l a t i v e abundance H a l f - l i f e Maximum energy I sotope i n nature, percent Decay (years (KeV)

l H 99 .985 s t a b l e

2HSD O .O15 s t a b l e

3H=T 1 0 1 8- -15 - 10-12*

2C 98 .89 s t a b l e

3c 1.11 s t a b l e -

4c 1 .2x10-10**) B

l 6 0 99.76 s t a b l e

l 7 0 O .O4 s t a b l e

8O O .20 s t a b l e

1 2 . 2 6

5730

1 8 . 1

1 5 6

* ) The lower f i g u r e r e f e r s t o t h e t r i t i u m conten t o f p r e c i p i t a t i o n b e f o r e 1 9 5 2 , t he h ighe r one t o t h a t reached i n 1 9 6 3 p r e c i p i t a t i o n i n t h e no r the rn hemisphere.

* * ) I n modern carbon be fo re 1 9 5 0 .

107

O

- 5

-10

-15

-20 - O s c - v -25

03

e

-3c

-35

-40

-45

- 50

ô18= O.695ta -13.6%0 ( ô D = 5 . 6 t a - 1 0 0 % 0 ) Marion i s -+

Thorshavn -+

Stat WilkesS, 66's 4 Little America 78"s i3OOlA /

Station Nord 82' N

Ellsworth 77'5

North Greenland

11201 Horlick Mts 85's

F i g u r e 3 .6-1 The annual mean6180 o f p r e c i p i t a t i o n as a f u n c t i o n o f t h e annual mean a i r temperature a t surface. i n d i c a t e t h e - t o t a l th ickness ( i n cm) o f t h e i n v e s t i g a t e d snow l a y e r s (Dansgaard, 1 9 6 4 ) .

The f i g u r e s i n parenthes is

1 0 8

The v a r i a t i o n s o f t h e deuter ium and oxygen-18 conten ts i n p r e c i p i t a t i o n are l i n e a r l y c o r r e l a t e d (See f i g u r e 3 . 6 - 2 ) . The r e l a t i o n s h i p :

6D0/,, = 8 6 1 0 0 0 / 0 , + 1 0 (3 .6 -2 )

b e s t f i t s t h e p o i n t s rep resen t ing t h e i s o t o p i c composi t ion o f p r e c i p i t a t i o n samples f rom a l l over the wor ld , a t l e a s t f o r va lues o f ô l 8 0 lower than zero w i t h respec t t o SMOW. I n some reg ions o f t h e wor ld , a d i f f e r e n t i n t e r c e p t on t h e ôD a x i s i s observed, but a s lope o f 8 i s g e n e r a l l y preserved.

P r e c i p i t a t i o n which has undergone s i g n i f i c a n t evaporat ion d u r i n g i t s f a l l does n o t obey equat ion ( 3 . 6 - 2 ) . Evaporat ion does tend t o e n r i c h b o t h t h e heavy iso topes i n water but n o t i n t h e r e l a t i v e p r o p o r t i o n i n d i c a t e s by t h e above r e l a t i o n s h i p (Cra ig, 1961a; Ehha l t e t a l . , 1 9 6 3 ; Woodcock and Friedman, 1 9 6 3 ) .

3.6.1.2 I s o t o p i c composi t ion o f groundwater. When p r e c i p i t a t i o n i n f i l t r a t e s t o recharge groundwater, m i x i n g i n t h e unsatura ted zone dampens t h e i s o t o p i c v a r i a t i o n s so t h a t water i n t h e sa tu ra ted zone has a composi t ion corresponding t o t h e mean i s o t o p i c composi t ion o f t he i n f i l t r a t i n g water i n t h e area. Th is composi t ion may d i f f e r s l i g h t l y f rom the mean i s o t o p i c cornposit ion o f p r e c i p i - t a t i o n i n t h e area due t o t h e f a c t t h a t t h e p r o p o r t i o n o f t h e p r e c i p i t a t i o n t h a t i n f i l t r a t e s v a r i e s d u r i n g t h e year (Thatcher, 1967; Gat and T z u r , 1 9 6 7 ) . For example, a t temperate c o n t i n e n t a l s i t e s s p r i n g and summer p r e c i p i t a t i o n p a r t i a l l y o r t o t a l l y re-evaporates f rom t h e s o i l be fo re i n f i l t r a t i o n can occur.

The i s o t o p i c composi t ion o f water i n t h e a q u i f e r does n o t change f u r t h e r un less exchange w i t h t h e oxygen o f t h e rocks occurs. Th is process o f exchange i s , i n genera l , ve ry slow a t t h e temperatures normal ly o c c u r r i n g i n aqu i fe rs , and i s o f importance on ly f o r h i g h temperature thermal waters (Cra iq, 1 9 6 3 ) .

The i s o t o p i c composi t ion o f groundwater i s thus r e l a t e d t o t h e i s o t o p i c composi t ion o f p r e c i p i t a t i o n i n t h e recharge r e g i o n o f t h e a q u i f e r a t t h e t ime of recharge. Groundwater may be ve ry o ld , on t h e o rde r o f seve ra l thousand o r tens o f thousands o f years, and t h e c l i m a t i c c o n d i t i o n s o f t h e r e g i o n a t t he t i m e o f recharge may have been d i f f e r e n t f rom today. Th is i m p l i e s t h a t t he i s o t o p i c composi t ion o f p r e c i p i t a t i o n cou ld have been d i f f e r e n t f rom t h a t occu r r i ng a t t he present t ime, due t o t h e c o r r e l a t i o n - between 6 va lues and temperature (Gat, 1971).

Groundwater may be recharged a l s o by l a t e r a l seepage from sur face waters, such as r i v e r s and lakes, o r by v e r t i c a l i n f i l t r a t i o n f rom ponded waters. I f most o f t h e recharge i s f rom l a t e r a l seepage, t h e groundwater should r e f l e c t t he mean i s o t o p i c composi t ion o f t h e r i v e r o r t h e l a k e i n s t e a d o f t h a t o f l o c a l p r e c i p i t a t i o n which cou ld be r a t h e r d i f f e r e n t . ' The r i v e r may c o l l e c t water which o r i g i n a t e s f rom p r e c i p i t a t i o n i n a complete ly d i f f e r e n t area, f o r in- stance i n a h i g h mountain reg ion; i n t h i s case i t s heavy i so tope conten t would be lower than t h a t o f p r e c i p i t a t i o n i n t h e p l a i n , due t o t h e a l t i t u d e e f f e c t .

Water from lakes o r ponds may be cons iderab ly enr iched i n heavy i so topes through evaporat ion. The enr ichment i s l i m i t e d by d i r e c t i s o t o p i c exchange w i t h atmospheric mois ture. I t i s c l e a r t h a t t h i s enrichment i s h i g h e r where the evaporat ion i s more i n tense w i t h respec t t o t h e t o t a l volume o f water , e.g. i n c losed lakes and ponds o r lakes and r i v e r s i n a r i d areas. I n t h e l a t t e r case, t h e atmospheric r e l a t i v e h u m i d i t y i s low and thus t h e i s o t o p i c exchange i s l e s s impor tant .

Waters which have undergone evapora t ion a re e a s i l y i d e n t i f i e d by t h e i r i s o t o p i c composi t ion (See f i g u r e s 3.6-2 and 3 . 6 - 3 ) . T h e i r heavy i so tope conten t i s h ighe r than t h a t o f non-evaporated waters i n t h e r e g i o n and they do n o t obey t h e r e l a t i o n s h i p (3 .6 -2 ) (C ra ig and Gordon, 1965; Fontes and Gonfian- t i n i , 1967 ; D incer , 1 9 6 8 ) .

3.6.2 T r i t i u m i n the h y d r o l o g i c a l cyc le . T r i t i u m ( 3 H o r T) i s a r a d i o a c t i v e iso tope o f hydrogen hav ing atomic mass 3 , a h a l f - l i f e o f 12 .26 years, B- rad ia t ion o f maximum energy 18 .1 KeV, and no y r a d i a t i o n . I t occurs i n the environment as a r e s u l t o f b o t h n a t u r a l and man-made processes. T r i t i u m i s produced n a t u r a l l y by t h e i n t e r a c t i o n o f cosmic r a d i a t i o n w i t h t h e n i t r o g e n and oxygen of t h e upper atmosphere a t a r a t e o f about 0.25 atoms/cm2/sec (La1 and

10 9

100

O

- 100

- s I

n L a

-200

-300

- 50 -40 -30 - 20 - 10 O 10 20 6 1801%01

F igu re 3.6-2 Deuterium and oxygen-18 c o r r e l a t i o n i n p r e c i p i t a t i o n and surface waters. Closed bas in waters do n o t f i t t h e genera l l i n e a r cor- r e l a t i o n , because o f evaporat ion. Po in ts which f i t t h e dashed l i n e a t t h e upper end o f the curve a re r i v e r s and lakes from East A f r i c a ICra ia, 1961a).

F igu re 3.6-3 Deuterium and oxygen-18 c o r r e l a t i o n i n two Sahara Lakes going dry. One o f them conta ined s a l t water ( f i l l e d p o i n t s ) : a t h i g h values o f t he s a l t concent ra t ion , t he i s o t o p i c compostion o f water dev ia tes f rom t h e l i n e a r c o r r e l a t i o n ( f rom Fontes and Gon f ian t i n i , 1 9 6 7 ) .

110

Suess, 1 9 6 8 ) . Large amounts o f man-made t r i t i u m were re leased t o t h e atmo- sphere by thermonuclear t e s t s i n t h e period. 1 9 5 3 - 6 2 , and minor amounts a re be ing re leased by i n d u s t r i a l nuc lea r a c t i v i t i e s .

Most t r i t i u m produced i n t h e atmosphere i s r a p i d l y o x i d i z e d t o t r i t i a t e d water (HTO) and inco rpo ra ted i n t h e h y d r o l o g i c a l c y c l e where i t c o n s t i t u t e s a ve ry u s e f u l marker f o r water t h a t has been i n t h e atmosphere w i t h i n t h e p a s t 3 0 years. The g r e a t d i l u t i o n b y H 2 0 r e s u l t s i n ve ry low t r i t i u m concent ra t ions which can o n l y be measured by means o f t r i t i u m ' s r a d i o a c t i v i t y , u s u a l l y a f t e r an i s o t o p i c enrichment t reatment .

The t r i t i u m . con ten t o f n a t u r a l waters i s expressed i n T r i t i u m U n i t s (T .U. ) . One T r i t i u m U n i t corresponds t o a concen t ra t i on o f 1 t r i t i u m atom p e r 1 0 l 8 hydrogen atoms.

3 . 6 . 2 . 1 H i s t o r y o f t r i t i u m i n t h e atmosphere. Cosmic r a d i a t i o n e s t a b l i s h e s a concen t ra t i on o f about 1 0 T.U. i n temperate zone c o n t i n e n t a l meteor ic waters. Th is was t h e concen t ra t i on observed b e f o r e 1 9 5 3 i n p r e c i p i t a t . i o n i n t h e Nor th - e r n Hemisphere. A f t e r 1 9 5 3 , t h e t r i t i u m conten t o f p r e c i p i t a t i o n inc reased as a r e s u l t o f thermonuclear t e s t i n g (Brown and G r u m m i t t , 1 9 5 6 ; Brown, 1 9 6 1 ) . Values up t o 10 ,000 T.U. were reached i n t h e Nor the rn Hemisphere i n 1 9 6 3 f o l l o w i n g ex tens ive t e s t i n g i n 1 9 6 - 6 2 (Thatcher and Payne, 1 9 6 5 ) . The t r i t i u m co i i ten t o f p r e c i p i t a t i o n decreased s i g n i f i c a n t l y from 1 9 6 3 t o 1 9 6 8 a s a conse- quence o f t h e moratorium e s t a b l i s h e d f o r t h e exp los ion o f thermonuclear dev ices i n t h e atmosphere. The h i s t o r y o f t r i t i u m i n p r e c i p i t a t i o n i s r e p o r t e d i n F igu re 3 .6-4 .

Most thermonuclear t r i t i u m was depos i ted i n t h e s t ra tosphere . About h a l f of t h e s t r a t o s p h e r i c i n v e n t o r y i s t r a n s f e r r e d t o t h e troposphere i n t h e s p r i n g and summer months o f each year (Brown, 1 9 7 0 ) r e s u l t i n g i n a c o n t i n u i n g seasonal c y c l e o f t r i t i u m p r e c i p i t a t i o n , w i t h maximum i n summer and m i n i m u m i n w i n t e r .

There i s cons iderab le geograph ica l v a r i a t i o n o f t h e t r i t i u m con ten t o f p r e c i p i t a t i o n . Lower va lues occur a t oceanic and c o a s t a l s i t e s than a t c o n t i - n e n t a l s i t e s because t h e ocean serves as a s i n k f o r t r i t i a t e d water (HTO) through i s o t o p i c exchange between t h e atmospheric water vapour and ocean water hav ing low t r i t i u m conten t . Low concent ra t ions occur i n e q u a t o r i a l and south- e r n reg ions as the r e s u l t o f seve ra l f a c t o r s . Most t r i t i u m was re leased i n t h e Nor thern Hemisphere and i s t r a n s f e r r e d from t h e s t ra tosphere t o t h e t roposphere p r e f e r e n t i a l l y a t high l a t i t u d e s . I n a d d i t i o n , t h e h i g h e r p r o p o r t i o n o f ocean sur face i n t h e Southern Hemisphere a.nd t h e high vapour p ressure i n e q u a t o r i a l req ions p rov ide more "washout" and d i l u t i o n . The t r i t i u m con ten t o f p r e c i p i t a - t i o n i n t h e Southern Hemisphere was about one t e n t h t h a t i n t h e Nor the rn Hemisphere i n 1 9 6 3 (See f i g u r e 3 . 6 - 5 ) .

The I n t e r n a t i o n a l Atomic Energy Agency (I.A.E.A.) ( 1 9 6 9 , 1 9 7 0 , 1 9 7 1 , 1 9 7 3 ) pub l i shes da ta on t h e concen t ra t i on o f t r i t i u m i n p r e c i p i t a t i o n c o l l e c t e d a t a l a r g e number o f s t a t i o n s around t h e g lobe, f rom which i t i s p o s s i b l e t o e s t i - mate the t r i t i u m d e p o s i t i o n a t most p laces o f i n t e r e s t .

3.6.2.2 T r i t i u m i n ground water . The t r i t i u m con ten t o f p r e c i p i t a t i o n i s used t o es t imate t h e input o f t r i t i u m t o groundwater systems. Allowance must be made f o r t h e f a c t t h a t recharge i s o f t e n seasona l ly se lec ted . I n vegeta ted areas, most p r e c i p i t a t i o n (and t r i t i u m ) o f t h e growing p e r i o d may be r e t u r n e d t o t h e atmosphere by evapo t ransp i ra t i on . A t semi-ar id s i t e s , l i g h t p r e c i p i t a - t i o n i s evaporated from t h e s o i l b e f o r e i t can i n f i l t r a t e .

I n groundwater s tud ies , t r i t i u m measurements g i v e i n f o r m a t i o n on t h e t ime o f recharge 'Fo t h e system. I n t h e absence o f mix ing , t h e f o l l o w i n g cases ( cons ide red - fo r a Nor thern Hemisphere c o n t i n e n t a l s i t e i n 1 9 7 2 ) can occur:

1. The water has a concen t ra t i on o f 3 T.U. T h i s means t h a t no water younger than 20 years i s p resent . ' T h a t i s , more t h a n 2 0 years a re r e q u i r e d f o r water t o reach the sampling p o i n t From t h e recharge area. T h i s i s t h e case € o r most conf ined aqu i fe rs . P h r e a t i c a q u i f e r s can have low t r i t i u m con ten t due t o (i) very s l i g h t i n f i l t r a t i o n ( a r i d and semi-ar id reg ions ) ; (ii) l o n g pe rco la - t i o n t ime ( low t r a n s m i s s i v i t y , g r e a t depth o f water t a b l e ) ; (iii) age s t r a t i f i c a t i o n o f water below t h e water tab le .

111

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2. The t r i t i u m conten t i s 3-20 T.U. A smal l amount o f thermonuclear t r i t i u m i s present , i n d i c a t i n g most probably water o f t h e f i r s t t e s t per iod , 1954-61 .

3. The t r i t i u m conten t i s >20 T.U. The water o f high t r i t i u m conten t i s obv ious ly o f recen t o r i g i n . If v a r i a t i o n s occur through t h e year and are r e l a t e d t o t h e v a r i a t i o n s i n p r e c i p i t a t i o n over the recharge area, t h e f low-- through i s r a p i d and d i r e c t and t h e t r a n s i t t ime may be evaluated from the t ime- lag i n appearance o f t he annual peaks. t h e v a r i a b i l i t y may a l s o be caused by a seasonal change i n t h e source o f water o r t he r e l a t i v e p ropor t i ons o f water f rom d i f f e r e n t sources, e.g. a t r i t i u m - f r e e water o f deep c i r c u l a t i o n and a young water o f high t r i t i u m content , genera l l y o f a more s u p e r f i c i a l c i r c u l a t i o n .

The fo rego ing i m p l i e s t h a t groundwater remains q u i t e d i s c r e t e l y segregated accord ing t o age d u r i n g t r a n s i t . I n p r a c t i c e , t h i s i s n o t t h e case because o f d i s p e r s i v e e f f e c t s o f t h e g ranu la r a q u i f e r m a t e r i a l . T r i t i u m peaks and t roughs a re smoothed o u t and t h e above g u i d e l i n e s i n d i c a t e per iods r a t h e r than s p e c i f i c years o f recharge. A l l cases may be sub jec t t o m ix ing o f waters o f d i f f e r e n t ages hav ing w ide ly d i f f e r e n t t r i t i u m content . A smal l p o r t i o n o f recen t water combined w i t h a major p o r t i o n o f t r i t i u m - f r e e water may l o o k l i k e cases 1 o r 2 above.

A f u r t h e r c o n d i t i o n i s o f t e n observed: T r i t i u m conten t o f 20-200 T.U. showing no f l u c t u a t i o n and changing o n l y s lowly . Th i s i n d i c a t e s young water w e l l mixed i n t h e a q u i f e r w i t h o l d e r water. The s i z e o f t h e groundwater r e s e r v o i r dampens a l l t h e f l u c t u a t i o n s i n t h e recharge. The system may be t r e a t e d as a "wel l -mixed r e s e r v o i r " showing exponent ia l d ischarge and a Mean Resident Time o f water w i t h i n t h e system est imated ( N i r , 1 9 6 4 ; D incer and Davis, 1 9 6 7 ) .

From t h e fo rego ing d i scuss ion i t can be seen t h a t t he t r i t i u m content o f groundwater i s seldom c o r r e l a t e d i n a s imple way w i t h t h a t o f p r e c i p i t a t i o n . or a q u a n t i t a t i v e i n t e r p r e t a t i o n o f t r i t i u m data, i t i s necessary t o use a mathematical model t h a t i s reasonable f rom t h e hydrogeo log ica l s tandpoint . Then, t h e parameters o f t he model may be ad jus ted t o match t h e t r i t i u m conten t o f p r e c i p i t a t i o n (input f u n c t i o n ) and t h a t o f qroundwater (ou tpu t f unc t i on ) t o o b t a i n va lues o f t h e mean res idence t ime (age) o f t he groundwater.

3.6.3 Carbon iso topes i n the h y d r o l o g i c a l cyc le . Carbon-14 emi ts be ta r a d i - a t i o n w i t h a maximum energy o f 1 5 6 KeV and has a h a l f - l i f e o f 5,730 years. L i k e t r i t i u m , i t occurs as the r e s u l t o f b o t h n a t u r a l and man-made processes. The n a t u r a l p roduc t i on o f carbon-14 by the i n t e r a c t i o n o f cosmic ray-produced neutrons w i t h 14N atoms i n the t o t a l atmosphere i s est imated t o be 2.5 atoms/ cmZ/s (La1 and Suess, 1 9 6 8 ) . The carbon-14 i s then o x i d i z e d t o carbon d iox ide , mixes w i t h t h e carbon d i o x i d e o f t h e atmosphere and en te r t h e g l o b a l carbon cyc le .

The n a t u r a l carbon-14 concen t ra t i on has been demonstrated t o va ry du r ing t h e l a s t seven thousand years o r so by measurements o f t he 1 4 C conten t o f t r e e r i n g s o f t h e Sequoia g iqantea and B r i s t l e c o n e p i n e (Damon e t a l . , 1 9 6 6 ; Suess, 1 9 6 7 ) . However, t he u n c e r t a i n t y t h i s causes i n us ing 1 4 C i n hydro logy i s much smal le r than o t h e r e r r o r s which may a r i s e i n t h i s a p p l i c a t i o n .

The 1 4 C concen t ra t i on i s expressed as a percentage o f t h e modern (pre-- bomb) 1 4 C con ten t o f atmospheric carbon d iox ide . Product ion o f 1 4 C by the de tona t ion o f nuc lea r exp los ives caused the atmospheric 14c concent ra t ion i n the Nor thern Hemisphere t o about double i n 1 9 6 3 . Increases were a l s o observed i n the Southern Hemisphere, but t h e peak va lue was on ly about 6 0 percent above t h e pre-bomb l e v e l . C l e a r l y these v a r i a t i o n s are o n l y o f importance when young waters a re b e i n g measured f o r t h e i r 1 4 C conten t (Olsson, 1 9 6 8 ) .

3.6.3.1 Bas is o f carbon-14 d a t i n g o f groundwater. The use o f 14Ç f o r dat. ing o f groundwater was f i r s t proposed i n 1 9 5 7 (Munnich, 1 9 5 7 ) . I t i s based on the f a c t t h a t s o i l zone carbon d i o x i d e i s o f b iogen ic o r i g i n , r e s u l t i n g from the r e s p i r a t i o n o f p l a n t r o o t s and. p l a n t decay and hence conta ins 1 4 C der ived by p l a n t s f rom the atmosphere. Th is b iogen ic CO2 d i sso l ves i n i n f i l t r a t i n g water and i s c a r r i e d down t o t h e groundwater r e s e r v o i r . I t s 14c content decreases by r a d i o a c t i v e decay and t h e f r a c t i o n o f t he o r i g i n a l remaining i s a

1 1 4

measure o f t h e t ime s ince i t was removed from t h e s o i l zone, i . e . t h e t ime s ince i n f i l t r a t i o n o f the assoc ia ted water. The equat ion which i s a p p l i e d i s :

t (years) = 8270 I n - C

(3.6-3)

where 8270 i s t he mean. l i f e o f 1 4 C i n years, C i s t he i n i t i a l 1 4 C concentra- t i o n and C i s t he 1 4 C concen t ra t i on i n t h e sampfe.

14C i s measured r e l a t i v e t o t h e t o t a l carbon conten t o f t he sample, SO one must consider the o r i g i n o f b o t h the 1 4 C and t h e s t a b l e carbon o f t h e sample. Not a l l o f t h e s t a b l e carbon of groundwater carbonate i s o f t h e same o r i g i n as the 1 4 C . I n f i l t r a t i n g water, con ta in ing carbon d i o x i d e d i sso l ved f rom t h e s o i l zone, d i sso l ves carbonate m ine ra l s i n the s o i l :

- ~ 2 ~ 0 3 7 H C O ~ + H+ ( 3 . 6 - 4 )

C ~ C O ~ + H+ - H C O ~ + Ca++ (3 .6 -5 ) - -

However, t he carbon o r i g i n a t i n g f rom l imestone i n genera l con ta ins no 4C , so t h a t t h e water reach ing t h e water - t a b l e con ta ins -- d i sso l ved carbon ( i n t h e chemical forms' o f H2CO3, HCO3 and CO3 1 w i t h a 1 4 C conten t lower than t h a t p resent i n the s o i l b iogen ic C 0 2 . The e v a l u a t i o n o f t h e d i l u t i o n o f s o i l CO2 o r i g i n a l l y c o n t a i n i n g 1 0 0 percent o f modern 1 4 C w i t h 14C-free carb0na.t.e t o es t imate t h e i n i t i a l 1 4 C concen t ra t i on i n recharge water reach ing the water t a b l e c o n s t i t u t e s t h e most d i f f i c u 1 . t problem i n t h e 1 4 C age determi- n a t i o n o f water.

3.6.3.2 C o r r e c t i n g f o r m i n e r a l carbonates. D i f f e r e n t procedures have been proposed f o r t he eva lua t i on o f t he i n i t i a l 1 4 C concent ra t ion .

O n t he b a s i s o f a l a r g e number o f groundwater 14C: analyses from Europe and A f r i ca , i t appears t h a t o n l y a few samples show more than 90 percent ( r e l a t i v e t o modern) 14C content , and some o f them a re c l e a r l y contaminated by thermo- nuc lear 1 4 C . There i s , on t h e con t ra ry , a l a r g e number o f samples which con ta in 80 t o 90 percent o f 14C;' t he re fo re , a va lue o f 8 5 percent would be a good average f o r t he 1 4 C conten t OF recent , prethermonuclear waters. T h i s va lue ha.s been proposed as t h e i n i t i a l 1 4 C conten t o f carbon d i s s o l v e d i n groundwater (Vogel, 1 9 7 0 ) .

* Another method f o r e v a l u a t i n g t h e i n i t i a l 14C cont.ent o f groundwater uses the d i f f e r e n t 1 3 C / 1 2 C r a t i o s o f b iogen ic CO2 and l imestone, (mean abundance 1 2 C = 98.9%, 1 3 C = 1.1%). The 1 3 C conten t i s measured by mass spectrometry and expressed as p e r m i l l e r e l a t i v e d e v i a t i o n (ô13C0/ , , ) f rom t h e PDB standard (Cra ig, 1957) , which has a 1 3 C / 1 2 C r a t i o c lose t o t h a t o f marine l imestone. I n temperate c l imates , s o i l b iogen ic C 0 2 , de r i ved f rom p l a n t r e s p i r a t i o n and t h e decay o f o rgan ic mat te r , has a ô 1 3 C va lue o f -25 f 3 O / , , , corresponding t o t h a t observed i n l o c a l p l a n t s . I s o t o p i c f r a c t i o n a t i o n on d i s s o l u t i o n o f t h i s CO2 i n water and convers ion t o b icarbonate r a i s e s t h e va lue t o -17 k 3O/,,. Limestone has, i n genera l , a 6 1 3 C va lue o f O f 2,/,,. The ô 1 3 C va lues o f carbon species d i sso l ved i.n groundwater range from -20 t o -5 i n most cases. A s imple p r o p o r t i o n g i ves t h e f r a c t i o n o f b iogen ic carbon p resen t i n a groundwater which corresponds t o t h e f r a c t i o n o f modern 1 4 C p resen t i n groundwater a t t h e t ime o f recharge (Pearson, 1965).

A ?mowledge o f t h e o v e r a l l chemist ry o f t h e system as w e l l as t h e i s o t o p i c composi t ion i s r e q u i r e d i n many isotb$e s tud ies (Pearson and Hanshaw, ' 1 9 7 0 ) . Knowledge-of t h e pH i s necessary t o eva lua te t h e r e l a t i v e amounts o f H2CO3 and HCO3 p resen t and t o take i n t o account t h e i s o t o p i c f r a c t i o n a t i o n occu r r i ng between them.

The e f f e c t of o the r ions, such as sodium a n d magnesium, on t h e carbonate e q u i l i b r i u m cannot be ignored. I n t h e case o f sodium b icarbonate waters, ca lc ium i o n s may have been removed from s o l u t i o n by exchange w i t h t h e sodium o f c l a y minera ls , so p e r m i t t i n g a d d i t i o n a l CaC03 t o be d isso lved. T h i s would then r e s u l t i n more p o s i t i v e ô 1 3 C values.

A d i f f i c u l t y i n a r i d areas o r areas where impor tan t c l i m a t i c changes may have occurred s ince t h e t ime o f i n f i l t r a t i o n o f water i s our l i m i t e d knowledge

115

o f t h e c l i m a t i c c o n d i t i o n e f f e c t on *he i s o t o p i c composi t ion o f vege ta t i on (and consequently o f t h e s o i l CO*). A t present, t h e r e a r e r e l a t i v e l y few pub- l i s h e d data f o r p l a n t s i n a r i d reg ions, but ô 1 3 C values o f about - 1 2 O / , , a re non uncommon. Th is may a f e c t s t r o n g l y t h e e v a l u a t i o n o f t h e i n i t i a l 1 4 C con ten t based on 1 3 C values.

The p o s s i b i l i t y o f exchange o f 1 4 C between the d i s s o l v e d b icarbonate and t h e carbonates o f t h e m a t r i x o f t h e a q u i f e r m a t e r i a l has been recognized ( T h i l o and Munnich, 1 9 7 0 ) . However, i t appears t h a t t h i s e f f e c t i s sma l l i n nature f o r waters which have n o t been submit ted t o h i g h temperatures. For thermal waters t h e r e i s some evidence € o r exchange w h i c h , t h e r e f o r e , r e q u i r e s t h a t i n t e r p r e t a t i o n o f 1 4 C da ta be t r e a t e d w i t h cau t i on i n such cases.

3.6.3.3 A p p l i c a b i l i t y . The 14C method can be used f o r waters younger than 30,000 years. I n general , i t i s a p p l i e d t o study t h e movement o f water i n con f ined a q u i f e r s . Where recharge occurs o n l y i n t h e ou tc rop area and t h e water chemis t ry and i s o t o p i c composi t ion o f d i s s o l v e d carbon species are r e l a t i v e l y un i fo rm, t h e age d i f f e r e n c e s i n space a re a f f e c t e d by the u n c e r t a i n t i e s which a f f e c t t h e abso lu te age de terminat ion o f water. Thus , i t i s p o s s i b l e t o determine t h e f low v e l o c i t y o f water by determin ing the age d i f f e r e n c e s between two sampling p o i n t s separated by a known d is tance. Th is p rov ides a h y d r o l o g i s t w i t h an es t imate o f t he mean r e g i o n a l p e r m e a b i l i t y .

14c measurements may a l s o g i v e i n f o r m a t i o n on m i x i n g processes o f waters o f d i f f e r e n t ages w i t h i n a g i ven a q u i f e r .

3.7 Appendices

3.7.1 Concent ra t ion u n i t s and conversion f a c t o r s (Appendix I ) .

Terms and symbols: w t = we igh t

gm = gram

d = d e n s i t y o f s o l u t i o n (gms/cm3)

ppm = p a r t s p e r m i l l i o n

mg/R = m i l l i g r a m s p e r l i t e r

gew - gram e q u i v a l e n t we igh t

gfw = gram formula weight

epm = equ iva len ts p e r m i l l i o n

meq/k = m i l l i g ram-equ iva len ts p e r l i t e r

m = m o l a l i t y

M = m o l a l j - t y

m o l / & = m i l l i m o l e s !M x l o 3 ) p e r l i t e r

U n i t s : A s o l u t e i s an i o n i c o r molecular species d i s s o l v e d i n water. A l l u n i t s g i ven a re o f t he s o l u t e un less o therw ise i nd i ca ted .

ppm = w t / ï 0 6 w t u n i t s o f water

mg/k = m g / l i t e r o f s o l u t i o n

116

gew = g€w/valence

epm = ppm/gew

meqlt = (mg/a) /gew

moles = gmsjgfw

m = moles/ l03 gms o f water

M = m o l e s / l i t e r o f s o l u t i o n

m = - [wt s o l u t i o n ) / ( w t s o i t u i o n - w t so lu tes ) I d

ppm = [ ( w t s o l u t i o n ) / w t s o l u t i o n - w t so lu tes ) 1

m = p p m / g f w x 1 0 3 = epm/valence x l o 3

~~

Si02

~ i 3 +

Fe 2+

Fe 3+

Mn 2+

Mn '+ Ca2+

Mg2+

Sl-2+

K+

H+

Na+

- HCO 3

CO 3 2'

s o p -

c1- -

F

Nog-

POL, 3'

6 0 .O8

26.98

55.85

11

54.94

II

40 .O8

2 4 . 3 1

87.62

22 .99

39.10

1 .O08

6 1 .O2

60 . O 1

96 .O6

35.45

19.00

6 2 . O 1

94.97

--- 8.99

27.93

18 .62

27.47

13 .74

20.04

12 .16

4 3 . 8 1

22.99

39.10

1 .O08

6 1 .O2

3 0 . O 1

48 .O3

35.45

1 9 .O0

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31.66

--- O . 1112

O .O3581

O .O5372

O .O3640

O .O7281

O .O4990

O .O8224

O , 02282

O .O4350

O .O2558

O . 9 9 2 1

O .O1639

O . 03333

O .O2082

O .O2820

O .O5263

O .O1613

O .031.59

117

3 . 7 . 2 Tables o f water analyses (Appendix II). Chemical analyses o f sea water, and some carbonate groundwaters f rom Mexico, N o r t h A f r i c a , Syr ia , Tun is ia , and t h e U n i t e d States. S p e c i f i c conductance ( U ) i s i n micromhos a t 25OC. Values o f pH marked w i t h an a s t e r i s k were probably measured i n t h e l abo ra to ry , and as such a re o f d o u b t f u l s i g n i f i c a n c e . S I and S I a re the s a t u r a t i o n i n d i c e s o f c a l c i t e and do lomi te (see t e x t ) . measured i n t h e l a b o r a t o r y r a t h e r than the f i e l d and lo r temperatures have been assumed, va lues o f S I and S I a re o f quest ionable s ign i f i cance . Computer c a l c u l a t i o n o f ' ~ 0 2 , S I c and B I d was done assuming t h e presence o f i o n p a i r s .

Wfiere corqesponding pH values were

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4 . Hydrology of carbonate areas

4 . 1 I n t r o d u c t i o n (Harry E. LeGrand)

The genera l p h y s i c a l laws and p r i n c i p l e s o f hydro logy apply t o b o t h porous granu lar m a t e r i a l s , such as sarids, and t o carbonate rocks. Yet carbonate rocks t h a t have been k a r s t i f i e d tend t o have some unique h y d r o l o g i c features. There i s l i t t l e agreement as t o what i s a t y p i c a l o r average charac ter f o r many fea tures o f carbonate rocks, as i l l u s t r a t e d as fo l l ows : i n k a r s t areas; bare rock and th in s o i l s a re common, but so a re t h i c k s o i l s ; ve ry h i g h l y permeable l imestones a re common, but so a r e p o o r l y permeable ones; and rugged k a r s t topographic fea tu res w i t h u n d e r l y i n g s o l u t i o n caverns a r e common, but so a re f l a t , n e a r l y fea tu re less topographic cond i t i ons . I t f o l l o w s t h e r e f o r e t h a t some cond i t i ons o f carbonate te r ranes a re s u i t a b l e t o man's needs and i n t e r - es ts , such as t h e use o f some permeable a q u i f e r s as sources o f water supply and the e x p l o i t a t i o n o f caves f o r tour ism, w h i l e o t h e r s p resen t many problems inc lud ing : p e r m e a b i l i t y t o o low f o r adequate water supply o r so high w i t h a p o s i t i o n above t h e main zone o f s a t u r a t i o n t h a t t h e a q u i f e r r e t a i n s t o o l i t t l e water f o r use during pe r iods o f f a i r weather, s o i l s t o o th in f o r growing o f crops and f o r adequate f i l t r a t i o n o f wastes near t h e ground sur face, i n s t a b i l i t y o f t h e ground f o r b u i l d i n g s and foundat ions i n areas prone t o s inkhole development, and unusua l l y rugged topography. Some o f t h e many v a r i a b l e cond i t i ons a re r e a d i l y observable, but o the rs can be determined o n l y by c a r e f u l geo log ic and h y d r o l o g i c s tud ies i n c l u d i n g s tud ies o f r u n o f f , d ischarge and i n f i l t r a t i o n .

4.2 Runoff and d ischarge (B. I . Kude l in )

4.2.1 Runoff and d ischarge c h a r a c t e r i s t i c s i n k a r s t i c areas. Runoff f rom k a r s t areas i s descr ibed i n t h e same way as r u n o f f f rom non-karst areas. D e s c r i p t i v e terms inc lude: mean long-term annual r u n o f f f o r a p a r t i c u l a r year, maximum, and m i n i m u m discharges.

The most impor tan t c h a r a c t e r i s t i c s o f t h e h y d r o l o g i c a l regime o f a r i v e r bas in are:

- - runof f c o e f f i c i e n t , i . e . t h e r a t i o o f amount o f r u n o f f t o t h e amount o f p r e c i p i t a t i o n i n t h e r i v e r bas in;

-- long-term v a r i a t i o n s o f r u n o f f , determined by means o f d i s t r i b u t i o n curves ;

--annual d i s t r i b u t i o n o f streamflow c o e f f i c i e n t , r u n o f f c o n t r o l b e i n g one o f i t s p r i n c i p a l i nd i ces , i .e . r a t i o o f t h e hydrograph area f o r t h e r i v e r below mean d ischarge t o t h e t o t a l area o f t he hydrograph. The i n f l u e n c e o f k a r s t on r u n o f f i s p r i n c i p a l l y govefned by t h e f o l l o w i n g

p e c u l i a r i t i e s : 1. Considérable d ischarge i n t o k a r s t depressions, r a p i d t rans fo rma t ion o f t h e

over land f l o w i n t o subsurface f low, and an i n tense i n f i l t r a t i o n o f p r e c i p - i t a t i o n through t h e unsatura ted zone, r e s u l t i n g i n decreases of l osses by evaporat ion and t r a n s p i r a t i o n .

2. Close r e l a t i o n s h i p between r i v e r and groundwater cha rac te r i zed by abrupt losses o f stream i n t o f i s s u r e s and ponors t o recharge groundwater, and equa l l y abrup t discharges o f groundwater back i n t o t h e sur face f l o w system.

3. Movement o f groundwater across t h e l i n e s marking sur face water d i v ides . Such movement may a c t t o inc rease o r decrease t h e d ischarge from a bas in , depending on whether groundwater i s . m o v i n g i n t o o r l e a v i n g t h e bas in .

1 3 1

I n many areas, groundwater i n f l o w i n t o r i v e r s i s more s i g n i f i c a n t than ove r land f low. Moreover, t h e r e l a t i v e importance o f ground-water and surface-water f l o w may change f r e q u e n t l y w i t h i n s h o r t d is tances even where bas ins r e c e i v e r e l a t i v e l y even ly d i s t r i b u t e d amounts o f p r e c i p i t a t i o n .

K a r s t may a f f e c t surface and subsurface waters o f a r i v e r b a s i n i n d i f - f e r e n t ways. A nega t i ve k a r s t e f f e c t on r i v e r r u n o f f i s a decrease i n ca lcu- l a t e d expected runo f f due t o losses o f surface water by i n f l o w i n t o k a r s t c a v i t i e s and by groundwater moving across l i n e s o f sur face drainage d i v i d e s i n t o ad jacent bas ins o r i n t o deep aqui fers . A p o s i t i v e k a r s t e f f e c t on r i v e r r u n o f f i s an inc rease i n stream f low: t h i s may be due t o groundwater resurgence from o u t s i d e t h e drainage bas in, and decreased evapora t ive and t r a n s p i r a t i v e losses w h i l e i n t h e subsurface. P o s i t i v e and negat ive k a r s t e f f e c t s are recognized most f requen t l y i n smal l ( l e s s than 1000 km2) bas ins i n mountainous areas. I n l a r g e bas ins t h e p o s i t i v e and nega t i ve k a r s t e f f e c t s tend t o compensate each o the r .

Streams t h a t r e c e i v e l a r g e amounts of recharge from groundwater sources i l l u s t r a t e one o f t h e r e s e r v o i r e f f e c t s of groundwater i n storage o r t r a n s i t i n k a r s t i c ter ranes. The maximum r u n o f f o f such streams i s l e s s than t h e maximum runof f o f s i m i l a r non-karst streams, and t h e i r m i n i m u m i s g rea te r .

The q u a n t i t a t i v e c h a r a c t e r i s t i c o f t he k a r s t e f f e c t on stream r u n o f f i s c a l c u l a t e d by comparing a c t u a l r u n o f f values o f k a r s t r i v e r s w i t h app rop r ia te zonal values. I n t h i s case "zona l runoff ' ' means r u n o f f t y p i c a l o f non -ka rs t i c bas ins w i t h s i m i l a r phys iog raph ica l features. Zonal r u n o f f may be e s t a b l i s h e d from water balance s tud ies as be ing t h e d i f f e r e n c e between p r e c i p i t a t i o n and evapo t ransp i ra t i on ( p o t e n t i a l and c l i m a t i c runo f f ) , o r i t may be es t imated by analogy w i t h an ad jacent non-karsted b a s i n o f s i m i l a r physiography.

I f i t i s imposs ib le t o l o c a t e a completely analogous area, zonal r u n o f f i s approximated from r e g i o n a l parameters such as p r e c i p i t a t i o n , snow storage, mean e l e v a t i o n o f t h e r i v e r bas in, e tc . , and the drainage area. For example, on the b a s i s o f data from non-ka rs t i c streams, i t i s p o s s i b l e t o e s t a b l i s h the depend- ence o f maximum s p e c i f i c d ischarge ('max) upon the drainage area:

( 4 -2-1)

where ô 1 and 6 2 are c o r r e c t i o n f o r percentages o f lakes, f o r e s t s , and swamps i n

are computed f o r t he k a r s t i c streams and 6 1 ô 2 t he bas in. Subsequently, va lues

are compared w i t h zonal r u n o f f f o r t h e eva lua t i on o f t he k a r s t e f f e c t . The r a t e and na tu re o f k a r s t e f f e c t on d i f f e r e n t r u n o f f c h a r a c t e r i s t i c s i s

revea led i n d i f f e r e n t ways; t h e r e f o r e the eva lua t i on o f t h i s e f f e c t should be made r e l a t i v e t o a l l p r i n c i p a l h y d r o l o g i c a l parameters.

When s tudy ing surface-water discharge from k a r s t i c basins, i t i s e s s e n t i a l t o eva lua te t h e groundwater discharge a t t he same t ime. The volume o f t he groundwater recharge t o sur face streams may be d e r i v e d by standard methods o f a n a l y s i s o f base f l o w on graphs o r by means of water balance computation. H y d r o l o g i c a l i n d i c e s o f t he i n t e n s i t y o f ground-water i n f l o w i n t o streams a re o f i n t e r e s t i n t h e study o f t he k a r s t percentage i n the b a s i n and the i n t e n s i t y o f k a r s t processes. [EDITOR'S NOTE: The reader i s d i r e c t e d t o Ozis, 1976, and Gravpe, I s a i l o v i c , and Yevjevich, 1976, f o r mathematical methods o f a n a l y s i s o f r u n o f f i n k a r s t terra-nes. I

4.2.2 R e l a t i o n between r u n o f f and p r e c i p i t a t i o n . Ana lys i s o f r e l a t i o n s between r u n o f f and p r e c i p i t a t i o n i s e s s e n t i a l t o t h e e v a l u a t i o n o f water regimes o f k a r s t areas and t h e computation and f o r e c a s t i n g o f t h e i r discharge.

T o t a l s a t u r a t i o n o f a r e g i o n determines i t s t o t a l annual r u n o f f , and t h e na tu re and t ype o f temporal d i s t r i b u t i o n of p r e c i p i t a t i o n determines the b a s i c p e c u l i a r i t i e s o f sur face and subsurface f low i n t h e k a r s t basin, and conse- q u e n t l y t h e laws o f r i v e r r u n o f f format ion a re c l o s e l y connected w i t h t he development o f k a r s t processes. For example, t he exposure o f bare (open) k a r s t as t h e r e s u l t o f s t r i p p i n g of t h e t o p cover may r e s u l t i n t h e subsequent decrease o f t h e over land f low. I t may a l s o inc rease r u n o f f i f k a r ç t i f i c a t i o n does n o t p r o v i d e e a s i l y recharged pe rmeab i l i t y . I t c o u l d a l s o dep le te the

1 3 2

groundwater storage c a p a b i l i t y where t h e r e g o l i t h i s h y d r a u l i c a l l y connected t o a c a v i t y system.

When computing and f o r e c a s t i n g stream r u n o f f f rom k a r s t bas ins i t i s e s s e n t i a l t o determine a p l u v i o m e t r i c l i m i t o f r u n o f f fo rmat ion , which ind i - cates t h e min imum amount o f e f f e c t i v e p r e c i p i t a t i o n .

Re la t i onsh ips between r u n o f f and p r e c i p i t a t i o n i n k a r s t reg ions may d i f f e r due t o p e c u l i a r i t i e s o f r u n o f f f o rma t ion (main ly due t o i n t e r r e l a t i o n s between sur face and subsurface f l o w ) , and r e g u l a t i n g c a p a c i t y o f k a r s t c a v i t i e s . Great v a r i a t i o n s o f losses o f sur face f l o w by k a r s t depressions a re respons ib le f o r d i s t u r b i n g r e l a t i o n s between r u n o f f and p r e c i p i t a t i o n .

Where t h e k a r s t i f i e d carbonate sequence i s t h i c k (measured i n 100's o f meters) and where t h e volume o f subsurface c a v i t i e s i s l a rge , t h e r e s e r v o i r e f f e c t o f t h e groundwater i n s to rage may c a r r y over from season t o season o r from year t o year. As t h e r e s e r v o i r e f f e c t increases, streamflow r e a c t s l e s s and l e s s d i r e c t l y t o p r e c i p i t a t i o n and r u n o f f - p r e c i p i t a t i o n r e l a t i o n s h i p s may be p r a c t i c a l l y imposs ib le t o e s t a b l i s h from shor t - te rm records. Fo r example , r u n o f f from heavy storms o c c u r r i n g a f t e r a d r y season may a l l go t o recharg ing the k a r s t groundwater r e s e r v o i r and r e s u l t i n l i t t l e o r no stream discharge. I n c o n t r a s t , a f t e r a wet season even a sma l l storm may produce cons iderab le stream f low.

Re la t i onsh ips between r u n o f f and p r e c i p i t a t i o n may be determined by means o f graph analyses f o r d i f f e r e n t t ime i n t e r v a l s (day, 10 days, month, year) and f o r i n d i v i d u a l storms. The r e l i a b i l i t y o f t h e r e s u l t s may be e s t a b l i s h e d by c o r r e l a t i o n c o e f f i c i e n t s . I n k a r s t areas i t i s u s u a l t o observe c l o s e r e l a t i o n s between r u n o f f f o r a p a r t i c u l a r year and ha l f -annua l p r e c i p i t a t i o n va lue f o r t h e g i ven and preced ing years o r between consecut ive means o f r u n o f f and p r e c i p i t a t i o n f o r 2 o r 3 years.

4.2.3 Roles o f o t h e r f a c t o r s .

4.2.3.1 Over l y ing deposi ts . The presence o f sur face depos i t s and s o i l regu- l a t e s t h e d i s t r i b u t i o n o f i n f i l t r a t i o n and i n f l o w i n t o k a r s t and f i s s u r e d rocks, which slows and reduces t h e r a t e and e x t e n t o f k a r s t development. The e x t e n t o f i n f l u e n c e o f t o p s o i l s on k a r s t development and on r i v e r r u n o f f i s a f a c t o r o f t h e i r t h i ckness and p e r m e a b i l i t y . Low p e r m e a b i l i t i e s o f t o p depos i t s reduce i n f i l t r a t i o n r a t e s and increase t h e volume o f over land f low. H i g h l y permeable t o p s o i l s p e r m i t i n t e n s i v e i n f i l t r a t i o n r a t e s and f a v o r t h e develop- ment o f v a r i o u s forms o f sur face k a r s t . I n t h e absence o f t o p depos i ts , i . e . i n case o f open k a r s t depressions, r a i n f a l l and snowmelt waters a re absorbed by k a r s t format ions, and sur face r u n o f f may n o t occur even i n sma l l areas o f t he bas in.

The accumulation of h i g h l y permeable t o p depos i t s i n r i v e r v a l l e y s i n k a r s t e d bas ins causes the fo rmat ion o f k a r s t strea.ms under the channel, cha.rac- t e r i z e d by t h e recharge t o t h e a q u i f e r due t o water losses from r i v e r s . Such streams may cause l o n g i t u d i n a l changes of r i v e r r u n o f f , i . e . decrease o f channel f l o w on the reaches o f water losses and sudden increase o f d ischarge a t t he s i t e s o f o u t f l o w o f a q u i f e r waters.

P l u v i o m e t r i c l i m i t o f r u n o f f i n k a r s t r i v e r bas ins i s ma in l y determined by p e c u l i a r i t i e s o f t h e development o f t o p depos i t s and t h e i r l i t h o l o g y , s ince these depos i t s produce a c e r t a i n r e g u l a t i n g e f f e c t on t h e d ischarge o f r a i n f a l l and snowmelt water. Therefore, i n t h e a n a l y s i s o f r e l a t i o n s between r u n o f f and p r e c i p i t a t i o n f o r k a r s t i c bas ins i t i s necessary t o cons ider t h e t o t a l r e g u l a t - ing e f f e c t upon r u n o f f f rom k a r s t fo rmat ions and t o p s o i l s .

4.2.3.2 Vegetat ion. Vegeta t ion has an i n d i r e c t i n f l u e n c e upon t h e r u n o f f regime o f t h e k a r s t bas in. I n general , f o r e s t cover tends t o inc rease r e - charge. The v e g e t a t i v e cover c o n t r i b u t e s t o t h e r e g u l a t i o n o f d ischarge by changing s o i l p r o p e r t i e s and thus i n c r e a s i n g i n f i l t r a t i o n r a t e s and waterhold- ing capac i t i es . i t a l s o a c t s t o p r o t e c t t h e t o p depos i t s and t o p s o i l aga ins t water eros ion. T r a n s p i r a t i o n by p l a n t s inc reases mo is tu re d ischarge f rom t h e unsatura ted zone and decreases t o t a l runo f f f rom t h e bas in. [EDITOR'S NOTE: The reader i s r e f e r r e d t o C o l v i l l e and Holmes, 1 9 7 2 and Set te rgreen and Boehm, 1972, f o r s i t e s tud ies on t h e e f f e c t o f p l a n t cover on r u n o f f and groundwater recharge i n k a r s t reg ions. ]

1 3 3

The e f f e c t o f t he vege ta t i ve cover on t h e water regime o f k a r s t bas ins i s d i f f e r e n t under d i f f e r e n t phys iographic cond i t ions . I n mountain areas where f o r e s t p l a n t s have a wel l -developed r o o t system t h e e l u v i a l cover tends t o be f i x e d and p r o t e c t e d from eros ion, thus making i n f l o w o f r a i n f a l l and snowmelt waters t o t h e subsurface more d i f f i c u l t and inc reas ing r u n o f f . I n p l a i n s and lowlands the e f f e c t o f vege ta t i ve cover i s ma in l y t o i n t e n s i f y t h e i n f i l t r a t i o n r a t e s by inc reas ing s o i l pe rmeab i l i t y . Thus t h e r a t e o f k a r s t i f i c a t i o n and the i n f l u e n c e o f t h e k a r s t i c f ea tu res on t h e water regimen are increased. Evalu- a t i o n o f t h e f o r e s t e f f e c t on k a r s t development requ i res cons ide ra t i on o f t he i n f l u e n c e o f f o r e s t l i t t e r as t h e source o f carbonic and humic ac ids c a r r i e d by t h e i n f i l t r a t i n g waters. Rates o f co r ros ion tend t o be h i g h a t t h e i n t e r f a c e between t h e l i t t e r and t h e u n d e r l y i n g carbonate rocks and between the over- burden and the u n d e r l y i n g carbonate rocks i f the overburden i s n o t t o o t h i c k .

To determine the vege ta t i on e f f e c t on t h e water regime o f k a r s t rocks i t i s e s s e n t i a l t o c o l l e c t da ta on t h e vege ta t i on types i n t h e bas in , t h e percent- age o f f o r e s t area, e t c .

4.2.3.3 Topography. The i n f l u e n c e o f topography on the r u n o f f i n k a r s t bas ins i s most c l e a r l y seen when comparing t h e c h a r a c t e r i s t i c s o f stream regimens i n mountain and p l a i n areas.

I n mountain areas, t h e u n d e r l y i n g sur face and subsurface bas ins do n o t necessa r i l y co inc ide , and groundwater may move i n t o o r o u t o f t h e area beneath a sur face drainage bas in . Favorable cond i t i ons f o r deep i n f i l t r a t i o n ( i n f l o w ) o f water w i t h subsequent movement i n t o lower bas ins can be respons ib le f o r decreases i n stream r u n o f f . These e f f e c t s increase i n v a r i a b i l i t y and i n t r i - cacy more o r l e s s d i r e c t l y w i t h i n c r e a s i n g l y complex g e o l o g i c a l s t ruc tu re . [EDITOR'S NOTE: The reader i s r e f e r r e d t o Konikow, 1969, f o r an i n v e s t i g a t i o n o f mountain r u n o f f and i t s r e l a t i o n t o p r e c i p i t a t i o n , groundwater, and recharge t o a carbonate aqu i fe r . ]

Surface k a r s t f ea tu res are b e s t e x h i b i t e d on p la teaus and lowlands. They are cha rac te r i zed by i n t e n s i v e absorp t ion o f sur face r u n o f f under t h e i n f l u e n c e o f k a r s t e v o l u t i o n , h i g h l y i r r e g u l a r p a t t e r n s o f stream f low, and long-term, annual o r longer , response o f stream f l o w t o p r e c i p i t a t i o n .

The e l e v a t i o n e f f e c t o f topography, p a r t i c u l a r l y a t h ighe r e leva t i ons , on r u n o f f i n and o u t o f k a r s t areas r e q u i r e s cons ide ra t i on o f c l i m a t i c f a c t o r s such as t h e orographic e f f e c t on p r e c i p i t a t i o n , v e g e t a t i o n a l changes w i t h a l t i t u d e , e t c . V a r i a t i o n s i n p r e c i p i t a t i o n a re most s i g n i f i c a n t because they determine the r a t e o f k a r s t e v o l u t i o n and k a r s t e f f e c t on r u n o f f .

The r o l e o f topography i n k a r s t bas ins should be considered i n combination w i t h o t h e r f a c t o r s , such as g e o l o g i c a l s t ruc tu re , e t c . Therefore, geomorpho- l o g i c a l i n v e s t i g a t i o n s made i n the f i e l d a re o f g r e a t importance p r o v i d i n g an understanding o f t he l o c a l water regime.

4.3 I n f i l t r a t i o n (Habib Zeb id i )

A f t e r r a i n f a l l s on a k a r s t t e r r a i n , i t i s common t o see t h e ove r f l ow ing o f spr ings and o f t h e ve ry smal les t seepages whose discharge increase g r e a t l y and which a re q u i c k l y t ransformed i n t o impetuous t o r r e n t s d ischarg ing water i n many p laces. Th is i n d i c a t e s t h e importance and t h e r a p i d i t y o f i n f i l t r a t i o n i n k a r s t .

4 .3 .1 I n f i l t r a t i o n c h a r a c t e r i s t i c s o f k a r s t t e r r a i n . K a r s t t e r r a i n s show a preponderance o f la rge-sca le p e r m e a b i l i t y i n the form o f f i s s u r e s , f a u l t s , and j o i n t s , which favo r i n f i l t r a t i o n ; hence evaporat ion and r u n o f f a re s t r i c t l y l i m i t e d .

Two types o f i n f i l t r a t i o n may be i d e n t i f i e d : --A type . o f i n f i l t r a t i o n which can be c lassed as normal and which i s o f

importance f o r t h e g rea te r number o f l imestone outcrops. --An i n f i l t r a t i o n l o c a t e d i n the beds o f c e r t a i n streams, o r i n an extreme

case where a whole r i v e r i s engu l fed i n a Ponor (swal low h o l e ) . The i n f i l t r a t i o n depends a l s o on t h e p r e c i p i t a t i o n , on i t s annual amount,

i t s seasonal d i s t r i b u t i o n , and above a l l on i t s i n t e n s i t i e s ; o n l y r a r e l y i s t he i n f i l t r a t i o n capac i t y o f a k a r s t fo rmat ion l e s s than the i n t e n s i t y o f the p r e c i p i t a t i o n . I n t h i s respec t , snow i s more favorab le f o r i n f i l t r a t i o n s ince

1 3 4

i t s g radua l m e l t i n g does n o t exceed t h e i n f i l t r a t i o n capac i t y o f t h e k a r s t and a l s o because i t s m e l t i n g a t t h e end o f w i n t e r de lays t h e onset o f drying-up.

The i n f i l t r a t i o n i s a l s o i n f l u e n c e d by t h e topography, i n c l u d i n g t e c t o n i c e f f e c t . A young topography favo rs normal i n f i l t r a t i o n compared w i t h a matured topography where t h e r e a re p o s s i b i l i t i e s o f b e n e f i t i n g f rom l a r g e r l o c a l i z e d i n f i l t r a t i o n .

4 .3 .2 Re la t i onsh ip o f p r e c i p i t a t i o n t o i n f i l t r a t i o n and r a t e o f i n f i l t r a t i o n . The importance o f i n f i l t r a t i o n i n k a r s t as compared w i t h evaporat ion and r u n o f f emphasizes t h e importance o f t h e p r e c i p i t a t i o n - i n f i l t r a t i o n r e l a t i o n s h i p and the i n f i l t r a t i o n r a t e de r i ved therefrom. The methods used can be va r ied , SO t h a t i t i s u s e f u l t o i d e n t i f y and d iscuss some methods t h a t have been used. [EDITOR'S NOTE: The reader i s r e f e r r e d t o V i l imonov ic , 1 9 6 8 , f o r d e t a i l s o f a method o f c a l c u l a t i n g t h e r a t e o f i n f i l t r a t i o n i n a k a r s t area.]

4 .3 .2 .1 Seasonal r a t e o f i n f i l t r a t i o n .

Case o f D y r e l Kef , T u n i s i a (H. Schoe l le r , 1 9 4 8 ) -- The s t r u c t u r e here i s a perched sync l i ne o f Eocene l imestones cover ing an area o f 5.8 km2, complete ly bare and w i t h on l y one d ischarge p o i n t , t he Kef Spr ing.

Since p r e c i p i t a t i o n occurs i n we l l -de f i ned seasons, H. Schoe l le r has determined t h e r a t e o f i n f i l t r a t i o n r e l a t i v e t o t h e r a i n f a l l cyc les by r e l a t i n g the y i e l d o f t he d ischarge p o i n t t o t h e r a i n o f t he corresponding p e r i o d (see Table 4.3-1) .

The author draws a t t e n t i o n t o t h e g r e a t v a r i a t i o n i n t h e r a t e o f i n f i l t r a - t i o n ( 3 0 percent t o 90 percent ) , a v a r i a t i o n which i s a f u n c t i o n n o t o n l y o f t he amount o f r a i n f a l l but a l s o o f t he i n t e n s i t y o f t h e p r e c i p i t a t i o n and t h e s t a t e o f t h e groundwater reserves a t t he end o f t h e dry season; hence i t i s p r e f e r a b l e t o determine t h e r a t e o f i n f i l t r a t i o n f o r seve ra l years i f one wishes t o have a r e l i a b l e s p e c i f i c c o e f f i c i e n t .

4.3.2.2 Annual i n f i l t r a t i o n f a c t o r .

Case o f D j . Chennata, Den Saidane and Zaghouan, Tun is ian (J. T i xe ron t , E. B e r k a l o f f , A. Gaine and E. Manduech, 1 9 5 1 ) -- A t t e n t i o n i s concentrated here on the annual p r e c i p i t a t i o n on t h r e e s t ruc tu res : t he f i r s t i s a monocl ine o f Senonian l imestones, t h e o t h e r two a re h o r s t s o f Ju rass i c l imestone. The r a t e o f i n f i l t r a t i o n (see Table 4.3-2) i s determined by r e l a t i n g t h e annual p r e c i p i t a t i o n (here g i ven i n r e l a t i o n t o t h e s t a r t and t h e end o f t h e r a i n s , t h a t i s t o say i n a g r i c u l t u r a l years) t o t h e q u a n t i t a t i v e va lue o f t h e d ischarge p o i n t s which i s cons idered as equated w i t h t h e i n f i l t r a t i o n .

Other Cases o f A n n u a l Rate o f I n f i l t r a t i o n -- Numerous o t h e r examples o f annual i n f i l t r a t i o n r a t e s f o r a l l p a r t s o f t h e w o r l d a re i n the, l i t e r a t u r e , so we r e f e r o n l y t o some o f s p e c i a l i n t e r e s t w i t h i n t h e Mediterranean bas in :

Morocco B o l e l l i ( 1 9 5 1 ) has found i n f i l t r a t i o n r a t e s l i s t e d i n t a b l e 4.3-3 € o r t h e P l io -P le is tocene l imestones.

Greece Aronis , Burdon and Z e r i s ( 1 9 6 1 ) ha.ve c a l c u l a t e d t h a t f o r a b a s i n o f 96 km2 the l imestones feed ing t h e group o f spr ings a t L i l a i a have an i n f i l t r a t i o n r a t e o f 51.6 percent , i n a r e g i o n where t h e average annual p r e c i p i t a t i o n i s 1,400 mm.

4.3.2.3 Average i n f i l t r a t i o n r a t e . Since i n t e r e s t i n t h e i n f i l t r a t i o n r a t e i s r e l a t e d t o t h e way i n which i t he lps t o f a c i l i t a t e t h e c a l c u l a t i o n o f t h e o rde r o f magnitude o f t h e i n f i l t r a t i o n , i t i s impor tan t t o g e t as c lose as p o s s i b l e t o t h e average r a t e o f i n f i l t r a t i o n and so t o e l i m i n a t e c e r t a i n r e s t r i c t i v e elements a l ready mentioned, which concern t h e i n t e n s i t y o f t h e p r e c i p i t a t i o n and the s i t u a t i o n o f t h e reserves o f groundwater a t t he end o f t h e dry season.

The s imp les t method i s t o average t h e annual r a t e s o f i n f i l t r a t i o n which have been obtained, but t h i s does n o t remove any e r r o r a r i s i n g f rom t h e s t a t e o f t he groundwater reserves a t t he end o f t h e dry season. I t i s f o r t h i s

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Table 4.3-1 - C o r r e l a t i o n o f p r e c i p i t a t i o n amounts and i n f i l t r a t i o n r a t e s a t D y r e l Kef, Tun is ia (Schoel ler , 1 9 4 8 ) .

Y i e l d o f t h e Y i e l d Expressed Amount o f Pe r iod o f Discharge as Thickness R a i n f a l l i n I n f i l t r a t i o n Rain f a 11 P o i n t (m3) o f Water (mm) Pe r iod (mm) Rate ( % )

l/ 1 / 2 7 - 1 0 / 1 2 / 2 7 9 0 5 , 484

1 0 / 1 2 / 2 7 - 1 0 / 1 1 / 2 8 2,094,925

1 0 / 1 1 / 2 8 - 1 / 1 0 / 2 9 3 ,260 ,011

1 / 1 0 / 2 9 - 1 / 1 2 / 3 0 2,610,930

1 / 1 2 / 3 0 - 2 0 / 1 1 / 3 1 2,441,372

2 0 / 1 1 / 3 1 - 1 2 / 2 / 3 2 3,160,738

l o / 2 / 3 3 - 2 0 / 1 1 / 3 3 1,567,586

2 0 / 1 1 / 3 3 - 1 0 / 1 0 / 3 4 2,617,209

1 5 4

356

5 5 4

444

415

5 3 7

266

445

463.5 33.2

643.0 55.4

616 . O 90.0

633 .6 70 .2

513.7 80.8

676.6 79.5

348.2 76.4

606.0 73.6

1 3 6

Table 4.3-2 - I n f i l t r a t i o n r a t e s from a study i n Tun is ia , T i xe ron t , e t a l , 1 9 5 1

D j . Chounata D j . Ben Saidane D i . Zaghouan Amount o f Measure Rain I n f i l t Rate Rain I n f i l t Rate R a i n I n f i l t Rate

m m % mm mm % mm mm %

1 9 4 5 -4 6 5 7 9 1 8 8 3 3 3 3 5 7 0 2 1 304 5 0 1 6

1946-47 7 2 1 3 8 2 5 3 3 0 0 O O 3 7 3 100 30

1947-48 7 8 0 2 1 6 3 7 4 8 3 70 1 4 4 2 2 1 8 5 43

1948-49 6 1 7 2 7 6 44 7 5 2 390 5 1 7 0 6 3 4 5 49

1949-50 6 6 9 257 3 8 4 9 1 1 2 2 5 1 1 5 0 --

Table 4.3-3 - I n f i l t r a t i o n r a t e s i n Morocco, from B u l e l l i , 1 9 5 1 .

Annual P r e c i p i t a t i o n (mm)

Rate o f I n f i l t r a t i o n ( % )

500 5 5 0 6 0 0

1 4 .O 16.5 19.5

Table 4.3-4 - I n f i l t r a t i o n r a t e s from a study i n Tun is ia , €3. L e b i d i , 1 9 6 3 .

Average Annual Average Annual Aver age Per iod o f Volume o f Y i e l d o f t h e Fac to r o f Measurements P r e c i p i t a t i o n Discharge P o i n t s i n f i l t r a t i o n (years 1 ( 1 0 6 meter’) ( 1 0 6 meter31

1 9 4 9 / 50 t o 1 9 5 9 / 6 0 13 .8 2.5 1 8

1 3 7

reason t h a t i t i s des i rab le t o consider the water balance over as l o n g a p e r i o d o f t ime as i s poss ib le .

Case o f D j e b e l Bargou, T u n i s i a (H. Zebid i , 1 9 6 3 ) -- D j e b e l Bargou i s a syn- c l i n a l g u t t e r ( d r a i n ) o f A p t i a l l imestone, extending over 1 9 km2, and w i t h a p a r t i a l cover o f maquis-type vegeta t ion . The components o f t h e water balance have been computed one by one, and t h e i n f i l t r a t i o n f a c t o r has been c a l c u l a t e d from t h e r e l a t i o n s h i p between t h e y i e l d o f t h e d ischarge p o i n t s and the volume o f t h e p r e c i p i t a t i o n . The r e s u l t s a re shown i n t a b l e 4.3-4.

Other Cases o f average i n f i l t r a t i o n f a c t o r s -- I s r a e l Mer0 ( 1 9 5 8 ) has found f o r t he 200 km2 drainage bas in o f Midd le Creta- ceous l imestone feed ing t h e Na'am s p r i n g t h a t t he average i n f i l t r a t i o n r a t e i s 53 pe rcen t f o r an average annual p r e c i p i t a t i o n o f 600 mm c a l c u l a t e d f o r t he 1927-57 per iod .

S y r i a Burdon ( 1 9 6 1 I t e m I V - 3 ) r e p o r t s a r a t e o f i n f i l t r a t i o n and r e i n f i l t r a - t i o n o f 4 1 percent i n t h e Damascus bas in f o r an area o f 5,123 km2 and w i t h an average annual p r e c i p i t a t i o n o f 2 6 2 mm.

The i n f i l t r a t i o n , i n con junc t i on w i t h t h e reduced r o l e p layed by evapora- t i o n and r u n o f f i n t h e water balance, draws a t t e n t i o n t o the p a r t i c u l a r way i n which the p r e c i p i t a t i o n - i n f i l t r a t i o n r e l a t i o n s h i p occurs.

I t i s always wise t o d e f i n e and t o c a l c u l a t e the average r a t e o f i n f i l t r a - t i o n which i s n o t a s imple a r i t h m e t i c mean o f t h e annual o r seasonal r a t e s , but i t should be the r e s u l t o f a water balance determined over as l o n g a p e r i o d o f measurement as poss ib le , i f i t i s des i red t o make a r a t i o n a l use o f t he r a t e o f i n f i l t r a t i o n i n connect ion w i t h development t o p rov ide d e f i n i t e q u a n t i t a t i v e a n a l y s i s f o r supp l ies o f water i n a k a r s t i c reg ion .

4.4 O u t l e t s (M. Herak and D.J. Burdon)

Spr ings, and i n p a r t i c u l a r l a r g e spr ings and even resurgent underground streams, a re among t h e most s t r i k i n g o f k a r s t hydrogeo log ica l phenomena; so, t h e r e i s a v a r i e d terminology f o r them, as may be seen from t h e " M u l t i l i n g u a l Glossary o f K a r s t Terms". A few t e r m i n o l o g i c a l p o i n t s may be no ted here. Any k a r s t s p r i n g can be descr ibed as an emergence o r r i s e ; but resurgence i s r e s t r i c t e d t o spr ings which o r i g i n a t e d i n p a r t o r t o t a l l y f rom sur face i n f l o w i n t o ponors (swal low ho les) a t a h ighe r l e v e l , w h i l e exsurgence r e f e r s t o a s p r i n g f e d by d i f f u s e f low. A q u i e t upwe l l i ng s p r i n g may be known as a b l u e ho le , but a t u r b u l e n t u p w e l l i n g i s known as a b o i l i n g , gushing, vauc lus ian, o r founta in - type spr ing. I n t e r m i t t e n t o r p e r i o d i c spr ings a re s i m i l a r , and t h e i r f l o w v a r i e s ( o r ceases) Seasonal ly i n harmony w i t h t h e p r e c i p i t a t i o n o r snow- mel t . Ebb-and-flow spr ings show p e r i o d i c v a r i a t i o n s ( r e g u l a r ) i n discharge, unconnected w i t h seasonal, t i d a l , o r o the r i d e n t i f i a b l e in f luences ; s iphon ic a c t i o n i s o f t e n invoked as an explanat ion. K a r s t openings which seasonal ly d ischarge groundwater and seasonal ly take i n sur face o r sea water a re known as es tave l l es ; those which suck i n sea-water a re u s u a l l y q u a l i f i e d as sea- es tave l l es , sea-ponors, o r sea-mi l ls .

Discharge o f groundwater f rom k a r s t a q u i f e r s takes p lace from two broad ca tegor ies o f o u t l e t s - - d i f f u s e and concentrated. These o u t l e t s may discharge water on t h e surface, t he u s u a l s i t u a t i o n , o r i n t o bodies o f sur face waters, such as lakes o r ponds; they may discharge i n t o the seas, and i n the subsurface t o a l l u v i a l o r o t h e r aqu i fe rs .

There a re many o t h e r ways t o group and c l a s s i f y k a r s t spr ings. Such would i n c l u d e c l a s s i f i c a t i o n as t e r r e s t r i a l , l a c u s t r i n e , c o a s t a l and submarine occur- rences; o r cont inuous discharge, i n t e r m i t t e n t d ischarge and reversed discharge ( e s t a v e l l e ) ; o r accord ing t o t h e hydrogeo log ica l s t r u c t u r e , f r e e o r conf ined. [EDITOR'S NOTE: The rea.der i s r e f e r r e d t o B o g l i , 1 9 8 0 , f o r a d iscuss ion o f seve ra l methods o f c l a s s i f y i n g k a r s t spr ings. See a l s o Meinzer, 1 9 4 2 , Tolman, 1947, and Schoe l le r , 1955.1

4 . 4 . 1 D i f f u s e o u t l e t s . These may genera l l y be descr ibed as exsurgent spr ings. There a re two major f a c t o r s which g i v e r i s e t o groundwater d ischarge through

138

d i f f u s e spr ings o r seepages; one i s r e l a t e d t o the a q u i f e r , t h e o t h e r t o t h e type o f b a r r i e r which causes t h e groundwater t o i ssue from the a q u i f e r .

D i f f u s e o u t l e t s a re common from a q u i f e r s i n which t h e groundwater i s spread through t h e whole body o f t h e rock due t o p r imary o r secondary p o r o s i t y , and moves as a cont inuous nappe t y p i c a l o f g ranu la r format ions. However, d i f f u s e o u t l e t s occur i n carbonate format ions o n l y under s p e c i a l circumstances. Thus, sandstone beds, o r o the rs w i t h i n t e r g r a n u l a r i n t e r s t i c e s , sandwiched between massive and impermeable l imestones a re l i k e l y t o g i v e r i s e t o d i f f u s e discharge. Y i e l d s tend t o be low, but a l s o t o be l e s s a f f e c t e d by seasonal v a r i a t i o n s , s ince t h e r a t e o f groundwater movement i s l e s s r a p i d than i n most k a r s t i f i e d format ions.

C e r t a i n types o f b a r r i e r s tend t o produce d i f f u s e discharge. One example i s bedrock, where t h e moving f r e s h groundwater o v e r l i e s s t a t i c s a l i n e water i n c o a s t a l k a r s t ; t h e zone o f d ischarge l i e s a long the t r a c e o f a h o r i z o n t a l p lane and SO d i f f u s e d ischarge i s usua l . Again, where d ischarge takes p lace a t t he base o f a f a u l t e d scarp, t he t a l u s cover may d i f f u s e t h e d ischarge and spread i t over a wide b e l t . I n these cases, d i f f u s e d ischarge can occur even though the f l ow i n the a q u i f e r i t s e l f was p a r t i a l l y concentrated.

4.4.2 Concentrated o u t l e t s . These may g e n e r a l l y be descr ibed as resurgent spr ings. Spr ings o f d i f f e r e n t types, but f e d t o t a l l y o r i n p a r t by concen- t r a t e d f l o w i n t h e a q u i f e r , a re t h e c h a r a c t e r i s t i c form o f d ischarge o f k a r s t aqu i fe rs . As k a r s t i f i c a t i o n o f an a q u i f e r system develops, t he re i s a tendency f o r spr ings t o capture o t h e r spr ings and so f o r l a r g e r spr ings t o grow b i g g e r a t t he expense and eventua l drying-up of smal le r spr ings. The l a r g e r t h e volume o f aggressive groundwater f l o w i n g towards an o u t l e t , t h e more r a p i d l y the opening w i l l be enlarged, thereby f a c i l i t a t i n g flow:

Recharge t o such a q u i f e r s w i l l o f t e n be through ponors (swal low ho les) and from the bed o f streams and seasonal lakes; d i r e c t i n f i l t r a t i o n o f p r e c i p i t a - t i o n o r snow-melt w i l l a l s o occur. The response o f these major spr ings t o p r e c i p i t a t i o n and i n f i l t r a t i o n w i l l be qu ick ; t h e i r waters may c o n t a i n mud and o the r i n s o l u b l e ma t te r a t peak discharges soon a f t e r heavy r a i n s . Under such circumstances, t h e spr ings may be f e d from catchment areas which ove r lap w i t h o thers and have entangled subsurface d i v i d e s which do n o t co inc ide w i t h t h e surface topographic watersheds.

Hydrodynamical ly, k a r s t spr ings may be descending, ascending, o r combined. Descending spr ings d r a i n a q u i f e r s under unconf ined (water - tab le ) groundwater cond i t ions . They tend t o be seasonal o r p e r i o d i c and may dry up e n t i r e l y . An ana lys i s o f t h e i r regress ion curve w i l l o f t e n y i e l d much da ta as t o t h e s i z e o f t h e i r catchment and volume o f water i n storage. Some examples o f descending spr ings are found i n Yorksh i re , England, where perched s p r i n g l i n e s occur on h i l l s i d e s where perched water - tab les i n l imestones o v e r l i e sha le and l e s s permeable bands. The descending s p r i n g a t Deeside, Jamaica, i n t h e Queen o f Spain 's V a l l e y has a normal wet season f l o w o f about 30 f t 3 / s e c , but d u r i n g t h e d r y season the f l o w i s min ima l (Sweeting, 1 9 7 3 ) .

Ascending spr ings a re u s u a l l y f e d f rom con f ined a q u i f e r s where the water i s under h y d r o s t a t i c pressure; s iphona l e f f e c t s may occur. V a r i a t i o n s i n discharge occur but a re due t o pressure changes i n t h e a q u i f e r system r a t h e r than t o t h e p h y s i c a l a r r i v a l a t t h e o u t l e t o f t h e newly i n f i l t r a t e d ground- water. Hence, such spr ings a re l e s s l i k e l y t o d ischarge muddy water except f rom r o o f co l l apse o r f rom increased underground v e l o c i t i e s o f f low. Ascending spr ings a l s o tend t o be more r e g u l a r i n t h e i r d ischarge and n o t t o dry-up. Likewise, t h e i r temperature and chemical composi t ion a re more un i fo rm. Exam- p l e s o f such spr ings a re A i n F igeh i n S y r i a and Fonta ine de Vaucluse e a s t o f Airgnon, France.

T r u l y ascendant k a r s t spr ings a r e r a r e on land, and most concentrated o u t l e t s a re o f a combined type. Such may i n c l u d e deeper groundwater moving towards some b a r r i e r under h v d r o s t a t i c pressure. "Ebb-and-flow" sp r ings a re o f t e n exp la ined as be ing due t o s iphon ic ac t i on ; they should be d i s t i n g u i s h e d from seasonal o r p e r i o d i c spr ings, whose a l t e r n a t i o n o f f l o w a n d dry pe r iods correspond t o v a r i a t i o n s i n o r absence of p r e c i p i t a t i o n and snow-melt. Coasta l spr ings of mixed o r i g i n may show e f f e c t s o f in tercommunicat ion w i t h t h e sea. Such spr ings may n o t o n l y d i s p l a y v a r i a t i o n s o f d ischarge r e l a t e d t o t h e s t a t e o f t he t i d e s ( t i d a l v a r i a t i o n ) , but may a l s o have a more un i fo rm d ischarge i n a

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seasonal p e r i o d i o c i t y than would o therw ise be expected because the u n d e r l y i n g sea-water p rov ides an e l a s t i c bot tom t o the groundwater r e s e r v o i r , s i n k i n g a f t e r a high i n f l o w o f f r e s h water i n t o the c o a s t a l a q u i f e r and r i s i n g t o m a i n t a i n d ischarge a f t e r such i n f l o w has ceased.

K a r s t spr ings o f t h e resurgent type e x h i b i t t r u l y l a r g e discharges o f groundwater. T h i s a p p l i e s t o t h e i r average d ischarge over t h e year, and even more so t o t h e i r peak discharge. Those w i t h high average d ischarge a re o f t e n o f t h e ascendant type, coming from l a r g e bas ins and f l o w i n g through con f ined aqu i fe rs . Thus Ras-el-Ain i n S y r i a has an average annual d ischarge o f 38.7 m3/sec, and o n l y a s l i g h t v a r i a t i o n over the year (Burdon and Safadi , 1 9 6 3 ) . O n t h e o t h e r hand, T r e b i s v n j i c a s p r i n g i n Yugoslavia has a maximum discharge o f 3 0 0 m3/sec, but dec l i nes t o a m i n i m u m o f 2 m3/sec (Mi lanovic , 1 9 7 9 ) .

4.4.3 Spring d ischarge i n t o ponds and lakes. K a r s t lakes and ponds f r e q u e n t l y occur w i t h i n co l l apse s t ruc tu res , and are fed by, o r communicate d i r e c t l y w i t h , t he groundwater t a b l e o f t h e area. Since such groundwater t a b l e s o f t e n show s t rong seasonal f l u c t u a t i o n s , t h e lakes and ponds may be f e d by k a r s t spr ings a t one season and l a t e r , a f t e r a d e c l i n e i n groundwater l e v e l s , t h e same lakes a c t as r e s e r v o i r s recharg ing t h e groundwater by i n f l o w through t h e same open- ings . Such openings a re es tave l l es ; they a c t as d ischarge p o i n t s (spr ings) one season and as i n f l o w p o i n t s (ponors) another season. Cases have been repo r ted where i n one p a r t o f a k a r s t l a k e t h e r e i s a d ischarge from underground i n t o t h e lake, w h i l e i n another p a r t t h e r e i s simultaneous o u t f l o w from the l a k e i n t o a ponor. The Obod s p r i n g i n the Fa tn i ca P o l j e i n the D i n a r i c k a r s t i s an e s t a v e l l e (Sweeting, 1 9 7 3 ) .

4.4.4. Subsurface d ischarge t o a l l u v i a l aqu i fe rs . Many k a r s t a q u i f e r s i n c l i f f s o r r i d g e s a re i n d i r e c t con tac t w i t h a l l u v i a l v a l l e y s and p l a i n s ; t he p o i n t o f con tac t may be covered w i t h v a r y i n g th icknesses o f t a l u s and piedmont m a t e r i a l . Wherever such con tac t zones have been i n v e s t i g a t e d w i t h care, evidence has u s u a l l y been found t h a t t he re i s cons iderable f l o w o f groundwater d i r e c t l y f rom t h e l imestone i n t o the a l luv ium. The amount o f f l o w i s d i f f i c u l t t o measure, but t h e r e can be no doubt t h a t t h i s subsurface t r a n s f e r o f ground- water i s la rge . Where the a l l u v i u m i s impermeable c lay , border spr ings and seepages occur and a re c l e a r l y v i s i b l e . As an in te rmed ia te case, t h e r e may be d ischarge i n w i n t e r and spr ing, when t h e groundwater t a b l e r i s e s i n t h e l ime- stone; i n summer and autumn, when t h e water t a b l e dec l ines , t h e r e i s o n l y sub- sur face t r a n s f e r o f groundwater f rom the l imestone t o the a l luv ium.

I n Morocco i t has been shown (Mor t i e r , 1 9 6 1 ) t h a t t h e p l a i n o f Anngad rece ives o n l y 1 5 pe rcen t o f i t s groundwater by d i r e c t i n f i l t r a t i o n ( 7 percent o f 3 4 2 mm), w h i l e l a t e r a l t r a n s f e r f rom the L i a s s i c l imestone a q u i f e r s border- ing t h e p l a i n supply some 5 0 percent t o 7 0 percent o f t h e groundwater e x t r a c t e d from t h e a l luv ium. The amount i s o f t h e order o f 500 t o 700 l i t e r s p e r second. M o r t i e r f u r t h e r r e p o r t s t h a t t h i s k a r s t groundwater can be i d e n t i f i e d by a temperature w h i c h i s apprec iab ly lower than t h a t o f groundwater formed by d i r e c t i n f i l t r a t i o n i n t o t h e a l luv ium.

4.4.5 Submarine s p r i n g discharge. Submarine o r drowned spr ings a re a s p e c i a l t ype o f ascendant spr ing . They a re abundant i n the eas tern Mediterranean where they appear t o be spr ings which were above sea l e v e l i n t h e p a s t and have cont inued t o f u n c t i o n as spr ings o r e s t a v e l l e s a f t e r t h e sea rose t o drown them. The water be ing d ischarged has t o be under s u f f i c i e n t pressure t o overcome the we igh t o f o v e r l y i n g seawater; t h i s pressure i s i n p a r t due t o the head i n t h e channel o r passage d i scha rg ing the water and i n p a r t due t o d i f f e r - ences i n s p e c i f i c g r a v i t y between t h e a q u i f e r water and t h e sea water. The a q u i f e r water may be f resh , but o f t e n has mingled w i t h t he sea water and i s b rack ish . The amount o f sea water m i n g l i n g u s u a l l y v a r i e s seasonal ly and w i t h t h e t i d e s and i s r e f l e c t e d i n the volume o f d ischarged water. Submarine spr ings a re known t o occur on the coas t o f Yugoslavia ( B o g l i , 1 9 8 0 ) . I n a d d i t i o n , submarine spr ings may reverse, and seasonal ly suck i n sea water, and SO change t o submarine ponars o r sea-mi l ls , such as those on Kepha l len ia i n the I o n i c I s l a n d s ( B o g l i , 1 9 8 0 ) .

The h y d r o s t a t i c s and hydrodynamics of groundwater i n c o a s t a l k a r s t aqui- f e r s i n communication w i t h t h e sea a re very complex. Severa l t heo r ies e x i s t t o

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e x p l a i n t h e mechanism f o r t h e m i x i n g o f f r e s h and s a l t waters. Lehmann (1932) in t roduced t h e suck ing- in phenomenon. G ju ras in ( 1 9 4 2 , 1943) showed t h a t such a phenomenon must be ve ry r a r e , and t r i e d t o e x p l a i n t h e o r i g i n o f b r a c k i s h spr ings, submarine spr ings, sea es tave l l es , o r sea-mi l l s on t h e b a s i s o f t h e d i f f e r e n c e s i n t h e s p e c i f i c d e n s i t y between f r e s h and s a l t water. Kuscer (1950) e labora ted on the same idea. M i x i n g by d i f f u s i o n , which a l s o e x i s t s , has been shown t o be a ve ry slow process which occurs i n qu iescent as w e l l as i n moving waters. Hence, i t s r o l e i n t h e mechanism o f submarine spr ings i s n e g l i g i b l e .

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5 . Geomorphology

5 . 1 I n t r o d u c t i o n (L. A . He ind l )

The unique charac ter o f carbonate-rock hydro logy i s nowhere b e t t e r expressed than i n the spectacular a n d d i s t i n c t i v e k a r s t s o f t h e wor ld . Long be fo re t h e r e was any p a r t i c u l a r concern w i t h t h e hydro logy o f carbonate te r ranes , t h e r e was, and cont inues t o be, an i n tense i n t e r e s t i n k a r s t i c landforms. Those i n t e r e s t e d i n k a r s t i c geomorphology and speleology a l s o f a r outnumber those concerned w i t h i t s hydrology, and much o f t he d e s c r i p t i v e i n f o r m a t i o n u s e f u l t o hydro logy comes f rom these f i e l d s . I n t h i s guide, however, t h e emphasis i s on the hydro logy a n d t h e use o f k a r s t i c geomorphic phenomena i n improv ing the understanding o f hyd ro log i c phenomena o f carbonate rocks.

The phys iographic forms c a l l e d k a r s t s a re t h e most obvious aspect o f a dynamic i n t e r a c t i o n between geo log ica l , c l i m a t o l o g i c a l and b i o l o g i c a l m a t e r i a l s and processes i n reg ions o f carbonate rocks. The major m a t e r i a l s a re rocks and water, w i t h p l a n t s o r l a c k o f cover se rv ing a secondary but key r o l e ; t h e major immediate processes are eros ion, s o l u t i o n and t r a n s p o r t a t i o n by f l o w i n g water. The growth process o f p l a n t s mod i f i es t h e e f f e c t s o f f l o w i n g water and i n the more d i s t a n t background are t h e l ong term, a l though n o t always slow, processes o f s t r u c t u r a l adjustment.

K a r s t i c landforms have a s i g n i f i c a n t e f f e c t on the sur face and groundwater regimen. Most obvious i s t h e e f f e c t on stream f l o w and l e s s obvious, but a c t u a l l y more impor tan t , t h e e f f e c t o f subsurface k a r s t fea tures on groundwater movement. Though t h i s d i scuss ion i s d i r e c t e d a t hydro logy, se lec ted geomor- pho log ic re fe rences are c i t e d because they p rov ide i n s i g h t i n t o t h e hyd ro log i c processes o f concern. No e f f o r t i s made t o summarize, rev iew o r o therw ise present t h e l i t e r a t u r e concerned w i t h k a r s t fea tures . [EDITOR'S NOTE: The reader i s r e f e r r e d t o Sweeting, 1 9 7 3 , Jacus, 1 9 7 7 and ROgl i , 1 9 8 0 f o r d e t a i l e d presenta t ions on k a r s t landforms, t o Drake, 1 9 8 3 , f o r a d i scuss ion o f t he e f f e c t s o f geomorphology on t h e chemis t ry o f carbonate groundwater, and t o S t r i n g f i e l d , LeGrand, and LaMoreaux, 1 9 7 7 , f o r a d i scuss ion o f t h e e f f e c t s o f k a r s t development on p e r m e a b i l i t y and t h e c i r c u l a t i o n o f ground water. ]

The importance o f landforms cannot be minimized, however, because o f t h e i r i n f l uence on human use and demand f o r water i n k a r s t i c te r ranes . I n d e s c r i b i n g the geography o f t h e D i n a r i c k a r s t , f o r example, Rog l i c ( 1 9 6 9 , p. 3 6 ) s t a t e s 'Tectonic movements and t h e complex i n t e r r e l a t i o n s h i p s o f b a s i c composi t ion and morphogenetic processes have toqether model led t h a t s p e c i f i c k a r s t t e r r a i n which has f o r so l o n g been t h e b a s i s o f a way o f l i f e t h a t has d i f f e r e d i n d i f f e r i n g per iods . ' He descr ibes some o f t h e i n f l uences o f t h e D i n a r i c t e r r a n e on the development o f t h e Republ ic o f Ragus (Dubrovyik) (sheep husbandry, a g r i c u l t u r e , n a t i o n a l defense, and tou r i sm) . The i n t r i c a c i e s o f i n t e r r e l a t i o n - sh ips between k a r s t i c hydro logy and t h e hea l th , w e l l be ing, and day t o day a c t i v i t i e s o f people on t h e D i n a r i c Coast i s w e l l descr ibed i n a s e r i e s o f sho r t papers e d i t e d by P e t r i and Herak ( 1 9 6 9 ) .

5 .2 K a r s t landform fea tu res and c l a s s i f i c a t i o n s

K a r s t i c landscapes and subsurface landforms a re ma in l y the r e s u l t o f s o l u t i o n , b o t h a t a n d below t h e surface, and c o l l a p s e induced by t h e s o l u t i o n . The most impor tan t t r a n s p o r t i v e f u n c t i o n o f moving water i s t o remove chemica l l y sa tura ted water f rom the area and t o b r i n g i n l e s s chemica l l y sa tu ra ted f lows. Mechanical e ros ion , abras ion and co r ros ion i s minor; a l though, as i n a l l genera l l y minor processes , i t may be s i g n i f i c a n t i n some p laces.

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C l a s s i f i c a t i o n s o f k a r s t i c landforms a re almost as numerous as the k a r s t s themselves.

5.2.1 C l a s s i f i c a t i o n based on landform. A sys thes is by LeGrand and S t r i n g f i e l d (1971d) c l a s s i f i e s k a r s t t e r rane e x c l u s i v e l y on the b a s i s o f sur face form (see f i g u r e 5.2-1) .

1. Undu la t ing p l a i n w i t h s inks (see F igu re 5.2- la) . R o l l i n g topography c o n s i s t i n g o f s inks and i n t e r v e n i n g convex slopes , (examples , (a) B lue Grass Region o f Kentucky where l o c a l topographic r e l i e f i s subdued (White and others, 1970) , and (b) t h e Cockp i t Country o f Jamaica, (Zans, 1951) , where l o c a l topographic r e l i e f i s apprec iab le ) .

2. Denuded homoc l ina l p l a i n w i t h s inks 7see F igu re 5.2-lb). D i p o f l ime- stone and l a n d sur face co inc ide t o form a homocl ina l coastward s lope w i t h sca t te red s inks, some o f which have v e r t i c a l w a l l s (examples, N u l l a r b o r P l a i n o f South A u s t r a l i a , Jennings, 1962, and n o r t h coast o f Yucatan, Mexico, Back and Hanshaw, 1970).

3. P o l j e s (see F igu re 5.2-lc) . F l a t a l l u v i a l v a l l e y s bordered by r e l a - t i v e l y steep, bare l imestone r i d g e s w i t h t h e v a l l e y s rang ing from h a l f a m i l e t o seve ra l m i l e s i n w i d t h and b e i n g somewhat e longated (examples, v a l l e y s o f southwestern Yugoslavia, some o f which are many m i l e s i n length , and Nassau Va l l ey , Jamaica).

4. Haystack o r mogote p l a i n (see F igu re 5 . 2 - i d ) . A n e a r l y f l a t p l a i n u n d e r l a i n by l imestone and veneered w i t h a l l u v i u m o r r e s i d u a l s o i l on which c o n i c a l l imestone h i l l s (mogotes) r i s e as much as 300 f e e t above the p l a i n (examples, p a r t s o f t h e n o r t h coas t l imestone o f Puer to Rico (Monroe, 1 9 6 6 & 1 9 6 8 ) and p a r t s o f Nor th Vietnam and South C h i n a ( S i l a r , 1 9 6 5 ) .

5. Carbonate v a l l e y between noncarbonate h i l l s (see F igu re 5.2- le) . Va l l eys formed on carbonate rocks l y i n g between r i d g e s composed o f more r e s i s t a n t sandstones and shales (examples, Shenandoah V a l l e y o f - V i r g i n i a , and t h e Sesquatchie V a l l e y o f Tennessee and Alabama, M i l i c i , 1967). These g e n e r a l l y a re breached a n t i c l i n e s o r o the r s t r u c t u r e s where carbonate rocks are exDosed a f t e r e ros ion o f t h e o v e r l v i n u l e s s so lub le beds.

6 . Noncarbonate lowland betwee; carbonate r i d g e s (see F igu re 5 . 2 - l f ) . Va l l evs formed on shale o r o t h e r noncarbonate rocks l y i n q between denuded -. .-

carbonate r i d g e s (examples S i e r r a Madre near Monterey , Mexico (Lesser and Jones, 1 9 6 7 , ) S i e r r e de Los Organos, Lehmann, H., 1 9 6 0 , and t h e S i l l a Gibara areas o f eas t Cuba). ~~

7 . Escarpment and low l y i n g l imestone p l a i n (see F igu re 5.2-lg) . Near ly f l a t p l a i n u n d e r l a i n by carbonate rocks, mant led by th in s o i l s , and bordered by a subdued escarpment- and an upland p l a i n capped by l e s s so lub le rocks (examples, N a s h v i l l e Basin-Highland R i m area o f Tennessee, Hack, 1966, Dougherty P l a i n - T i f t o n Upland o f south Georgia, Salem P la teau -Spr ing f i e ld P la teau o f Missour i , and t h e Dripping Springs-Chester escarpment o f Kentucky and Ind iana ) .

8. Escarpment and h ighe r p l a t e a u capped by carbonate rocks (see F igure 5 . 2 - l h ) . Cuesta on which carbonate rocks are more r e s i s t a n t than a re the u n d e r l y i n g rocks (examples, Niagara Limestone o f Wisconsin, London Chalk o f southeast England, and seve ra l cuestas i n t h e Western Deser t o f Egypt.)

5.2.2 C l a s s i f i c a t i o n system proposed by Qu in lan ( 1 9 6 6 ) . A more complex system o f c l a s s i f i c a t i o n has been proposed by Qu in lan (1966). Th i s i s g i ven i n f u l l because i t at tempts t o focus on n e a r l y a l l aspects o f k a r s t types and so forms a va luab le check l i s t o f f ea tu res and processes t o be no ted i n t h e f i e l d .

'Ka rs t types may be c l a s s i f i e d on t h e b a s i s o f t h e i r f o l l o w i n g major a t t r i b u t e s : (1) cover, ( 2 ) l i t h o l o g y ; ( 3 ) c l imate , ( 4 ) geo log ic s t ruc tu re , (5) physiography, and sometimes a l s o ( 6 ) m o d i f i c a t i o n s d u r i n g o r a f t e r k a r s t i f i c a t i o n . ' I.. Cover ( i t s presence, absence, o r i g i n , r e l a t i o n t o topography, and age)

A. Present (covered k a r s t ) 1. ' Subso i l k a r s t (new term) covered w i t h i t s residuum and

subsoi l . . . 2 . Mantled k a r s t (new term) covered w i t h a l lochthonous rock o r

sediment: p a r t o f contemporary landscape; o l d e r than i t s cover.. .

1 4 4

z

l- z

J

Lz X

W

0

a

a

c O

14

5

3. Bu r ied k a r s t covered w i t h a l lochthonous r o c k o r sediment; n o t p a r t o f contemporary landscape: o l d e r than i t s cover...

4. I n t e r s t r a t a l k a r s t (new term) covered w i t h autochthonous rock o r sediment; may o r may n o t be p a r t o f contemporary landscape: younger than i t s cover; formed by the s o l u t i o n o f so lub le rock beneath, o r q u i t e r a r e l y , immediately above r e l a t i v e l y i n s o l u b l e rock such as sandstone or cher t ; t y p i c a l l y t h e te rm r e f e r s t o a r e a l so lu t i on : i t does n o t p e r t a i n t o development o f caves w i t h i n so lub le rock: t h e term i s a l s o app l i cab le t o re juvenated mant led k a r s t and b u r i e d k a r s t ; s u b s o i l k a r s t i s t r a n s i t i o n a l t o i n t e r s t r a t a l kars t . . .

B. Absent (exposed k a r s t ) 1. Naked k a r s t K a r s t developed and mainta ined w i t h o u t any cover;

some naked k a r s t s may develop beneath a temporary cover o f snow o r water. . .

2. Denuded k a r s t Subso i l k a r s t o r i n t e r s t r a t a l k a r s t t h a t has been exposed by e ros ion o f i t s cover.

3 . Exhumed k a r s t Mant led k a r s t o r b u r i e d k a r s t which has been d i ves ted o f i t s cover by eros ion: i t i s the reexposed p a r t o f a former k a r s t landscape.

4 . R e l i c t k a r s t (new term) The topographic o r p h y s i c a l remains o f a k a r s t ( t y p i c a l l y a naked k a r s t o r a s u b s o i l k a r s t , and r a r e l y a mant led k a r s t ) t h a t has n o t been covered and i n which a l l o r most o f t h e k a r s t i c rock has been removed by eros ion. Example, a doughnut- l ike h i l l formed by the p a r t i a l cementat ion o f a s inkho le f i l l o f a gypsum k a r s t i n which a l l t h e gypsum has been subsequently removed by eros ion. R e l i c t k a r s t i s n e i t h e r common o r r a r e . There are no equ iva len t terms f o r r e l i c t k a r s t .

II. L i t h o l o g y A. Rocks

1. Carbonate a. Limestone and do lomi te b. Chalk c . Ca l iche d. Carbonate cemented s i l i c i c l a s t i c rock e. Marble

2. Evapor i t e a. Gypsum and anhydr i t e ( s u l f a t e k a r s t ) b. S a l t

3. S i l i c i c l a s t i c (Rraunstein, 1 9 6 1 ) 4 . Igneous a.nd metamorphic (except marble)

1. Carbonate (syngenet ic k a r s t ) 2. Evapor i t e (syngenet ic k a r s t ) 3. S i l i c i c l a s t i c ( i n c l u d i n g calcareous loess

B. Sediments

co l luv ium) and

I I. Climate ( A f t e r T r o l l a n d Paf fen, i n Landsburg, Lippman, Pa f fen ani T r o l l , 1965). Each c l i m a t e can be subcl=sed accord ing t o b o t h the amount and d i s t r i b u t i o n o f annual p r e c i p i t a t i o n a n d the f l u c t u a t i o n o f mean monthly temperature, and i t i s cha rac te r i zed by s p e c i f i c types o f vegetat ion. Cl imates o f mountains and h igh lands are a l t i t u d i n a l v a r i a t i o n s o f t he adjacent c l i m a t i c zone. (Example, t y p i c a l l y , a l p i n e c l i m a t e i s a h i g h a l t i t u d e v a r i a t i o n o f a c o o l temperature c l i m a t e ) . A. P o l a r and subpolar B. Cold temperate b o r e a l C. Cool temperate D. Warm temperate s u b t r o p i c a l E. T r o p i c a l

I V . Geologic- S t r u c t u r e A. Underformed

1. F l a t l y i n g 2. Homocl ina l

1 4 6

B. Deformed 1. Folded 2. F a u l t e d 3. Fo lded and f a u l t e d

Physiography A. Coasts ( i n t e r t i d a l k a r s t ) B. P l a i n s C. P la teaus D. V a l l e y and r i d g e ( t y p i f i e d by t h e fo lde l

E. Mountains and i s o l a t e d mass i fs Un i ted Sta tes)

V.

V I M o d i f i c a t i o n d u r i n g o r a f t e r k a r s t i f i c a t i o n A. No m o d i f i c a t i o n

Appalachian mountains o f t he

B. Changes i n c l i m a t e C. B u r i a l mant led k a r s t and b u r i e d k a r s t D. Rejuvenat ion ( e s p e c i a l l y o f mant led k a r s t and b u r i e d k a r s t ) E. Drowning (submerged by changes i n sea o r l a k e l e v e l ) F. M i n e r a l i z a t i o n and a l t e r a t i o n ( f rom weather ing and o t h e r supergene

G. G l a c i a t i o n (covered and eroded by moving i c e ) H. M e l t i n g o f g l a c i a l i c e o f permaf ros t Poss ib l y some k a r s t s i n rocks o f permaf ros t t e r ranes had t h e i r i n i t i a l

development beneath permafrost a f t e r , r a t h e r than b e f o r e o r during, t h e f reez ing o f t h e ground. L ikewise, some k a r s t s may have had t h e i r i n i t i a l development beneath a g l a c i e r .

and hypogene processes)

5 .3 Pseudokarst

K a r s t - l i k e fea tu res i n noncarbonate and nonevapor i te rocks which have t h e morphology (and sometimes t h e h y d r o l o g i c f low p a t t e r n s ) o f k a r s t phenomena i n carbonate and evapor i t e rocks, but which are n o t produced by t h e k a r s t processes l i s t e d i n Sect ion 5 .2 .2 a re pseudokarst.

'Pseudokarst i s b e s t c l a s s i f i e d accord ing t o t h e dominant process operat ive. Genera l ly each process i s l i m i t e d t o one o r a few k i n d s o f rock , SO types o f pseudokarst have g e n e r a l l y been named on the b a s i s o f e i t h e r l i t h o l o g y o r dominant process. . . ' (Quinlan, 1 9 6 6 ) .

Four b a s i c types o f psuedokarst may be c l a s s i f i e d accord ing t o the dominant ope ra t i ve processes:

1. Mechanical su f fos ion . Example, c las toka rs t . . . . i n s o i l , c l ay , s i l t ,

2. D i f f e r e n t i a l mechanical eros ion. Example, i n t e r t i d a l psuedokarst. 3. Me l t i ng . Example, g l a c i e r psuedokarst ( i n i c e ) and thermokarst i n

4. D i f f e r e n t i a l s o l i d i f i c a t i o n and f l o w o f lava . Example, l a v a

v o l c a n i c ash, tu f f , loess, and sandy grave l .

sediments and s o i l s o f permaf ros t ter ranes.

pseudokarst.

5.4 Thermomineral k a r s t ( A r i e I s s a r )

The term thermomineral k a r s t i s a p p l i e d he re t o k a r s t phenomena formed by ascending warm water r i c h i n m ine ra l s i n c l u d i n g C02 . I n the abundant l i t e r a t u r e d e a l i n g w i t h thermomineral spr ings one f r e q u e n t l y f i n d s re fe rences t o caves and s o l u t i o n channels l i n e s w i t h depos i ts o f va r ious m ine ra l s i nc lud ing : c a l c i t e , aragoni te , i r o n and manganese oxides, e t c . (Moret, 1946).

E x p l o r a t i o n w e l l s d r i l l e d i n t h e v i c i n i t y o f thermal spr ings i n I r a n revealed the ex is tence o f caves and l a r g e s o l u t i o n channels i n t h e l imestone rocks i n t h e p r o x i m i t y o f t h e spr ings ( I s s a r , 1 9 6 9 ) .

I t i s o u t o f t h e scope of t h i s d i scuss ion t o d e a l w i t h t h e o r i g i n o f t h e thermomineral water and gasses. I t should o n l y be mentioned t h a t t h e source o f t he water may be e i t h e r meteor ic water which r i s e s by h y d r a u l i c pressure a f t e r hav ing descended t o a g r e a t depth o r f o s s i l water which ascends due t o gas pressure o r thermal energy. A smal l percentage o f j u v e n i l e water may a l s o be present. A m i x t u r e o f d i f f e r e n t sources i s f r e q u e n t l y found (White, D.E.,

1 4 7

1 9 5 7 ) . M ine ra l s and gases may be e i t h e r p r i m a r i l y j u v e n i l e o r de r i ved from d i s s o l u t i o n processes a t depth.

Temperature e l e v a t i o n s may a l s o have d i f f e r e n t o r i g i n s , e i t h e r a normal geothermal g r a d i e n t a f f e c t i n g t h e water i n depth o r a geothermal anomaly connected w i t h t he p r o x i m i t y o f a vo l can ic emanation.

The processes causing cave fo rmat ion a re equ iva len t t o those o f o r d i n a r y k a r s t , i .e., by carbonic acid; however, i n t h e case of thermomineral water t he processes a re more complicated, as t h e d i s s o l v i n g p o t e n t i a l o f t h e CO2 c o n t a i n i n g water i s i nve rse t o i t s temperature. A t constant CO2 pressure t h e s o l u b i l i t y o f ca lc ium carbonate w i l l increase w i t h decreases i n temperature; however, when t h e temperature i s constant, t h e s o l u b i l i t y o f CaC03 w i l l i nc rease w i t h increases i n CO;! pressure. Thus i n a system o f ascending thermomineral water, where t h e temperature and gas pressure change cons tan t l y as t h e water r i s e s , a change i n modes o f d i s s o l u t i o n and redepos i t i on o f carbonates and m ine ra l s may be expected a t a c e r t a i n depth ( M i l l e r , 1 9 5 2 ) .

Apar t f rom t h e m i n e r a l i z a t i o n which cha rac te r i zes thermomineral k a r s t , t h i s t ype o f k a r s t d i f f e r s f rom t h e o r d i n a r y one i n t h a t i t i s r e s t r i c t e d t o t h e v i c i n i t y o f r e g i o n a l f a u l t l i n e s and vo l can ic emanations; i t i s n o t a widespread phenomenon.

Thermomineral waters may i n some cases be r a t h e r poor i n s a l t s , and, a f t e r d e p o s i t i n g t h e i r i r o n and manganese, may be u s e f u l f o r i r r i g a t i o n o r even domestic use.

I n t h e case o f f o s s i l thermomineral k a r s t , chemical ana lys i s o f t he depos i ts accompanying t h e k a r s t may h e l p t o d i s c l o s e whether o r n o t t he thermal s p r i n g was highly minera l i zed . I n some cases the area around an e x t i n c t o u t l e t o f ascending water may prove t o be h i g h l y permeable, a f a c t t h a t i s ve ry impor tan t i n l o c a t i n g water resources i n a r i d zones where k a r s t i c phenomena are ra re . O n t h e o t h e r hand, h i g h l y m ine ra l i zed fac i l t zones may con ta in underground s a l i n e water assoc iated w i t h e x t i n c t thermomineral spr ings.

5.5 Pa leokars ts (D.J. Burdon) When carbonate sediments, i n v a r y i n g stages o f l i t h i f i c a t i o n , a re u p l i f t e d above sea l e v e l , they become exposed t o weather ing and thus t o k a r s t i f i c a t i o n processes. Past k a r s t i f i c a t i o n s tend t o be mod i f i ed o r removed when the format ions a re aga in submerged by a t ransgress ive sea. The m o d i f i c a t i o n s c o n s i s t i n p a r t o f removal o f t h e upper sur face o f t he rock and t h e p a r t i a l o r t o t a l i n f i l l i n g o f openings w i t h sand, c lay , o r new p r e c i p i t a t e . Some o f t he o l d k a r s t f ea tu res may however remain when the carbonates are once again exposed and may be confused w i t h l i v e (as opposed t o f o s s i l ) k a r s t . LeGrand and S t r i n g f i e l d (1971a) no te 'The f a c t t h a t p resent day and anc ien t k a r s t i f i e d fea tu res Co-exist i n many p laces may cause m i s i n t e r p r e t a t i o n o f h y d r o l o g i c cond i t i ons , un less t h e h y d r o l o g i c a l h i s t o r y i s known adequately. '

Burdon and Sa fad i ( 1 9 6 3 and 1 9 6 4 ) r e p o r t t h a t i n S y r i a pa leokars ts were developed on Upper Ju rass i c rocks due t o emergences during t h e Lower Cretaceous and the Paloegene when nummul i t ic l imestone were deposi ted on a sur face c u t on f o l d e d Turonian-Cenomanian l imestone. Moreover, t he Upper Ju rass i c rocks have again been exposed s ince Oligocene-Miocene t ime, and i t i s p a r t i c u l a r l y d i f f i c u l t t o d i s t i n g u i s h t h e k a r s t developed i n the e a r l i e r p a r t o f t he Ol igocene-to-present emergente f rom those developed more recen t l y . I n Kuwait, t he Dammam Limestone was k a r s t i f i e d d u r i n g an Oligocene emergence, and Burdon and A l Sharhan ( 1 9 6 8 ) cons ider t h i s k a r s t i f i c a t i o n t o s t i l l have a major i n f l u e n c e on t h e c i r c u l a t i o n and e x t r a c t i o n o f ground water f rom t h i s impor tan t aqu i fe r .

I n genera l , i n t e r r e l a t i o n s h i p s o f l i t h o l o g i c a l c h a r a c t e r i s t i c s i n c l u d i n g the s i z e and shape, sequence o f beds, and pa leo -h i s to ry determine much o f a u n i t ' s water-bear ing c a p a b i l i t y . For example, i f a l imestone bed t h a t i s o v e r l a i n by a t h i c k depos i t i s never e leva ted t o where ground water can c i r c u l a t e , s o l u t i o n w i l l n o t occur and f r a c t u r e s w i l l n o t be enlarged t o inc rease t h e pe rmeab i l i t y . I n con t ras t , i f a l imestone depos i t has no o v e r l a y i n g depos i ts and i s u p l i f t e d t o where water can erode i t s sur face and c i r c u l a t e through i t s f rac tu res , t h e r e s u l t w i l l be a k a r s t i f i e d l imestone un i t o f h i g h p e r m e a b i l i t y (LeGrand and S t r i n g f i e l d , 1971a).

I t i s obvious t h a t an o l d e r l imestone un i t has had more oppor tun i t y t o be exposed t o s u b a e r i a l e ros ion than a younger one. Many l imestone sequences show

148

evidence o f seve ra l pe r iods o f u p l i f t and depression and i n c l u d e seve ra l u n i t s i n the sequence w i t h p a l e o k a r s t i c features (Burdon and Safadi , 1 9 6 4 , S t r i n g f i e l d and LeGrand, 1971a). Once t h e network o f s o l u t i o n channels and f r a c t u r e s i s enlarged, i t becomes a dominant f a c t o r i n t h e f u t u r e development o f t h a t un i t as an a q u i f e r and i n t h e f u r t h e r s o l u t i o n o f ad jacent and, i n p a r t i c u l a r , o v e r l y i n g beds.

The e x t e n t and depth o f t h e network o f s o l u t i o n channels depends t o some ex ten t on the base l e v e l t h a t i n genera l c o n t r o l s t h e g r a d i e n t o f t h e movement o f water on t h e sur face of and through t h e rocks. Three types o f paleogeographic base- leve l c o n t r o l s need t o be considered: (1) sea l e v e l s , p a r t i c u l a r l y near c o a s t a l areas: ( 2 ) p e r e n n i a l g a i n i n g streams t h a t c o n t r o l l o c a l base l e v e l s : ( 3 ) u n d e r l y i n g impervious fo rmat ions t h a t a c t t o develop l o c a l perched water tab les . I d e n t i f i c a t i o n o f t he base- leve l c o n t r o l serves t o d e f i n e d ischarge zones, and t o approximate t h e d i r e c t i o n i n which recharge areas occur as w e l l as the approximate h y d r a u l i c g rad ien t .

As a base l e v e l i s maintained, t h e c i r c u l a t i n g water d i sso l ves t h e l imestone, t h e p e r m e a b i l i t y increases, and t h e water t a b l e dec l i nes t o success ive ly lower l e v e l s . Even tua l l y t h e water t a b l e tends t o become f l a t and develop a p lane t h a t has been des ignated as t h e e q u i l i b r i u m sur face o f s o l u t i o n channel ing. The g r e a t e s t amount o f s o l u t i o n occurs a t o r immediately below e q u i l i b r i u m sur faces o r temporary approximat ions of these sur faces, can be recognized i n some p laces by rough p lanes i n t h e a l ignment o f channels.

5.6 Ana lys is o f geomorphic processes

5.6.1 Q u a n t i t a t i v e ana lys is . Q u a n t i t a t i v e analyses o f landforms have, a t t imes, been concentrated on dra inage bas ins as t h e b a s i s f o r understanding geomorphological processes. Such s tud ies have used b o t h s imple and complex s t a t i s t i c a l methods f o r t h e i r purposes and have prov ided many u s e f u l i n s i g h t s , p a r t i c u l a r l y o f b a s i n geometry t o streamflow. The b a s i c concepts u n d e r l y i n g the use o f r i g o r o u s q u a n t i t a t i v e a n a l y s i s o f landforms was t o p rov ide numer ica l data o f p r a c t i c a l value. S t r a h l e r ( 1 9 6 4 , pp. 4 4 0 - 4 4 1 ) summarizes t h e b a s i c concepts as fo l l ows :

O f fundamental importance i s t he concept o f a dra inage b a s i n as an open system tend ing t o achieve a steady s t a t e o f opera t ion . S t r a h l e r app l i ed open system b i o l o g i c concepts t o a graded dra inage system. An open system impor ts and expor t s ma t te r and energy through system bound- a r i e s and must t rans fo rm energy u n i f o r m l y t o m a i n t a i n opera t ion . I n a drainage b a s i n the l a n d sur face w i t h i n t he l i m i t s o f t he b a s i n per imeter c o n s t i t u t e s a system boundary through which p r e c i p i t a t i o n i s imported. M ine ra l ma t te r supp l ied f rom w i t h i n t h e system and excess p r e c i p i t a t i o n leave the system through t h e b a s i n mouth. I n a graded dra inage bas in , t he steady s t a t e man i fes ts i t s e l f i n t h e development o f c e r t a i n topographic c h a r a c t e r i s t i c s which achieve a t ime independent s t a t e . E r o s i o n a l and t r a n s p o r t a t i o n a l processes, meanwhile, produce a steady f l o w (averaged over pe r iods o f years o r tens o f years) o f water and,waste f rom t h e bas in . P o t e n t i a l energy o f p o s i t i o n i s t ransformed i n t o k i n e t i c energy o f water and d e b r i s mot ion o r i n t o heat. Considered over a ve ry l o n g span o f t ime, however, c o n t i n u a l re-adjustment o f components i n t h e steady s t a t e i s requ i red as r e l i e f lowers and a v a i l a b l e energy d imin ishes. The topographic forms w i l l cor respondingly show a slow evo lu t i on .

Where geo log ic events have brought i n t o b e i n g a new l a n d mass n o t p r e v i o u s l y ac ted upon by water, t he steady s t a t e i s preceded by a t r a n s i e n t s t a t e i n which a new channel system grows and deepens r a p i d l y as the ground slopes are t ransformed t o c o n t r i b u t e most e f f i c i e n t l y t o the drainage network. I n t h e terminology o f t h e e a r l i e r , c l a s s i c a l d e s c r i p t i v e geomorphology, t he t r a n s i e n t s t a t e was r e f e r r e d t o as t h e stage o f you th i n t h e c y c l e of eros ion: t he steady s t a t e as t h e stage o f m a t u r i t y .

V a l i d i t y o f t he Hor ton system o f f l u v i a l morphometry depends upon t h e theory t h a t f o r a g i ven i n t e n s i t y o f e ros ion process, a c t i n g upon a mass o f g i ven p h y s i c a l p r o p e r t i e s , t h e cond i t i ons of surface r e l i e f , s lope and

1 4 9

channel c o n f i g u r a t i o n reach a t ime independent steady s ta te , i n which morphology i s ad jus ted t o t r a n s m i t through the system j u s t t h e q u a n t i t y o f d e b r i s and excess water c h a r a c t e r i s t i c a l l y produced under the c o n t r o l l i n g regimen of c l ima te . Should c o n t r o l l i n g f a c t o r s o f c l i m a t e o r geo log ic m a t e r i a l be changed, the steady s t a t e w i l l be upset. Through a r e l a t i v e l y r a p i d s e r i e s o f adjustments, se rv ing t o r e - e s t a b l i s h a steady s ta te , app rop r ia te new values o f b a s i n geometry a re developed. I n b r i e f , steady s t a t e man i fes ts i t s e l f by i n v a r i a n t geometry: t r a n s i e n t s t a t e by r a p i d changes i n geometry i n which new se ts o f forms rep lace the o ld .

Some s tud ies r e l a t i n g b a s i c geometry t o stream f l o w are summarized by S t r a h l e r ( 1 9 6 4 , p. 472-473) :

E f f e c t of drainage b a s i n c h a r a c t e r i s t i c s upon un i t hydrograph l a g and peak f l o w has been repo r ted by Tay lo r and Schwartz ( 1 9 5 2 ) us ing t h e da ta o f 20 bas ins rang ing i n area from 20 t o 1,600 square m i l e s l oca ted i n the N o r t h and Midd le A t l a n t i c [ sec t i ons o f the ] Un i ted States. Drainage area, l e n g t h o f l onges t watercourse, main stream l e n g t h t o [ c e n t e r ] o f area, and equ iva len t main stream s lope were judged the most s i g n i f i c a n t geomet r ica l va r iab les .

A reg ress ion of peak stream discharge upon f a c t o r s o f topography, b a s i n area and r a i n f a l l was determined e m p i r i c a l l y by P o t t e r ( 1 9 5 3 ) f o r 5 1 bas ins i n the Appalachian P la teau [ o f t he Un i ted S ta tes ] . P o t t e r ' s "T" f a c t o r , rep resen t ing b a s i n geometry, i s t he r a t i o o f longes t l e n g t h o f p r i n c i p a l stream t o square r o o t o f average channel s lope from head t o mouth. The T f a c t o r was judged t o be s i g n i f i c a n t i n m u l t i p l e regress ion w i t h b a s i n area and r a i n f a l l i n t e n s i t y and frequency.

Morisawa (1959a) s u b s t i t u t e d o the r geomorphic p r o p e r t i e s f o r P o t t e r ' s T f a c t o r i n an e f f o r t t o e x p l a i n s t i l l more o f t h e observed var iance. When [ t h e ] r e l i e f r a t i o , c i r c u l a r i t y r a t i o , and frequency o f f i r s t o rder streams were combined as a p roduc t t o y i e l d a new T f a c t o r , m u l t i p l e regress ion f o r 10 o f P o t t e r ' s bas ins on r a i n f a l l i n t e n s i t y and frequency y i e l d e d an equat ion i n which the standard e r r o r o f est imate was cons iderab ly reduced and a h i g h c o r r e l a t i o n was es tab l i shed w i t h peak i n t e n s i t y o f r u n o f f . I n another study, Morisawa (195933) es tab l i shed s i g n i f i c a n t regress ions f o r average r u n o f f and peak r u n o f f on stream length , r e l i e f r a t i o , and shape r a t i o w i t h i n subd iv is ions o f a smal l watershed.

Maxwell (1.960 ) used d i g i t a l computers t o r e l a t e stream discharge c h a r a c t e r i s t i c s t o seve ra l elements o f drainage b a s i n geometry i n the Sau Dimas Exper imenta l Fo res t o f southern C a l i f o r n i a . He computed m u l t i p l e c o r r e l a t i o n s between peak d ischarge and storm r a i n f a l l , cover dens i ty , antecedent r a i n f a l l and n i n e geomorphic p r o p e r t i e s , [us ing ] f i v e a t a t ime. The geomorphic v a r i a b l e s considered were [ o f t h e ] f i f t h order area and diameter: means o f second order area, diameter, r e l i e f , drainage dens i t y , channel frequency, and r e l i e f r a t i o : and watershed b i f u r c a t i o n length , d iameter, and area r a t i o s . I t was concluded t h a t f i f t h - and second-order areas o r diameters, together with second order drainage d e n s i t y and r e l i e f r a t i o , p rov ide a good es t imate o f t he v a r i a b i l i t y i n peak d ischarge [ t h a t ] can be expla ined by [ a l geomorphic v a r i a t i o n between watersheds.

These and o the r s tud ies even tua l l y l e d t o the computer- based e f f o r t s t o s imu la te f low records. The d e t a i l s o f these s tud ies a re n o t i nc luded as they are beyond t h e scope o f t h i s sect ion.

The geomorphic e f f e c t s o f groundwater are summarized by Wi l l i ams ( 1 9 6 9 , p. 269-284) , but. as i n many geomorphological ly o r i e n t e d s tud ies , the emphasis i s on the e f f e c t s o f hydro logy on landforms, r a t h e r than the e f f e c t s o f landforms on hydrology, a t which t h i s s e c t i o n i s d i rec ted .

5.6.2 Q u a l i t a t i v e s tud ies. More q u a l i t a t i v e s tud ies o f te r ranes a l s o have as t h e i r o b j e c t i v e t h e improvement o f t he understanding o f hyd ro log i c cond i t ions . LeGrand and S t r i n g f i e l d (1971d) summarize f a c t o r s i nvo l ved i n d i f f e r e n t i a l

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eros ion o f carbonate te r ranes as a b a s i s f o r making ' b e t t e r i n fe rences o f subsurface h y d r o l o g i c cond i t i ons than cou ld otherwise be t h e case.'

A c o n t r a s t i n topographic r e l i e f i s c h a r a c t e r i s t i c o f carbonate rocks. The r e l i e f may be l o c a l and sma l l as expressed by many shal low s inkholes, o r large, as expressed by i n t e r i o r v a l l e y s . I n a d d i t i o n t o r e l i e f w i t h i n a k a r s t te r rane, s i g n i f i c a n t r e l i e f commonly occurs where a b e l t o f carbonate rocks i s ad jacent t o a b e l t o f noncarbonate rocks. Cuesta topography occurs where t h e adjacent rocks are o n l y s l i g h t l y i n c l i n e d ; carbonate rocks l i e under an i n s o l u b l e caprock and crop o u t near t h e base o f escarpments i n some h u m i d reg ions, but carbonate rocks are t h e more r e s i s t a n t cappings o f many cuestas. Folded rocks c o n t a i n l o n g carbonate v a l l e y s between sandstone r i d g e s i n some h u m i d reg ions, but r idge- forming carbonates between shale v a l l e y s are a l s o common.

D i f f e r e n t i a l e ros ion r e s u l t s f rom a combinat ion of p h y s i c a l and chemical processes. Each component needs t o be considered i n r e l a t i o n t o o t h e r components. P h y s i c a l e ros ion may be considered i n terms o f decomposi t ion o f rocks i n t o d e t r i t u s , t he movement o f d e t r i t u s on slopes and i n t o t h e r i v e r bed, and the e ros ion o f t h e r i v e r bed. The chemical o r s o l u t i o n a l e ros ion may be considered i n terms of f ac to rs favorable f o r rock t o d i s s o l v e and f o r t he d isso lved m a t e r i a l t o be c a r r i e d away. "Prepara t ion € o r e ros ion" i s a p r e r e q u i s i t e f o r b o t h p h y s i c a l and s o l u t i o n a l eros ion. Decomposit ion o r d i s i n t e g r a t i o n o f rock i s e s s e n t i a l f o r p h y s i c a l eros ion; a permeable s o i l cover a l lows slow i n f i l t r a t i o n o f water c o n t a i n i n g carbon d i o x i d e and a i d s s o l u t i o n a l e ros ion of harder rock. I n t h e Western Deser t o f Egypt b o t h Cretaceous and Eocene l imestones have ex tens ive l imestone escarpments, t h e l imestones exposed on t h e escarpments ha-ving been more r e s i s t a n t t o e ros ion than adjacent shales. Severa l major r e e n t r a n t s i n t o t h e escarpments a re topograph ica l l y low enough f o r oases t o form. I t i s b e l i e v e d t h a t escarpments i n Egypt formed e a r l i e r when the c l i m a t e was more h u m i d than a t present .

Two o r more b e l t s o f cuestas may occur where t h e s t r a t i g r a p h i c sequence i s represented by two o r more r e l a t i v e l y i n s o l u b l e fo rmat ions separated by more carbonate format ions and where t h e r e g i o n has been u p l i f t e d ( S t r i n g f i e l d and LeGrand, 1969a, p. 3 5 8 ) . One example i s t h e Ozark P la teau Prov ince o f M i s s o u r i where M iss i ss ipp ian l imestones o f t h e S p r i n g f i e l d P la tueu l i e below t h e Boston Mountain Escarpment which i s capped by r e s i s t a n t Pennsylvanian sandstone; t h e S p r i n g f i e l d P la teau l y i n g above t h e Eureka Spr ings Escarpment i s capped by r e s i s t a n t c h e r t y l imestone and t h e lower l y i n g ( s t r a t i g r a p h i c a l l y ) Salem P la teau on which o l d e r Paleozoic l imestone occurs (Thornbury, 1 9 6 5 , p. 267-270) . Another example i s i n c e n t r a l Tennessee where t h e N a s h v i l l e Bas in extends eastward and i s h ighe r t o p o g r a p h i c a l l y and s t r a t i g r a p h i c a l l y than t h e Eastern Highland R i m Plateau, e a s t o f which i s t he h i g h e r Cumberland Plateau; t he escarpments between them a re d i ssec ted by numerous f r a c t u r e s and l imestone i s widespread on t h e N a s h v i l l e Bas in and H igh land R i m Plateau.

E a r l i e r workers i n the Ozark P la teau (Bre tz , 1965) and i n the c e n t r a l Tennessee area (Hayes, 1 8 9 4 ) cons idered t h r e e d i s t i n c t i v e pe r iods o f u p l i f t and th ree cyc les o f e ros ion t o account f o r t h e s t e p - l i k e p l a i n s i n these reg ions. The d e l i c a t e balances and imbalances of p h y s i c a l and s o l u t i o n a l e ros ion are adequate t o e x p l a i n these c o n d i t i o n s w i t h o u t t h e requi rement o f seve ra l e ros iona l cyc les ( S t r i n g f i e l d and LeGrand, 1969a). T h i s l a t t e r v iew i s i n accord w i t h s tud ies by S t r a h l e r (1944) i n t h e Kaibab P la teau o f Ar izona, by Me is le r ( 1 9 6 3 ) i n t h e f o l d e d Paleozoic carbonate rock t e r r a n e o f Pennsylvania, and by Hack ( 1 9 6 6 ) i n t h e H igh land R i m r e g i o n o f Tennessee.

Two base l e v e l s o f s o l u t i o n a l e ros ion appear t o be necessary €o r t h e development o f two carbonate p l a i n s o f d i f f e r e n t e l e v a t i o n s separated by a l e s s so lub le fo rmat ion a t an escarpment. A p e r e n n i a l stream i s o r has been t h e base l e v e l f o r t h e lower l y i n g carbonate p l a i n , and t h e l e s s so lub le fo rmat ion near the top o f t h e escarpment i s t h e base l e v e l o f t he upper carbonate p l a i n . O n t he lower carbonate rocks, t h e r e s u l t o f p h y s i c a l and s o l u t i o n a l e ros ion has been g rea te r than t h a t on t h e l e s s so lub le rocks of t h e escarpment; t h e sandstones o r o t h e r rocks composing t h e escarpment a re l e s s prone t o s o l u t i o n eros ion and a re n o t l i k e l y t o he p h y s i c a l l y eroded t o a g r e a t e x t e n t becauçe no p e r e n n i a l streams occur near t h e base of t h e escarpment t o c a r r y away r o c k ma te r ia l s . Eros ion a n - t h e upper and lower carbonate rocks i s concurrent , but n o t necessa r i l y equa l i n i n t e n s i t y o r s t a t e o f development. As t h e base l e v e l o f t he upper carbonate rocks i s t h e u n d e r l y i n g l e s s so lub le rocks and n o t t h e

1 5 1

same base w i t h o u t a s o i l cover, ve ry l i t t l e carbon d i o x i d e ( t h a t i s necessary f o r s o l u t i o n ) i s generated.

Cons idera t ion o f s o i l cover leads t o the f o l l o w i n g s i g n i f i c a n t p r i n c i p l e . Eros ion i n carbonate rock te r ranes i s favorable under moderate r a t h e r than under extreme cond i t i ons o f cover, pur i t y o f t h e carbonate rock, topographic r e l i e f , and p r e c i p i t a t i o n . Fo r example, denuded carbonate rocks are much more r e s i s t a n t t o p h y s i c a l and chemical e ros ion than a re carbonate rocks w i t h a moderately th in s o i l cover; where t h e s o i l cover i s ve ry t h i c k , p h y s i c a l e ros ion o f t h e covered bed i s impossib le and chemical e ros ion i s re ta rded because o f r e t a r d e d water c i r c u l a t i o n . The extreme l i m i t s o f t he cond i t i ons o f pur i t y o f carbonate rocks, r e l i e f , and p r e c i p i t a t i o n t h a t tend t o be un favorab le f o r e ros ion are r e l a t e d t o extremes i n cover. For example, pu re carbonates y i e l d no i n s o l u b l e res idue t o form a cover; a lso, in tense p r e c i p i t a t i o n tends t o s t r i p o f f a th in cover and t o keep t h e rock denuded, e s p e c i a l l y on steep slopes. Thus, t h e degree of cover on a carbonate te r rane i s an impor tan t key t o d i f f e r e n t i a l e ros ion and t o o much o f t he topographic r e l i e f . A f t e r p h y s i c a l e ros ion of most o f a t h i c k cover such as a r e s i s t a n t and t h e i n s o l u b l e Pennsylvanian format ions o f t he N a s h v i l l e Dome and the Ozark u p l i f t have almost exposed u n d e r l y i n g carbonates, chemical e ros ion becomes impor tant ; i n such a case, l ower ing o f t he surface o f t h e carbonates i s more r a p i d than t h a t o f t h e r e s i s t a n t beds forming t h e escarpment. There i s a tendency f o r denuded upland rocks t o s tay denuded, and the re i s a tendency f o r smal l amounts o f s o i l t o move i n t o ad jacent low areas t o a i d so lu t i on . Th is combinat ion o f tendencies causes topographic r e l i e f . t o increase u n t i l t he low areas have reached a k a r s t base l e v e l .

5.7 E f fec ts of k a r s t types on stream f l o w regimes ( M i l a n Herak) One o f t he dominant fea tures o f k a r s t areas i s t he s c a r c i t y o f sur face streams a n d v a r i a b i l i t y i n t h e i r f l o w regimes due t o l i t h o s t r a t i g r a p h i c a l sequences, t e c t o n i c s e t t i n g and c l ima te , p a r t i c u l a r l y t he r a t i o o f p r e c i p i t a t i o n t o evaporat ion.

Streams i n k a r s t t e r ranes can have k a r s t c h a r a c t e r i s t i c s i n b o t h recharge and d ischarge areas ( sp r ings o r e s t a v e l l e s fed by waters f rom k a r s t i f i e d recharge area, l a c k o f surface watershed, ponors i n p o l j e o r l a n d v a l l e y bottom, marg ina l p o l j e ponors , e t c . ) . Some streams may be a l l o g e n i c w i t h non-kars t i c recharge areas and t y p i c a l k a r s t i c discharge through ponors. Others can have t y p i c a l k a r s t recharge areas w i t h o n l y p a r t i a l k a r s t i c discharge. And f i n a l l y some may have t y p i c a l k a r s t i c recharge and non-kars t i c discharge. [EDITOR'S NOTE: The reader i s r e f e r r e d t o Mi lanov ic , 1 9 8 1 , f o r example o f k a r s t streams. I

The occurrence of t he types of surface k a r s t streams mentioned above depends upon t h e presence o f d i f f e r e n t types of k a r s t . The d i f f e r e n t k a r s t types have seve ra l impor tan t c h a r a c t e r i s t i c s , i n c l u d i n g c h a r a c t e r i s t i c stream f low regimes, as i n d i c a t e d i n t h e f o l l o w i n g examples.

5 . 7 . 1 Tabular shal low k a r s t . Th i s type o f k a r s t occurs as caps on non-karst e l e v a t i o n s (Paleogene l imestone o v e r l y i n g c l a s t i c Cretaceous-Paleogene rocks i n Nor th A f r i c a ) , o r i t covers some p la t fo rms , p a r t i a l l y o r completely. I n the f i r s t case t h e r e are most o f t e n no i n d i v i d u a l i z e d sur face streams because the water f rom p r e c i p i t a t i o n pe rco la tes i n t o the j o i n t e d carbonate body, t he surface f low be ing t o o s h o r t t o form a normal s u r f i c i a l stream. The second case belongs t o the group o f areas known as f l u v i o k a r s t .

5 .7 .2 Bas in k a r s t . Th is k a r s t i s l i m i t e d t o sediments l a i d down i n depressions upon an o l d e r impervious orogenic basement. K a r s t beds are on ly p a r t i a l l y exposed, c h i e f l y a long t h e margins o f basins; t he r e s t o f them are covered by impervious o r l e s s perv ious c l a s t i c beds. Thus, t he recharge i n t o the k a r s t beds i s f a c i l i t a t e d w h i l e the subsurface d ischarge i s miss ing o r s t r o n g l y at tenuated. Therefore, t he covered bas in k a r s t i s o f t e n sa tura ted by conf ined ground water. Normal streams may occur i n bas in k a r s t areas. Examples o f b a s i n k a r s t areas i n c l u d e the Pannonian Basin, P a r i s Basin and Moscow Basin.

1 5 2

I n t h e cases where subsurface dra inage e x i s t s due t o t h e presence o f a perv ious basement, t h e sur face streams may be p e r i o d i c because o f p e r i o d i c dec l i nes i n ground-water l e v e l s , o r t h e sur face f l o w may be s t r o n g l y diminished. I n extreme cases, t h e f l o w i s complete ly underground during dry per iods when t h e subsurface dra inage and r a t e o f evapora t ion are g rea te r than p r e c i p i t a t i o n . An example i s t h e Konya c losed b a s i n i n Turkey.

5.7.3 F l u v i o k a r s t . Some k a r s t areas may be l e n t i c u l a r o r may be d i ssec ted by ’ v a l l e y s u n t i l t h e non-carbonate base i s exposed (complete ly o r

f l o w a long the v a l l e y s i s permanent and leakage f rom t h e carbonates i s excep t iona l and l o c a l . Numerous examples a re t o be found i n t h e Alps, Carpathians, and n o r t h f l a n k o f t h e D i n a r i c Mountains.

p a r t i a l erOS ton? y ) . Both k a r s t and e r o s i o n a l landscapes occur i n such te r ranes . The

5.7.4 Folded shal low k a r s t . Th i s type o f k a r s t i s developed most f r e q u e n t l y i n e x t e r n a l p a r t s o f chains formed by A l p i n e orogeny where t h e r e a re a l t e r n a t i n g carbonate and non-carbonate l i t h o s t r a t i g r a p h i c u n i t s . The t e c t o n i c s e t t i n g i s cha rac te r i zed by f o l d s w i t h carbonate cores and non-carbonate f lanks ; consequently t h e carbonate cores a r e mos t l y con f ined w i t h o n l y a l i m i t e d v e r t i c a l and l a t e r a l movement o f groundwater. The confinement r e s u l t s i n shal low k a r s t i f i c a t i o n w i t h o u t rega rd t o t h e depth o f t h e carbonate sequence. The f o l d axes d i r e c t n o t o n l y t h e groundwater f l o w but, toge the r w i t h t he main f a u l t s , i n f l u e n c e t h e sur face stream network. The permanent f l o w o f t he streams i s n o t d i s t u r b e d by leakage r e s u l t i n g f rom k a r s t f ea tu res but by i n f i l t r a t i o n o f waters i n t o t h e a l l u v i a l m a t e r i a l and/or by losses t o evaporat ion. The most c h a r a c t e r i s t i c examples a re t h e streams f l o w i n g a long and across some carbonate b e l t s i n N o r t h A f r i c a and i n t h e marg ina l zone ( “marg ina l f o l d s “ ) o f t he Zagros Mountains.

5.7.5 Deep k a r s t . T h i s type o f k a r s t i s cha rac te r i zed n o t o n l y by a t h i c k sequence of carbonate but a l s o by the depth o f k a r s t i f i c a t i o n which penet ra tes below the deepest v a l l e y s and t o some e x t e n t below sea l e v e l ( a t l e a s t i n c o a s t a l reg ions ) . T h i s type o f k a r s t i s normal ly formed w i t h i n geosync l i na l sequences o f rocks w i t h a predominance o f carbonates. Examples o f such areas are t h e D inar ides , He l len ides , and Taur ides. Deep k a r s t i s r a r e i n t h e e p i c o n t i n e n t a l sequences: but examples e x i s t i n Jamaica and Cuba. I t i s n o t easy t o determine t h e a c t u a l base o f k a r s t i f i c a t i o n i n deep k a r s t areas. Among the impor tan t morphologica l f ea tu res which cha rac te r i ze deep k a r s t a re p o l j e s w i t h complex hydro logy and k a r s t p l a i n s . E s t a v e l l e s and l o s t r i v e r s (ponornica) a re common i n t h e h ighe r p a r t s o f k a r s t areas, w h i l e submarine spr ings occur a long coas t l i n e s . The sur face watersheds do n o t c o i n c i d e w i t h t he subsurface watersheds, as t h e subsurface ones a r e n o t i n accordance w i t h t he topography. Th is genera l p a t t e r n o f t h e deep k a r s t i s o n l y a common b a s i s f o r i n d i v i d u a l v a r i e t i e s w i t h i n i t s framework. The v a r i e t y o f deep k a r s t which occurs depends upon t h e t e c t o n i c s e t t i n g a n d d i s t r i b u t i o n o f imperv ious o r l e s s perv ious elements a long w i t h o t h e r f a c t o r s (Herak, 1 9 7 7 ) . However, an area which predominant ly d i s p l a y s deep k a r s t - f e a t u r e s may a l s o con ta in smal le r areas o f shal low k a r s t as w e l l as l e n t i c u l a r o r t a b u l a r k a r s t and f l u v i o k a r s t t h a t l a c k c h a r a c t e r i s t i c s t y p i c a l o f deep k a r s t hydro logy. The presence o f o t h e r k a r s t types does n o t a f f e c t t h e main c h a r a c t e r i s t i c s o f t h e deep k a r s t .

The subsurface water network i s more impor tan t than t h e s u r f i c i a l one i n a l l deep k a r s t areas. T h i s i s due t o t h e f a c t t h a t sur face streams may be miss ing over la‘rge areas; those which a re p resen t g e n e r a l l y have a s h o r t sur face f l o w w i t h seasonal v a r i a t i o n s o f water q u a . n t i t i e s f rom n i l t o seve ra l hundred cub ic meters. These streams most o f t e n occur i n k a r s t p o l j e s . The T r e b i s n j i c a and Cet ina R ive rs i n t h e D i n a r i c k a r s t a re c h a r a c t e r i s t i c examples o f r i v e r s i n deep k a r s t areas. Both f l o w i n t h e h i g h k a r s t reg ion; t h e i r recharge areas a l s o i n c l u d e t h e system o f h i g h e r e leva ted p o l j e s and t h e i r mountainous margins. The recharge area o f t h e T r e b i s n j i c a R i v e r i nc ludes the water systems o f Gatacko p o l j e (predominant ly) , Cern icko p o l j e , and Fa tn i cko p o l j e (predominant ly) . Th i s area i s smal le r than t h a t o f t he R i v e r Cet ina, which i nc ludes a p a r t o f t he system o f Kupresko p o l j e (Mi lac) , t h e waters o f

15 3

Duvanjsko p o l j e (Suica) , and L i van jsko p o l j e (Plouca) together w i t h Busko B l a t o (R ic ina ) , as w e l l as p a r t s o f D inara Mountain and S v i l a j a Mountain. There are numerous spr ings i n each drainage system which d i s p l a y a c l e a r correspondence w i t h ponors o f h ighe r p o l j e s . Th is c o r r e l a t i o n i s most pronounced i n t h e case o f t h e Cet ina R iver . An example i s t h e correspondence o f water l e v e l s o f t he l o s t r i v e r (ponornica) R i c i n a i n Busko B l a t o and the s p r i n g Mala Ruda a t t he margin o f S in j sko p o l j e (see F igu re 5.7-1) . The T r e b i s n j i c a R i v e r i s a t r u e l o s t r i v e r . The leakage e x i s t s i n t h e lower p a r t o f t he v a l l e y , and t h e r i v e r complete ly disappears i n Popov0 p o l j e f l o w i n g underground f rom t h e r e t o the lower p a r t o f t h e Neretva R i v e r o r d i r e c t l y t o the sea. The Cet ina R i v e r f lows s u r f i c i a l l y toward t h e sea, but f rom S in j sko p o l j e onward i t loses some water t o the lower p a r t o f t he v a l l e y i t s e l f , and o the r water t o t h e Jadro R i v e r near S p l i t , or d i r e c t l y t o some n o t y e t p r e c i s e l y de f i ned submarine spr ings.

Though t h e two mentioned r i v e r s d i f f e r i n many fea tures , t h e i r f l ow regimes (concerning v a r i a b i l i t y and imbalance) a re almost i d e n t i c a l , d i s p l a y i n g a maximum i n t h e l a t t e r h a l f o f autumn, a secondary one i n t h e spr ing, and a m i n i m u m i n t h e summer (see F igu re 5 .7 -2 ) . The s i m i l a r i t i e s i n f l o w regimes are due t o the f a c t these r i v e r s have n e a r l y i d e n t i c a l s e t t i n g s o f recharge areas, o f r a t e o f p r e c i p i t a t i o n , and o f evapot ransp i ra t ion .

Some l o s t r i v e r s which f l o w w i t h i n t h e D i n a r i c k a r s t and elsewhere are complete ly recharged f rom non-carbonate areas; they are known as . a l l o g e n i c r i v e r s . The most s t r i k i n g examples a re the P ivka R ive r and t h e Reka R ive r i n t h e c l a s s i c a l k a r s t area o f Slovenia. They are recharged e x c l u s i v e l y from Paleogene f l ysch , f l o w over it, and disappear i n t o t h e marg ina l Mesozoic carbonate rocks.

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Figure 5.7-2 V a r i a b i l i t y i p discharge, 1925-1955, o f (1) t h e T r e b i ç n j i c a R i v e r a t A r s l a n a g i c br idge and ( 2 ) t h e C e t i n a R i v e r a t K r i l j ; a f t e r M i l k u l e c and Tumic , 1 9 6 9 .

1 5 6

Part II: Practices

6. Methods of investigation

6 . 1 I n t r o d u c t i o n (L. A. He ind l )

The method used t o i n v e s t i g a t e t h e h y d r o l o g i c a l regime i n carbonate te r ranes i nc ludes a broad spectrum o f techniques from t h e f i e l d s of geology, geohydrol- ogy, hydrology, phys ics , chemistry, mathematics, and o t h e r d i s c i p l i n e s . Some o f t h e methods a re q u i t e simple; o t h e r s a re h i g h l y soph is t i ca ted . I t i s impor tan t f o r t h e i n v e s t i g a t o r t o always remember t h a t any techniques he chooses t o use i s no b e t t e r than t h e use he makes o f it. The most impor tan t method of i n v e s t i g a t i o n i s thinking, and a wide v a r i e t y o f t o o l s , be they as simple as a hammer o r as complex as r e f l e c t i o n seisomometry o r m u l t i v a r i a b l e analys is . These t o o l s cannot p r o v i d e answers beyond e i t h e r t h e i r c a p a b i l i t i e s o r t he c a p a b i l i t y o f t h e i r users. The adage used i n computer work, "Garbage in; Garbage out , " a p p l i e s e q u a l l y w e l l t o a l l i n v e s t i g a t i o n s . As a f i r s t c o r o l l a r y , i t i s p o s s i b l e t o say t h a t a s o p h i s t i c a t e d method i s n o t a sub- s t i t u t e f o r t h e da ta a c a r e f u l observer can o b t a i n w i t h s imple hand t o o l s . The s o p h i s t i c a t e d t o o l s serve t o augment t h e i n f o r m a t i o n c o l l e c t e d by more simple methods, b u t t h e i r use i s determined by t h e e a r l y s t u d i e s o f a f i e l d hydro- l o g i s t .

The i n v e s t i g a t i o n should be organ ized on t h e b a s i s o f a c a r e f u l a n a l y s i s of t he problem. P r e l i m i n a r y surveys o f l a r g e unknown areas do n o t r e q u i r e t h e s o p h i s t i c a t e d methodologies used i n d e t a i l e d s tud ies o f h i g h l y s p e c i a l i z e d problems where much background da ta a r e a l ready a v a i l a b l e . Research i n t o a l o c a l phenomenon r e q u i r e s a d i f f e r e n t approach than t h e assessment o f t h e water resources o f a r i v e r basin. Thus, t h e f i r s t steps a re t o analyze t h e problem and t o determine what methods and procedures should be used.

I n general , an i n v e s t i g a t i o n should beg in w i t h a d e t a i l e d annotated o u t l i n e t h a t p resents a l l phases o f t h e problem, t h e types o f s o l u t i o n s and a l t e r n a t e s which a re sought, t h e i n t e r p r e t a t i o n s and hypotheses which w i l l l e a d t o those s o l u t i o n s , t h e da ta which must be c o l l e c t e d t o p r o v i d e t h e b a s i s f o r t h e i n t e r p r e t a t i o n s , and t h e methods and techniques t h a t w i l l p r o v i d e t h e data. The annotated o u t l i n e should be d i r e c t e d a t a work p l a n schedul ing phases o f work so t h a t t h i n g s are done i n a l o g i c a l sequence and w i t h a min ima l amount o f t ime wasted on m i s d i r e c t e d e f f o r t s , l a c k o f coo rd ina t i on , and back t rack ing . I f a r e p o r t i s requ i red , t h e t ime o f t h e au thors and e f f o r t s o f stenographic and d r a f t i n g a s s i s t a n t s should be i nco rpo ra ted i n t o the i n v e s t i g a t i v e p lan . The annotated o u t l i n e o f t e n can a c t as a v i r t u a l f i r s t d r a f t o f t h e r e p o r t .

I n the process of deve lop ing t h e o u t l i n e , i t i s adv i sab le t o make a thorough search o f a l l p rev ious work - pub l i shed and unpubl ished - r e l a t e d t o the problem. E a r l i e r r e p o r t s , comp i la t i ons o f da ta from f i l e s , and d iscuss ions w i t h e a r l i e r workers should be compiled and analyzed. T h i s e f f o r t w i l l p r o v i d e i n s i g h t i n t o many f a c e t s o f t h e i n v e s t i q a t i o n . I t w i l l p r o v i d e h i s t o r i c a l data necessary f o r long-term pe rspec t i ves on changes and f l u c t u a t i o n s and, i n some instances, i t may r e v e a l unexpected ways t o approach t h e problem. Occasion- a l l y , t h i s e f f o r t a lone may show t h a t t h e proposed i n v e s t i g a t i o n i s n o t necessary because t h e work has a l ready been done. A l l t h a t may be r e q u i r e d i s r e s u r r e c t i o n f rom t h e f i l e s .

Once f i e l d da ta c o l l e c t i o n begins, t h e f i r s t procedures should be t h e simplest . Fo r example, i f a e r i a l photographs and g e o l o g i c a l maps a r e a v a i l - able, they should be s t u d i e d t o i n d i c a t e t h e key p laces t o examine f o r geolog- i c a l r e l a t i o n s h i p s and h y d r o l o g i c a l phenomena. Streamflows should be es t imated

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o r measured a t a few se lec ted l o c a t i o n s be fore an adequate network o f gages i s i n s t a l l e d . Depths t o water should be measured by tape and cons ide ra t i on g i ven t o t h e hyd ro log i c s i g n i f i c a n c e o f t h e l o c a t i o n o f and a q u i f e r tapped b e f o r e s i t e s a re se lec ted f o r water l e v e l recorders. Water samples should be c o l l e c t e d f o r p a r t i a l analyses and f i e l d de terminat ion made be fo re a f u l l program o f s p e c i a l i z e d l a b o r a t o r y s tud ies i s undertaken.

Moreover, i n the va r ious stages o f work a l l types o f i n f o r m a t i o n - &geo log ica l , h y d r o l o g i c a l , chemical, and topograph ica l - should be c o l l e c t e d more o r l e s s contemporaneously so t h a t i t w i l l be p o s s i b l e a t t he e a r l i e s t f e a s i b l e t ime t o make an assessment o f t he v a l i d i t y o f work p l a n developed f o r t h e i n v e s t i q a t i o n s . Such assessments should be made p e r i o d i c a l l y i n o rde r t o e i t h e r cont inue, ad jus t , o r a l t e r t h e o r i g i n a l p l a n i n a conscious manner. Every i n v e s t i g a t i o n w i l l uncover unexpected i n f o r m a t i o n o r unforeseen d i f f i c u l t i e s t h a t may r e q u i r e a m o d i f i c a t i o n o f t h e o r i g i n a l ob jec t i ves . I n a few r a r e instances, even the o b j e c t i v e s o f an i n v e s t i g a t i o n may be changed.

I n most i n v e s t i g a t i o n s , a r e p o r t i s requ i red . I t i s sound p r a c t i c e t o r e q u i r e p e r i o d i c , but n o t f requent , i n t e r i m r e p o r t s b o t h on progress o f t he i n v e s t i g a t i o n and on spec ia l , o f t e n unexpected, aspects which deserve p u b l i c a t i o n .

One o f t h e s i g n i f i c a n t purposes o f an i n v e s t i g a t i o n i s t o p rov ide i n f o r m a t i o n and conclus ions t h a t w i l l be used by persons o the r than the i n v e s t i g a t o r s . I n o rde r t o make the i n v e s t i g a t i o n wor th i t s investment, i t s i n f o r m a t i o n and conclus ions must be presented i n such manner as t o be usable by those who must make po l i t i ca l - soc io -economica l dec is ions on t h e i r content . Consequently, t h e r e p o r t s o f i n v e s t i g a t i o n must be w r i t t e n i n such a manner t h a t they w i l l be a t a l e v e l t h a t would be compat ib le t o the in tended audience. Reports f o r s c i e n t i f i c co l leagues may be organized, w r i t t e n , and i l l u s t r a t e d i n a f a r d i f f e r e n t f ash ion from those prepared f o r a l a y group hav ing decision-making r e s p o n s i b i l i t i e s . Reports are prepared f o r t he b e n e f i t o f t he user , n o t t h e author , and t h e author must always keep t h i s uppermost i n h i s m i n d when p lann ing and w r i t i n g h i s repo r t s .

I n summary, t h e f o l l o w i n g g u i d e l i n e s apply: 1. Def ine , f o r a l l concerned, the purpose a n d scope o f t he i n v e s t i g a t i o n

2. Determine the b e s t p o s s i b l e approach t o t h e s o l u t i o n o f t h e problem

3. Proceed from t h e s imp les t o r e a s i e s t t o the more complex. 4 . Ma in ta in coo rd ina t i on between a l l d i s c i p l i n e s invo lved. 5 . Require p e r i o d i c i n t e r i m r e p o r t s as a b a s i s f o r coo rd ina t i on and

6. A t s e t i n t e r v a l s assess progress and modi fy t h e o r g i n a l p l a n as

7. Reports should be prepared f o r a s p e c i f i c audience and w r i t t e n and

and the l i m i t a t i o n s o f t ime and manpower.

w i t h i n t h e de f i ned l i m i t a t i o n s .

assessment.

necessary.

i l l u s t r a t e d s o t h a t t h e in tended audience can understand the content .

6 .2 Geo log ica l s tud ies (L. A. He ind l , H. E. LeGrand, and V. T. S t r i n g f i e l d )

I t i s d i f f i c u l t , i f n o t impossib le , t o compartmental ize a l l aspects o f a f i e l d problem, as must be done f o r t h i s guide. A t v i r t u a l l y a l l t imes, geolog ic , hydrogeologic , geomorphologic, hyd ro log i c , eco log ic , and a l l o the r evidence must be considered more o r l e s s s imul taneously and i n con junc t i on w i t h each o ther . By do ing t h i s , t h e s e l e c t i o n a n d q u a l i t y o f t he da ta can be improved w h i l e i t i s be ing co l l ec ted .

Geologic s tud ies i nc lude two p r i n c i p a l stages: 1. F i e l d mapping; and 2. I n t e r p r e t a t i o n o f r e s u l t s r e l a t e d t o the i n v e s t i g a t i o n .

The na tu re o f t he f i e l d mapping program w i l l be determined by the o b j e c t i v e s of t h e i n v e s t i g a t i o n . The form and conten t o f t he i n f o r m a t i o n needed t o f u l f i l l t he o b j e c t i v e s determines the type o f data. t o be c o l l e c t e d , t he sca le o f t he mapp ing , t h e accuracy and r e l i a b i l i t y o f t he r e s u l t s , and the methods and techniques r e l e v a n t t o the study.

The f i r s t r e s p o n s i b i l i t y o f t h e hydrogeo log is t i s t o be acquainted w i t h t he methodology o f h i s and r e l a t e d profess ions so t h a t he may advise on the s e l e c t i o n o f t he most app rop r ia te methods t o a t t a i n t h e ob jec t i ves .

158

I n genera l , t h e geo log ic and hyd ro log i c da ta i s c o l l e c t e d a t the.same t ime. Thus, t h e hydrogeo log is t must be equipped w i t h h i s s tandard t o o l s , p l u s those t h a t can f a c i l i t a t e h i s work w i t h o u t s lowing h i m down. Some o f t h e r e s p o n s i b i l i t i e s can be delegated t o ass i s tan ts , but the geohydro log is t must do enough o f t h e f i e l d work t o be thorough ly f a m i l i a r w i t h t h e c o n d i t i o n s i n v o l v e d i n the i n v e s t i g a t i o n . I n a d d i t i o n t o examining t h e geo log ic fea tures , he should, f o r example, walk t h e outcrops, c o l l e c t t h e specimens, measure t h e depths t o water, and es t imate s p r i n g and streamflows t o become p e r s o n a l l y f a m i l i a r w i t h t h e f i e l d cond i t i ons . T h i s f a m i l i a r i t y pe rm i t s e v a l u a t i o n and i n t e g r a t i o n o f a l l subsequent i n f o r m a t i o n f rom s p e c i a l i z e d s tud ies t o be made based on i t s re levance t o a p a r t i c u l a r problem.

6 .2 .1 F i e l d s tud ies . Under most circumstances, an overwhelming p r o p o r t i o n o f t he major p a r t o f t h e i n f o r m a t i o n c o l l e c t e d during a h y d r o l o g i c i n v e s t i g a t i o n i s from f i e l d s tud ies . F i e l d s tud ies a s used i n t h i s gu ide a re de f i ned t o mean those s tud ies t h a t can be made l a r g e l y by observa t ion and t h e use o f s imple hand inst ruments. The most e s s e n t i a l commonly used ins t ruments a re a hand lens, c l inometer , measuring tape, stopwatch, thermometer, k n i f e , g e o l o g i s t ‘ s p i c k , h y d r o c h l o r i c a c i d f o r e s t i m a t i n g ca lc ium carbonate (CaC03) conten t , and a pocket pH k i t . A carpenter ’s square €o r e s t i m a t i n g t h e d ischarge o f w e l l s , an anero id barometer €o r e s t i m a t i n g a l t i t u d e s , and a hand l e v e l may be considered simple, e a s i l y c a r r i e d inst ruments. Spec ia l i zed s tud ies done i n t h e f i e l d but u s i n g complex ins t ruments a re u s u a l l y r e f e r r e d t o by some te rm which i n d e n t i f i e s t h e i r rea lm o f s p e c i a l i z a t i o n . These s tud ies i n c l u d e t h e seve ra l types o f s tud ies such as geophysica l ( e l e c t r i c a l r e s i s t i v i t y , grav imeter , magnetometer, r e f l e c t i o n seismograph, e t c . ) , r a d i o i s o t o p e and o t h e r t r a c e r methods, eng ineer ing t e s t s , and geochemical analyses.

Recogni t ion o f p e r t i n e n t g e o l o g i c a l f ea tu res and t h e i r r e l a t i o n s h i p t o t h e hyd ro log i c regime i s t h e pr imary f i e l d task. Table 6.2-1 o u t l i n e s t h e p r i n c i p a l geo log ic and geomorphologic ( topographic) f ea tu res t h a t should be looked f o r i n t h e f i e l d . C lose ly r e l a t e d h y d r o l o g i c fea tu res t h a t should a l s o be noted are o u t l i n e d i n t a b l e 6.2-2. Other fea tu res t h a t may be recognized on ly through a combinat ion o f f i e l d , l abo ra to ry , and a n a l y t i c a l s tud ies , but f o r which t h e geohydro log is t should be a l e r t a re g i ven i n t a b l e 6.2-3.

6.2.2 I n t e r p r e t a t i o n o f r e s u l t s . I n t e r p r e t a t i o n o f da ta i s an i n t r i c a t e process. These i n t e r p r e t a t i o n s should consider t h e o b j e c t i v e s o f t h e s tudy and t h e u l t i m a t e use o f t h e i n t e r p r e t a t i o n s and conclus ions i n decision-making by the in tended audience.

The te r ranes :

1.

2.

f o l l o w i n g hydrogeologic c o n d i t i o n s commonly occur i n carbonate r o c k

I r r e g u l a r and unpred ic tab le pe rmeab i l i t y . Carbonate rock fo rmat ions g e n e r a l l y have unpred ic tab le combinat ions o f highly and p o o r l y permeable zones. The r o c k i t s e l f i s commonly p o o r l y permeable t o r e l a t i v e l y impermeable, but t h e development o f s o l u t i o n channels may r e s u l t i n t h e un i t be ing, a t l e a s t l o c a l l y , a highly p roduc t i ve zone as a source o f water. H igh p e r m e a b i l i t y alone, however, i s no guarantee o f high produc t ions . The high p e r m e a b i l i t y may a l s o be an i n d i c a t i o n o f a water t a b l e so low above t h e u n d e r l y i n g rocks, o r f l o w so rap id , t h a t t h e amount o f water i n s torage i s minimal. Moreover, i f the low water . table o v e r l i e s s a l t water, t h e waters o f t h e th in fresh-water zone and t h e s a l t water may be pumped o u t together , thus y i e l d i n g water o f poor q u a l i t y if n o t a c t u a l l y induc- ing sa l t -water encroachment. I n a d d i t i o n , rock fo rmat ions w i t h h i g h p e r m e a b i l i t y sometimes do n o t f i l t e r o u t contaminants and p o l l u t a n t s , again p r o v i d i n g an unusable water f o r c e r t a i n purposes. The p o o r l y Permeable l imestones, o f course, a r e poor aau i fe rs . S c a r c i t y o r undependab i l i t y o f p e r e n n i a l su;face streams. I n w e l l developed k a r s t te r ranes , t h e increased Permeab i l i t y o f t h e carbonate rocks may cause t h e water t a b l e t o occur below t h e l e v e l o f some streams. The increased pe rmeab i l i t y , however, commonly i s i r r e g u - l a r l y d i s t r i b u t e d SO t h a t streams may disappear underground and then re-emerge a t t h e sur face f a r t h e r downstream. The i r r e g u l a r i t y , l o c a l

159

Table 6.2-1. Geologic and geomorphologic fea tures p e r t i n e n t t o f i e l d s tud ies .

GEOLOGIC STRUCTURE Near ly h o r i z o n t a l beds AND SETTING Raised Coasta l P l a i n o r

p l a t e au B e l t e d Coasta l P l a i n - Breached dome Moderately s teep ly

dipp i.ng beds A n t i c 1 i n e Sync l ine o r b a s i n Complex - f a u l t e d and

f o l d e d Other No cover Cover

cuestas

Permeab l e Th in Th ick

Th in Th ick

R e l a t i v e l y impermeable

TOPOGRAPHY Drainage d e n s i t y c lose (normal) Sparse ( k a r s t ) R e l i e f

S l i q h t r e l i e f Few s inks Many s inks Uvalas

Thickness o f l imestone O- 1 0 f e e t

10 - 4 0 f e e t 40-200 f e e t more than 200 f e e t L i t h o l o g y o f l imestone Massive , pure Massive , impure Thin-bedded, pure Thin-bedded, impure

Pr imary Secondary

Permeab i l i t y o f l imestone

( J o i n t s , f rac tu res , s o l u t i o n channels)

I n f l u e n c e o f s t r u c t u r e on f l o w

Retards A ids D i v e r t s g r e a t l y R e l a t i v e l y un impor tant Unknown

Great r e l i e f R e l i e f r e s u l t i n g f rom mogotes, haystacks, r e s i d u a l knobs, o r deep s inks

R e l i e f f rom normal stream

P o l j e s Escarpments-l imestone as

Escarpments-l imestone

i n c i s i o n

caprock,

beneath r e s i s t a n t caprock

Below water t a b l e Caverns and s o l u t i o n

openings

SOLUTION FEATURES Above water t a b l e RELATED Sinkholes TOPOGRAPHY No s inkho les

Nat U r a 1 we 1 1 s No caverns and no Caverns a.nd s o l u t i o n s o l u t i o n openings

openings (dry)

160

Table 6.2-2. Hydro log ic fea tu res t o be s tud ied i n the f i e l d .

TEMPERATURE Temperature Win ter less - warm Midd le l a t i t u d e s

Summerless - c o l d moderate

POSITION OF Where cover i s p resent WATER TABLE OR I n cover - above t o p OTHER PIEZOMETRIC o f l imestone SURFACE Water t a b l e i n cover

h ighe r than water l e v e l o f l imestone

Water l e v e l o f l ime- stone h ighe r than water t a b l e i n cover

a l t e r n a t i n g i n t ime o r space

I n l imestone - a few f e e t o r a few tens o f f e e t below top o f l imestone

I n lj-mestone a t depths g rea te r than 5 0 f e e t

I n u n d e r l y i n g m a t e r i a l a l l o f l imestone i n zone o f a e r a t i o n

Both water l e v e l s

DISCHARGE LEVEL CONTROL Coasta l Area

Sea l e v e l Permanent streams Under ly ing impermeable

o r non-soluble beds Not a p p l i c a b l e -

a r t e s i a n

P r e c i p i t a t i o n (median annual A r i d - l e s s than 1 5 inches Low-uneven seasonal

d i s t r i b u t i o n - 1 5 - 30 inches

High-uneven seasonal d i s t r i b u t i o n - g r e a t e r than 35 inches

Medium-uniform-20-35 inches

High-uni form-greater than 35 inches

Where t h e r e i s no cover Near t o p o f l imestone Near base o f l imestone I n u n d e r l y i n g m a t e r i a l a l l o f l imestone i n zone o f a e r a t i o n

Water l e v e l i n s inks Water t a b l e o f sur face

Water l e v e l i n l imestone Ponded water caused hy

impermeable c lay - bottomed s i n k

ma t e r i a l s

I n t e r i o r Permanent streams Under ly ing impermeable

o r non-soluble beds Not app l i cab le -a r tes ian Bur ied deeply-

e s s e n t i a l l y no d içcha r g e

1 6 1

Table 6.2-3. Features r e q u i r i n g combined f i e l d , l a b o r a t o r y and a n a l y t i c a l s tud ies .

PALEOHYDROLOGY Limestones never Conformab1.e r e l a t i o n s e leva ted i n t o a Degree o f compaction, f r e s h water system conso l i da t i on ,

water system f o r t h e Loosely conso l ida ted f i r s t t ime L igh t ly conso l ida ted

water system more than once

Unconformity a t t op o f l imestone

Emergence i n t o f r e s h r e c r y s t a l l i z a t i o n

Emergence i n t o f r e s h R e c r y s t a l l i z e d

QUALITY BOUNDARIES S a l t water l a t e r a l l y No s a l t water 1 a t e r a . l l y S a l t water below No s a l t water below Gradual inc rease i n m ine ra l i zed water w i t h depth ( n o t c h l o r i d e )

boundar ies No s i g n i f i c a n t q u a l i t y

S a l t water throughout

Table 6.2-4. D iagnos t ic c h a r a c t e r i s t i c s o f t he p r i n c i p l e rock- forming carbonate minera ls .

Spec i f i c R e f r a c t i v e S o l u b i l i t y i n Genera 1 G r a v i t y I n d i c e s co ld , d i l u t e a c i d Remarks

Hexagonal (Rhombohedral)

C a l c i t e 2 . 7 1 1.658-1.486 E f fervescent L a m e l a r tw inn ing

Magnesite 3.06 1.717-1.515 Slow Rare i n sediments

Do l o m i t e 2.87 1.682-1.503 Slow Rhombs;curved face

An ake r i t e 3.0 1.727-1.534 Slow Weathers ye l l ow

S i d e r i t e 3.89 1.873-1.633 I n s o l u b l e L imon i te s t a i n s

Orthorhombic

Argon i t e 2.94 1.53-1.68-1.69 E f fe rvescent Pr ismat ic ; uns tab le

162

s c a r c i t y , and undependab i l i t y o f p e r e n n i a l streamflow i n k a r s t t e r ranes r e s u l t i n l o c a l problems of water supply and waste d isposa l .

3. M i n e r a l i z e d water . A common c h a r a c t e r i s t i c o f water f rom carbonate rock a q u i f e r s i s i t s "hardness". Water w i t h excessive hardness r e s u l t s i n i n c r u s t a t i o n o f i r o n p ipe . I n a d d i t i o n , "hard" water i s ob jec t i onab le f o r some domestic and i n d u s t r i a l uses.

4 . S o i l . The s o i l s and t h e i r d i s t r i b u t i o n s t r o n g l y i n f l u e n c e t h e r a t e s o f i n f i l t r a t i o n and r u n o f f , and t h e d i s t r i b u t i o n o f ground water i n carbonate rock te r ranes . Many carbonate rock format ions a re r e l a - t i v e l y pure, l e a v i n g almost no i n s o l u b l e res idue as a r e s u l t o f weather ing a t t h e surface t o form s o i l s . Less pure carbonate rocks have a t h i c k e r res idue and, thus, p o t e n t i a l l y a t h i c k e r s o i l . The development o f a t h i c k s o i l g e n e r a l l y i n d i c a t e s a p o t e n t i a l f o r a h i g h l y permeable u n d e r l y i n g rock; t h i s s i t u a t i o n o f t e n r e s u l t s i n t h e fo rmat ion o f a shal low a q u i f e r a t t h e base o f t h e r e s i d u a l s o i l . A non-ex is tant , thin, o r i r r e g u l a r l y d i s t r i b u t e d s o i l may i n d i c a t e an u n d e r l y i n g l imestone carbonate rock t h a t i s r e l a t i v e l y impermeable.

5. Topography p rov ides many c lues t o t h e i n t e r r e l a t i o n s h i p s o f t h e geo log ic and hyd ro log i c regime. The c l a s s i c a l k a r s t topography, composed o f s inks , depressed areas, and i s o l a t e d r idges , mounds, and h i l l s , p rov ides a s t rong i n d i c a t i o n o f p o t e n t i a l problems. For example, an area cha rac te r i zed by s inks may be one i n which excess ive pumping from w e l l s may cause subsidence. S i m i l a r l y , heavy s t r u c t u r a l l oad ing may a l s o r e s u l t i n subsidence w i t h t h e consequent c o l l a p s e o f t h e s t r u c t u r e . The same c h a r a c t e r i s t i c , excessive ease i n t h e development o f s o l u t i o n channels, may be put t o good use i n o t h e r instances. The g r o u t i n g o f wide wings t o a dam i n a t e r r a n e o f highly permeable carbonate rock may r e s u l t i n an underground storage o f much l a r g e r capac i t y than the sur face r e s e r v o i r , p rov ided t h a t s u i t a b l e l a t e r a l c o n d i t i o n s p reven t t h e ground water f rom m i g r a t i n g o u t o f t h e area.

6.2.3 P resen ta t i on o f r e s u l t s . Representat ion o f g e o l o g i c a l f ea tu res may be accomplished by maps, c ross sec t ions , diagrams, and t e x t . Each has i t s advantages and disadvaptages, and t h e r e i s no s i n g l e s a t i s f a c t o r y method t o show the three-dimensional c o n d i t i o n s t h a t e x i s t i n t h e f i e l d and t h e i r dynamic changes through t ime as they a re s t ressed by c l i m a t i c , geo log ic , and man-made changes.

No at tempt i s made he re t o descr ibe t h e c h a r a c t e r i s t i c s o f t he p r i n c i p a l methods f o r p resen ta t i on o f g e o l o g i c a l i n fo rma t ion . The hyd rogeo log is t i s caut ioned, however, t h a t h i s r e s p o n s i b i l i t y i s t o p resen t geohydrology, n o t t h e geology, thus, a q u i f e r s and p o o r l y permeable rocks (hydrogeologic u n i t s ) should be shown r a t h e r than format ions and o t h e r geo log i c u n i t s . U n i t s should be i n terms o f pe rmeab i l i t y , i n c l u d i n g fo rma t iona l p e r m e a b i l i t y , o r t r a n s m i s s i v i t y , and c o n t i n u i t y o f p e r m e a b i l i t y r a t h e r than o f age and l i t h o l o g i c c o n t i n u i t y . i n essence, g e o l o g i c a l f a c t o r s must be mapped and i n t e r p r e t e d i n terms o f t h e i r hyd ro log i c c h a r a c t e r i s t i c s .

A second c a u t i o n i n regard t o p r e s e n t a t i o n i s t h e necess i t y f o r d i r e c t n e s s and s i m p l i c i t y . Us ing a v a i l a b l e evidence, t h e s imp les t s o l u t i o n i s t h e most l i k e l y t o be co r rec t ; t he re fo re , p r e s e n t a t i o n o f t h e i n f o r m a t i o n c o l l e c t e d should be the s imp les t and most d i r e c t p o s s i b l e f o r t h e s t a t e d purpose o f t h e presenta t ion . For example, a d i scuss ion of t h e e f f e c t o f t h e geology on ground-water occurrence should n o t be s ide t racked i n t o an ex tens ive d e s c r i p t i o n o f t he pa leonto logy o f t h e area. Each map, i l l u s t r a t i o n , and p iece o f t e x t should be t e s t e d €o r i t s re levance t o t h e purpose o f t h e i n v e s t i g a t i o n and t h e r e p o r t be ing prepared. A hydrogeologic c ross s e c t i o n should show t h e hyd ro loq i c fea tu res and t h e r e l e v a n t geo log ic c o n t r o l s . Moreover, a map, d i a - gram, o r t e x t m a t e r i a l t h a t i s complex and d i f f i c u l t f o r t h e p r o f e s s i o n a l t o i n t e r p r e t i s use less t o t h e nonprofess ional .

The sca le o f a map, t h e s i z e o f t h e symbols and l e t t e r i n g , and t h e s i z e of t he key fea tures should be such t h a t t h e reader can r e a d i l y understand t h e purpose o f t he i l l u s t r a t i o n . A l a r q e map t h a t i s d i f f i c u l t t o handle may be as useless as a map t h a t i s so smal l t h a t n e i t h e r fea tu res n o r wotd inq can be d iscerned w i t h o u t a magni fy ing g lass . I t i s t h e r e s p o n s i b i l i t y o f t h e

163

i n v e s t i g a t o r t o determine a t an e a r l y date i n the s tudy t h e proper sca le and s i z e a t w h i c h t h e o b j e c t i v e s can b e s t be shown and t o c o l l e c t o r reduce t h e da ta so i t can be understandably presented.

Geologic mapping- may be done i n a v a r i e t y o f ways, on a v a r i e t y o f bases, and a t a v a r i e t y o f scales. These a re determined i d e a l l y by t h e purpose o f t he i n v e s t i g a t i o n and, p r a c t i c a l l y , by t h e a v a i l a b i l i t y o f ma te r ia l s .

6.2.3.1 Base maps. Base maps a r e c r i t i c a l t o t h e q u a l i t y o f t he hydrogeologic mapping, because they s e t t h e p a t t e r n f o r h o r i z o n t a l and v e r t i c a l c o n t r o l and t h e procedure o f f i e l d s tud ies . An area f o r which t h e r e are no maps r e q u i r e s a d i f f e r e n t amount o f mapping t ime than one f o r which r e l i a b l e hatchured o r topographic maps are a v a i l a b l e a t a des i rab le sca le and contour i n t e r v a l .

Where t h e r e a re no base maps, t h e geo log ic mapping may be done by rough t r i a n g u l a t i o n c o n t r o l on s t a r s and prominent p o i n t s and fea tu res a t sca les compat ib le w i t h t he needs o r u s i n g a e r i a l photographs. Basic c o n t r o l may be by o r d i n a r y hand compass and a l t i m e t e r , p lane t a b l e and a l idade, o r by t r a n s i t . O n p r e l i m i n a r y s tud ies o f l a r g e areas, i t may be s a t i s f a c t o r y t o proceed t o do the geo loq ic mapping s imul taneously w i t h t he ground control by hand compass and a l t i m e t e r . For d e t a i l e d la rge-sca le s tud ies, i t may be expedient t o have topographic maps prepared b e f o r e t h e d e t a i l e d geo log ic s tud ies a r e made. seve ra l s tandard t e x t s p r o v i d e t h e d e t a i l s o f these methods.

Aer ia l . photographs form e x c e l l e n t base maps f o r geo log ic mapping. I n d i v i d u a l photographs, however, have a reasonably constant sca le o n l y i n t h e i r centers , and become i n c r e a s i n g l y d i s t o r t e d outward t o t h e i r edges. These d i s t o r t i o n s may be co r rec ted o r compensated f o r by manual procedures o r by t h e use o f one o f a v a r i e t y o f inst ruments. Some o f t he more modern (o r thograph ic ) a e r i a l photographs have v i r t u a l l y no d i s t o r t i o n , but those are n o t y e t w ide l y a v a i l a b l e i n many p a r t s o f t h e wor ld . F i e l d mapping r e q u i r e s ground c o n t r o l f o r h o r i z o n t a l d is tances and a l t i t u d e s . A c t u a l mapping may be done on i n d i v i d u a l photographs o r on mosaics o f t he c e n t r a l be t te r - sca led p a r t s o f i n d i v i d u a l photographs. A t r a c i n g o f t he drainage p a t t e r n o f a mosaic w i t h t he a d d i t i o n of t h e a l t i t u d e o f a few key p o i n t s p rov ides a reasonable p l a n i m e t r i c base on t o which the geo log ic data may be t rans fe r red . A more s a t i s f a c t o r y map may be prepared by t r a n s f e r r i n g the geology on a p l a n i m e t r i c map t o a copy o f t he mosaic base whose black-and-white tone has been subdued t o gray-ana-white. Th i s pe rm i t s t h e geo log ic fea tures t o stand o u t aga ins t t he gray base more prominent ly than they do aga ins t a b l a c k one.

Stereoqraphic p a i r s o f a e r i a l photographs p rov ide a va luab le study base be fore and d u r i n g mapping procedures. The three-dimensional v iew through o r d i n a r y s tereographic ins t ruments p rov ides a va luab le i n s i g h t i n t o s t r u c t u r a l and s p a t i a l r e l a t i o n s h i p s and the d i s t r i b u t i o n o f hyd ro log i c features. By u s i n g them i t i s p o s s i b l e t o i d e n t i f y key areas f o r d e t a i l e d study and mapping. The v e r t i c a l sca le i s h i g h l y exaggerated but, w i t h p r a c t i c e , t he user l ea rns t o compensate men ta l l y f o r t h e d i s t o r t i o n .

i n general , a e r i a l photographs a re e x c e l l e n t €or r a p i d mapping where c lose v e r t i c a l c o n t r o l i s a secondary requirement.

Hachured maps u s u a l l y have e x c e l l e n t h o r i z o n t a l c o n t r o l , but v e r t i c a l c o n t r o l i s l i m i t e d t o key p o i n t s . The shading e f f e c t o f well-drawn hatchures, however, g i ves a u s e f u l impress ion o f t he topographic r e l i e f . Such maps are n o t commonly made now, but many o f those made d u r i n g the seventeenth t o n ine- teen th c e n t u r i e s a re o f unpara l l ed excel lence i n engravinq.

Topographic maps g e n e r a l l y have u s e f u l t o e x c e l l e n t v e r t i c a l t o h o r i z o n t a l c o n t r o l and p rov ide t h e b e s t commonly a v a i l a b l e base maps. The v e r t i c a l c o n t r o l i s qood f o r most types o f r e l i e f , but i t i s v i s u a l l y l e s s s a t i s f a c t o r y than t h a t o f hachured maps. I t a l s o i s sometimes d i f f i c u l t t o d i s t i n g u i s h between contour l i n e s i n areas of h i g h r e l i e f and t o i n t e r p o l a t e between them i n areas o f low r e l i e f and i n areas hav ing a l a r g e contour i n t e r v a l . Nonethe- less , they a re probably t h e most commonly used bases f o r geo log ic mapping.

Some topographic maps today are p r i n t e d on a h o r i z o n t a l l y and v e r t i c a l l y co r rec ted a e r i a l photograph. T h i s type o f map, a l though n o t common, combines t h e advantages o f b o t h types o f maps and minimizes t h e i r disadvantages.

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6.2.3-2 Hydro log i c versus geo log ic mapping. C l a s s i c a l geo log i c mapping uses the geo log ic fo rma t ion as i t s base unit and most hydrogeologic maps a re s t i l l made t h i s way. Many w i l l p robab ly con t inue t o be made t h i s way f o r t h r e e reasons: (1) i n many ins tances they show t h e p r i n c i p a l ground-water u n i t s i n t h e i r p roper r e l a t i o n s h i p s ; (2) such maps can be used f o r o t h e r geo log i c purposes than water-resources i n v e s t i g a t i o n s ; ( 3 ) geohydro log i s t s a re t r a i n e d t o make geo log ic maps.

I n some ter ranes, and carbonate rock t e r r a n e s a r e an e x c e l l e n t example, t he p e r m e a b i l i t i e s a r e o n l y l o c a l l y c o n t r o l l e d by fo rma t ion boundaries. Elsewhere, t h e p e r m e a b i l i t i e s c ross t h e boundar ies i r r e g u l a r l y making the fo rma t iona l uni t inadequate t o show t h e h y d r o l o g i c regime o f t h e subsurface. I n such ins tances i t i s necessary e i t h e r t o abandon t h e fo rma t ion as a mapping un i t o r t o o v e r l a y i t w i t h a h y d r o l o g i c unit . I n some instances, seve ra l formations w i t h s i m i l a r p e r m e a b i l i t i e s a c t as a s i n g l e h y d r o l o g i c unit . Commonly, however, t h e s i t u a t i o n i s more complex and t h e g e o l o g i s t must map s i m i l a r p e r m e a b i l i t i e s and t h e c o n t i n u i t y O€ s i m i l a r p e r m e a b i l i t i e s i n t h e same way as he maps s i m i l a r l i t h o l o g i e s and t h e i r c o n t i n u i t i e s .

6.2.3.3 Scale. Th'e problem o f sca le i s s imple i n p r i n c i p l e but may be awkward i n p r a c t i c e . I n general , i t i s b e s t t o use a sca le t h a t shows t h e fea tu res t h e map i s in tended t o emphasize. L o c a l f e a t u r e s o f importance t h a t cannot be emphasized on a smal l -scale map may be shown a t smal le r sca les on i n s e t maps. S i m i l a r l y , r e g i o n a l f ea tu res t h a t a f f e c t t h e h y d r o l o g i c regime o f an area o f a Small-scale map may be shown on i n s e t maps o f l a r g e r scale. Wherever poss ib le , t he scales should be modular so t h a t one sca le i s 0 . 1 ~ ~ 0 . 5 ~ ~ 2x, 4x, o r some s i m i l a r f r a c t i o n o r m u l t i p l e o f t h e scale o f t h e smal l -sca le map. The i n s e t scales should be cons is ten t .

i n p r a c t i c e , t h e scale i s g e n e r a l l y determined by t h e a v a i l a b l e m a t e r i a l and equipment. I t i s poss ib le , i n most cases, t o have maps reduced o r en la rged pho tog raph ica l l y t o p r o v i d e t h e d e s i r e d modular scale. When t h i s i s done, the photographed maps commonly r e q u i r e r e d r a f t i n g . O n reduced maps, t h e l i n e s may need t o be th ickened and t h e l e t t e r i n g enlarged: f i n e l y meshed p a t t e r n s on t h e o r i g i n a l become s o l i d and must be replaced. Enlarged maps may need t o have contours and o t h e r l i n e s redrawn t o an unob t rus i ve but v i s i b l e th ickness , l e t t e r i n g must be redrawn, e t c .

Al though changing t h e scale of a map seems awkward, i t i s w e l l w o r t h t h e e f f o r t . There i s a tendency i n t h e f i e l d " t o f i l l t h e map" by r e c o r d i n g unnecessary d e t a i l on a map w i t h a sca le o f 1:10,000 because t h e r e i s room € o r it, a l though t h e requirements o f t h e i n v e s t i g a t i o n c o u l d be s a t i s f i e d w i t h a map having t h e d e t a i l v i s i b l e o n l y on a sca le o f 1:50,000. S i m i l a r l y , w i t h a map o f 1:50,000, t h e r e i s a tendency t o genera l i ze l o c a l f e a t u r e s t h a t may be impor tan t t o t h e i n v e s t i g a t i o n .

Some a r b i t r a r y g u i d e l i n e s have been suggested f o r maps o f one t ype o r another, but these g e n e r a l l y a re n o t app l i cab le . Maps a re a means f o r communi- c a t i n g i n f o r m a t i o n and must be used by people; i t i s g e n e r a l l y p r e f e r r e d t o have maps no l a r g e r than about 1.3m x l m . Large maps a re d i f f i c u l t t o h o l d and read w h i l e b e i n g h e l d o r spread on a t a b l e . Large maps may be put on w a l l s , but most l a r g e maps a re n o t planned t o be s t u d i e d t h a t way.

Some a r b i t r a r y g u i d e l i n e s have been suggested f o r t h e sca le o f maps o f one type and another, but these a re n o t g e n e r a l l y app l i cab le . Fo r example, t h e scale o f a country-wide map o f t h e USSR cannot be g i ven t h e same l a t i t u d e as on f o r T r i n i d a d and Tobago o r even Swi tzer land. I t i s f a r b e t t e r t o decide on a scale t h a t w i l l show t h e d e s i r e d i n f o r m a t i o n and p r o v i d e s p e c i a l i z e d fea tu res such as modular scales. When maps a r e made o f areas o r bas ins common t o two o r more coun t r i es , every p o s s i b l e a t tempt shou ld be made t o show t h e i n f o r m a t i o n a t common scales.

6.2.4 F i e l d i d e n t i f i c a t i o n o f m ine ra l s (D. J. Burdon). I t i s n o t always easy t o d i s t i n g u i s h t h e m ine ra l s i n carbonate rocks from each o the r , p a r t i c u l a r l y c a l c i t e and do lomi te . I t i s d i f f i c u l t t o determine t h e amount o f c a l c i t e t h a t i s p resent i n a r o c k exposure, even i n a quarry . The p r i n c i p a l f i e l d d i f - ferences a re hardness and form. C a l c i t e has a hardness o f 3 on Moh's scale, and do lomi te has a hardness o f 3 . 5 t o 4 . W i t h p r a c t i c e t h e d i f f e r e n c e i s

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r e a d i l y i n d e n t i f i a b l e by a k n i f e scratch. Cleavage o r f r a c t u r i n g o f c a l c i t e r e s u l t s i n a f l a t face, where, genera l l y , do lomi te c r y s t a l faces a re curved o r saddle shaped. I n add i t i on , do lomi te i s e s s e n t i a l l y a r e c r y s t a l l i z e d r o c k t h a t w i l l have p a t t e r n s o f s h e l l s , o o l i t e s , and c l a s t i c l imestone fragments, l a r g e l y w i t h o u t i n t e r n a l d e t a i l . Occasional ly , i t w i l l be p o s s i b l e t o see i n a dolo- m i t e rhombohedral c u t t he p r imary s t r u c t u r e o f f o s s i l s , c l e a r l y i n d i c a t i n g t h a t t h e do lomi te i s a replacement product . Many incomple te ly do lomi t i zed l ime- stones a re a l s o m o t t l e d owing t o t h e d i f ferences i n t h e composi t ion and t e x t u r e o f t h e do lomi t i zed p a r t s .

The main d i a g n o s t i c c h a r a c t e r i s t i c s o f t h e s i x minera ls , l i s t e d i n t a b l e 6.2-4, can be made by b a s i c l a b o r a t o r y equipment i n t h e f i e l d . D i f f e rences are emphasized, but s t i l l remain smal l . The r e l a t i v e s o l u b i l i t y o f these m ine ra l s i n d i s t i l l e d water and i n p r e c i p i t a t i o n con ta in ing d i sso l ved CO2 are d i s - cussed elsewhere i n t h i s Guide.

Limestone may c o n t a i n as much as 1 0 percent o f magnesia (6.03 percent magnesium); Hosking ( 1 9 5 6 ) g i ves a f i e l d t e s t f o r de termin ing whether t h MgO conten t i s high (6 -10 percent ) , medium (1-5 percent) , o r low. I' A drop o f 0 .1 percent T i t a n Yel low i s added t o a s t reak o f t h e rock sample made on a w e l l - v i t r i f i e d unglazed f l o o r t i l e . When the reagent has i n f i l t r a t e d i n t o the t i l e , a drop o f 5N sodium hydrox ide i s added. According t o whether the magnesia conten t i s h igh, medium, o r low, t h e c o l o r o f t h e t r e a t e d s t r e a k i s v e r m i l l i o n , orange, o r ye l low" . He a l s o descr ibes how t h i s technique can be used i n t h e l abo ra to ry .

6.3 Remote sensing (P. E. LaMoreaux and B. M. Wi lson)

A broad d e f i n i t i o n o f remote sensing inc ludes a l l methods o f c o l l e c t i n g i n f o r m a t i o n about an o b j e c t w i t h o u t be ing i n p h y s i c a l con tac t w i t h t h a t ob jec t . However, i n t h i s sec t ion , a more r e s t r i c t i v e d e f i n i t i o n i s used; i t inc ludes o n l y those methods t h a t employ e lect romagnet ic energy, i n c l u d i n g l i g h t , heat, and radiowaves, as means o f d e t e c t i n g and measuring t a r g e t c h a r a c t e r i s t i c s (Sabins, 1 9 7 8 ) . Geophysical methods t h a t would be i nc luded i n t h e broader d e f i n i t i o n a re discussed i n s e c t i o n 6.4. The major types o f remote sensing used i n carbonate hydro logy a re a e r i a l photography, s a t e l l i t e imagery, thermography, and radar . Sonar, down-hole t e l e v i s i o n cameras, and o t h e r remote sensing techniques a r e - a l s o used by carbonate hyd ro log i s t s .

The de terminat ion o f t h e optimum remote sensing band o r band r a t i o s ( i .e . , range o f de tec ted wave leng ths ) and the type of remote sensing t o be employed depends on t h e o b j e c t i v e o f t h e study and what fea tu res a re sought t o be enhanced. Th is optimum band o r band r a t i o s e l e c t i o n can be done by s t a t i s t i c a l methods (which g e n e r a l l y r e q u i r e use o f a computer) o r by manual techniques such as t h e co inc iden t s p e c t r a l p l o t methods descr ibed by Shourong ( 1 9 8 2 ) .

The s teps i n a q u i f e r mapping u s i n g remote sensing as l i s t e d by Moore ( 1 9 8 0 ) are: 'image ana lys i s , image i n t e r p r e t a t i o n , geo log ic i n t e r p r e t a t i o n , and groundwater i n t e r p r e t a t i o n . Image ana lys i s consi ,s ts o f o b j e c t i v e de tec t i on , c l a s s i f i c a t i o n , d e l i n e a t i o n , and i d e n t i f i c a t i o n o f l a n d cover and physiography. Image i n t e r p r e t . a t i o n i s t he v i s u a l and s u b j e c t i v e mapping o f landforms, dra inage c h a r a c t e r i s t i c s , l ineaments, and c u r v i l i n e a r s . A geo log ic i n t e r p r e t a t i o n begins w i t h s u r f i c i a l l i t h o l o g y and s t r u c t u r e , and then proceeds t o s u r f i c i a l geomorphic processes, subsurface geo log ic r e l a t i o n s h i p s , and geo log ic processes. A groundwater i n t e r p r e t a t i o n b u i l d s on the conceptual geology by i n f e r r i n g a q u i f e r c h a r a c t e r i s t i c s and water q u a l i t y . '

6 .3 .1 Examples o f uses. Remote sensing shows g r e a t promise i n the study o f a g r e a t v a r i e t y o f env i ronmenta l problems i n carbonate te r ranes such as a r e s e r v o i r - s i t e study (Powel l and o thers , 1 9 7 0 ; Sowers, 1 9 7 3 1 , management o f groundwater recharge areas t o p reven t contaminat ion, and l o c a t i o n o f vege ta t i on s t r e s s and p o t e n t i a l areas o f subsidence.

Some p r i n c i p a l land-use problems s tud ied by remote-sensing techniques inc lude: foundat ions, water-supply development, mining, a g r i c u l t u r a l a c t i v i t y , l o c a t i o n and c o n s t r u c t i o n o f dams, highway c o n s t r u c t i o n and maintenance, d i s p o s a l o f s o l i d and l i q u i d wastes, and land-use i n groundwater discharge areas.

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I n f o r m a t i o n de r i ved from t h e use o f these techniques i s p a r t i c u l a r l y va luab le i n t h e s tudy o f carbonate te r ranes and t h e problems assoc ia ted w i t h subsidence and co l lapse. Moreover, because l a r g e areas can be examined i n a very sho r t p e r i o d o f t ime, remote-sensing technology can be viewed as a t ime-saving t o o l . Poss ib le a p p l i c a t i o n i nc lude : (1) inven to ry o f s inkholes; ( 2 ) mon i to r i ng s inkho le development; (3 ) mapping s inkho le al ignments; ( 4 ) i n v e s t i g a t i n g the r e l a t i o n s h i p s among s inkho le development groundwater movement, f r a c t u r e t races , and l ineaments; ( 5 ) p repa r ing and upda t ing base maps; ( 6 ) d e l i n e a t i n g i n c i p i e n t co l l apse zones; ( 7 ) d e t e c t i n g areas o f abnormal sur face drainage; ( 8 ) mapping submarine and sur face k a r s t spr ings; ( 9 ) l o c a t i n g p o t e n t i a l water w e l l s i t e s ; ( 1 0 ) mapping r e g i o n a l geo log ic s t ruc tu res ; (11) l o c a t i n g exposures o f bedrock; and ( 1 2 ) a i d i n g i n genera l p r o j e c t p lanning.

S a t e l l i t e imagery and h i g h - a l t i t u d e photography have been used t o l o c a t e major r e g i o n a l s t r u c t u r e and l ineaments i n a study o f a s inkho le prone area i n Alabama, USA (LaMoreaux, 1 9 7 9 ) . More convent iona l a i r photographs, and

- photographs taken a t 500 f e e t above l a n d sur face, have been used f o r d e t a i l e d mapping o f geo log ic fea tures , subsidence, dra inage al ignments, and vege ta t i on s t ress and €o r c o r r e l a t i o n w i t h t h e sur face mapping o f geo log ic u n i t s , f a u l t s , j o i n t i n g , and the development o f s o l u t i o n c a v i t i e s .

Photographs taken a t r e g u l a r i n t e r v a l s a re an i n v a l u a b l e t o o l i n t r a c i n g the h i s t o r y o f subsidence problems. Of ten inaccura te i n fo rma t ion , based on personal i n te rv iews , can be e l i m i n a t e d by a complete photographic h i s t o r y . Thus, h i s t o r i c remote ly sensed da ta can p rov ide i n f o r m a t i o n on subsidence during pas t , as w e l l as p resent a c t i v e stages.

The p a t t e r n o f subsidence o f f e r s many c lues t o t h e causes o f i t s occurrence i n one area as opposed t o o t h e r nearby areas and many g i v e a d i r e c t i n d i c a t i o n o f under l y ing geo log ic s t ruc tu res . D i s t r i b u t i o n o f s inkho les a l s o can be used e f f e c t i v e l y i n choosing t h e b e s t l o c a t i o n f o r a w e l l o f l a r g e capac i ty i n a k a r s t i c area.

Surface dra inage fea tu res a re an impor tan t aspect o f t h e fo rmat ion o f recent s inkho les because sur face water, moving through t h e overburden i n t o bedrock openings, a i d s i n t h e process o f forming s inkholes. B lack and w h i t e i n f r a r e d photography o r thermography taken d u r i n g the l e a f l e s s season and a f t e r r a i n f a l l s w i l l r e v e a l where water i s e n t e r i n g t h e subsurface through j o i n t i n g o r s inkho le co l lapses . Th is w i l l save cons iderab le f i e l d t ime i n l o c a t i n g and p l o t t i n g t h e exact l o c a t i o n o f surface-water l oss .

Previous i n v e s t i g a t i o n s have shown t h e use fu lness o f remote ly sensed da ta i n d e t e c t i n g changes i n t h e s o i l mo is tu re conten t and sur face temperature anomalies t h a t a re caused by subsurface development o f uncol lapsed c a v i t i e s (Coker, Marsha l l , and Thomson, 1969; Newton, Copeland, and Scarbrough, 1 9 7 3 ) .

Voids i n t h e r e s i d u a l c l a y s t h a t have l i t t l e o r no sur face express ion can sometimes be de tec ted by s p e c i f i c s ignatures on photographs t h a t reco rd vege ta t i ve v i g o r o r l a c k o f v i g o r . I n open f i e l d s , c i r c u l a r v e g e t a t i v e p a t t e r n s i n d i c a t e t h a t water may be concentrated on t h e sur face due t o subsidence over a subsurface c a v i t y , o r t h a t water i s d r a i n i n g i n t o openings i n the ground. The vege ta t i on may show increased v i g o r due t o e x t r a water. Vegetat ive anomalies may a l s o r e s u l t f rom evapora t ion beneath t h e l a n d sur face where c a v i t i e s i n residuum have progressed upward i n t o t h e r o o t zone. The borders o f these c i r c u l a r vege ta t i ve p a t t e r n s sometimes appear as r i n g - l i k e features. Trees may show a l a c k o f growth v i g o r as a r e s u l t o f subsurface co l lapse exposing t h e i r r o o t zones t o excessive evaporat ion. Such a c o l l a p s e cou ld a l s o cause t r e e s t o t o p p l e and d ie . Subsurface v o i d s i n t h e residuum beneath o r near a t r e e cou ld cause a decrease i n mois tu re i n t h e s o i l t h a t would be de tec ted by vege ta t i on s t r e s s and thus recorded on i n f r a r e d f i l m . Some c o r r e l a t i o n has been observed on c o l o r - i n f r a r e d photographs between p i n e t r e e " k i l l s " by i n s e c t s and t h e occurrence of co l l apses i n Shelby County, Alabama, U.S.A. The death o r weakening o f t r e e s caused by co l l apses o r t he format ion of subsurface vo ids i n r o o t zones r e s u l t s i n i n f e s t a t i o n by b e e t l e s o r o the r i n s e c t s because o f t h e i r a f f i n i t y f o r a t t a c k i n g t r e e s i n a s t ressed cond i t ion .

Format ion o f s inkho les i n areas o f extreme dewater ing fol! m i n i n g has been s tud ied ex tens i ve l y i n South A f r i c a (Jennings, 1966) , Pennsylvania, U.S.A. (Foose, 19531, and Alabama, U.S.A. fPowel l and LaMoreaux, 1969; Newton and others, 1973).

1 6 7

I n F l o r i d a , U.S.A., Coker, Marsha l l , and Thomson ( 1 9 6 9 ) used m u l t i s p e c t r a l scanning equipment, seve ra l types of photography, and a special-purpose computer t o d e t e c t s t ressed vege ta t i on and te r rane-sur face temperature anomalies t h a t were assoc ia ted w i t h areas o f impending co l lapse. They concluded t h a t such an approach c o u l d p o t e n t i a l l y d e t e c t hydrogeo log ica l phenomena as much as 100 f e e t below t h e l and surface. I n Pennsylvania, U.S.A., Lattman and Par izek ( 1 9 6 4 ) i n v e s t i g a t e d the r e l a t i o n s h i p between s o l u t i o n c a v i t i e s and photogeologic f r a c t u r e t races i n a carbonate area w i t h i n t he V a l l e y and Ridge phys iograph ic prov ince. The r e s u l t s demonstrated a r e l a t i o n s h i p between groundwater movement and f r a c t u r e t races. The more e x o t i c s t u d i e s should be combined w i t h standard hydrogeologic i n v e s t i g a t i o n s because o f t h e complex n a t u r e o f occurrence o f groundwater i n carbonate rocks.

Fo r example, a t t he U n i v e r s i t y o f M o n t p e l l i e r , France, Pro fessor Jacques Avias ( 1 9 6 8 ) has c a r r i e d o u t research u s i n g sur face g r a v i t y , r e s i s t i v i t y , and seismic methods t o d e l i n e a t e s o l u t i o n systems i n l imestone, and a down-hole t e l e v i s i o n camera t o d e l i n e a t e s i z e and shape o f s o l u t i o n - c a v i t y development. M u l t i s p e c t r a l photography was a l s o used t o study discharge from submarine spr ings. Ex tens ive sur face and subsurface geo log ic work, d e t a i l e d w e l l and s p r i n g i n v e n t o r i e s and fo l low-up t e s t d r i l l i n g , support h i s conclusions based on remote sensing i n t e r p r e t a t i o n . S i m i l a r techniques have a l s o been used by some o f t he S t a t e surveys i n t h e U.S. and the U.S. Geo log ica l Survey.

' I n Yugoslavia , t h e Marine Oceanographic Research I n s t i t u t e i n S p l i t has used a sonic-depth f i n d e r t o map s inkho les i n the l imestone on the sea f loo r t h a t d ischarge water i n t o t h e open sea. Thermal measuring devices and c u r r e n t meters were then used by scubs. d i v e r s t o make discharge measurements o f t h e marine s p r i n g f low.

6.3.2 A e r i a l photographs. Photographs taken from a i r c r a f t are ve ry u s e f u l i n carbonate hydrology. They make e x c e l l e n t base maps, as discussed i n s e c t i o n 6.2. S te reopa i r s can be used f o r three-dimensional study o f hyd ro log i c features.

The a e r i a l cameras c o l l e c t and r e c o r d v i s i b l e e lec t romagnet ic r a d i a t i o n o f about 0.4 t o 0.7 microns i n wavelength on c o l o r and on b l a c k and w h i t e i n f r a r e d f i l m (Cate, 1 9 7 2 ) . A e r i a l cameras can be arranged through the use o f d i f f e r e n t f i l m and f i l t e r combinations, t o reco rd e lec t romagnet ic r a d i a t i o n s imu l taneous ly i n seve ra l d i f f e r e n t s p e c t r a l bands. For example, simultaneous photographs were taken f o r an area i n Shelby County, Alabama, U.S.A. , t h a t i s p r e s e n t l y s u b j e c t t o a c t i v e subsidence and co l l apse . These photographs were taken on the morning o f February 22, 1 9 7 3 , by a NASA/Ames U-2 a i r c r a f t f l y i n g a t 65,000 f e e t . The t h r e e images r e c o r d r e f l e c t e d blue-green, r e d and i n f r a r e d e lec t romagnet ic r a d i a t i o n . The blue-green band g i v e s good water p e n e t r a t i o n and i s u s e f u l i n mapping si l j .ceous rocks; t he r e d band c l e a r l y shows c u l t u r a l features; t h e n e a r - i n f r a r e d band enhances land/water contacts , topography, and d i f f e r e n c e s between v a r i o u s exposed carbonate u n i t s . These photographs can be s t u d i e d separa te ly o r combined i n t o a composite w i t h c o l o r added. Each photography covers an area o f rough ly 1 5 by 1 6 m i les .

A photograph from t h e same U-2 a i r c r a f t w i t h an a e r i a l mapping camera recorded r e f l e c t e d i n f r a r e d r a d i a t i o n o f 0 . 5 1 t o 0.9 microns i n wavelength. R e f l e c t e d green r a d i a t i o n i s recoirded as b l u e on t h e f i l m , r e f l e c t e d r e d r a d i a t i o n i s recorded as green, and r e f l e c t e d n e a r - i n f r a r e d r a d i a t i o n i s recorded as red; hence t h e name f a l s e c o l o r i s o f t e n used f o r t h i s f i l m type ( A l l u m , 1 9 7 3 ) . Since h e a l t h y p l a n t s r e f l e c t h i g h l y i n t h e near - i n f ra red reg ion, v e g e t a t i v e v i g o r i s g e n e r a l l y i n d i c a t e d by t h e c o l o r red. Vegeta t ion t h a t i s under s t r e s s w i l l undergo a change i n r e f l e c t a n c e i n the i n f r a r e d r e g i o n o f t he spectrum (e.g. , some types o f s t ressed vege ta t i on show up i n a b l u i s h hue).

Panchromatic , c o l o r , and i n f r a r e d photography have been used e f f e c t i v e l y t o l o c a t e f r a c t u r e t r a c e s i n a l imestone te r rane i n n o r t h e r n Alabama. These f r a c t u r e s c o n t r o l t he development o f s o l u t i o n c a v i t i e s which become the p r e f e r e n t i a l f l o w zones f o r movement o f groundwater (Sonderegger, 1 9 7 0 ) .

6.3.3 S a t e l l i t e imagery. Remote sensing from space has been done by b o t h manned and unmanned s a t e l l i t e s i n c l u d i n g Landsat (ERTS) , Gemini, Apol lo ,

168

Skylab, and t h e space s h u t t l e . The unmanned s a t e l l i t e s , l i k e Landsat, use a m u l t i s p e c t r a l scanner system w h i l e some o f t h e manned miss ions have produced s a t e l l i t e photography.

M u l t i s p e c t r a l scanners c o l l e c t e lec t romagnet ic r a d i a t i o n s imu l taneous ly i n seve ra l reg ions o f t h e v i s i b l e ( rough ly 0 .4 t o 0.7 microns i n wavelength), and n e a r - i n f r a r e d (approximately 3 t o 1000 microns i n wavelength) spectra. A scanner u s u a l l y c o n s i s t s o f t h r e e b a s i c elements: (1) an o s c i l l a t i n g m i r r o r t h a t sweeps a p a t h pe rpend icu la r t o t h e f l i g h t l i n e o f t h e sensor p l a t f o r m ; (2) a de tec to r t h a t senses t h e e lec t romagnet ic energy reach ing t h e scanner; and ( 3 ) some type o f reco rd ing device. An example o f such an i ns t rumen t i s t h e four-channel M u l t i s p e c t r a l Scanner Sub-system (MSS) on board the N a t i o n a l Aeronaut ics and Space A d m i n i s t r a t i o n ' s (NASA) E a r t h Resources Technology S a t e l l i t e s (ERTS) , now c a l l e d Landsat.

One o f t h e Landsat images o f no r theas te rn Alabama, U.S.A. , f o r example, recorded o n l y i n f r a r e d r a d i a t i o n o f an area t h a t i s about 1 1 5 by 115 m i les . I t c l e a r l y shows t h e V a l l e y and Ridge phys iograph ic p rov ince and t h e f a u l t e d and f o l d e d rocks o f Paleozoic age. The r e l a t i v e l y und is tu rbed Pa leozo ic rocks o f t he Cumberland P la teau i n t h e southeastern U.S. a re l o c a t e d t o t h e west o f t h e V a l l e y and Ridge prov ince. The igneous and metamorphic rocks o f t h e Piedmont are exposed i n t h e southeastern p a r t o f t h a t area. Cretaceous sediments l a p onto the Plateau, V a l l e y and Ridge, and Piedmont p rov inces from t h e south. Sediments o f t h e Coasta l P l a i n p rov ince can be d i s t i n g u i s h e d from t h e f l a t - l y i n g rocks o f t h e Cumberland P la teau p rov ince by d i f f e r e n c e s i n t e x t u r e o f drainage and stream-meander c h a r a c t e r i s t i c s . Th i s photo-imagery, e s p e c i a l l y t he n e a r - i n f r a r e d band, can be an e x c e l l e n t a i d i n r e g i o n a l s t r u c t u r a l i n t e r p r e t a t i o n . Powell , Copeland, and Drahovzal (1970) a l s o found t h i s t o be t r u e o f A p o l l o 9 photography i n t h e same area i n eas te rn Alabama. The Shelby County s inkho les do n o t show up as d i s c e r n i b l e features, ' as t h e diameter o f t h e l a r g e s t s i n k (about 300 f e e t ) approaches t h e l i m i t o f t h e sma l les t o b j e c t t h a t t h e MSS can de tec t ; however, l a rge -sca le l ineaments, t o which s o l u t i o n a c t i v i t y may be r e l a t e d , are ve ry apparent.

Kahout e t a l . ( 1 9 8 1 ) used TIROS-N weather s a t e l l i t e imagery and A p o l l o I X photography i n con junc t i on w i t h thermal i n f r a r e d imagery and c o l o r and i n f r a r e d photography from N a t i o n a l Aeronaut ics and Space A d m i n i s t r a t i o n a i r c r a f t f l i g h t s t o study t h e r e l a t i v e m e r i t s o f v a r i o u s imaging methods i n t h e d e t e c t i o n o f submarine sp r ings i s s u i n g from cavernous l imestones.

Table 6 .3 -1 l i s t s fea tu res d i s c e r n i b l e on Landsat images t h a t a re u s e f u l i n t h e study o f carbonate hydrology.

6.3.4 Thermal i n f r a r e d imagery (thermography). Thermograms a re images o f thermal r a d i a t i o n which a r e recorded w i t h s e n s i t i v e thermal scanners. The b e s t images a re ob ta ined d u r i n g night f l i g h t s a t low a l t i t u d e s during unusua l l y c o l d weather (Moore, 1 9 8 0 ) .

Thermal i n f r a r e d images a r e t h e b e s t images f o r i n v e n t o r y i n g seeps and spr ings. Brown (1972) used the rma l i n f r a r e d imagery t o l o c a t e d k a r s t sp r ings i n Canada. Kahout e t a l . (1981) s u c c e s s f u l l y used the rma l i n f r a r e d images along w i t h c o l o r and i n f r a r e d s a t e l l i t e and a e r i a l photography t o d e t e c t submarine sp r ings i n Jamaica. I n f r a r e d and thermal i n f r a r e d photography have a l s o been s u c c e s s f u l l y used by Coker and o t h e r (1969) , Newton and o t h e r s (19731, and Warren and Wielchowsky (1973) f o r t h e study o f sinkhole-prone areas o f t h e southeastern U n i t e d States.

6.3.5 Radar. Th i s t ype o f remote sensing apparatus c l a s s i f i e d as a c t i v e , as opposed t o pass ive systems such as a e r i a l photograph and m u l t i - s p e c t r a l scanning, because i t generates i t s own source o f e lec t romagnet ic energy. The energy r e t u r n e d from t h e t e r r a n e i s de tec ted by t h e system and recorded as imagery. The two main types o f rada r used i n carbonate hydro logy a r e s ide - look ing rada r and ground-penetrat ing radar .

S ide- look ing a i rbo rne r a d a r (SLAR) generates e lec t romagnet ic energy by use o f a p u l s e t r a n s m i t t e r t o sense e a r t h o b j e c t s i n t h e microwave reg ion. The r e t u r n s i g n a l f rom t h e ground o r t a r g e t i s a f u n c t i o n o f t e r r a n e roughness and complex d i e l e c t r i c cons tan t (Waite, 1973) . T h i s sensor i s e s p e c i a l l y va luab le as a t o o l f o r f r a c t u r e and f a u l t - t r a c e mapping s ince t h e " l o o k " d i r e c t i o n o f

169

Table 6.3-1 Features t h a t a r e impor tan t f o r mapping conso l i da ted rock a q u i f e r s on Landsat MSS images ( f rom Moore, 1 9 8 2 ) .

Rock t ype :

1. 2.

3. 4 . 5 .

6. 7. 8 .

9.

Landform; topographic r e l i e f ; e r o s i o n a l c h a r a c t e r i s t i c s . Outcrop pattern--banded p a t t e r n f o r sedimentary rocks; l o b a t e o u t l i n e f o r b a s a l t f lows; a rcuate o r f a u l t e d boundaries f o r igneous i n t r u s i o n s . Drainage p a t t e r n and drainage t e x t u r e ( d e n s i t y ) . F r a c t u r e t ype and symmetry (as i n d i c a t e d by l ineaments). Topographic p o s i t i o n ; steepness o f slope; presence o r absence o f e r o s i o n a l t e r r a c e s on h i l l s i d e s . Shape o f r i d g e l i n e and p l a t e a u edge. Type and d e n s i t y o f vege ta t i on cover; l a n d use. Presence o f s inkho les ( v i s i b l e o n l y where occupied by water o r d i s t i n c t i v e vege ta t i on ) . Tone o r hue; image tex tu re .

Fo lds :

1. Ridge and v a l l e y topography; mountain, dome, and e l l i p t i c a l h i l l ; shor t , p a r a l l e l and i n t e r s e c t i n g r i d g e c r e s t s w i t h V-shaped sec t i ons (complexly f o l d e d metamorphic rocks ) ; cuesta o r hogback.

2. F l a t i r o n s on dip slope and i r r e g u l a r topography on back slope; p a r a l l e l t o d e n d r i t i c drainage on dip slope and angulate o r t r e l l i s - d r a i n a g e on back slope; u n i f o r m d i s t r i b u t i o n o f vege ta t i on on dip slope and vege ta t i on banding p a r a l l e l t o r i d g e c r e s t s on back slope.

3. Banded ou tc rop p a t t e r n n o t r e l a t e d t o topography. U-shaped t o V-shaped map p a t t e r n o f r i dges .

4. T r e l l i s , r a d i a l , annular, o r c e n t r i p e t a l drainage p a t t e r n ; p a r t l y developed p a t t e r n o f these types.

5 . Major d e f l e c t i o n i n stream channel; change i n meander wavelength o r change from meandering t o s t r a i g h t o r b r a i d e d channel.

6 . Assymmetric drainage; channel n o t centered between drainage d i v i d e s .

Lineaments:

1. Continuous and l i n e a r stream channel o r v a l l e y ; d iscont inuous but s t r a i g h t

2. Elongate o r a l i g n e d lakes, l a r g e s inkholes, and volcanoes. 3. I d e n t i c a l o r oppos i te d e f l e c t i o n s (such as doglegs) i n ad jacent stream

channels o r v a l l e y s ; a l ignment o f nearby t r i b u t a r i e s and t r i b u t a r y j unc t i ons .

4 . Elongate o r a l i g n e d p a t t e r n s of n a t u r a l vegeta t ion ; th in s t r i p o f r e l a t i v e l y open (may be r ight -of -way) o r dense vegeta t ion .

5. Al ignment o f dark o r l i g h t s o i l tones.

and a l i g n e d v a l l e y s , draws, swags, and gaps.

170

t he radar i s a f u n c t i o n o f f l i g h t path. I n a d d i t i o n , SLAR has e x c e l l e n t c l o u d p e n e t r a t i o n a b i l i t y and can be operated a t n i g h t because i t p rov ides i t s own " i l l u m i n a t i o n . 'I

Ground-penetrat ing rada r i s operated on t h e ground. The sensor i s drawn across the ground a t speeds o f one t o f o u r m i l e s p e r hour, and p rov ides a continuous coverage, a t shal low depths, g e n e r a l l y l e s s than one hundred f e e t i n carbonate ter ranes, w i t h a g raph ic cross s e c t i o n r e c o r d i n r e a l t ime.

Ground-penetrat ing rada r has been used i n F l o r i d a , U.S.A., t o d e t e c t k a r s t c a v i t i e s (Benson, 1977). I t may a l s o be used t o d e t e c t o rgan ic contaminants a t hazardous waste s i t e s .

6.3.6 Data sources. A e r i a l photography and i n f r a r e d imagery f l i g h t s may be arranged f o r coverage o f a s p e c i f i c study area, but such f l i g h t s a re expensive and r e q u i r e s p e c i a l exper t i se . Fo r tuna te l y , a e r i a l photographs and s a t e l l i t e images are a l ready a v a i l a b l e f o r many p a r t s o f t h e wor ld. Table 6.3-2 l i s t s sources o f some a v a i l a b l e images.

H i s t o r i c a l U.S. a e r i a l photographs a re a v a i l a b l e from t h e U.S. Army Corps o f Engineers D i s t r i c t O f f i c e s , t h e U.S.D.A. - S o i l Conservat ion Serv ice and o t h e r Federa l and S ta te agencies.

Worldwide, t h e a v a i l a b i l i t y o f a e r i a l photographs depends upon n a t i o n a l r e g u l a t i o n s and r e s t r i c t i o n s , but t h e r e a r e no r e s t r i c t i o n s on t h e a v a i l a b i l i t y o f Landsat images. Some Landsat images a re a v a i l a b l e f rom t h e EROS Data Center; o t h e r s a re a v a i l a b l e o n l y from n a t i o n a l o r r e g i o n a l d i s t r i b u t i o n centers. EROS Data Center w i l l supply i n f o r m a t i o n on t h e a v a i l a b i l i t y o f Landsat images from non-U.S. r e c e i v i n g s t a t i o n (Moore, 1 9 8 0 ) .

6.4 Geophysical p rospec t i ng

Geophysical methods have become i n c r e a s i n g l y impor tan t i n carbonate hydrology. These methods may be c l a s s i f i e d as sur face methods, boreho le methods, and a i rbo rne methods.

6 .4 .1 Surface methods (J. L. A s t i e r ) I n calcareous o r d o l o m i t i c areas, geophysical p rospec t i ng i s used t o l o c a t e e i t h e r permeable zones r e s u l t i n g f rom a k a r s t i f i c a t i o n o r underground r i v e r s . There a re some p a r t i c u l a r problems i n c o a s t a l areas.

Limestones and do lomi tes a re dense, compact and e l e c t r i c a l l y r e s i s t a n t rocks. The k a r s t i f i c a t i o n leads t o t h e s u b s t i t u t i o n o f p a r t o f these rocks b y vo ids, water, o r c lays . T h i s phenomenon a f f e c t s t h e i r p h y s i c a l p r o p e r t i e s such as densi ty , e l a s t i c i t y , and r e s i s t i v i t y . Thus, i n k a r s t i c hydrogeo log ic research, g r a v i t y , seismic, e l e c t r i c , and e lec t romagnet ic methods a re most commonly used.

A r t i c l e s have been pub l i shed on t h e p o s s i b i l i t i e s o f f e r e d b y t h e spontaneous and induced p o l a r i z a t i o n . The former u t i l i z e s t h e e l e c t r i c a l p o t e n t i a l produced by t h e water f low, t h e l a t t e r cons iders t h e p r o p e r t y o f t h e f i l m o f c l a y i n s i d e c a v i t i e s t o a t t r a c t e l e c t r i c a l charges j u s t l i k e a capac i to r . However, these two methods a re n o t discussed he re in . [EDITOR'S NOTE: The reader i s r e f e r r e d t o M i lanov ic , 1981, f o r re fe rences on geothermal methods and t o B u t l e r , 1977 and Benson, 1977 f o r read ings on t h e use o f geophysical methods i n c a v i t y d e t e c t i o n i n l imestones.]

6.4.1.1 P r i n c i p l e methods. The p r i n c i p l e geophysical methods used i n carbonate hydrology a re g r a v i t y , seismic, and e l e c t r i c a l p rospec t ing .

6.4.1.1.1 G r a v i t y p rospec t ing . The e a r t h g r a v i t y f i e l d i s o n l y a p a r t i c u l a r case o f t h e u n i v e r s a l a t t r a c t i o n . By a p p l y i n g Newton's law, t h e we igh t o f a body i s equal t o t h e e a r t h a t t r a c t i o n :

(6.4-1) m g = Y F Mm

1 7 1

Table 6.3-2. Data sources f o r remote sensing (adapted from Moore, 1 9 8 0 ) .

Source Data t ype Coverage

U.S. Geo log ica l Survey, Eros Data Center Landsat images, World ( p a r t i a l ) User Serv ice Sec t i on Skylab photographs World ( p a r t i a l )

U.S.A. Sioux F a l l s , South Dakota 57198 a e r i a l photography U.S.

N a t i o n a l A i r Photo L i b r a r y 615 Booth S t r e e t Ottawa, O n t a r i o K1A OE9 Canada

A e r i a l photography Canada

User Assistance and Marke t i ng U n i t Lands a t image s Canada Canadian Centre f o r Remote Sensing 717 B e l f a s t Road Ottawa, O n t a r i o K1A OY7 Canada

European Space Agency Ear thne t User Services V ice G a l i l e o G a l i l e i O00 4 4 F r a s c a t i , I t a l y

Landsat images I t a l y

172

where m and M a re t h e body and e a r t h masses, r e s p e c t i v e l y r t h e e a r t h r a d i u s ,

second (c.g.s.1 , g i s t h e a c c e l e r a t i o n of g r a v i t y expressed i n cm/sec3 o r g a l , i n memory o f G a l i l e o . The p r a c t i c a l un i t used i n g r a v i t y p rospec t i ng i s t h e m i l l i g a l (10-3 g a i ) .

I f the e a r t h were homogeneous, p e r f e c t l y s p h e r i c a l , and a l s o mot ion less i n a completely empty space, g would be cons tan t a l l over i t s surface. I n f a c t g v a r i e s a l l over t h e w o r l d t o an apprec iab le ex ten t .

G r a v i t y p rospec t i ng c o n s i s t s o f measuring t h e v a r i a t i o n s o f g, and then app ly ing some c o r r e c t i o n s t o t h e raw values, thus e l i m i n a t i n g t h e i n f l u e n c e s o f o t h e r space bodies, and o f t h e shape and r o t a t i o n o f t h e e a r t h , i n o rde r t o keep o n l y t h e underground d e n s i t y anomalies. The g v a r i a t i o n s a re measured w i t h a gravimeter, a kind o f v e r y s o p h i s t i c a t e d s p r i n g balance. For d e t a i l e d s tud ies, accuracy reaches mgal.

A Bouguer anomaly map i s es tab l i shed , g i v i n g a t every s t a t i o n t h e d i f f e r e n c e between co r rec ted g va lues a t t h e s t a t i o n and a t t h e re fe rence s t a t i o n .

Y t h e u n i v e r s a l g r a v i t a t i o n cons tan t equa l t o 2 0 / ( 3 - 1 0 Q ) i n c e n t i rams p e r

6.4.1.1.2 Seismic p rospec t ing . When a shock wave i s c rea ted i n t h e ground, e l a s t i c waves a re generated. The propagat ion o f t h e e l a s t i c waves f o l l o w s t h e same r e f r a c t i o n and r e f l e c t i o n laws as does l i g h t . The t ime necessary t o reach recep to rs o r geophones, depends on t h e na tu re and s t r u c t u r e o f t h e g e o l o g i c a l format ions. The study o f t h e _ p r o p a g a t i o n t ime, t, i s t h e b a s i s o f seismic p rospec t ing .

The propagat ion v e l o c i t y V o f seismic waves i s 0.33 km.sec-l i n t h e a i r , 1.45 km.sec i n water, f rom 0.2 t o 0.6 km.sec-l i n d r y l oose s o i l (weathered zone o r W Z ) and from 1.8 t o 2 .3 km.sec-l i n c lays . Fo r l imestones and do lomi tes t h e v e l o c i t y ranges f rom 2.5 t o 5 km.sec depending on whether they are v e r y k a r s t i f i e d o r ve ry compact.

The e l a s t i c waves a r e g e n e r a l l y c rea ted b y t h e exp los ion o f a sma l l amount o f dynamite b u r i e d a t shal low depth. The geophones a r e composed o f an i n d u c t i o n c o i l and a magnet arranged i n such a way t h a t a v e r t i c a l movement induces an e l e c t r i c a l c u r r e n t . T h i s c u r r e n t i s a m p l i f i e d and recorded simultaneously w i t h t h e exp los ion t ime and re fe rence l i n e s w i t h a 1 0 m i l l i s e c o n d s i n t e r v a l . The r e f r a c t i o n o r r e f l e c t i o n methods make use r e s p e c t i v e l y o f t h e waves r e f r a c t e d by o r r e f l e c t e d on t h e l a y e r s .

6.4.1.1.2.1 Seismic r e f r a c t i o n . As an example o f t h i s method see F i g u r e 6.4-1 which i l l u s t r a t e s a r e c t i l i n e a r seismographic a r r a y w i t h a shot -po in t and twe lve r e g u l a r l y spaced geophones l a i d i n an area where t h e g e o l o g i c a l s e c t i o n c o n s i s t s o f t h r e e l a y e r s o f i n c r e a s i n g v e l o c i t i e s VI, V2, and V3. The f i r s t wave recorded b y t h e ne ighbor ing geophones i s t h e d i r e c t wave which t r a v e l s a t t h e ground sur face l e v e l . For t h e o t h e r geophones t h e f i r s t recorded wave i s t h e one which has been t o t a l l y r e f r a c t e d on t h e f i r s t o r second g e o l o g i c a l contact . The i n v e s t i g a t i o n depth inc reases w i t h t h e l e n g t h o f t h e geophone array.

I f t r a v e l i n g t imes, t, are p l o t t e d versus t h e explosion-geophone d is tance, x, a dromochronic curve i s ob ta ined (see F igu res 6.4.-1). I t i s composed o f t h r e e segments, t h e slopes of which a re equa l t o t h e r e c i p r o c a l o f t h e v e l o c i t i e s . I t i s easy t o compute t h e th icknesses e l and e2 u s i n g t h e o rd ina tes a t t h e o r i g i n T1 and T g o f t h e l a s t two segments and t h e v e l o c i t i e s V I , V2, and V3.

6.4.1.1.2.2 Seismic r e f l e c t i o n . The example i n F i g u r e 6.4-2 uses t h e same a r r a y as used i n t h e p rev ious example, but t h e waves a re r e f l e c t e d on t h e g e o l o g i c a l contacts . Fo r each contact , t h e curve showing t h e t r a v e l t ime versus t h e explosion-geophone i s a branch of a hyperbola. Fo r t h e geophone c l o s e s t t o t h e explosion, t h e c o n t a c t depth, Pl equals V m * t / 2 , Vm b e i n g t h e average v e l o c i t y o f t h e l a y e r s on t o p o f t h e contact .

For t h e r e f l e c t i o n method, t h e i n v e s t i g a t i o n depth does n o t depend on t h e l e n g t h of t h e array.

173

t A

T2

i = arc sinVi/V2 Ti

time-distance curve

O shot geophones X

P”f ,si I I l I I I I I I (SI2 A e1 vi

v 2

- c

ray- paths I I I ’ I I I I I I -

v 3

\

A

F igu re 6 . 4 - 1 Schematic diagram o f the p r i n c i p l e o f t he seismic r e f r a c t i o n method.

1 1 1 1 1 1 1 1 1 I

I /

I \ \ // \ I 7 P \ 1

X O >

time - distance

t v

i time - distance

t t

F i g u r e 6.4-2 Schematic diagram o f t h e p r i n c i p l e o f t h e seismic r e f l e c t i o n met ho d.

1 7 4

Seismic r e f l e c t i o n i s seldom used f o r depths o f l e s s then 200 m because the e l a s t i c waves r e f l e c t e d on t h e shal low con tac ts reach the geophones b e f o r e v i b r a t i o n s caused by t h e d i r e c t wave and t h e waves r e f r a c t e d on t h e bot tom o f t h e weathered zone a re damped out .

6.4.1.1.3 E l e c t r i c a l prospect ing. The e l e c t r i c a l c o n d u c t i b i l i t y o f c lays , mar ly l imestone, l imestones and 'do lomi tes has an e l e c t r o l y t i c o r i g i n . The r e s i s t i v i t y o f rocks w i t h an e l e c t r o l y t i c c o n d u c t i b i l i t y , p f i s g i v e n by Arch ie ' s formula:

P = pe/pm ( 6 . 4 - 2 )

w i t h pe = s torage water r e s i s t i v i t y P = t o t a l rock p o r o s i t y m = v o i d d i s t r i b u t i o n c o e f f i c i e n t .

For s t r a t i f i c a t i o n rocks, t he r e s i s t i v i t y v a r i e s w i t h t h e c u r r e n t d i r e c t i o n . The an iso t ropy c o e f f i c i e n t sometimes goes up t o seve ra l u n i t s .

The s a l i n e c l a y r e s i s t i v i t y i s o f some ohm-meterZ/meter ( o r ohm-m) whereas t h a t o f compact l imestone i s seve ra l l o 3 ohm-m. Limestones w i t h a 20 percent p o r o s i t y and sa tu ra ted w i t h water c o n t a i n i n g 1 g / E NaCl have a r e s i s t i v i t y c lose t o 250 ohm-m.

The e l e c t r i c a l methods most o f t e n used i n carbonate hydro logy are r e s i s t i v i t y , ground connect ing, and e lect romagnet ic prospect ing.

6.4.1.1.3.1 R e s i s t i v i t y methods. I f a d i r e c t cu r ren t , i, i s sent between two e lec t rodes A and B i n a homogeneous s t r a t a o f r e s i s t i v i t y , p f accord ing t o Ohm's law, i t produces a p o t e n t i a l d i f f e r e n c e , A V , between two o t h e r e lect rodes, M and NI such as:

The t r u e r e s i s t i v i t y p can be de r i ved f rom t h i s formula:

AV i p = k -

(6 .4 -3 )

(6.4-4)

where k i s t h e geometr ic c o e f f i c i e n t o f t h e measuring device. I f t h e r e are seve ra l l aye rs , t h e above formula g i ves an apparent

r e s i s t i v i t y p r e l a t e d t o t h e t r u e r e s i s t i v i t y and t o t h e th i ckness o f a l l t h e invo lveda ' layers . The apparent r e s i s t i v i t y i s de f i ned as the t r u e r e s i s t i v i t y o f an imaginary, homogeneous and i s o t r o p i c medium, equ iva len t t o t h e t r u e heterogeneous and a n i s o t r o p i c medium.

The study o f apparent r e s i s t i v i t y v a r i a t i o n s i s t h e p r i n c i p l e o f t h e r e s i s t i v i t y method. I n t h e f i e l d , an AMNB symmetr ical and r e c t i - l i n e a r a r ray i s most o f t e n used: t h e d i s tance MN i s as s h o r t as p o s s i b l e (Schlumberger a r ray ) .

Two techniques a re used: e l e c t r i c a l sounding and r e s i s t i v i t y p r o f i l e . The e l e c t r i c a l sounding c o n s i s t s i n drawing t h e v a r i a t i o n curve o f t h e apparent r e s i s t i v i t y versus depth f o r a g i ven s t a t i o n . The i n v e s t i g a t i o n depth i s s e t by v a r y i n g t h e d is tance AB o f t h e two c u r r e n t i n j e c t i n g e lec t rodes (see F i g u r e 6.4-3) . The r e s i s t i v i t y p r o f i l e g i v e s va lues o f t h e apparent r e s i s t i v i t y €or l i n e s up s t a t i o n s r e g u l a r l y spaced by means o f an AMNB quadr ipo le o f cons tan t leng th . Thus, t h e i n v e s t i g a t i o n i s c a r r i e d o u t a t a cons tan t depth.

The r e s u l t s a re i n t e r p r e t e d main ly by matching t h e f i e l d graphs w i t h master curves. The e l e c t r i c a l soundings g i v e d i r e c t l y t h e t r a n s v e r s a l res is tance, ep, o f t h e r e s i s t a n t l a y e r s and t h e l o n g i t u d i n a l conductance, e/p, o f t h e conduct ive layers .

6.4.1.1.3.2 Loca t ion o f conduct ive bodies w i t h an access ib le p o i n t . A s p e c i a l method c a l l e d 'ground connect ing ' may be used t o determine t h e shape o f

17 5

D. C .Genera tor

I 1'-

F i g u r e 6.4-3 P r i n c i p l e o f t h e e l e c t r i c a l sounding method.

n

Hp: primary magnetic field generated by the alternating current flowing in the

H,: Secondary magnetic field

Ht : Total magnetic field

transmitter coil

F i g u r e 6.4-4 P r i n c i p l e of t h e e lec t romagnet ic method.

1 7 6

conduct ive bod ies t h a t have a reachable p o i n t (o re lode, s a l i n e subterranean r i v e r s o r l a k e s ) .

A d i r e c t c u r r e n t i s sent i n t h e ground th rough a l o n g cable AB w i t h one e lec t rode connected t o t h e conduct ive body. A p o t e n t i a l map i s then drawn around t h e grounded e lec t rode . The e q u i p o t e n t i a l l i n e s g i v e t h e shape o f t h e conduct ive body, as t h e p o t e n t i a l d rop w i t h i n i t i s v e r y small .

6.4.1.1.3.3 Electromagnet ic p rospec t ing . The p r i n c i p l e upon which a l l e lectromagnet ic methods a r e based i s as f o l l o w s : I f a b u r i e d conduct ive body i s submit ted t o an a l t e r n a t i n g magnetic f i e l d , an induced c u r r e n t i s generated w i t h i n i t s mass which i n turn c rea tes a magnetic f i e l d . The study o f t h e r e s u l t i n g t o t a l magnetic i n d i c a t e s t h e l o c a t i o n o f t h e conduct ive body (see F i g u r e 6.4-4).

The p r imary magnetic f i e l d i s produced by an a l t e r n a t i n g c u r r e n t t h a t i s sent i n t o t h e ground e i t h e r d i r e c t l y o r by i nduc t i on . The l a t t e r case t h e i nduc ing c u r r e n t c i r c u l a t e s i n an i s o l a t e d , f i x e d o r movable t r a n s m i t t e r c o i l . The frequencies used range from 100 t o 5,000 Hz. The t o t a l magnetic f i e l d generates an induced c u r r e n t i n a r e c e i v e r c o i l ; i t i s t h i s c u r r e n t t h a t i s studied. Var ious c h a r a c t e r i s t i c s o f t h e t o t a l f i e l d may be measured i n c l u d i n g ampli tude, d i f f e r e n c e i n phase, o r i n c l i n a t i o n compared t o t h e p r imary f i e l d .

The i n v e s t i g a t i o n depth i s p a r t l y a f u n c t i o n o f two a d j u s t a b l e parameters: t he t r a n s m i t t e r - r e c e i v e r d is tance, and t h e i nduc ing c u r r e n t frequency. I n a f i r s t approximation, i t v a r i e s between 0.5 and 1.5 t imes t h e t r a n s m i t t e r - r e c e i v e r distance.

When t h e c u r r e n t i s t r a n s m i t t e d i n t t h e ground, one o f t he e lec t rodes can be ground connected i f t h e conduct ive mass can be reached.

6.4.1.2 Loca t ion o f k a r s t i f i e d zones. Geophysical techniques may be used i n the mapping o f c a v i t i e s and water i n v a r i o u s types o f k a r s t ter ranes.

6.4.1.2.1 K a r s t i f i e d zones r e l a t e d t o f a u l t s .

6.4.1.2.1.1 Grav i t y , r e s i s t i v i t y and seismic r e f r a c t i o n methods. Consider a l imestone fo rmat ion cha rac te r i zed by a g l o b a l p o r o s i t y o f 1 0 percent, a d e n s i t y o f 2.5, a r e s i s t i v i t y o f 600 ohm-m and a v e l o c i t y o f 5 km.sec.-l.

I n k a r s t i f i e d f a u l t e d areas t h e g l o b a l p o r o s i t y may reach 20 pe rcen t and t h e dens i t y , r e s i s s i v i t y , and v e l o c i t y may r e s p e c t i v e l y decrease t o 2.35, 1 2 0 ohm-m and 4 km.sec l.

I f t h e s o i l cover i s thin, a crushed zone, 1 0 m wide and 100 m high, may r e s u l t in: (1) a s t rong conduct ive anomaly, e a s i l y determined w i t h r e s i s t i v i t y p r o f i l e s (see F i g u r e 6.4-5) ; ( 2 ) a s l i g h t g r a v i t y anomaly o f about 0.1 m i l l i g a l , de tec tab le by a v e r y p r e c i s e g r a v i t y survey; (3) a h a r d l y d e t e c t a b l e t ime de lay o f o n l y 0.5 m i l l i s .

I n t h e case of t h i c k overburden, t h e k a r s t i f i e d zones assoc ia ted w i t h f a u l t s become b a r e l y de tec tab le un less they a re s e v e r a l hundred meters wide.

6.4.1.2.1.2 Seismic r e f l e c t i o n . F i g u r e 6.4-6 p resents a seismic r e f l e c t i o n s e c t i o n showing a l imestone format ion. I t c l e a r l y shows a 20 m f a u l t throw and an approximately 300 m wide crushed ne ighbor ing zone where t h e r e f l e c t i o n s a r e s u b s t i t u t e d by d i f f r a c t i o n s .

6.4.1.2.2 K a r s t i f i e d zones w i t h g r e a t l a t e r a l extension. I n te r ranes u n d e r l a i n by calcareous rocks t h e g e o l o g i c a l sequence i s genera l l y , i n descend ing .order f rom t h e surface: a r g i l l a c e o u s s o i l and c l a y i s h weathered zone; dry k a r s t i f i e d l imestone; water logged k a r s t i f i e d l imestones; and compact l imestone. R e s i s t i v i t y and seismic r e f r a c t i o n a re u s e f u l methods i n t h i s t ype o f ter rane.

177

F i g u r e 6 .4 -5 R e s i s t i v i t y p r o f i l e perpend icu la r t o a conduct ive k a r s t i f i e d zone. AB = a, MN = p/2 .

0-

400 -

F igu re 6.4-6 Seismic r e f l e c t i o n s e c t i o n showing a f a u l t w i t h a twenty meter throw.

1 7 8

6.4.1.2.2.1 R e s i s t i v i t y p rospec t ing . A r g i l l a c e o u s s o i l and k a r s t i f i e d waterlogged l imestone a re conduct ive compared t o d r y k a r s t i f i e d l imestones and t o compact l imestones. The r e s i s t i v i t y r a t i o o f t h e compact o r d r y k a r s t i f i e d l imestones t o t h e waterlogged l imestones can be as much as 5.

The e l e c t r i c a l soundings a re s i m i l a r t o t h e one shown on F i g u r e 6.4-7. They t h e o r e t i c a l l y a l l o w t h e de te rm ina t ion o f : (1) t h e depth o f k a r s t i f i e d waterlogged l imestones; (2) the depth o f t h e c o n t a c t between t h e k a r s t i f i e d and t h e compact l imestones; (3 ) t h e areas where t h e sa tu ra ted k a r s t i f i e d l imestones have t h e lowest r e s i s t i v i t y and consequently a r e t h e most porous.

The depth o f t h e con tac ts i s o f t e n ha rd t o determine. O n t h e o t h e r hand, i t i s easy t o prepare a map showing t h e t o t a l conductance o f t h e water logged k a r s t i f i e d l imestones. The h i g h l y conduct ive zones a re t h e most favo rab le f o r d r i l l i n g € o r water.

6.4.1.2.2.2 Seismic r e f r a c t i o n . Seismic r e f r a c t i o n soundings p r o v i d e t h e same i n f o r m a t i o n as t h e e l e c t r i c a l soundings. I n a d d i t i o n , they g i ven some i n d i c a t i o n o f t h e f a c i e s v a r i a t i o n s o f t h e compact 'rock. T h i s i s impor tan t because t h e comparison between t h e v e l o c i t y v a r i a t i o n s i n k a r s t i f i e d and n o n k a r s t i f i e d l imestones he lps determine i f a v e l o c i t y decrease i s due t o an increase i n p o r o s i t y o r t o a f a c i e s change. (The p o r o s i t y inc rease o n l y a f f e c t s the k a r s t i f i e d l imestones whereas a f a c i e s change a l s o a f f e c t s t h e compact l imestones.)

6.4.1.3 L o c a t i o n o f underground streams. A d i s t i n c t i o n must be made between the underground channels which a re p a r t i a l l y f i l l e d w i t h water and those where t h e water f i l l s t h e whole a v a i l a b l e sect ion. [EDITOR'S NOTE: Fo r read ing on t r a c i n g o f underground streams b y geophys ica l methods, t h e reader i s r e f e r r e d t o Z o t l ( 1 9 7 4 ) and M i lanov i t i ( 1 9 8 1 ) .I

6.4.1.3.1 P a r t i a l l y w a t e r - f i l l e d g a l l e r i e s . Geophysic ists cons ider these g a l l e r i e s as v o i d spaces. G r a v i t y and r e s i s t i v i t y p rospec t i ng a re t h e o n l y s u i t a b l e methods f o r t h e i r de tec t i on .

A 1.2 meters wide underground g a l l e r y , t h e cen te r o f which i s 1.7 meters deep, can be de tec ted by r e s i s t i v i t y p rospec t i ng ( a 25 pe rcen t anomaly) but n o t by the g r a v i t y method. O n t h e o t h e r hand, a 1 0 m wide g a l l e r y l o c a t e d 36 meters below t h e sur face i s revea led by grav imet ry but n o t by t h e e l e c t r i c method.

Thus, t h e g r a v i t y method must be used when t h e g a l l e r y b e i n g considered i s deep and t h e r e s i s t i v i t y method must be used f o r shal low depth.

6.4.1.3.2 I naccess ib le w a t e r - f i l l e d g a l l e r i e s . G r a v i t y and r e s i s t i v i t y methods can be used t o l o c a t e comple te ly f i l l e d g a l l e r i e s , but electromagnet ism and seismic methods are a l s o s u i t a b l e .

6.4.1.3.2.1 G r a v i t y and r e s i s t i v i t y methods. The d e t e c t i o n o f w a t e r - f i l l e d g a l l e r i e s i s more d i f f i c u l t u s i n g t h e g r a v i t y method and e a s i e r u s i n g t h e e l e c t r i c a l p rospec t i ng method.

For the g r a v i t y method, the d e n s i t y c o n t r a s t i s reduced from about 2.35 t o 1.35. I n r e s i s t i v i t y p rospec t i ng t h e r e s u l t s a re more conc lus i ve as t h e water i s more conduct ive.

6.4.1.3.2.2 Electromagnetism. P o r t Miou g a l l e r y (see F i g u r e 6.4-8a) i s a good example o f t h e l o c a t i o n o f an underground g a l l e r y by e lec t romagnet ic p rospec t ing .

The g a l l e r y i s about 1 0 meters wide and l o c a t e d 70 meters below t h e .sur face. I t has been c u t i n ve ry had Urgonian l imestones and i s comple te ly f i l l e d w i t h sea water. According t o t h e o r e t i c a l c a l c u l a t i o n s , t h i s g a l l e r y would cause n e g l i g i b l e d e n s i t y o f r e s i s t i v i t y anomalies.

179

Compact limestone 2 1

5 j 4

.- Clayey soil

Dry k limesî

/ /

1 1 5 10 i o {O 10 200 560 AB/2

F igure 6.4-7 T y p i c a l e l e c t r i c a l sounding i n a calcareous zone.

180

6.4.1.3.2.3 Seismic method. A n o i s y impor tan t f l o w i n a g a l l e r y w i l l generate ground v i b r a t i o n s de tec tab le by sur face geophones. The ampl i tude o f t h e v i b r a t i o n s i s i n v e r s e l y p r o p o r t i o n a l t o t h e square o f t h e d i s tance t o t h e stream; an ampl i tude o f 1 0 f o r t h e geophone immediately above t h e r i v e r i s reduced t o 5 f o r t h e geophone l o c a t e d a t a d i s tance equa l t o t h e depth o f t h e g a l l e r y .

I n t e r f e r e n c e s caused by c i t i e s , f a c t o r i e s , o r roads g r e a t l y reduce t h e e f f i c i e n c y o f t h i s method.

6.4.1.3.3 W a t e r - f i l l e d g a l l e r i e s access ib le a t one p o i n t . The methods used f o r t h i s t ype g a l l e r y i n c l u d e e lec t romagnet ic p rospec t ing , e l e c t r i c p o t e n t i a l mapping, and t h e use o f geo-bombs.

6.4.1.3.3.1 Electromagnet ic p rospec t ing . When a w a t e r - f i l l e d g a l l e r y can be reached a t one p lace, t h e use o f t h e e lec t romagnet ic method w i t h one e m i t t i n g e lec t rode i n s i d e t h e water must be considered f o r de termin ing i t s course. I f the stream discharge i n t o t h e g a l l e r y i s smal l , s a l t (sodium c h l o r i d e ) can be a r t i f i c i a l l y i n t roduced i n t o t h e stream t o inc rease t h e chances o f success.

F igures 6.4-8a and 6.4-8b show t h e e lec t romagnet ic r e s u l t s f o r t h e Port-Miou g a l l e r y . The southern end o f t he t r a n s m i t t e r cable has been put i n t o the r i v e r through t h e n o r t h open p i t . The g a l l e r y p a t t e r n i s much c l e a r e r on the map p rov ided by t h i s method (see F i g u r e 6.4-833) than on t h e one ob ta ined w i t h t he standard method.

6.4.1.3.3.2 P o t e n t i a l map. The p o t e n t i a l map reproduced on F i g u r e 6.4-9 was ob ta ined upstream o f a k a r s t i c o u t l e t by plunging one o f t h e t r a n s m i t t i n g e lec t rodes i n t h e o u t l e t i t s e l f . The e q u i p o t e n t i a l l i n e s a re represented by nested h a l f - e l l i p s e s , the major a x i s o f t h e h a l f - e l l i p s e s co inc ides w i t h t h e stream t h a t f l ows t o the o u t l e t .

6.4.1.3.3.3 Geo-bomb method. The geo-bomb method i s a s p e c i a l i z e d seismic method p a r t i c u l a r l y s u i t e d t o i n v e s t i g a t i o n s i n t o t h e l o c a t i o n o f underground watercourses i n k a r s t . The method was suggested by D. A rand je lov ie ( 1 9 6 9 ) and has been used i n Yugoslavia s ince 1970 (MilanoviC, 1 9 8 1 ) . The method i s based on t h e hypothes is t h a t an a c t i v a t e d , ba l l -shaped geo-bomb w i t h a s p e c i f i c g r a v i t y o f approximately 1 g /cm3 (water) can t r a v e l l o n g d i s tances th rough k a r s t channels w i t h f l o w c a p a c i t i e s o f seve ra l cub ic meters p e r second. The geo-bomb should c o n t a i n a s u f f i c i e n t q u a n t i t y o f exp los i ve t o produce a de tec tab le e l a s t i c wave.

The geo-bomb i s encased i n heavy p l a s t i c m a t e r i a l capable o f w i t h s t a n d i n g c o l l i s i o n s and j o s t l i n g . The bomb c o n s i s t s o f two h a l f - b a l l s , one empty and the o t h e r packed w i t h 930 g o f p l a s t i c exp los ive . The div id ing p l a t e between those two h a l f - b a l l s ho lds t h e de tona t ion device, e l e c t r i c b a t t e r y f o r a c t i v a t i o n o f detonator , and o t h e r mechanisms. The de tona t ion t ime shou ld n o t dev ia te more than 10-15 sec f rom t h e s e t t ime even though t h e mechanism i s sub jec t t o v i b r a t i o n s and j a r r i n g which cannot be avoided when t r a v e l l i n g through k a r s t channels.

The bombs a re i n s e r t e d i n t o the channel where they a re c a r r i e d by t h e water u n t i l t h e i r a c t i v a t i o n . R s e t o f geophones i s used on t h e sur face t o d e t e c t t h e exp los i ve de tonat ion . The geophones a r e s e t up i n two pe rpend icu la r l i n e s and a re connected t o a standard seismometer. The a r r i v a l t imes o f e l a s t i c waves a re i n d i c a t e d on t h e measuring tape as ve ry c l e a r jumps. C a l c u l a t i o n o f t h e l o c a t i o n o f exp los ion p o i n t a l l ows t h e l o c a t i o n o f t h e k a r s t channel t o be mapped.

6 .4 . l . 4 Coas ta l area problems. I n c o a s t a l areas t h e p a r t i c u l a r problems are: (1) determinat ion o f t h e freshwater-seawater i n t e r f a c e ; i 2 ) l o c a t i o n o f underground r i v e r s w i t h year-round changing s a l i n i t i e s ; ( 3 ) l o c a t i o n o f submarine sp i i ngs .

1 8 1

I

7

I

5

4

3 2

1

0 P I 7

I

s 4

a 2 1

O

I

I 7

6

I 4

3

a 1

A

B

C o

I e/-- " I -N-

A B

F igu re 6 . 4 - 8 Loca t ion of t h e Port-Miou g a l l e r y by e lec t romagnet ic methods: (A) standard Turam method, (B) Turam method w i t h one e m i t t i n g e l e c t r o d e i n s i d e t h e g a l l e r y ( a f t e r Cournet e t . a l . )

I Probable axis of the subterranean stream

- O 50 100 200m

F i g u r e 6.4-9 L o c a t i o n o f t h e subterranean Mala Ruda R ive r w i t h an i s o p o t e n t i a l map produced w i t h one t r a n s m i t t i n g e l e c t r o d e ( a f t e r Kovac iv i c and K r u l c l 1967).

1 8 2

6.4.1.4.1 Determinat ion o f t h e f reshwa te r / sa l twa te r i n t e r f a c e . As t h e rock r e s i s t i v i t y i s d i r e c t l y p r o p o r t i o n a l t o t h e water r e s i s t i v i t y , r e s i s t i v i t y p rospec t i ng i s t h e b e s t method t o l o c a t e t h e f reshwa te r / sa l twa te r i n t e r f a c e .

I n t h e case o f a k a r s t i f i e d l imestone hav ing a 1 0 pe rcen t t o t a l p o r o s i t y , t he r e s i s t i v i t y v a r i e s from 700 ohm-m t o 150 ohm-m whether t h e water s a l i n i t y i s 2 g NaCl/R o r 1 0 g NaCl/&.

The f reshwater -sa l twater i n t e r f a c e can t h e r e f o r e be e a s i l y de tec ted by r e s i s t i v i t y p r o f i l e s pe rpend icu la r t o t h e c o a s t l i n e . The depth t o t h e freshwater-seawater con tac t can be eva lua ted by e l e c t r i c a l soundings.

6.4.1.4.2 Loca t ion o f underground streams w i t h v a r i a b l e s a l i n i t y . Close t o the sea, t h e s a l i n i t y o f underground streams sometimes changes during t h e year was a r e s u l t o f changes i n t h e discharge; they a re g e n e r a l l y more s a l i n e i n l a t e summer than i n l a t e w i n t e r .

A r e s i s t i v i t y map i s c a r r i e d o u t i n l a t e summer and another one i n l a t e w i n t e r w i t h t h e measurements b e i n g made e x a c t l y a t t h e same s t a t i o n s . The map o f t h e w i n t e r r e s i s t i v i t y / s u m m e r r e s i s t i v i t y r a t i o d i r e c t l y i l l u s t r a t e s t h e p a t t e r n o f t h e stream.

6.4.1.4.3 Loca t ion o f submarine spr ings. Underground stream water i s c o o l e r and more r e s i s t i v e than seawater.

. Temperature and r e s i s t i v i t y p r o f i l e s have sometimes been made o f f o f calcareous coasts f o r l o c a t i n g undersea ou t f l ows o f k a r s t i c stream such as those i n t h e T r i e s t G u l f (see F i g u r e 6 .4-10) .

6.4.2 Borehole methods. Geophysical i n v e s t i g a t i o n s i n d r i l l e d w e l l s , g e n e r a l l y termed ' l o g g i n g ' , a r e used t o determine t h e boreho le cond i t i ons . Logging methods a re i n d i r e c t approaches t o t h e problem. Surface c o n d i t i o n s need t o be eva lua ted i n t h e l i g h t o f t h e geology and hydro logy o f t h e area. O n t he o the r hand, l ogg ing p rov ides an -- i n s i t u measurement o f p h y s i c a l parameters o f t h e e a r t h p r o p e r t i e s . W e l l l o g g i n g i s most p r o d u c t i v e when d i f f e r e n t methods a re used i n proper combination w i t h each o the r . The method should be se lec ted accord ing t o t h e boreho le cond i t i ons . [EDITOR'S NOTE: Macclay and Smal l 's 1 9 7 6 r e p o r t on t h e use o f boreho le geophysical methods i n s t u d i e s o f t he Edwards Aqu i fe r , Texas, i s an e x c e l l e n t example o f t h e use o f these methods i n carbonate hydrology.]

6.4.2.1 E l e c t r i c logging. An e l e c t r i c l o g of a w e l l i s u s u a l l y a r e c o r d o f t he r e s i s t i v i t y o r s e l f p o t e n t i a l o f t h e format ions ad jacent t o t h e d r i l l ho le . Induced p o t e n t i a l , i nduc t i on , and d i e l e c t r i c l ogs may a l s o be used i n carbonate i n v e s t i g a t i o n s . P r o p e r t i e s a re measured i n t h e uncased p a r t o f t h e w e l l by lower ing probes o r sondes i n t o t h e w e l l .

6.4.2.1.1 R e s i s t i v i t y logs. Apparent r e s i s t i v i t y o f t h e fo rmat ions i s measured i n ohm-meters by sending an e l e c t r i c c u r r e n t i n t o t h e boreho le and de termin ing t h e p o t e n t i a l drop. Equipment used i n making these measurements c o n s i s t s o f a system o f e lec t rodes o r o f an e l e c t r o d e t h a t t rave rses t h e borehole cont inuous ly . Depth measurements a re recorded by a measuring wheel w h i l e t h e e l e c t r o d e i s lowered o r r a i s e d by a winch. E l e c t r i c a l ins t ruments c o n s i s t o f a measuring uni t and a recorder .

The r e s u l t a n t e l e c t r i c l o g i s a r e c o r d o f t h e r e s i s t i v i t y o f t h e rock m a t e r i a l s and may be i n t e r p r e t e d l i t h o l o g i c a l l y and s t a t i s t i c a l l y .

6.4.2.1.2 S e l f p o t e n t i a l (SP) logs. The s e l f p o t e n t i a l l o g i s t h e sum o f t h e n a t u r a l e a r t h p o t e n t i a l s . I n sha l low w e l l s , SP g e n e r a l l y has an e lec t rochemica l o r i g i n . The d i f f e r e n c e i n chemical a c t i v i t y o f t h e fo rma t ion water and d r i l l i n g mud i n t h e boreho le represents a p o t e n t i a l r e f e r r e d t o as e lec t rochemica l p o t e n t i a l . The p o t e n t i a l i s a measure o f t h e d i f f e r e n c e i n t h e l e v e l o f i o n i c a c t i v i t i e s i n t h e d i f f e r e n t m a t e r i a l s .

1 8 3

I n

profile and reference points

small and diffused permanent discharge

small and diffused discharge during high - water season

< permanent discharge point

[e 9 discharge point during high - water season

Reference points

F igu re 6.4-10 Loca t ion of k a r s t i c sp r ings i n the G u l f o f T r i e s t by continuous r e c o r d i n g o f t h e water c o n d u c t i v i t y and temperature, ,

1 8 4

The SP curve i s recorded versus depth as t h e d i f f e r e n c e i n p o t e n t i a l between f i x e d sur face e l e c t r o d e and t h e e l e c t r o d e i n t h e borehole.

6.4.2.2 Rad ioac t ive logging. R a d i o a c t i v i t y l o g s a re named accord ing t o t h e i r sources and de tec tors . The measurement o f n a t u r a l r a d i o a c t i v i t y i s r e f e r r e d t o as gamma-ray logging. Gamma-gamma p o r o s i t y , nèutron, and n a t u r a l gamma r a y l ogg ing are common r a d i o a c t i v e t o o l s use.d i n e x p l o r i n g water w e l l s .

6.4.2.2.1 Gamma r a y logs. Gamma r a d i a t i o n o r i g i n a t e s i n t h e spontaneous d i s i n t e g r a t i o n o f atomic n u c l e i o f v a r i o u s r a d i o a c t i v e elements. Gamma r a d i a t i o n o f r a d i o a c t i v e i so topes t h a t occur n a t u r a l l y i s .measured i n t h e borehole w i t h gamma s e n s i t i v e de tec to rs . The change i n r a d i a t i o n between sand and shale i s g e n e r a l l y unmistakable i n sedimentary format ions. The average depth o f p e n e t r a t i o n o f gamma r a y s i s about one f o o t . The ins t rumen t used i n gamma r a y l o g g i n g measured t h e r a d i a t i o n i n t e n s i t y o f t h e boreho le i n terms o f t he number o f t h e r a y s s t r i k i n g O n t h e d e t e c t i n g counter p e r uni t t ime. The uni t o f r a d i a t i o n f l u x i s roentgens p e r hour. I n p r a c t i c a l l o g g i n g i t i s more convenient t o use e i t h e r microroentgens o r m i l i r o e n t g e n s p e r hour. The re fe rence r a d i a t i o n f l u x o f USA N a t i o n a l Bureau o f Standards i s a p o i n t source o f 50 m ic rocu r ies o f radium a t a d i s tance o f 1 0 8 inches w i t h a f l u x o f 5 microroentgens p e r hour.

De tec t i on i s done by a s c i n t i l l a t i o n counter. I t c o n s i s t s o f a t h a l l i u m - a c t i v a t e d sodium i o d i d e c r y s t a l and phototube. The c r y s t a l em i t s a smal l f l a s h o f l i g h t when i t absorbs a gamma ray . The.phototube i s coupled t o the c r y s t a l . I t conver ts l i g h t t o e l e c t r i c a l pu lses, which then a re a m p l i f i e d and r a t e d i n e l e c t r o n i c c i r c u i t s l o c a t e d i n t h e gamma r a y t o o l . The r a d i a t i o n i s s t a t i s t i c a l i n nature, and t h e number o f gamma r a y s reach ing t h e counter f l u c t u a t e s w ide ly . A t ime cons tan t c i r c u i t i s used t o average these s t a t i s t i c a l v a r i a t i o n s .

6.4.2.2.2 Gamma-gamma and neut ron logs. These l o g g i n g methods r e q u i r e r a d i a t i o n sources and de tec to rs . Neutron l o g g i n g g i v e s the d e n s i t y o r p o r o s i t y o f t h e format ions ad jacent t o t h e ho le . Neutron l o g g i n g p r i m a r i l y records a func t i on o f t h e q u a n t i t y o f hydrogen p e r un i t volume i n t h e v i c i n i t y o f t h e e lect rode. Th is has a neut ron source and a de tec to r . Slow neutrons a re detected by a s c i n t i l l a t i o n counter and a re c a l l e d ep i the rma l neutrons. F a s t neutrons are de tec ted by p r o p o r t i o n a l counters and a re c a l l e d thermal neutrons. I t i s a l s o p o s s i b l e t o d e t e c t gamma r a d i a t i o n t h a t r e s u l t s f rom t h e c o l l i s i o n o f neutrons i n t h e format ion. T h i s i s c a l l e d a neutron-gamma log ; i t measures water sa tu ra ted zones. I n a cased w e l l , i t i s p o s s i b l e t o i d e n t i f y a perched water zone above t h e water t a b l e (Keys, 1 9 6 8 ) . L i k e every r a d i a t i o n l o g i t can be used i n uncased o r cased w e l l s .

There i s another s p e c i f i c t o o l c a l l e d t h e neut ron mo is tu re meter, which can be used i n water spreading a p p l i c a t i o n s ( a r t i f i c i a l recharge) . T h i s i s a l s o a neut ron counter. When i t i s c a l i b e r a t e d , i t i s used t o determine t h e mois tu re percentage as i t changes w i t h depth above t h e water t a b l e . I n water-spreading opera t ions s e r i a l measurements can i n d i c a t e t h e p e n e t r a t i o n r a t e o f water t o t h e water t a b l e .

6.4.2.3 C a l i p e r logging. The v a r i a t i o n o f bo reho le 'd iamete r w i t h depth i s recorded. For t h e w e l l s d r i l l e d i n dense and ha rd format ions, t h i s method i s a va luab le t o o l t o c o r r e l a t e s o l u t i o n openings and bedding planes.

6.4.2.4 Temperature logging. A temperature l o g i s a reco rd o f t h e temperature o f rocks surrounding t h e ho le . Because o f t he known r e l a t i o n between e l e c t r i c a l c o n d u c t i v i t y and temperature i t i s va luab le t o measure t h e change o f temperature. For l i t h o l o g i c s tud ies temperature g r a d i e n t l o g s a re l e s s u s e f u l than e l e c t r i c o r r a d i a t i o n logs.

1 8 5

6.4.2.5 F l u i d r e s i s t i v i t y o r c o n d u c t i v i t y logging. Th is t ype o f l o g i s t h e r e c o r d o f e l e c t r i c a l c o n d u c t i v i t y o f t h e boreho le f lu id . I n case o r uncased w e l l s , i t i s a va luab le t o o l f o r hyd ro log i c s tud ies.

6.4.2.6 Fïowmeter logging. Flow meter l ogs reco rd t h e magnitude o f t h e v e l o c i t y and d i r e c t i o n o f water movement i n w e l l s .

6.4.2.7 Sonic logging. Sonic l ogs measure the t r a n s i t t ime o f sound waves th rough t h e rocks. They a re used as i n d i c a t o r s of t he p o r o s i t y o f rock m a t r i x because sonic waves t r a v e l f a s t e r through a s o l i d m a t r i x than they do through vuggy l a y e r s (Macclay and Small, 1 9 7 6 ) .

6.4.3 A i rbo rne methods. Magnetic and e l e c t r i c a l geophysical surveys a re f r e q u e n t l y made from a i r c r a f t . The r e s u l t s o f these i n v e s t i g a t i o n s are used i n much t h e same manner as those ob ta ined u s i n g sur face methods. A i rborne techniques p r o v i d e a r a p i d means o f surveying an area and p rov ide good i n f o r m a t i o n r e g i o n a l t rends.

6.5 Geochemical methods

6.5.1 D isso lved s o l i d s and gases i n v e s t i g a t i o n s . The o b j e c t i v e t o be a t t a i n e d through a study o f t h e n a t u r a l v a r i a t i o n o f d i sso l ved s o l i d s i n t h e groundwaters o f carbonate rocks should be de f i ned w i t h g r e a t accuracy be fo re a survey i s undertaken. U s e f u l da ta can be c o l l e c t e d and use less f i e l d w o r k and unnecessary l a b o r a t o r y analyses w i l l be e l iminated. As n o t a l l u s e f u l data can be i d e n t i f i e d b e f o r e t h e hydrochemical survey commences, a c e r t a i n f l e x i b i l i t y must be i nco rpo ra ted i n t o t h e p lann ing .

d e a l i n g Va l l ey .

1.

2.

3.

4 .

5.

6 .

7.

6.5.1.1 P lann ing o f survey (D. J. Burdon). The amount o f d e t a i l t o be c o l l e c t e d , determined and analyzed w i l l depend on the purpose and scope o f t h e i n v e s t i g a t i o n , on t h e s i z e o f t h e area studied, and on t h e va lue o f t h e i n f o r m a t i o n t o be ob ta ined i n r e l a t i o n t o the expend i tu re i n t ime, money, resources and s t a f f a v a i l a b l e f o r t h e study (see Chabotarev 1952 , p. 1 3 7 , reproduced here as Table 6.5-1) .

Some ideas on t h e survey p lann ing a re g iven by Geof f roy and W u ( 1 9 7 0 ) w i t h z i n c m i n e r a l i z a t i o n t h e l imestones o f t h e upper M i s s i s s i p p i

Composit ion and r e l a t e d c h a r a c t e r i s t i c s (pH, temperature, t u r b i d i t y , e t c . ) o f normal o r average groundwater, g i v i n g t h e balanced anions and ca t i ons . Aggressiveness, n e u t r a l i t y o r s a t u r a t i o n o f t h e water w i t h respec t t o t h e carbonate m ine ra l s w i t h which i t i s i n contact . Presence o f above-average c h l o r i n e , i n d i c a t i n g ( i n c o a s t a l areas) some m i x i n g w i t h sea water. Presence o f above-average sulphate, i n d i c a t i n g con tac t w i t h gyps i fe rous o r anhydr i t e -depos i t s . R a t i o o f Ca t o Mg, i n d i c a t i n g the amount o f do lomi te w i t h which the groundwater has come i n contact . Any one o r number o f suspected p o l l u t a n t s o r t h e i r i n d i c a t o r s such as n i t r a t e ; t h e BOD l e v e l s may a l s o be des i rab le . Poss ib l y one o r more t r a c e elements, where presence o f m i n e r a l i z a t i o n m ix ing w i th o t h e r f l u i d s , o r some. s p e c i a i g e o l o g i c a l s t r u c t u r e o r h i s t o r y may i n d i c a t e t h e presence o f s p e c i f i c t r a c e elements which a re water -so lub le and l i k e l y t o y i e l d d i a g n o s t i c gene t i c in format ion.

The number o f samples which r e q u i r e l a b o r a t o r y analyses can be i d e n t i f i e d i n t h e f i e l d , and t h e i r number reduced w h i l e the i n fo rma t ion they g i v e can be g r e a t l y expanded th rough some simple f i e l d t e s t s and observat ions. Minimal f i e l d de terminat ions should i nc lude :

1. Temperature:

186

Table 6.5-1. Types o f water analyses f o r d i f f e r e n t purposes. General r e l a t i o n s h i p s between purposes o f a hydro-chemical survey and t h e d e t a i l i n which sampling and analyses a re requ i red . The t a b l e r e f e r s t o a l l types o f hydrochemical surveys, and n o t s p e c i f i c a l l y t o those r e s t r i c t e d t o carbonate rock te r rane. (Chabotarev. 1952, p. 137).

Stage o f search Determinat ion r e q u i r e d C h a r a c t e r i s t i c s o f Ana lys i s Purposes

1. T o t a l s a l i n i t y Qu ick and cheap p r e l i m i n a r y General P re l im ina ry 2 . Q u a l i t a t i v e t e s t i n g ( f i e l d ) ana lys i s . charac ter - Te s t i n g o f hardness, ch lo - i s t i c s o f

r i d e , sulphate, b i - waters by carbonate, n i t r a t e , r e g i o n a l e t c . hydro-

3. C l ' , SO4", HC03', S i m p l i f i e d f i e l d l a b o r a t o r y l o g i c a l hardness. ana lys is ; a l k a l i n e e a r t h i s survey.

computed summary a l k a l i e s conten t i s f i g u r e s o u t by d i v e r s i t y .

NH3r N205r N2031 f i g u r e d o u t by d i v e r s i t y . l o g i c a l pH, t o t a l s a l i n i t y . N20s1N203-qual i tat ive. charac ter -

Rout ine C l ' , S O 4 ' : , HC93', Rout ine l a b o r a t o r y anal- D e t a i l e d Study C o g " , Ca , Mg , y s i s ; a l k a l i e s conten t i s hydro-

i s t i c s o f t he area s tud ied. 1 Selected C l ' , s 0 4 ' : l HC03:r Determina- Ana 1 y s i s C O 3 ' l r Ca , Mg , t i o n a r y l abo ra to ry . Re- t i o n o f t h e

Na +K , f r e e C02 , s u l t s a l l o w t o c o n t r o l gene t i c aggressive C02 , pH, t h e ana lys is . t ypes o f t o t a l s a l i n i t y . waters.

D e t a i l N03'1 NO2'i C l ' r Aims t h e a n a l y s i s o f t h e Geochemical Stud-y S 0 ~ " r H C ~ 3 1 r C o g ' : , p a r t i c u l a r l y se lec ted i n t e r p r e t a -

C a r M g , N a , K , samples. t i o n o f t h e NH4 , f ree C02 , pH, da ta a v a i l - S i o p , Fe703, A1703. able.

de termina t ion i n t r a c e t h e s i m i l a r i t y and s tudy o f s p e c i a l casesr t h e v a r i e t y between d i f f e r e n t subterran- a d d i t i o n a l compo- types o f water o r t h e ean waters , nents such as J * , s u i t a b i l i t y o f water f o r o i l f i e l d Be', F I , P, OH ' , s p e c i a l purposes. areas, m i n - r a d i o a c t i v i t y , e t c . e r a 1 wa-

Spec i a 1 Besides ment ion ing Ana lys i s a l l o w e i t h e r t o Spec ia l

t e r ç , e t c .

187

2. E l e c t r i c a l c o n d u c t i v i t y , and so t o t a l s o l u b l e s a l t s (Hem, 1970, p.

3 . pH (as Baines, 1 9 6 4 ) . Thus, during test-pumping, samples f o r chemical analyses a re r e q u i r e d o n l y

i f - and when - t h e r e i s a change i n e l e c t r i c a l c o n d u c t i v i t y o r temperature. These two can be read f r e q u e n t l y , and c a l l f o r no e labo ra te l a b o r a t o r y work o f p l o t t i n g and i n t e r p r e t a t i o n o f data.

I f t h e r e a re problems o f groundwater p o l l u t i o n , t h e hydrochemical survey should check on some simple component o f such p o s s i b l e p o l l u t i o n . For o rgan ic p o l l u t i o n , n i t r a t e s should be determined; i f n i t r a t e s and c h l o r i d e s inc rease together , o rgan ic p o l l u t i o n i s i n d i c a t e d . Streams from b a t - i n f e s t e d caves i n k a r s t a r e o f t e n high i n n i t r a t e s . Since groundwater i n k a r s t i n many p laces i s n o t sub jec ted t o f i l t e r i n g , p o l l u t i o n problems can be severe.

9 6 ) ;

6.5.1.2 P resen ta t i on o f r e s u l t s . Resu l ts may be presented i n a number o f ways i n c l u d i n g : (1) t a b u l a t i o n s , ( 2 ) diagrams and graphs, ( 3 ) maps.

A f a c o t r t o be decided b e f o r e under tak ing a hydrochemical survey i s t he form i n which t h e r e s u l t s a re t o be presented. The da ta may be s t o r e d i n a number o f ways. The mass o f da ta which w i l l accumulate r a p i d l y should be foreseen. T h i s da ta can be k e p t on punched cards, o r even i n a computer. A t t e n t i o n must be p a i d t o t h e need f o r qu i ck and accurate r e t r i e v a l , and f o r t h e use o f data, s t a r t i n g from simple averages and r a t i o s t o more s o p h i s t i c a t e d r e l a t i o n s h i p s . P o s s i b i l i t i e s o f p l o t t i n g da ta a u t o m a t i c a l l y w i t h v a r y i n g r a t i o s o f s a l t s , e tc . , should n o t be overlooked.

[EDITOR'S NOTE: The reader i s r e f e r r e d t o Mostafa and Lloyd, 1 9 7 7 , as an example o f t h e p r e s e n t a t i o n of r e s u l t s f rom a hydrochemical study i n a l imestone a q u i f e r . ]

Hydrochemical maps should show d i s t r i b u t i o n o f q u a l i t y c h a r a c t e r i s t i c s , such as composit ion, a l k a l i n i t y , temperature, and sediment, among others, and i n d i c a t e changes i n q u a l i t y i n space and t ime. Recommended c o l o r s f o r these maps a re l i s t e d i n t h e " I n t e r n a t i o n a l Legend f o r Hydrogeo log ica l Maps (Unesco-IASH-IAH, 1 9 7 0 ) . [EDITOR'S NOTE: See a l s o Paloc, 19751.

I n i t s s imp les t form, a hydrochemical map should i n d i c a t e known areas o f water o f good q u a l i t y , poor o r unusable q u a l i t y water, and some degree o f t he range i n between. Good and poor a re g iven i n s u b j e c t i v e terms; t h e terms w i l l have d i f f e r e n t meaning i n a r i d , temperate, and humid areas. I n some circumstances, a l l water resources may be impor tant ; t he re fo re , i t i s as impor tan t t o r e c o r d t h e presence o f b rack ish , s a l i n e , and p o l l u t e d waters as those o r o r d i n a r i l y undes i rab le q u a l i t y .

Maps o f p a r t i c u l a r importance a re c o n s t i t u e n t s and q u a l i t y c h a r a c t e r i s t i c s maps, showing v a r i a t i o n s i n t ime and space, and water temperature and r e s i s t i v i t y maps. Normal ly maps o f water temperatures and water r e s i s t i v i t i e s a re used as t o o l s by t h e hyd rogeo log is t t o i n t e r p r e t phenomena o f t he area be ing i n v e s t i g a t e d . General ly, these types o f maps are more o f s c i e n t i f i c and a p p l i e d i n t e r e s t . However, t h e p o s s i b l e s p e c i a l i z e d use o f h o t o r warm waters should n o t be over looked and t h e i r e x t e n t and a v a i l a b i l i t y i n d i c a t e d when they appear t o be s i g n i f i c a n t .

6.5.1.3 Measurement o f major chemical c h a r a c t e r i s t i c s (Donald Langmuir). A wide v a r i e t y O € methods are a v a i l a b l e €o r t h e chemical a n a l y s i s o f n a t u r a l waters. The cho ice o f method must depend on such cons ide ra t i on as: (1) c o s t t o purchase, ma in ta in , and operate t h e necessary inst rumentat ion; ( 2 ) b r e v i t y , s i m p l i c i t y , and r e p e t i t i v e convenience o f a method; ( 3 ) speed, p r e c i s i o n , and accuracy o f a method; and ( 4 ) a d a p t a b i l i t y o f a method t o f i e l d use. The choice method must a l s o take i n t o account the u l t i m a t e purpose o f t he study. For example, an a r e a l reconnaissance of a few major species i n groundwater does n o t demand high accuracy and p r e c i s i o n o f ana lys i s . I f t h e study i s o n l y concerned w i t h t h e q u a l i t y o f water d e l i v e r e d t o consumers, then f i e l d chemical analyses a re unnecessary. I f , however, t he study w i l l at tempt t o decipher t h e geochemistry and e v o l u t i o n o f t h e groundwater w i t h i n t h e a q u i f e r , f i e l d chemical measurements become necessary. I n t h i s case a l l species o r parameters o f i n t e r e s t t h a t would change upon c o l l e c t i o n and be fo re l a b o r a t o r y de te rm ina t ion must be analyzed i n t h e f i e l d , o r t r e a t e d so as t o preserve t h e i r

1 8 8

composi t ion u n t i l l a b o r a t o r y analyses can Ge performed. Among those c h a r a c t e r i s t i c s which must be measured i n t h e f i e l d because p r e s e r v a t i o n i s imposs ib le a re temperature, pH, and o x i d a t i o n p o t e n t i a l o r Eh. As a r u l e concent ra t ions o f a l l d i s s o l v e d gases o r species r e l a t e d t o gases must be e i t h e r f i e l d analyzed o r preserved upon c o l l e c t i o n f o r l a b o r a t o r y ana lys i s . These i n c l u d e CO2, O p , H2S, CH4, H2, and N2. As l o n g as p r e c i p i t a t i o n o f carbonates does n o t occur because o f CO2 losses a f t e r c o l l e c t i o n , t h e a l k a l i n i t y oxygen meter, and p o r t a b l e s p e c i f i c conductance meter o f app rop r ia te sca le f o r t h e waters t o be measured a re a l s o fundamental t o o l s f o r t h e hydrochemist.

F i e l d measured va lues o f , f o r example, Na , by i o n e lec t rode , s p e c i f i c conductance, and a l k a l i n i t y , a r e r a r e l y as r e l i a b l e when measured i n t h e f i e l d as i n t h e l abo ra to ry . However, t h e r e i s an advantage t o o b t a i n i n g i n f o r m a t i o n on water q u a l i t y as a groundwater sampling program proceeds. Such i n f o r m a t i o n pe rm i t s t h e i n v e s t i g a t o r t o mod i fy h i s sampling program as i t proqresses so as t o focus on water q u a l i t y problem areas as they a r e i d e n t i f i e d . T h i s approach w i l l u s u a l l y save t ime and manpower and generate more u s e f u l r e s u l t s than one i n which t h e d e n s i t y and l o c a t i o n o f a l l sampling p o i n t s i s r i g i d l y prearranged, w i t h a l l t h e chemical analyses performed i n t h e l a b o r a t o r y a f t e r sampling i s completed.

+

6.5.1.3.1 Temperature. The measurement o f water temperature i n t h e f i e l d may be performed u s i n g g l a s s - l i q u i d thermometers, o r t h e r m i s t o r s o r thermocouples w i r e d t o a p o r t a b l e meter o r recorder . Thermometers must be hand h e l d during measurement. Thermistors o r thermocouples may be p o s i t i o n e d i n t h e water many meters d i s t a n t from t h e observer and t h e i ns t rumen t which i n d i c a t e s t h e temperature. They o f f e r t h e o n l y means o f measuring temperatures o f subsurface waters i n s o i l s and t h e sa tu ra ted zone w i t h o u t pumping t h e water.

G l a s s - l i q u i d thermometers f o r f i e l d use should be housed i n a p r o t e c t i v e me ta l o r p l a s t i c casing. Groundwater temperatures i n a g i ven area r a r e l y range from than k5OC over t h e year. The thermometer se lec ted should t h e r e f o r e have t h e sma l les t read ing range a v a i l a b l e t h a t s t i l l i nc ludes a l l temperatures o f i n t e r e s t . T h i s op t im izes measurement p r e c i s i o n . To i n s u r e b e s t accuracy, thermometers f o r f i e l d use should be c a l i b r a t e d i n t h e l a b o r a t o r y aga ins t one standardized a t two o r more f i x e d temperatures near t h e temperature range o f i n t e r e s t by an agency such as t h e N a t i o n a l Bureau o f Standards (U.S.). I f a l l these precaut ions a re taken, r e s u l t a n t f i e l d temperatures may be ob ta ined w i t h a p r e c i s i o n o f about fO.2OC , and an accuracy o f IO.5OC o r s l i g h t l y b e t t e r .

Thermistors operate on t h e p r i n c i p l e t h a t t h e e l e c t r i c a l r e s i s t a n c e o f a w i r e increases w i t h i n c r e a s i n g temperature. Thus a c u r r e n t source and ohmmeter are needed t o determine temperatures u s i n g a the rm is to r . Commercially a v a i l a b l e t h e r m i s t o r probes and p o r t a b l e meters a re capable o f a read ing p r e c i s i o n o f f0 .2OC and accuracy o f fO.5OC.

A thermocouple, which c o n s i s t s o f a j u n c t i o n o f two d i s s i m i l a r metals, generates a v o l t a g e p r o p o r t i o n a l t o t h e temperature, which may be read on a po ten t iometer . Thermocouples f o r low temperature use a re o f t e n made o f chromel-alumel, which has a response o f 1.00 mv p e r degree a t 25OC. A measurement p r e c i s i o n o f f O . l ° C thus r e q u i r e s a meter read ing p r e c i s i o n o f f 0 . l m v . Thermistor and thermocouple probes f o r f i e l d use should be embedded i n g lass, p l a s t i c o r o t h e r w a t e r - t i g h t p r o t e c t i v e s h i e l d .

Spring water temperatures may be recorded as soon as t h e thermometer o r o t h e r i n d i c a t i n g device i s b rought t o t h e water temperature. A w e l l , however, should be pumped u n t i l t h e water .temperature becomes cons tan t b e f o r e i t i s recorded. Constancy o f w e l l water temperature (and f i e l d s p e c i f i c conductance) i s i n f a c t a good i n d i c a t i o n t h a t s tand ing waters around a w e l l ' s cas ing and screen have been withdrawn, and t h a t t h e pumped water i s r e p r e s e n t a t i v e o f t h a t p resent i n t h e a q u i f e r as a whole.

6.5.1.3.2 E l e c t r i c a l c o n d u c t i v i t y and r e s i s t i v i t y .

6.5.1.3.2.1 Measurement. The e l e c t r i c a l c o n d u c t i v i t y o f a s o l u t i o n depends d i r e c t l y on t h e charge and m o b i l i t y o f t h e i o n s and t h e i r concent ra t ions .

189

E l e c t r i c a l r e s i s t i v i t y , t h e i n v e r s e o f c o n d u c t i v i t y , i s t h e r e s i s t a n c e o f an amount o f l i q u i d hav ing a th i ckness o f one cent imeter p e r cm and i s measured i n ohm-centimeters, w h i l e t h e c o n d u c t i v i t y i s measured i n mhos p e r cm. Because n a t u r a l waters a re r e l a t i v e l y d i l u t e , t h e u s u a l u n i t s o f conductance (LI) are micromhos (1 micromho = mhos).

Most measuring devices a r e based on t h e Wheatstone b r idge , and a re zeroed by a galvanometer, earphones, o r a cathode r a y tube. To a v o i d e l e c t r o l y s i s phenomena i t i s necessary t o employ a l t e r n a t i n g cu r ren t . The opposing e lec t rodes used t o measured U u s u a l l y c o n s i s t o f two p a r a l l e l p l a t i n u m p l a t e s , o r p l a t i n i z e d rods o r p l a t e s o f a m a t e r i a l such as carbon, p r o t e c t e d by a g lass o r p l a s t i c sh ie ld .

The temperature o f t h e water t o be measured should be determined w i t h a thermometer hav ing a one-tenth degree accuracy, i f a conductance accuracy o f about k0.3 pe rcen t i s des i red. The e lec t rodes should be r e p l a t i n i z e d , and t h e e l e c t r o d e and conductance meter c a l i b r a t e d p e r i o d i c a l l y f o r b e s t r e s u l t s . C a l i b r a t i o n , f o r example, may be w i t h a standard 0.00702 N K C 1 s o l u t i o n , i n which U = 1000 micromhos a t 25OC. Before use, t h e e lec t rode uni t should be r i n s e d w i t h t he water t o be measured. The c e l l i s then immersed completely i n t h a t water, which should be s t i r r e d b e f o r e t h e measurement t o remove a i r bubbles which may c l i n g t o t h e e lect rodes.

6.5.1.3.2.2 I n f l u e n c e o f temperature. C o n d u c t i v i t y increases and r e s i s t i v i t y decreases w i t h r i s i n g temperatures. Fo r most s a l t s o l u t i o n s t h e conductance increases by about t h r e e pe rcen t p e r degree. Conductances are normal ly s tandard ized t o 25OC f o r comparison purposes. An approximate c o r r e c t i o n method i n v o l v e s m u l t i p l y i n g t h e measured conductance, LI, by a f a c t o r , which i s t h e r a t i o o f t h e conductance o f some pure s o l u t i o n a t 25OC t o i t s conductance a t t he measurement temperature. Values o f r based on t h e conductance o f K C 1 s o l u t i o n s a re g i ven i n Table 6.5-2. Values a t i n te rmed ia te temperatures may be ob ta ined by i n t e r p o l a t i o n from a graph o f r versus TOC.

T r a d i t i o n a l l y , r va lues based on the conductance o f K C 1 s o l u t i o n s are used t o c o r r e c t U. However, a more r e a l i s t i c approach € o r carbonate waters i s t o assume t h e temperature v a r i a t i o n o f conductance i s t h e same as f o r a pure Ca(HC03)2 s o l u t i o n . Values o f r based on t h i s approach are a l s o l i s t e d i n Table 6.5-2. Whichever r va lues a re used should be s p e c i f i e d i n any case.

D e t a i l e d i n f o r m a t i o n on procedures f o r conductance measurement a re g i ven by Brown e t a l . (1970) and i n Standard Methods ( 1 9 7 6 ) .

6.5.1.3.2.3 R e l a t i o n t o s a l t content. S p e c i f i c conductance i s t h e most r e a d i l y measurable, and a l s o t h e most u s e f u l s i n g l e chemical measurement t h a t can be made on a water. W i t h a s p e c i f i c conductance value, i t i s p o s s i b l e t o es t ima te t h e t a t a 1 d i s s o l v e d s o l i d s (TDS) con ten t and t h e i o n i c s t r e n g t h and t o check on t h e r e l i a b i l i t y o f a n a l y s i s o f major chemical species i n a water.

Some approximate r e l a t i o n s between conductance and TDS i n d i f f e r e n t water types a re g i ven i n s e c t i o n 6.5.1.2.3. Brown e t a l . (1970) descr ibe how t o compute t h e conductance o f a sample from c o n t r i b u t i o n s o f a l l major i o n i c species t o the conductance. Comparison o f t h i s computed va lue w i t h t he measured conductance p rov ides a check on the accuracy o f chemical analyses o f t he water.

Several workers have shown how t o r e l a t e t h e equ iva len ts p e r m i l l i o n amounts o f i n d i v i d u a l i o n s t o t h e s p e c i f i c conductance of t h e s o l u t i o n (Rossum, 1 9 4 9 ; Logan, 1 9 6 1 ) . As a s imple approximat ion f o r a l l waters, Cepm = 0 . 0 1 ~ , where Cepm i s t h e t o t a l equ iva len ts p e r m i l l i o n o f d i sso l ved c a t i o n s o r anions, o r t h e i r average.

S p e c i f i c conductance measurements are a l s o ve ry u s e f u l i n s tud ies o f groundwater chemis t ry i n carbonate rocks t o d e t e c t changes i n d i s s o l v e d s o l i d s con ten t w i t h t ime, o r w i t h s p r i n g water discharge, o r groundwater l e v e l v a r i a t i o n s . These a p p l i c a t i o n s assume t h a t t he p r e v a l e n t chemical charac ter o f t h e water (see s e c t i o n 3.5.3) remains n e a r l y constant.

A more accurate genera l equat ion i s Cepm = 0 . 0 1 ~ ~ ~ ~ .

6.5.1.3.3 T o t a l d i s s o l v e d s o l i d s . The t o t a l d i s s o l v e d s o l i d s (TDS) conten t may be found by (1) evapora t ing t h e water and weighing t h e residue; ( 2 )

190

Table 6.5-2. Values o f r = 1 1 ( 2 5 ~ C ) / v ( T ~ C ) based on II measured i n a 0 . 0 1 N K C 1 s o l u t i o n , and f o r Ca(HC03)2 so)utions based on t h e l i m i t i n g equ iva len t conductances o f Ca2 from Robinson and Stokes ( 1 9 7 0 ) and o f HCO3 f rom Jacobson and Langmuir ( 1 9 7 4 ) .

O 1 .82

5 1.58

1 0 1 .39

1 5 1.23

20 1.11

25 1 .O0

1 . 8 3 30 O . 912

1 .60 3 5 O .837

1 . 4 4 40 O .769

1 . 2 7 4 5 0 . 7 1 1

1 . 1 3 5 0 0.656

1 .O0

O .89

O .80

0.72

0 .66

0.60

191

summation o f t h e concen t ra t i ons o b t a i n i n a complete chemical a n a l y s i s o f t he major d i s s o l v e d species; o r (3 ) by c a l c u l a t i o n from t h e s p e c i f i c conductance o f t h e water. The TDS found by summing a l l we igh ts i n a complete chemical a n a l y s i s w i l l g e n e r a l l y exceed t h e TDS ob ta ined by evaporat ion. T h i s - i s c h i e f l y because t h e evapora t ion process conver ts d i s s o l v e d HCO3 t o C 0 3 2 - i n t h e res idue. For t h e evapora t ive and summation aeproaches t o g i v e comparable r e s u l t s i t i s necessary t o m u l t i p l y t h e HCO3 (mg/k) va lue by 0.4917 t o o b t a i n t h e e q u i v a l e n t we igh t o f C 0 3 2 ( m g l a ) . The l a t t e r value i s then used i n s t e a d i n t h e summation (see Brown e t a l . , 1970; Hem,-l970).

Summation o f d i s s o l v e d concent ra t ions by weight w i t h HCO3 co r rec ted t o C032' w i l l u s u a l l y g i v e a TDS va lue s l i g h t l y lower o r f10 -20 mg/R compared t o t h e TDS obta ined by evaporat ion, where TDS = 100-500 mg/%. A t h i g h e r TDS va lues t h i s d i f f e r e n c e increases.

I f t h e p r e v a l e n t chemical charac ter o f water i s known, TDS (C032- corrected) may be es t imated from t h e s p e c i f i c conductance ( U ) measurement. For conductances below about 1000 micromhos the f o l l o w i n g approximations have been found u s e f u l .

TDS = 0.55 1i (NaCL t ype water) TDS = 0.60 1i (Ca o r Mg(HC03) type water) TDS = 0.65 1i (genera l case) TDS = 0.68 1i (CaSO4 t ype water)

Al though these c a l c u l a t i o n s g e n e r a l l y p rov ide t h e l e a s t accurate TDS values, they are s u f f i c i e n t l y r e l i a b l e f o r most purposes.

6.5.1.3.4 Hydrogen i o n concen t ra t i on (pH) . Fo r accurate r e s u l t s , groundwater pH must be measured i n t h e f i e l d . T h i s i s because changes f o r example i n temperature, m e t a l o x i d a t i o n s t a t e , CO2, 0 2 , H2S, NH3 o r o t h e r gas content , t h e p r e c i p i t a t i o n o f minera ls , and algae o r b a c t e r i a i n samples a f t e r c o l l e c t i o n w i l l u s u a l l y change t h e pH between t h e f i e l d and l a b o r a t o r y by I O . l t o f l . O u n i t s a f t e r a few days storage (Roberson e t a l , 1 9 6 3 ; Barnes, 1964; Hem, 1979, p. 94).

The pH i s determined c o l o r i m e t r i c a l l y o r more o f t e n e l e c t r o m e t r i c a l l y . C o l o r i m e t r i c pH measurement i n v o l v e s adding a co lo red pH-sens i t i ve i n d i c a t o r t o t h e sample, and v i s u a l l y o r p h o t o m e t r i c a l l y comparing t h e c o l o r t h a t develops t o t h a t o f standards c o n t a i n i n g t h e same i n d i c a t o r . There are many l i m i t a t i o n s t o u s i n g c o l o r i m e t r i c methods i n n a t u r a l environments. F i r s t , co lo red o r turbid samples make i t imposs ib le t o determine p r e c i s e l y t h e i n d i c a t o r c o l o r . Second, each i n d i c a t o r g i v e s i t optimum accuracy ( f 0 . 0 5 t o 0 .1 pH u n i t s ) over a range o f 1 o r 2 pH u n i t s , so t h a t seve ra l i n d i c a t o r s may be r e q u i r e d t o cover t h e range o f i n t e r e s t . I n a d d i t i o n , t h e i n d i c a t o r i t s e l f has a capac i t y f o r protons, and may t h e r e f o r e change sample pH i f the sample i s p o o r l y b u f f e r e d (Langmuir, 1971).

The most convenient and g e n e r a l l y p r e c i s e and accurate method o f r o u t i n e pH measurement i s t$e e l e c t r o m e t r i c technique. The pH o f t h e s o l u t i o n i s determined w i t h an H i o n s e n s i t i v e g lass i n d i c a t o r e lec t rode and re fe rence e l e c t r o d e ( u s u a l l y KC1-saturated calomel o r Ag-AgC1) w i t h read ings taken on an e lec t rometer . A combination pH-reference e l e c t r o d e i s more convenient and r e l i a b l e than a re i n d i v i d u a l pH and re fe rence e lec t rodes f o r f i e l d o r l a b o r a t o r y analyses. A f u l l y t r a n s i s t o r i z e d pH meter i s f a r super io r t o a vacuum tube-type i n terms o f s t a b i l i t y and freedom from i n t e r f e r e n c e s under f i e l d cond i t i ons .

E lec t rodes and meter f o r pH de terminat ion must be c a l i b r a t e d i n standard b u f f e r s o f known pH b e f o r e measurement. Two pH b u f f e r s whose pH's b racke t t he pH of t h e unknown s o l u t i o n should be used. These b u f f e r s and t h e e lec t rodes should be brought t o and h e l d a t groundwater temperature ( f l o c ) during measurement. The sample should be p laced i n a beaker o r o t h e r vesse l w i t h o u t s t i r r i n g d u r i n g pH measurement. Th i s avoids f l o w i n g p o t e n t i a l e r r o r s , which may amount t o as much as -0.3 t o -1.0 pH u n i t s . For t h e same reason pH should n o t be measured d i r e c t l y i n a r a p i d l y f l o w i n g stream, spr ing, o r w e l l water. Because o f u n c e r t a i n t i e s i n t h e pH's of b u f f e r s , and ins t rumen ta l l i m i t a t i o n s , f i e l d measured pH's a re r a r e l y known b e t t e r than t o k0.05 pH u n i t s , o r l a b measured pH's more a c c u r a t e l y than f 0 . 0 2 pH u n i t s (Langmuir, 1 9 7 1 ) .

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6.5.1.3.5 D isso lved oxygen and o x i d a t i o n p o t e n t i a l . D i sso l ved oxygen (DO) may be measured i n t h e f i e l d w i t h a DO e l e c t r o d e and p o r t a b l e meter, o r i n t h e l a b o r a t o r y by t h e Wink le r method i f t h e oxygen con ten t o f t h e sample i s prepared upon c o l l e c t i o n i n t h e f i e l d . These and o t h e r a n a l y t i c a l methods f o r DO a n a l y s i s a re descr ibed i n d e t a i l by Mancy and J a f f e ( 1 9 6 6 1 , Brown e t a l . ( 1 9 7 0 ) , Standard Methods (1976) and i n t h e Manual o f Methods f o r Chemical Ana lys is o f Water and Wastes ( 1 9 7 4 ) . Because f i e l d measurement o f DO w i t h an e lec t rode i s as r e l i a b l e as, and more r a p i d than t h e Wink le r method, i t i s t h e p r e f e r r e d a n a l y t i c a l approach. Unless h i g h l y p o l l u t e d , as by sewage, t h e DO conten t o f shal low unconf ined groundwaters i n carbonate rocks i s c l o s e t o s a t u r a t i o n w i t h respec t t o oxygen l e v e l s i n t h e atmosphere. The n o r v l s e a l l e v e l atmosphere (water saturated) has a p a r t i a l oxygen pressure ( 0 2 ) o f 0.2094 atm. A t t h i s p ressure t h e s o l u b i l i t y o f atmospheric oxygen i n pure water i s 14.5, 11 .26 , 9.09, and 8.25 mg/R a t O , 10 , 20 and 25OC, r e s p e c t i v e l y (Carpenter, 1 9 6 6 ) .

The s o l u b i l i t y o f atmospheric oxygen i n water decreases w i t h decreasing t o t a l p ressure (and thus e l e v a t i o n ) w i t h i n c r e a s i n g s a l t content, and i n c r e a s i n g temperature. Standard Methods (1971) g i v e s c o r r e c t i o n s f o r a l l these e f f e c t s . More exac t s o l u b i l i t y da ta on oxygen a r e g i ven by Carpenter (1966), and Green and C a r r i t t (1967).

DO l e v e l s below 0.01 m/R a re n o t uncommon i n a r t e s i a n carbonate qroundwaters where t h e oxygen i n groundwater recharge has been dep le ted by organ ic and i n o r g a n i c processes. Only when DO l e v e l s a re l e s s than 0 .01 mg/R should Eh measurements be considered t o measure t h e o x i d a t i o n s t a t e o f t h e water. Such measured a re performed i n t h e f i e l d w i t h a p l a t i n u m i n d i c a t o r e lec t rode and a calomel o r s i l v e r - s i l v e r c h l o r i d e re fe rence e l e c t r o d e and e lec t rometer (Langmuir, 1971). Ox id ized carbonate groundwaters g e n e r a l l y con ta in n e g l i g i b l e concen t ra t i ons o f t h e species which .can become i n v o l v e d i n r e v e r s i b l e ox ida t i on - reduc t i on r e a c t i o n s ( f o r example S o and H2S, Fe2+ and Fe(OH)3(s), and Mn2+ and Mn02(s) ) . For t h i s reason Eh measurements i n such waters a re o f q u a l i t a t i v e va lue only . I n reduced carbonate groundwaters (DO 0.01 mg/R) s i g n i f i c a n t concen t ra t i ons o f t h e e l e c t r o a c t i v e species j u s t descr ibed may make t h e measurement o f a thermodynamical ly mean ing fu l Eh p o s s i b l e (see Langmuir, 1 9 7 1 ) .

6.5.1.3.6 Calcium and magnesium. Samples f o r ca lc ium o r magnesium a n a l y s i s should be a c i d i f i e d i n the f i e l d t o a pH below 4-5 t o avo id CaC03 p r e c i p i t a t i o n b e f o r e l a b o r a t o r y ana lys i s . Calcium and magnesium a re g e n e r a l l y determined i n t h e l a b o r a t o r y by complexiometr ic t i t r a t i o n , o r by atomic adsorp t ion spectroscopy. T i t r a t i o n i s w i t h d isodium dihydrogen ethylenediamine t e t r a a c e t a t e (Na2EDTA). The procedure i n v o l v e s Na2EDTA t i t r a t i o n a n a l y s i s o f t he t o t a l hardness ( t h e t o t a l a l k a l i n e e a r t h s p resen t - u s u a l l y o n l y ca l c ium and magnesium), separate Na2EDTA t i t r a t i o n f o r calc ium, which i s d i f f i c u l t t o do accu ra te l y , and c a l c u l a t i o n o f t h e magnesium by d i f f e r e n c e . Calcium and magnesium may a l s o be determined i n d i v i d u a l l y by atomic absorp t ion . When numerous samples a re t o be analyzed, t h e speed o f t h e l a t t e r method makes i t p r e f e r a b l e t o Na2EDTA t i t r a t i o n . T i t r i m e t r i c and spec t romet r ic methods a re o f rough ly comparable p r e c i s i o n and accuracy. D e t a i l e d i n f o r m a t i o n on b o t h a n a l y t i c a l methods a re g i ven by Brown e t a l . (1970) and i n Standard Methods ( 1 9 7 1 ) . These sources a l s o e x p l a i n how t o compute t h e hardness as ca lc ium carbonate.

6.5.1.3.7 Sodium and potassium. The a l k a l i meta ls sodium and potassium a r e g e n e r a l l y measured by atomic abso rp t i on spectroscopy on f i e l d a c i d i f i e d samples (Brown e t a l . , 1970). They may a l s o be measured w i t h g lass, s p e c i f i c i o n e lec t rodes and a po ten t iometer i n u n a c i d i f i e d samples ( T r u e s d e l l and Jones, 1969). Samples f o r e l e c t r o d e measurement need n o t be d i l u t e d , whereas those f o r atomic abso rp t i on must o f t e n be be fore ana lys i s . However, t h e e l e c t r o d e methods a re g e n e r a l l y l e s s accura te and p r e c i s e than atomic absorp t ion .

6.2.1.3.8 Carbonate species. The d i s t r i b u t i o n o f carbonate species, H', and OH as a f u n c t i o n of pH a r e shown i n F i g u r e 6 .5 -1 f o r a t o t a l carbonate

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concen t ra t i on o f molar. By convent ion d i s s o l v e d CO2 i s g e n e r a l l y assumed p resen t as und issoc ia ted carbonic a c i d ( H ~ C O ~ ) . However, t he e q u i l i b r i u m cons tan t f o r t h e r e a c t i o n

C02(aq) + H20 = H2CO3 (6.5-1)

i s K = [H2CO31/[C02] = 2.6 x a t 25OC, where t h e brackets d e n o t g q a c t i v i t i e s . Thus, i n f a c t H2CO3 i s l e s s than 0.3 pe rcen t o f t h e d i s s o l v e d CO2 present . F i g u r e 6.5-1 shows t h a t H2C02 ( a c t u a l l y C02,aq) i s t h e predominant carbonate species a t pH's below 6.35. Between 6.35 and 10.33, HCO3 i s predominant, which C032- the major species a t h ighe r

. pH's.

6.5.1.3.8.1 Carbon d iox ide . pThe CO2 conten t o f a water i s u s u a l l y expressed as a gas p a r t i a l pressured ( CO21 2n atm (atmospheres), o r as m i l l i m o l e s o r m i l l i g r a m s p e r l i t e r . Computed CO2 values a re concep tua l l y convenient, even when a gas phase i s absent (as i?, a r t e s i a n a q u i f e r s ) and such va lues are t h e o r e t i c a l on l y . Conversion of CO2 t o d i sso l ved CO2 i n v o l v e s the gxpression f o r K C 0 2 which v a r i e s w i t h temperature. I n genera l C02(atm) = CO2(mmol/ll) x 10 3/KC02, and C02(mmol/a) = 0.227 x

co2(mg/a). A t 25OC, P 2(atm) = 0.0347 x C02(mmol/R). The CO2 con ten t 59 s o i l gases may be measured d i r e c t l y . M io tke (1974)

discusses t h e design, opera t ion , and r e s u l t s ob ta ined u s i n g CO2 gas de tec to rs i n s o i l a i r a t depths up t o 1 m. The CO2 conten t o f water samples 'may be computed from a f i e l d pH and prompt l a b o r a t o r y biocarbonate ana lys i s , u s i n g equat ion ( 3 . 2 - 1 3 ) . Such c a l c u l a t i o n s a re a l s o d e t a i l e d by Brown e t a l . (1970, and i n Standard Methods ( 1 9 7 1 ) . CO2 i n water may a l s o be measured immediately upon sample c o l l e c t i o n i n t h e f i e l d by T i t r a t i o n w i t h a standard sodium carbonate o r sodium hydrox ide s o l u t i o n t o t h e i n f l e c t i o n p o i n t near pH = 8.3 (Standard Methods, 1971).

6.5.1.3.8.2 Bicarbonate and a l k a l i n i t y . A l k a l i n i t y i s t h e a c i d - n e u t r a l i z i n g c a p a c i t y o f water. I t r e f l e c t s t h e presence o f carbonate and bicarbonate, ammonia, bora tes , phosphates, s i l i c a t e s , o rgan ic anions, and hyd roxy l i o n (Stumm and Morgan, 1981). I n most n a t u r a l waters, t he pH i s between 5 a.nd 8, so t h a t a l k a l i n i t y - (C,) i s due c h i e f l y t o the presence o f weak a c i d anions, among which HCO3 i s u s u a l l y t h e predominant species. I n unpo l l u ted r e l a t i v e l y f r e s h carbonate groundwater, t he d e f i n i t i o n o f a l k a l i n i t y (C,) i s

- cB = H C O ~ + 2c032- + OH- - H+ (6.5-2)

where species concen t ra t i ons a re i n moles p e r l i t e r . Hydroxy l a l k a l i n i t y r a r e l y exceeds 1 percen t o f CB un less t h e pH i s above 9 (see F i g u r e 6 . 5 - 1 ) . Carbonate a l k a l i n i t y i s un impor tan t (<l percent o f CB) i n samples w i t h pH's below about 8.3. A t sample pH's below 8.3 t h e carbonate conten t can be determined by computation from t h e b icarbonate and the pH v i a expression (3.2-13b) f o r K2 (see s e c t i o n 3 . 2 . 2 ) . I n genera l t h i s approach i s more accurate than t h e carbonate a l k a l i n i t y t i t r a t i o n f o r waters whose pH's are below 9.

Carbonate and b icarbonate a l k a l i n i t i e s are determined by t i t r a t i o n w i t h a standard a c i d t o t h e i n f l e c t i o n p o i n t s near 8.3, and between 4 and 5, r e s p e c t i v e l y (Barnes, 1 9 6 4 ) . The pH's o f these i n f l e c t i o n p o i n t s depend on the s a l i n i t y and a l k a l i n i t y and are lowest f o r h i g h a l k a l i n i t y waters (Stumm and Morgan, 1 9 8 1 ) .

Samples f o r a l k a l i n i t y de te rm ina t ion need n o t he analyzed i n t h e f i e l d , but should be r e f r i g e r a t e d immediately upon c o l l e c t i o n , and analyzed i n the l a b o r a t o r y w i t h 48 hours, j u s t a f t e r b e i n g brought t o room temperature. The t i t r a n t i s u s u a l l y a d i l u t e s o l u t i o n of s t rong ac id, such as H2SO4, HC1, o r HNO3 (Brown e t a l . , 1 9 7 0 ) . Because of t he e f f o r t r e q u i r e d t o standardize these acids, and t h e i r r e l a t i v e i n s t a b i l i t y , a 0.0100 normal s o l u t i o n o f potassium b i i o d a t e ( K H ( I 0 3 ) 2 1 i s o f t e n a more convenient a l k a l i n i t y t i t r a n t . The oven-dr ied s a l t may be d i sso l ved d i r e c t l y i n water and need n o t be standardized. I t cannot however be used t o t i t r a t e waters which con ta in

194

O" "- I

19

5

s i g n i f i c a n t amounts o f reduced species, a l though t h i s i s r a r e l y t h e case f o r sha l low carbonate groundwaters.

C a l c u l a t i o n o f t h e a l k a l i n i t y o f a water as e q u i v a l e n t o f CaC03 i s descr ibed i n Standard Methods ( 1 9 7 1 ) .

6.5.1.3.9 Other species. S i l i c a ( c h i e f l y p resen t i n water as monomeric s i l i c i c acid, H4Si04) i s u s u a l l y analyzed by the molybdate b l u e method, o r more r a p i d l y by atomic abso rp t i on spectroscopy (Brown e t a l . , 1970).

Convent ional methods o f s u l f a t e a n a l y s i s are adequately descr ibed i n such oeferences as Brown e t a l . (1970). S u l f a t e may be measured more r a p i d l y u s i n g a l e a d s o l i d s t a t e s p e c i f i c i o n e l e c t r o d e and t i t r a t i n g t h e sample w i t h standard Pb(N03)2 s o l u t i o n . The e lec t rode senses a r a p i d r i s e i n Pb2 once t h e s u l f a t e has been l a r g e l y p r e c i p i t a t e d as PbS04. The r e l a t i v e l y s h o r t u s e f u l l i f e and t h e high c o s t o f t h e l e a d e l e c t r o d e somewhat m i t i g a t e aga ins t i t s use f o r t h i s purpose, however.

C h l o r i d e va lues a re g e n e r a l l y determined t i t r i m e t r i c a l l y (Brown e t a l . , 1 9 7 0 ) . The s o l i d s t a t e c h l o r i d e s p e c i f i c i o n e l e c t r o d e p rov ides r e s u l t s n e a r l y as p r e c i s e as t h e t i t r i m e t r i c method, and pe rm i t s a g r e a t e r speed o f a n a l y s i s when numerous samples a re i nvo l ved .

The s o l i d s t a t e f l u o r i d e e l e c t r o d e i s supp lan t ing o t h e r techniques o f f l u o r i d e a n a l y s i s i n most U n i t e d S ta tes ' l a b o r a t o r i e s (see t h e Manual o f Methods f o r Chemical Ana lys i s o f Water and Wastes, 1974).

The bas-permeable membrane ammonia e lec t rode i s now an accepted method o f a n a l y s i s o f t h e U.S. Environmental P r o t e c t i o n Agency ( i b i d ) . The n i t r a t e l i qu id exchange e l e c t r o d e has been shown t o g i v e r e s u l t s comparable t o t h e Bruc ine Method (Langmuir and Jacobson, 1970). Both ammonia and n i t r a t e e l e c t r o d e analyses a r e more r a p i d and l e s s ted ious than o l d e r convent iona l methods, w i t h o u t s a c r i f i c i n g e i t h e r p r e c i s i o n o r accuracy.

6.5.2 Neutron a c t i v a t i o n ana lys i s . A c t i v a t i o n a n a l y s i s i s a s e n s i t i v e means of e lementa l ana lys i s . I t has found widespread a p p l i c a t i o n i n geochemistry, g i v i n g much new i n f o r m a t i o n on the composi t ion o f t he e a r t h ' s c r u s t , sea water, me teo r i t es , l u n a r samples, e t c . I t i s o f h y d r o l o g i c a l i n t e r e s t f o r t h e measurement o f n a t u r a l l y - o c c u r r i n g t r a c e elements i n waters, and as a means o f d e t e c t i n g and measuring chemical t r a c e r s i n j e c t e d i n t o a system.

A c t i v a t i o n a n a l y s i s i n v o l v e s r a t h e r s p e c i a l i z e d equipment and techniques. The p r i n c i p l e s , techniques, s e n s i t i v i t i e s f o r s p e c i f i c elements and f o r p a r t i c u l a r a p p l i c a t i o n s have been d e a l t w i t h i n a number o f t e x t s (Kruger, 1971, Lerehan and Thomas, 1 9 6 5 , and. B r u n f e l t and Steinnes, 1971) , and w i l l n o t be considered i n d e t a i l here. I n p r i n c i p l e , t he m a t e r i a l t o be analyzed, i n t h e case o f water samples u s u a l l y t h e res idue on evapora t ion o r a concentrate e x t r a c t e d chemica l l y from t h e water samples, i s i r r a d i a t e d w i t h neutrons i n a r e a c t o r o r a c c e l e r a t o r and t h e induced r a d i o a c t i v i t y measured as an i n d i c a t i o n o f t h e amount o f element o f i n t e r e s t present. The element be ing analyzed must have s u i t a b l e neut ron abso rp t i on p r o p e r t i e s and a c t i v a t i o n products. Modern y-ray spec t romet r ic equipment o f high r e s o l u t i o n has g r e a t l y improved and extended t h e technique, i n many cases e l i m i n a t i n g any need f o r rad iochemica l separa t ions a f t e r i r r a d i a t i o n thus p e r m i t t i n g the a n a l y s i s o f s h o r t e r - l i v e d a c t i v a t i o n products.

I n t r a c i n g s tud ies, as w e l l as hav ing s u i t a b l e a c t i v a t i o n c h a r a c t e r i s t i c s , t h e chemical t r a c e r compound must meet the requirements o f s t a b i l i t y and n o n - i n t e r a c t i o n w i t h t h e a q u i f e r system. Since neut ron i r r a d i a t i o n a c t i v a t e s s p e c i f i c isotopes, a chemical enr iched i n a s t a b l e i so tope hav ing p a r t i c u l a r l y f avo rab le a c t i v a t i o n c h a r a c t e r i s t i c s may be used t o achieve u l t i m a t e s e n s i t i v i t y . Th i s technique has t h e advantage o f h i g h s e n s i t i v i t y o f d e t e c t i o n w i t h o u t t h e i n t r o d u c t i o n o f r a d i o a c t i v e m a t e r i a l i n t o t h e h y d r o l o g i c a l system. However, t h e a n a l y s i s i s dependent on t h e a v a i l a b i l i t y o f neut ron i r r a d i a t i o n f a c i l i t i e s , cannot be done i n t h e f i e l d and i s expensive, p a r t i c u l a r l y if enr iched s t a b l e i so tope chemicals a re t o be used.

6 . 5 . 3 Environmental i so tope hydrogeology ( I n t e r n a t i o n a l Atomic Energy Agency S t a f f ) . Environmental i so tope hydrogeology uses t h e i so tope v a r i a t i o n s

196

o c c u r r i n g i n water t o g a i n hyd rogeo log ica l and h y d r o l o g i c a l i n fo rma t ion . Environmental i s o t o p e s t u d i e s a r e most s u i t a b l e f o r r e g i o n a l i n v e s t i g a t i o n s . The t r a c i n g c o n d i t i o n s have been e s t a b l i s h e d by n a t u r e over a b road space and t ime scale. They cannot be c o n t r o l l e d b y man, but can be observed and i n t e r p r e t e d t o g a i n i n f o r m a t i o n on t h e o r i g i n , t u rnove r , and t r a n s i t t imes o f water i n t h e system.

The p r i n c i p l e s o f t h e use o f environmental i so tope da ta have been discussed i n chapter 3. Here, p r a c t i c a l cons ide ra t i ons o f c a r r y i n g o u t a study and examples o f a p p l i c a t i o n s a r e g i ven t o i l l u s t r a t e t h e n a t u r e and va lue o f such studies.

6.5.3.1 P r o j e c t p lanning. I so tope techniques a re a complimentary t o o l f o r hydrogeo log ica l i n v e s t i g a t i o n s . The amount and t h e q u a l i t y o f i n f o r m a t i o n t h a t they are able t o p r o v i d e i s ve ry dependent on t h e degree o f hyd rogeo log ica l knowledge o f t h e area under i n v e s t i g a t i o n . I t i s ev iden t , f o r instance, t h a t s e l e c t i o n of t h e sampling p o i n t s i n a g i ven area must be made on the b a s i s o f t h e i n f o r m a t i o n a v a i l a b l e f o r each p o i n t . I n t e r p r e t a t i o n o f t h e r e s u l t s w i l l - be more r e l i a b l e when the main hyd rogeo log ica l f ea tu res o f t h e groundwater body be ing s tud ied are w e l l known. The i n f o r m a t i o n g i ven by t h e d i f f e r e n t environmental i so topes i s u s u a l l y complimentary, SO a f u l l e r i n t e r p r e t a t i o n i s p o s s i b l e i f data on a l l area a v a i l a b l e . I n t h i s way t h e r e i s a va luab le i n t e r p l a y between t h e d i f f e r e n t da ta which leads t o t h e optimum use o f these techniques.

6.5.3.1.1 Development o f an i so tope hydrogeology study. I d e a l l y , an i so tope hydrogeology study should develop as f o l l o w s : The f i e l d hyd rogeo log is t f i r s t makes the b e s t p o s s i b l e a p p r a i s a l o f t h e area under i n v e s t i g a t i o n , d e f i n e s t h e main hydrogeo log ica l problems a n d e s t a b l i s h e s p o s s i b l e work ing hypotheses. A t t h i s p o i n t , t h e hyd rogeo log is t and t h e e x p e r t i n t h e a p p l i c a t i o n o f i so tope techniques i n hydrology (whom we may r e f e r t o as an i so tope h y d r o l o g i s t ) s e l e c t and discuss those problems which c o u l d be s t u d i e d w i t h i s o t o p e techniques, and the hypotheses which cou ld be tested. Al though a v i s i t t o t h e area by t h e i so tope h y d r o l o g i s t may n o t seem s t r i c t l y necessary, i n p r a c t i c e i t i s h i g h l y recommended. The more r e a l i s t i c p i c t u r e gained o f t h e area under i n v e s t i g a t i o n i s almost e s s e n t i a l f o r c o r r e c t s e l e c t i o n o f sampling p o i n t s and subsequent i n t e r p r e t a t i o n o f r e s u l t s . The v i s i t a l s o p rov ides t h e i s o t o p e h y d r o l o g i s t w i t h an o p p o r t u n i t y t o i n s t r u c t t h e l o c a l personnel , under f i e l d cond i t i ons , on sampling techniques r e q u i r e d t o a v o i d contaminat ion o r a l t e r a t i o n o f samples. Sometimes, t h e i so tope h y d r o l o g i s t w i l l recogn ize unforeseen s i t e c o n d i t i o n s t h a t necess i ta te s p e c i a l p recau t ions which would n o t seem r e l e v a n t t o a person who i s n o t f a m i l i a r w i t h i so tope techniques.

A t l e a s t two sampling campaigns a re recommended whenever poss ib le . The samples c o l l e c t e d i n t h e f i r s t campaign should cover a l l t h e main problems under i n v e s t i g a t i o n , but n o t n e c e s s a r i l y a l l o f them w i l l be i s o t o p i c a l l y analyzed. The r e s u l t s ob ta ined from t h i s f i r s t s e t o f reconnaissance samples w i l l p rov ide answers t o b a s i c ques t ions such as:

1. Are t h e r e s i g n i f i c a n t i s o t o p e d i f f e r e n c e s among t h e waters i n t h e

2. 3. How does t h i s i s o t o p i c da ta agree w i t h t h e h y d r o l o g i c a l hypotheses?

O n t h e b a s i s o f t h i s i n fo rma t ion , a second more d e t a i l e d sampling should be organized f o r those problems f o r which i s o t o p i c techniques l o o k promising.

I n t h e case t h a t v a r i a t i o n s o f i s o t o p i c composi t ion w i t h t ime are expected ( f o r instance i n k a r s t i c systems, o r any system hav ing r a p i d c i r c u l a t i o n ) sampling should be c a r r i e d o u t r e g u l a r l y i n t ime (say, two t o f o u r samples p e r year a t each sampling p o i n t ) . I f recharge i s l i k e l y t o be markedly seasonal, e.g. because o f p r e c i p i t a t i o n d i s t r i b u t i o n o r s p r i n g snow me l t , i t i s adv i sab le t o schedule samplings f o r t h e end o f t h e wet and dry , o r f l o o d and base f l o w per iods. I n t h e f i r s t stage o f t h e study o n l y a few samples need be analyzed t o l e a r n o f t h e degree o f v a r i a b i l i t y occu r r i ng . O n t h e b a s i s o f t h e r e s u l t s , i t should be decided whether i t i s wor thwh i le t o make more analyses.

The i n t e r p r e t a t i o n o f i s o t o p i c r e s u l t s and t h e p r e p a r a t i o n o f t h e r e p o r t should be made by c o l l a b o r a t i o n o f t h e i s o t o p e h y d r o l o g i s t and t h e

197

system which may serve t o i d e n t i f y them? What a re t h e ranges o f va lues f o r t r i t i u m and carbon-14 ( 1 4 C ) .

hydrogeo log is t . Some hypotheses cou ld seem reasonable from t h e h y d r o l o g i c a l s tandpo in t , but be unacceptable f rom t h e p o i n t o f v iew o f t he i s o t o p i c r e s u l t s , and v i c e versa. I t i s then necessary t o decide which o f t h e p o s s i b l e hypothes is b e s t f i t s a l l t h e i s o t o p i c , geochemical, geophysical and hyd rogeo log ica l data.

6.5.3.1.2 Sampling. I n study t h e i so tope conten t o f groundwater, a major requirement i s t o o b t a i n an uncontaminated sample r e p r e s e n t a t i v e o f a g iven a q u i f e r o r zone. T h i s r e q u i r e s c a r e f u l se lec t i on , i f f e a s i b l e , o f w e l l s f o r which r e l e v a n t i n f o r m a t i o n i s a v a i l a b l e . A few c a r e f u l l y se lec ted samples are more va luab le than dozens f o r which t h e necessary suppor t ing da ta are u n r e l i a b l e .

I t i s impor tan t t o avo id contaminat ion o f t h e sample from upper zones penet ra ted by t h e w e l l . T h i s i s e s p e c i a l l y impor tan t i n t r i t i u m and carbon-14 sampling because i n many areas t h e uppermost groundwater may have a much h ighe r concen t ra t i on o f these iso topes than t h e zone o f i n t e r e s t . S u f f i c i e n t water must be removed by pump ing o r o t h e r means t o rep lace the volume o f water s tand ing i n t h e w e l l b e f o r e a sample i s taken f o r i so tope ana lys i s . Water s tand ing i n an unused w e l l w i l l g e n e r a l l y g i v e spur ious i so tope r e s u l t s .

Sampling o f w e l l s during d r i l l i n g o f f e r s p o s s i b i l i t i e s o f de termin ing i s o t o p i c s t r a t i f i c a t i o n o f water, but contaminat ion o f samples w i t h d r i l l i n g f l u id may e a s i l y occur. Samples should be taken o n l y a f t e r s u f f i c i e n t water has been removed from t h e h o l e t o assure t h a t format ion water has been sampled.

For s t a b l e i so topes and t r i t i u m , r e l a t i v e l y sma l l samples are r e q u i r e s - 20 m l a re s u f f i c i e n t f o r s t a b l e isotopes, 500 m l f o r t r i t i u m . Containers must be a i r t i g h t t o a v o i d evapora t ion and exchange. P l a s t i c b o t t l e s w i t h i n n e r po l ye thy lene cones i n t h e i r screw caps are g e n e r a l l y used. B o t t l e s should be f i l l e d completely and care taken t o minimize exposure o f t h e samples t o t h e atmosphere. For long-term s to rage (more than one year) samples should be k e p t i n we l l - sea led g lass b o t t l e s .

Carbon-14 sampling i s done by separa t ing d i s s o l v e d carbonate and CO2 from a l a r g e enough volume o f water ( u s u a l l y 50-100 a ) t o y i e l d 3-4 g o f carbon, p r e f e r a b l y a t t h e sample s i t e . Two d i f f e r e n t methods may be used: p r e c i p i t a t i o n o r gas e v o l u t i o n . I n t h e f i r s t method, the water sample i s ad jus ted t o pH 9 w i t h carbonate f r e e NaOH s o l u t i o n added t o p r e c i p i t a t e BaC03. The Bac03 p r e c i p i t a t e i s al lowed t o s e t t l e d i n t o a b o t t l e f o r shipment t o t h e l a b o r a t o r y f o r 14C ana lys i s . A d e t a i l e d d e s c r i p t i o n o f t h i s method i s d i s t r i b u t e d on request by the Sec t ion o f I so tope Hydrology o f I .A.E.A.

The second method c o n s i s t s o f a c i d i f y i n g t h e water sample t o re lease i t s CO2 which i s purged by a c i r c u l a t i n g gas system and c o l l e c t e d i n an a l k a l i n e s o l u t i o n f o r shipment t o t h e l a b o r a t o r y (Vogel, 1 9 6 7 ) .

I n b o t h methods, i t i s impor tan t t o minimize exposure o f t h e i n i t i a l water sample and t h e carbonate concent ra te t o the a i r t o avo id pick-up o f atmospheric CO2 hav ing modern carbon-14.

I n f o r m a t i o n t o accompany t h e samples i nc ludes da ta normal ly p a r t o f a w e l l o r s p r i n g h i s t o r y , such as: p l a c e o f sampling, date, t h e depth o f t h e w e l l , i n t e r v a l tapped, a q u i f e r , s t a t i c l e v e l , water temperature, pH, chemical composit ion, depth o f water, whèther a q u i f e r i s conf ined, e tc .

Sample t r a n s p o r t and storage a re a sma l l p a r t o f t h e expense o f a f i e l d t r i p and subsequent ana lys i s , SO i t i s d e s i r a b l e t o take more samples d u r i n g the i n i t i a l stages o f t he i n v e s t i g a t i o n than m i g h t a t f i r s t seem necessary. Sampling cannot be back dated.

6.5.3.2 S p e c i f i c a p p l i c a t i o n i n carbonate rock reg ions. T r i t i u m and the s t a b l e i so topes deuterium, D, and oxygen-18, l 8 0 a re w e l l - s u i t e d f o r i n v e s t i g a t i n g k a r s t i c areas where r e l a t i v e l y r a p i d f l o w through i s usual . I n general , i t i s necessary t o extend sampling and measurement over a p e r i o d o f t ime l o n g enough ( s e v e r a l years) t o separate shor t - te rm f l u c t u a t i o n s - due t o f a s t response t o p r e c i p i t a t i o n v i a s h o r t c i r c u i t s i n t h e water pa ths - from long-term f l u c t u a t i o n s - due t o slow accumulation o r l o s s o f t r i t i u m i n the bulk o f t h e water r e s e r v o i r .

198

Table 6.5-3. Radioisotope t r a c e r f o r t h e i n v e s t i g a t i o n o f groundwater.

D e t e c t a b i l i t y Maximum l i m i t o f t h e permis- r a d i o i s o t o p e

y quanta s i b l e con- o r chemical energy i n c e n t r a t i o n compound i n water

Radioisotope MeV and pe rcen t i n d r i n k i n g and i t s chem- H a l f - o f quanta p e r water r i c i / m 3 i c a l form l i f e d i s i n t e g r a t i o n (IAEA, 1 9 6 6 ) r i C i / m 3 g/cm3

1 2 3 4 5 6

NH482Br

98AUC13

9 9 ~ 0 on i o n exchange r e s i n

99mTc m i l k e d from r e s i n

K 1 3 1 1

5 l ~ r - EDTA

K 3 "CO (CN) 6

58c0 - EDTA ( 3 v a l e n t )

Na2 'SO4 ( n o t d e t e c t ab l e i n s i t u )

11 OmAg (CN) 2

HTO ( n o t de tec tab le i n s i t u )

36.6 h

2.7 d

2.8 d

6.0 h

8.14 d

27.8 d

7 2 d

88 d

253 d

5 . 3 y

12.3 y

.55 t o 1.48

0.68 ( 1 % ) ; 0 . 4 1 ( 9 5 % )

O .14 490%)

.25 t o .64

.325 ( 9 % )

.805 ( 1 0 0 % )

. 5 1 1 ( 3 0 % ) (€rom a n n i h i - l a t i o n )

0 .167 6 p a r t i c l e s , no Y

.66 t o 1 .51

1 .17 (100%) 1.33 ( 1 0 0 % )

0.018 B p a r t i c l e s , no Y

3000 . O2

50

2 0 0

3000

2

2000

1 0 0

60

.O8 10'18

- .8

. O6 1.4 10-14

. O3 - 50 . O3 - 3 0 .

3000 O .5* 10'15 (106T.U.) ( 1 5 0 T.U.)

* d e t e c t i o n l e v e l w i t h o u t i s o t o p i c enrichment

199

F o l l o w i n g a r e some o f t h e c o n d i t i o n s t h a t have been observed t o occur, and

1. I so topes i n t h e discharge water o f a s p r i n g may show a c y c l i c p a t t e r n which can be r e l a t e d t o t h e seasonal cyc les o f these iso topes i n p r e c i p i t a t i o n . A s h i f t i n phase may a l l o w r e c o g n i t i o n o f a t r a n s i t t ime through the system o f a few months.

2. A s p r i n g may show a s i g n i f i c a n t concen t ra t i on o f bomb t r i t i u m w i t h l i t t l e f l u c t u a t i o n o r decrease during seve ra l years. We conclude t h a t t h e system has a l a r g e storage volume i n t o which c u r r e n t recharge i s mixed q u i t e completely. We may es t imate t h e l o n g Mean Residence Time on t h e b a s i s o f a m ix ing model hav ing an exponen t ia l d i s t r i b u t i o n o f t r a n s i t t imes. The t r i t i u m concent ra t ions i n such sp r ings rose s l o w l y during seve ra l years a f t e r t h e 1 9 6 3 p r e c i p i t a t i o n - t r i t i u m peak and w i l l now take a l o n g t ime t o be washed out.

3 . A s p r i n g may show t h e super -pos i t ion o f a c y c l i c t r i t i u m p a t t e r n on a low "base-f low" o f t r i t i u m . The system discharge i s a m i x t u r e o f base f l o w o f low t r i t i u m , o r t r i t i u m - f r e e water and v a r y i n g amounts o f r e c e n t p r e c i p i t a t i o n which by-pass t h e main storage volumes o f t h e system, o r perhaps, skim across the t o p o f a deep, dead storage r e s e r v o i r .

Most o f t h e Mediterranean k a r s t i c systems extend t o t h e seacoast and beyond, SO ques t ion o f p o s s i b l e sea water i n t r u s i o n i n case o f d i v e r t i n g o r w i thdrawing water from nearby c o a s t a l subterranean channels i s o f importance. I so tope s tud ies, t oge the r w i t h water chemistry data, may r e s o l v e t h e mixed water i n such systems i n t o i t s component p a r t s and g i v e i n f o r m a t i o n on seasonal o r o t h e r f l u c t u a t i o n s i n composit ion.

Many deep boreholes i n t h e l imestone Alps y i e l d waters hav ing ages i n t h e range o f thousands o f years and I 4 C measurement a re o f value.

[EDITOR'S NOTE: The reader i s r e f e r r e d t o Harmon ( 1 9 7 7 ) , a chemical and i s o t o p i c study o f carbonate groundwaters i n Pennsylvania, U.S.A. ; t o Pearson and Rettman ( 1 9 7 6 ) f o r a s i m i l a r study of t h e Edwards Aqu i fe r , Texas, U.S.A.; and Pearson, Rettman and Wyerman ( 1 9 7 5 ) f o r a r e p o r t on an ex tens ive study o f environmental t r i t i u m i n t h e Edwards Aqui fer . ]

t h e i r h y d r o l o g i c a l s i g n i f i c a n c e :

6.5.3.2.1 A c o a s t a l k a r s t i c s p r i n g i n Crete. As p a r t o f a l a r g e r environmental i so tope study, Almyros spr ing, s i t u a t e d about 1 km from the sea and 8 km west o f Ke rak l i on , has been s tud ied ( IAEA 1 9 7 1 ) . I t i s fed from the l imestone a q u i f e r s o f t h e I d a massi f , but i t s water conta ins up t o 25 percent sea water a t t imes o f low discharge. Knowledge of t he phenomena lead ing t o sea water i n t r u s i o n and t h e volume o f t h e freshwater r e s e r v o i r were r e q u i r e d f o r cons ide ra t i on o f development as a f reshwater supply f o r t h e Herak l i on area.

The discharge o f t he Almyros s p r i n g cou ld be broken down i n t o t h e f o l l o w i n g components based on t h e i r c h a r a c t e r i s t i c s t r i t i u m concent ra t ions :

1. A p e r e n n i a l €low hav ing l i t t l e annual v a r i a t i o n and low t r i t i u m

2. A t r a n s i e n t f l o w hav ing a s t rong monthly v a r i a t i o n and high t r i t i u m

3. Sea water. The sea water component was separated on the b a s i s o f t he c h l o r i d e conten t

o f t h e s p r i n g water. Since t h e t r i t i u m conten t o f t h e sur face sea water near Cre te was 20 T.U., t h e t r i t i u m conten t o f t he r e s u l t a n t o f t he p e r e n n i a l and t h e t r a n s i e n t f l ows c o u l d be ca l cu la ted . I t was observed t h a t h i g h t r i t i u m concen t ra t i ons were assoc ia ted w i t h h i g h discharge and t h a t t he lowest t r i t i u m concen t ra t i on co inc ided w i t h t h e lowest discharge. Th is m i n i m u m t r i t i u m concen t ra t i on was considered t o represent the concen t ra t i on o f t h e p e r e n n i a l f l o w components. I t i s u n l i k e l y t h a t i t would change apprec iab ly over the p e r i o d o f t h e study and was used t o es t imate the t r i t i u m concent ra t ions o f t h e t r a n s i e n t f l o w component. These were found t o be ve ry s i m i l a r t o t h a t o f p r e c i p i t a t i o n during t h e months o f recharge, thus showing t h a t t h e t r a n s i e n t f l o w i s ve ry r a p i d .

The t r i t i u m concen t ra t i on of t h e p e r e n n i a l f low was a l s o used t o p lace some l i m i t s on t h e mean res idence t ime o f t h i s component and thus the volume of t he r e s e r v o i r . The input 'of t r i t i u m t o the system was es t imated from Ottawa

200

concent ra t ion :

concent ra t ion ;

and Vienna p r e c i p i t a t i o n - t r i t i u m records and a shor t - te rm c o r r e l a t i o n between Herak l i on and Vienna. The l e n g t h o f r e c o r d o f t h e t r i t i u m concen t ra t i on o f Almyros s p r i n g was i n s u f f i c i e n t t o i n d i c a t e t h e most app rop r ia te tu rnove r model, so maximum and m i n i m u m va lues o f t he mean t r a n s i t t ime o f t h e water were es t imated us ing, r e s p e c t i v e l y , an exponen t ia l t r a n s i t t ime d i s t r i b u t i o n and p i s t o n f l o w w i t h no mix ing. A maximum va lue o f 75 years and a m i n i m u m va lue o f 10 years were ca l cu la ted . These and t h e d ischarge r a t e o f t h e p e r e n n i a l f l o w i n d i c a t e a f reshwater storage volume between 1 and 7 x 109m3, much o f i t l y i n g below sea l e v e l .

Other s tud ies i n t h e area i nc luded boreholes. Cons idera t ion o f t h e i r s a l i n i t y and oxygen-18 con ten ts p rov ided i n f o r m a t i o n on t h e o r i g i n o f t h e i r s a l i n i t y and whether t h i s contaminat ion was s t i l l i n progress.

6.5.3.2.2 I n te rconnec t ions between lakes, sp r ings and r i v e r s i n Southern Turkey (Dincer and Payne, 1 9 7 1 ) . I n t h e r e g i o n o f An ta l ya (Turkey) , some l a r g e k a r s t i c sp r ings near t h e coas t were b e l i e v e d t o be f e d by i n l a n d lakes i n t h e p l a t e a u a t t h e n o r t h o f t h e Taurus Mountains which were known t o l a k e impor tan t amounts o f water through s inkho les and f r a c t u r e s . Turnover t imes o f t h e l akes and the f r a c t i o n o f water l o s t by leakage were eva lua ted on t h e b a s i s o f an i s o t o p i c study o f t he l a k e water (Dincer, 1 9 6 8 ) . The l 8 O and D analyses o f t he s p r i n g waters ( - 8 ° / 0 0 , -70°/,,) showed n o t o n l y t h a t t h e c o n t r i b u t i o n from t h e lakes was almost n e g l i g i b l e but a l s o t h a t t h e recharge area o f t h e sp r ings was l o c a t e d on t h e southern s i d e o f t h e Taurus Mountains. I n f a c t , c r o s s i n g t h e mountains t h e r e i s a change i n t h e va lue o f t h e i n t e r c e p t o f t h e meteor ic water l i n e on t h e GD-axis because o f t h e d i f f e r e n t o r i g i n o f t h e p r e c i p i t a t i o n . O n t h e o t h e r hand, i t was es t imated t h a t t h e i n l a n d lakes c o n t r i b u t e up t o 30 percent o f t h e base f l o w o f some r i v e r s o f t h e south coas t v i a subterranean channels.

T r i t i u m v a r i a t i o n s o f t h e sp r ings over seve ra l years were i n t e r p r e t e d t o show t r a n s i t t imes o f water between recharge and sampling and t h e t ime s t r u c t u r e o f water i n t h e k a r s t r e s e r v o i r . The s tud ies a l s o showed f l o w i n t h e k a r s t system cons is ted o f seasonal f l o w th rough s o l u t i o n channels and much slower movement through t h e base k a r s t r e s e r v o i r .

6.5.3.2.3 A l p i n e k a r s t i c systems. The Totes Gebirge i s an A l p i n e k a r s t mass i f i n t h e no r theas te rn Limestone A lps o f c e n t r a l A u s t r i a , which has been s t u d i e d by spore l a b e l l i n g and environmental i s o t o p e measurements (Dincer e t a l , 1972). L a b e l l i n g experiments w i t h c o l o r e d spores had shown t h a t t h e sma l l l akes i n t h e high T a u p l i t z Lake P la teau i n t h e south a l l d r a i n underground i n t o t h e l imestone o f t h e main massi f . The waters reach sp r ings 20 t o 30 km away i n t h e west and n o r t h o f t h e mountains even sooner than they reach nearby southern spr ings. I n c r e a s i n g se t t l emen t around t h e high lakes presented a p o t e n t i a l p o l l u t i o n problem f o r communities around t h e base o f t h e mass i f u s i n g sp r ings f o r water supply.

Measurements o f t r i t i u m , deuter ium and oxygen-18 i n t h e most impor tan t sp r ings o f t h e Totes Gebirge p rov ided a genera l h y d r o l o g i c a l c h a r a c t e r i z a t i o n o f t h e area. The seasonal c h a r a c t e r i s t i c s o f i so topes concen t ra t i ons p e r m i t t e d t h e d i f f e r e n t i a t i o n o f summer r a i n w a t e r and s p r i n g snowmelt i n t h e d ischarge o f t he spr ings. Replenishment o f t h e groundwater v a r i e s seasonal ly, r a i n w a t e r and mel ted snow f o l l o w i n g each o t h e r i n cyc les and m i n g l i n g i n d i f f e r e n t p r o p o r t i o n s i n d i f f e r e n t reg ions. The r e s u l t s o f t h e l a b e l i n g experiments and t h e i so tope s tud ies were, by and . large, i n accord. I n some spr ings, t h e i s o t o p i c composi t ion showed t h a t connect ions i n d i c a t e d by l a b e l i n g count n o t c o n t r i b u t e a s i g n i f i c a n t amount t o t o t a l d ischarge.

The most impor tan t conc lus ion drawn from t h e i so tope measurements was t h a t t h e r e i s no apprec iab le storage o f water i n t h e k a r s t mass i f o f t h e Totes Gebirge. FrQm t h e t r i t i u m and oxygen-18 con ten t o f t h e s p r i n g and t h e l a k e waters, i t i s ev iden t t h a t a l l t h e feed water i n t h i s area i s a c t i v e , i .e. i t l i e s above t h e a l t i t u d e o f t h e l o w - l y i n g sp r ings and lakes. T h i s i s i n c o n t r a s t t o t h e u s u a l Mediterranean k a r s t i c systems where a deep k a r s t r e s e r v o i r p rov ides long-term storage, evidenced by low t r i t i u m con ten ts and no seasonal f l u c t u a t i o n i n t r i t i u m o r s t a b l e isotopes.

2 0 1

The decreased i n t r i t i u m con ten t from t h e Funtenen s p r i n g near Meir ingen (Swi tzer land) whose water showed cons tan t va lues f o r temperatures, chemical composi t ion and l 8 0 content, has been fo l l owed over t h r e e years. The i n t e r p r e t a t i o n , according t o t h e exponen t ia l model, showed a lower l i m i t f o r t h e age o f about f o u r years and an average water age o f t h i r t e e n years. The k a r s t s p r i n g Vend l i n (Swi tzer land) a l s o showed a cons tan t l 8 0 conten t but, i n c o n t r a s t t o t h e s p r i n g Funtenen, a marked seasonal. v a r i a t i o n o f t h e T concent ra t ion , w i t h a s t r o n g peak i n w i n t e r . Th i s r e s u l t was i n t e r p r e t e d by assuming seve ra l mixed r e s e r v o i r s o f d i f f e r e n c e ages where t h e m i x i n g r a t i o v a r i e s w i t h t ime (S iegentha le r e t a l . , 1970; Seigenthaler, 1971). Th i s example c l e a r l y shows t h e use fu lness o f combined i so tope i n v e s t i g a t i o n s .

6.5.3.2.4 Carbon-14 measurements i n carbonate aqu i fe rs . An example o f t he use o f carbon-14 i n a carbonate a q u i f e r i s p rov ided by a study i n t h e Ocala l imestone i n c e n t r a l F l o r i d a (Hanshaw e t a l . , 1 9 6 5 ) . Samples taken from a s e r i e s o f a r t e s i a n w e l l s ex tend ing over a d i s tance o f 137 km i n d i c a t e d a groundwater f l o w r a t e o f about 7 mlyear, i n agreement w i t h h y d r o l o g i c a l est imates.

I n t h e area o f t h e "Fontaine de Vaucluse", a k a r s t s p r i n g between the Rhone v a l l e y and the A lps w i t h a discharge between 5 and 150 m3/s t r i t i u m and 1 4 C i n v e s t i g a t i o n s c a r r i e d o u t s ince 1 9 6 6 have g i ven i n f o r m a t i o n on t h e k a r s t water f l o w system as a f u n c t i o n o f t h e h y d r a u l i c c o n d i t i o n ( M a r g r i t a e t a l . , 1970; Roth e t a l . , 1 9 7 1 ) .

6.5.3.3 A v a i l a b i l i t y o f more d e t a i l e d i n f o r m a t i o n and advice. Advise on the s u i t a b i l i t y o f i s o t o p e techniques f o r s p e c i f i c h y d r o l o g i c a l s tud ies i s a v a i l a b l e from t h e Sec t ion o f I so tope Hydrology, I n t e r n a t i o n a l Atomic Energy Agency, Vienna, A u s t r i a . T h i s group has accumulated cons iderab le experience th rough p a r t i c i p a t i o n i n UNDP-sponsored i n v e s t i g a t i o n s i n v a r i o u s coun t r i es . Equipment and exper t s a re p rov ided i n t h i s f i e l d w i t h i n t h e t e c h n i c a l ass is tance programs o f t h e IAEA and t h e UNDP. [EDITOR'S NOTE: The reader i s a l s o r e f e r r e d t o Gaspar and Oncescu, 1 9 7 2 , and Rodriguez and de Monroy, 1980.1

6.5.4 A r t i f i c i a l i so tope hydrogeology. A r t i f i c i a l i so tope hydrogeology makes use o f r a d i o a c t i v e i so topes i n t e n t i o n a l l y i n j e c t e d a t a w e l l - d e f i n e d p o i n t o f t he system under i n v e s t i g a t i o n . Radioisotopes can be measured i n extremely low concent ra t ion , o f t e n i n s i t u , making p o s s i b l e t h e de te rm ina t ion o f d i l u t i o n r a t e s and d i r e c t i o n o f f l o w through w i t h i n a boreho le t o l e a r n t h e v e l o c i t y and d i r e c t i o n o f groundwater f l o w and a q u i f e r p r o p e r t i e s such as p o r o s i t y , t r a n s m i s s i v i t y and d i s p e r s i v i t y . Radioisotopes may a l s o be used f o r p o i n t - t o - p o i n t t r a c i n g i n t h e same types of problems s tud ied w i t h chemical and dye t r a c e r s t o inc rease t h e number of t r a c e r s a v a i l a b l e f o r m u l t i - t r a c e r experiments, o r avo id problems o f absorp t ion w i t h i n t he a q u i f e r . I n f o r m a t i o n ob ta ined by t h e use o f i n j e c t e d t r a c e r s may be q u i t e p r e c i s e but i t s v a l i d i t y i s r e s t r i c t e d t o a l i m i t e d area around t h e i n j e c t i o n p o i n t and t o cond i t i ons p resen t a t t h e t ime o f i n j e c t i o n . Nevertheless, measurements performed a t a s u f f i c i e n t number o f p o i n t s and repeated a t d i f f e r e n t t imes can p rov ide a good d e s c r i p t i o n o f t h e l o c a l h y d r o l o g i c a l system inves t i qa ted .

6.5.4.1 P r a c t i c a l cons idera t ions . Radioisotopes present t h e problem o f h e a l t h hazard, which inc reases c o s t due t o t h e e x t r a care needed i n t h e i r use and handl ing. I n some cases, t h e use o f a r a d i o i s o t o p e may p resen t an unacceptable h e a l t h hazard. Even where i t can be demonstrated t h a t t h e hazard t o h e a l t h i s non-ex is ten t , l o c a l r e s i d e n t s may oppose i t s use. Therefore, be fo re cons ide r ing t h e use o f an a r t i f i c i a l r a d i o i s o t o p e as a t r a c e r i n present o r p o t e n t i a l water suppl ies, t h e hyd rogeo log is t should assure h i m s e l f t h a t o ther , non- rad ioac t ive substances such as dyes o r c h l o r i d e s would n o t meet the needs o f h i s problem.

Since commercial se rv i ce i n the a p p l i c a t i o n o f these techniques i s seldom a v a i l a b l e , i t i s adv isab le t o seek t h e coopera t ion o f u n i v e r s i t i e s o r research i n s t i t u t e s i n t h e i n i t i a l use o f t h e methods. Some d i f f i c u l t i e s i n per fo rming

202

f i e l d measurements may be expected u n t i l t h e experimenter becomes exper ienced i n the new techniques i nvo lved . Some o f t h e r a d i o m e t r i c methods a r e s t i l l i n t h e development stage and s i m p l i f i c a t i o n and improvements i n technique can be expected i n t h e f u t u r e .

A t y p i c a l l i s t o f exper imenta l d e t a i l s t o be considered s p e c i f i c a l l y i s as fo l l ows :

1. I n f o r m a t i o n sought. 2. S e l e c t i o n o f t r a c e r , amount requ i red , means o f p roduc ing i t a t t h e

r e q u i r e d t ime. 3. P r o v i s i o n o f r e q u i s i t e i n j e c t i o n and d e t e c t i o n equipment and pumping

equipment o f adequate capac i t y . 4. Means o f d i s p o s a l o f pumped water t o p reven t i t s r e c i r c u l a t i o n t o t h e

borehole. 5 . T ranspor ta t i on t o t h e temporary s to rage o f t h e r a d i o a c t i v e t r a c e r a t

t h e exper imenta l s i t e . 6. R a d i o l o g i c a l s a f e t y o f t he o p e r a t i n g personnel . 7. Assurance t h a t no s i g n i f i c a n t amount o f t r a c e r w i l l g e t i n t o p u b l i c

8 . Eva lua t i on o f t h e r e s u l t s . The experimenter must acqua in t h i m s e l f w i t h a l l s a f e t y and l e g a l

requirements connected w i t h t h e hand l i ng o f r a d i o a c t i v e m a t e r i a l s . The I n t e r n a t i o n a l Atomic Energy Agency's "Guide t o t h e Safe Hand l ing of Radioisotopes i n Hydrology" ( 1 9 6 6 ) , serves as a v e r y u s e f u l i n t r o d u c t i o n t o t h i s subject .

water suppl ies.

6.5.4.2 S e l e c t i o n o f r a d i o a c t i v e t r a c e r s . The cho ice o f t he a r t i f i c i a l i so tope t o be used depends on t h e fea tu res of t h e problem. I n general , t h e f o l l o w i n g p o i n t s should be taken i n t o cons ide ra t i on :

1. The i so tope should have a l i f e comparable t o t h e presumed d u r a t i o n o f t h e observat ions. Unnecessar i ly l o n g - l i v e d i so topes w i l l p o l l u t e t h e water c r e a t i n g a p e r s i s t e n t h e a l t h hazard and i n t e r f e r i n g w i t h r e p e t i t i o n of t h e experiment.

2. The i so tope should n o t be adsorbed by the s o i l components. 3. Fo r most problems, i t should be p o s s i b l e t o measured t h e a c t i v i t y i n

t h e f i e l d . B-emit ters o f h i g h energy, l i k e ch lo r ine-38 , a re s u i t a b l e , but' y -emi t te rs a re p r e f e r r e d , i n general .

4. The i so tope must be a v a i l a b l e when and where r e q u i r e d a t a reasonable cost .

Some o f t he most f r e q u e n t l y used r a d i o a c t i v e t r a c e r s a re l i s t e d i n Table 6.5-3.

The chemical form o f t h e r a d i o a c t i v e s o l u t i o n used i n water t r a c i n g experiments p l a y s an impor tan t r o l e . I n many cases, c a t i o n s serve as t r a c e r s . I n t h e form i n which they a re commonly d e l i v e r e d , they may be sub jec t t o s t r o n g adsorp t ion i n t h e ground, i n t e r f e r i n g w i t h t h e v a l i d i t y o f t h e i r t r a c i n g o f t h e water mass. To minimize t h i s e f f e c t w i t h i n an a q u i f e r , t r a c e r s i n a complex form are o f t e n used. The most commonly used i n h y d r o l o g i c a l p r a c t i c e i s a che la ted m e t a l l i c compound formed by means o f ethylene-diamine t e t r a c e t i c a c i d (EDTA) .

Lallemand and Gr ison (1970) have made a systemat ic study o f 1 2 rad io i so topes i n c a t i o n i c , a n i o n i c and complexed forms i n s i x types o f a r g i l l a c e o u s rock and t h r e e types o f sand i n t h e &resence o f deminera l i zed s p r i n g and sea water. They conclude t h a t t r i t i u m , B r as bromide and 3 5 S as sulphate a re t h e b e s t t r a c e r s rega rd less o f m i n e r a l o g i c a l composi t ion and t ype o f water.

T r i t i u m , a l though n o t meet ing t h e h a l f - l i f e and r a d i a t i o n requirements mentioned above, i s an i d e a l marker f o r water s ince i t i s i nco rpo ra ted i n t h e water molecule. Hence i t i s used i n s p i t e o f t h e f a c t t h a t i n s i t u d e t e c t i o n i s n o t p o s s i b l e and samples mu.st be analyzed i n t h e l a b o r a t o r y subsequent t o an experiment. The use o f a r t i f i c i a l t r i t i u m should be kept. on t h e l owes t p o s s i b l e l e v e l t o minimize i n t e r f e r e n c e w i t h groundwater resource s t u d i e s based on environmental t r i t i u m .

203

6.5.4.3 Techniques. The i n t r o d u c t i o n o f a t r a c e r i n t o a boreho le may be done by pour ing through a th in p ipe, by c rush ing an ampoule a t t he depth o f i n t e r e s t o r by u s i n g a s p e c i a l i n j e c t i o n device. I n j e c t i o n can be performed a t one o r seve ra l depths t o f a c i l i t a t e m i x i n g o f t he t r a c e r s o l u t i o n w i t h t he s tand ing water o f t h e borehole. A f t e r t h e re lease and mix ing, t he r a d i o a c t i v i t y i n the boreho le i s measured by a probe, u s u a l l y a s c i n t i l l a t i o n counter but sometimes a rugged Geiger counter, i n s e r t e d a t t h e chosen depth. Spec ia l i zed probes have been cons t ruc ted which s e a l o f f a d e f i n e d volume o f t h e borehole by i n f l a t a b l e b ladders , re lease t h e r a d i o t r a c e r i n t o t h i s volume and measure t h e r a d i o a c t i v i t y by d e t e c t o r s i n o r immediately above t h e re lease volume (see F i g u r e 6.5-2, G u i z e r i x e t a l . , 1 9 6 3 ) .

I n a technique used by Kaufman and Todd ( 1 9 6 2 ) , tagged water was c i r c u l a t e d between an i s o l a t e d segment o f a boreho le and t h e ground sur face by a sma l l pump. Thus, cont inuous g e n t l e m ix ing was ob ta ined and i n j e c t i o n and measurement o f r a d i o a c t i v i t y were done a t t he sur face w i t h o u t t he necess i t y f o r a s p e c i a l probe.

I n t h e S i n g l e W e l l D i l u t i o n Technique (Halevy e t a l . , 19671, t he d i l u t i o n r a t e of t h e t r a c e r by t h e n a t u r a l f l o w o f water th rough the boreho le i s observed. I n t h e S i n g l e W e l l Pulse Technique (Borowczyk e t a l . , 1 9 6 7 ) , t h e t r a c e r i s f o rced i n t o t h e a q u i f e r by pumping water i n t o t h e w e l l and then r e c a l l e d by p u m p i n g water o u t o f t h e w e l l .

When movement o f water between boreholes i s t o be observed - M u l t i p l e W e l l Technique - t h e obse rva t i on w e l l i s u s u a l l y pumped and t h e r a d i o a c t i v i t y o f t h e pumped water mon i to red a t t h e sur face (Halevy and N i r , 1962). I t i s impor tan t t h a t such pumped water be disposed o f i n such a way t h a t i t cannot r e t u r n i n a d v e r t e n t l y t o t h e system under i n v e s t i g a t i o n . I n some experiments, water pumped from t h e obse rva t i on w e l l i s r e t u r n e d t o the i n j e c t i o n w e l l i n t e n t i o n a l l y t o e s t a b l i s h a c losed c i r c u i t .

The c l a s s i c a l case o f water t r a c i n g i n a k a r s t i c r e g i o n i s t h e study o f i n te rconnec t ions e x i s t i n g between s inkho les and spr ings. Fo r t h i s purpose, t he r a d i o a c t i v e i s o t o p e i s re leased i n the s inkho le and i t s concen t ra t i on con t inuous ly mon i to red a t t he s p r i n g by a submersible de tec to r , u s u a l l y a s c i n t i l l a t i o n counter. The appearance o f t he r a d i o i s o t o p e and the e v o l u t i o n o f i t s concen t ra t i on ( c o r r e c t e d f o r r a d i o i s o t o p e decay) w i t h t ime a t t h e d e t e c t i o n p o i n t p rov ides an e v a l u a t i o n o f t he f r a c t i o n o f water coming from the i n j e c t i o n p o i n t and o f t he t r a v e l t ime between t h e two p o i n t s .

I n t h i s and t h e f o l l o w i n g sec t i ons o n l y l i m i t e d i n f o r m a t i o n on techniques and t h e i r a p p l i c a t i o n s can be given. Many exper imental d e t a i l s and examples o f a p p l i c a t i o n s i n carbonate rock reg ions are g iven i n Isotopenmethoden i n der Grundwasserkunde" l i s t e d i n the B ib l iography , (Drost e t a l . , 1 9 7 2 ) .

6.5.4.4 Groundwater f l o w v e l o c i t y . Groundwater f l o w v e l o c i t y may be measured d i r e c t l y by i n j e c t i n g t h e t r a c e r i n t o a w e l l and then f o l l o w i n g i t s decrease

i n concen t ra t i on w i t h t i m e (see F i g u r e 6 .5 -3 ) . The p r i n c i p l e a p p l i e s f o r any t r a c e r , but r a d i o a c t i v e isotopes a re eas ie r

t o d e t e c t i n s i t u w i t h a high degree o f accuracy, a t ve ry low concent ra t ions (Moser e t a l . , 1957, 1963; Ma i rho fer , 1963 ; G u i z e r i x e t a l . , 1 9 6 3 ) .

The h o r i z o n t a l f i l t r a t i o n v e l o c i t y Vf o f water (sometimes a l s o c a l l e d pore v e l o c i t y ) i s g i ven by:

- U 1 n C - - Uf - - CtFt (6.5-3)

Where v i s t h e measuring volume ( t h e borehole volume i n which d i l u t i o n takes p lace ) , F i s t h e c ross s e c t i o n o f t h e measuring volume perpend icu la r t o the d i r e c t i o n o f t h e und is tu rbed groundwater f low, and t i s t h e t ime i n t e r v a l between measurement of concent ra t ions C and C. CL i s a c o r r e c t i o n f a c t o r account ing f o r t h e d i s t o r t i o n o f t he f i 8 ~ l i n e s due t o the presence o f t he borehole. C a l c u l a t i o n o f t he va lue of a on t h e b a s i s o f w e l l c o n s t r u c t i o n data i s discussed by Halevy, e t a l ( 1 9 6 7 ) . The above expression i s a p a r t i c u l a r s o l u t i o n o f t he d i f f e r e n t i a l equat ion d e s c r i b i n g d i l u t i o n r a t e o f t he t r a c e r .

I n p r a c t i c e , seve ra l read ings are r e q u i r e d t o d e r i v e r e s u l t s n o t a f f e c t e d by incomplete m i x i n g processes and r e s i d u a l currenks. The v e l o c i t y lower l i m i t , determined ma in l y by the d i f f u s i o n r a t e , i s 10 m/s. Measurements i n

204

seals

probe with detector

collimator

propellers

injector

coup ling

electric valve

tank for tracer

F i g u r e 6.5-2 Ins t rument for boreho le d i l u t i o n measurements (Gu ize r i x e t a l . , 1963) .

2 0 5

J

F i g u r e 6.5-3 Schematic diagram showing how t h e t r a c e r concen t ra t i on changes w i t h t ime i n a boreho le d i l u t i o n experiment (Moser e t a l . 1 9 6 3 ) .

RATE

TUBE L 2 3

-TIME

SWITCH BOX FOR INJECTOR

IN J ECTO R

z 1

F i g u r e 6.5-4

206

Arrangement o f a s e t o f de tec to rs f o r de termin ing v e r t i c a l f l o w i n a boreho le (Moser e t a l . , 1963) .

d i f f e r e n t w e l l s and a t d i f f e r e n t depths are necessary t o e s t a b l i s h a good p i c t u r e o f t he groundwater f l o w i n a g i ven a q u i f e r .

I f t h e p o t e n t i a l g r a d i e n t o f t h e groundwater f i e l d i s known, t h e kf value, t he p e r m e a b i l i t y o f t h e a q u i f e r , can be c a l c u l a t e d :

- - vf kf g r a d i e n t

(6 .5 -4 )

Thus, two parameters t h a t p l a y a d e c i s i v e r o l e i n ques t ions o f groundwater e x t r a c t i o n and waste-water d i s p o s a l as w e l l as i n problems o f eng ineer ing geology are obtained.

D ros t ( 1 9 7 1 ) r e p o r t s some r e c e n t f i e l d experiments comparing t h e kf va lue determined by sma l l sca le pump t e s t s w i t h t h a t from d i l u t i o n experiments. I n 3 8 comparative measurements, t h e p r o p o r t i o n o f p a i r s showing agreement as t o o rder o f magnitude was 8 5 percent . I n 35 pe rcen t o f t h e t o t a l t h e d i f f e r e n c e was I 2 5 - 5 0 percent.

6.5.4.5 V e r t i c a l f l o w v e l o c i t y . Knowledge o f t h e v e r t i c a l v e l o c i t y component i n a borehole i s impor tan t i n such problems as de te rm ina t ion o f t h e amount o f water e n t e r i n g o r l e a v i n g t h e w e l l f rom d i f f e r e n t zone l o c a t i o n s o f permeable s t r a t a , o r amount o f in te rchange between zones. During t h e d r i l l i n g o f k a r s t w e l l s i t i s o f t e n d i f f i c u l t t o l o c a t e t h e water-bear ing l a y e r s o f t h e k a r s t system and so decide on t h e p o s i t i o n o f t h e screens. These can o f t e n be ascer ta ined by measuring t h e v e r t i c a l f l ows i n t h e w e l l b o t h when i n use and when not .

A s i n g l e w e l l d i l u t i o n technique may be a p p l i e d f o r t h e measurement o f v e r t i c a l f l o w v e l o c i t y . A s e r i e s o f d e t e c t o r s p laced a t d i f f e r e n t h e i g h t s i n the borehole i s commonly used (see F i g u r e 6 . 5 - 4 ) . Recent ly t r a c e r l o g techniques have been developed (Drost , 1 9 7 0 ) i n which a moving probe scans t h e r a d i o t r a c e r p r o f i l e d . The method may be s p e c i a l l y recommended when expected v e r t i c a l f l o w v e l o c i t i e s a r e smal le r than 2.10-2 m/s; i n t h i s reg ion , due t o the i n f l u e n c e o f f r i c t i o n , t r a c e r ~ methods a re more e f f i c i e n t than t h e use o f mechanical c u r r e n t meters. The lower v e l o c i t y l i m i t i s es t imated a t m/s. I n t u r b u l e n t f low, accuracy o f measurement i s r e p o r t e d t o be b e t t e r than 10 percent but l e s s i s known aboÛt t h e accuracy i n laminar f l o w (Halevy e t a l . , 1 9 6 7 ) .

6.5.4.6 D i r e c t i o n o f groundwater f low. M u l t i w e l l technique can be used t o determine t h e d i r e c t i o n o f groundwater f l o w e s p e c i a l l y when r a d i a l symmetry i n w e l l l o c a t i o n e x i s t s , o r i f obse rva t i on w e l l s a re found i n t h e approximate d i r e c t i o n o f f low. D i r e c t i o n o f f l ow , however, may a l s o be determined by t h e means o f a s i n g l e w e l l technique. Tracer i s added t o a segment o f a boreho le and i s c a r r i e d away i n t h e d i r e c t i o n o f t h e f low. A c t i v i t y i s then de tec ted by a s p e c i a l d i r e c t i o n a l l y o r i e n t e d probe r o t a t e d by means o f a s t i f f m e t a l l i c rod. A diagram l i k e t h a t o f F i g u r e 6.5-5 i s t hen obtained, which shows t h e d i r e c t i o n o f t h e water f low. I n t h i s case, c o n t r a r y t o t h e f l o w v e l o c i t y measurements, rad io i so topes a r e t h e most app rop r ia te ones t o use. Gold-198 c h l o r i d e ( 98AuC13) and chromium-51 c h l o r i d e ( l C r C 1 3 ) a re commonly used. I n most l a b o r a t o r y t e s t s t h e d i f f e r e n c e between measured and t h e t r u e f l o w d i r e c t i o n was l e s s then 3 degrees. The r e p r o d u c i b i l i t y o f t h e method i n t h e f i e l d i s b e t t e r than + l o percent . A s i m p l i f i e d v e r s i o n o f t h e method has been used by Wurzel and Ward (1965). .A c y l i n d r i c a l me ta l qauze p l a c e i n t h e w e l l a t t h e i n j e c t i o n p o i n t adsorbs r a d i o a c t i v e t r a c e r ( l C r C 1 3 ) . The gauze i s removed, c u t i n many sec t i ons p a r a l l e l t o t h e a x i s and t h e a c t i v i t y o f each s e c t i o n i s measured i n t h e l a b o r a t o r y . The s e c t i o n g i v i n g t h e h i g h e s t a c t i v i t y i n d i c a t e s t h e d i r e c t i o n o f water f low.

I n a. s i m i l a r method proposed by Hazzaa (19701, t h e r a d i o a c t i v e t r a c e r 3 2 ~ ( h a l f - l i f e 14 .3 d) i s adsorbed on two c o a x i a l m e t a l l i c screens. Subsequent b e t a rad iog raph ic examinat ion o f b o t h screens y i e l d s i n f o r m a t i o n on t h e b a s i s o f which f i l t r a t i o n v e l o c i t y and d i r e c t i o n o f f l o w can be determined.

Observat ion o f t h e d i r e c t i o n o f groundwater f l o w by t h e s i n g l e w e l l d i l u t i o n technique descr ibed above, has proved a g r e a t va lue i n de terminat ions o f t he drainage area of a groundwater f i e l d , p r o t e c t i o n zones f o r drinking

207

8oo

F i g u r e 6.5-5 D i a g r a m o f w a t e r f l o w d i r e c t i o n d e t e r m i n a t i o n i n a b o r e h o l e . A c t i v i t y in jected, 0.6 m C i ( H a l i v y e t a l . , 1 9 6 7 ) .

2 0 8

water catchments, communications between two o r more bod ies o f water, and t h e l o a d on t h e groundwater as a r e s u l t o f foundat ion, t r a f f i c and h y d r a u l i c eng ineer ing works.

6.5.4.7 P o i n t - t o - p o i n t t r a c i n g i n k a r s t reg ions. I n f i s s u r e d and f r a c t u r e s rocks, p o i n t - t o - p o i n t experiments, e i t h e r between boreho les o r from s inkho les t o spr ings, are used f o r i n v e s t i g a t i n g t h e ex i s tence o f d i r e c t and r a p i d i n te rconnec t ions between d i f f e r e n t point 's i n an a q u i f e r . They make i t p o s s i b l e t o l o c a t e subterranean watersheds, f o l l o w t h e progress o f waste-contaminated surface waters i n t h e k a r s t body and r a t i o n a l l y d e l i m i t drinking water p r o t e c t i o n zones. The combined use o f seve ra l d i f f e r e n t r a d i o t r a c e r s and the dy t r a c e r s rhodamine WT, sulphorhodaminr G e x t r a and uranium which a re de tec tab le i n each o t h e r ' s presence makes p o s s i b l e t h e simultaneous but d i s t i n c t i v e l a b e l i n g o f a number o f i n j e c t i o n p o i n t s .

I t should be p o i n t e d o u t t h a t o n l y p o s i t i v e r e s u l t s g i v e a c l e a r - c u t s o l u t i o n o f t h e problem. Absence o f t r a c e r a t t h e sampling p o i n t does n o t necessa r i l y i m p l y absence o f connect ions w i t h t h e i n j e c t i o n p o i n t because d i l u t i o n may reduce t h e i s o t o p e concen t ra t i on below t h e d e t e c t i o n l i m i t s , o r because t h e t ime r e q u i r e d t o cover t h e d i s tance between t h e two p o i n t s may be t o o l ong w i t h respec t t o t h e h a l f - l i f e o f t h e r a d i o i s o t o p e used o r t h e p e r i o d o f observat ion. S tud ies o f environmental t r i t i u m may be u s e f u l i n f o r e c a s t i n g the p r o b a b i l i t y o f success o f an i n j e c t e d t r a c e r experiment and should be done be fo re t h e re lease o f a r t i f i c i a l t r i t i u m i s considered.

One o f t h e f i r s t k a r s t water t r a c i n g experiments w i t h a r a d i o a c t i v e i so tope ( t r i t i a t e d water) was c a r r i e d o u t by Burdon e t a l (1963) t o i n v e s t i g a t e the communication between two swallow ho les i n t h e T r i p o l i s k a r s t p l a t e a u i n Greece and seve ra l sp r ings on t h e Peloponnesian coast. Two connect ions were proved and t h e f l o w r a t e s and t h e capac i t y o f t h e r e s e r v o i r were asce r ta ined from the f l o w t imes. More r e c e n t l y , f u r t h e r s t u d i e s have been done i n t h i s area u s i n g Na1311, 5iCrEDTA e x t r a c t e d from t h e d ischarge waters by charcoa l and i n a c t i v e NH,Br subsequently determined by neu t ron a c t i v a t i o n a n a l y s i s (Leontiades and D i m i t r o u l a s , 1 9 7 1 ) .

Er iksson e t a l (1963) i n v e s t i g a t e d t h e l i n k s between a d isappear ing r i v e r i n t h e T r i e s t i n e k a r s t o f Yugoslavia and sp r ings on t h e A d r i a t i c coast. The r e s u l t s showed t h a t t h e r i v e r cont inues t o f l o w underground p a r a l l e l t o t h e coas t and surrenders water t o t h e i n d i v i d u a l sp r ings a t v a r i o u s p o i n t s . Since n o t a l l t h e i n j e c t e d t r a c e r c o u l d be found a t t h e sur face o u t l e t s , i t was concluded t h a t some o f t h e water f l ows o u t v i a submarine spr ings.

I n a s e r i e s o f l a b e l i n g experiments i n t h e malm k a r s t o f t h e Franconian Jura i n Bavar ia, an i n v e s t i g a t i o n was made o f t h e connect ions between a l a r g e number o f d o l i n e s which d r a i n o f f sur face waters, seve ra l w e l l s , and t h e Danube and Al tmuhle r i v e r s . I n a d d i t i o n t o da ta on t h e subterranean watershed between t h e Al tmuhle and t h e Danube was determined (Ifr, 1970; Apel, 1971). The source o f contaminat ion i n a w e l l t o t h e n o r t h o f Regensburg i n Bavar ia was t r a c e d by means o f r a d i o a c t i v e iso topes t o a swallowhole 200 m away, i n t o which sewage was discharge from a d ra in . S a l t t r a c e r exper imen ts .p rev ious l y conducted on t h e swallow h o l e had y i e l d e d no i n fo rma t ion (Batsche, 1971).

The importance o f l a b e l i n g i n k a r s t reg ions prompted t h e Graz Assoc ia t i on f o r H y d r o l o g i c a l Research t o h o l d symposia on t h e s u b j e c t o f groundwater and k a r s t water tagging. I n t h e course o f t h e f i r s t two symposia, h e l d a t Graz i n 1 9 6 6 and a t F r e i b u r g i n 1970, h y d r o l o g i c a l i n v e s t i g a t i o n s i n k a r s t reg ions were c a r r i e d ou t , t oge the r w i t h demonstrat ions o f t h e measurement techniques used f o r t h e v a r i o u s l a b e l i n g substances. I n 1966, two bod ies of k a r s t water i n t h e Graz area were i n v e s t i g a t e d separate ly , and i n 1969-70 t h e connect ion between seepage from t h e Danube a t T u t t l i n g e n and t h e source o f t h e Aach were ascertained. I n these i n v e s t i g a t i o n s p a r t i c u l a r a t t e n t i o n was p a i d t o t h e comparison o f t h e va r ious l a b e l i n g substances as regards t h e i r m i g r a t i o n p r o p e r t i e s and r e c o v e r a b i l i t y (Batsche, e t a l . , 1967, 1970a).

6.5.5 Combined use o f environmental i so topes and a r t i f i c i a l t r a c e r s . The use o f environmental i so topes and a r t i f i c i a l rad io i so topes , o r o t h e r " tags" such as spores, dyes, o r d i s t i n c t i v e chemical composi t ions i n combinat ion i s p a r t i c u l a r l y app rop r ia te i n k a r s t i c areas. The two s t u d i e s p r o v i d e

209

complementary i n fo rma t ion . The environmental i so topes g i v e a genera l h y d r o l o g i c a l c h a r a c t e r i z a t i o n o f t he area i n c l u d i n g a measure o f t r a n s i t t imes through v a r i o u s p a r t s o f t h e system thus i n d i c a t i n g where p o i n t - t o - p o i n t t r a c i n g m i g h t be f e a s i b l e . The p o i n t - t o - p o i n t s tud ies then p r o v i d e p r e c i s e i n f o r m a t i o n on i n te rconnec t ions . The Totes Gebirge study repo r ted p r e v i o u s l y ( s e c t i o n 6.5.3.2.3) was, i n f a c t , o f such a nature, d e r i v i n g complementary and con f i rma to ry i n f o r m a t i o n from spore t r a c e r s and environmental t r i t i u m and oxygen-18 data. I n t h e f o l l o w i n g paragraph, taken from “Isotopenmethoden i n der Grundwasserkunde” (Drost e t a l . , 19721, another such study i s b r i e f l y described. The study i s r e p o r t e d i n d e t a i l by Batsche e t a l (1970a).

The Danube, about 20 km a f t e r i t s source, breaks through t h e Schwabische A l b and s u f f e r s from water losses i n t h e calcareous depos i ts o f t h e upper Jura which r e s u l t s i n drying o u t o f t h e r i v e r bed a t low water l e v e l . The water o f t h e Danube thereby en te rs i n t o an ex tens ive k a r s t water system whose main e x i t i s t h e Aach s p r i n g i n t h e south (mean discharge 8.8 m3 /s ) . Tracer s tud ies have been done on t h i s k a r s t water system s ince 1 8 7 7 because o f i t s g r e a t economic importance. The l a r g e s t such study was made i n 1 9 6 9 where 1 3 t race rs , i n c l u d i n g r a d i o a c t i v e 5 1 C r and s t a b l e La and B r f o r l a t e r neut ron a c t i v a t i o n ana lys i s , were a p p l i e d a t 9 places. The p o s s i b l e t r a c e r reappearance was observed a t 33 spots i n the obse rva t i on area o f 505 m2 ( a t spr ings, boreholes and sur face wa te rs ) . The t e s t showed a c l e a r p i c t u r e o f t he k a r s t water f low. A l l o f t he 5 1 C r i n j e c t e d i n t h e Danube seepage s i t e near F r i d i g e n reappeared a t t h e Aachen s p r i n g a f t e r about 4 days. These r e s u l t s were supplemented markedly by p rev ious water-chemical i n v e s t i g a t i o n s and i so tope measurements o f k a r s t waters, c a r r i e d o u t d u r i n g t h e year preceding t h e t r a c e r experiments. The T and 14C measurements made i n t h i s p e r i o d gave t h e residence t ime o f t he r e s p e c t i v e sample water i n t h e k a r s t water body, whereby a s imple model was d e r i v e d based on t h e k a r s t water b e i n g composed o f v a r i o u s components, t he p o r t i o n s o f which decrease e x p o n e n t i a l l y w i t h i n c r e a s i n g residence t ime. The samples (about 3 5 ) o f d i f f e r e n t o r i g i n s showed mean residence t imes o f 2 th rough 1,500 years. Besides t h i s T and 14C i n v e s t i g a t i o n , D measurements were made a t 11 sampling p o i n t s (Batsche e t a l , 1 9 7 0 b ) . The D va lues over a t ime span o f about 2 weeks from t h e sampling p o i n t s Immendingen and F r i d i n g e n i n the Danube v a l l e y (about 20 km a p a r t ) and from Aach s p r i n g (about 15 km d i s t a n t ) show f a i r l y w e l l t h e h y d r o l o g i c connect ion between t h e Danube and Aach spr ing. The approximate s i m i l a r i t y o f ampl i tudes o f t h e curves f o r Danube and Aach s p r i n g leads t o t h e conclusions t h a t no s u b s t a n t i a l m ix ing o f water o f a d i f f e r e n t ôD va lue takes p l a c e i n t h e underground water f low.

The f o l l o w i n g books a r e recommended f o r more d e t a i l e d i n f o r m a t i o n and examples o f s t u d i e s i n I so tope Hydrology: Working Group on Nuclear Techniques i n Hydrology, 1968; D r o s t e t a l . , 1972 ; Rodriguez and deMonroy, 1 9 8 0 .

6.6 Determinat ion o f a q u i f e r c h a r a c t e r i s t i c s ( G i l b e r t Castany)

P o r o s i t y and p e r m e a b i l i t y may be determined e i t h e r by t e s t i n g rep resen ta t i ve rock samples i n t h e l a b o r a t o r y o r by means o f f i e l d t e s t s . The c o e f f i c i e n t s o f storage and t r a n s m i s s i v i t y a re ob ta ined by conduct ing pumping t e s t s . The h y d r a u l i c c h a r a c t e r i s t i c s determined by l a b o r a t o r y t e s t s can o n l y be i m p i r i c a l l y r e l a t e d t o c h a r a c t e r i s t i c s i n the area under study.

Pumping t e s t s i n t h e f i e l d .us ing c l o s e l y c o n t r o l l e d c o n d i t i o n s - i .e . pumping - q u a n t i t y - can p r o v i d e r e l i a b l e data.

6.6.1 Labora tory de terminat ions o f p o r o s i t y . The methods used f o r t he 1aboratory .determinat ion o f t h e p o r o s i t y o f carbonate rocks a re g e n e r a l l y s i m i l a r t o those used f o r o t h e r rocks.

6.6.1.1 T o t a l p o r o s i t y . Labora tory t e s t s used t o determine t o t a l p o r o s i t y can be made by immersion i n l i q u i d s , d e n s i t y t e s t s , and gas porosi ty-meters.

210

6.6.1.1.1 Immersion i n water. The specimen i s covered w i t h a thin f i l m (such as p a r a f f i n o r p l a s t i c ) and then immersed i n graduated c y l i n d e r f i l l e d w i t h d i s t i l l e d water (see F i g u r e 6 .6-1) . The volume o f t h e d i sp laced water g i v e s t h e t o t a l volume, V, o f t h e specimen.

The s p e c i f i c d r y we igh t i s then ob ta ined by d r y i n g t h e sample i n an oven a t a temperature o f 105 t o l l O ° C f o r 24 hours. The we igh t o f t h e specimen a f t e r c r y i n g i s W 1 .

The sa tu ra ted we igh t W 2 o f t h e specimen i s o b t a i n a f t e r immersing t h e specimen i n d i s t i l l e d water u n t i l i t reaches complete s a t u r a t i o n . The t o t a l p o r o s i t y "n" i s g i ven by t h e expression:

(6.6-1)

where Vv i s t he volume o f v o i d s i n the specimen.

6.6.1.1.2 Immersion i n mercury. The specimen i s sa tu ra ted by a l c o h o l and then al lowed t o dry. I f t h e d r y we igh t o f t h e sample i s W1 and i t s we igh t when immersed i n mercury a f t e r d r y i n g i s W p , then:

w 2 = w1 - w

and

(6.6-2)

(6.6-3)

where w i s t he bouyant force (Archimedes f o r c e ) a c t i n g upon t h e specimen when immersed i n mercury and d i s t h e d e n s i t y o f mercury.

The t o t a l volume V may a l s o be ob ta ined by immersing the d r i e d specimen i n mercury and de termin ing t h e e q u i v a l e n t volume o f t h e d i sp laced mercury (see F i g u r e 6.6-2) .

6.6.1.1.3 Densi ty . The apparent dens i t y , P , i s determined from t h e va lues o f t he d r y we igh t W 1 and t h e t o t a l volume V as f o l l o w s :

W 1 - P a - - V (6.6-4)

(6.5-5) L

where pr i s t h e d e n s i t y determined by a pycnometer.

6.6.1.1.4 Gas i n j e c t i o n . A l l p rev ious methods have t h e common d i f f i c u l t y o f d r y i n g t h e rock. Complete drainage o f t h e l iqu id from w i t h i n t h e pore spaces i s d i f f i c u l t under u s u a l l a b o r a t o r y cond i t i ons . As a . r e s u l t , t h e p o r o s i t y values c a l c u l a t e d from t h e p rev ious methods have in te rmed ia te va lues between those o f t h e t o t a l and e f f e c t i v e p o r o s i t y . P r e c i s i o n can be improved by u s i n g a gas poros i ty -meter 'see F i g u r e 6.6-3) t oge the r w i t h c a l i b r a t i o n curves (see F i g u r e 6.6-4).

The t o t a l volume, VI o f t h e specimen i s determined o f an immersed sca le (see F i g u r e 6.6-5) . A f t e r r e c o r d i n g t h e we igh t o f t h e sample W l , i t i s then f i x e d i n a f l o a t and immersed i n mercury. E q u i l i b r i u m i s r e s t o r e d by adding weights W 2 on t h e balance pan. The t o t a l volume o f t h e specimen i s g i ven by the expression:

w2 - w1 V = 7 (6.6-6)

where d i s t h e d e n s i t y o f mercury.

2 1 1

= V

1 2 Determination of ,;wume v of sample

D r y i n g oven

3

5

,a Dry weight

4

I Saturated weight

6

F i g u r e 6 . 6 - 1 Determinat ion o f t o t a l p o r o s i t y by immersion i n i iqÙîd.

212

I

'I' Figure 6.6-2 Determinat ion o f t o t a l p o r o s i t y by immersion i n mercury.

2 1 3

Sample holder 4

- To Vaciium B=

Figure 6 .6-3 Monometer tube and specimen holder f o r Washburn-Bunting porosi ty meter.

214

h in cm

m E u

O I

II

E E c

F igu re 6.6-4 C a l i b r a t i o n curve f o r p o r o s i t y determinat ion/ .

Sample hl II

I Sample

I III

Figure 6.6-5 Schematic diagram showing t h e procedure f o r measuring t o t a l volume V o f specimen.

215

The volume V o f t h e s o l i d c o n s t i t u e n t s i s ob ta ined by a manometer tube (see F i g u r e 6.6-38. The sample i s i n t roduced i n t o a con ta ine r and vacuum i s produced by l i f t i n g t h e mercury column i n t h e upper branch o f t h e manometer tube u n t i l t h e meniscus reaches t h e upper bulb. The t i g h t l i d o f t h e con ta ine r i s then replaced. The t h r e e way v a l v e i s then ad jus ted t o connect t he upper branch w i t h t h e atmosphere, a f t e r which t h e mercury column i s lowered w h i l e compressing t h e a i r i n s i d e t h e sample conta iner . The sca le h corresponding t o the min iscus o f t h e mercury i s recorded. Two c a l i b r a t i o n curves are used t o compute p o r o s i t y (see F i g u r e 6.6-4).

6.6.1.2 Determinat ion o f e f f e c t i v e p o r o s i t y . The t o t a l p o r o s i t y , n, o f a sample i s determined by standard procedures. The sample i s immersed f o r 2 4 hours i n d i s t i l l e d water t o a stage o f complete o r n e a r l y complete s a t u r a t i o n . I t i s then d ra ined i n a h u m i d atmosphere f o r another 2 4 hours. The amount d ra ined i s measured and represents g r a v i t a t i o n a l water, Ve. The sa tu ra ted rock p o r o s i t y , o r t h e s p e c i f i c r e t e n t i o n , n i s measured by a poros i ty -meter (see F i g u r e 6 .6-3) . i s ob ta ined by t h e f o l l o w i n g formula:

The e f f e c t i v e p o r o s i t y s ' n

'e

e '

(6.6-7) S = - V

6.6.2 Labora tory measurement o f p e r m e a b i l i t y . Two types o f permeameters most commonly used a re t h e cons tan t head permeameter and t h e v a r i a b l e head permeameter (see F i g u r e 6.6-6).

6.6.2.1 Constant head permeameter. The opera t i on o f t h i s ins t rument i s based on t h e p r i n c i p l e o f Darcy 's experiment. Dur ing a t ime i n t e r v a l , t, a volume Q o f water i s a l l o w s t o p e r c o l a t e through a sample o f a g i ven length, R (see F i g u r e 6.6-6a). The d i f f e r e n c e between the constant water l e v e l s i s t he head, h. The p e r m e a b i l i t y , KI i s then:

(6.6-8)

6.6.2.2 V a r i a b l e head permeameter. A volume of water, dQ, pe rco la tes through a sample o f l e n g t h 11 and s e c t i o n a l area A d u r i n g a t ime i n t e r v a l , dt, under v a r i a b l e head h l - ho = h (see F i g u r e 6 .6 -7 ) :

According t o Darcy 's law:

K . h * A * d t dQ = II (6.6-9)

where A i s t h e c ross -sec t i ona l area. I f a i s t h e s e c t i o n o f t h e manometric tube, t he volume o f the water Q i s :

Q = a(ho - h l ) = -ah (6 .6 -10)

o r (6 .6 -11 )

dQ = -a dh (6 .6 -12 )

r e p l a c i n g dQ i n (6.6-9) by i t s va lue i n (6.6-12) :

K h d t A R -a dh = - (6.6-13 )

I f D i s t h e diameter o f t h e c y l i n d e r c o n t a i n i n g t h e sample and d i s t he diameter o f t h e manometer, then:

2 1'6

K A * d t - K D a d t - -dh - - h - a R dz II (6.6-14)

and by i n t e g r a t i o n :

- In h = 7’’ D a &- + Constant (6.6-15)

When t = O , h = ho and h l = h, t = tl, then - In ho = cons tan t (6.6-16)

F i n a l l y , r e p l a c i n g t h e n a t u r a l by t h e common logar i thm:

da II h K = 2.302 D a tl Lo9 ho (6.6-17)

6.6.2.3 V a r i a b l e head a i r permeameter. Fas te r and more p r e c i s e r e s u l t s a re ob ta ined by t h e use o f t h e v a r i a b l e head a i r permeameter, such as t h a t designed by the “ I n s t i t u t F ranca is du P e t r o l e “ (see F i g u r e 6 . 6 - 7 ) . A c y l i n d r i c a l sample, cored o u t o f t h e rock i s washed and d r i e d i n an oven. The specimen i s then p laced i n t h e core con ta ine r w i t h i t s upper s e c t i o n exposed t o t h e atmosphere. The lower s e c t i o n i s i n con tac t w i t h t h e s u c t i o n bulb G, which can be disconnected from t h e r e s t o f t h e dev ice by t h e needle v a l v e H. When t h e needle va l ve i s open, t h e water l e v e l i s f o r c e d t o r i s e i n t h e tube from t h e tank by app ly ing the s u c t i o n bulb u n t i l t h e water l e v e l reaches t h e upper mark ( K I .

The needle v a l v e i s then closed. A g l a s s tube below the sample con ta ine r has i t s t o p i n c o n t a c t w i t h t h e sample and i t s bo t tom below t h e sur face o f a cons tan t water l e v e l tank, E. T h i s tube i s composed o f t h r e e segments whose cross sect ions inc rease from t o p t o bo t tom i n t h e o rde r 1, 10, and 50, p r o v i d i n g t h r e e ranges o f s e n s i t i v i t y . The lower s e c t i o n has a mark c o i n c i d i n g w i t h t he water sur face i n t h e tank.

’ When t h e needle v a l v e i s closed, t h e water column i s lowered c r e a t i n g a vacuum which a l l ows t h e a i r t o f l o w through t h e sample. The t ime, t, necessary f o r t he meniscus t o t r a v e l from t h e upper t o t h e lower mark i s recorded. The p e r m e a b i l i t y i s computed by t h e formula:

where : k =

l J = Y = B = ! L = t = A =

k = - BII t a

p h y s i c a l p e r m e a b i l i t y (K = k y i n m i l l i d a r c y ) lJ

(6.6-18)

dynamic v i s c o s i t y s p e c i f i c we igh t a c o e f f i c i e n t whose va lue i s g i v e n by c a l i b r a t i o n l e n g t h o f t h e sample i n cm t ime o f t r a v e l between the two marks i n seconds sample c ross s e c t i o n a l area i n cm2.

I n a l l these- experiments, t h e o r i e n t a t i o n o f t h e f i s s u r e s , w i t h respec t t o t h e f l ow d i r e c t i o n i n t h e apparatus, must be noted.

A t l e a s t two p e r m e a b i l i t y de termina t ions should be made i n which t h e samples are o r i e n t e d i n two d i f f e r e n t d i r e c t i o n s pe rpend icu la r t o t h e f i s s u r e s .

6.6.3 F i e l d t e s t s . The storage c o e f f i c i e n t , S , and t h e p e r m e a b i l i t y ( o r t h e t r a n s i s s i v i t y T = KH = Ke) can be determined by f i e l d t e s t s . The two most commonly used t e s t i n g methods are: de te rm ina t ion o f t h e h y d r a u l i c parameters by means o f bore h o l e t e s t s (Open End Tests - Lugeon t y p e ) ; and de te rm ina t ion o f t h e t r a n s m i s s i v i t y and storage c o e f f i c i e n t by means o f pumping t e s t s .

6;6.3.1 Pe rmeab i l i t y and f i s s u r a t i o n , data a n a l y s i s and study scale. The p e r m e a b i l i t y o f a f i s s u r e d rock i s c l o s e l y r e l a t e d t o t h e p o s i t i o n and s p a t i a l

217

o r i e n t a t i o n o f each s e t o f f i s s u r e s . A d e t a i l e d s t r u c t u r a l f i e l d study must precede an e v a l u a t i o n o f t h e p e r m e a b i l i t y .

Some authors (C. Louis , 1 9 6 9 ) p r e f e r t o use t h e te rm h y d r a u l i c c o n d u c t i v i t y i n s t e a d o f p e r m e a b i l i t y , because t h e water f l o w i s somewhat channeled through t h e f i s s u r e s . However, t he te rm p e r m e a b i l i t y (Darcy p e r m e a b i l i t y , K I i s used i n t h i s t e x t f o r t h e sake o f consistency.

F i ssu res may have s p a t i a l d i s t r i b u t i o n t h a t i s i r r e g u l a r , random, o r o r i e n t e d g e n e r a l l y i n one, two o r t h r e e se ts o f d i r e c t i o n s . The most commonly o c c u r r i n g f i s s u r e system has t h r e e se ts o f f r a c t u r e s KI, K2, K g (see F i g u r e 6.6-EA). Once t h e s p a t i a l d i s t r i b u t i o n i s w e l l def ined, t h e p e r m e a b i l i t y o f each s e t should be measured and eva lua ted i n r e l a t i o n s h i p t o t h e p e r m e a b i l i t i e s o f t h e o t h e r e s t s SO as t o o b t a i n a weighted es t ima te o f t he p e r m e a b i l i t y o f t he area o f study. The average p e r m e a b i l i t y , K , o f a f i s s u r e d rock mass under laminar f low c o n d i t i o n s i s g i ven by:

e K = - K + Km b f (6.6-19)

where : K = p e r m e a b i l i t y o f t h e elementary rock mass

= p e r m e a b i l i t y o f a f i s s u r e

= average opening o f t he f i s s u r e s e t under cons ide ra t i on K f = p e r m e a b i l i t y o f t he rock m a t r i x ( u n f i s s u r e d rock )

b = average spacing o f t h e f i s s u r e s , i n t h e same set. Bu t t he p e r m e a b i l i t y K o f t he rock m a t r i x i s n e g l i g i b l e as compared t o

t h e p e r m e a b i l i t y K o f t h e aemen ta ry rock mass (see F i g u r e 6.6-833). 'rhus i t f o l l o w s t h a t : -

-

K =

The laminar f l o w v e l o c i t y v i n a

+ -P

( 6 .6 -20 ) e b Kf -

f i s s u r e , i s g i ven by Darcy 's law as:

p = h y d r o s t a t i c pressure Z = e l e v a t i o n head

= uni t we igh t o f water. gw+ p / y = 9 , t h e h y d r a u l i c p o t e n t i a l a t a s p e c i f i c p o i n t P, i n the

Recharge o r d ischarge d i s t o r t s t h e p iezomet r i c sur face i n t o cones o f a c c r e t i o n o r depression due t o the groundwater f low. The r e s u l t i n g f l o w p a t t e r n can be represented by an or thogona l network o f e q u i p o t e n t i a l i j and stream ( f l o w ) l i n e s $ (see F i g u r e 6 .6 -10 ) .

When t h e f l o w i s laminar, i f t h e water l e v e l i n a boreho le i s above the i n i t i a l p iezomet r i c sur face o f t h e aqui fer , t h e parameters are r e l a t e d by t h e expression:

f i g s u r e (see F i g u r e 6.6-9) .

(6.6-22)

g = uni t r a t e o f f l o w i n t h e f i s s u r e a = s lope angle o f t h e p lane o f t he f i s s u r e s e t w i t h t he h o r i z o n t a l b = sa tu ra ted th i ckness + and 0 = h y d r a u l i c p o t e n t i a l s a t r a d i i r and r r e s p e c t i v e l y ,

as 8etermined from t h e f l o w p a t t e r n (see F i g u r e 8.6-10). A c t u a l l y , seve ra l f i s s u r e s i n t h e same system may e x i s t w i t h i n t he

th i ckness L o f the boreho le (see F i g u r e 6.6-9). As t h e discharge from i n d i v i d u a l f i s s u r e s , q , i s unknown, a l i n e a r average Q/L i s used, i n which Q i s t h e t o t a l d ischarge o f t h e t e s t , then:

218

(6.6-23)

1 continuous flow

costant level

over ftow I d

a- Constent h e a d b- V a r i a b l e h e a d

F igure 6 .6 -6 Constant head and v a r i a b l e head permeameters

B Support

Figure 6.6-7 V a r i a b l e head a i r permeameters " I n s t i t u t F rança is du P é t r o l e " .

219

b

F i g u r e 6.6-8 Pe rmeab i l i t y de te rm ina t ion o f system o f f i s s u r e s . (a) Representa- t i o n o f t h r e e f i s s u r e se ts : ‘K1,K2,K3. p e r m e a b i l i t y K i n f i s s u r e s e t K1.

(b) Test t o determine

220

Equipotential lines +

F igu re 6.6-9 P e r m e a b i l i t y de te rm ina t ion i n a system o f f i s s u r e s ; d e f i n i t i o n o f va r ious parameters.

P i e z o m e t r i c l e v e I

K f

Elevation Head = Z

F i g u r e 6.6-10 Sketch of a f l o w n e t o f e q u i p o t e n t i a l and f low l i n e s i n a recharge t e s t i n an i n c l i n e d f i s s u r e ( a f t e r Louis , 1 9 6 9 ) .

2 2 1

When CL = O , t he p lane o f t he s e t o f f i s s u r e s becomes h o r i z o n t a l , then:

(6.6-24)

If t h e water l e v e l i n t h e t e s t w e l l o r boreho le i s above the i n i t i a l p iezomet r i c surface, a n a t u r a l groundflow e x i s t s ( v e l o c i t y Vo l , equat ion (6.5-24) becomes:

I n - + I X X + I y - Q/L 2 nK

- - r Y O

m - bo (6 .6-25)

where I and I a r e t h e components o f t h e h y d r a u l i c g r a d i e n t I o f t h e

The t e s t i n g method i n t h e f i e l d i s chosen according t o the manner i n which t h e f i s s u r e s a re d i s t r i b u t e d and t h e purpose o f da ta c o l l e c t i o n (see Table 6.6-1). I n t h e s tud ies o f groundwater development on a l a r g e o r r e g i o n a l scale, t h e pumping t e s t method should be used, rega rd less o f t h e f i s s u r e system. O n t h e o t h e r hand, i n problems i n v o l v i n g r e l a t i v e l y smal l water volumes such as foundat ion works (dams, br idges, e t c . ) o r water seeping t o t h e mines, t h e o n l y recommended procedure i s t h a t o f t he m o d i f i e d Lugeon t e s t .

n a t u r a l %low. Y

6.6.3.2 P e r m e a b i l i t y de te rm ina t ion by borehole recharge t e s t s (open end o r Lugeon-type t e s t s ) . The boreho le t e s t s , open end o r Lugeon-type, are s u i t a b l e f o r s tudy ing t h e h y d r a u l i c parameters o f f i s s u r e d rocks (Louis, 1 9 6 9 ) . They a re performed i n uncased boreholes. Water i s g e n e r a l l y pumped i n r a t h e r than o u t because, i n t h e l a t t e r case, submersible pumps have t o be used below depth o f 6 - 7 m.

Three types o f i n j e c t i o n t e s t s a re i n common use: 1. Standard Lugeon t e s t , which i s s imple and g i ves an average r e g i o n a l

h o r i z o n t a l p e r m e a b i l i t y w i t h o u t t a k i n g i n t o account t h e an iso t ropy o f t h e fo rmat ion (see F igu res 6.6-8 and 6.6-11) i s performed on t h e b a s i s o f t h e r e l a t i v e o r i e n t a t i o n o f t he t e s t h o l e t o the system o f f i s s u r e s .

2. M o d i f i e d Lugeon t e s t , by which a d i r e c t i o n a l p e r m e a b i l i t y on t h e b a s i s o f r e l a t i v e o r i e n t a t i o n o f t he t e s t h o l e t o the system o f f i s s u r e s i s determined.

3. Pe rmeab i l i t y t e s t by mean o f a t r i p l e h y d r a u l i c r i g which g i v e s d i r e c t i o n a l p e r m e a b i l i t i e s d i r e c t l y and a lso, whenver the f r a c t u r e scale p e r m i t s ( t h e a n i s t r o p i c p e r m e a b i l i t y tensor standard).

6.6.3.2.1 Standard Lugeon t e s t . I n the standard Lugeon p e r m e a b i l i t y t e s t , water i s i n j e c t e d i n t o the boreho le i n f i x e d steps taken a t p resc r ibed t ime i n t e r v a l s . The water p ressure i s increased and decreased i n steps such as: O , 1, 2.5, 5., 7.5, 1 0 then 7.5, 5 , 2.5, 1 and O bars. (one b a r i s equ iva len t t o 10.2 meters head o f water.) The t ime i n t e r v a l commonly i s 1 0 minutes.

The exper imenta l device, sketched i n F igu re 6.5-11 i nc ludes mainly: 1. A pump, p r e f e r a b l y c e n t r i f u g a l , capable o f a m i n i m u m pressure

2. A f l o w meter ( p r e c i s i o n : 1 l i t e r ) ; 3. Two manometers: 0-6 b a r a n d 0-12 b a r ( p r e c i s i o n : 0 .1 b a r ) ; 4. A chornometer; 5. Tubes, p ipes, va lues f o r assembling. The t e s t i s performed f o r a se lec ted zone, l e n g t h LI above the bottom o f a

fo reho le . The upper end o f t h e se lec ted zone i s c losed by a plug (see F igu re 6 .6-11) . . The t e s t i s performed by t a k i n g measurements o f t h e decrease o f p ressure as t h e successive steps i n i n c r e a s i n g and decreasing water pressure a re made.

The t e s t r e s u l t s a re va luab le and meaningful when t h e predetermined schedule o f p ressure changes a r e e x a c t l y fo l lowed and t h e changes i n pressures a re p r e c i s e l y measured.

Accurate g e o l o g i c a l and hydrogeo log ica l l ogs o f t he d r i l l i n g and study o f t h e s t r u c t u r a l geology should p r o v i d e the o r i e n t a t i o n and the s p a t i a l

222

capac i t y o f 10 b a r a t 50 t o 100 l / m i n . ;

F igu re 6 . 6 - 1 1 Standard Lugeon t e s t , exper imenta l set-up and parameters.

Static Water Level ------__

Depleation Curve

permeability K Horizontal

permeability

F igu re 6 .6 -12 Standard Lugeon t e s t , d e f i n i t i o n s necessary t o i n t e r p r e t t e s t r e s u l t s .

2 2 3

d i s t r i b u t i o n o f t h e f i s s u r e s : l o c a t i o n e leva t i on ; o r i e n t a t i o n (perpendicular, i n c l i n e d o r p a r a l l e l o r i e n t a t i o n w i t h respec t t o t h e bo re a x i s ) ; and the e x t e n t o f opening and f i l l i n g . I n t h e boreho le t e s t s , t h e f i s s u r e s p a r a l l e l t o t h e a x i s o f t h e boreho le a re extremely impor tant .

6.6.3.2.1.1 Tes t zone th ickness. The th ickness L o f t h e t e s t zone i s a f u n c t i o n o f t h e average spacing o f t h e f i s s u r e s and t h e e x t e n t o f groundwater f l o w ( a p p l i c a t i o n t o a dam, foundat ions, mine drainage, e t c . ) . . The i d e a l depth i s equa l t o t h e s i z e o f t h e g r i d used i n t h e numer ica l s o l u t i o n o f t h e f l o w ( e q u i p o t e n t i a l and stream l i n e s ) . I t v a r i e s from 3 t o 5 m, w i t h a common th i ckness o f 5 m. I t i s necessary t o reduce t h e th ickness t o 2 m o r even 1 m i n e x t e n s i v e l y f i s s u r e d rocks which have a high capac i t y t o absorb the main f low.

6.6.3.2.1.2 I n j e c t i o n pressure. The c o n t r o l l e d i n j e c t i o n pressure i s used p r i m a r i l y t o m a i n t a i n t h e laminar groundwater f l o w around t h e t e s t ho le.

The l i m i t a t i o n i s s i g n i f i c a n t i n the shal low l a y e r s o f t h e fo rmat ion (0-20 m deep) t o p reven t any changes i n t h e geometry o f t h e f i s s u r e s and hence t h e p e r m e a b i l i t y . Phenomena such as opening o f t he f i s s u r e s , crack ing, and s o i l upheaval, c o u l d produce l i q u i f a c t i o n . The t e s t should be l i m i t e d t o pressure steps o f 1, 2, 3, 4, 3, 2, and 1 b a r a t O t o 1 0 m depth, and o f 1, 2, 4, 6 , 4, 2 and 1 b a r a t 1 0 t o 20 m. When t h e high p e r m e a b i l i t y o f t h e mass does n o t a l l o w a t t a i n i n g t h e p r e s c r i b e d pressures (10 b a r ) , i t i s s u f f i c i e n t t o per fo rm t h e t e s t during a p e r i o d o f 10 minutes, a t t he maximum obta ined pressure, and t h e corresponding f l o w r a t e Q i s recorded.

6.6.3.2.1.3 E f f i c i e n c y o f t h e packer. A t each t e s t , t h e packer should be checked t o be sure t h a t i t i s p laced and f u n c t i o n i n g p roper l y . The water l e v e l must n o t r i s e abnormally i n t h e boreho le above t h e packer ( a to le rance o f a sma l l pe rcen t o f t h e t e s t p ressure i s acceptable).

6.6.3.2.1.4 I n t e r p r e t a t i o n o f t h e t e s t s . The data ob ta ined from the t e s t area: t h e l o c a t i o n o f t he t e s t zone and i t s th ickness L; t h e depth o f t he p iezomet r i c l e v e l H i n meters; t h e h e i g h t o f t h e manometer, H ( i n meters) r e l a t i v e t o &e ground l e v e l ; t he i n j e c t i o n pressure head p, PRrfneters o f water, o r i n bar; r e c o r d o f t he ground manometer; and t h e i n j e c t i o n f l o w r a t e Q i n l i t e r s p e r minute (see F i g u r e 6 .6 -12 ) .

The f l o w p a t t e r n around t h e t e s t zone depends on t h e o r i e n t a t i o n o f t he systems o f f i s s u r e s as r e l a t e d t o the a x i s o f t he borehole: p a r a l l e l ( l o n g i t u d i n a l f i s s u r e s ) o r pe rpend icu la r (see F i g u r e 6.6-13). I n the case o f p a r a l l e l f i s s u r e s , even w i t h one f i s s u r e , t h e i n j e c t e d f l o w r a t e s are very high compared t o those o f i n c l i n e d f i s s u r e s . I n t h i s case, a s p e c i a l ana lys i s i s necessary. W i t h h o r i z o n t a l f i s s u r e s (perpendicu lar t o t h e borehole) o r even i n c l i n e d f i s s u r e s , t he a n a l y s i s o f t h e t e s t i s p o s s i b l e by i n t r o d u c i n g t h e approach o f t h e above metnioned c y l i n d r i c a l f low. I n t h e v i c i n i t y o f t he t e s t zone, c y c l i n d r i c a l f l o w i s more ex tens ive i n th ickness (3 t o 5 m) r e l a t i v e t o i t s diameter (about 0.8 m) and t h e f l o w i s approximately r a d i a l and p lanar .

The s i m p l i f i e d formula t o the c y l i n d r i c a l f l o w would t h e r e f o r e be v a l i d :

r 2 nK r I n - H o - H = - Q/L

O (6 .6 -26 )

where : H and Ho = the p iezomet r i c heads (meters) measured a t d is tance r

Q/L = t h e uni t r a t e f low, i n l i t e r s p e r minute p e r meter R /m in /m and ro (diameters) from the a x i s o f t he b o r i n g

L = t h e th i ckness o f t he t e s t zone K = t h e p e r m e a b i l i t y perpend icu la r t o the a x i s o f t h e borehole

The formula used by t h e U.S. Bureau o f Reclamation (see F i g u r e 6 . 6 - 1 4 ) , ( h o r i z o n t a l p e r m e a b i l i t y ) i n l i t e r s p e r minute

when L 2 l o r o , i s :

224

Packer

a

L e a k a g e flow l ine

Packer

Leakage flow line

F igu re 6.6-13 I n f l u e n c e o f t he d i r e c t i o n o f f i s s u r e s on the f l o w d u r i n g water t e s t s : (a) F i ssu res p a r a l l e l t o borehole, (b) F issures n o t p a r a l l e l t o borehole.

I / / / / / .

Packer,

F igu re 6.6-14 Schematic diagram o f t h e t e s t used by U n i t e d Sta tes Bureau o f Reclamation.

225

(6.6-27)

where : h = water pressured head i n t h e t e s t h o l e L = th ickness o f t e s t zone.

As p iezomet r i c pressures i n t h e t e s t zone a re seldom ava i l ab le , two re fe rence p o i n t s may be a r b i t r a r i l y chosen: the t e s t h o l e o f t h e r a d i u s r ( r c lose t o 4 cm) , and a p o i n t l o c a t e d a t a d is tance RI equa l t o the r a d i d o fO in f l uence o f t h e t e s t (see F i g u r e 6 .6 -12 ) . The va lue o f R i s g iven by the S i c h a r d t ' s formula as:

R = 3000 [(Ho - HR) fi] (6.6-28)

where : H = p iezomet r ic head i n t h e borehole Ho = head a t a d is tance R.

The u n f t s i n t h e above equat ion should be i n meters and seconds. I n f a c t , t h e e r r o r i n e v a l u a t i n g R i s n e g l i g i b l e because i t has

p r a c t i c a l l y no e f f e c t on t h e t e s t r e s u l t s , R L O. The te rm Ho - HR i s then excess head AH i n t h e t e s t h o l e , w i t h respec t

t o t h e p iezomet r i c l e v e l (see F i g u r e 6 .6 -12 ) . The p e r m e a b i l i t y i s g iven by t h e formula:

K = 'IL l n ( R / r o ) (6 .6-29) 2 r A H

l n ( R / r ) = constant O

21T 16.6-30)

P r a c t i c a l l y , I n R / r o v a r i e s s l i g h t l y , and i t can be assumed t h a t

l n ( R / r o ) E 7 (6.6-31)

Then f o r numer ica l computations:

K (m/sec) = 1.85 x BH Q/L (6 .6 -32 )

The Lugeon un i t , Lu, i s d e f i n e d s i m i l a r l y t o t h e p e r m e a b i l i t y o f a rock mass, f l o w o f one l i t e r o f water p e r minute through one meter o f t e s t e d m a t e r i a l , under an e f f e c t i v e pressure o f i n j e c t i o n o f 10 b a r ( o r 100 m o f water) i n t h e t e s t ho le.

1 Lu = 1 R/min /m under 10 b a r The formula ( 6 . 5 - 3 2 ) becomes:

(6.6-33) Q/L AH K ( L u ) = 100 -

K (m/sec) = 1.85 x 10-7(Lu) (6.6-34)

The excess head AH i n t h e t e s t h o l e i s equ iva len t t o t h e e f f e c t i v e app l i ed + H ) , l e s s t h e head losses AHp and AH due t o t h e

PC pressure (p + H p ipes and the pa#e%, r e s s e c t i v e l y . Thus:

These q u a n t i t i e s a re measured on t h e s i t e during t e s t . The t e s t da ta a re presented g r a p h i c a l l y . The pressures, i n bar, a re

p l o t t e d as abscissa, and t h e i n j e c t e d s p e c i f i c f l o w ra tes , i n l i t e r s pe r minute as ord ina tes . Flow r a t e versus excess pressure head c h a r a c t e r i s t i c curves are ob ta ined f o r a l l t h e t e s t s (see F i g u r e 6.6-15). The most rep resen ta t i ve curve i s se lec ted €o r the ana lys i s o f t h e t e s t . The reg ion o f rock mass a f f e c t e d by the t e s t i s about 20 t imes t h e borehole diameter.

226

(3

0,59 I

292

0,34

Q/L

3 5

P

/

P

A H F i g u r e 6.6-15 C h a r a c t e r i s t i c curves f o r recharge t e s t ( a f t e r Louis , 1 9 6 9 ) .

(a) I n t e r p r e t a t i o n o f Lungeon t e s t a t a dam s i t e . (b) Cor rec t t e s t g ives a r e v e r s i b l e cyc le . ( c ) Graph o f a c o r r e c t t e s t .

227

A c o r r e c t t e s t has t o g i v e a matching r e v e r s i b l e c y c l e (see F i g u r e 6.6-15), i n d i c a t i n g no changes i n the v o i d geometry. Any s u b s t a n t i a l d is tu rbances as opening o r c l o g g i n g o f t h e f i s s u r e s , are de tec ted from the c h a r a c t e r i s t i c curves (see F i g u r e 6.6-16) .

6.6.3.2.2 M o d i f i e d Lugeon t e s t . I n t h e standard s imple t e s t , t h e t e s t boreho le o r i e n t a t i o n does n o t t ake i n t o account t h e p o s i t i o n and the o r i e n t a t i o n o f the f i s s u r e s o f t h e rock mass. Yet t h e data are n o t considered va luab le un less t h e system o f f i s s u r e s i s w e l l de f i ned (perpend icu la r o r i n c l i n e d r e l a t i v e t o t h e a x i s o f t h e t e s t h o l e ) .

T h i s method i s t h e o n l y one p o s s i b l e i n such cases where t h e f i s s u r e s are randomly d i s t r i b u t e d . When t h e spreading o f t h e f i s s u r e s i s ve ry l a r g e and i r r e g u l a r , t h e medium can be considered cont inuous f o r t h a t scale. But genera l l y , one, two o r t h r e e f i s s u r e d systems can be i d e n t i f i e d (see F i g u r e 6.6-8). I n t h i s case, i t i s necessary t o determine t h e p e r m e a b i l i t i e s KI, K2, and K 3 , independent ly f o r each system of f i ssu res .

These t e s t s r e q u i r e a d e t a i l e d f i e l d study o f t h e s t r u c t u r a l geology t o determine the d i r e c t i o n and t h e spacing o f t h e f i s s u r e s systems.

The d r i l l i n g o f a boreho le has t o be c a r e f u l l y o r i e n t e d i n o rde r t o s i n g l e o u t ’ o n l y one f i s s u r e d system (see F igu res 6.6-8 and 6.6-9). Genera l l y , t he d i r e c t i o n o f t h e i l l u s t r a t e d boreho le i s s e t t o t e s t t h e K 1 systems and i t s o r i e n t a t i o n i s approximately perpend icu la r t o t h e considered system KI.

I t can be considered t h a t t h e i n f l u e n c e o f o t h e r systems i s n e g l i g i b l e . S t a t i s t i c a l l y , t h e p r o b a b i l i t y o f i n t e r s e c t i n g a f i s s u r e K2 o r K3 i s ve ry smal l . I n t h e event o f a boreho le i n t e r c e p t i n g a l o n g i t u d i n a l f i s s u r e , t h e i n j e c t e d f l o w r a t e Q would be ve ry high, and t h e g r a p h i c a l rep resen ta t i on would r e v e a l t h i s f a c t .

The accuracy o f t h e p e r m e a b i l i t y da ta can be g r e a t l y enhanced by t a k i n g records a t two d i s t i n c t p o i n t s : a t t h e t e s t boreho le and a t another boreho le a few meters away a long t h e f l o w ax i s . I n such t e s t s , two se ts o f d r i l l i n g data would be a v a i l a b l e .

6.6.3.2.3 Tests by t r i p l e h y d r a u l i c r i g . The p e r m e a b i l i t y tensor o r t he d i r e c t i o n a l p e r m e a b i l i t i e s can be ‘ ob ta ined by the t r i p l e h y d r a u l i c r i g (C. L o u i s 19661, where records a re taken - in t h r e e approp r ia te d i r e c t i o n s . The h y d r a u l i c r i g i s composed o f t h r e e p o r t i o n s r e l a t e d t o t h r e e t e s t zones and capable o f o p e r a t i n g under equa l o r d i f f e r e n t pressures (see F i g u r e 6 .6-17) . The t e s t zones a re separated by t h r e e o r f o u r packers. Two procedures may be used t o per fo rm t h e t e s t (pressures and f l o w r a t e s ) : h y d r a u l i c and e l e c t r i c a l means. The l a t t e r has t h e advantage o f be ing automatic.

6.6.3.3 Determinat ion o f t h e t r a n s m i s s i v i t y and the storage c o e f f i c i e n t . Numerous f i e l d s tud ies , have i n d i c a t e d t h a t , t h e f i e l d pumping t e s t emthods used i n porour fo rmat ions can be used i n f i s s u r e d format ions i n c l u d i n g k a r s t s t o determine t h e t r a n s m i s s i v i t y and storage c o e f f i c i e n t s . The r e s u l t s are adequate and w i t h i n t h e p e r m i s s i b l e margin o f e r r o r s i n f i e l d measurements. The procedures o f these t e s t s a re a v a i l a b l e i n numerous p u b l i c a t i o n s , t h e r e f o r e , i t i s s u f f i c i e n t i n t h i s t e x t t o p resent o n l y the genera l concept.

F i r s t , i t should be r e i t e r a t e d t h a t t h e es tab l i shed expressions are v a l i d f o r a homogeneous and i s o t r o p i c medium. The scale’ conç ide ra t i on i s thus impor tant . ‘ In p r a c t i c e , t h e medium a f f e c t e d by t h e t e s t zone may be assumed t o s a t i s f y those cond i t i ons . Th is f a c t w i l l be v e r i f i e d g e o l o g i c a l l y , and by means o f some boreho le t e s t o f t h e mod i f i ed Lugeon type. The f o l l o w i n g cases a re success ive ly discussed:

1. Homogeneous and i s o t r o p i c a q u i f e r s o f i n f i n i t e a r e a l e x t e n t w i t h no

2. Aqu i fe rs w i t h f i n i t e e x t e n t w i t h v e r t i c a l impervious boundaries o r

3. Leaky a q u i f e r s w i t h semi-pervious upper o r lower beds.

recharge through t h e upper and lower beds.

w i t h cons tan t p o t e n t i a l recharge boundaries,

228

Q/L

Disturbance of original fracture conditions

Clogging

c

O AH

F igu re 6.6-16 C h a r a c t e r i s t i c curves o f recharge t e s t s f o r d i f f e r e n t medium geometry ( a f t e r Lou is , 1 9 6 9 ) .

2 2 9

a

Figure 6.6-17 T r i p l e hydraul ic r i g ( a f t e r Louis, 1 9 6 9 ) : ( a ) P e r m e a b i l i t y t e s t i n a homogeneous medium, ( b ) P e r m e a b i l i t y t e s t i n a f i ssu red medium.

230

6.6.3.3.1 Homogeneous and i s o t r o p i c a q u i f e r s o f i n f i n i t e a r e a l e x t e n t w i t h no recharge th rough t h e upper o r lower beds. The s i m p l i f i e d express ion o f t h e Theis formula g i ven by C. E. Jacob, and c a l l e d l o g a r i t h m i c approximat ion i s used:

O . 183Q 2.25 T t (6.6-36) T log r 2 s s =

Th is formula i s v a l i d w i t h a f i v e pe rcen t e r r o r when:

1 0 r 2 S t L 4 T

o r s imply when:

t 2 1 2 to (to i n hours) (6.6-37)

s = Q = T = t =

t =

r = !3=

drawdown measured i n an obse rva t i on w e l l i n m: cons tan t r a t e o f pumping i n mg/sec.; t r a n s m i s s i v i t y i n m2/sec.: t ime, i n seconds, elapsed s ince t h e s t a r t o f pumping: t ime, a t zero drawdown, determined from t h e semi-log p l o t : t h e storage c o e f f i c i e n t , dimensionless; d i s tance between t h e obse rva t i on w e l l and t h e a x i s o f t h e pump w e l l .

The recovery o f t h e water l e v e l i s g i ven by t h e formula:

0.183 Q log t + t ' T t ' s = (6 .6-38)

t = t ime s ince pump ing s ta r ted : t ' = t ime s ince pump ing stopped.

The da ta recorded i n t h e pump ing t e s t o f cons tan t d ischarge a r e t h e drawdown s , and t h e corresponding t imes t, s ince t h e s t a r t o f pumping (see F i g u r e 6.6-18). These da ta a re o r d i n a r i l y analyzed by t h e use o f g r a p h i c a l semi-log p l o t s . O n such a p l o t , t h e abscissa represents t h e l o g a r i t h m sca le of t h e t ime, and t h e o r d i n a t e represents t h e drawdowns. The t imes a re i n seconds o r hours, and t h e drawdowns i n meters. The same r e p r e s e n t a t i o n i s used i n t h e recovery t e s t s (see F i g u r e 6.6-19).

A s t r a i q h t l i n e i s drawn throuqh t h e p l o t t e d data p o i n t s , a f t e r a c e r t a i n pumping t ime- p e r i o d ( 1 t o 2 hours) .- T h i s - i s t h e r e p r e s e n t a t i v e s t r a i g h t l i n e o f w e l l behavior. The i n t e r s e c t i o n o f t h i s l i n e w i t h t h e t ime a x i s g i v e the t ime to.

6.6.3.3.1.1 Eva lua t i on o f t r a n s m i s s i v i t y T. The C. E. Jacob fo rmula p e r m i t t e d t h e determine o f T f rom t h e g r a p h i c a l s o l u t i o n . The cons tan t f a c t o r i s i n f a c t t h e s lope o f t h e s t r a i g h t l i n e on t h e g r a p h i c a l p l o t :

Q = cons tan t (6.6-39) T -

I f C i s t h e s lope o f t h i s l i n e , t hen C i s equa l t o t h e change o f t he drawdown s , corresponding t o one l o g a r i t h m i c c y c l e on t h e t i m e sca le o f t h e p l o t . Then (F igu re 6.6-18) :

0.183 Q . = (6.6-40) T

6.6.3.3.1.2 Eva lua t i on o f storage c o e f f i c i e n t S . Determin ing t h e va lue to from t h e semi-log p l o t and s u b s t i t u t i o n g i v e s t h e S value:

2.25 T to

rz s = (6.6-41)

2 3 1

to Time ' t '

Figure 6 .6-18 pumping t e s t of constant discharge from an aquifer of i n f i n i t e a r e a l extent; Discharge t e s t was i n a calcareous karst mass ( a f t e r Jacobs, 1947).

Straight l i n e p l o t o f a

t+ t ' Time x' > t'

t '

Figure 6 .6-19 Recovery straight l i n e p l o t .

to Time 't ' D

ti

Figure 6 .6-20 Straight l i n e p l o t of a pumping t e s t o f constant discharge i n an aquifer l imi ted by l a t e r a l b a r r i e r i n Mania rock, Madagascar.

t i Time ' t '

Figure 6 . 6 - 2 1 Straight l i n e p l o t of a pumping test o f constant discharge i n an aquifer l imi ted by a l a t e r a l constant potent ial (recharge boundary) i n calcareous rock, Jura.

2 3 2

S i m i l a r l y , t h e recovery da ta p l o t t e d on semi-log paper l e a d o n l y t o t h e de terminat ion o f t h e a q u i f e r c h a r a c t e r i s t i c s (see F i g u r e 6.6-19).

6.6.3.3.2 A q u i f e r s w i t h v e r t i c a l b a r r i e r o r cons tan t p o t e n t i a l boundaries. V e r t i c a l b a r r i e r boundar ies r e s u l t from t h e presence o f impervious l a y e r ( s ) , r e d u c t i o n o f t h e a q u i f e r th ickness , o r f a u l t zone a c t i n g as b a r r i e r t o t h e f l o w w h i l e recharge boundar ies under a cons tan t p o t e n t i a l are p rov ided by f ree waters such as r i v e r , stream, lake, ocean.

6.6.3.3.2.1 A q u i f e r s w i t h v e r t i c a l b a r r i e r boundaries. I n t h e p rev ious cases o f ex tens ive a q u i f e r s , t h e time-drawdown p l o t r e s u l t s i n t o one s t r a i g h t l i n e . W i t h s p e c i a l boundary cond i t i ons , t h e i n e i s broken up i n two segments:

1. A s t r a i g h t l i n e corresponding t o t h e i n f i n i t e a q u i f e r ( t h e pumping i s n o t i n f l u e n c e d by t h e f a r away boundary). The f i r s t segment i s then represented by t h e formula:

0.183 Q log 2.25 T t T r2 S s = (6.6-42)

2. Another segment o f s t r a i g h t l i n e whose s lope i s t w i c e t h e s lope o f t h e f i r s t one i s represented by the formula:

0.183 Q 2.25 T t T log r 2 d S s = (6.6-43)

d = t h e d i s tance from t h e w e l l a x i s t o t h e impervious boundary, i n meters.

I t should be no ted t h a t F i g u r e 6.5-20:

0.366 Q T c 2 = 2 C l = (6.6-44)

C 2 = t h e slope o f t h e second l i n e , C 1 i s t h e s lope o f t h e f i r s t l i n e .

The t ime t., corresponding t o t h e i n t e r s e c t i o n o f t h e two segments, and t h e correspondihg drawdown si can be determined g r a p h i c a l l y (see F i g u r e

When t h e pumping cone o f depression reaches t h e boundary s ide, a t t i m e t , i t can be proved t h a t t h e drawdown s2 , o f an image w e l l , i s equa l t o z&ro and acco rd ing l y t h e f o l l o w i n g expression i s es tab l i shed:

6.6-20) .

d = 0.75 (6.6-45)

(6.6-46)

6.6.3.3.2.2 A q u i f e r s w i t h a recharge boundary of cons tan t p o t e n t i a l . When t h e cone o f depression reaches t h e boundary a s t a b i l i z a t i o n o f t h e drawdowns would r e s u l t due t o t h e e x t e r n a l -recharge i n t r o d u c i n g a s teady-s ta te c o n d i t i o n (see F i g u r e 6.6-21).

The beg inn ing o f t h e l i n e b e f o r e t h e cone reaches t h e boundary, corresponds t o an i n f i n i t e a q u i f e r and i s governed by t h e formula:

0.183 Q log 2.25 T t s = T r2 S

The l i n e a r f u n c t i o n o f t h e h o r i z o n t a l p o r t i o n i s :

(6.6-47)

(6.6-48)

233

d b e i n g t h e d i s tance between t h e w e l l a x i s and t h e cons tan t p o t e n t i a l recharge boundary.

The t ime, t ., corresponding t o the i n t e r s c t i o n o f t he two segments a l l o w s t h e de te rm ina t ion of t h e d i s tance o f t h a t boundary u s i n g t h e same expressions as those f o r a b a r r i e r boundary.

6.6.3.3.3 .Leaky a q u i f e r s w i t h semi-impervious c o n f i n i n g upper o r lower beds. I n Jacob's equations, i t i s assumed t h a t t h e upper and lower c o n f i n i n g l a y e r s a r e impervious. R u t i n p r a c t i c e t h e c o n f i n i n g format ions a re f r e q u e n t l y semi-pervious, and a l l t h e a q u i f e r s i n a sedimentary b a s i n c o n s t i t u t e one h y d r a u l i c system. Under t h e i n f l u e n c e o f pumping, t h e con f ined a q u i f e r i s recahrged by t h e upper and/or lower c o n f i n i n g beds t h a t t r a n s f e r t h e groundwaters, w i t h a t ime l a g , by p e r c o l a t i o n th rough the semi-permeable format ions. T h i s i s a l s o c a l l e d leakage (see F i g u r e 6.6-22).

Under these c o n d i t i o n s t h e pumping data, when p l o t t e d on semi - logar i thmic paper, g i v e s a s t r a i g h t l i n e a t t h e beg inn ing o f t h e t e s t . Once t h e leakage has begun a f t e r a t ime t, t h e l i n e dev ia tes (see F i g u r e 6.6-23). The i n f l e c t i o n p o i n t on t h e curve i s s i g n i f i c a n t and has t h e coord ina tes s . and t . The va lue o f t h e maximum drawdown, s i s ob ta ined by ex tend in4 the s é r a i g h t l i n e p o r t i o n rep resen t ing t h e i n i t i a ? m x ' p e r i o d o f pumping.

The s o l u t i o n i s g i ven by t h e expression:

- Q - - e r/B KO ( r / B ) 'max 4 sT

(6.6-49)

(6.6-50)

The f u n c t i o n s KO (x ) and ex KO (x) are t a b u l a t e d u s i n g (x) = r / B (see

B i s t h e leakage f a c t o r (see F i g u r e 6.6-22): Table 6.6-2) .

' = , / T K I + b '

b ' = t h e th i ckness o f t h e semi-pervious upper-bed; K ' = p e r m e a b i l i t y o f t h e semi-previous upper-bed.

The i n t e r s e c t i o n drawdown si, i s g iven by:

(6.6-5 1)

(6.6-52)

The hyd rogeo log ica l c h a r a c t e r i s t i c s a re g i ven b y t h e f o l l o w i n g formulas:

T = 0.1834 C e - r /B (6.6-53)

2 T ti

B r s = (6 .6-54)

(6.6-55) K ' T .b' Ba

- = -

c = s lope o f t h e curve a t t h e p o i n t o f i n f l e c t i o n ti = t ime a t t h e p o i n t o f i n f l e c t i o n .

6.6.3.4 I n t e r p r e t a t i o n of da ta f o r extremely heterogeneous and a n i s o t r o p i c media. When f i s s u r e d medium i s extremely heterogeneous and a n i s o t r o p i c , t h e p r e c i s i o n o f t h e r e s u l t s can be improved b y i n t r o d u c i n g the t r a n s m i s s i v i t y tensors I n t h e C. E. Jacobs formulas t h a t have been p r e v i o u s l y exp la ined (Papadopulos, 1969). The t r a n s m i s s i v i t y tensors can be determined by b o r i n g t e s t s , Lugeon type, w i t h t h e t r i p l e h y d r a u l i c r i g .

234

-.p.- d n i t i a l . - .- .- . piezometric surface

- - -- Drawdown(s1

Ki = Piezometric surface of confined aquifer after pumping

lmprmiabie bed/

F igu re 6.6-22 Schematic diagram o f leakage.

Substrat um

/ / - - - f - .

inflection point

I I l I I I I I I

ti

L

Time ' t' V

F igu re 6.6-23 I n t e r p r e t a t i o n o f a semi log p l o t i n d i c a t i n g t h e p o i n t o f i n f l e c t i o n o f a pumping t e s t i n a leaky a q u i f e r i n calcareous rock, Mateur P l a i n , Tunesia, ( a f t e r Hantusch, 1 9 5 6 ) .

235

Table 6.6-1. F - i e l d t e s t methods; usage and sca le o f i n v e s t i g a t i o n .

D i s t r i b u t i o n o f f i s s u r e s I n v e s t i g a t i o n

S ize o f area

i n v e s t i g a t i o n method under Tes t

i r r e g u l a r

Determinat ion o f average I n t h e order Standard h o r i z o n t a l pe rmeab i l i t y ; few km2 Lugeon foundat ions: c o n s t r u c t i o n t e s t works; mine drainage: p o l l u t i o n , e tc .

Determinat ion o f t h e Greater than p u m p i n g h o r i z o n t a l p e r m e a b i l i t y 100 k m 2 t e s t f o r groundwater devel - opment; water resources eva lua t ion .

Determinat ion o f t h e I n t h e order M o d i f i e d average h o r i z o n t a l o f few km2 Lugeon

works, mine drainage, p o l l u t i o n , e t c .

.............................................................

_____------_--------___________________c---------------------------------------

1, 2, o r 3 pe rmeab i l i t y : founda- t e s t f i s s u r e d se ts t i o n s , c o n s t r u c t i o n

Table 6.6-2. A b r i e f t a b l e o f eXKo(x) , where x = r / B ( a f t e r Raudkiv i and Cal lander , 1 9 7 6 ) .

0 .039 O . 0 3 8 0.035 0.036 0.037 - - X

eXKo(x) = 3.5933 3 .5678 3.5430 3.5189 3.4955

X - O .O40 O . O 4 1 0.042 O .O43 O .O44

3 - 4 7 2 7 3.4505 3.4289 3.4079 3.3874 e X Ko(x ) =

0.045 O .O46 O .O47 0.048 O .O49

3.3673 3.3478 3.3287 3.3100 3.2918

- - X X e Ko(x) =

2 3 6

I n t r o d u c i n g two t r a n s m i s s i v i t y tensors,

T = (6.6-56)

( w i t h x and y a r b i t r a r i l y chosen i n a two-dimensional o r thogona l system) i n t h e C. E. Jacob formula of l o g a r i t h m i c approximat ion (6.6-36), then:

F 7

* T - T

h X x y 2 + T Y Y x 2 - 2T XY X Y

0.183 Q log Li;.. xx Y Y

X Y

s = * T - T

Y Y

6.6.4 Parameters o f massive calcareous rocks. The hyd rogeo log ica l c h a r a c t e r i s t i c s t h a t have t o be determined i n t h e f i e l d a t t h e r e g i o n a l sca le o f t h e carbonate rocks which may be homogeneous, a r e t h e f o l l o w i n g :

1. Storage capac i t y , by ana lyz ing t h e d e p l e t i o n curves o f t h e o u t l e t s . 2. Storage c o e f f i c i e n t . 3. T r a n s m i s s i b i l i t y and r e l a t e d .pumping t e s t . 4. V e l o c i t y o f t h e groundwaters.

6.7 Hydro log ic observa t ions and t h e i r i n t e r p r e t a t i o n s (B.I. Kude l i n )

I n any i n v e s t i g a t i o n , purpose determines method. The f i r s t requirement i n p lann ing h y d r o l o g i c i n v e s t i g a t i o n s i s t o have an e x p l i c i t i d e n t i f i c a t i o n o f purpose and o b j e c t i v e s . The second requirement i s t h a t t h e r e be c o n s i d e r a t i o n € o r a l l aspects o f t h e h y d r o l o g i c c y c l e i n t h e study area. The t h i r d requirement i s t o assess a l l a v a i l a b l e resources i n terms o f funding, manpower, t ime, and f a c i l i t i e s . The f i n a l process i s t o a d j u s t t h e elements o f each o f t h e t h r e e requirements u n t i l a p r a c t i c a l p l a n o f i n v e s t i g a t i o n i s developed.

Consider ing t h e wide v a r i e t y o f c o n d i t i o n s under which h y d r o l o g i s t s work, t h e f o l l o w i n g suggestions a re o f f e r e d as guides t o t h e implemention o f t h e second requirement, t h a t o f cons ide ra t i on o f t h e h y d r o l o g i c regime, a re included. Each p r i n c i p a l i n v e s t i g a t o r must mod i fy these guides i n accordance w i t h l o c a l cond i t i ons . An e x c e l l e n t rev iew o f cons ide ra t i ons i n v o l v e d i n e s t a b l i s h i n g h y d r o l o g i c networks i s con ta ined i n t h e World M e t e o r o l o g i c a l Organ iza t ion ( W O ) Guide t o Hydrometeorological P r a c t i c e s (1965, Chapter 3 ) .

The b a s i c approach t o t h e h y d r o l o g i c regime o f a t e r r a n e i s t o develop a water balance, o r t h e more s t a t i c phrase, water budget. Carbonate te r ranes have one s i g n i f i c a n t d i f f e r e n c e t o o t h e r ter ranes: t h e sur face and subsurface bas ins may n o t co inc ide . Consequently, t h e u n i t - b a s i n approach must be used w i t h care, and i t i s f a r more impor tan t than i n non-ka rs t i c rocks t o measure a l l major elements o f t h e water regime. For example, i t i s common p r a c t i c e t o es t imate evapora t ion as t h e remainder i n formulas such as:

E = I - O - AS (6 .7-1)

E = t h e evaporat ion; I = t h e input ( p r e c i p i t a t i o n and r u n o f f ) ; O = t h e ou t f l ow ; and AS = t h e change i n storage.

However, t h i s fo rmula presumes t h a t t h e area i n v o l v e d i n de termin ing s to rage changes i s t h e same as f o r t h e o t h e r f a c t o r s . Where t h e storage area i s e i t h e r l a r g e r o r smal le r than t h e sur face bas in, t h e formula does n o t apply. I t then become necessary t o measure o r es t imate evapora t ion separa te ly , o r t o study i n c r e a s i n g l y extended areas u n t i l t h e formula may be appl ied.

6.7.1 Observa t iona l networks. To o b t a i n a reasonably adequate q u a n t i t a t i v e assessment o f t h e water regimes o f an area, i t i s necessary t o measure o r consider a l l t h e major elements o f t h e h y d r o l o q i c cyc le . I t i s a l s o p r e f e r a b l e

237

t o work w i t h a complete bas in, ( t h a t i s , an e s s e n t i a l l y c losed system) rega rd less o f t h e sca le o f t h e i n v e s t i g a t i o n . Bas in l i m i t s a r e d i f f i c u l t t o determine i n k a r s t i c areas where t h e sur face water and groundwater d i v i d e s may be q u i t e d i f f e r e n t and may n o t even be i d e n t i f i a b l e . Nonetheless, t h e r e are some obvious necess i t i es : gauging s t a t i o n s a re needed on r i v e r s , lakes, and a t s i t e s o f k a r s t spr ings; me teo ro log i ca l s t a t i o n s should be e s t a b l i s h e d w i t h some c a p a b i l i t y f o r measuring o r e s t i m a t i n g evaporation: p iezomet r i c s t a t i o n s should be s e t up u s i n g a v a i l a b l e o r s p e c i a l l y d r i l l e d boreholes f o r observa t ions o f groundwater l e v e l s : app rop r ia te underground measurements i n caverns and access ib le channels m i g h t g i v e h e l p f u l chemical q u a l i t y and r e l a t e d c h a r a c t e r i s t i c s such as temperature and pH should be observed: sediment d ischarge needs t o be monitored: and some b a s i s f o r measuring o r e s t i m a t i n g s o i l mo is tu re i n t h e unsatura ted zone must be es tab l i shed .

The d i s t r i b u t i o n o f sur face and subsurface observa t ion s t a t i o n s and t h e program o f measurement w i l l depend on t h e phys iog raph ica l f ea tu res o f t h e b a s i n and i t s underground. There i s no f i r m s e t o f recommendations rega rd ing t h e i r d i s t r i b u t i o n , and i n many i n v e s t i g a t i o n s , i t i s adv isab le t o s h i f t s t a t i o n l o c a t i o n s o r t o mod i fy t h e da ta c o l l e c t i o n p l a n a f t e r t h e da ta beg ins t o be c o l l e c t e d . General ly, t h e b e s t approach i s t o eva lua te r a t i o n a l l y t h e phys iograph ic and h y d r o l o g i c a l elements. For example, i n mountain areas an o b s e r v a t i o n a l network should be d i s t r i b u t e d i n such a manner as t o compensate f o r a l t i t u d i n a l changes; i n t h e p l a i n s , t h e b e s t guide remains t h e landscape i t s e l f as i t r e f l e c t s t h e u n d e r l y i n g geology.

Where k a r s t i c t e r ranes form o n l y a p a r t o f t h e b a s i n o r an area o f study, i t g e n e r a l l y i s necessary t o eva lua te t h e c h a r a c t e r i s t i c s o f t h e k a r s t i c rocks separa te ly , p a r t i c u l a r l y t h e i r e f f e c t s on r u n o f f . To do t h i s , i t i s adv isab le t o compare t h e r u n o f f regimes i n k a r s t i c and a d j o i n i n g non-kars t i c te r ranes , i t may be necessary t o mon i to r and compare c h a r a c t e r i s t i c s o f seve ra l bas ins t h a t a re equa l i n area and t h a t have rough ly homogeneous phys iog raph ica l f ea tu res but have d i f f e r e n t p r o p o r t i o n s o f k a r s t . The a n a l y s i s o f t h e r e s u l t i n g r u n o f f data w i l l e s t a b l i s h t h e e f f e c t o f d i f f e r e n t p r o p o r t i o n s o f k a r s t on t h e water regime o f t h e basin.

I n keeping w i t h t h e o b j e c t i v e s of t h e i n v e s t i g a t i o n s , h y d r o l o g i c a l observa t ions may be taken r e g u l a r l y o r p e r i o d i c a l l y over s h o r t o r l o n g pe r iods o f t ime. The number o f o b s e r v a t i o n a l p o i n t s , t h e i r du ra t i on , and t h e i r frequency o f measurement should be s u f f i c i e n t t o p rov ide f o r r e l i a b l e i n t e r p o l a t i o n o f t h e i n v e s t i g a t e d c h a r a c t e r i s t i c s o f t h e sur face and subsurface water regimes over t h e bas in.

6.7.2 P r e c i p i t a t i o n . The measurement o f p r e c i p i t a t i o n - r a i n , snow, e tc . , - over t h e b a s i n i s e s s e n t i a l f o r t h e study o f t h e sur face and subsurface waters, i n c l u d i n g t h e a n a l y s i s o f r u n o f f c h a r a c t e r i s t i c s , t h e computation o f water balances, and t h e i n v e s t i g a t i o n o f k a r s t processes. Measurements o f r a i n f a l l and snow a re made u s i n g g e n e r a l l y accepted methods such as those descr ibed i n the WMO Guide t o Hydrometeorological. P r a c t i c e s (1965, p. II. 1 t o II. 2 0 ) .

The t o t a l number o f obse rva t i on p o i n t s e s t a b l i s h e d f o r p r e c i p i t a t i o n measurements and t h e i r d i s t r i b u t i o n i s a f u n c t i o n o f many f a c t o r s (WMO, 1965, p. III. 1 - III. 11). I n carbonate ter ranes, i t i s impor tan t t o have a s u f f i c i e n t d e n s i t y o f p r e c i p i t a t i o n measurements upstream o f t h e stream-gauging s t a t i o n s t o o b t a i n a reasonable approximat ion of t h e mean p r e c i p i t a t i o n va lue f o r t h e drainage area. T h i s i s impor tan t i n e s t a b l i s h i n g the r e l a t i o n s h i p s o f t h e sur face and subsurface bas ins.

The m i n i n u m d e n s i t y o f s t a t i o n s recommended by WMO (see Table 6.7-1) f o r t h r e e broad ca tegor ies o f landscape i s n o t always adequate f o r s tud ies i n k a r s t i c regimes. Experience i n the USSR leads t o the recommendation o f a t l e a s t one p r e c i p i t a t i o n s t a t i o n f o r 200-250 km2 i n a p l a i n s r e g i o n and one s t a t i o n f o r 25-50 kma and p e r e l e v a t i o n change o f 200-300 m i n mountainous areas.

Under c e r t a i n circumstances t h e use of rada r t o approximate p r e c i p i t a t i o n should be considered f o r i n v e s t i g a t i o n s i n mountainous areas o r i n t e r r a n e o therw ise d i f f i c u l t t o reach o r i n which t o make measurements, i . e . over l a r g e l akes o r areas o f l i t t l e p o p u l a t i o n (WMO, 1965, p. II. 10-15).

2 3 8

Table 6.7-1. Suggested m i n i m u m d e n s i t y o f p r e c i p i t a t i o n s t a t i o n networks, a f t e r WMO, 1965.

Range o f norms Range o f p r o v i s i o n a l f o r m i n i m u m norms t o l e r a t e d i n network d i f f i c u l t c o n d i t i o n s - l/

Area i n kma f o r Area i n kma f o r Type o f Region one s t a t i o n one s t a t i o n

I . F l a t r e g i o n o f temperate, mediterranean and t r o p i c a l zones

II. Mountainous reg ions o f ternperate, mediterranean and t r o p i c a l zones.

Small mountainous i s l a n d s w i t h ve ry i r r e g u l a r p rec ip - i t a t i o n s , ve ry dense hydrographic network.

600-900

1 O0 -2 50

25

III. A r i d and p o l a r zones 2/ 1,500-10,000 - 3 1

900-3,000 - 4 /

250-1,000 - 4 1

- l/ L a s t f i g u r e o f t he range should be t o l e r a t e d o n l y under excep t iona l l y d i f f i c u l t cond i t ions .

- 2 1 Great dese r t s a re n o t inc luded.

- 3 / Depending on f e a s i b i l i t y .

- 4 / Under ve ry d i f f i c u l t c o n d i t i o n s t h i s may extend t o 20,000 km2.

239

6.7.3 Runoff . Runoff measurements i n k a r s t i c areas a re made t o eva lua te the p r i n c i p a l r u n o f f c h a r a c t e r i s t i c s , i n c l u d i n g t h e de te rm ina t ion o f losses and ga ins as t h e streams c ross carbonate rocks, and the t o t a l d ischarge o u t o f t he bas ins under study. Streamflow da ta a l s o a re used i n computation o f t he water balance and f o r t h e assessment o f t h e i n t e r r e l a t i o n s h i p s o f r u n o f f and the l o c a l k a r s t i c development.

I n a d d i t i o n t o e s t a b l i s h i n g and l o c a t i n g stream-gauging s t a t i o n s according t o t h e u s u a l c r i t e r i a (WMO, 1965, II. 29) , they a l s o should be es tab l i shed a t t h e boundar ies o f changes o f l i t h o l o g y and p a r t i c u l a r l y o f con tac ts o f k a r s t i c and non-ka rs t i c ter ranes. General ly, i t i s assumed t h a t no d i f f e r e n c e s i n r u n o f f can be measured i f t h e k a r s t i c area forms l e s s than 1 5 percent o f t he basin. I n h i l l y and mountainous regions, t h e network o f gauging s t a t i o n s should seek t o p r o v i d e i n s i g h t i n t o the i n f l u e n c e o f a l t i t u d e and slope exposure on r u n o f f .

Moreover, i n k a r s t i c areas w i t h l a r g e caverns, every reasonable at tempt should be made t o gauge t h e underground f l o w and i t s v a r i a t i o n s , f o l l o w i n g t h e same genera l guides as on t h e surface. Th is i s e s p e c i a l l y t r u e where f l o w i s known t o s p l i t i n t o d i v e r g i n g channels t o discharge a t d i f f e r e n t p o i n t s , p o s s i b l y n o t even i n t h e same topographic bas in.

I n e s t a b l i s h i n g gauging s t a t i o n s under o r d i n a r y cond i t i ons , i t i s good p r a c t i c e t o l o c a t e t h e s t a t i o n s f a r enough a p a r t on the same stream so t h a t d i f f e r e n c e s i n r u n o f f , g e n e r a l l y c a l c u l a t e d on t h e b a s i s o f drainage areas, w i l l exceed t h e l i m i t s o f accuracy o f t he hydromet r ic ins t ruments and methods. In. k a r s t i c t e r r a n e , t h e same g u i d e l i n e a p p l i e s , except t h a t t h e emphasis must be on t h e a c t u a l d i f f e r e n c e s i n discharge, r a t h e r than on t h e d i f f e r e n c e s computed f rom changes i n drainage areas.

The s e l e c t i o n o f gaug ing-s ta t ion s i t e s should be made on t h e b a s i s o f t he a n a l y s i s o f a l l p o s s i b l e i n f o r m a t i o n rega rd ing t h e geology, c l ima te , physiography, and stream-flow v a r i a t i o n s o f t h e basin. Spec ia l reconnaissance surveys, a l s o known as seepage runs, p rov ide a d d i t i o n a l d e t a i l by e s t a b l i s h i n g p o i n t s where discharge i s l o s t o r gained a long t h e r i v e r ' s channel. The most accurate observa t ions a re ob ta ined d u r i n g low f l o w i n temperate c l ima tes and during moderate f l o w i n a r i d and semiar id c l imates. Such reconnaissance surveys a r e b e s t made under u n i f o r m weather cond i t i ons , and i d e a l l y by makinq a l l measurements a long t h e r i v e r s imultaneously. Th i s u s u a l l y i s i m p r a c t i c a l . The p r a c t i c a l approach i s t o take a l l p recaut ions needed t o p rov ide a good i n d i c a t i o n o f where gauges should be i n s t a l l e d . Reconnaissance surveys should be made b y teams composed o f a g e o l o g i s t t o i d e n t i f y p robab le p o i n t s o f s i n k i n g o r emerging water and t o no te t h e g e o l o g i c a l con tex t o f t h e p o i n t s where they occur; h y d r o l o g i s t , t o measure stream discharges; chemist t o sample and measure c r i t i c a l f i e l d c h a r a c t e r i s t i c s o f t h e q u a l i t y o f t h e water. I n areas where seasonal f l o w s v a r y g r e a t l y , reconnaissance surveys may be needed a t d i f f e r e n t t imes o f t h e year.

The preced ing d i scuss ion i n d i c a t e s some o f t h e d i f f i c u l t i e s i n l o c a t i n g stream-gauging s i t e s i n k a r s t i c ter ranes. Bear ing i n m i n d t he unusual c o n d i t i o n s i n areas o f carbonate rocks, i t i s s t i l l w e l l t o consider the m i n i m u m d e n s i t y o f stream-gauging s t a t i o n s i n hydrometr ic networks suggested by WMO (1965, p. III. 8 ) (see Table 6 . 7 - 2 ) .

Experiments w i t h t h e i n j e c t i o n o f t r a c e r m a t e r i a l s (spores, dyes, isotopes) i n t o k a r s t i c channelways may be u s e f u l i n p r o v i d i n g i n fo rma t ion , n o t o n l y on stream v e l o c i t y and d i r e c t i o n s o f f low, but a l s o rega rd ing poss ib le gauge s i t e s .

The a n a l y s i s o f i n f o r m a t i o n from a l l sources should p r o v i d e the b a s i s f o r c o r r e l a t i n g measured discharges down the r i v e r w i t h t h e p e c u l i a r i t i e s o f l i t h o l o g y , s t r u c t u r e s , and k a r s t i c phenomena. Th is a n a l y s i s i d e n t i f i e s zones o r p o i n t s o f i n f l o w and resurgence, t h e i r probable importance t o the year-around. f l u c t u a t i o n s i n r u n o f f , and t h e i r s i g n i f i c a n c e t o t h e o b j e c t i v e s o f t he i n v e s t i g a t i o n . T h i s a n a l y s i s a l s o makes i t p o s s i b l e t o i d e n t i f y gauge s i t e s most u s e f u l t o t h e i n v e s t i g a t i o n .

Under circumstances i t i s adv isab le t o e s t a b l i s h t u n o f f p l o t s on t y p i c a l s lope areas. Where l akes form permanent p a r t s o f t h e sur face water regime o f a k a r s t i c area, p r o v i s i o n should be made t o observe lake-water l e v e l s , i n f l o w , out f low, p r e c i p i t a t i o n , and evapora t ion from b o t h t h e water sur face and the ad jacent b a s i n and temperature, q u a l i t y o f water and i c e phenomena.

240

Table 6.1-2. Suggested m i n i m u m d e n s i t y o f hydromet r ic networks, a f t e r WMO, 1 9 6 5 .

Range o f norms Range o f p r o v i s i o n a l f o r m i n i m u m norms t o l e r a t e d i n network d i f f i c u l t c o n d i t i o n s LI

Area i n km2 f o r Area i n km2 f o r Type o f Region one s t a t i o n one s t a t i o n

I. F l a t r e g i o n o f temperate, mediterranean and t r o p i c a l zones

II. Mountainous reg ions o f temperate, mediterranean and t r o p i c a l zones.

III. A r i d and p o l a r zones 2-1

1,000-2,500

3 Q O - 1 , O O O

5,000-20,000 31

3,000-10,000

1,000-5,000 - 4 1

- 11

- 2 1

- 3 1 Depending on f e a s i b i l i t y .

- 4 1 Under ve ry d i f f i c u l t c o n d i t i o n s t h i s may extend t o 20,000 kma.

L a s t f i g u r e o f t h e range should be t o l e r a t e d o n l y under e x c e p t i o n a l l y d i f f i c u l t cond i t i ons .

Great dese r t s a r e n o t inc luded.

2 4 1

Temporary o r ephemeral k a r s t i c lakes may be more d i f f i c u l t t o mon i to r because permanent i n s t a l l a t i o n may seem t o be l e s s w e l l j u s t i f i e d , b e i n g used o n l y p a r t o f a year o r f o r o n l y a few years i n a row. Under these circumstances every e f f o r t should be made t o p rov ide good topographic maps o f t he p e r i o d i c a l l y inundated area, a m o n i t o r i n g system t o gauge t h e r i s e , f a l l and f l u c t u a t i o n s o f t h e lake, and measurements o f water temperature and chemical composi t ion o f t h e water. Groundwater l e v e l s i n ad jacent areas should be monitored.

I n o rde r t o assess t h e d i f f e r e n c e s between r u n o f f c h a r a c t e r i s t i c s i n k a r s t i c and non-ka rs t i c t e r ranes , comparable bas ins i n two phys iograph ic areas must be instrumented and monitored. Such comparative s t u d i e s should e s t a b l i s h t h e key parameters r e l a t i n g r i v e r r u n o f f t o topography and geology.

6.7.4 Evapora t ion and r e l a t e d me teo ro log i ca l observat ions. Evaporat ion i s perhaps t h e most e l u s i v e aspect of t h e hyd ro log i c c y c l e t o measure. Most o f t h e i n s t r u m e n t a t i o n a t a wel l -equipped weather s t a t i o n i s t h e r e main ly t o p rov ide d i r e c t and i n d i r e c t approaches t o t h i s d i f f i c u l t problem. The d i r e c t methods i n c l u d e pan-evaporation and l ys ime te rs . I n d i r e c t methods are based on p r e c i p i t a t i o n , temperature, humid i t y , a i r pressure, vapor pressure, w i n d c h a r a c t e r i s t i c s , and on energy budget measurements and c a l c u l a t i o n s . .In areas o f carbonate rocks , as s t a t e d e a r l i e r , i t i s impor tan t t o measure evapora t ion d i r e c t l y because t h e sur face and subsurface parameters may n o t be comparable. Otherwise, t h e b a s i c standard techniques apply (WMO, 1965, p. II. 20 - II. 2 8 and p. III. 5 ) .

I t i s a l s o impor tan t under some circumstances t o measure evapora t ion i n the subsurface, p a r t i c u l a r l y i n rega rd t o a combination o f in te rconnected sur face and subsurface storage i n lakes and r e s e r v o i r s .

The d i s t r i b u t i o n and number o f s t a t i o n s designated t o o b t a i n evapora t ion measurements o r es t imates w i l l va ry w i t h t he i ns t rumen ta t i on . F u l l y equipped meteo ro log i ca l s t a t i o n s ( w i t h evapora t ion pans) should have no lower d e n s i t y than suggested f o r p r e c i p i t a t i o n networks i n Table 6.7-1: l y s i m e t e r s t a t i o n s , i f they a re deemed necessary and do n o t o therw ise reduce funds a v a i l a b l e f o r s imp ler i ns t rumen ta t i on , may be l o c a t e d on a f a r wider g r i d .

6.7.5 I n f i l t r a t i o n and i n f l o w . The o r d i n a r y d i f f i c u l t i e s o f t he study o f water movement i n and th rough the unsatura ted zone a re made s t i l l more d i f f i c u l t by t h e combination o f i n f i l t r a t i o n and i n f l o w i n k a r s t i c areas. Observat ions o f b o t h o f these types o f f l o w should be i nc luded i n the program o f an h y d r o l o g i c a l i n v e s t i g a t i o n .

I n f i l t r a t i o n and i n f l o w o f r a i n f a l l and snowmelt t o t h e unsatura ted zone are s t u d i e d t o eva lua te t h e amounts o f water d i v e r t e d t o t h e subsurface: t h e losses by which over land f l o w i s decreased w i l l i d e n t i f y t he c h a r a c t e r i s t i c s o f t h i s recharge and p r o v i d e i n f o r m a t i o n f o r t he management o f water i n the bas in.

The i n f i l t r a t i o n va lue i n t h e unsatura ted zone may be determined during r e g u l a r observa t ions o f s o i l moisture, performed f o r water balance i n v e s t i g a t i o n s i n the bas ins. D e t a i l e d i n v e s t i g a t i o n s o f i n f i l t r a t i o n should be done i n s p e c i a l l y s i m e t e r s by i n f i l t r o m e t e r s o r by s p r i n k l i n g . Where groundwater recharge r e s u l t s o n l y from i n f i l t r a t i o n i t s e f f e c t may be computed u s i n g da ta on water t a b l e f l u c t u a t i o n s .

The d i s t r i b u t i o n o f p o i n t s f o r i n f i l t r a t i o n measurements i n a study area i s based on t h e same genera l p r i n c i p l e s used f o r o t h e r k i n d s o f h y d r o l o g i c a l observat ions. These measurement s i t e s should be l o c a t e d t o t i e c l o s e l y t o s i t e s f o r groundwater observat ions.

I n i l o w u s u a l l y occurs a t h i g h l y l o c a l i z e d p o i n t s , such as ponors, o r a long l i n e a r fea tu res such as f i ssu res . I n most areas the topography i s rugged, and i t i s d i f f i c u l t t o l oca te , observe, and measure t h e i n f l o w .

Rates and volumes of i n f i l t r a t i o n may be es t imated from anomalies i n the computation of r e l a t i o n s h i p s between p r e c i p i t a t i o n and over land f l o w and from seasonal f l u c t u a t i o n s o f water l e v e l s i n w e l l s and underground c a v i t i e s .

6.7.6 Springs. Spr ings i n k a r s t i c areas can p rov ide da ta f o r t h e q u a n t i t a t i v e e v a l u a t i o n o f t h e dynamics o f groundwater flow, o f f l o w i n t h e unsatura ted

2 4 2

zone, o f t h e charac ter o f t h e r e l a t i o n s h i p between sur face and subsurface waters, and o f groundwater recharge t o streams. Ana lys i s o f t h e r e l a t i o n s h i p between s p r i n g discharge and p r e c i p i t a t i o n may be used t o determine storage c a p a c i t i e s and r e t e n t i o n r a t e s i n t h e b a s i n above t h e spr ing.

A l l sp r ings i n a study area should be i n v e n t o r i e d and have t h e i r p h y s i c a l and chemical c h a r a c t e r i s t i c s measured a t l e a s t once. Large sp r ings may war ran t permanent measurement i n s t a l l a t i o n s (wei rs , stage gauges, e tc . ) and r e g u l a r o r continuous mon i to r ing . Spr ings o f moderate s i z e and c e r t a i n l y t y p i c a l sp r ings i n d i f f e r e n t hyd rogeo log ica l s e t t i n g s should be mon i to red r e g u l a r l y on a schedule ad jus ted t o l o c a l f l u c t u a t i o n s . Water temperature, pH, s p e c i f i c c o n d u c t i v i t y , and tu rb id i ty should be measured i n the f i e l d c o n c u r r e n t l y w i t h a l l d ischarge measurements. Chemical q u a l i t y and sediment conten t shou ld be measured as f r e q u e n t l y as needed. Ana lys i s o f f i e l d da ta w i l l q u i c k l y i n d i c a t e which spr ings deserve d e t a i l e d chemical analyses, how f requen t l y , and how long.

Temporal v a r i a t i o n s i n d ischarge p rov ide da ta f o r d e r i v i n g c o e f f i c i e n t s o f dynamics o f t h e groundwater f l o w by showing t h e r a t i o o f maximum and m i n i m u m discharges f o r se lec ted t ime i n t e r v a l s (day, month, season, y e a r ) .

I n general , methods f o r ana lyz ing s p r i n g regimes do n o t d i f f e r f rom t h e methods f o r ana lyz ing stream f low. Together w i t h a n a l y t i c a l p rocess ing o f data on o t h e r f i e l d parameters, t hey p r o v i d e data f o r p l o t t i n g p r e c i p i t a t i o n - r u n o f f r e l a t i o n s h i p diagrams and c o r r e l a t i o n s between s p r i n g discharge and o t h e r f a c t o r s a f f e c t i n g groundwater f l o w such as evaporat ion, water l e v e l s , e t c .

6 . 7 . 7 Groundwater observat ions. Groundwater observa t ions a r e aimed a t o b t a i n i n g * q u a n t i t a t i v e i n f o r m a t i o n rega rd ing t h e groundwater resources and toward de termin ing t h e i n t e r r e l a t i o n s h i p s o f groundwater f l u c t u a t i o n s t o stream f l o w and t o k a r s t i c development.

K a r s t i c water regimes a re remarkable f o r t h e i r g r e a t v a r i e t y , steep gradients , and r a p i d r e a c t i o n t o p r e c i p i t a t i o n . The l o c a t i o n and d e n s i t y o f groundwater observa t ion s t a t i o n s , i n t h e form o f w e l l s , subsurface caverns and channels, and spr ings, must be determined by l o c a l cond i t i ons . A t t h e beg inn ing o f an i n v e s t i g a t i o n , t h e r e must be an assessment o f a l l a v a i l a b l e l o c a l i n fo rma t ion , i n c l u d i n g maps o f a l l types so as t o determine gauge s i t e l o c a t i o n s and f i e l d procedures. I f t h e i n f o r m a t i o n i s inadequate i t may be necessary t o i n i t i a t e f i e l d reconnaissances, such as seepage runs, a e r i a l photography, and remote sensing surveys. However, these should be undertaken o n l y a f t e r thorough rev iew o f e x i s t i n g i n fo rma t ion .

P iezomet r ic l e v e l obse rva t i on s t a t i o n s ( w e l l s ) shou ld be s i t e d wherever the physiography appears t o i n d i c a t e d i s t i n c t i v e se ts o f sur face and groundwater cond i t i ons . I n p a r t i c u l a r , cons ide r ing t h e s t r a t i f i e d development o f k a r s t s , t h e r e should be i n d i v i d u a l observa t ion w e l l s f o r every a q u i f e r .

P iezomet r ic s t a t i o n s may be e s t a b l i s h e d i n d i v i d u a l l y o r i n groups, o r one c a r e f u l l y cons t ruc ted w e l l may be used t o measure water l e v e l s i n s e v e r a l zones. Where a p a t t e r n o r group o f observa t ion w e l l s i s es tab l i shed , t h e w e l l s may be s i t u a t e d a t t h e corners o f a t r i a n g l e ( t h r e e w e l l s ) , o r o f a square ( f i v e w e l l s - i . e . f o u r w e l l s a t t h e corners and one w e l l i n t h e c e n t e r ) . Such a b a t t e r y o f w e l l s can p r o v i d e water l e v e l f l u c t u a t i o n s da ta u s e f u l f o r t h e hydrodynamic a n a l y s i s o f water l e v e l f l u c t u a t i o n s and t h e i d e n t i f i c a t i o n o f f l o w g rad ien ts and d i r e c t i o n s . P iezomet r ic s t a t i o n s a l s o should be l o c a t e d a t o r c lose t o stream-gauging s t a t i o n s so as t o eva lua te r e l a t e d groundwater and sur face water discharges. Where poss ib le , p iezomet r i c s t a t i o n s equipped t o measure water l e v e l f l u c t u a t i o n s should be e s t a b l i s h e d i n l a r g e subsurface c a v i t i e s , e s p e c i a l l y i f these c a v i t i e s a re connected w i t h a r i v e r .

I n a d d i t i o n , wherever poss ib le , e x i s t i n g o r new w e l l s shou ld be test-pumped t o determine l o c a l shor t - te rm and long-term c o e f f i c i e n t s o f s to rage and t r a n s m i s s i v i t y . Such t e s t s shou ld i n c l u d e c a r e f u l a t t e n t i o n t o r a t e s and amounts o f water t a b l e d e c l i n e s i n obse rva t i on w e l l s , t o t h e e f f e c t o f t h e t e s t on nearby stream f lows, and t o t h e e f f e c t on known underground channels f lows. I n a d d i t i o n , recovery r a t e s should be mon i to red a t a l l obse rva t i on p o i n t s es tab l i shed f o r t he pumping t e s t . Be fore i n i t i a t i n g a d i scha rge - tes t i ng program, a l l a v a i l a b l e i n f o r m a t i o n on l o c a l rock and fo rma t ion p e r m e a b i l i t y must be taken t o assure t h a t : (1) t h e t e s t i n g program i s adequate t o measure the r jrobable t r a n s m i s s i v i t y , and ( 2 ) t h a t i t i s n o t excess i ve l y more than adequate. I t i s a waste of e f f o r t t o a t tempt t o t e s t a h i g h l y permeable

243

a q u i f e r w i t h a sma l l pump; i t i s an e q u a l l y w a s t e f u l e f f o r t t o i n s t a l l a l a r g e pump t o t e s t a p o o r l y permeable s e c t i o n o f rock. I n k a r s t i c carbonate rocks, where abrupt v e r t i c a l and h o r i z o n t a l changes a re common, i t i s necessary t o a d j u s t standard pumping t e s t s t o l o c a l cond i t i ons .

Th9 program o f observa t ions f o r p iezomet r i c s t a t i o n s should i n c l u d e measurement o f water temperatures and water q u a l i t y , i n c l u d i n g chemical composit ion, p h y s i c a l c h a r a c t e r i s t i c s , and sediment load.

Water temperature should be measured a t d i f f e r e n t depths and w i t h i n t h e d i f f e r e n t a q u i f e r s . Water temperatures p rov ide e x c e l l e n t c l u e s t o , and and may he used as t h e b a s i s f o r , e s t i m a t i n g r a t e s o f water exchange w i t h i n and between a q u i f e r s and between subsurface and sur face water. Observat ions o f water q u a l i t y make i t p o s s i b l e t o determine l o c a l s i t e s o f s o l u t i o n , t o i d e n t i f y exchanges between and among ground and sur face waters, and t o i d e n t i f y l e v e l s and sources o f p o l l u t i o n .

A comprehensive a n a l y s i s f rom p iezomet r i c and o t h e r hydrogeo log ica l s t a t i o n s makes i t p o s s i b l e t o a r r i v e a t q u a n t i t a t i v e es t imates o f groundwater storage and movement, i t s d i r e c t i o n s o f f l o w and i t s seasonal v a r i a t i o n s . Moreover, t h e da ta p r o v i d e a b a s i s f o r c o r r e l a t i n g groundwater l e v e l s and p r e c i p i t a t i o n , stream l e v e l s , and i n f l o w losses through f i s s u r e s and o the r openings, as w e l l as o t h e r me teo ro log i ca l and phys iograph ic f a c t o r s .

6.7.8 I n t e r p r e t a t i o n and p r e s e n t a t i o n o f r e s u l t s . I n t e r p r e t a t i o n o f t he cumula t ive h y d r o l o g i c a l observa t ions made during an i n v e s t i g a t i o n ,should p r o v i d e q u a n t i t a t i v e approximat ions o r es t imates o f t h e i n d i v i d u a l elements o f t h e water regime i n s p e c i f i c t ime i n t e r v a l s , t h e i r i n t e r r e l a t i o n s h i p s , and t h e dynamic sequence o f t h e i r s p a t i a l and temporal v a r i a t i o n s . However, observed and c a l c u l a t e d sequences of h y d r o l o g i c a l events do n o t always co inc ide. I n sho r t , our techniques a re n o t always adequate t o so lve t h e problem. Th is s i t u a t i o n has been w e l l summarized by Eagleson (1970, p. 8-9) as fo l l ows :

' I n p r i n c i p l e , these r e l a t i o n s h i p s a re p rov ided i n a l l cases by s o l u t i o n o f t h e complete equat ions of momentum, energy, mass, and s ta te . I n p r a c t i c e , however, our f o r m u l a t i o n o f these equat ions i s inaccurate, owing i n t h e ve ry l e a s t , t o :

1. Inadequate knowledge o f p h y s i c a l behavior: 2. Unknown system he te rogene i t i es and an iso t rop ies ; 3. Unknown t ime dependence o f system parameters; 4. Approximations i n t roduced f o r computat ional economy.' 'For these reasons t h e r e i s o f t e n a h i g h l y v a r i a b l e d i f f e r e n c e

between t h e observed and c a l c u l a t e d behav io r o f hyd ro log i c processes under t h e same e x c i t a t i o n . T h i s leads many h y d r o l o g i s t s t o abandon t h e causal d e t e r m i n i s t i c f o r m u l a t i o n o f process behav io r i n favo r o f a noncausal s t o c h a s t i c r e p r e s e n t a t i o n o f t h e ou tpu t v a r i a b l e which omi ts any cons ide ra t i on o f process dynamics. The u t i l i t y o f b o t h approaches can be be apprec ia ted by examining i n more d e t a i l t h e major ca tegor ies o f h y d r o l o g i c problems:

1 I.

2.

3.

Mean values. These a re the problems o f concern t o water resource p lanners and p o l i c y makers and i n v o l v e monthly, seasonal, annual, o r o t h e r long-term t ime averages o f p r e c i p i t a t i o n , stream f low, evaporat ion, groundwater l e v e l , e t c . which a re themselves s p a t i a l averages over geographical areas o f t e n so l a r g e as t o be c l i m a t o l o g i c a l l y , g e o l o g i c a l l y , and t o p o g r a p h i c a l l y heterogeneous. Extreme values. Maximum o r m i n i m u m va lues o f p r e c i p i t a t i o n , stream f low, r i v e r stage, groundwater l e v e l , e tc . , a re s u a l l y t h e c r i t e r i a which, along w i t h economics, determine the h y d r a u l i c eng ineer ing s p e c i f i c a t i o n s f o r s p i l l w a y s i z e and e l e v a t i o n s , levee and f l o o d w a l l he igh t , pump s i z e s and pumping r a t e s , b r i d g e openings and e leva t i ons , c u l v e r t s izes, r e s e r v o i r volume, storm i n l e t s and sewer s izes, water-treatment f a c i l i t i e s , i r r i g a t i o n works, and many o t h e r design problems. Time h i s t o r i e s . O p t i m i z a t i o n o f t h e design and opera t i on o f systems o f h y d r a u l i c s t ruc tu res , as w e l l as rea l - t ime fo recas t i ng , o f t e n r e q u i r e s t h e complete t ime h i s t o r y o f t he response o f a h y d r o l o g i c system t o some p a r t i c u l a r e x c i t a t i o n . '

2 4 4

'Problems i n category 3 r e q u i r e s i m u l a t i o n o f t h e system dynamics, w h i l e problems i n ca tegor ies 1 and 2 can u s u a l l y be handled adequately by cons ide r ing o n l y t h e s t a t i s t i c s o f t h e h y d r o l o g i c v a r i a b l e i n quest ions. However, i n t h e l a t t e r case, these v a r i a b l e s a re o f t e n t h e dependent ( i .e., "ou tpu t " ) v a r i a b l e s o f a n o n l i n e a r h y d r o l o g i c h y d r a u l i c system, t h e parameters o f which are i n c r e a s i n g l y s u b j e c t t o change b y man. I t then becomes convenient i n these problems, a lso, t o o b t a i n t h e d e s i r e d "ou tpu t " s t a t i s t i c s by pass ing t h e s t a t i s t i c ' s o f t h e independent ( i .e . , " input") v a r i a b l e through a s i m u l a t i o n o f t h e system dynamics.' One o f t h e standard devices f o r o b t a i n i n g a genera l o v e r a l l i n t e r p r e t a t i o n

o f t h e h y d r o l o g i c a l observa t ions balance equat ion i s t h e water i n a p a r t i c u l a r r i v e r b a s i n o r i n a c h a r a c t e r i s t i c b a s i n area. I n t h e water balance equat ion, t h e volumes o f i n d i v i d u a l elements i n v o l v e d a re g i ven f o r a s p e c i f i c t ime unit , u s u a l l y a month o r a year. The method uses mean va lues and presents a s t a t i c format which i s u s e f u l f o r many p l a n n i n g purposes. Combined w i t h more s u b j e c t i v e i n s i g h t ob ta ined from f i e l d observa t ions o f t h e h y d r o l o g i c a l phenomena, t h e water balance method o f t e n p rov ides a p r e l i m i n a r y i n s i g h t i n t o the processes and dynamics. Some b e l i e v e i t i s t h e most u s e f u l a n a l y t i c a l t o o l we have, but i f t h i s i s so, i t i s a r e f l e c t i o n o f t he p resen t l i m i t s o f our understanding o f hydrodynamics under f i e l d cond i t i ons .

Nonetheless, i t i s t r u e t h a t i n many ins tances t h e water balance method prov ides a ready means t o e s t a b l i s h r e g i o n a l r e l a t i o n s h i p s between i n d i v i d u a l water balance elements and f a c t o r s such as a l t i t u d e , b a s i n exposure towards t h e p r i n c i p a l d i r e c t i o n o f a i r masses, d i s tance from t h e sea, percentage o f k a r s t i n the basin, e t c .

The e f f e c t o f k a r s t on t h e i r r u n o f f c h a r a c t e r i s t i c s may be made by comparing the a c t u a l r u n o f f from t h e k a r s t i f i e d area w i t h t h e r u n o f f va lues ob ta ined th rough water balance i n v e s t i g a t i o n s o f non -ka rs t i c bas ins under s i m i l a r phys iograph ic fea tu res ( e l e v a t i o n , drainage area, e t c . ) .

The i d e n t i f i c a t i o n o f t h e genera l s t a t i s t i c a l r e l a t i o n s h i p s between sur face and subsurface waters i n k a r s t i c bas ins i s p a r t i c u l a r l y u s e f u l i n t h e a n a l y s i s o f h y d r o l o g i c a l obse rva t i on r e s u l t s . Among t h e r e l a t i o n s h i p s t o be examined are: comparison o f measured water discharges over t h e r i v e r length; stream discharge r e l a t i v e t o water l e v e l f l u c t u a t i o n s ; comparison o f stream hydrographs i n t h e bas in; r e l a t i o n s h i p s o f k a r s t s p r i n g discharge and underground f low. P r e l i m i n a r y s t a t i s t i c a l comparisons should be checked aga ins t computation o f t h e hydrodynamic r e l a t i o n s h i p s , h e a t f l o w i n f l u e n c e , and the hydrochemical dynamics. A l l these w i l l make i t p o s s i b l e t o determine o b j e c t i v e l y t h e n a t u r e and t h e r a t e o f i n t e r r e l a t i o n s h i p s o f stream and groundwater regimes.

Discharge c h a r a c t e r i s t i c s o f t h e k a r s t areas and t h e i r water balance components should be summarized u s i n g mean long-term and extreme va lues f o r va r ious p e r i o d s o f t ime.

Because o f t h e high degree o f v a r i a b i l i t y i n t h e sur face ' and subsurface water regimes i n k a r s t i c reg ions, care should be taken t o a v o i d e x t r a p o l a t i n g l o c a l l y d e r i v e d parameters i n t o s u p e r f i c i a l l y s i m i l a r areas where t h e parameters may n o t be v a l i d . Al though t h e s p e c i a l o b j e c t i v e s o f an i n v e s t i g a t i o n w i l l determine a r e p o r t ' s p r i n c i p a l recommendations, i t o f t e n i s w e l l t o p resen t observa t ions o r recommendations on p r a c t i ' c a l aspects n o t necessa r i l y c e n t r a l t o t h e purpose o f t h e study. Such observa t ions m i g h t concern stream f l o w c o n t r o l , p r o t e c t i o n o f water q u a l i t y , .water use, a r t i f i c i a l recharge and t h e u t i l i z a t i o n o f k a r s t c a v i t i e s f o r purposes such as water and waste storage o r s u i t a b i l i t y o f p r e s e r v a t i o n as n a t i o n a l he r i t ages .

The g e n e r a l i z a t i o n should r e s u l t i n t h e r e g i o n a l i z a t i o n o f k a r s t areas according t o environmental c o n d i t i o n s and key f a c t o r s .

Wherever poss ib le , t h e r e s u l t s o f t h e i n v e s t i g a t i o n should i n d i c a t e whether an area i s r e p r e s e n t a t i v e of s i m i l a r t e r ranes and t h e e x t e n t t o which i n fo rma t ion can be e x t r a p o l a t e d t o ad jacent areas and o t h e r reg ions.

Two examples of t h e use o f h y d r o l o g i c a l methods i n i n v e s t i g a t i o n s o f k a r s t i c areas a re g i ven below:

Example 1. A long-term water-balance i n v e s t i g a t i o n was c a r r i e d o u t i n a k a r s t e d h igh land composed o f Ordov ic ian do lomi tes and l imestones (see F i g u r e 6.7-1) i n o rde r t o determine t h e amount o f p r e c i p i t a t i o n l o s t by recharge through i n f i l t r a t i o n and i n f l o w t o t h e deep a q u i f e r s t h a t were n o t d ra ined by r i v e r s .

245

- boundaries of karst area; area of interior surface drainage

endorheic part of the highland t gauging station

0 meteorological station

H evaporation plot

0 observation well

F igure 6 . 7 - 1 D i s t r i b u t i o n scheme o f gauging s t a t i o n s on r i v e r s d r a i n i n g h igh land C.

2 4 6

The c e n t r a l p a r t o f t h e h igh land, compris ing about 1000 kmz, i s dry . P r e c i p i t a t i o n i s completely absorbed, a l though a few streams o r i g i n a t e on the h i g h l a n d margin where t h e l imestones and do lomi tes come i n c o n t a c t w i t h non-kars t i c rocks.

To so lve the problem w i t h i n t h e k a r s t area ( 3 0 1 3 kmz) o f t he h igh land, t he f o l l o w i n g parameters were observed:

1. P r e c i p i t a t i o n and o t h e r me teo ro log i ca l elements a t e i g h t me teo ro log i ca l s t a t i o n s ;

2 . Discharge o f sp r ings and sur face f l o w a t 11 streams and r i v e r s f l o w i n g down t h e highland;

3. Evapora t ion from s o i l i n the f o r e s t and i n t h e f i e l d and from snow cover on two evapora t ion p l o t s where condensation was a l s o monitored;

4 . Groundwater f l u c t u a t i o n s a t a network o f obse rva t i on w e l l s . The water-balance components o f t h e h i g h l a n d C were es t imated and g i ven i n

terms o f mean annual depths i n m i l l i m e t e r s f o r 1951-1962. P r e c i p i t a t i o n was presented as t h e a r i t h m e t i c a l mean o f data from e i g h t s t a t i o n s . Other f a c t o r s were t o t a l d ischarge o f sp r ings and t o t a l annual f low, s o i l evapora t ion and condensation (mean va lue by t h e data from two evapora t ion p l o t s ) , changes o f groundwater storage (accord ing t o groundwater l e v e l f l u c t u a t i o n s and water y i e l d c o e f f i c i e n t ) , and groundwater i n t a k e (see Table 6 . 7 - 3 ) .

The volume o f water b e i n g recharged t o t h e deep a q u i f e r s n o t d ra ined by r i v e r s was c a l c u l a t e d as t h e d i f f e r e n c e between i n f l o w i n g and o u t f l o w i n g components o f water balance.

Example 2.. I n b a s i n K (see F i g u r e 6.7-2) , t h e lower reach o f t h e r i v e r i s i n h e a v i l y f i s s u r e d and k a r s t e d l imestones o f Midd le and o f Upper Devonian and o f Carboni ferous ages. I n v e s t i g a t i o n s were made t o determine r u n o f f losses w i t h i n t he k a r s t e d zone. The carbonate rock sequence i s now be ing k a r s t i f i e d .

To study the water regimes, f o u r gauges were e s t a b l i s h e d i n t h e channel o f t he r i v e r K: gauge I, above t h e k a r s t e d zone, gauges II and III, above and below the reach o f t he most i n t e n s i v e channel f l o w absorpt ion; and gauge I V , a t t h e r i v e r mouth, where long-term stage and water discharge mea.surements a re made.

W i t h i n t h e k a r s t e d p a r t o f r i v e r K ' s bas in, t h e mean annual water recharge was found t o be 1,200,000 m3. Recharge o c c u r r i n g between t h e gauges II and III was 544,000 m3, and between gauges III and I V , 500,000 m3 (see Table 6 .7 -4 ) .

The average long-term r u n o f f losses i n t h e b a s i n o f r i v e r K were es t imated by comparing the observed mean annual r u n o f f (M) o f r i v e r K w i t h an es t imated r u n o f f (M,) f o r a non -ka rs t i c b a s i n o f t h a t s ize.

M,=M,-M (Rlsec p e r k m z ) (6 .7-2)

V=Mz*A-3.15*103 m3/year (6.7-3)

V = recharge volume A = drainage area

The r u n o f f (M,) f o r t h e b a s i n was es t imated on t h e b a s i s of d ischarge

Est imated average annual recharge f o r a p e r i o d o f 1 5 years i s shown i n f o r t he upper non -ka rs t i c p a r t o f t h e b a s i n as measured a t gauge 1.

Table 6.7-4.

6.8 Water balance c a l c u l a t i o n s (Habib Z e b i d i and H. Schoel ler )

Q u a n t i t a t i v e s tud ies o f carbonate rock a q u i f e r s t h a t r e l a t e t o t h e i r e x p l o i t a t i o n and augmentation o f t h e resources a r e considered i n t h i s sect ion. W e l l d e l i m i t e d s t ruc tu res , i n area and w i t h rega rd t o t h e i r hydrogeologic cond i t i ons a re favorab le f o r q u a n t i t a t i v e ana lys i s . A p a r t i c u l a r example i s t h e case o f perched sync l i nes where the e x t e n t o f t h e a q u i f e r and a l l o f i t s d ischarge p o i n t s a re f u l l y known so t h a t t h e r e remains no u n c e r t a i n t y as t o t h e way the h y d r a u l i c system func t i ons .

Methods o f i n v e s t i g a t i o n are r e l a t e d t o t h e ex i s tence o f piezometers o r o f boreholes t h a t can g i v e complete i n f o r m a t i o n a long w i t h r e g u l a r measurements o f t he n a t u r a l d ischarges t h a t a r e more commonly used.

247

12 Il 10 9 8

Distance from the mouth 7 6 5 4 3 2 1 km

0 karsted rocks tectonic disturbance

a non karstic rocks a karst cavity

ground flow direction ea gauging station

spring

F igu re 6.7-2 Graph o f v a r i a t i o n s o f low f l o w s p e c i f i c d ischarges down the r i v e r l e n g t h and d i s t r i b u t i o n scheme o f temporary gauging s ta t i ons .

2 4 8

Table 6.7-3. Water balance components ( i n mm) i n t h e h i g h l a n d C.

I n f l o w Out f low

E f fec- Change Evapo- Water t i v e o f

Discharge r a t i o n Con- i n f i l - ground Recharge P r e c i p i - Conden- ------------------- from sump- t r a - water o f deep t a t i o n s a t i o n Spr ings Streams s o i l t i o n t i o n storage a q u i f e r

+655 +45 -234 -17 - 4 3 1 -2 +16 +6 2 2

Table 6.7-4. Losses o f r u n o f f i n t h e k a r s t e d area o f t he r i v e r b a s i n K.

Es t imate o f Runoff losses Percent Recorded r u n o f f f o r ........................

Gauging area, k a r s t , "M" rocks, M, Recharge M, volume "V" s t a t i o n kmz "A" % 111 sec/km2 k l sec/km2 klseclkma m, I year

Drainage age o f r u n o f f , non -ka rs t i c Recharge

1 44 .O O 8.4 8.4 - - 2 5 5 .O 8 7.5 8.4 0.9 156,000

3 59.8 1 8 4.7 8.4 3.7 700,000

4 6 8 . 1 25 2.8 8.4 5.6 1,200,000

2 4 9

Examples g i ven a re based on geo log ic s t r u c t u r e s i n T u n i s i a w i t h r e l a t i v e l y s imple outcrops. The genera l case s t a r t s w i t h t h e o v e r a l l water balance and t h e es tab l i shment o f a s imple r e l a t i o n s h i p between t h e p r e c i p i t a t i o n and the i n f i l t r a t i o n .

6 .8 .1 General case o f o v e r a l l water balance. I t i s necessary t o measure o r t o c a l c u l a t e t h e d i f f e r e n t components o f t he balance comprised i n t h e genera l equat ion :

where P = average annual I = average annual R = average annual

E. = averaae annual

P = I + R + E t

p r e c i p i t a t i o n i n m i l l i m e t e r s i n f i l t r a t i o n i n m i l l i m e t e r s r u n o f f i n m i l l i m e t e r s evapo t ransp i ra t i on i n m i l l i m e t e r s

(6.8-1)

f o r ax m i n i m u m p e r i o d o f o i e year -over a geohydrologic s t r u c t u r e o f which a l l t he elements a re known i n c l u d i n g :

1. t h e areas o f t he h y d r o l o g i c and geohydrologic drainage basins; 2. t h e e x t e n t and the th i ckness o f t h e rocks p r o v i d i n g storage space: 3. t h e discharge p o i n t s and f u t u r e e x p l o i t a t i o n by w e l l s o r g a l l e r i e s . The components o f t h e water balance can be ob ta ined as fo l l ows : 1. R a i n f a l l . I t i s necessary t o have a r e l a t i v e l y dense network o f

s t a t i o n s and, i f poss ib le , t o a l l o w f o r f l u c t u a t i o n s owing t o t h e season and t o t h e a l t i t u d e g rad ien t . I f poss ib le , c o r r e l a t i o n w i t h longer pe r iods o f measurement w i l l e s t a b l i s h t h e s i n g l e year under study i n a more genera l framework than p rov ided by t h e long-term average.

2. I n f i l t r a t i o n . I n f i l t r a t i o n i s equal t o t h e y i e l d from t h e n a t u r a l o r a r t i f i c i a l d ischarge p o i n t s . I t i s necessary t o determine t h e y i e l d o f t he sp r ings during t h e study pe r iod , i n c l u d i n g t h e m i n i m u m and f l o o d discharges. I t i s w i t h respec t t o t h a t t h a t t he annual type o f water balance i s commonly weak; i t does n o t always a l l o w f o r changes i n t h e discharge p o i n t s between the beg inn ing and t h e end o f t he p e r i o d under study. Hence, i t i s necessary t o i n t roduce a c o r r e c t i n g f a c t o r t o take note o f t h e s t a t e of t h e reserves a t t he s t a r t o f t h e year under study o r t o extend t h e observa t ions over a much longer p e r i o d t o o b t a i n average values.

3 . Evapo t ransp i ra t i on . Th is i s c e r t a i n l y t h e f a c t o r t h a t i s most d i f f i c u l t t o o b t a i n so i t i s g e n e r a l l y c a l c u l a t e d from some e m p i r i c a l formula; thus i n t r o d u c i n g a margin o f e r r o r . I n Tun is ia , and i n p a r t i c u l a r i n the n o r t h c o a s t a l zone where t h e average annual r a i n f a l l exceeds 300 m i l l i m e t e r s , t he Turo formula, which g i ves t h e a c t u a l evapo t ransp i ra t i on i n terms o f t he r a i n f a l l and o f t h e average annual temperature, t h e r e s u l t s a re s u f f i c i e n t l y concordant t o be quoted here.

4. Runoff. I n carbonate rock format ions, t h e sur face r a r e l y needs t o be considered s ince t h e p r e c i p i t a t i o n pe rco la tes downward as soon as the p r e c i p i t a t i o n occurs; moreover, carbonate rock outcrops are g e n e r a l l y covered by a j o i n t system ( l a p i a z ) t h a t f avo rs i n f i l t r a t i o n . Nevertheless, c o n d i t i o n s f a v o r i n g r u n o f f can occur, n o t a b l y when p r e c i p i t a t i o n f a l l s w i t h such high i n t e n s i t i e s as t o be absorbed by t h e carbonate rock o n l y w i t h d i f f i c u l t y . A t t e n t i o n i s g i ven here t o t h i s f a c t o r so as t o ma in ta in the genera l charac ter o f t h e water balance.

Example. a t D j e b e l Bargou (Tun is ia ) , (H. Zebedi, 1963) . The D j e b e l Bargou i s a dome o f Ap t ian organ ic l imestone i n Central. Tun is ia

about 100 km southwest o f Tunis. I t i s composed o f two a n t i c l i n a l f o l d s enc los ing a w e l l - d e f i n e d s y n c l i n a l g u t t e r ( d r a i n ) , where t h e l imestones r e s t on a t h i c k substratum o f marls, and c o n t a i n an underground f l o w which discharges (see F i g u r e 6.8-1) through two p r i n c i p l e spr ings: A i n Bou Saadia and A i n Faouar .

The study i s based on the behav io r o f t h i s g u t t e r as measurements cover a p e r i o d o f t e n years ( 1 9 4 9 / 5 0 t o 1 9 5 9 / 6 0 ) and a l l o w changes i n groundwater storage t o be e l im ina ted .

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Geolog ica l and topograph ica l c h a r a c t e r i s t i c s : km2 Area o f t h e hyd ro log i c drainage basin...................... 55.5

Area of carbonate rock outcrops. ........................... 19.0 Area o f m a r l outcrops ...................................... 13.0 Area covered by Quaternary depos i ts ........................ 23.5

Annual volume o f p r e c i p i t a t i o n .......................

Average a l t i t u d e o f t h e drainage basin..................... 800m

R a i n f a l l : 42.6x106m3

Annual volume f a l l i n g on t h e l imestone outcrops.... .. 13.8x106m3 Evapot ransp i ra t ion . The a c t u a l evapo t ransp i ra t i on has been c a l c u l a t e d

from t h e Turo formula as fo l l ows :

- P

P' 0.9 + - L 2

Et - (6.8-2)

and L = 300 + 2 5 t + 0.05 t3 (6.8-3)

w i t h P annual........................559.7 mm

Hence: E = 513.4 mm, o r 28.72 x 106m3/year

f r o m t h e d ischarge p o i n t s :

t average annual................18.1°C

I n f i l t r a t i o n . Th is i s determined from t h e t o t a l s o f t he annual y i e l d s

A i n Bou Saadia........................... 1.8 x 106m3 A i n Faouar............................... 0.7 x 106m3 Total.................................... 2.5 x lObm3

From t h i s we can c a l c u l a t e t h e c o e f f i c i e n t s o f i n f i l t r a t i o n i n r e l a t i o n t o the r a i n f a l l ; t h e va lue determined i s i = 1 8 percent .

Runoff . We have n o t y e t determined the q u a n t i t a t i v e va lue o f t h e r u n o f f , owing t o i n s u f f i c i e n t measurements; never the less, t he a v a i l a b l e da ta i n d i c a t e s t h a t o n l y i n tense r a i n f a l l w i t h an i n t e n s i t y equal t o o r g rea te r than 45 mm/hour w i l l produce r u n o f f .

Conclusion. A water balance o f t h i s type encounters many d i f f i c u l t i e s and l i k e w i s e i s subjected t o l a r g e margins o f e r r o r , i n p a r t i c u l a r f o r those components c a l c u l a t e d from a formula such as f o r evapot ransp i ra t ion . I t i s n o t i n d i s p e n s i b l e i f t h e water resources o f t he a q u i f e r a re the so le concern o f t he s tudy . 6.8.2 Recession curve. I n t h i s second method, t h e r u n o f f i s ignored ( t h i s i s p l a u s i b l e i n s o f a r as the a q u i f e r i s n o t complete ly saturated) as w e l l as t h e evapo t ransp i ra t i on ( a negat ive i t e m i n the balance sheet) and t h e task i s t o know t h e regime o f t h e a q u i f e r so as t o i d e n t i f y t he i n f i l t r a t i o n and, thus, t he annual water resources t h a t a re the o b j e c t i v e o f t he study. The discharge regime i s g i ven by t h e recess ion curve ( r a t e of d r y i n g up); t h a t i s , t he curve o f y i e l d aga ins t t ime under genera l recharge cond i t i ons (see F i g u r e 6 .8-2) .

Knowing t h e recess ion law, t h e volume o f water h e l d i n reserve a t t h e end o f t h e r a i n y season can be deduced; i t corresponds t o t h e i n f i l t r a t i o n o f t he p a s t p r e c i p i t a t i o n . Th is method i s easy i n the Mediterranean c l imate , p a r t i c u l a r l y i n Tun is ia , where t h e r a i n y and dry season a re r e g u l a r and d i s t i n c t .

The M a i l l o t formula i s g e n e r a l l y used a l l o w i n g f o r an exponent ia l decrease o f d ischarge as a f u n c t i o n o f t ime o r :

( 6 . 8 - 4 )

where Qt = y i e l d a t i n s t a n t "t" ( i n m3/sec) Q ko = recess ion c o e f f i c i e n t e = base o f Nap ie r ian logar i thms (2 .718) t = t ime elapsed ( i n days) f rom s t a r t o f d r y i n g up.

= y i e l d a t i n s t a n t "to'' from s t a r t o f drying up ( i n mg/sec)

By i n t e g r a t i n g t h i s equat ion, t h e volume i n s torage a t t he s t a r t o f d r y i n g up ( s t a r t o f genera l recharge cond i t i ons ) i s obtained; i t corresponds t o the i n f i l t r a t e d p r e c i p i t a t i o n , o r

252

time (days)

F igure 6.8-2 Recession curves f o r t he s p r i n g o f Dyr e l Kef i n Tun is ia . Turbu len t f l o w i s superimposed on laminar f l o w Caf te r Schoe l le r , 1 9 4 8 ) .

253

v = - QO K

(6.8-5)

T h i s a l s o a l l ows us t o c a l c u l a t e t h e c o e f f i c i e n t o f i n f i l t r a t i o n . Example o f use a t Dyr e l Kef Sync l ine (H. Schoel ler , 1948). D y r e l Kef Sync l i ne (see F i g u r e 6.8-3) i s a perched s y n c l i n e of Lower

Eocene l imestones r e s t i n g on Danian-Montian c l a y s and marls; i t forms an a q u i f e r f l o w i n g from a s i n g l e discharge p o i n t , known as Kof spr ing.

Topographic c h a r a c t e r i s t i c s : Area.......................... 5.8 kmz Maximum alt i tude... . . . . . . . . . . . 1 ,084 meters Length o f t h e sync l i ne ........ 7.4 km

R a i n f a l l . T h i s i s determined from the cont inuous r e c o r d i n g r a i n gage a t t h e Kef s t a t i o n .

I n f i l t r a t i o n . The recess ion curves i n d i c a t e t h a t t h e r e a re two groundwater f l o w regimes: (1) through l a r g e f i s s u r e s hav ing high gradients , and (2) a second o f g r e a t e r importance by f l o w through sma l l f i s s u r e s corresponding t o t h e f o l l o w i n g equat ion:

-k (t-t ) 4 = q o * e O (6.8-6)

where q = y i e l d a t t ime "t" ( l i t e r s / s e c o n d l qo = y i e l d a t t ime lit ' I , from s t a r t o f d r y i n g up ( l i t e r s / s e c o n d ) . e = base o f Nap ie r ia8 ( n a t u r a l ) l oga r i t hms t = t ime i n days t = t ime (days) from s t a r t o f d r y i n g up ko = 0.00654, recess ion c o e f f i c i e n t .

T h i s second regime represents the f l o w o f reserves accumulated during t h e r a i n y season; t h e i r among can be ob ta ined by i n t e g r a t i o n , so t h a t :

9, - q 86.4 Q , - Q = O. 00645 (6.8-7)

where

Fo r thg years under cons idera t ion , qo v a r i e s from 30 t o 80 l i t e r s p e r second, so t h a t i f t h e mean o f 50 l i t e r s p e r second i s considered, t he volume i n storage was

Q = volume o f water i n storage corresponding t o discharge "q" Q = volume o f water i n storage a t s t a r t o f d r y i n g up.

Q, = 0.670 x 1 0 % ~ (6.8-8,)

I n a d d i t i o n , i t i s found t h a t t h e i n f i l t r a t i o n c o e f f i c i e n t v a r i e s f rom 1 6 t o 25 pe rcen t during d r y s p e l l s , but can have much h i g h e r va lues during a f l o o d pe r iod .

6.8.3 Spec ia l case o f observa t ion w e l l s o r piezometers. When a f u l l y p e n e t r a t i n g obse rva t i on w e l l o r piezometer i s a v a i l a b l e t h a t i s developed i n an a q u i f e r t h a t i s considered homogeneous and f u l l , i t i s p o s s i b l e t o determine q u a n t i t a t i v e l y t h e r a i n f a l l i n f i l t r a t i o n r e l a t i o n s h i p w i t h o u t de termin ing r u n o f f . Th i s i s g e n e r a l l y t h e case where groundwater e x t r a c t i o n i s by pumping o r by an i n f i l t r a t i o n g a l l e r y t h a t d i s t u r b s the normal f l o w regime. Hence, an a t tempt i s made t o e s t a b l i s h a r e l a t i o n s h i p between the volume o f water e x t r a c t e d and changes i n water l e v e l i n t h e r e s e r v o i r ; t h i s a l l ows the v a r i a t i o n s i n t h e volume o f reserve t o be determined a f t e r any f i x e d p e r i o d o f r a i n f a l l ; thus, t h e i n f i l t r a t i o n and t h e groundwater resources o f t h e a q u i f e r can be determined.

Example o f use a t D j . Chennata and D j . Ben Saidane (Tun is ia ) (J. T ixe ron t , e t a l . , 1 9 5 9 ) .

The study dea ls w i t h l imestone mass i fs o f l i m i t e d ex ten t , a l l o f whose discharge p o i n t s a re known and which c o n s i s t s o f a l imestone monocl ine enclosed b y mar l s as a r e s u l t o f f a u l t i n g (see F igu res 6.8-4 and 6 .8-5) .

254

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- .-O-

- - r +

- c - , O* . ,

- ,b 0 O L - 2 - -6 O 0;-

I I 4 0 gd-- O 1

-i 7 - - km

- 1 5 7 Talus and landslide deposits.

E] Clastic deposits [Lower Eocene].

E l Limestone [Lower Eocene].

rj Clastic deposits [Cretaceous Eocene]

F igure 6.8-3 Geologic map o f Dyr e l Kef sync l ine , T u n i s i a ( a f t e r Schoel ler , 1 9 4 8 ) .

255

Topographical c h a r a c t e r i s t i c s .

S t ruc tu res D i . Chennata D j . Ben Saidane

Area kma 1.8

17.0 8 1 8 L i a i

H ighes t P o i n t (m) Age o f Limestone 232 CamDanian

R a i n f a l l . Th i s have been e x t r a p o l a t e d from the neares t gaging s t a t i o n and con ta ins a v a r i a b l e margin o f e r r o r : t h e f i g u r e s , based on a f i ve -yea r average ( 1 9 4 5-1 95 O ) a re :

D j . Chennata..................... 633 mmlyear D j . Ben Saidane.................. 427 mmlyear

I n f i l t r a t i o n . Fo r D j . Chennata and D j . Ben Saidane, t h e r e a re observa t ion w e l l s t h a t p e r m i t t h e r e l a t i o n s h i p between t h e volume o f water discharged and t h e l e v e l o f water t a b l e t o be determined: t h e r e l a t i o n s h i p was as f o l l o w s f o r t he 1945-1940 pe r iod :

D j . Chennata..................... 27,000 t o 13,000 m3 pe r meter

D j . Ben Saidane.................. 750,000 m3 p e r meter o f lower-

D j . Chennata..................... 264 mm D j . Ben Saidane.................. 10.8 mm

D j . Chennata..................... 369 mm D j . Ben Saidane.................. 3 6 4 mm

o f l ower ing

ing Hence t h e average annual i n f i l t r a t i o n was determined as fo l l ows :

I n f i l t r a t i o n d e f i c i t . Th i s was ob ta ined by s u b t r a c t i o n and represents the evapo t ransp i ra t i on , as:

Forecas t o f t h e water balance. The r a i n f a l l l i n f i l t r a t i o n r e l a t i o n s h i p has served as t h e b a s i s f o r t h e development o f a formula t o f o r e c a s t t he water balance which may be w r i t t e n as f o l l o w s :

I = S(P-Ho - aE) (6.8-9)

where I = volume o f i n f i l t r a t e d water (m3) S = sur face r e c e i v i n g t h e r a i n f a l l (ma) P = amount o f p r e c i p i t a t i o n (meters) H = c a p a c i t y o f s o i l t o r e t a i n mo is tu re (equ iva len t i n meters) EO = amount o f evapora t ion (meters) a = a numer ica l c o e f f i c i e n t I n t h e two cases under cons idera t ion , t h e values o f "Ho1' and o f "a" can

have va lues as f o l l o w s : D j . Chennata..................... a = 0.45: H = 60 mm D j . Ben Saidane.................. A = -.4: Hoo= 85 mm

6.8.4 Conclusion. I n s o f a r as t h e main i n t e r e s t l i e s w i t h t he water resources aspect o f t h e water balance i n a carbonate rock a q u i f e r , t h e r e a re advantages i n concen t ra t i ng on t h e r a i n f a l l i n f i l t r a t i o n r e l a t i o n , t h a t i s i n the genera l case, i n t h e recess ion ( r a t e o f d r y i n g up) curve o f the p r i n c i p l e discharge p o i n t s : these curves a l l o w a p i c t u r e t o be cons t ruc ted o f t he h y d r a u l i c regime o f t h e a q u i f e r and t o c a l c u l a t e t h e e x p l o i t a b l e reserves a t t h e commencement o f t he d r y season, such reserves form t h e p r i n c i p a l i n t e r e s t o f these s t ruc tu res . Hence i t i s o f va lue t o make r e g u l a r discharge measurements on t h e spr ings over as l o n g a p e r i o d as p o s s i b l e as w e l l as t o c o l l e c t r a i n f a l l records.

W i t h r e g a r d t o carbonate r o c k a q u i f e r s developed by boreholes ( o f which the e s s e n t i a l advantage i s t h e a r t i f i c i a l r e g u l a t i o n o f resources), t h e i r water balance may be e s t a b l i s h e d from t h e r e l a t i o n s h i p between changes i n y i e l d and i n t h e l e v e l o f t h e water t a b l e o f t h e sa tu ra ted zone; t h i s a p p l i e s where the re i s a w e l l - d e l i m i t e d s t r u c t u r e t h a t a c t s l i k e a t r u e nappe.

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8

6.9 Hydro log ic mapping (Bashi r A. Memon and B e t t y M. Wi lson)

Geologic mapping i s discussed i n s e c t i o n 6.2 and hydrochemical maps i n s e c t i o n 6.5. See Paloc, 1975 f o r examples o f types o f h y d r o l o g i c maps and a l i s t o f some o f t h e e x i s t i n g maps.

6.9.1 Hydrogeo log ica l mapping. Hydrogeo log ica l maps d e p i c t s u r f ace water and groundwater resources on a base map 'which shows t h e topography and geology o f t he area. These maps a re ve ry impor tan t i n p a r t i c u l a r t o h y d r o l o g i s t s and hydrogeo log is ts working i n carbonate areas and i n genera l a re used by engineers, economists, admin i s t ra to rs , and a g r i c u l t u r a l i s t s and o the rs i n v o l v e d i n town and coun t ry p lann ing and p lann ing o f water suppl ies.

6.9.1.1 Purpose. Hydrogeo log ica l maps are used t o i l l u s t r a t e v a r i o u s hydrogeo log ica l c h a r a c t e r i s t i c s i n r e l a t i o n t o geology on a l o c a l o r r e g i o n a l bas i s , depending upon the u l t i m a t e use o f t h e map. These maps show the major groundwater bod ies o r t he s c a r c i t y o f groundwater, depending upon t h e area i n quest ion, t h e presence of a r t e s i a n basins: occurrence o f po tab le and non-potable groundwater; and l o c a t i o n s o f s a l i n e waters. Hydrogeologic maps should a l s o show a v a i l a b l e i n f o r m a t i o n on p iezomet r i c s u r f a c e ( s ) o r groundwater t a b l e ( s ) , t h e d i r e c t i o n o f groundwater f low: groundwater q u a l i t y v a r i a t i o n s ; l o c a t i o n s o f boreholes and w e l l s : and a l l sur face water bodies. These maps should a l s o show c l i m a t o l o g i c a l data, i n c l u d i n g p r e c i p i t a t i o n and evaporat ion, and t h e geometry o f water-bear ing format ions. The maps should i n c l u d e enough s t r u c t u r a l and geo log ic i n f o r m a t i o n t o f a c i l i t a t e a p roper understanding o f t h e hydrogeologic cond i t i ons , but geology should n o t be a l lowed t o obscure o r dominate t h e hydrology.

6.9.1.2 Map compi la t ion . Maps r e q u i r e d t o c o n s t r u c t an adequate hydrogeologic map a re (1) topographic maps: ( 2 ) geo log i c maps: ( 3 ) so i l -mo is tu re maps t h a t i n d i c a t e t h e mo is tu re l e v e l i n t h e zones o f ae ra t i on ; ( 4 ) me teo ro log i ca l maps t h a t show p r e c i p i t a t i o n , evapora t ion , temperature and o t h e r r e l e v a n t data such as p r e v a i l i n g w i n d d i r e c t i o n s and speed: ( 5 ) sur face water maps t h a t i n c l u d e sur face water sources ( i n c l u d i n g r i v e r s , lakes, spr ings, r e s e r v o i r s , and ponars) and stream f l o w c h a r a c t e r i s t i c s ; and (6) sur face water and groundwater q u a l i t y maps.

The scale a t which a hydrogeologic map should be prepared depends upon t h e a v a i l a b l e i n f o r m a t i o n which i s t o be i nc luded and t h e requirements o f d i f f e r e n t c o u n t r i e s . Some c o u n t r i e s have s p e c i f i c c l a s s i f i c a t i o n s o f l a r g e , medium and smal l sca le maps. These t h r e e ca tegor ies o f maps a re g e n e r a l l y used f o r t eçhn ica l , p r e l i m i n a r y reconnaissance, and s c i e n t i f i c purposes, r e s p e c t i v e l y .

The base map should be a topographic map on which the l o c a t i o n o f a l l e x i s t i n g boreholes and w e l l s a re marked. The geology o f t h e area i s then added t o the base map; t h e fea tu res which should be i nc luded a r e a q u i f e r s , aqu i ta rds , aquacludes, and p e r t i n e n t s t r u c t u r a l f ea tu res such as f a u l t s and j o i n t s , swallow holes, s inkholes, e t c , which a f f e c t t h e p e r m e a b i l i t y o f t h e a q u i f e r ( s ) . P r e c i p i t a t i o n , evaporat ion, temperature, and s o i l mo is tu re d e f i c i t a re superimposed on base map t o d e l i n e a t e c l i m a t o l o g i c a l v a r i a t i o n s w i t h i n t h e study area. Rivers, l akes and sp r ings a re dep ic ted on t h e hydrogeologic map t o i n d i c a t e sur face water sources o f recharge.

Suggested standard symbols and a r e p r e s e n t a t i v e geo log ic map a re presented i n t h e Unesco p u b l i c a t i o n , " I n t e r n a t i o n a l Legend f o r Hydrogeo log ica l Maps", pub l i shed i n 1970. The p u b l i c a t i o n l i s t s topographic, c l i m a t o l o g i c , geo log ic , l i t h o l o g i c , hydrographic, hyd rogeo log ica l and hydrochemical symbols as w e l l as symbols f o r boreholes, w e l l s , and r e l a t e d i tems. An appendix t o t h e p u b l i c a t i o n presents symbols s p e c i f i c a l l y f o r spr ings, swallow holes, s inkho les and n a t u r a l c a v i t i e s .

Hydrogeo log ica l maps can be compiled f o r i n a c c e s s i b l e areas w i t h t h e use o f b l a c k and w h i t e and c o l o r a e r i a l photography, s a t e l l i t e photography and imagery, i n f r a r e d imagery and o t h e r types o f remote sensing.

2 59

6.9 .1 .3 Hydrogeologic map f o r carbonate areas. A hydrogeologic map o f a carbonate r o c k area, i n p r i n c i p l e , i s e x a c t l y t h e same as a map o f any o t h e r water b e a r i n g m a t e r i a l . D i f f e r e n c e s a r i s e because carbonate r o c k hydrology r e q u i r e s i n t e r p r e t a t i o n o f some g e o l o g i c a l f ea tu res p e r c u l i a r t o so lub le rocks. The s t r u c t u r a l and h i s t o r i c a l aspects o f t h e geology i n some carbonate areas i s as, or more, impor tan t than t h e l i t h o l o g y and t h e l i t h o l o g i c c h a r a c t e r i s t i c s i n i n f l u e n c i n g a q u i f e r c h a r a c t e r i s t i c s .

Surface features, such as l ineaments, shown on hydrogeologic maps o f carbonate r o c k te r ranes g e n e r a l l y should be used as guides t o l o c a t i n g permeable zones a t and below t h e surface. Topographic maps a t s u f f i c i e n t l y l a r g e scales may show k a r s t f e a t u r e s whereas a t l a r g e r scale, t h e same fea tu res may be completely masked. The symbols used should be ad jus ted t o i n d i c a t e the degree o f d e t a i l and dependab i l i t y .

A q u i f e r c h a r a c t e r i s t i c s such as p o r o s i t y , p e r m e a b i l i t y , t r a n s m i s s i v i t y and storage c o e f f i c i e n t / s p e c i f i c y i e l d a r e p l o t t e d as i s o m e t r i c o r contour l i n e s . The depth t o t h e water t a b l e o r p iezomet r i c sur face and t h e l o c a t i o n s o f caverns and s i n k s should a l s o be shown u s i n g i s o m e t r i c l i n e s . L i k e hyd rogeo log ica l maps o f o t h e r ter ranes, those carbonate areas should show w e l l s , spr ings, s inks, stream channels and o t h e r hydro logy fea tu res on t h e surface. These maps a l s o should show t h e e x t e n t o f t h e v a r i o u s rock u n i t s i n v o l v e d i n t h e water problem and o f t h e u n i t s which form and a d j o i n t h e a q u i f e r s . I t i s o f t e n d i f f i c u l t , however, t o decide where a hydrogeologic map stops and a water resources p l a n n i n g map s t a r t s .

6 . 9 . 2 i n t e r p r e t i v e maps. These a re s p e c i a l purpose maps which show o n l y t h a t i n f o r m a t i o n which i s necessary f o r t h e study o r i n t e r p r e t a t i o n o f a p a r t i c u l a r hydrogeologic aspect o r i n t e r r e l a t i o n s h i p .

An example o f such a map i s one which shows t h e v a r i o u s types o f bedrock i n t h e area a long w i t h l o c a l v a r i a t i o n s i n sur face and groundwater q u a l i t y . T h i s map may be used t o study the i n f l u e n c e of bedrock types on water q u a l i t y . Another example i s a map which shows groundwater occurrences and geology s t r u c t u r e . Maps d e l i n e a t i n g recharge areas o f contaminated a q u i f e r s and t h e l o c a t i o n s of i n d u s t r i e s , waste d i s p o s a l s i t e s , and o t h e r p o s s i b l e sources o f contaminat ion may be used f o r clean-up and resources p r o t e c t i o n s tud ies.

I n t e r p r e t i v e maps a re used i n con junc t i on w i t h t h e genera l hydrogeologic map o f t he area, and may o f t e n by generated from i n f o r m a t i o n which i s a l ready p l o t t e d on t h e genera l map.

6 . 9 . 3 Water resources maps. A water resources map may be cons iderab ly more s i m p l i f i e d than a hydrogeologic map and i n most cases should be more s i m p l i f i e d . The purpose o f a water resources map i s t o s i m p l i f y and summarize the i n f o r m a t i o n on a hyd rogeo log ica l map so t h a t n o n - s p e c i a l i s t s may become r e a d i l y aware o f t h e genera l water resource s i t u a t i o n . A t y p i c a l water resources map f o r example, w i l l i n d i c a t e areas where groundwater i s recharged from t h e surface. Fo r carbonate te r ranes such a map shou ld a l s o show where t h e r e i s no sur face r u n - o f f and where groundwater emerges. S i m i l a r l y t he maps should show t h e areas where groundwater r i s e s below t h e sur face o f a sea o r a lake, o r where they may leave carbonate rocks below t h e sur face t o f l o w d i r e c t l y i n t o r i v e r gravels . The l i m i t s o f t h e a q u i f e r s on and below the sur face a re a l s o o f use but o f more va lue i s t h e approximate depth t o which w e l l s must be d r i l l e d t o o b t a i n a water supply o r d i f f e r e n t ranges i n q u a n t i t y and q u a l i t y . I f waste q u a l i t y i s t h e problem then t h e water q u a l i t y aspects should be summarized i n d e t a i l on a map.

A water resources map should p r o v i d e guidance f o r l o c a t i o n and development o f t h e b e t t e r a q u i f e r s . Where f a u l t zones o r o t h e r geo log i c s t r u c t u r e s c o n t r o l t he k a r s t i f i c a t i o n o f l imestones causing them t o be more permeable water c o n t r o l l i n g e f f e c t s should be shown on the water resources map as guides t o w e l l l o c a t i o n s . Other u s e f u l types o f water resources maps i n c l u d e maps o f depths t o d i f f e r e n t water-bear ing zones, maps d e p i c t i n g areas o f d i f f e r e n t p o t e n t i a l w e l l y i e l d and water a v a i l a b i l i t y , and maps i n d i c a t i n g areas of environmental concern such as recharge areas o f a q u i f e r s which are use f o r drinking water (see Moser e t a l . , 1971) . I n summary, a water resources map should show t h e most s i g n i f i c a n t r e s u l t s o f t h e h y d r o l o g i c i n v e s t i g a t i o n i n a form and i n terms which non-hydro log is ts can e a s i l y use.

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7. Development and management of karst groundwater resources

7.1 I n t r o d u c t i o n (Stanley W. Posey)

I n t h i s Chapter o f t h e Guide, emphasis changes from i n v e s t i g a t i o n t o implemen- t a t i o n . The f o l l o w i n g d iscuss ions presume t h a t t h e k a r s t ground-water resource has been i d e n t i f i e d and i s i n t h e process o f b e i n g evaluated. I n many, i f n o t most cases, t h e i n v e s t i g a t i o n s w i l l n o t have been an end i n themselves but w i l l have been d i r e c t e d toward i d e n t i f i c a t i o n o f a water resource f o r some s p e c i f i c developmental o b j e c t i v e . Methods o f i n v e s t i g a t i o n and e v a l u a t i o n r e f e r r e d t o i n t h i s Chapter a re discussed i n d e t a i l elsewhere i n t h i s Guide.

I n v e s t i g a t i o n and eva lua t i on , development, and management a re n o t e n t i r e l y separate aspects o f k a r s t hydrology. Even though each aspect may be d i r e c t e d by d i f f e r e n t agencies, work on each draws from and b u i l d s upon t h e others. I n t h e u s u a l case, s i g n i f i c a n t economies o f t ime, e f f o r t , and money can be r e a l i z e d i f t h e e f f o r t s a r e i n t e g r a t e d from t h e o u t s e t and c o n t i n u i t y o f work i s maintained.

C h a r a c t e r i s t i c s o f b o t h development and management o f k a r s t ground-water resources a re dependent upon t h e s p e c i f i c a p p l i c a t i o n . T h i s chapter discusses genera l o b j e c t i v e s and p r i n c i p l e s which may be used as g u i d e l i n e s f o r p lann ing and implementat ion o f development and management programs.

7.2 Resource e v a l u a t i o n

U t i l i z a t i o n o f a k a r s t ground-water resource must o f course be preceded by i d e n t i f i c a t i o n and e v a l u a t i o n o f t h a t resource. Parker (1973) s t a t e s t h a t success fu l development and management r e q u i r e s a "de te rm ina t ion o f how much o f what kind o f water i s where and how i t v a r i e s i n q u a n t i t y and q u a l i t y , b o t h i n space and i n t ime." The i n v e s t i g a t o r y work necessary t o a p a r t i c u l a r development p r o j e c t depends upon t h e nature, scope and a p p l i c a b i l i t y o f p rev ious i n v e s t i g a t i o n s which have been c a r r i e d o u t i n t h e area and t h e r e s u l t s o f which are a v a i l a b l e . Regional resource assessments may p r o v i d e s u f f i c i e n t i n fo rma t ion f o r la rge-sca le development programs but be o f o n l y genera l a p p l i c a t i o n t o a l o c a l p r o j e c t .

7.2.1 Q u a n t i t a t i v e e v a l u a t i o n (Stanley W . Posey). Geologic and hydrogeologic i n v e s t i g a t i o n s i d e n t i f y a k a r s t ground-water resource, and q u a n t i t a t i v e e v a l u a t i o n p rov ides t h e da ta f o r de termin ing i t s a v a i l a b i l i t y as a water supply f o r t h e d e s i r e d use. The p r imary o b j e c t i v e o f t h e q u a n t i t a t i v e e v a l u a t i o n should be a de te rm ina t ion o f how much water can be produced under t h e s p e c i f i c hydrogeologic cond i t i ons .

A q u a n t i t a t i v e e v a l u a t i o n may encompass a range o f p h y s i c a l and h y d r a u l i c c h a r a c t e r i s t i c s o f t h e a q u i f e r under study such as p o r o s i t y , p e r m e a b i l i t y o r t r a n s m i s s i v i t y , and c o e f f i c i e n t o f storage. Methods o f e v a l u a t i o n a re discussed i n d e t a i l i n Chapter 6 . Storage capac i t y should be considered as an impor tan t - f a c t o r i n b o t h development and management, e s p e c i a l l y where demand and a v a i l a b i l i t y a r e s u b j e c t t o seasonal v a r i a t i o n s . Storage c a p a b i l i t y i s a l s o a d i f f i c u l t parameter t o q u a n t i f y i n k a r s t a q u i f e r s due t o t h e complex secondary p o r o s i t y and p e r m e a b i l i t y common t o k a r s t i c hydrogeo log ic systems.

7.2.1.1 P r e l i m i n a r y i n v e s t i g a t i o n s (Bashi r A. Memon and B e t t y M. W i l son ) . The p r e l i m i n a r y i n v e s t i g a t i o n s necessary f o r q u a n t i t a t i v e a n a l y s i s o f water resources are:

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2.

3.

4 .

5 .

6 .

7.2.1.2

A l l a v a i l a b l e i n f o r m a t i o n (publ ished and on f i l e ) r e l a t e d t o t h e s p e c i f i c s i t e should he c o l l e c t e d from u n i v e r s i t i e s , i n d u s t r y , g e o l o g i c a l surveys, government agencies, l o c a l w e l l d r i l l e r s , and l o c a l p r o p e r t y owners. Data on t h e sur face and subsurface geology should be c o l l e c t e d from sur face and subsurface geo log ic maps. Hydrogeologic maps are t o be prepared t o d e f i n e water-bear ing u n i t s , a q u i f e r systems. Contour maps on t o p o f t h e bedrock and isopach maps should be prepared t o determine t h e th i ckness o f t h e a q u i f e r . Regional s t r u c t u r a l geo log ic maps and photos should be s tud ied t o determine l ineaments and l o c a l f r a c t u r e t rends which enhance the storage and t r a n s m i t t a l c a p a b i l i t i e s o f t h e rock u n i t s i n the area. The use o f geo log ic c ross sec t i ons coupled w i t h t he i n t e r p r e t a t i o n o f t h e geophysical l o g s f u r t h e r h e l p t o d e l i n e a t e t h e a q u i f e r l i m i t s on r e g i o n a l and l o c a l s e t t i n g . A l l o f t h e w e l l s i n t h e area o f i n v e s t i g a t i o n should be i n v e n t o r i e d t o r e c o r d t h e l o c a t i o n o f t h e w e l l , water l e v e l , depth o f t he w e l l , depth o f cas ing and screen, water q u a l i t y , date and method o f d r i l l i n g and o t h e r r e l e v a n t i n fo rma t ion . New w e l l s should be d r i l l e d where necessary t o f i l l gaps i n data f o r i n t e r p r e t a t i o n . These w e l l s are t o be d r i l l e d i n a manner t o o b t a i n t h e r e q u i r e d da ta (geolog ic , o r hydrogeo log ic ) . Pump w e l l s a re t o be d r i l l e d and cons t ruc ted according t o t h e s p e c i f i c d ischarge requ i red . The depth and spacing o f t he w e l l s i s g e n e r a l l y d i c t a t e d b y t h e l o c a l geo log ic s i tuat ion, , a q u i f e r c h a r a c t e r i s t i c s , and boundary cond i t i ons . Water l e v e l data c o l l e c t e d from observa t ion w e l l s f o r an extended p e r i o d should be used t o c o n s t r u c t hydrographs f o r key w e l l s . These p l o t s a re used t o e i t h e r i n t e r p o l a t e o r e x t r a p o l a t e s t a t i c water l e v e l s f o r t h e w e l l s which are n o t monitored and a l s o determine the e f f e c t s o f pumping and recovery as shown by t h e change i n water l e v e l i n d i c a t e d on these hydrographs.

Pump t e s t s (Bashi r A. Memon a n d B e t t y M. W i l son ) . Q u a n t i t a t i v e a p p r a i s a l s can be made u s i n g t h e a q u i f e r l i m i t s ànd c h a r a c t e r i s t i c s . Aqu i fe r c h a r a c t e r i s t i c s a re determined by a c o n t r o l l e d pumping t e s t ( s ) . I n a r e g i o n a l i n v e s t i g a t i o n , t he f i r s t i t e m i n t h e work program should be a s i n g l e w e l l s h o r t du ra t i on , t e s t o f t h e drawdown, recovery and step-drawdown. These t e s t s may n o t p r o v i d e data f o r t h e i n t e r p r e t a t i o n of t h e hydrogeologic parameters, but w i l l , a t l e a s t , y i e l d r e l i a b l e da ta on the s p e c i f i c capac i t y o f t h e w e l l , and may f u r n i s h va luab le q u a l i t a t i v e i n fo rma t ion , thereby a i d i n g i n t h e s e l e c t i o n o f s i t e s f o r more e labo ra te t e s t s t o determine t h e q u a n t i t a t i v e c h a r a c t e r i s t i c s o f t h e a q u i f e r .

The pumping should be f o r a t lease two t o f o u r hours even though s i g n i f i c a n t water l e v e l changes may be observable o n l y during p a r t o f t h i s t ime. The pumping p e r i o d should be fo l l owed by measurements o f t h e r a t e o f recovery o f t h e water l e v e l . A f t e r t h e t e r m i n a t i o n o f pumping, t he water l e v e l should be mon i to red a t f requent i n t e r v a l s as l ong as a n o t i c e a b l e recovery o f water l e v e l can be observed. As a r u l e o f thumb, one may es t imate t h a t s i g n i f i c a n t recovery l a s t s about h a l f as l o n g as t h e d u r a t i o n o f t he pumping phase; however, t h e recovery phase cou ld be s h o r t e r i f t h e t r a n s m i s s i v i t y i s h igh.

The s tep drawdown t e s t i s c a r r i e d o u t a f t e r t h e recovery pe r iod . The whole sequence o f t e s t s may r e q u i r e 8 -14 hours. A f t e r t he analyses and e v a l u a t i o n o f these t e s t s , a c o n t r o l l e d pumping t e s t i n v o l v i n g one pumping w e l l and s e v e r a l w e l l s o r boreholes used as observa t ion p o i n t s cou ld be c a r r i e d o u t i n s e l e c t e d l o c a t i o n s . A t e s t o f t h i s kind may take one t o seve ra l days. E x i s t i n g w e l l s should be used wherever poss ib le . C o s t l y obse rva t i on boreholes should be d r i l l e d as a l a s t r e s o r t .

7.2.1.2.1 P r e - t e s t requirements. These steps should be taken b e f o r e a pumping t e s t i s begun:

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2.

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R a i n f a l l da ta should be mon i to red b e f o r e and a f t e r t h e pumping p e r i o d so as t o determine t h e e f f e c t s o f n a t u r a l replenishment. Mon i to r t h e d i u r n a l changes o f ba romet r i c p ressure o r t i d e s i n t h e area p r i o r t o , during and a f t e r t h e pump ing t e s t ( s ) . The measured water l e v e l s need t o be ad jus ted accord ing ly , e s p e c i a l l y i n a r t e s i a n cond i t i ons . Care should a l s o be taken t o r e c o r d e r r a t i c no ises caused by pressure waves emanating from t r a f f i c on highways o r r a i l r o a d s . Mon i to r water l e v e l ( s ) and . e f f e c t o f any pumping i n and around t h e area SO t h a t t h e measured water l e v e l during t e s t can be ad jus ted accord ing ly . I f p o s s i b l e , t e rm ina te a l l pump ing i n t h e area f o r a t l e a s t 2 4 hours so t h a t t h e r e c o r d o f t h e water l e v e l p r i o r t o pumping i n t h e observa t ion w e l l s i n v o l v e d i n t h e t e s t can be s t a b i l i z e d f o r 8-12 hours p r i o r t o pumping. M o n i t o r i n g o f t h e water l e v e l data i n t h e pumping w e l l and observa t ion w e l l s i n v o l v e d should be done manually o r by automat ic recorders. The s t a b i l i z e d water l e v e l s should be recorded d u r i n g a one h a l f hour p e r i o d b e f o r e and a f t e r a s i n g l e w e l l t e s t , o r during seve ra l hours b e f o r e and a f t e r t e s t s i n v o l v i n g seve ra l boreholes.

7.2.1.2.2 Test procedures. The person i n charge o f c a r r y i n g o u t t h e t e s t should understand a t l e a s t t h e b a s i c p r i n c i p l e s o f ground-water h y d r a u l i c s and should be a r e s o u r c e f u l person capable o f overcoming many u n p r e d i c t a b l e problems t h a t can occur during f i e l d work. The person should be a b l e t o communicate and coo rd ina te w i t h t h e f i e l d p a r t y respons ib le f o r t h e c o l l e c t i o n o f water l e v e l data d u r i n g and a f t e r t h e pumping t e s t . The i n v e s t i g a t o r must a l s o c a r e f u l l y mon i to r t h e i ns t rumen t read ings and water l e v e l da ta c o l l e c t e d so as t o i n s u r e t h a t e v e r y t h i n g i s running smoothly and t h e r e i s no m iss ing data.

During t h e i n i t i a l p e r i o d o f t h e pumping t e s t , t h e water l e v e l s a re t o be measured i n t h e pump w e l l and a l l obse rva t i on w e l l s a t f requen t i n t e r v a l s . The frequency o f water l e v e l measurements should be ad jus ted so t h a t a s i g n i f i c a n t change, o f 0 .1 i n c h o r 0.5 cm, occurs between two successive readings. When changes occur r a p i d l y , t h e frequency o f measurements must be as r a p i d as poss ib le , a t one minute i n t e r v a l s o r l e s s . Slow changes may be s u f f i c i e n t l y w e l l monitored by read ings a t 5-10 minutes o r even longer i n t e r v a l s . A f t e r t he f i r s t hour o r two o f record ing , t he frequency o f water l e v e l measurements may be one h a l f hour t o an hour o r even more depending upon t h e change i n water l e v e l e f f e c t e d by pumping.

The r a t e o f d ischarge o f t h e pumping w e l l should be measured f r e q u e n t l y and should be main ta ined cons tan t a t a predetermined l i m i t .

A f t e r t h e t e r m i n a t i o n o f pumping, recovery da ta a re t o be c o l l e c t e d i n a fashion s i m i l a r t o t h a t descr ibed above. A f t e r t h e complet ion o f t h e t e s t observat ions, a l l computations of t ime i n t e r v a l s , drawdowns, discharges, e t c . are done on the o r i g i n a l f i e l d sheets. The da ta a r e then p l o t t e d on a standardized format and t h e i r i n t e r p r e t a t i o n s and t h e c a l c u l a t i o n s a re marked on the graphs.

The i n v e s t i g a t o r may n o t always know beforehand whether t h e a q u i f e r under i n v e s t i g a t i o n i s conf ined, l eaky o r water t a b l e . The p l o t o f time-drawdown i n d i c a t e s t h e c o n d i t i o n s o f t h e a q u i f e r ; t h e r e f o r e , t h e t ype curves such as Thies (1935) , Walton ( 1 9 7 0 ) , B o l t o n ( 1 9 6 3 ) , e t c . a re used t o match t h e f i e l d data and i n t e r p r e t t h e r e s u l t s .

7.2.1.3 Storage i n k a r s t i c a q u i f e r s ( A r i e I s s a r ) . Regional k a r s t i c a q u i f e r s w i t h a developed k a r s t i c system a re considered i n t h e f o l l o w i n g d iscuss ion . Loca l k a r s t i c phenomena and l a r g e k a r s t i c caverns (which may be t r e a t e d as open r e s e r v o i r s ) r e q u i r e a d i f f e r e n t t rea tment and a r e n o t discussed here.

7.2.1.3.1 Storage requirements ( A r i e I s s a r ) . Storage i s r e q u i r e d i n f l o w processes where water demand and immediate supply a r e v a r i a b l e over t ime and v a r i a t i o n s a re n o t co inc iden t . A storage f a c i l i t y i s an i n te rmed ia te subsystem

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between t h e area o f recharge and t h e p o i n t ( s ) o f d ischarge which i s ab le t o s t o r e l a r g e amounts o f water and t o d ischarge i t when requ i red . The s torage f a c i l i t y d iscussed here i s t h e in te rconnected pr imary and secondary pore volume o f a k a r s t aqu i fe r .

When t h e bulk o f t h e f l o w passes through t h e s torage system, the s torage i s "on l i n e " . When t h e main f l o w bypasses t h e s torage system and o n l y sur- p luses en te r it, t h e s torage i s " o f f l i n e " . Th i s " o f f - l i n e " s torage may be e s p e c i a l l y impor tan t i n water t a b l e k a r s t a q u i f e r s which t y p i c a l l y have w e l l - developed secondary p o r o s i t y above t h e normal water l e v e l . O f f - l i n e storage o f t h i s type may n o t be q u a n t i f i e d i n standard a q u i f e r t e s t s . Groundwater a q u i f e r s serve as on l i n e s torage f a c i l i t i e s f o r t h e i r own n a t u r a l rep len i sh - ment, and as o f f l i n e s torage f a c i l i t i e s f o r sur face water resources.

A p r i n c i p a l c h a r a c t e r i s t i c o f s torage o f a k a r s t i c a q u i f e r i s volume o f water which i s requ i red . Dynamic s torage volume equals the maximum accumulated d i f f e r e n c e between i n f l o w t o and o u t f l o w from t h e s torage f a c i l i t y . I n a d e t e r m i n i s t i c system where t h e demand does n o t exceed t h e ou t f low, the s torage volume r e q u i r e d i s unique. O n t he o the r hand, i n a s tochas t i c system t h e o u t f l o w may sometimes f a i l t o meet the demand, and t h e r e q u i r e d storage volume i s v a r i a b l e and depends on t h e magnitude o f t he d e f i c i e n c y and the r e q u i r e d l e v e l o f r e l i a b i l i t y (expressed as: 1.0 - accepted f a i l u r e p r o b a b i l i t y ) .

Another c h a r a c t e r i s t i c o f s torage i s t ime, o r t he storage cyc le . Country- wide and r e g i o n a l water resources u t i l i z a t i o n s have seasonal and in te r -annua l s torage cyc les; l o c a l water supply systems may a l s o have d a i l y and weekly s torage cyc les. I n a r i d and semi-ar id reg ions a seasonal storage c y c l e i s common s ince n a t u r a l replenishment t y p i c a l l y occurs o n l y i n w in te r , and t h e water i s used f o r i r r i g a t i o n main ly i n summer. For example, i n the c e n t r a l k a r s t i c a q u i f e r o f I s r a e l , n a t u r a l replenishment occurs f rom November t o March, w h i l e t h e demand f o r water i n t h a t p e r i o d amounts t o o n l y 30 percent o f t h e annual t o t a l . The seasonal s torage volume r e q u i r e d i s t h e r e f o r e 70 percent o f t he n a t u r a l replenishment i f t h e excess i s t o be r e t a i n e d f o r use when demanded. Another c h a r a c t e r i s t i c o f a r i d and semi-ar id c l ima tes i s t h e high v a r i a b i l i t y o f t h e annual n a t u r a l replenishment which r e q u i r e s s torage from wet t o dry years. The d e v i a t i o n i n t h e storage volume o f t h e c e n t r a l k a r s t i c a q u i f e r o f I s r a e l amounts t o h a l f o f t h e annual replenishment: s i m i l a r v a r i a t i o n s a re t y p i c a l i n t h e eas tern Mediterranean semi-ar id c l imate .

Storage requirements may be evaluated by advanced opera t ions research techniques. A s i m p l i f i e d method o f approx imat ing s torage requirements suggested by Hurs t (1965) r e l a t e s t h e storage r e q u i r e d (R) t o the s tandard d e v i a t i o n o f t h e annual f l o w ( 6 ) and t o the number o f years t h a t t he s torage f a c i l i t y w i l l be e f f e c t i v e (NI .

R = 1 . 2 5 6 f i (7.2-1)

Assuming a des ign p e r i o d o f 50 years ( g i v i n g t h e equat ion an approximate 98 percent l e v e l o f r e l i a b i l i t y ) and a standard d e v i a t i o n equal t o h a l f o f t he average replenishment, t he r e s u l t i n g in te r -annua l s torage r e q u i r e d i s 4.4 t imes the average annual replenishment. I f the a v a i l a b l e s torage volume i s l e s s than the computed requirements, a p o r t i o n of t he n a t u r a l replenishment w i l l be l o s t t o o u t f l o w from t h e aqu i fe r . I t i s wor thwhi le t o ment ion t h a t advanced opera t ions research techniques u t i l i z i n g r e a l economic and p h y s i c a l parameters a r r i v e a t a s torage requirement o f t h ree t o f i v e t imes the annual replenishment f o r t h e same c l i m a t i c cond i t i ons .

7.2.1.3.2 Storage volume i n k a r s t i c a q u i f e r s ( A r i e I s s a r ) . The e f f e c t i v e volume o f . a ground-water r e s e r v o i r depends on i t s area, a q u i f e r th ickness, e f f e c t i v e p o r o s i t y and maximum and m i n i m u m water l e v e l s . I t may be d i f f i c u l t t o determine t h e s torage volume o f a k a r s t i c a q u i f e r d i r e c t l y because t h e e f f e c t i v e p o r o s i t y i s l a r g e l y secondary and cannot be d i r e c t l y measured.

The volume o f a groundwater r e s e r v o i r depends on i t s area, s torage c o e f f i c i e n t , and maximum and m i n i m u m water l e v e l s . When t h e d i s t r i b u t i o n o f w e l l s d i f f e r s f rom the d i s t r i b u t i o n o f n a t u r a l replenishment, t h i s volume a l s o become dependent on t h e t r a n s m i s s i v i t y . Areas w i t h low t r a n s m i s s i v i t y va lues may reduce t h e a c t i v e area o f t h e aqu i fe r .

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I n p h r e a t i c a q u i f e r s t h e s to rage c o e f f i c i e n t equals p o r o s i t y . There a re two types o f p o r o s i t y i n k a r s t i c a q u i f e r s : (a) i s o l a t e d pores, and (b) a system o f in te r -connected i n t e r s t i c e s , f i s s u r e s , and j o i n t s . O n l y t h e second type i s considered t o c o n s t i t u t e t h e e f f e c t i v e storage. S p e c i f i c f i e l d va lues o f k a r s t i c p h r e a t i c a q u i f e r s range from two pe rcen t t o t e n percent . I n conf ined a q u i f e r s , t h e s to rage c o e f f i c i e n t i s due t o t h e e l a s t i c i t y o f format ions and t h e c o m p r e s s i b i l i t y o f water. Limestone fo rmat ions a re r e l a t i v e l y r i g i d and t h e i r con f i ned s to rage c o e f f i c i e n t i s n e g l i g i b l e . When a k a r s t i c a q u i f e r i s composed o f b o t h con f ined and p h r e a t i c areas, an apparent storage c o e f f i c i e n t i n s t r u c t u r a l l y con f ined areas can be observed due t o high t r a n s m i s s i v i t y which enables t h e water t o f l o w from t h e p h r e a t i c t o t h e conf ined areas. The storage c o e f f i c i e n t o f t h e con f ined a q u i f e r can be determined by c o n t r o l l e d pumping t e s t s .

7.2.1.3.3 Storage losses and s to rage e f f i c i e n c y ( A r i e I s s a r ) . Groundwater a q u i f e r s a re u s u a l l y l eaky r e s e r v o i r s . Under n a t u r a l cond i t i ons , a dynamic e q u i l i b r i u m e x i s t s between n a t u r a l replenishment and o u t f l o w . Out f low can be through spr ings, base f l o w t o r i v e r s , evapo t ransp i ra t i on , f l o w t o ad jacent aqu i fe rs , and f l o w t o t h e sea by d i r e c t c o n t a c t o r by submerged spr ings. When water l e v e l s a r e lowered, g r a d i e n t s and f l o w r a t e s decrease. A s p r i n g may completely s top f l o w i n g when t h e water l e v e l o f t h e a q u i f e r drops below t h e s p r i n g base. Water volumes added t o t h e a q u i f e r f o r s to rage r e s u l t i n r i s i n g water l e v e l s and e v e n t u a l l y t o inc reased ou t f l ows . A d d i t i o n a l o u t f l o w due t o l a c k o f storage capac i t y may be descr ibed as a storage l o s s .

Subsurface water storage has seve ra l advantages over sur face storage. One obvious advantage common t o a l l t ypes o f a q u i f e r s i s t h e absence o f evapora t ion losses. I n some k a r s t i c reg ions ground-water storage has another advantage, as seepage losses from sur face r e s e r v o i r s a re v e r y high due t o f i s s u r e s and c racks near the surface; thus, sur face r e s e r v o i r s cons t ruc ted i n k a r s t i c reg ions a c t as a r t i f i c i a l ground-water recharge f a c i l i t i e s . An a d d i t i o n a l advantage o f ground water r e s e r v o i r s i n r e l a t i o n t o sur face r e s e r v o i r s i s t h e u s u a l l y smal ler c a p i t a l c o s t i n v o l v e d and t h e p o s s i b i l i t y o f h a n d l i n g t h e development and investment i n stages. The savings i n c a p i t a l c o s t i n ground-water s to rage may exceed t h e h i g h e r energy c o s t s needed t o l i f t water from underground. Surface storage f a c i l i t i e s may be used t o supplement ground-water s to rage where underground storage volume i s inadequate. I t may a l s o be p o s s i b l e t o i nc rease the underground storage e f f i c i e n c y , f o r example, by r a i s i n g t h e l e v e l o f d ischarge p o i n t s t o take advantage o f a d d i t i o n a l s to rage volume above t h e dynamic water l e v e l o r by drawing down t h e l e v e l i n p e r i o d s o f low f l o w t o c rea te storage space t h a t would be f i l l e d during replenishment per iods. Care must be taken i n r a i s i n g water l e v e l s t o avo id losses a t h i g h e r d ischarge p o i n t s and i n lower ing l e v e l s t o a v o i d i nduc ing i n f l o w o f water o f undes i rab le q u a l i t y .

7.2.2 Q u a l i t a t i v e e v a l u a t i o n (Stanley W. Posey). A complete k a r s t ground-water resource e v a l u a t i o n must i n c l u d e water q u a l i t y i n v e s t i g a t i o n s . K a r s t systems may p resen t water q u a l i t y problems v e r y d i f f e r e n t f rom those encountered i n g ranu la r a q u i f e r s because o f t h e r e l a t i v e l y high r a t e o f movement through a k a r s t a q u i f e r and t h e absence o f f i l t r a t i o n c a p a c i t y i n t h e f low p a t h i n a k a r s t system. Chemical p r o p e r t i e s o f k a r s t ground water and methods o f i n v e s t i g a t i o n f o r water q u a l i t y a re discussed elsewhere i n t h i s Guide.

Water q u a l i t y i n v e s t i g a t i o n s can be undertaken as a means o f de te rm in ing the o r i g i n and behav io r o f t h e water o r can be d i r e c t e d toward assessing t h e s u i t a b i l i t y o f t h e water f o r a p a r t i c u l a r use. I t i s p r i m a r i l y t h e l a t t e r

Water q u a l i t y must be g i v e n c o n s i d e r a t i o n i n any development scheme because o f p o s s i b l e r e s t r i c t i o n s on t h e use o f t h e water. K a r s t ground water i s sub jec t t o b a c t e r i a l con taminat ion because o f t h e l a c k of f i l t r a t i o n capac i t y i n a k a r s t system (Burdon and Papakis, 1963) which may make i t u n s u i t a b l e f o r domestic use. Developers i n c o a s t a l areas may encounter problems w i t h s a l t water i n t r u s i o n . L o c a l c o n d i t i o n s may r e s u l t i n v a r i o u s k i n d s o f domestic, a g r i c u l t u r a l o r i n d u s t r i a l con taminat ion t h a t c o u l d f o r c e

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, o b j e c t i v e t h a t i s o f i n t e r e s t f o r development purposes.

consumers t o t r e a t t h e water o r c o u l d make the water u n s u i t a b l e f o r use. Water q u a l i t y may d e t e r i o r a t e over t ime where ground water w i thdrawals induce o r a l l o w i n f i l t r a t i o n o f lower q u a l i t y water. The e f f e c t o f t h e water q u a l i t y w i l l v a r y depending on t h e d e s i r e d end use; f o r example, water t h a t i s u n s u i t a b l e f o r human consumption may be adequately s u i t a b l e f o r a g r i c u l t u r a l o r i n d u s t r i a l use.

Water q u a l i t y analyses should be a p a r t o f t h e i n i t i a l resource e v a l u a t i o n and should be repeated p e r i o d i c a l l y a f t e r development i s begun t o d e t e c t any changes.

7.2.3 System a n a l y s i s (Stanley W . Posey). The r e s u l t s o f a comprehensive ground-water resources e v a l u a t i o n may be used t o analyze and p r e d i c t t h e behav io r o f t h e system. A comprehensive e v a l u a t i o n as contemplated here would i n c l u d e s t u d i e s o f geology, ground- and surface-water hydro logy and hydrogeology, and c l ima te . The v a r i o u s d i s c i p l i n e s may then be i n t e g r a t e d t o analyze t h e o v e r a l l h y d r o l o g i c regime.

A most u s e f u l t o o l i n t h i s t ype o f a n a l y s i s i s a model. A model may be d e f i n e d as a s imu la t i on , by means o f d e s c r i p t i o n , s t a t i s t i c a l data, o r analogy, o f a phenomenon o r process t h a t cannot be observed d i r e c t l y o r t h a t i s d i f f i c u l t t o observe d i r e c t l y (Bates and Jackson, eds., 1 9 8 0 ) . Models va ry g r e a t l y i n f u n c t i o n , u t i l i t y , and complex i ty and must be chosen and a p p l i e d accord ing ly . A p r o p e r l y designed and v e r i f i e d model can s imulate t h e behav io r o f t h e h y d r o l o g i c system and can be used t o p r e d i c t changes i n t h e system under v a r i o u s cond i t i ons , such as pumping o r drought.

Models a re g e n e r a l l y o f two types, analog and d i g i t a l . The p r i n c i p a l d i f f e r e n c e between them i s t h a t t h e system and i t s behav io r are s imu la ted by a r e s i s t o r - c a p a c i t o r network i n an e l e c t r i c - a n a l o g model and are s imu la ted by mathematical r e l a t i o n s h i p s i n a d i g i t a l model (Moore, 1 9 7 9 ) . The analog model r e q u i r e s a p h y s i c a l c o n s t r u c t i o n which r e s t r i c t s i t s wide-spread a p p l i c a b i l i t y . D i g i t a l models i n v o l v e t h e s o l u t i o n o f mathematical f unc t i ons , which r e q u i r e s a computer f o r t h e more s o p h i s t i c a t e d models. R e l a t i v e l y s imple s imu la t i ons may be done by hand. Po r tab le o r hand-held c a l c u l a t o r s may be used f o r some computations, as discussed by Cro ley ( 1 9 7 7 ) . Whi le t h e use o f d i g i t a l models was once l i m i t e d by computer a v a i l a b i l i t y and capaci ty , developments i n computer technology and programming have made computers more power fu l , f a s t e r , l e s s expensive, s imp ler t o program and operate, and more w i d e l y a v a i l a b l e . D i g i t a l models may be used t o determine t h e e f f e c t s o f economic and l e g a l c o n s t r a i n t s on water use as w e l l as t o s imu la te the p h y s i c a l behav io r o f t he system. Models have been used t o eva lua te e f f e c t s o f i r r i g a t i o n w e l l s on stream f low, ground-water m i n i n g , s a l t water i n t r u s i o n , e f f e c t s o f l ock - and dam- c o n s t r u c t i o n on t h e water t a b l e , t r a n s p o r t o f contaminants, and subsidence due t o ground-water w i thdrawal (Moore, 1 9 7 9 ) .

One o f t h e more impor tan t c h a r a c t e r i s t i c s o f a model i s i t s a b i l i t y t o i n t e g r a t e and concur ren t l y eva lua te t h e component p a r t s o f a hyd ro log i c system, such as sur face water, ground water i n s i n g l e o r m u l t i p l e aqu i fe rs , p r e c i p i t a t i o n , and evapo t ransp i ra t i on . Th is process may be as s imple as f o r m u l a t i o n o f a r e g i o n a l water budget (which may be thought o f as a model) i n an undeveloped area. A more compl icated s i m u l a t i o n would be necessary f o r a h i g h l y developed m e t r o p o l i t a n o r i n d u s t r i a l system w i t h complex h y d r o l o g i c i n t e r a c t i o n s . Th is i n t e g r a t i o n func t i on can o n l y be performed i f t h e r e are s u f f i c i e n t , r e l i a b l e data a v a i l a b l e on each component o f t h e system.

Moore (1979) i d e n t i f i e d f o u r major steps i n an i n t e n s i v e h y d r o l o g i c study u s i n g a model as fo l l ows :

1. C o l l e c t and i n t e r p r e t data; 2. Develop t h e model: 3. V e r i f y t h e model; 4 . Use t h e model f o r e v a l u a t i o n o f water problems and p r e d i c t i o n o f

Data c o l l e c t i o n and i n t e r p r e t a t i o n should beg in w i t h a rev iew o f e x i s t i n g da ta t o d e f i n e t h e genera l cha rac te r o f t h e system and t o develop a broad, conceptual model o f t h e system. Based on t h i s review, da ta d e f i c i e n c i e s can be i d e n t i f i e d and a program o f da ta c o l l e c t i o n can be developed. The data c o l l e c t i o n program should be coord ina ted w i t h t he model development t o i n s u r e t h a t t h e r e q u i r e d data w i l l be gathered.

f u t u r e changes.

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Model development may range i n complex i ty from minor m o d i f i c a t i o n o f an e x i s t i n g model t o c r e a t i o n o f a new s i m u l a t i o n technique. There are l i t e r a l l y hundreds o f p u b l i c l y a v a i l a b l e models f o r h y d r o l o g i c s imu la t i on . Bachmat e t a l . (1978). compiled a l i s t o f 250 d i g i t a l models, ca tegor i zed i n t o p r e d i c t i o n , management, and d a t a management; Walton (1979) l i s t e d 35 a n a l y t i c a l - m o d e l s . Many o f t h e models l i s t e d a re p u b l i c l y a v a i l a b l e . These and o t h e r models may be usable i n a p a r t i c u l a r s i t u a t i o n w i t h v a r y i n g degrees o f m o d i f i c a t i o n o r a l t e r a t i o n requ i red . S imu la t i on concepts and techniques were discussed by Domenico (19721, Fleming (1975) and Bachmat, e t a l . ( 1 9 7 8 ) ; research and techno log ica l advances cont inue t o improve these techniques and t h e i r a p p l i c a t i o n .

Once a model i s developed, i t s a p p l i c a b i l i t y t o t h e system must be v e r i f i e d . The a c t u a l behav io r o f t h e system under v a r i o u s c o n d i t i o n s , determined by d i r e c t measurement and obse rva t i on o f t h e system components, should be compared t o t h e behav io r p r e d i c t e d by t h e model. Attempts t o v e r i f y t he model may r e v e a l data d e f i c i e n c i e s o r inadequacies which must be e l i m i n a t e d be fo re model t e s t i n g can cont inue. I f m o d i f i c a t i o n s t o t h e model a re then requi red, t h e v e r i f i c a t i o n procedure must be repeated u n t i l a c t u a l and p r e d i c t e d behav io r co inc ide o r d i f f e r e n c e s f a l l w i t h i n acceptable l i m i t s . System m o n i t o r i n g should be cont inued as a long-term v e r i f i c a t i o n and m o d i f i c a t i o n e f f o r t .

When t h e model has been v e r i f i e d , i t may be used t o p r e d i c t system behavior. T h i s p r e d i c t i v e f u n c t i o n of t h e model i s most va luab le i n development and management as i t a l l ows de te rm ina t ion o f t h e e f f e c t s o f v a r i o u s development schemes and management techniques.

Models may be o f p a r t i c u l a r use fu lness i n k a r s t systems because o f t h e complex hydrogeology and t h e t y p i c a l l y c l o s e r e l a t i o n s h i p s among ground water, surface water, and c l ima te . Many o f t h e models discussed i n t h e l i t e r a t u r e have been developed and t e s t e d i n g ranu la r aqu i fe rs ; g r e a t care must be taken i n adapt ing and a p p l y i n g these t o k a r s t systems. Granular a q u i f e r models may be a p p l i c a b l e t o l a rge -sca le ( r e g i o n a l o r basin-wide) analyses o f k a r s t systems; Basmaci and Sendlein (1977) concluded t h a t g ranu la r mass models cou ld be a p p l i e d t o s o l u t i o n channel f l o w where t h e study area was so l a r g e t h a t t h e d i f f e r e n c e s i n f l o w c h a r a c t e r i s t i c s were o n l y a m a t t e r o f scale. I n genera l , however, model s t u d i e s a re r e q u i r e d f o r smal le r areas and models s p e c i f i c a l l y developed f o r k a r s t systems should be p r e f e r r e d . Mode l l i ng p r i n c i p l e s and t h e o r i e s f o r k a r s t a q u i f e r a p p l i c a t i o n have been discussed by a number o f researchers i n c l u d i n g Basmaci and Send le in (1977) , T h r a i l k i l l and B e i t e r (19741 , and T ivadar (1971). D r e i s s (1980) d id a study o f t h e a p p l i c a t i o n o f systems a n a l y s i s t o k a r s t a q u i f e r s . I t must always be remembered t h a t a model o f any type can o n l y be as accura te o r r e l i a b l e as t h e da ta supp l i ed f o r it.

Model development f o r a p a r t i c u l a r k a r s t system may i n many cases f o l l o w models prepared f o r s i m i l a r k a r s t systems elsewhere. These models may r e q u i r e o n l y minor m o d i f i c a t i o n o r adapta t ion , depending on t h e degree o f s i m i l a r i t y between t h e systems. Among t h e many models developed and t e s t e d are those f o r t he f o l l o w i n g k a r s t areas: c o a s t a l p l a i n o f I s r a e l (Bear, 1 9 6 6 ) ; Kairovan, Tun is ia (Besbes and deMarsi ly, 1978); A q u i t a i n Basin o f France (Besbes, e t a l . , 1978); t h e Hortus r e g i o n o f France (Bonnett , e t a l . , 1979); San Anton io reg ion , Texas, USA (Klemt, e t a l . , 1 9 7 9 ) ; Winnipeg area, Canada (Render, 1971); wes t -cent ra l Kentucky, USA ( T h r a i J k i l l , 1974); R i o Cobre, Jamaica (Wi l l i ams and B l a i r , 1969); and wes t -cen t ra l F l o r i d a , USA (Wilson and Gerhart , 1979).

7 . 3 Development ( A r i e I s s a r and Stan ley W. Posey)

As discussed he re in , 'development" r e f e r s t o t h e c a p t u r i n g o r e x t r a c t i o n o f t h e ground-water resource i d e n t i f i e d by t h e hydrogeologic i n v e s t i g a t i o n s and resource eva lua t ions . Development o f k a r s t waters can take p l a c e e i t h e r a t , o r i n connect ion w i t h , t h e known p o i n t s o f n a t u r a l i s s u e a t sp r ings o r by t h e development o f new p o i n t s of issue, such as boreholes o r g a l l e r i e s . T h i s d i scuss ion presumes t h a t p rev ious s t u d i e s have i d e n t i f i e d k a r s t ground-water resources s u i t a b l e f o r development.

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7.3.1 P r e l i m i n a r y s tud ies. P r i o r t o i n i t i a t i o n o f any o f t h e development techniques discussed below s p e c i a l i z e d s tud ies must be undertaken t o i n s u r e e f f i c i e n t and economical development. The r e s u l t s o f t h e eng ineer ing and economic s t u d i e s should be combined w i t h those o f t h e hydrogeologic i n v e s t i g a t i o n s and resource eva lua t i ons t o design a development p r o j e c t t h a t i nco rpo ra tes b o t h e x p l o i t a t i o n and conserva t ion o b j e c t i v e s and i s c o s t e f f e c t i v e . Methods o f c o s t e s t i m a t i o n f o r t he v a r i o u s aspects o f a development p r o j e c t a re discussed elsewhere i n t h i s Guide.

7.3.2 Development techniques. The f o l l o w i n g d i scuss ion o f development techniques i s n o t meant t o cover a l l p o s s i b l e techniques. Development techniques a re s u b j e c t t o c o n t i n u i n g improvement and c u r r e n t l i t e r a t u r e should be consu l ted f o r t h e l a t e s t advances.

7.3.2.1 We l l s and w e l l f i e l d s . An i n c r e a s i n g l y common method o f k a r s t ground-water e x p l o i t a t i o n i s by pump ing from a w e l l (borehole) o r from a system of w e l l s known as a w e l l f i e l d . Fo r many development purposes, a s i n g l e w e l l w i l l produce s u f f i c i e n t volumes; l a r g e r p r o j e c t s such as a m e t r o p o l i t a n water supply may r e q u i r e an ex tens i ve w e l l f i e l d .

Because o f t h e c o s t o f d r i l l i n g w e l l s i n k a r s t , p r e l i m i n a r y s tud ies must be c a r e f u l l y executed t o l o c a t e p rospec t i ve w e l l s where t h e p o s s i b i l i t y o f success i s t h e h ighest . The i n f o r m a t i o n f o r de termina t ion o f t h e optimum w e l l l o c a t i o n may come from e x p l o r a t o r y boreholes o r f rom t h e hydrogeologic i n v e s t i g a t i o n s . I n some cases i t w i l l be p o s s i b l e t o conver t e x p l o r a t o r y boreho les t o p r o d u c t i o n w e l l s . K a r s t a q u i f e r s a re t y p i c a l l y most p roduc t i ve where secondary p o r o s i t y has developed a long f a u l t s and zones o f f r a c t u r i n g and j o i n t i n g . Lattman and Par izek ( 1 9 6 4 ) found f r a c t u r e t r a c e s t o i n d i c a t e zones of inc reased weathering, s o l u t i o n i n g , and pe rmeab i l i t y ; l ineaments as i d e n t i f i e d by i n t e r p r e t a t i o n o f a e r i a l photographs were r e l a t e d t o t h e l o c a t i o n s of h i g h - y i e l d w e l l s by LaRicc ia and Rauch ( 1 9 7 7 ) . S a t e l l i t e imagery was a l s o used t o l o c a t e l ineaments and h i g h - y i e l d w e l l s i n a k a r s t area by Moore, e t a l . (1977) and by Par i zek ( 1 9 7 6 ) . W e l l l o c a t i o n may be cons t ra ined by non-geologic f a c t o r s such as where an i n d u s t r i a l developer i s l i m i t e d t o l o c a t i o n s d e f i n e d by p r o p e r t y ownership. Governmental o r p u b l i c development p r o j e c t s a r e n o t commonly r e s t r i c t e d by such cons idera t ions .

There a re a number o f w e l l d r i l l i n g methods t h a t can be used i n k a r s t ter ranes. O f these, percuss ion ( o r cab le - too l ) and a i r r o t a r y methods have been and cont inue t o be t h e most w i d e l y employed. A study o f water w e l l d r i l l i n g i n t h e U n i t e d States i n 1 9 7 8 showed t h a t percussion and r o t a r y methods were used on n e a r l y 75 pe rcen t o f t h e w e l l s d r i l l e d , w i t h r o t a r y methods account ing f o r almost 6 0 pe rcen t o f t h e t o t a l ( N a t i o n a l Water W e l l Assoc ia t ion , 1 9 8 1 ) .

The percussion, o r c a b l e - t o o l method, i s based on t h e pounding and c rush ing o f t h e rock by a v e r t i c a l l y moving heavy s t e e l b i t . The f o r c e on t h e rock i s a p p l i e d by t h e l i f t i n g and dropping o f t he b i t . The crushed rock i s removed from t h e h o l e by a b a i l e r , equipped i n i t s lower p a r t w i t h a t r a p p i n g device, t h a t i s lowered i n t o t h e h o l e a f t e r a c e r t a i n amount o f progress has been made. The r o t a r y method i s based on t h e g r i n d i n g o f t h e rock by a r o t a t i n g b i t . The f o r c e on t h e rock i s supp l ied by the r o t a t i o n o f t he b i t and downward pressure from t h e r i g and t h e we igh t o f t he d r i l l rods. Cleaning o f t he h o l e as w e l l as c o o l i n g o f t he b i t i s done by c i r c u l a t i n g d r i l l i n g f lu id , mud o r a i r which i s pumped down through the ho l l ow d r i l l i n g rods and then ascends th rough t h e annulus between the rods and t h e w a l l o f t he hole. Th is mud coats t h e w a l l s o f t h e h o l e and he lps prevent cav ing and l o s s o f d r i l l i n g f lu id .

7.3.2.1.1 Choice of d r i l l i n g methods. The dec i s ion as t o what d r i l l i n g method t o choose f o r a p a r t i c u l a r j o b depends on seve ra l f a c t o r s i n c l u d i n g the w e l l depth, t h e pumping head, r e l a t i v e costs , r i g and crew a v a i l a b i l i t y , and the r e q u i r e d y i e l d o f t h e w e l l , which d i c t a t e s the w e l l diameter. Other impor tan t f a c t o r s are t h e na tu re o f t h e rock i n the subsurface, t h e a v a i l a b i l i t y o f a water supply f o r d r i l l i n g mud, t h e t ime a v a i l a b l e f o r d r i l l i n g , t he space

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a v a i l a b l e f o r t he d r i l l i n g s i t e , and t h e a v a i l a b i l i t y o f dependable i n f o r m a t i o n on the subsurface geology.

The r o t a r y method i s u s u a l l y p r e f e r r e d when w e l l depths exceed 500 meters w i t h an expected pumping depth of more than 200 m and r e q u i r e d y i e l d s a re on t h e o rde r o f magnitude o f hundreds o f cub ic meters p e r hour. The r o t a r y method i s a l s o favored when i n t e r b e d d i n g o f mar l y l a y e r s between t h e l imestone and d o l o m i t i c l a y e r s i s expected. I n t h i s case, i f one were d r i l l i n g by percussion, t h e danger o f t h e mar l s cav ing i n would r e q u i r e p r o t e c t i n g t h e w a l l s o f t h e d r i l l h o l e w i t h cas ing d u r i n g d r i l l i n g . The use o f cas ing would r e q u i r e a f requent r e d u c t i o n o f t h e diameter o f t h e w e l l which cou ld r e s u l t i n an i n s u f f i c i e n t h o l e s i z e f o r a h i g h c a p a c i t y pump.

The a v a i l a b i l i t y o f a water supply f o r t h e d r i l l i n g mud i s impor tan t i n p lann ing p ioneer w e l l s where t h e r e i s no e x i s t i n g water supply i n t h e v i c i n i t y and where t r a n s p o r t i n g water f rom f a r away would inc rease t h e c o s t o f d r i l l i n g beyond economic l i m i t s . I n cases where a t o t a l l o s s o f c i r c u l a t i o n i s expected, h a u l i n g water by tanke rs may n o t p r o v i d e a s u f f i c i e n t water supply t o guarantee the cont inuous o p e r a t i o n o f t h e r i g . I n such cases, t h e i n i t i a l d r i l l i n g may be c a r r i e d o u t by a percuss ion r i g . A sma l l d iameter r o t a r y r i g u s i n g the a i r f l u s h method may a l s o be used. However, when o r d i n a r y equipment i s used f o r a i r r o t a r y d r i l l i n g , t h e w e l l must have a r a t h e r sma l l diameter. The use o f high c a p a c i t y compressors and foam i n s t e a d o f d r y a i r below t h e water t a b l e now enables one t o d r i l l deep, l a r g e diameter w e l l s w i t h t h e a i d o f a r e l a t i v e l y sma l l supply o f water. Those methods, however, r e q u i r e h i g h l y t r a i n e d d r i l l e r s and s p e c i a l equipment.

The d r i l l i n g t ime r e q u i r e d f o r r o t a r y method i s much s h o r t e r than f o r t h e percuss ion method, e s p e c i a l l y when t h e crew and work a re e f f i c i e n t l y organized. I t i s d i f f i c u l t t o compare t h e d r i l l i n g p rogress f o r t h e two methods a s t h e r a t e d i f f e r s f rom s i t e t o s i t e . I t can be g e n e r a l l y s t a t e d t h a t t h e r a t e o f progress i n r o t a r y d r i l l i n g may be between t h r e e t o t e n t imes more than f o r percuss ion d r i l l i n g . However, as t h e e r e c t i o n and d i s m a n t l i n g o f l a r g e r o t a r y r i g s and p r e p a r a t i o n o f t h e s i t e takes more t ime than f o r t h e percuss ion r i g , t h e d e c i s i o n i n cases o f r e l a t i v e l y shal low w e l l s may s t i l l be i n favo r o f t h e percuss ion r i g .

I n rega rd t o t h e s i z e o f t h e d r i l l i n g s i t e , t h e percuss ion r i g needs l e s s space and i n areas where space i s l i m i t e d , t h e d e c i s i o n may be i n favo r o f t h e percussion r ig .

I n some ins tances t h e need f o r r e l i a b l e i n f o r m a t i o n on t h e subsurface may be a f a c t o r i n p r e f e r r i n g one method over t h e o the r . I n percuss ion d r i l l i n g , samples a re brought up every few meters by t h e b a i l e r and t h i s makes i t p o s s i b l e t o keep a cont inuous obse rva t i on and r e c o r d o f t h e na tu re o f t h e rocks be ing d r i l l e d through. I n r o t a r y d r i l l i n g i n carbonate rocks, l o s s o f c i r c u l a t i o n i s q u i t e f requent , which prec ludes cont inuous sample c o l l e c t i o n . Samplings i n t h i s case have t o be c a r r i e d o u t by c o r i n g devices which a re r a t h e r expensive; geophysical l o g g i n g and a r a t e o f p e n e t r a t i o n l o g h e l p i n i n t e r p r e t i n g t h e data.

On t h e o t h e r hand, core samples ob ta ined from r o t a r y d r i l l i n g a re u s e f u l when l a b o r a t o r y t e s t s have t o be c a r r i e d o u t on samples. I t should, however, be borne i n mind t h a t t h e p e r m e a b i l i t y o f carbonate rocks may, a t t imes, be a r e s u l t of l a r g e f i s s u r e s and s o l u t i o n channels which w i l l n o t be i n d i c a t e d by core samples.

The f o l l o w i n g i s a summary of t h e advantages and disadvantages o f t h e two methods :

Percussion - advantages 1. Large q u a n t i t i e s o f water o r a i r f o r d r i l l i n g a re unnecessary. 2. 3. Good i d e n t i f i c a t i o n o f l a y e r s during d r i l l i n g . 4 . Requires a r e l a t i v e l y smal le r space f o r d r i l l i n g s i t e . 5. Requires o n l y average s k i l l e d d r i l l e r s .

No danger o f c l o g g i n g l a y e r s by d r i l l i n g mud: -

Percussion - disadvantages 1. Slow Droaress.

L d

2. Requires cas ing f o r p r o t e c t i n g t h e w a l l s where cav ing fo rmat ions a re penetrated; as a r e s u l t , t h e h o l e diameter has t o be reduced

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a t predetermined i n t e r v a l s . Problems may a l s o a r i s e a t t he end when t h e casings used during d r i l l i n g are t o be p u l l e d ou t .

Rotary - advantages 1. Fas t progress. -~ 2. Seldom r e q u i r e s casing, thus can r e t a i n l a r g e diameter t o g rea te r

3. Can pene t ra te g r e a t e r depths. depths.

Rotary - disadvantages 1. Needs a cont inuous supplv o f water, a i r . o r foam. ..- - 2. Sampling o f rock and water i s n o t co.ntinuous n o r dependable, and

3. Requires ample space and h i g h l y s k i l l e d technic ians.

Two o f t h e most impor tan t m o d i f i e d d r i l l i n g methods f o r k a r s t a p p l i c a t i o n s a re downhole-hammer ( a l s o c a l l e d a i r -pe rcuss ion r o t a r y ) d r i l l i n g and a v a r i a t i o n o f r e v e r s e - c i r c u l a t i o n r o t a r y d r i l l i n g .

Downhole-hammer d r i l l i n g uses a percuss ion "machine" a t tached t o the bo t tom o f t he d r i l l s t r i n g . The power f o r t h e hammer i s supp l i ed by the c i r c u l a t i o n o f compressed a i r ; t h e o t h e r p a r t s o f t h e d r i l l i n g apparatus are t h e same as f o r conven t iona l a i r - c i r c u l a t i o n r o t a r y d r i l l i n g . Water o r foam may be added t o t h e compressed a i r t o c o o l t h e b i t , f a c i l i t a t e removal o f c u t t i n g s , and suppress dust. T h i s method i s most comparable t o a i r - r o t a r y d r i l l i n g , though t h e p e n e t r a t i o n r a t e i s t y p i c a l l y much g r e a t e r f o r t he downhole-hammer.

Reverse -c i r cu la t i on d r i l l i n g i s s i m i l a r t o r o t a r y d r i l l i n g except t h a t water ( o r mud) i s supp l i ed th rough t h e annulus o f t h e h o l e and t h e water and c u t t i n g s a re drawn up through t h e d r i l l rods. Th is method r e q u i r e s l a r g e volumes o f water where permeable fo rmat ions a re encountered o r c i r c u l a t i o n l o s s may be expected. A v a r i a t i o n o f r e v e r s e - c i r c u l a t i o n r o t a r y d r i l l i n g uses a s p e c i a l d u a l - w a l l d r i l l r o d which has a c i r c u l a t i o n tube conta ined w i t h i n t he d r i l l rod. F l u i d ( a i r o r water) and c u t t i n g s a re drawn up t h e i n t e r n a l p ipe; t h e d r i l l i n g f l u i d i s supp l i ed i n the annulus between the i n t e r n a l and e x t e r n a l p ipes. Th is method i s n o t a f f e c t e d by l o s s o f c i r c u l a t i o n as would be common i n k a r s t areas and p rov ides continuous, uncontaminated samples (Bruner, 1 9 7 9 and Ingerso l l -Rand Co., 1 9 7 8 ) . Th i s method r e q u i r e s s p e c i a l equipment which may n o t be r e a d i l y a v a i l a b l e .

For f u r t h e r read ing on d r i l l i n g methods and technology the reader may r e f e r t o Campbell and Lehr ( 1 9 7 3 ) .

r e q u i r e s s p e c i a l co r ing , logging, and water sampling devices.

7.3.2.1.2 W e l l s t i m u l a t i o n . W e l l s t i m u l a t i o n has been de f i ned as t rea tment o f a w e l l by mechanical, chemical, o r o t h e r means f o r t h e purpose o f reduc ing o r removing an underground r e s i s t a n c e t o f l o w (Koenig, 1 9 6 0 ) . S t i m u l a t i o n may i n v o l v e t rea tment o f t h e w e l l and/or t h e a q u i f e r .

Campbell and Lehr ( 1 9 7 3 ) i d e n t i f i e d and discussed i n d e t a i l f i v e major ca tegor ies o f s t i m u l a t i o n methods: surging, j e t t i n g , a c i d i z i n g , b l a s t i n g , and h y d r a u l i c f r a c t u r i n g . Surging and j e t t i n g i n v o l v e f l u s h i n g a c t i o n and h i g h pressure water o r a i r , r e s p e c t i v e l y , t o remove s i l t s , c lays, d r i l l i n g muds, and f i n e m a t e r i a l t h a t may be b l o c k i n g t h e w e l l screen o r f r a c t u r e s i n t h e a q u i f e r . E i t h e r method may be enhanced by t h e a d d i t i o n o f chemicals t o t h e f lu id .

A c i d i z a t i o n i s t h e most impor tan t method used f o r improving w e l l c a p a c i t i e s i n carbonate rocks. Th is method i s based on t h e d i s s o l u t i o n which carbonate rocks undergo when they come i n con tac t w i t h ac id . These processes cause openings, such as f i s s u r e s and s o l u t i o n channels, t o enlarge. A c i d i z a t i o n methods were f i r s t used i n o i l w e l l s , and o n l y s ince the 1940s has t h i s p r a c t i c e become widespread i n t h e f i e l d o f water w e l l s .

A survey o f t h e r e s u l t s ob ta ined from a c i d i z a t i o n o f about 500 w e l l s was done by Koenig ( 1 9 6 0 ) . Th i s survey found t h a t t he a c i d most o f t e n used i s h y d r o c h l o r i c (HC1) a l though a c e t i c , f o rm ic and o t h e r ac ids a re a l s o used.

The chemical r e a c t i o n between a c i d and rock i n t h e case o f h y d r o c h l o r i c a c i d i s :

2HC1 + CaC03 - CaC12 + CO2 + H20 (7.3-1)

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The s o l u b i l i t y o f CaC12 i s high (about 900 kg t o 1 m 3 ) and t h e r e s u l t i n g s o l u t i o n may be t o t a l l y removed from t h e w e l l by pumpage. The r a t e o f t h e r e a c t i o n (unit q u a n t i t y o f a c i d / u n i t area o f r o c k / u n i t o f t ime) i s e f f e c t e d by temperature, pressure, t h e concen t ra t i on o f t h e ac id , and t h e n a t u r e o f t h e rock t o be t r e a t e d .

While h i g h e r temperatures s t i m u l a t e t h e r a t e o f r e a c t i o n , high pressures r e t a r d the r e a c t i o n . I t was found t h a t t h e o p t i m a l concen t ra t i on o f a c i d i s between 2 2 and 2 4 pe rcen t (Van Poolen and Jargon, 1 9 6 8 ) . I t was a l s o found t h a t one o f t h e f a c t o r s r e t a r d i n g , and even a r r e s t i n g , t h e r e a c t i o n i s t he r a p i d p roduc t i on o f CO2 which, i n the form o f gas, p revents a d i r e c t c o n t a c t between t h e rock and the ac id . Th is i n d i c a t e s a p re fe rence i n some ins tances f o r l e s s a c t i v e ac ids such as n i t r i c (HNO3), phosphor ic (H~POL,) o r a c e t i c (CH3COOH). However, i t was found t h a t HC1 i s u s u a l l y t h e most economical a c i d due t o i t s lower cost . I n o rde r t o r e t a r d the r a t e o f p r o d u c t i o n o f CO2 and t o lengthen t h e t ime o f c o n t a c t between t h e a c i d and t h e rock, v a r i o u s re ta rdan ts a re used, such as d i f f e r e n t k i n d s o f ge l s . When m e t a l p a r t s a re present, c o r r o s i o n i n h i b i t o r s a l s o need t o be appl ied. The r e t a r d a n t s and i n h i b i t o r s as w e l l as an t i - foam m a t e r i a l s a re manufactured by t h e l e a d i n g chemical companies under v a r i o u s names.

I n o rde r t o p l a n f i e l d ope ra t i ons according t o t h e s p e c i f i c c o n d i t i o n s i n each w e l l , l a b o r a t o r y equipment was developed by t h e o i l i n d u s t r y f o r t e s t i n g w e l l samples. Al though t h e r e s u l t s o f these t e s t s may a l s o be r e l e v a n t f o r water w e l l s , i t should be borne i n m i n d t h a t t h e secondary p e r m e a b i l i t y o f carbonate rocks i s ma in l y due t o r a t h e r l a r g e s o l u t i o n channels and f i s s u r e s which cannot be seen from w e l l samples o r even cores, and any deduct ion f rom core t e s t s may be erroneous.

Another problem i s t h e cho ice o f c r i t e r i a f o r t h e assessment o f t h e b e n e f i t t o he d e r i v e d from t h e a c i d i z i n g react io 'n. T h i s i s impor tan t i n p lann ing t h e investment i n a f i e l d o f w e l l s ( f o r example, t h e economics o f a c i d i z i n q a number o f w e l l s versus d r i l l i n g a new w e l l ) as w e l l as f o r de termin ing t h e number o f a c i d i z i n g opera t i ons i n a p a r t i c u l a r w e l l .

The most widespread method i s t h e assessment o f t h e ( a ) and ( B ) c o e f f i c i e n t s accord ing t o p u m p i n g t e s t r e s u l t s (Jacob, 1 9 4 7 ) by t h e use o f t h e formula:

s = aQ + BQ2 (7.3-2)

where s = drawdown (m)

Q = discharge (m3 /h )

a = c o e f f i c i e n t o f l o s s due t o fo rma t ion charac ter

B = c o e f f i c i e n t o f l o s s due t o w e l l charac ter

When a comparison o f t h e pumping t e s t s b e f o r e and a f t e r a c i d i z i n g shows a r e d u c t i o n i n ( a ) t h i s i n d i c a t e s t h a t t h e main i n f l u e n c e o f t he a c i d was on t h e format ion. A r e d u c t i o n o f ( 8 ) i n d i c a t e s t h a t t h e major i n f l u e n c e was on t h e w a l l s o f t h e w e l l , which i s ma in l y t h e case i n w e l l s d r i l l e d by t h e r o t a r y method.

From a l i t e r a t u r e survey c a r r i e d o u t seve ra l years ago (Kinsky, e t a l . , 1 9 7 2 ) , i t was found t h a t i n o n l y 10 pe rcen t o f t h e cases ( 6 pe rcen t i n o l d w e l l s ) t he a c i d i z i n g f a i l e d . F a i l u r e s were found t o be due ma in l y t o t h e f o l l o w i n g f a c t o r s :

1. Rocks o f e s p e c i a l l y low p e r m e a b i l i t y . 2. We l l s c o n t a i n i n g c l a y l a y e r s causing water t u r b i d i t y . 3. T h i n and l i m i t e d a q u i f e r s . F u l l knowledge o f t h e n a t u r e o f t h e rock and t h e r e s u l t s o f t he pumping

t e s t must be acqu i red p r i o r t o a c i d i z a t i o n i n o rde r t o i n s u r e t h e success o f any a c i d i z i n g opera t ion .

The cos ts o f a c i d i z i n g va ry w i d e l y and depend on t h e s p e c i f i c c o n d i t i o n s o f each w e l l . I n most cases a c i d i z i n g i s more expensive than su rg ing but i s

2 7 1

cheaper than o t h e r s t i m u l a t i o n methods such as h y d r a u l i c f r a c t u r i n g and b l a s t i n g .

B l a s t i n g ( o r shoot ing) may be used where a w e l l d r i l l e d i n t o a known k a r s t system has f a i l e d t o encounter p r o d u c t i v e f r a c t u r e s o r openings. B l a s t i n g can be used t o c r e a t e f r a c t u r e s , connect ing the w e l l bo re t o t h e water-bear ing openings i n t h e a q u i f e r . B l a s t i n g g e n e r a l l y i n v o l v e s de tona t ion o f a massive charge o f exp los i ve i n t h e w e l l ; a v a r i a t i o n o f t h i s , c a l l e d v i b r a t o r y exp los ion , i n v o l v e s exp los ion o f r e l a t i v e l y smal l , shaped charges i n a r a p i d sequence, which produces a v i b r a t i o n i n the w e l l bore and t h e format ion. Any form o f b l a s t i n g should be considered dangerous and should o n l y be c a r r i e d o u t by t r a i n e d personnel .

H y d r a u l i c f r a c t u r i n g i s a w e l l s t i m u l a t i o n technique developed f o r o i l w e l l s which i n v o l v e s i n j e c t i o n o f a f r a c t u r i n g f l u i d i n t o t h e w e l l a t ve ry h i g h pressures t o f o r c e open e x i s t i n g f r a c t u r e s and c rea te new ones. Sand i n j e c t e d w i t h o r a f t e r t h e f r a c t u r i n g f l u i d ho lds t h e f r a c t u r e s open. Hydrau l i c f r a c t u r i n g may be q u i t e expensive and r e q u i r e s s p e c i a l equipment and m a t e r i a l s which may n o t be r e a d i l y a v a i l a b l e .

Aqu i fe r t e s t s should be performed be fo re and a f t e r use o f any o f these w e l l s t i m u l a t i o n procedures. Assessment o f t h e e f f e c t i v e n e s s o f the s t i m u l a t i o n w i l l be u s e f u l f o r ana lys i s o f t h e w e l l and f o r p lann ing s t i m u l a t i o n s f o r o t h e r w e l l s .

7.3.2.1.3 W e l l c o n s t r u c t i o n and equipment. W e l l c o n s t r u c t i o n and equipment w i l l v a r y g r e a t l y depending on t h e c h a r a c t e r i s t i c s o f t h e , p a r t i c u l a r development p r o j e c t and of t h e sur face and subsurface geology. A d e t a i l e d d i scuss ion o f w e l l c o n s t r u c t i o n and equipment i s beyond t h e scope o f t h i s Guide; methods o f c o s t e s t i m a t i o n f o r w e l l equipment are discussed i n a l a t e r chapter. Campbell and Lehr (1973) compiled d e t a i l e d analyses o f water w e l l technology and Johnson D i v i s i o n (1975) has pub l i shed an e x c e l l e n t re fe rence f o r a l l aspects o f water w e l l d r i l l i n g and cons t ruc t i on .

7.3.2.2 A d i t s , sha f t s , and g a l l e r i e s . Ad i t s , shafts, and g a l l e r i e s are types o f excavat ions which were more commonly used f o r ground-water resource e x p l o i t a t i o n p r i o r t o t h e development and widespread use o f d r i l l i n g technology. A d i t s a re h o r i z o n t a l o r s l i g h t l y i n c l i n e d openings d r i v e n from the surface, s h a f t s a re v e r t i c a l openings, and g a l l e r i e s a re h o r i z o n t a l o r subhor i zon ta l openings d r i v e n outward from a sha f t (Burdon and Papakis, 1 9 6 3 ) . These c o n s t r u c t i o n s were most commonly d i r e c t e d toward t h e c a p t u r i n g o r augmentation o f s p r i n g f low. G a l l e r i e s were d r i v e n i n t o carbonate a q u i f e r s t o inc rease t h e y i e l d from sp r ings by e n l a r g i n g the s o l u t i o n channels feeding them o r by d i v e r t i n g f l o w from o t h e r seepages o r openings t o a main spr ing.

The p r i n c i p a l advantage o f excavat ions o f t h i s t ype i n carbonate a q u i f e r s i s t h e i r s ize. Because k a r s t ground water e x i s t s i n f r a c t u r e s , j o i n t s , and secondary p o r o s i t y spaces r a t h e r than i n the rock m a t r i x , a l a r g e r opening such as a s h a f t would have a b e t t e r chance than a s i n g l e w e l l o f encounter ing p r o d u c t i v e volumes o f water. Groundwater e x t r a c t i o n from these excavat ions would be by p u m p i n g from s h a f t s and g a l l e r i e s , by g r a v i t y f l o w i n the case o f a v e r t i c a l l y i n c l i n e d a d i t , o r by s p r i n g e x p l o i t a t i o n techniques where the development i s assoc ia ted w i t h o r r e s u l t s i n spr ing- type f low.

Modern technology can f a c i l i t a t e development of t h i s type; however, i t i s q u i t e expensive. These techniques may be economical where cheap manual l a b o r can be used and c o n d i t i o n s p r o h i b i t d r i l l i n g .

7.3.2.3 E x p l o i t a t i o n o f spr ings. The pr imary method o f s p r i n g development, beyond capture and d i s t r i b u t i o n o f normal f low, h i s t o r i c a l l y has been by the c o n s t r u c t i o n o f dams a t t h e s p r i n g o u t l e t . These dams g e n e r a l l y served two purposes: storage of a p a r t o f t h e s p r i n g f low f o r use i n pe r iods of low y i e l d and r a i s i n g t h e h y d r a u l i c head t o a i d g r a v i t y f l o w d i s t r i b u t i o n f o r i r r i g a t i o n . Such dams a re r e p o r t e d i n Lebanon (Ayoub, 1953) and Mon tpe l i e r and Toulon, France (Paloc, 1 9 6 5 ) . Such a dam may r e s u l t i n t h e l o s s o f water due t o the o v e r f l o w o f t h e water s t o r e d beh ind t h e dam i n t o s o l u t i o n c a v i t i e s e x i s t i n g

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above the water t a b l e w i t h d ischarge from another p a r t o f t h e system away from the area o f p lanned use.

A more t e c h n o l o g i c a l l y modern method o f c a p t u r i n g sp r ings which i s a l s o more c o n t r o l l a b l e i s t h e r e d u c t i o n o f f l o w th rough t h e carbonate a q u i f e r s i n t h e d i r e c t i o n o f t h e s p r i n g by means o f a planned overpumpage o f t h e a q u i f e r by a number o f w e l l s . Th i s method i s e s p e c i a l l y f avo rab le i n areas where the water i s needed f o r i r r i g a t i o n ma in l y i n t h e h o t d r y season, and where t h e maximum s p r i n g f l o w occurs during, o r a t t h e end o f , t h e c o l d r a i n y season (A ron is e t a l . , 1 9 6 1 ) .

Th i s method o f e x p l o i t a t i o n i s designed t o take c e r t a i n q u a n t i t i e s o f water s to red i n t h e a q u i f e r d u r i n g t h e p e r i o d o f h i g h demand and low f low b y a r t i f i c i a l l y l ower ing t h e water t a b l e i n t h e a q u i f e r t h a t feeds t h e sp r ing . T h i s may r e s u l t i n a t o t a l o r p a r t i a l cessa t ion o f s p r i n g f l o w (Schneider, 1 9 6 4 1 , but c rea tes storage f o r f i l l i n g i n p e r i o d s o f maximum f low. Th is method o f e x p l o i t a t i o n r e q u i r e s a d e t a i l e d knowledge o f t h e h y d r o l o g i c a l regime.

U n p r o f i t a b l e investments may occur i n cases where t h e r e g i o n a l water storage, i n c l u d i n g the s p r i n g and t h e w e l l s , i s t o o smal l . Thus, w e l l p u m p i n g may dry up t h e s p r i n g w i t h o u t producing a s i g n i f i c a n t r e g i o n a l low i n t h e water t a b l e which cou ld be recharged d u r i n g t h e p e r i o d o f maximal f low. I n k a r s t i c regimes, e s p e c i a l l y those f l o w i n g a long an anc ien t system o f channels, t h e l ower ing o f t h e water t a b l e may r e s u l t i n changing t h e p a t t e r n o f f l o w i n t h e system. Th is may r e s u l t i n t h e nonrecovery o f t h e f l o w even when t h e pumpage i s stopped. Another danger which has t o be taken i n t o cons ide ra t i on , espe- c i a l l y i n c o a s t a l areas (Custodio, e t a l . , 1 9 7 7 ) , i s t h a t o f drawing s a l i n e water i n t o t h e a q u i f e r from s a l i n e water bod ies k e p t i n e q u i l i b r i u m by t h e head o f t h e f r e s h water tab le .

The i n t e r c e p t i o n o f t h e f r e s h f l o w above t h e s p r i n g o u t l e t may have a d u a l b e n e f i t i n cases where t h e r e e x i s t s a m i x i n g o f f r e s h and s a l i n e water near t h e o u t l e t , which causes t h e s p r i n g f l o w t o become b rack i sh . I n t h i s case, t h e c o n t r o l o f t h e s p r i n g f l o w i s achieved toge the r w i t h t h e c a p t u r i n g o f t h e f r e s h water b e f o r e i t become s a l i n e (Mandel, 1957; Mandel and Mero, 1 9 6 1 ) .

Springs i n c o a s t a l areas may have t h e i r d ischarge p o i n t s o f f s h o r e , and a l l t h e f l o w may be l o s t t o t h e sea. The l o c a t i o n s o f these submarine sp r ings may be determined by remote sensing, u s i n g techniques descr ibed by Kohout, e t a l . (1979). Th i s f l o w may be captured by pumping f rom t h e a q u i f e r landward o f t he discharge o r by some means o f e x t r a c t i o n a t t h e discharge p o i n t . Great care must be taken i n e i t h e r case t o p reven t contaminat ion by m i x i n g o f f r e s h and s a l i n e waters. Development o f submarine sp r ings i s discussed b y P o t i e and Tard ieu (1977) and Burdon and Papakis (1963) ; examples o f s p e c i f i c submarine s p r i n g s tud ies a re g i ven b y Kohout (1977, no r theas te rn F l o r i d a , U.S.A.) and M i s t a r d i s (1969, southern Greece) . 7.3.3 D i s t r i b u t i o n systems (Stanley W. Posey). A comprehensive development p l a n must be concerned w i t h b o t h e x t r a c t i o n and d i s t r i b u t i o n o f water. I n some cases, t he ground water resource w i l l be l o c a t e d f a r from t h e end use r which may r e q u i r e an ex tens i ve network o f p i p e l i n e s o r canals. A complex d i s t r i b u t i o n system may be requ i red , as i n t h e case o f development fol: mun ic ipa l use. Whi le d i s t r i b u t i o n systems a re beyond t h e scope o f t h i s Guide, they are mentioned because they a re e s s e n t i a l elements o f any development scheme and must be considered i n assessing t h e f e a s i b i l i t y o f a p a r t i c u l a r development p r o j e c t w i t h p a r t i c u l a r a t t e n t i o n g i v e n t o t h e area t o be t r a v e r s e d by t h e system. Spec ia l p recau t ions must be taken when l i n e s c ross areas which a re prone t o s inkho le development o r f a u l t i n g .

7.3.4 Consequences o f development (Stanley W. Posey) . Development o f a k a r s t ground-water resource may have wide-ranging environmental , s o c i a l , and l e g a l consequences, b o t h p o s i t i v e and negat ive. Most of t h e p o s i t i v e e f f e c t s w i l l be in tended o b j e c t i v e s o f t h e development p r o j e c t such as inc reased o r more r e l i a b l e water supply f o r domestic, a g r i c u l t u r a l , and/or i n d u s t r i a l use. I n d i r e c t b e n e f i t s may i n c l u d e g r e a t e r c rop y i e l d s and increased i n d u s t r i a l output .

Development may a l s o have unintended consequences, some o f which may be negat ive. Establ ishment o f o r improvements i n a m u n i c i p a l water supply may

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l e a d t o urban growth and i n f l u x o f people f rom o t h e r areas which may p lace new and p o s s i b l y unbearable demands on a c i t y ' s resources. Popu la t ion growth may r e s u l t i n human and urban p o l l u t i o n o f water and a i r ; i n d u s t r i a l growth cou ld have s i m i l a r e f f e c t s . Development o f water resources f o r i r r i g a t i o n cou ld l e a d t o g r e a t e r use o f chemical f e r t i l i z e r s which cou ld contaminate sur face waters by r u n o f f o r p e r c o l a t e t o groundwater. Ground-water e x t r a c t i o n o r cap tu r ing o f s p r i n g f l o w may r e s u l t i n d i v e r s i o n o f water f rom p r i o r users; f o r example, l ower ing o f t h e water t a b l e cou ld cause i n f l o w s and l o s s o f surface-water f low. Changes i n l a n d use should be a n t i c i p a t e d w i t h many, i f n o t most, development p r o j e c t s . Ground-water q u a l i t y may be degraded over t ime from human, urban, i n d u s t r i a l , o r a g r i c u l t u r a l p o l l u t i o n o r where e x t r a c t i o n induces i n f l o w o f more m ine ra l i zed sur face water.

A p a r t i c u l a r problem r e l a t e d t o e x t r a c t i o n o f water f rom a k a r s t water - tab le a q u i f e r i s l a n d subsidence and s inkho le development. The l o s s o f sur face support by a r t e s i a n pressure which f o l l o w s lower ing o f t he p o t e n t i o m e t r i c head o f an a r t e s i a n system can cause subsidence i n o v e r l y i n g sediments, which may be gradua l (Davis, e t a l . , 1 9 6 3 ) . S inkhole development can r e s u l t f rom c o l l a p s e o f o v e r l y i n g sediments i n t o a s o l u t i o n c a v i t y l e f t by w i thdrawal o f ground water. Sinkholes may develop g radua l l y causing subsidence (Kaufman, 1967 ; Powel l and LaMoreaux, 1 9 6 9 ) ; ca tas t roph ic co l l apse i s n o t uncommon (Foose, 1 9 6 7 ; LaMoreaux and Warren, 1 9 7 3 ) . Remote sensing may be a va luab le a i d i n i d e n t i f y i n g s inkhole-prone areas , as discussed by Warren and LaMoreaux ( 1 9 7 5 ) and Newton ( 1 9 7 6 ) ; geophysica l techniques were used by J o i n e r and Scarborough ( 1 9 6 9 ) and Turner ( 1 9 7 7 ) .

Such consequences as can be p r e d i c t e d should be considered i n p lann ing a k a r s t ground-water resource development p r o j e c t . Economic impacts o f these consequences w i l l a f f e c t p r o j e c t f e a s i b i l i t y ; a p p l i c a t i o n s o f economic eva lua t i on techniques t o water resource p lann ing are discussed by James and Lee (1971).

The preceding examples o f p o t e n t i a l consequences of k a r s t ground-water resource development demonstrate t h a t p lann ing must be an i n t e r d i s c i p l i n a r y e f f o r t i n v o l v i n g , where appropr ia te , s o c i a l , p o l i t i c a l , l e g a l , i n d u s t r i a l , environmental , and land-use exper ts as w e l l as hydrogeologis ts . The i n s t i t u t i o n a l framework f o r p lann ing and development and the e x t e n t o f t he r e q u i r e d p lann ing e f f o r t w i l l va ry by p r o j e c t and by area. The r o l e o f t he hydrogeo log is t i n t h i s e f f o r t i s d iscussed by LeGrand ( 1 9 7 7 ) and Montgomery ( 1 9 7 7 ) . U l t i m a t e l y , p lann ing dec is ions w i l l be based on a cos t -bene f i t ana lys is , t he r e l i a b i l i t y o f which w i l l be impai red i f a l l consequences cannot be a n t i c i p a t e d and i f t h e impact o f c e r t a i n elements o f t he a n a l y s i s cannot be expressed i n monetary terms.

7 . 4 Management (Stanley W. Posey)

Management of a k a r s t ground-water resource w i l l n o t normal ly be conceptua l l y o r o p e r a t i o n a l l y d i f f e r e n t f rom genera l ground-water resource management. Management concepts and techniques used i n o t h e r types o f ground-water systems a re t h e r e f o r e a p p l i c a b l e t o k a r s t ground-water systems w i t h appropr ia te mod i f i ca t i ons . C h a r a c t e r i s t i c s p e c u l i a r t o k a r s t regimes w i l l be accounted f o r as v a r i a b l e s i n the appl . icat ion o f management concepts t o a p a r t i c u l a r system.

I d e a l l y , a ground-water management system should be es tab l i shed as soon as t h e resource i s i d e n t i f i e d . Ground-water resource e x p l o i t a t i o n may then proceed on an o r d e r l y bas i s , i n s u r i n g b o t h e f f i c i e n t development and p r o t e c t i o n o f t h e resource. The o p p o r t u n i t i e s f o r such o r d e r l y processes t o be fo l l owed are r e s t r i c t e d t o areas where p r i o r development has been l i m i t e d o r nonex is ten t and where t h e necessary i n s t i t u t i o n a l framework e x i s t s o r can be es tab l i shed. Too o f t e n , comprehensive management i s o n l y an a f te r though t , considered when shortages occur o r t h e resource i s s e r i o u s l y depleted.

The s t r u c t u r e and opera t i on o f management programs depend on the c h a r a c t e r i s t i c s o f t h e water resources, management ob jec t i ves , and the i n s t i t u t i o n a l framework f o r implementat ion of t he program. The f o l l o w i n g d i scuss ion i s in tended t o p rov ide genera l g u i d e l i n e s f o r estab l ishment o f a management program.

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7.4.1 General cons idera t ions . Ground-water resources management may be an independent e f f o r t o r may be an element i n a comprehensive water resources management system t h a t i nc ludes sur face waters. I n e i t h e r case, e f f e c t i v e management r e q u i r e s c l e a r l y d e f i n e d management o b j e c t i v e s and p o l i c i e s , d e t a i l e d knowledge about t h e water resource, and some management o r g a n i z a t i o n w i t h b o t h t h e a b i l i t y and t h e power t o implement t h e program. These genera l cons idera t ions a re a p p l i c a b l e t o management on a l o c a l , r e g i o n a l , n a t i o n a l , o r i n t e r n a t i o n a l scale.

Management o b j e c t i v e s may be d e f i n e d by l e g a l , economic, and p o l i t i c a l cons idera t ions , w i t h i n t h e l i m i t s e s t a b l i s h e d by t h e c h a r a c t e r i s t i c s o f t h e water resource. Management p o l i c i e s may determine p r i o r i t i e s among competing users and p r o v i d e t h e b a s i s f o r management dec i s ions , such as acceptable r a t e s o f ground-water w i thdrawals and approva l o f new development p r o j e c t s . I n some cases, management o b j e c t i v e s and p o l i c i e s w i l l be e s t a b l i s h e d i n c o o r d i n a t i o n w i t h o the r management o rgan iza t i ons o r may be d i r e c t e d by p o l i c i e s s e t by a h ighe r p o l i t i c a l a u t h o r i t y . Wi lson ( 1 9 7 8 ) d iscusses c o o r d i n a t i o n o f water resources p o l i c i e s among s t a t e agencies i n t h e U n i t e d S ta tes and t h e r o l e o f t he s t a t e s i n f o r m u l a t i o n o f a n a t i o n a l water p o l i c y .

The accumulation o f knowledge about t h e water resource system should be a con t inu ing e f f o r t . The i n i t i a l resource e v a l u a t i o n p rov ides da ta f o r p r e l i m i n a r y development gu ide l i nes . E f f e c t i v e resource management r e q u i r e s cont inued m o n i t o r i n g o f a l l elements o f t h e system, i n c l u d i n g q u a l i t y and q u a n t i t y , and p o l i c i e s and mechanisms f o r app rop r ia te response t o any changes t h a t are detected.

The use o f t h e term "management" i m p l i e s t h a t t h e r e e x i s t s an approp r ia te o r g a n i z a t i o n f o r c a r r y i n g o u t t h e management program.. Such an o r g a n i z a t i o n i s t y p i c a l l y a government agency o r group o f agencies: p r i v a t e p a r t i e s may be involved, as i n c e r t a i n areas o f t h e U n i t e d Sta tes where p r i v a t e consumers form "Water Management D i s t r i c t s " c h a r t e r e d and supervised by t h e l o c a l o r s t a t e government. Whatever i t s form, a management o r g a n i z a t i o n must have t h e t e c h n i c a l e x p e r t i s e t o implement t h e management program and t h e power t o mon i to r compliance and en force such r e g u l a t i o n s as i t may impose.

Models may be o f p a r t i c u l a r u t i l i t y i n water resources management. Whereas the resource e v a l u a t i o n / p r e d i c t i o n models cons ider o n l y t h e p h y s i c a l C h a r a c t e r i s t i c s o f t he water resource system, management models may a l s o i nco rpo ra te l e g a l , s o c i a l , economic, p o l i t i c a l , and o r g a n i z a t i o n a l f a c t o r s . These models may operate t o determine t h e optimum management s t r a t e g y w i t h i n d e f i n e d o b j e c t i v e s , p o l i c i e s , and system c o n s t r a i n t s . A model may a l s o s imu la te system behav io r under v a r i o u s combinations [which may themselves be generated by a model (Chang, e t a l . , 1 9 8 2 ) l o f o p e r a t i o n a l parameters. Bachmat, e t a l . (1978) discusses t h e c h a r a c t e r i s t i c s and a v a i l a b i l i t y o f a number o f resource management models, b o t h f o r ground-water resources a n d f o r i n t e g r a t e d surface- and ground-water resource management.

Management , whether u s i n g a model o r n o t , r e q u i r e s b o t h i n i t i a l a n a l y s i s and long-term p r e d i c t i o n of t h e p h y s i c a l , economic, s o c i a l , p o l i t i c a l , and environmental elements o f management dec is ions . Matalas, e t a l . (1982) discusses t h e importance of and impact o f e r r o r s i n these p r e d i c t i o n s : t h e r e l i a b i l i t y o f long-term management and p l a n n i n g i s considered i n terms o f t h e s t a t i s t i c a l p r o b a b i l i t y t h a t e r r o r s e x i s t i n b a s i c p r e d i c t i o n s . The importance of these p r e d i c t i o n s i n p lann ing and t h e 1 i k e l i h o o d . o f d e v i a t i o n s f rom t h e p r e d i c t i o n s over t ime emphasize t h e need f o r f l e x i b i l i t y i n management. P e r i o d i c rev iew should be made of these p r e d i c t i o n s and o f t h e management o b j e c t i v e s , p o l i c i e s , and opera t i ons based on those p r e d i c t i o n s .

7.4.2 Ground-water management func t i ons . Within t h e o p e r a t i o n o f t h e t o t a l water resource management system, ground-water management f u n c t i o n s may be g e n e r a l l y considered under t h e f o l l o w i n g ca tegor ies : r e g u l a t i o n o f consump- t i o n , augmentation o f supply, and resource p r o t e c t i o n . Though discussed separa te ly here, these f u n c t i o n s may be c l o s e l y r e l a t e d .

7.4.2.1 Regu la t ion o f consumption. Regu la t ion of consumption may be employed as a means o f p r e v e n t i n g excessive w i thdrawals o f ground water. The mechanics o f such r e g u l a t i o n w i l l va ry g r e a t l y . Regu la t ion may be d i r e c t , by a l l o c a t i o n ,

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o r i n d i r e c t , by a fee o r t a x on consumption. Where cohsumers draw from a common source o r where they a r e served by a common d i s t r i b u t i o n system, r e g u l a t i o n may be r e l a t i v e l y simple. A more d i f f i c u l t problem i s presented where ground-water w i thdrawals a re by i n d i v i d u a l l y c o n t r o l l e d w e l l s . Regu la t ion i n t h a t case would r e q u i r e ex tens ive m o n i t o r i n g and t h e power t o impose and en force sanct ions. Where d i r e c t r e g u l a t i o n i s imposs ib le o r i m p r a c t i c a l , reduc t i ons i n w i thdrawals may be achieved by encouraging and a s s i s t i n g conserva t ion and more e f f i c i e n t use among consumers as has been done i n t h e Southwest F l o r i d a Water Management D i s t r i c t (Parker, 1973).

The acceptable volume o f ground-water w i thd rawa l w i l l be a management dec is ion. Where w i thd rawa l r a t e s exceed recharge, t h e a q u i f e r i s s a i d t o be "mined". M i n i n g o f a q u i f e r s over extended p e r i o d s c o u l d r e s u l t i n complete d e p l e t i o n o f t h e resource. I n t h e s h o r t term, m i n i n g may be a sound management p o l i c y , as where development o f a d d i t i o n a l recharge capac i t y i s expected o r where m i n i n g r e s u l t s i n a d d i t i o n a l storage volume t h a t w i l l be f i l l e d d u r i n g p e r i o d s o f n a t u r a l replenishment.

7.4.2.2 A r t i f i c i a l recharge. I n ground-water management, t he storage o f water i n t h e a q u i f e r i s inc reased b y means o f a r t i f i c i a l recharge t o t h e a q u i f e r . A r t i f i c i a l recharge r e q u i r e s an a v a i l a b l e source o f recharge water o f acceptable q u a l i t y and storage c a p a c i t y i n the a q u i f e r .

The most common recharge water source i s excess sur face water. Surface f l o w t h a t would o therw ise be l o s t t o t h e sea o r evapora t ion may be captured by a v a r i e t y o f techniques and d i v e r t e d t o recharge. Other p o s s i b l e sources i n c l u d e r e c y c l i n g o f m u n i c i p a l and i n d u s t r i a l wastewater, d e s a l i n a t i o n o f b r a c k i s h o r s a l i n e waters, and i m p o r t a t i o n o f water from o t h e r areas (Parker, 1 9 7 3 ) . Development o f recharge sources may be l i m i t e d by t e c h n o l o g i c a l and economic f e a s i b i l i t y .

Storage c a p a c i t y i s no rma l l y increased by m i n i n g t h e a q u i f e r . T h i s may be seasonal o r may have occurred over many years. I n many cases, a r t i f i c i a l recharge i s n o t considered o r i s n o t economical ly f e a s i b l e u n t i l t he a q u i f e r i s a l ready s e r i o u s l y depleted. I n water - tab le k a r s t a q u i f e r s , s i g n i f i c a n t storage capac i t y may e x i s t above the normal water l e v e l , but t h e a q u i f e r ' s a b i l i t y t o r e t a i n t h e a d d i t i o n a l water may be l i m i t e d by t h e l e v e l o f n a t u r a l d ischarge p o i n t s .

The most common means o f a r t i f i c i a l recharge are l and spreading and i n j e c t i o n th rough w e l l s . Land spreading i s t h e a p p l i c a t i o n of recharge water over t h e a q u i f e r ou tc rop o r o t h e r n a t u r a l recharge p o i n t s , such as swallow holes. Recharge by i n j e c t i o n c rea tes new recharge p o i n t s where w e l l s are d r i l l e d i n t o t h e a q u i f e r and water i s supp l ied by f l o w down t h e w e l l bore. LaMoreaux ( 1 9 7 9 ) used s p e c i a l l y cons t ruc ted w e l l s t o u t i l i z e water h e l d i n a s u r f i c i a l a q u i f e r t o recharge a lower a r t e s i a n k a r s t i c a q u i f e r i n F l o r i d a . Water f lowed from t h e s u r f i c i a l a q u i f e r i n t o t h e w e l l bore and downward t o t h e lower a q u i f e r . Th i s method p e r m i t t e d t h e capture o f water t h a t would o therw ise have been l o s t t o r u n o f f o r evapo t ransp i ra t i on and made use o f t h e f i l t r a t i o n c a p a c i t y o f t h e g ranu la r s u r f i c i a l a q u i f e r . Other s p e c i f i c a p p l i c a t i o n s o f recharge techniques i n carbonate aqu i fe rs are g i ven by Brown and Signor ( 1 9 7 3 , southern high p l a i n s of Texas and New Mexico, USA) , Forkasiecwicz and Guil lame (1967, France), and Reeder, e t a ï . (1976 , Minnesota, USA). Brown and Signor (1974) d iscuss recharge techniques i n general and p r o v i d e an ex tens ive b i b l i o g - raphy o f works on recharge water sources, storage capaci ty , s i t e - s p e c i f i c s tud ies , and recharge system opera t ions .

7.4.2.3 Resource p r o t e c t i o n . P r o t e c t i o n o f a ground-water resource has b o t h q u a n t i t a t i v e and q u a l i t a t i v e aspects. Q u a n t i t a t i v e p r o t e c t i o n i n v o l v e s proper management t o i n s u r e t h e a v a i l a b i l i t y o f adequate supp l i es o f water. Th i s may be accomplished by es tab l i shment o f management p o l i c i e s t h a t p r o t e c t aga ins t excessive w i thdrawals and p r o v i d e the proper balance between supply and demand.

Q u a l i t a t i v e p r o t e c t i o n i n v o l v e s p reven t ion o f d e t e r i o r a t i o n o f water q u a l i t y . Q u a l i t a t i v e p r o t e c t i o n has an o p e r a t i o n a l aspect i n t h a t development i t s e l f may cause t h e d e t e r i o r a t i o n , Th is i s e s p e c i a l l y t r u e i n c o a s t a l areas where t h e r e i s a danger o f s a l t water contamination; e n t i r e w e l l f i e l d s have been destroyed along the west coas t o f F l o r i d a because excessive p u m p i n g

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p e r m i t t e d s a l t water encroachment (Parker, 1 9 7 3 ) . Groundwater q u a l i t y may a l s o d e t e r i o r a t e i f a r t i f i c i a l recharge systems use poor q u a l i t y water o r i f the l ower ing o f water l e v e l s induces i n f l o w o f lower q u a l i t y water f rom o t h e r a q u i f e r s o r sur face streams.

An aspect o f q u a l i t a t i v e p r o t e c t i o n t h a t p resents s p e c i a l problems i n k a r s t systems i s t h e p r e v e n t i o n o f con taminat ion by d i s p o s a l o f human, a g r i c u l t u r a l , and i n d u s t r i a l waste. Contamination can r e s u l t f rom d i r e c t d i sposa l o f t he waste i n t h e recharge area o f t he a q u i f e r o r by p e r c o l a t i o n o f water through a waste d i s p o s a l s i t e i n t o t h e a q u i f e r . Problems o f ground-water contaminat ion and danger t o consumers o f t h a t water a re magn i f i ed i n k a r s t systems. The r a t e o f f l o w through a k a r s t system does n o t a l l o w as much d i spe rs ion and d i l u t i o n o f contaminants as a g ranu la r a q u i f e r and t h e f l o w through s o l u t i o n a l l y en la rged openings does n o t p r o v i d e f i l t r a t i o n . S tud ies o f k a r s t ground-water contaminat ion from v a r i o u s sources have been made by Jax and Wolfe ( 1 9 7 4 , d i s p o s a l o f human sewage i n a s inkho le ) , Tennyson and Se t te rg ren (1977, l and spreading o f sewage e f f l u e n t over a k a r s t outcrop) , and Wedderburr ( 1 9 7 7 , c a u s t i c waste d i s p o s a l i n a k a r s t a q u i f e r recharge a rea ) . General cons idera t ions concerning l o c a t i o n o f waste d i s p o s a l s i t e s i n k a r s t areas have been discussed by Sendlein and Palmquist ( 1 9 7 7 ) and Burger ( 1 9 7 9 ) .

Both q u a n t i t a t i v e and q u a l i t a t i v e p r o t e c t i o n r e q u i r e comprehensive mon i to r i ng and approp r ia te mechanisms f o r response t o de tec ted changes.

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8 . Methods of cost estimation (D. J. Burdon)

8 . 1 I n t r o d u c t i o n

[EDITOR'S NOTE: Even though much t a b u l a t e d da ta i s f o r p rev ious p e r i o d s o f record, i t i s b e l i e v e d va luab le i n f o r m a t i o n as a genera l guide t o c o s t f o r a c t i v i t i e s . Some cos ts can be p r o j e c t e d t o c u r r e n t va lues by a m u l t i p l e c o r r e c t i n g f o r i n f l a t i o n . The da ta a l s o w i l l p r o v i d e a v e r y impor tan t k

The methods o f e s t i m a t i n g t h e c o s t and va lue o f groundwater developed and produced from carbonate rock aqu i fe rs do n o t d i f f e r s u b s t a n t i a l l y from those used i n s i m i l a r s tud ies o f groundwater from o t h e r a q u i f e r s . There are, how- ever, a few p o i n t s which need more c a r e f u l a t t e n t i o n : f o r example, s p e c i a l techniques, such as a c i d i z i n g and use o f exp los i ves f o r development, which a re seldom used except w i t h carbonate rocks.

There i s a d e f f i c i e n c y l a c k o f da ta on cos ts o f groundwater i n v e s t i g a - t i o n s , development, e x t r a c t i o n , recharge and management i n carbonate rock ter ranes, as surveys a re g e n e r a l l y f o r reg ions o r areas which a re u n d e r l a i n by mixed aqu i fe rs , even though carbonate rocks may predominate. As t h e use o f t h e methods and examples o f c o s t g i ven here a re a l s o a p p l i e d t o carbonate rock areas and assoc ia ted non-carbonate format ions, t h e f a c t t h a t t h e da ta a r e s l i g h t l y heterogeneous i s n o t n e c e s s a r i l y a disadvantage.

Th is Sec t ion o f t h e Guide devotes a t t e n t i o n t o t h e cos ts o f : (1) surveys and i n v e s t i g a t i o n s : ( 2 ) development o f groundwater through t h e d r i l l i n g , t e s t i n g and equ ipp ing o f boreholes, and ( t h e use o f ) s h a f t s and g a l l e r i e s ; ( 3 ) e x t r a c t i o n o f groundwater, w i t h emphasis on f i x e d and o p e r a t i n g costs: and ( 4 ) recharqe and management where methods o f c o s t i n g have had t o be developed f o r recharge and a re s t i l l somewhat imprec ise w i t h rega rd t o management. Three o t h e r aspects o f c o s t i n g o f groundwater a re t r e a t e d more b r i e f l y . They are: ( 5 ) c o s t o f groundwater f o r i r r i g a t i o n , cons ide r ing ( s t u d i e s o f ) c o s t s o f producing water i n d i f f e r e n t c o u n t r i e s and t h e p r i c e p a i d by farmers (mainly i n the circum-Mediterranean c o u n t r i e s ) f o r i r r i g a t i o n waters; ( 6 ) comparative cos ts o f sur face and underground water, however v a l i d comparisons must be r e s t r i c t e d t o each s p e c i f i c problem and area, and g e n e r a l i z a t i o n s a re seldom v a l i d : and ( 7 ) f e a s i b i l i t y study f o r p lann ing and investment purposes, drawing a t t e n t i o n t o t h e manner i n which such work i s c a r r i e d o u t by t h e FAO/IBRD Cooperative Programme.

Much o f t h i s Sec t ion concerns governmental o r p u b l i c groundwater develop- ment. P r i v a t e programs d i f f e r l a r g e l y i n terms o f scope and o b j e c t i v e . The data presented a re t o a g r e a t e x t e n t f rom FAO's experience, b o t h f rom t h e execut ion o f f i e l d p r o j e c t s f inanced LJNDP (Un i ted Nat ions Development Programme) , by Funds-in-Trust, by SIDA (Swedish I n t e r n a t i o n a l Development Associat ion) and from o t h e r sources, and from desk s t u d i e s and comp i la t i ons made by FAO o f f i c e r s a t Headquarters and a t t h e Regional O f f i c e s and t h e N a t i o n a l Water W e l l Assoc ia t ion . Where a c t u a l cos ts a r e g i ven , t h e e f f e c t i v e date and currency a re a l s o given, and users should cons ider subsequent v a r i a t i o n s i n cos ts and currency exchange r a t e s . T h e i r v a l i d i t y can o n l y be determined by d e t a i l e d reeva lua t i on . Simple i n f l a t i o n adjustments a re o f t e n u n s a t i s f a c t o r y because o f t h e d i f f e r e n t i a l c o s t e s c a l a t i o n o f t h e v a r i o u s i tems such as f u e l and labo r . Whi le c o s t s o f equipment and supp l i es tend t o be based on i tems manufactured i n developed coun t r i es , t h e c o s t s of f i e l d ope ra t i ons

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tend t o be those p r e v a i l i n g i n developing c o u n t r i e s where resources are under a c t i v e development.

8.2 Cost o f surveys and i n v e s t i g a t i o n s

I n v e s t i g a t i o n s t o determine the l o c a t i o n , t he amount, t he q u a l i t y , t he c o s t and t h e va lue of groundwater resources i n carbonate (and o the r ) a q u i f e r s a re made by means of f i e l d surveys and desk s tud ies employing va r ious combinations o f t h e d i s c i p l i n e s and techniques descr ibed elsewhere i n t h i s Guide. These s tud ies assess t h e development p o t e n t i a l o f t he groundwater regime under i n v e s t i g a t i o n , u s u a l l y i n t e g r a t i n g da ta on p r e c i p i t a t i o n and sur face waters. Such i n v e s t i g a t i o n s a re commonly r e f e r r e d t o as "groundwater resources surveysll o r "pre- investment groundwater resources surveys".

V a r i a t i o n s i n n a t u r a l cond i t i ons , o r g a n i z a t i o n a l set-up, t h e m i x t u r e o f d i s c i p l i n e s r e q u i r e d and r e l a t e d f a c t o r s determine t h e c o s t o f each such groundwater resources survey; t h e t h i r t e e n most impor tan t o f these f a c t o r s are l i s t e d under I t e m 8.2.1. Thereaf te r , examples o f cos ts expressed i n terms o f d o l l a r s p e r square k i l omete r o f area surveyed a re g iven i n I t e m 8.2.2. F i - n a l l y , I t e m 8.2.3 g i ves cos ts on a p r o j e c t bas is , us ing a h y p o t h e t i c a l UNDP/FAO p r o j e c t reques t as an example.

8 .2 .1 General f a c t o r s de termin ing c o s t o f surveys and i n v e s t i g a t i o n s . The genera l f a c t o r s de termin ing t h e c o s t o f pre- investment and pre-development groundwater surveys o f areas o r reg ions w i t h e n t i r e l y o r predominant ly k a r s t a q u i f e r s do n o t d i f f e r f rom these which a f f e c t s i m i l a r surveys i n non-karst aqu i fe rs . However, i t i s genera l l y accepted t h a t k a r s t aqu i fe rs , i n p a r t i c u l a r i n tec ton i zed zones, a re among t h e most d i f f i c u l t t o i nves t i ga te ; there fore , t he s k i l l , t r a i n i n g and exper ience o f t h e s t a f f c a r r y i n g o u t t he work a re emphasized as fact.ors i n determin ing costs .

The genera l f a c t o r s determin ing o r a f f e c t i n g the c o s t o f groundwater resources surveys i n k a r s t reg ions may be l i s t e d as fo l lows:

1.

2.

3 .

4 .

5.

6.

N a t u r a l Condi t ions. These r e f e r t o t h e complex i ty or s i m p l i c i t y o f t he geology, t he mountainous o r open charac ter o f t he area, p r o x i m i t y t o t h e sea coast, t he c l imate , and amount o f p r e c i p i t a t i o n . I n genera l , i n t h e circum-Mediterranean count r ies , n a t u r a l cond i t i ons are " d i f f i c u l t " i n carbonate rock t e r r a i n and tend t o r a i s e t h e cos t o f operat ions. Scope o f Survey. I n general , t he l a r g e r the area t o be surveyed, the lower t h e c o s t p e r square k i l omete r . I n p a r t t h i s i s due t o the f a c t t h a t over l a r g e areas, i n t e n s i t y o f i n v e s t i g a t i o n i s low; more i n t e n s i v e (and c o s t l y ) work i s focused on smal ler areas o f g rea te r p o t e n t i a l groundwater development i n t e r e s t . Aims o f Survey. Costs w i l l increase as t h e aims o f t he survey move from a genera l reconnaissance o f groundwater resources t o those o f f u l l development f o r s p e c i f i c purposes, economic management, poss ib le groundwater recharge and opera t i on o f the k a r s t rese rvo i r s . Phys i ca l I n f r a s t r u c t u r e . The b e t t e r t he physical i n f r a s t r u c t u r e , such as access roads, f a c i l i t i e s and supp l ies p rov ided by towns and v i l l a g e s , communication media, sometimes presence' o f a i r f i e l d s and p o r t s , and r e l a t e d support f a c i l i t i e s , t he cheaper w i l l i t be t o execute t h e survey. A v a i l a b i l i t y o f Data. I f good a e r i a l photographic cover and mosaics, topographica l , g e o l o g i c a l and h y d r o l o g i c a l maps and support da ta a re a v a i l a b l e , t h e cos ts w i l l be lower f o r t h e groundwater survey. The ex is tence o f r e l i a b l e , w e l l - i n d i c a t e d benchmarks a t n o t t o o d i s t a n t i n t e r v a l s w i l l d i r e c t l y reduce cos ts o f l e v e l i n g for de terminat ion o f t he e l e v a t i o n o f a q u i f e r s and groundwater surfaces. Time Factor . Genera l ly , t h e qu icker the work must be done, the more ?t w i l l cos t . The need f o r severa l years o f r e l i a b l e c l i m a t o l o g i c a l and h y d r o l o g i c a l da ta o f t e n se ts a lower l i m i t ( f o r example th ree we t /w in te r seasons) t o the d u r a t i o n o f such a survey. Where seasonal changes o f c l i m a t e are l a rge , c a r e f u l p lann ing a l l ows maximum advantage t o be taken o f such changes.

280

7.

8 .

9.

10.

11.

1 2 .

Government Organ iza t i on and Lega l P o s i t i o n . An e f f i c i e n t government o r g a n i z a t i o n i s a major h e l p i n reduc ing t h e c o s t o f groundwater surveys, whether t h e work i s undertaken d i r e c t l y o r by-agreements w i t h s p e c i a l i s t o r g a n i z a t i o n s o r f i r m s . I n f a c t , un less t h e r e i s a s u i t a b l e government o r p u b l i c o r g a n i z a t i o n t o p lan , t o supervise, t o rece ive , t o r e c o r d and t o use t h e r e s u l t s , t h e money spent on t h e survey, l a r g e o r smal l , i s l i k e l y t o b e a t o t a l waste. Lega l aspects must be considered, i n c l u d i n g r i gh t t o e n t e r and t o d r i l l . Impor t p e r m i t s a re a l s o r e l a t e d t o o r g a n i z a t i o n and t h e l e g a l p o s i t i o n . S k i l l . K a r s t groundwater resource surveys r e q u i r e a high degree o f s k i l l , t r a i n i n g and experience b o t h on t h e p a r t o f t h e t o p exper t s and o f such key men as t h e d r i l l i n g foremen. A l i t t l e e x t r a i n v e s t i - g a t i o n , a l i t t l e g r e a t e r exper ience i n r e l a t i n g t h e morphology t o hidden s t r u c t u r e s c o n t r o l l i n g groundwater c i r c u l a t i o n , may enable one survey t o s i t e t h e f i r s t c r u c i a l boreho le t o p r o v i d e b a s i c da ta e a r l y i n t h e i n v e s t i g a t i o n , whereas another survey r e q u i r e s longer , slower and hence more c o s t l y routes. Necessary M i x t u r e o f Techniques. The d i s c i p l i n e s and techniques employed on k a r s t groundwater surveys a re many and they va ry t r e a t l y i n uni t and t o t a l cost ; f o r example, d r i l l i n g i s v e r y expensive, temperature observa t ions a re cheap, w h i l e p r e c i p i t a t i o n da ta c o l l e c - t i o n i n v o l v e s t h e lapse o f much t ime. These many d i s c i p l i n e s a re employed i n v a r y i n g p r o p o r t i o n s on k a r s t groundwater surveys accord- ing t o n a t u r a l cond i t i ons , aims, t i m i n g and o t h e r c o n t r o l s . S k i l l i n employing and m i x i n g t h e techniques and d i s c i p l i n e s i n v o l v e s cons ide ra t i on o f b o t h s c i e n t i f i c o b j e c t i v e s and c o s t e f f i c i e n c y and r e q u i r e s a p roper balance t o p reserve t h e v a l i d i t y and scope o f t h e r e s u l t s which a re t o be obtained. Organ iza t i on o f Operations. Good o r g a n i z a t i o n o f ope ra t i ons can do much t o reduce t h e c o s t o f k a r s t groundwater surveys. Organ iza t i on and t i m i n g o f f i e l d opera t ions g e n e r a l l y r e c e i v e g r e a t e r a t t e n t i o n than t h a t p a i d t o t h e process ing o f t h e da ta ob ta ined by t h e survey t o achieve the survey o b j e c t i v e s . Storage, r e t r i e v a l , modes o f a n a l y s i s and form o f da ta and r e s u l t p r e s e n t a t i o n should be an i n t e g r a l p a r t o f ope ra t i on o rgan iza t i on ; f o r example, See DUTCHER ( 1 9 7 2 ) . Mode o f Execution. K a r s t groundwater surveys may be made d i r e c t l y by government, m i n i s t r y o r i n s t i t u t e , by government i n coopera t ion w i t h t he UNDP and i t s execut ing agency, o r by an agreement w i t h a f i r m o f c o n s u l t i n g engineers. They a re almost never done b y p r i v a t e i n d i v i d - ua l s . Fac to rs o f t ime, t r a i n i n g , build-up o f i n s t i t u t i o n s and s t a f f , a v a i l a b i l i t y o f equipment, source o f funds, f o r e i g n exchange regu la - t i o n s and o t h e r cons ide ra t i ons determine t h e mode o f execu t ion o f these surveys and a l s o i n f l u e n c e t h e i r costs . Support F a c i l i t i e s . Techn ica l support f a c i l i t i e s may be good and e f f i c i e n t i n some c o u n t r i e s and areas. These i n c l u d e chemical l a b o r a t o r i e s and we l l -o rgan ized g e o l o g i c a l and h y d r o l o g i c a l surveys ready t o p r o v i d e input i n t k e areas under groundwater survey, and r e l a t e d support. The p h y s i c a l i n f r a s t r u c t u r e i s a t ype o f support f a c i l i t y . Support f a c i l i t i e s a l s o i n c l u d e . repa i r and maintenance workshops, s k i l l e d techn ic ians , and r e l a t e d support o f t h i s nature. Presence o r absence o f such support can g r e a t l y lower o r inc rease t h e c o s t o f groundwater surveys and i n v e s t i q a t i o n s . Mode o f Cost inq. There a re many ways i n which cos ts can be a l l o c a t e d i n such groundwater resource surveys. Some surveys may amor t i ze a l l t h e d r i l l i n g equipment and t r a n s p o r t aga ins t t h e f i r s t survey on which they are employed, say over a four -year pe r iod : as a r e s u l t t h e n e x t survey may bear no such costs . These, and o t h e r c o s t i n g proce- dures, must be borne i n m i n d when de termin ing t h e c o s t o f k a r s t groundwater surveys and i n v e s t i g a t i o n s .

8.2.2 Est imates o f c o s t i n u n i t s o f area i nves t i ga ted . Whi le t h e c o s t s o f a number o f groundwater surveys over f i x e d areas a re known i n cons iderab le d e t a i l , these c o s t s va ry g r e a t l y f o r seve ra l reasons, and i n ve ry few cases do

2 8 1

they d e a l s o l e l y w i t h groundwater i n carbonate r o c k aqu i fe rs . Hence t h e da ta g i ven here, and i n p a r t i c u l a r i n Tables 8.2-1 and 8.2-2 must be understood i n the l i g h t o f t h e l i m i t a t i o n s descr ibed i n t h e t e x t .

As r e p o r t e d i n "Hydrogeological C o n t r o l o f Development i n Saudi Arabia" (Burdon and Otkum, 1968) major surveys were made by consu l tan t f i r m s under agreements w i t h t h e M i n i s t r y o f A g r i c u l t u r e and Water t o o b t a i n an o v e r a l l i n v e n t o r y and assessment o f t h e water and a g r i c u l t u r a l resources o f t h e Kingdom o f Saudi A rab ia w i t h a v iew t o t h e i r p roper development, u t i l i z a t i o n and management. Whi le these surveys d i d i n c l u d e some l imestone-dolomite aqu i fe rs , i n genera l t h e sub jec ts o f t h e groundwater i n v e s t i g a t i o n s were n o t k a r s t , and t h e work e n t a i l e d s o i l , a g r i c u l t u r a l and s tock i n v e s t i g a t i o n s as w e l l as t h e p u r e l y hyd rogeo log ica l and h y d r o l o g i c a l work. However, t he r e s u l t s a re o f i n t e r e s t i n t h i s Guide, and a re g i ven here i n Table 8.2-1. Whi le these a c t u a l f i g u r e s have l i t t l e c u r r e n t a p p l i c a b i l i t y , they may be u s e f u l f o r comparison o f r e l a t i v e costs .

Turning from these ve ry l a r g e surveys, where t h e aim was t o i d e n t i f y t h e ex i s tence o f resources which c o u l d l a t e r be s t u d i e d and appraised i n more d e t a i l f o r development, some r e s u l t s from U n i t e d Nat ions Development Programme "Spec ia l Fund" pre-investment groundwater surveys a re given. These surveys were made i n t h e 1960-64 pe r iod , when such pre-investment resource surveys were sharp ly focused on water; cos ts have been ad jus ted t o 1 9 7 2 ra tes .

These r e s u l t s f o l l o w f a i r l y l o g i c a l l y those g i ven i n Table 8.2-1 where c o s t s f o r areas o f 100,000 t o 400,000 square k i l o m e t e r s were about $ 1 8 p e r square k i l o m e t e r . As t h e area decreases, so t h e i n t e n s i t y o f t h e study in- creases - w i t h concomitant increases i n un i t costs . For ex tens ive pre- investment groundwater surveys cos ts were i n t h e o rde r o f $30 t o $100 p e r square k i l o m e t e r over areas i n t h e 10,000 t o 60,000 square k i l o m e t e r s range, w h i l e f o r i n t e n s i v e surveys, cos ts were i n t h e range o f $200 t o $500 p e r square k i l o m e t e r over areas i n t h e 1,000 t o 5,000 square k i l o m e t e r s range.

These f i g u r e s shou ld be considered as g u i d e l i n e s t o t h e r e l a t i v e cos ts f o r work i n k a r s t areas. O f course, i n a l l cases, t he c o n t r o l l i n g f a c t o r s men- t i o n e d under I t e m 8.2.1 and t h e poss ib le unbalancing e f f e c t o f ex tens ive d r i l l i n g must be borne i n mind .

8.2.3 Est imates o f c o s t by p r o j e c t approach. For some types o f i n v e s t i g a t i o n s i n t o t h e groundwater resources o f k a r s t a q u i f e r s , t he area approach i s n o t s u i t a b l e , and may be rep laced o r supplemented by t h e p r o j e c t approach. For example, t h e task o f i n v e s t i g a t i n g and developing c o a s t a l o r submarine spr ings i n reg ions where the carbonate rock a q u i f e r s reach t h e sea i s l e s s a ma t te r o f areas and more o f s p e c i f i c work i n and around t h e sp r ings as i n S t r i n g f i e l d and LeGrand (1971). The number o f sp r ings t o be i n v e s t i g a t e d and t h e submarine problems a re o f g r e a t i n f l u e n c e i n such cos t es t ima t ion .

The systemat ic approach developed by t h e U n i t e d Nat ions Development Programme (UNDP) i n 1972 t o t h e fo rmu la t i on o f p r o j e c t s i n which t h e Government o f t h e country , t h e UNDP and an Execut ing Agency (such as the Food and A g r i c u l - t u r e Organ iza t i on o f t h e U n i t e d Nat ions) a re t h e j o i n t p a r t i c i p a n t s ; may be used as a gu ide t o o u t l i n e the components and the cos ts o f such a p r o j e c t .

8.3 Cost o f groundwater development

The c o s t o f development covers (1) t he d r i l l i n g o f boreholes, ( 2 ) t he development o f boreholes, ( 3 ) t h e t e s t i n g o f boreholes, ( 4 ) t h e cas ing and screening o f boreholes, ( 5 ) t h e supply and i n s t a l l a t i o n o f pump and motor, and ( 6 ) t h e sur face f i t t i n g s , as pump-house, switchboard, e t c . [EDITOR'S NOTE: The reader i s r e f e r r e d t o Campbell and Lehr (1973) as a re fe rence on w e l l c o s t analys is . ] I n some cases, s h a f t s and g a l l e r i e s are used i n s t e a d o f boreholes; t h e i r c o n s t r u c t i o n i s a l s o a p a r t o f t he c o s t o f groundwater development. Many o f these cos ts are common t o groundwater development o f a l l types o f aqu i fe rs ; t h i s a p p l i e s i n p a r t i c u l a r t o equipment, such as casing, screens, pumps and motors. D r i l l i n g c o s t s tend t o d i f f e r according t o format ions and k a r s t p resents i t s own s p e c i a l d r i l l i n g problems which a re o f t e n r e f l e c t e d i n h i g h d r i l l i n g costs . L ikewise , s p e c i a l d r i l l i n g methods are r e q u i r e d i n k a r s t and i t i s c l e a r t h a t methods and cos ts o f t u b e w e l l c o n s t r u c t i o n i n a l l u v i a l

2 82

Table 8.2-1. Cost o f resource surveys f o r 1 ,281 m i l l i o n square k i l o m e t e r s o f Saudi Arab ia , c a r r i e d o u t from 1 9 6 5 t o 1 9 7 0 ; t h e importance o f d r i l l i n g and t e s t i n g f o r groundwater i s c l e a r , though t h e surveys covered many i tems bes ide water. (Burdon and O t k u n , 1 9 6 8 ) .

$ 2 1

$ 42

$145

$300

D r i l l i n g - Tes t Groundwater

$ 3 3

$ 6 6

$ 2 2 0

$450

% Cost p e r km2 T o t a l c o s t .$

Square K i lome t e r s

--------- Balance Areas

Area I

Area II + III J.M.T.

Area I V

Area V

Area V I

370,000

232,000

18 ,000

362,000

105,000

194,000

7,500,000

5,425,000

910,000

4,735,000

2,000,000

2,900,000

1,900,000

1,575,000

120 ,000

1 ,280,000

300,000

730,000

5.14

6.78

6.66

3.53

2.85

3.77

15 .13

16 .60

43.90

9.54

16 .20

11 .18

S i x Areas 1 ,281,000 23 ,470 ,.O00 5,905,000 4.62 13 .72

Table 8.2-2. Range o f c o s t s i n d o l l a r s p e r square k i l o m e t e r f o r p re- investment groundwater surveys i n areas w i t h a l l o r high percentage o f carbonate a q u i f e r s (Burdon, 1 9 6 5 ) .

I Rate Per km2

A c t u a l Area km2

Ac t u a 1 c o s t us $ Country Type o f Survey

t

S y r i a

S y r i a

Jordan

Yemen

Extensive; open coun t ry

Extensive; r o l l i n g

Extensive; deep a q u i f e r s

I n t e n s i v e ; l o c a l

48,000

24,000

60 ,000

1,000

1 ,000,000

1,000,000

2,200,000

300,000

2 8 3

a q u i f e r s have no r e l a t i o n t o methods and cos ts i n l imestones. Where poss ib le , equipment and supp l i es should be purchased on t h e b a s i s o f compe t i t i ve b i d s , as should a l l con t rac ted o r subcontracted i tems, such as d r i l l i n g and construc- t ion.

Accord ing ly , t h e f i g u r e s presented here a re i n p a r t genera l f i g u r e s , but where p o s s i b l e s p e c i f i c da ta on cos ts i n k a r s t a re given. The f i r s t subheading (8.3.1) dea ls w i t h a genera l c a l c u l a t i o n f o r t h e o v e r a l l c o s t o f an equipped borehole, and t h i s i s f o l l owed by some s p e c i f i c no tes on t h e c o s t s i n k a r s t under s p e c i f i c i tems.

8.3.1 General case - c o s t o f boreholes and pumps. Based on a study o f 1 4 3 m u n i c i p a l and i n d u s t r i a l w e l l s d r i l l e d i n I l l i n o i s i n 1 9 6 4 - 6 6 ( p r i c e s ad jus ted t o 1 9 6 6 va lues ) , Dawes (Dec. 1970) c a l c u l a t e d the r e l a t i o n s h i p s between depth, bottom diameter and c o s t o f w e l l s d r i l l e d i n d i f f e r e n t format ions, i n c l u d i n g sha l low sandstone, l imestone and dolomite. He developed a genera l equation:

WC = K.dn (8.3-1)

where WC = w e l l cos t , i n 1 9 6 6 U.S. d o l l a r s ; K = i s a cons tan t ( r e l a t e d t o diameter o f w e l l , e t c . ) ; d = depth o f w e l l , i n fee t ; and n = slope o f reg ress ion l i n e a t a g iven o p e r a t i n g head.

The c o s t (WC, w e l l c o s t ) comprises (1) s e t t i n g up and removing the d r i l l i n g equipment; (2) d r i l l i n g t h e a c t u a l w e l l ; ( 3 ) a l l cas ing a n d , l i n e r s i n c l u d i n g c o n s t r u c t i o n casing; ( 4 ) g r o u t i n g and sea l i ng , as requi red; ( 5 ) w e l l screens and f i t t i n g s ; ( 6 ) gravel-pack, where requi red; ( 7 ) developing t h 8 w e l l , exc lud ing b l a s t i n g ; and (8) conduct ing an 8-hour pumping t e s t .

For w e l l s w i t h depths o f from 100 t o 600 f e e t i n sandstone, l imestone o r do lomi te , t h e genera l equat ion has the f o l l o w i n g values, as shown on f i g u r e 8.3-1.

WC = 2.070 x d 1.471 f o r a w e l l w i t h bot tom diameter o f 1 5 " t o 2 4 "

WC = 0.983 x d 1.450 f o r a w e l l w i t h bot tom diameter o f 8 " t o 1 2 "

(8 .3-2)

(8 .3-3)

WC = 0.716 x d lm413 f o r a w e l l w i t h bot tom diameter o f 6 " (8 .3 -4 )

From these equat ions i t can be c a l c u l a t e d t h a t a 10" diameter (bottom) water w e l l , d r i l l e d t o a depth o f 500 f e e t w i l l have a c o s t o f $8,000 ( i n 1 9 6 6 ) more o r l ess .

Th is same methodology c o u l d be a p p l i e d t o develop c u r r e n t genera l c o s t e s t i m a t i o n equat ions f o r any g i ven geographic o r hyd ro log i c r e g i o n where s u f f i c i e n t da ta are a v a i l a b l e . Large-scale groundwater surveys cou ld incorpo- r a t e such equat ions f o r use i n l o c a l development p r o j e c t s .

Dawes (Dec. 1970) a l s o c a l c u l a t e d cos ts f o r d i f f e r e n t types o f pumps i n s t a l l e d i n the water w e l l s . These cos ts cover t h e " d i r e c t expenses i n v o l v e d i n f u r n i s h i n g and i n s t a l l i n g a b a s i c pumping p l a n t o f a g iven s i z e and type. The cos ts o f w e l l houses and c o n t r o l systems are n o t i nc luded i n t h e i n s t a l l e d pump cos ts " (p. 4 0 9 ) . For the two types o f pumps considered, t h e b a s i c equa- t i o n was:

n m PC = K.Q .H

where PC = pump cost , i n 1 9 6 6 $; K = constant; Q = c a p a c i t y o f pump i n g a l l o n s (US) p e r minute; n = slope o f reg ress ion l i n e a t a g iven opera t i ng head; H = t o t a l pumping head; and m = slope o f reg ress ion l i n e a t a g iven pump capaci ty .

As shown on f i g u r e 8 .3-2 , t h e genera l s o l u t i o n f o r t he i n s t a l l e d pump cos ts f o r an e lec t ro -submers ib le t u r b i n e pump i s g i ven by i n s e r t i n g the f i g u r e s f o r K, n and m i n t h e equat ion; thus

PC = 5.629 Q 0.541H0.658

284

(8.3-5)

DEPTH OF WELL [dj IN FEET

F i g u r e 8.3-1 R e l a t i o n s h i p between c o s t ( 1 9 6 6 S 1 , depth and diameter o f water w e l l s cons t ruc ted i n sandstone, l imestone, o r do lomi te i n I l l i n o i s ; f rom Dawes ( 1 9 7 0 ) .

285

F i g u r e 8 .3 -2 R e l a t i o n s h i p between c o s t ( 1 9 6 6 $ ) , c a p a t i t y and t o t a l head o f e l e c t r o - submersible t u r b i n e pumps i n s t a l l e d i n wa te rwe l l s i n I l l i n o i s ; from Dawes ( 1 9 7 0 ) .

2 8 6

From f i g u r e 8.3-2 and f rom t h e above, i t can be seen t h a t t h e c o s t o f an i n s t a l l e d e lec t ro -submers ib le t u r b i n e pump pumping 500 ga l lons /minu te aga ins t a t o t a l head o f 300 f e e t would be about $7,000 ( i n 1 9 6 6 ) .

Combining t h e two est imates, i t can be seen t h a t a cased, equipped bore- h o l e o f 5 0 0 ' depth i n l imestone i n I l l i n o i s , capable o f pumping 500 gpm aga ins t a t o t a l head o f 3 0 0 ' would have c o s t $15,000 i n 1966. Whi le these cos ts were based on da ta f o r m u n i c i p a l and i n d u s t r i a l w e l l s , they a re l i k e l y t o app ly a l s o t o i r r i g a t i o n w e l l s ; t h e heterogeneous c o n d i t i o n s i n so many carbonate a q u i f e r s make i t d i f f i c u l t t o pre-design s tandard 'wa te r w e l l s which w i l l e x p l o i t t h e i r groundwaters on a s tandard ized p a t t e r n .

Where these i tems a re purchased on a compe t i t i ve b i d b a s i s , these estima- t i o n equat ions c o u l d be u s e f u l i n assessing b i d s and i n f o r m u l a t i n g b i d d i n g gu ide l i nes .

8.3.2 Cost o f d r i l l i n g . D r i l l i n g i n k a r s t i c carbonate rocks i n v o l v e s many comp lex i t i es due t o t h e hardness o f t h e rock, j o i n t i n g which d r a i n s away t h e d r i l l i n g f l u i d and tends t o d e f l e c t t h e borehole, t h e occas iona l presence o f c h e r t nodules which adverse ly a f f e c t s r o t a r y d r i l l i n g , co l l apses r e l a t e d t o j o i n t i n g , presence o f t e r r a rossa and o t h e r c lays , and t h e w e t t i n g o f t h e borehole by t h e d r i l l i n g f lu id . To overcome these d i f f i c u l t i e s , v a r i a t i o n s o f standard r o t a r y d r i l l i n g o r percuss ion d r i l l i n g may be employed. I n r e c e n t years "down-the-hole" hammer d r i l l i n g has been used w i t h success, i n p a r t i c u l a r i n d r y format ions and above t h e l e v e l o f t h e groundwater. The cho ice o f t h e method o f d r i l l i n g i s o f course r e l a t e d t o t h e diameter ( o r diameters) and depth o f t h e borehole, which i n turn i s r e l a t e d t o t h e t ype and amount o f i n f o r m a t i o n t o be ob ta ined ( r o c k cores, water l e v e l s and samples, temperatures, test-pumping data o r a l l t h e main a q u i f e r c o e f f i c i e n t s , geophys ica l l ogg ing , e t c . ) . D i f f e r e n t methods o f d r i l l i n g c a l l f o r w i d e l y v a r y i n g equipment and, w h i l e d i r e c t cos ts can be compared, i t i s more d i f f i c u l t t o a l l o w f o r amort iza- t i o n o f t he main and t h e a u x i l i a r y equipment.

Table 8.3-1 l i s t s r e p r e s e n t a t i v e footage cos ts f o r cable and r o t a r y d r i l l i n g and f o r cas ing f o r w e l l s d r i l l e d i n t h e US i n 1980. These cos ts a re i t em ized by boreho le diameter.

The f o l l o w i n g da ta on c o s t s r e f e r s t o work done on a UNDP and Government o f Greece p r o j e c t executed by FAO i n 1960-63 "Ka rs t Groundwater I n v e s t i g a t i o n s " as r e p o r t e d by t h e D r i l l i n g O f f i c e r (Mr. C. K. Stapleton) i n h i s 1 9 6 3 r e p o r t "Methods and Costs o f D r i l l i n g and Test-Pumping K a r s t A q u i f e r s i n t h e Parnas- sos-Ghiona Region o f Greece" and a l s o by t h e P r o j e c t Manager and Co-Manager (Burdon and Papakis, 1 9 6 3 ) .

Fo r s i x f u l l - s i z e d boreho les t o t a l l i n g 8 1 5 meters, p l u s reaming o f 317 meters, d i r e c t cos ts came t o $21,910, o r $27 p e r meter o f completed borehole. These d i r e c t cos ts excluded s a l a r i e s and c o s t s n o t d i r e c t l y spent on t h e o f f i c e r s and crews o f t h e r i g s , and a m o r t i z a t i o n o f t h e equipment. The amount o f equipment supp l i ed by t h e UNDP ( i n c l u d i n g two Davey r i g s t o t a l l i n g $92,000) came t o $203,450; even a low d e p r e c i a t i o n r a t e o f f i v e pe rcen t would g r e a t l y inc rease c o s t p e r meter. Fo r e i g h t small-diameter boreholes ( 4 7 mm) t o t a l l i n g 6 5 1 meters, t h e average o v e r a l l c o s t p e r meter worked o u t a t $9.75. These cos ts r e f l e c t 1 9 6 3 c o n d i t i o n s and do n o t account f o r subsequent developments i n d r i l l i n g technology, c o s t v a r i a t i o n s , and i n f l a t i o n .

Rotary mud-f l u s h and r o t a r y a i r - f l u s h ( w i t h o u t a chip-tube) were used i n Parnassos-Ghiona, where t h e da ta i n t a b l e 8.3-2 were obtained.

I t should be no ted t h a t l a t e r i n t h i s p r o j e c t , a chip-tube was added t o t h e a i r - f l u s h method and v e r y g r e a t l y inc reased e f f i c i e n c i e s a t t h e 9.75" diameter. Down-the-hole hammer d r i l l i n g was a l s o used and a t 6.5" d iameter, d r i l l e d a t t h e high r a t e o f 4 .1 meters p e r hour (Burdon and Papakis, 1 9 6 3 , p. 2 8 ) ; c o s t was n o t determined.

8.3.3 Cost o f c leaning, a c i d i z i n g and b l a s t i n g boreholes. Cons idera t ion should be g i ven t o t h e need t o p r o v i d e a budget t o cover the cos ts o f c l e a n i n g boreholes d r i l l e d i n carbonate rocks and f o r p o s s i b l e a c i d i z i n g o r b l a s t i n g operat ions; c lean ing i n general , but a c i d i z i n g and b l a s t i n g a re s p e c i a l p roc- esses.

287

Table 8.3-1. Mean U.S. water w e l l and cas ing costs , 1 9 8 0 . ( a f t e r Water W e l l Journa l , 1 9 8 1 ) .

D r i l l i n g cos ts p e r f o o t

I i ame t e r

D r i l l i n g cos ts p e r f o o t

2

4

5

6

7

8

1 0

1 2

1 6

Rotary r i g s Cable t o o l r i g s Cable t o o l r i g s

$ 5.07

7.09

7.69

10.76

8 .09

13 .22

27.68

28.36

4 4 . 3 1

$ 3.51

5.05

6.80

7.30

6.48

11.53

16 .30

20.47

26.70

$ 2.16

4.67

23.70

11 .53

6.67

7.15

7.57

1 2 . 4 1

14 .50

Rotary r ig :

$ 1.00

2.52

3.42

5 .O7

3.09

7.69

14 .72

11.02

12 .34

2 8 8

Table 8.3-2. Cost o f d r i l l i n g k a r s t l imestones u s i n g core ù r i l l f o r 47 mm and r o t a r y mud-f lush and a i r - f l u s h on boreholes o f v a r y i n g diameter ( f rom Stapleton, 1 9 6 3 , Table 1 7 ) .

-

I

-

A I R FLUSH

Rate o f Pumping

T o t a l Dynamic Head

HP o f Engine

Ac tua l HP o f

( l i t / s e c o n d ) 3 0

(TDH) (m) 38

Required 20.

Engine 26

Cost o f U n i t , FOB ( $ 1 2,667

Cost o f U n i t , CIF ( $ 1 2,933

A I R ------------- Meters D r i l l e d

4

7

FLUSH

c o s t $ Per Meter

3 1 .

6 9

39

58

-

5,290

ost : l i t / s e c x meter l i f t 2.57

o s t : Required HP 1 4 2 t 4.15 4.65 2.43

203 2 5 2 1 3 1

BOREHOLE DIAMETER

338 .40

90.00

18 .54x

60. 66x

26.97+

80.30

6.72

14 .86

27. 4OX

22. 85x

13.35'

16.83

47 mn

6 1 / 4

6 1 / 2 II

8 3 / 4 II

9 3 / 4 'I

1 2 1 / 4

x' Inc ludes some c

136 .26 3.80

1 8 7 .O7

30.62'

12 .85

24.14+

+ A l l d r i l l i n g below thé water tab le .

Table 8.3-3. A c t u a l cos ts o f supp ly ing deep-well t u r b i n e pumps powered by d i e s e l engines through gears t o n i n e UNDP P r o j e c t s executed by FAO i n 1 9 7 0 t o 1 9 7 2 . Average c o s t p e r " l i t e r / s e c o n d y i e l d x 1 meter o f dynamic head" comes t o $2.88 and t h i s i s a u s e f u l CIF c o s t i n g f i g u r e (desk study, A. E. P a l l i s t e r ) .

YUG 7 2

PDY 7 1

JOR 7 1

PHI 7 2

PHI 70

95

3 6

6 0

88

5,876

5,226

1.82

1 0 2

2 8 9

3 0

20 .

1 2 .

2 1

2,289

2,515

3 0

1 7

9.

1 2 .

2,158

2,373

1 0 0

55

9 6 .!

1 2 5

,938

,246

3 0

5 0

23 .

3 7

,190

,540

4 2

5 0

3 9

5 0

,364

,650

40

1 2 0

7 3

1 1 0

1,890

I I I I

I I I

1.68

9 6

2 . 2 1

1 1 9

2.70

1 6 2

3.69

2 3 9

Medium, sma l l and ve ry smal l s i zed openings i n carbonate rocks are o f t e n t h e means whereby water moves through t h e a q u i f e r , and such openings are r e a d i l y b locked i n t h e course o f d r i l l i n g . Such blockage must be removed by "developing" t h e borehole: t h e choice o f method depends on what has caused t h e blockage. Blockage may be by d r i l l i n g mud, by ch ips and c u t t i n g s , o r by t e r r a rossa c u t i n t h e d r i l l i n g and fo rced i n t o t h e openings. The openings i n t h e rock can be c lea red by v igorous pumping, but surg ing w i t h a i r o r water, o r by u s i n g polyphosphates and o t h e r m a t e r i a l t o soak i n t o and render f l u i d t h e b l o c k i n g mud o r c lay . A l l such work and a d d i t i v e s c o s t a d d i t i o n a l money.

I n some cases, t r e a t i n g a borehole w i t h hyd roch lo r i c o r su lphu r i c a c i d may open o r en la rge sma l l c racks and j o i n t s , and g r e a t l y increase t h e y i e l d o f t h e w e l l . As much as 4,000 k i l o s o f 20 percent h y d r o c h l o r i c a c i d and f i v e t o s i x days work may be r e q u i r e d t o open up and increase y i e l d s f rom two t o ten- fo ld . Costs can be h igh.

B l a s t i n g i s sometimes used when a borehole has f a i l e d t o c u t a f i s s u r e d zone known t o e x i s t c lose t o t h e borehole. Such b l a s t i n g may open up new cracks and j o i n t s , and thus b r i n g t h e borehole i n t o con tac t w i t h a f i s s u r e d o r k a r s t i f i e d zone w i t h c i r c u l a t i n g groundwater. Costs o f b l a s t i n g can be h igh.

I t i s n o t p o s s i b l e t o g i v e any f i r m o r genera l f i g u r e s f o r t he cos ts o f these operat ions. Cleaning by pumping, surg ing and polyphosphates i s commonly employed and i s n o t c o s t l y . A c i d t reatment and b l a s t i n g a re l e s s common, and cos ts w i l l va ry accord ing t o i n d i v i d u a l circumstances. I n a l l cases, t he e f f i c i e n c y o f t h e work can be measured i f the y i e l d (and T) determined b e f o r e and a f t e r t h e "development" o f t h e borehole has been measured and analyzed.

8.3.4 Cost o f t e s t pumping. Test-pumping, ma in l y t o determine a q u i f e r c h a r a c t e r i s t i c s , should be cont inued over a p e r i o d o f 7 2 hours, and can be expensive. A p r e l i m i n a r y t e s t w i t h a i r l i f t may be u s e f u l , p rov ided no f i s s u r e s o r openings e x i s t above t h e s t a t i c water t a b l e i n t o which the ascending a i r - water m i x t u r e can escape and n o t reach surface. Cost es t ima t ion should con- s i d e r purchase o r r e n t a l o f necessary equipment, o p e r a t i o n a l expenses, and labor .

8.3.5 Cost o f cas ing and screens. Boreholes i n normal competent l imestone o r do lomi te w i l l s tand w i t h o u t casing. There i s , however, always a danger t h a t a smal l o r l a r g e p iece w i l l spa11 o f f , o r a rock j o i n t w i l l a l l o w a s l i p , and the borehole w i l l be blocked. I n t h i s way a pump can r e a d i l y be l o s t . Since k a r s t boreholes almost never pump sand o r s i l t , they seldom need screens. Casing and screen ( i f necessary) cos ts a re sub jec t t o wide v a r i a t i o n depending on m a t e r i a l and s i z e s p e c i f i c a t i o n s and a v a i l a b i l i t y . These i tems cou ld be bought on a compet i t i ve b i d b a s i s i f p r a c t i c a b l e .

8.3.6 c o s t o f pumps and motors. Whi le some data has a l ready been g iven ( 8 . 3 ) on t h e genera l c o s t o f pumps and motors, they d e a l w i t h e l e c t r i c a l submersible pumps i n USA, and may n o t have world-wide a p p l i c a t i o n . Here cos ts are g iven (See t a b l e 8 .3 -3 ) on t h e a c t u a l 1970-72 cos ts o f v e r t i c a l t u r b i n e pumps powered by d i e s e l engines coupled t o t h e pump-head by a r i gh t -ang le gear d r i v e . Costs were worked o u t i n terms o f U.S. d o l l a r s pe r un i t o f " l i t e r s p e r second l i f t e d through meters o f t o t a l dynamic head." Th is had an average va lue o f $2 .88 pe r l i t / s e c / m e t e r , and f o r a borehole w i t h a y i e l d o f 3 0 l i t e rs / second , and a t o t a l dynamic head o f 4 0 meters, t h e c o s t would be $ 2 . 8 8 x 30 x 40 - $3 ,456 , o r say $3,500. From t a b l e 8.3-3 a l s o i t can be seen t h a t t he average cos t p e r "HP Required" was $161. The horse power (HP) r e q u i r e d f o r t he above borehole ( 3 0 l i t / s e c . aga ins t a t o t a l dynamic head of 4 0 meters) would be about 2 1 HP; the c o s t based on HP would then be $ 1 6 1 x 2 1 - $ 3 , 3 8 1 o r say $3,400. The two methods o f c a l c u l a t i o n g i v e ve ry c lose r e s u l t s i n t h i s case; i n some o thers the spread i s wider . These f i g u r e s show the r e l a t i v e e f f e c t s of p u m p i n g r a t e and t o t a l dynamic head on power requirements and c o s t but have l i t t l e a p p l i c a b i l i t y t o c u r r e n t cos ts . A c t u a l c u r r e n t cos ts w i l l va ry s i g n i f i c a n t l y ; purchases should be made from compet i t i ve b i d s where p r a c t i c a b l e .

2 9 0

8.3.7 Cost o f sur face f i t t i n g s and access. Surface f i t t i n g s can v a r y f rom ve ry s imple and smal l f o r a borehole equipped w i t h an e lec t r i c - submers ib le pump, t o an e labo ra te pump-house and f u e l and water s torage tanks f o r a bore- h o l e w i t h a l a r g e d i e s e l engine dr iv ing t h e pump. C o n t r o l and da ta c o l l e c t i n g equipment i n w e l l s va ry f rom requirement t o requirement; t e lemete r ing equipment i s o f t e n adv isable. Est imates o f c o s t f o r such i n s t a l l a t i o n s a re so v a r i a b l e t h a t s p e c i f i c examples can have o n l y l i m i t e d use. I t i s necessary t o p rov ide a reasonable budget i t e m f o r such expenses, and t o ensure t h a t s p e c i f i c a t i o n s and cos ts a re i nc luded i n any groundwater development programme.

Access roads, r ights-of -way f o r power and p i p e l i n e s and r e l a t e d i tems such as fenc ing a re a l l c o s t l y . I n p a r t i c u l a r , access roads t o a l l o w the d r i l l i n g r i g and supp l i es t o reach a.nd work on t h e s i t e , and t o p r o v i d e access a f t e r groundwater p roduc t i on has commenced, can be ve ry c o s t l y . Here again, s p e c i f i c examples are o f l i t t l e va lue, and each s i t e must be costed accord ing t o e x i s t i n g cond i t i ons and ownership o f t h e p roper t y .

8.3.8 Cost o f s h a f t s and g a l l e r i e s . V e r t i c a l boreholes predominate over a l l o the r means o f access t o t h e underground i n groundwater i n v e s t i g a t i o n s , and so a t t e n t i o n has been focused on t h e d i r e c t and a n c i l l a r y cos ts o f d r i l l i n g such boreholes o f v a r y i n g s i z e and depth and cons t ruc ted by d i f f e r e n t d r i l l i n g methods. But some cons ide ra t i on has t o be g i ven t o v e r t i c a l s h a f t s and w e l l s , and t o h o r i z o n t a l and s l i g h t l y i n c l i n e d g a l l e r i e s and a d i t s put o u t f rom t h e bottom o f s h a f t s o r d r i v e n i n t o t h e h i l l s i d e s as a means o f e x p l o r i n g ground- water i n carbonate rocks.

Const ruc t ion o f v e r t i c a l s h a f t s and w e l l s can range f rom an open w e l l some 20 t o 30 f e e t deep and w i t h a diameter o f as l i t t l e as t h r e e f e e t t o l a r g e sha f t s which resemble min ing o p e r a t i o n a l sha f t s . Open w e l l s , dug t o depths o f up t o 20 meters and l e s s than 2 meters i n diameter can be dug by l o c a l l a b o r and t h e i r cos ts w i l l depend on l a b o r cos ts and p r i c e o f exp los ives . Work o f t h i s type i s cus tomar i l y con t rac ted t o s p e c i a l i s t s i n t h e f i e l d .

H o r i z o n t a l and s l i g h t l y i n c l i n e d g a l l e r i e s and a d i t s , w i t h a c ross-sec t ion o f about t h r e e square meters may range f rom $100 t o $200 p e r meter when o r i g i - n a t i n g a t t he sur face o f t h e ground; they would be dearer i f put o u t f rom t h e bot tom o f a w e l l o r sha f t . Once they went beyond 1 0 0 meters, cos ts would r i s e r a p i d l y 'due t o l i g h t i n g , v e n t i l a t i o n , mucking, p r o t e c t i o n aga ins t f a l l s and o the r operat ions.

8 . 4 Cost o f groundwater e x t r a c t i o n

Once the surveys and i n v e s t i g a t i o n s o f t he groundwater have been brought t o a successfu l conc lus ion, t h e n e x t t a s k t o be undertaken i s t o es t imate t h e c o s t o f develop ing and u s i n g t h e groundwater resources so i d e n t i f i e d . The main o b j e c t i v e i s t o determine t h e t r u e c o s t o f groundwater p roduc t ion , a f i g u r e o f t e n g i ven i n cents p e r cub ic meter o f water d e l i v e r e d a t t h e well-head. Though t h i s f i g u r e can be determined as accu ra te l y as des i red, i t w i l l be found t h a t i t i s n o t an abso lu te f i g u r e but depends on seve ra l v a r i a b l e s as w e l l as on severa l f i x e d costs ; i n p a r t i c u l a r , t h e g rea te r t h e volume o f water pumped each year (o the r t h i n g s be ing equa l ) , t h e lower i s t he c o s t p e r un i t o f water.

The c o s t o f groundwater e x t r a c t i o n has two main'components: (1) F i x e d Costs which a r i s e and are c a l c u l a t e d independent ly on t h e amount o f water pumped: and ( 2 ) Operat ing ( o r D i r e c t ) Costs w h i c h a re r e l a t e d t o hours o f ope ra t i on and volume o f water pumped. I t i s proposed i n t h i s Guide t o s e t o u t a t y p i c a l example o f a borehole c u t t i n g a l imestone a q u i f e r , equipped and used t o i r r i g a t e as much l a n d as poss ib le , and then t o show how t h e c o s t o f t he water and t h e water charges p e r hec tare i r r i g a t e d a re ca l cu la ted . Cost f i g u r e s i n t h e f o l l o w i n g example a r e i nc luded f o r i l l u s t r a t i o n purposes only ; a c t u a l cos ts must be determined on a case-by-case bas is .

8 .4 .1 The groundwater development and p r o t e c t i o n s i t u a t i o n . A borehole has been d r i l l e d t o 1 3 0 meters, a t 1 4 " d iameter throughout. From O t o 80 m i t c u t ha rd but s p a l l i n g marl ; f rom 80 t o 1 2 5 m i t c u t a k a r s t i f i e d ha rd l imestone; and from 1 2 5 t o 1 3 0 m i t was i n a b l a c k c layey mar l . Good-qual i ty groundwater

2 9 1

was c u t from 85 t o 1 2 5 m, and rose SO t h a t i t s s t a t i c water l e v e l was a t 60 meters below t h e c o l l a r o f t h e borehole. Test-pumping e s t a b l i s h e d t h a t t he safe y i e l d was 60 l i t / s e c ( 1 2 6 m3/hr) , € o r a steady drawdown o f 1 0 m, so t h a t working water l e v e l was a t 70 meters below t h e c o l l a r .

I t was decided t o s e t t h e pump a t 85 meters depth i n the bore, and t o p r o v i d e cas ing (13 3 / 8 " API) t o 90 meters, so as t o p r o t e c t t h e pump aga ins t f a l l s from t h e s p a l l i n g marl : no screens were requ i red . To pump 216 m"hr aga ins t a t o t a l dynamic head o f 8 2 meters ( l i f t , p l u s f r i c t i o n , p l u s angles, e tc . ) and t o cover t ransmiss ion losses and normal o v e r a l l e f f i c i e n c i e s , i t was found t h a t a 90 HP/d iese l motor would be requi red, d r i v i n g a v e r t i c a l t u r b i n e pump. ' A groundwater engineer should determined t h e b e s t equipment so as t o o b t a i n maximum o v e r a l l e f f i c i e n c y o f pumping ; t h i s i s a major f a c t o r i n reduc- i n g t h e c o s t o f groundwater e x t r a c t i o n .

The i r r i g a t i o n season would be 1 2 5 days ( 4 months) and t h e pump cou ld operate f o r 1 6 hours p e r day. The average water requirements o f t h e crops would be 600 mm o f i r r i g a t i o n water. I n 1 2 5 days o f 1 6 hours, t h e boreho le would produce 432,000 cub ic meters o f water. T h i s would i r r i g a t e 7 2 hec tares a t a du ty o f 600 mm p e r i r r i g a t i o n season o f 1 2 5 days.

i n t e r e s t r a t e s a re taken as f i x e d a t seven pe rcen t p e r annum. What are (1) t h e c o s t o f each cub ic meter o f water? ( 2 ) t h e c o s t o f t h e water supp l ied p e r hec ta re p e r annum? ( 3 ) t h e c a p i t a l investment r e q u i r e d t o p r o v i d e i r r i g a - t i o n water p e r hec ta re commanded?

8.4.2 F i xed costs . These a re t h e cos ts i n c u r r e d p e r year, regard less o f days operated o r volume o f water pumped. They a re shown i n t a b l e 8.4-1.

The method o f c a l c u l a t i n g d e p r e c i a t i o n c a l l s f o r some e labo ra t i on . Each i t e m o f t h e groundwater e x t r a c t i o n s t r u c t u r e i s g i ven an es t imated l i f e i n years, a t t h e end o f which t ime i t i s expected t o be worn-out and must be replaced. By t h i s t ime i t s c o s t must have been f u l l y recovered, t he r a t e o f recovery b e i n g spread over i t s years o f u s e f u l l i f e . Th i s c a p i t a l recovery c o s t depends on two f a c t o r s , t h e p r e v a i l i n g i n t e r e s t r a t e s f o r money and the l i f e o f t h e i n s t a l l a t i o n . The standard formula i s :

i ( 1 + i ) n ( l + n ) n - 1 C a p i t a l Recovery Fac to r = (8.4-1)

where "i" = i n t e r e s t r a t e and "n" = years o f u s e f u l l i f e .

Tables have been worked o u t i n d e t a i l f o r va r ious i n t e r e s t r a t e s and years of u s e f u l l i f e . They w i l l be found i n a c t u a r i e s t a b l e s but some f a c t o r s which a re u s e f u l i n groundwater c a l c u l a t i o n s have been e x t r a c t e d and form t a b l e 8.4-2 o f t h i s Guide. The f a c t o r s from these t a b l e s f o r 1 4 , 25 and 50 years o f u s e f u l l i f e a t t h e i n t e r e s t r a t e o f seven pe rcen t have been taken from t a b l e 8.4-2 and use i n t a b l e 8.4-1.

The u s e f u l l i f e o f each component o f t he groundwater e x t r a c t i o n s t r u c t u r e can be estimated. I n t h i s case, t h e pump and motor w i l l have t o be rep laced a f t e r 1 4 years, whereas t h e bo re and cas ing w i l l l a s t f o r 25 years. A f t e r 25 years, t h e bore may have t o be r e d r i l l e d and recased, but on t h e same s i t e which a l l ows t h e house t o be used f o r a f u r t h e r 25 years. I n some cases, t he i n d i v i d u a l components o f t h e pumping equipment may be assigned d i f f e r e n t years o f u s e f u l l i f e , and t h e u s e f u l l i f e r e l a t e d t o the amount o f work done, and so b r i n g i n g these f i x e d cos ts i n t o a d i r e c t r e l a t i o n s h i p w i t h t h e o p e r a t i n g costs. Some i n t e r e s t i n g data, based on p r a c t i c a l experience, i s g iven i n t a b l e 8.4-3.

8.4.3 Opera t ing costs . Opera t ing cos ts a re those d i r e c t l y r e l a t e d t o the number o f hours t h e pump worked and so t o t h e volume o f water produced a t t he w e l l head. They a re u s u a l l y considered under the heads o f (1) f u e l , ( 2 ) lubr i - c a t i n g o i l and grease, ( 3 ) maintenance and r e p a i r s , and ( 4 ) l a b o r costs.

How much f u e l i s r e q u i r e d ?

1. Fuel . I n one hour, one HP w i l l r a i s e 274 cub ic meters o f water through a v e r t i c a l h e i g h t o f one meter i n a t h e o r e t i c a l l y 100 pe rcen t e f f i c i e n t

292

Table 8.4-1. C a l c u l a t i o n o f deprec ia t ion , i n t e r e s t , insurance and taxes forming t h e f i x e d c o s t charges aga ins t a groundwater e x t r a c t i o n s t ruc tu re ; some da ta f rom FAO A g r i c u l t u r a l Economist G. H. Ward (JOR/9, Dec. 1 9 6 8 ) .

1 C a p i t a l L i f e o f I n t e r e s t Annual

c o s t I n s t a l l a - Rate o f Deprecia- $ t i o n , y r s 7 % t i o n , $

1'1) Deprec ia t i on

130m borehole ( 1 4 " diam) 7,800 25 O .O8581 669.3

90m cas ing (13 3 / 8 " A P I ) 2,000 25 O . 0 8 5 8 1 171 .6

Pump and 90 HP motor 8,200 1 4 O . 1 1 4 3 4 937.6

House, foundat ions, e t c . 2,000 50 O. 0 7 2 4 6 1 4 4 . 9

TOTAL 20,000

Annual dep rec ia t i on ( c a p i t a l recovery cos ts on i n s t a l l a t i o n 1,923.4

( 2 ) I n t e r e s t

700 .O c o s t va lue i n s t a l l e d ($20,000) x 7% 2 Annual i n t e r e s t cos ts =

Annual i n t e r e s t c o s t can be c a l c u l a t e d each year on thc deprec ia ted va lue of each i t e m f o r t h a t year. Over thc u s e f u l l i f e o f each i tem, i n t e r e s t would then be charge1 t h e f i r s t year on o r i g i n a l c o s t and t h e l a s t year 01

t h e averagc v i r t u a l l y zero deprec ia ted value. Hence, i n t e r e s t over t h e e n t i r e l i f e i s c a l c u l a t e d a t one ha1 t h e o r i g i n a l cos t .

( 3 ) Insurance

Th is i s taken a t 0.5% o f t h e o r i g i n a l c o s t over t h e f u l u s e f u l l i f e ; t h e argument i s as f o r annual i n t e r e s t ra tes . 100.0

( 4 ) Taxes

These a re n o t known; a nominal ba lanc ing f i g u r e i s used. 76.6

I TOTAL FIXED COSTS ON INSTALLATION: 2,800 .O

293

Table 8.4-2. C a p i t a l recovery f a c t o r f o r se lec ted years o f u s e f u l l i f e o f equipment a t v a r y i n g i n t e r e s t ra tes . Based on formula 8.4-1.

Years o f U s e f u l L i f e

8

9

1 0

11

1 2

1 3

1 4

1 5

2 0

25

3 0

5 0

1 0 0

--------- 1 0 %

O . 1 8 7 4 4

O . 17364

O. 1 6 2 7 5

O . 15396

O. 1 4 6 7 6

O . 14078

O . 1 3 5 7 5

O . 13147

O . 1 1 7 4 6

O .11017

O. 1 0 6 0 8

O . 10086

o . 1 0 0 0 1

O. 1 4 8 5 3

O . 1 3 4 4 9

O. 1 2 3 2 9

O . 1 1 4 1 5

O. 1 0 6 5 5

O . 1 0 0 1 4

0 .09467

O . 0 8 9 9 4

0 .07358

O . 0 6 4 0 1

O .O5783

O .O4655

O .O4081

I tem

Turbine Pump Bowl

Column ( o r s h a f t )

Gear Head

3 i e s e l Engine

Gasol ine Engine (water cooled)

E l e c t r i c Motor

O. 1 5 4 7 2

O. 1 4 0 6 9

O. 1 2 9 5 0

O . 1 2 0 3 9

0 .11283 .

O . 1 0 6 4 6

o. 1 0 1 0 2

O . 0 9 6 3 4

O. 0 8 0 2 4

O . 0 7 0 9 5

O. 0 6 5 0 5

O .O5478

O .O5038

I n t e r e s t Rate s

O. 1 6 1 0 4

O . 1 4 7 0 2

O . 1 3 5 8 7

O . 1 2 6 7 9

O . 1 1 9 2 8

O .11296

O. 1 0 7 5 8

O . 10296

0 .08718

O .O7823

O. 0 7 2 6 5

O .O6344

O .O6018

~~

O . 1 6 7 4 7

O . 1 5 3 4 9

O. 1 4 2 3 8

O . 1 3 3 3 6

O. 1 2 5 9 0

O . 1 1 9 6 5

O . 1 1 4 3 4

O . 1 0 9 7 9

O .O9439

O .O8481

O .O8059

O .O7246

O . 0 7 0 0 8

O. 1 7 4 0 1

O . 1 6 0 0 8

O . 1 4 9 0 3

O . 1 4 0 0 8

O. 1 3 2 7 0

O . 1 2 6 5 2

O. 1 2 1 3 0

O . 1 1 6 8 3

O. 1 0 1 8 5

O . 0 9 3 6 8

0 .08883

O .O8174

O .O8004

Table 8.4-3. Average u s e f u l l i f e o f d i f f e r e n t components o f groundwater pumping equipment; t he equipment i s expected t o be use f o r 2,000 hours p e r year.

I Estimated Years o f

U s e f u l L i f e

8 years, o r 16 ,000 h r s

1 5 years, o r 30,000 h r s

1 5 years, o r 30,000 h r s

1 4 years, o r 28,000 h r s

9 years, o r 18 ,000 h r s

25 years, o r 50,000 h r s

Cap i ta 1 Recovery

Factor , a t 65

O . 1 6 1 0 4

O . 10296

O . 1 0 2 9 6

O . l o 7 5 8

O . 1 4 7 0 2

O .O7823

2 9 4 . . .

2.

3.

4.

pumping i n s t a l l a t i o n . I n a good d i e s e l engine, one m e t r i c t o n o f f u e l o i l w i l l produce 4,000 HP hours, e q u i v a l e n t t o l i f t i n g 1,370,000 m3 o f water through one meter h e i g h t . I n t h e case under c o n s i d e r a t i o n here, i t i s necessary t o l i f t 432,000 m3 o f water through 8 2 meters h e i g h t every year. I t can be r e a d i l y c a l c u l a t e d t h a t 26 tons o f f u e l o i l w i l l be r e q u i r e d f o r t he 90 HP d i e s e l motor d r i v i n g t h e pump. V a r i a b i l i t i e s i n pump perform- ance and e f f i c i e n c y c o u l d a f f e c t t h i s c a l c u l a t i o n . Cost o f f u e l o i l d e l i v e r e d a t t h e engine s i t e i s a f f e c t e d by v a r i o u s f a c t o r s , t h e most impor tan t o f which are r e l a t e d t o the c o s t o f crude o i l which cannot be r e l i a b l y p red ic ted .

L u b r i c a t i n g o i l and grease. L u b r i c a n t requirements depend t o a g r e a t e x t e n t on t h e type of engine used. Proper maintenance reduces, t o a c e r t a i n degree, t h e consumption o f l u b r i c a n t and thus t h e cost . However, t he c o s t o f l u b r i c a n t s i s d i r e c t l y r e l a t e d t o t h e t ype and c o s t o f crude o i l .

Maintenance and r e p a i r s . These cover t h e pump, t h e motor, t h e housing and accessories. They a re ma in l y a f u n c t i o n o f t h e number o f hours o f work o f t h e pump and motor and t h e a b i l i t y o f t h e mechanic t o make necessary adjustments. Maintenance requirements a re dependent on t h e p a r t i c u l a r equipment. Repairs may be l a r g e l y c o n t r o l l e d by proper maintenance.

Labor. I f a s k i l l e d mechanic can be employed on a p a r t - t i m e bas i s , i t i s es t imated t h a t each diesel-powered pump w i t h good f u e l storage w i l l r e q u i r e t h r e e percent o f h i s t ime, o r he can serve some 3 3 such i n s t a l l a - t i o n s . For a petrol-powered uni t , he can serve but 2 0 . However, much o f t h e l a b o r tends t o be supp l i ed by t h e farmer o r h i s a g r i c u l t u r e l abo r ; when a pump i s o p e r a t i n g 1 6 hours a day, t h e r e w i l l be e x t r a hours f o r maintenance and c leaning, so t h a t two s h i f t s o f p a r t - t i m e l a b o r w i l l be requ i red . The expense must account f o r a c t u a l c o n d i t i o n s and a v a i l a b i l i t y o f l a b o r f o r each s e t o f groundwater e x t r a c t i o n i n s t a l l a t i o n s .

8.4.4 Cost o f water. As an example, t he f o l l o w i n g da ta i s r e q u i r e d t o ca lcu- l a t e (1) t h e c o s t o f i r r i g a t i o n water d e l i v e r e d a t t h e w e l l head, ( 2 ) t h e c o s t o f t h e water supp l i ed t o i r r i g a t e each hec ta re p e r year, and ( 3 ) t h e c a p i t a l investment p e r hec tare r e q u i r e d t o make a v a i l a b l e t h e i r r i g a t i o n water.

I t w i l l be noted, o f course, t h a t emphasis i s g i ven throughout t o t h e use of t h e water f o r i r r i g a t i o n . B u t t h e p r i n c i p l e s o f c o s t i n g used here app ly t o o the r uses o f t he groundwater.

The main elements of t h e computation are: (1) c a p i t a l c o s t o f i n s t a l l a - t i o n , ( 2 ) f i x e d cos ts p e r annum, (3) o p e r a t i n g c o s t s p e r annum, ( 4 ) t o t a l c o s t s p e r annum, (5) volume of water pumped p e r annum, and (6) area o f l a n d i r r i g a t e d p e r annum.

These elements may be used f o r pe r fo rm t h e f o l l o w i n g r e l e v a n t c a l c u l a - t i o n s :

1. Cost o f i r r i g a t i o n water:

t o t a l c o s t s p e r annum volume o f water pumped Cost p e r cub ic meter =

2. c o s t o f i r r i g a t i o n water p e r hec ta re i r r i g a t e d :

c o s t o f water pumped area irrigated Cost p e r hec ta re p e r year =

3. C a p i t a l c o s t p e r hec tare i r r i g a t e d :

(8.4-2)

(8.4-3)

(8.4-4) c a p i t a l c o s t

hec tares i r r i g a t e d Cost p e r hec tare =

295

Table 8.5-1. Rates o f groundwater recharge through w e l l s i n t o the Middle Cretaceous l imestones o f t he Judean f o o t h i l l s , 1 5 kms eas t o f T e l A v i v (Underground Water Storage Study - I s r a e l : FAO/SF:39/ISR-9, 1 9 6 9 ) .

1 9 6 4 / 6 5 Season 1 9 6 5 / 6 6 Season .............................. .............................. Recharge Days o f T o t a l Days o f

w e l l Recharge m3/hour m3 x l o 6 Recharge m3/hour m3 x l o 6

Yarkon 1 9 L ,960 4.4 36 2,350 2.0

Yarkon 2 n o t used 8 5 2,200 4.6

Lod 7 4 1 840 0.8 n o t used

Lod 2 2 7 0 1,190 2.0 86 7 6 0 1.6

O .9 Lod 30 n o t used -- -- Lod 3 1 n o t used 6 4 1,700 2.6

To ta l s 7.2 11 .7

Table 8.5-2. Costs o f groundwater recharge by f l o o d water spreading i n p e r i o d up t o 1966 ; data from Los Angeles F lood Con t ro l D i s t r i c t (USDA 1 9 7 0 , t a b l e 4 ) .

San San Gabr ie l G a b r i e l

Sante Spreading R ive r R io Pacoima Hansen Fe Grounds Channel Hondo

Gross Area (ha)

~ _ _ _ _

7 1 6 3 7 8 5 3 -- 2 3 1

Wetted Area (ha) 49 45 53 4 1 5 3 1 8 4

Capaci ty ( m 3 / h r ) D i ve rs ion 40,800 45,900 51,000 20,400 - __ 91,800

I n f i l t r a t i o n 1 6 , 8 0 0 21 ,400 22 ,400 8 ,200 12 ,000 40,800

Water Conserved (m3x10 6,

t o 3 1 / 3 / 6 6 99.3 1 1 0 .O 72.3 35.5 167.8 194.4

maximum season 13.4 24.2 29.2 6.8 46 .1 37.5

Costs t o 1 9 6 3 / 6 4 (cents/m3 )

~

1 . 668 1 .O95 O .844 O .298 1 .382 O .425

It should be no ted t h a t t h e c o s t p e r hec tare ( 3 ) i s f o r water a t t h e w e l l head, and does n o t cover t h e d i s t r i b u t i o n and dra inage system, l a n d l e v e l l i n g and o the r development costs .

8.5 Cost o f groundwater recharge and management

Grea t l y increased a t t e n t i o n has been p a i d t o groundwater recharge and ground- water management i n recen t years. Much o f t h e work has been done on a l l u v i a l and o the r unconsol idated format ions, and i n o n l y a few cases a re t h e r e da ta on recharge t o k a r s t aqu i fe rs . Costs o f exper imenta l work a re n o t always r e l e - vant , but a method o f c o s t e s t i m a t i o n has been developed f o r t h i s Guide w i t h respec t t o recharge through boreholes. Reference may be made t o a number o f recen t p u b l i c a t i o n s on t h e economics and cos ts o f groundwater recharge, as Brown and Signor ( 1 9 7 2 ) g i v i n g da ta on 1 5 recharge-through-wel ls schemes and 2 by water-spreadinq, Anon (1972) and Water Resource Board ( 1 9 7 2 ) on groundwater recharge i n England and Wales, Mawer and O'Kano ( 1 9 7 1 ) on economic f e a s i b i l i t y o f a r t i f i c i a l recharge and Zabludowski ( 1 9 7 1 ) ana lyz ing t h e economics o f groundwater recharge (unconsol idated aqu i fe rs ) i n I s r a e l .

Management cos ts a re a l s o highly v a r i a b l e , s ince on one hand management may be considered t o embrace a l l t e c h n i c a l , s o c i a l and economic aspects o f groundwater development and use i n an i n t e g r a t e d manner w i t h o t h e r water resources, and on the o t h e r hand t o be o n l y t h e c o s t o f a s p e c i f i c management post . I n t h i s Guide o n l y genera l l i n e s o f approach a re g i ven rega rd ing cos ts o f groundwater management.

8.5.1 Recharge o f k a r s t a q u i f e r s . Recharge t o k a r s t a q u i f e r s can be con- s idered under f o u r headings:

1. Watershed m o d i f i c a t i o n s t o inc rease d i f f u s e i n f i l t r a t i o n ,

2. Engineer ing s t r u c t u r e s t o r e g u l a t e and c o n t r o l ponors,

3. Water spreading over ou tc rop areas, and

4. Recharge through w e l l s and boreholes, o f t e n away from t h e ou tc rop areas.

I t i s considered t h a t watershed m o d i f i c a t i o n s r e f e r t o management aspects r a t h e r than s p e c i f i c recharge, w h i l e enq ineer ing s t r u c t u r e s t o r e g u l a t e ponors a re standard eng ineer ing p r a c t i c e s , adapted t o d e a l w i t h groundwater i n space and t ime. Water spreading over l imestone ou tc rop areas has n o t been costed y e t but should be s i m i l a r t o t h a t f o r o t h e r areas. Accord ing ly , a t t e n t i o n he re i s focused on cos ts o f groundwater recharge through w e l l s and boreholes.

Whi le cos ts o f boreholes f o r groundwater recharge can be c a l c u l a t e d as f o r groundwater e x t r a c t i o n purposes (See t a b l e 8.5-2) , t h e r a t e o f recharge w i l l determine t h e un i t c o s t p e r meter o f water recharged ( o r s to red) underground. Table 8 . 5 - 1 g i ves da ta f rom I s r a e l , where M idd le Cretaceous l imestones were s tud ied and t e s t e d f o r groundwater s torage as p a r t o f an FAO/Government p r o j e c t f inanced by UNDP and Government. I t w i l l be no ted t h a t recharge r a t e s o f over 2,000 m3/hour were achieved over t h e 50 t o 100 davs when t h e r e was su rp lus sur face water a v a i l a b l e f o r such recharge o r underground storage. T h i s method o f ope ra t i ng a l imestone a q u i f e r as t h e r e s e r v o i r f o r a groundwater use scheme i s f u r t h e r discussed i n such p u b l i c a t i o n s as Harpas and Schwarz i n t h e 1 9 6 7 I.A.S.H. Symposium on " A r t i f i c i a l Recharge o f Aqu i fe rs and t h e i r Management."

Work on underground storage o f water i n t h e cha lk o f t h e London Bas in i s repo r ted i n Water and Water Engineer ing (Anon, 1972) 'The use o f w e l l s i s s u i t a b l e wherever t h e a q u i f e r i s con f ined o r l a n d i s a t a premium; screens a re n o t r e q u i r e d i n f i s s u r e d aqu i fe rs . The use o f open bas ins f o r recharge i s a more f l e x i b l e method o f i n t r o d u c i n g water where t h e a q u i f e r i s a t o r near outcrop; bas ins occupy more space than w e l l s . I n t h e London Chalk, t h e Metro- p o l i t a n Water Board recharged l a r g e q u a n t i t i e s through open w a l l s w i t h a d i t s and obta ined 40 percent recovery; work stopped i n 1969. I n 1 9 7 2 , recharge experiments a re t a k i n g p lace a t Ridge Avenue, E n f i e l d , Middlesex ( 7 5 m boreho le t o t h e Chalk; 30 m borehole t o t h e Thanet Sands) and a t Ponders End.'

2 9 7

As r e p o r t e d by t h e Water Resources Board ( 1 9 7 2 , p. 4 5 ) t h e main conclu- s ions so f a r reached are:

'1) The hydrogeo log ica l cond i t i ons a re p a r t i c u l a r l y favorab le f o r a r t i - f i c i a l recharge i n t h e conf ined area i n two reg ions, t h e Lee v a l l e y and t h e Leyton-Dagenham area. P o t e n t i a l underground storage i n the Lee v a l l e y i s a t l e a s t 20,000 m i l l i o n g a l l o n s ( 9 1 m i l l i o n m3) and p o s s i b l y as much as 45,000 m i l l i o n g a l l o n s ( 2 0 5 m i l l i o n m 3 ) . I n the Leyton-Dagenham area s torage amounts t o 26 ,000 m i l l i o n ga l l ons ( 1 1 4 m i l l i o n m 3 ) . '

' 2 ) Recharge o f t h e Chalk a t ou tc rop should be f e a s i b l e i n t h e Wandle and Ravensbourne catchments. Storage f o r some 8,000 m i l l i o n ga l l ons ( 3 6 m i l l i o n m 3 ) cou ld p o s s i b l y be c rea ted by lower ing groundwater l e v e l s on a r e g i o n a l sca le. '

'The p r i n c i p a l source o f recharge water cou ld be the Thames. The R ive r Roding i s a l s o a p o s s i b l e source and i n t h e f u t u r e t h e R ive r Lee i f supple- mented by water from the Great Ouse bas in. H i g h l y t r e a t e d sewage e f f l u e n t i s a f u r t h e r p o s s i b l e source of water. The resources o f t h e Thames a re s u f f i c i e n t t o meet t h e demand f o r water f o r any r e g i o n a l recharge scheme f o r some t ime t o come. '

'S tud ies o f t h e eng ineer ing aspects and economic f e a s i b i l i t y o f la rge- sca le recharge are b e i n g made.' Bu t t h e f i g u r e s f o r cos ts were n o t a v a i l a b l e f o r use i n t h i s Guide.

The U.S. Department o f A g r i c u l t u r e has pub l ished ( 1 9 7 0 ) on groundwater recharge and g i ves some data o f c o s t o f groundwater recharge through spreading i n Los Angeles County F lood C o n t r o l D i s t r i c t . These a re reproduced here, i n p a r t f o r comparison w i t h c o s t o f recharge through w e l l s , and a l s o as such methods o f recharge can be a p p l i e d e i t h e r d i r e c t l y t o k a r s t outcrops o r more probably through a l l u v i u m o v e r l y i n g k a r s t outcrops, as i n r i v e r va l l eys . 'The D i s t r i c t r e p o r t s ... t h a t t he major o p e r a t i o n a l problem i s t o ma in ta in reasonable i n f i l t r a t i o n ra tes ; ... where s i l t y storm water entered t h e bas ins, s i l t depos i ts had t o be removed t o r e - e s t a b l i s h i n i t i a l i n f i l t r a t i o n ra tes . D isk ing i s favored by t h e D i s t r i c t r a t h e r than scrap ing an i n c h o r two from the bas in sur face. ' (USDA, 1970, p. 5 9 ) .

Table 8.5-2 g i ves the da ta f o r cos ts o f such recharge. I t i s on l y up t o 1963-64. Amor t i za t i on i s spread over a 50-year p e r i o d f o r t h e o r i g i n a l l and costs , over 10 years f o r temporary t imber s t r u c t u r e s and over 30 years f o r concrete s t ruc tu res . The un i t cos ts a re based on the amount o f storm water spread. I n years o f low f l o w the u n i t s cos ts would be high because o f f i x e d charges. These cos ts may be u s e f u l f o r purposes of comparison; a c t u a l c u r r e n t cos ts would be s i g n i f i c a n t l y d i f f e r e n t .

8.5.2 Example o f c o s t c a l c u l a t i o n f o r groundwater recharge. The f o l l o w i n g example i n d i c a t e s t h e way o f e s t i m a t i n g the c o s t o f recharge water sent down a borehole t o a b u r i e d k a r s t aqu i fe r . I t w i l l be noted t h a t t h e c o s t o f t he recharge water i s complete ly d i f f e r e n t f rom t h e c o s t o f recover ing t h i s water f o r use. I f recovery i s but 50 percent o f recharge, t he recovered water has t o bear the f u l l c o s t o f recharge and i t s c o s t i s double t h a t o f t he i n i t i a l recharge water; i f recovery i s but 10 percent , t h e recovered water has a cos t 10 t imes t h a t o f t h e recharge water. And t o t h i s i n i t i a l c o s t must be added t h e s tandard p u m p i n g costs .

The example used here i s based on recharge through a borehole somewhat s i m i l a r t o t h a t descr ibed i n I t e m 8.4.1. A stream has surp lus water f o r 8 0 days p e r year; t h i s surp lus amounts t o 500 m 3 / h r ( o r 960,000 m3/year) o f good q u a l i t y water which i s a v a i l a b l e t o the recharge scheme a t no cos t . The scheme r e q u i r e s a w e i r and c o l l e c t i n g tank t o con ta in t h e water, a pump and motor t o pump i t through a p i p e l i n e ( c o s t must i nc lude o b t a i n i n g r ight -of -way) t o the recharge borehole. The l a t t e r i s 1 3 0 m deep, 1 4 " i n diameter, and i s cased t o 90 meters s ince f o r most o f t h i s d is tance i t passes through m a r l which tends t o s p a l l . A d e s i l t i n g tank i s r e q u i r e d a t t he w e l l head. C o n t r o l s t ruc tu res must be prov ided t o feed t h e water i n t o the recharge borehole, o r t o be passed t o waste w i t h o u t causing damage.

2 9 8

Methods o f c o s t e s t i m a t i o n f o r equipment and se rv i ces descr ibed e a r l i e r should be app l i ed t o t h e c a l c u l a t i o n o f recharge costs . As before , t h i s c a l c u l a t i o n should consider b o t h f i x e d and opera t i ng cos ts .

8.5.3 Cost o f recove r ing recharged groundwater. U n l i k e normal groundwater, recharge groundwater has a l ready i n c u r r e d a c o s t i n g e t t i n g i t s e l f i n t o s torage i n the aqu i fe r . Looked a t f rom t h e recharge aspects, t h i s i s t h e t o t a l annual cos ts d i v i d e d by the volume o f water recharged. However, i f o n l y h a l f can be recovered by pumping, t h i s recovered water (which i s t h e o n l y d i r e c t l y u s e f u l p roduc t o f t h e operat ion; cons ide ra t i on o f water l e v e l s , p reven t ion o f seawater encroachment, e tc . , a re omi t ted here) has t o bear t h e f u l l c o s t o f t h e recharge operat ion; i n t h i s case, t h e c o s t p e r cub ic meter o f water doubles. I n addi - t i o n i t has t o bear the pumping costs . The two p r i n c i p a l f a c t o r s a f f e c t i n g t h e c o s t o f r e - e x t r a c t i o n ( o r s torage p l u s r e t r i e v a l ) a re e f f e c t i v e recovery percentage and t h e un i t cos ts f o r t h e recharged and abs t rac ted water. U n i t e d cos ts f o r e x t r a c t i o n may be taken as constant f o r t h i s example.

8.5.4 Ideas on cos ts o f groundwater management. Groundwater management i s Considered as capable o f c l e a r i d e n t i f i c a t i o n and d e f i n i t i o n a t two l e v e l s . F i r s t , t h e r e i s d i r e c t groundwater management d e a l i n g w i t h n a t u r a l and devel - oped e q u i l i b r i u m i n t h e groundwater r e s e r v o i r s o f any n a t u r a l unit . I t dea ls w i t h annual and long-term recharge ( n a t u r a l , improved, a r t i f i c i a l ) and d i s - charge ( n a t u r a l spr ings, pumped, mined) and changes i n composi t ion ( i n c l u d i n g s a l i n e water encroachment, p o l l u t i o n of k a r s t aqu i fe rs , e t c . ) ; i t s economic component dea ls w i t h methods o f f i n a n c i n g and repayment o f debts w i t h cos ts o f recharge water (cos t - f ree , indigeneous costed and impor ted t o t h e bas in ) , and w i t h cos ts o f compensation f o r l o s s o f water r i g h t s and f o r l e g a l opera t ions i n c l u d i n g c o s t o f adverse c o u r t dec is ions and f ines . Second, t h e r e i s water resources management which dea ls w i t h i n t e g r a t e d c o n t r o l and use o f p r e c i p i t a - t i o n , sur face water and groundwater, w i t h p o l i c y dec i s ions as t o where and how water can b e s t be u t i l i z e d f o r t h e good o f t h e people and t h e uni t o f manage- ment, a l t e r n a t i v e combinations and methods o f use w i t h respec t t o t ime (sea- sonal, immediate f u t u r e , long-term f u t u r e ) and t h e p r o t e c t i o n o f t h e a q u i f e r s , r i v e r s , s torage r e s e r v o i r s , i r r i g a t i o n and o t h e r d i s t r i b u t i o n systems and t h e genera l environment.

Whi le o p e r a t i o n a l aspects o f groundwater management have been s tud ied (as i n Walton, Chapter 9 , 1970; Jones e t a l , 1971; Pe ters , 1972; Weber and Hassan, 1 9 7 2 ) t he cos ts o f groundwater management a re n o t commonly i nc luded as an element o f such s tud ies . However, c e r t a i n components such as a r t i f i c i a l recharge, c o s t o f impor t i ng water t o d e f i c i t bas ins, c o s t o f l e g a l ac t i on , and c o u r t charges have been s t u d i e d i n some cons iderab le d e t a i l . I t i s c l e a r t h a t c o s t elements o f groundwater management may range from a percentage o f t h e D i r e c t o r o f Groundwater's sa la ry , t o t h e f u l l c o s t o f a Groundwater Manager's s p e c i f i c pos t , though t h e a l l o c a t i o n o f a percentage o f d i f f e r e n t o p e r a t i o n a l cos ts (as da ta c o l l e c t i n g and process ing, models c o n t r o l o f e x t r a c t i o n , c o s t o f watershed improvement, e tc . ) t o ass ign ing almost a l l t echn ica l , economic, l e g a l and a d m i n i s t r a t i v e cos ts t o a combined c o s t which can be c a l l e d " c o s t o f groundwater management".

Guidel ines t o c o s t i n g t h e management expenses o f ' k a r s t groundwaters must thus be r e s t r i c t e d t o drawing a t t e n t i o n t o a few p o i n t s which a re o f main importance. I n general , a p o s t f o r a "Techn ica l Groundwater Manager" o r s i m i l a r t i t l e should be es tab l i shed and budgeted; t h i s w i l l form a f o c a l p o i n t on which o the r cos ts o f groundwater management can be assembled.

The c o s t o f l e g a l and enforcement a c t i v i t i e s , i n c l u d i n g c o u r t cos ts , must be considered. Damage c la ims due t o l a n d subsidence a r e n o t uncommon c o s t s o f groundwater management; where t h e r e are dangers o f major co l lapses due t o l a r g e s o l u t i o n caverns i n a k a r s t i f i e d carbonate a q u i f e r , i t might be adv isab le t o i nsu re aga ins t damages f o l l o w i n g such co l lapse. Most groundwaters a r e l i a b l e t o p o l l u t i o n , and h e a l t h hazards f o l l o w i n g changes i n recharge procedures ( i n p a r t i c u l a r use o f sewage water f o r recharge, o r improper f l u i d waste d i sposa l ) cou ld l e a d t o major med ica l c la ims and cos ts aga ins t a k a r s t groundwater a u t h o r i t y .

299

8.6 Cost o f groundwater f o r i r r i g a t i o n

I r r i g a t i o n i s b o t h a g r e a t consumer o f water (groundwater, sur face water and p r e c i p i t a t i o n ) and one which can a f f o r d o n l y t h e lowest p r i c e s p e r un i t o f water consumed. Whereas m u n i c i p a l i t i e s and i n d u s t r i e s can pay high p r i c e s f o r water, farmers can o n l y pay a low p r i c e un less they produce s p e c i a l crops which can, f o r one reason o r another, command high p r i c e s . Accord ing ly , i t i s usua l f o r t h e Government t o subs id i ze i r r i g a t i o n water i n d i f f e r e n t ways, and t h i s makes i t d i f f i c u l t t o determine t h e t r u e p r i c e o f i r r i g a t i o n water and the maximum p r i c e farmers can pay f o r i r r i g a t i o n water. Th i s l i m i t a t i o n a p p l i e s t o a l l sources o f water whether i t comes from sur face o r underground, o r whether the a q u i f e r be a l l u v i a l sands o r k a r s t l imestone.

The t ime f a c t o r , cove r ing h i g h e r l i f t s , changing p r i c e s and i n f l a t i o n , are n o t o f g r e a t importance. I t would seem t h a t improved technology and b e t t e r power u n i t s have managed t o m a i n t a i n t h e c o s t p e r cub ic meter o f groundwater a t t h e same t r u e ( i . e . r e l a t i v e t o o t h e r cos ts ) cost . Th i s has been shown f o r Ar izona from 1 8 9 1 t o 1 9 6 7 i n a r e p o r t by M a r t i n and Archer (1971).

Th i s subsec t ion on t h e c o s t o f groundwater f o r i r r i g a t i o n i s l i m i t e d t o t h e p r e s e n t a t i o n o f da ta on (1) t h e a c t u a l cos ts o f p roduc ing groundwater f o r i r r i g a t i o n i n e i g h t c o u n t r i e s o f t h e w o r l d (See t a b l e 8.6-1) and ( 2 ) t h e p r i c e which farmers a c t u a l l y pay, o r which i s t h e upper l i m i t they can pay, f o r i r r i g a t i o n water (See t a b l e 8.6-2).

8.6.1 A c t u a l c o s t o f i r r i g a t i o n water ob ta ined from underground. Data from E l Salvador, I n d i a , Jordan, Pak is tan ( Indus Basin) , South Yemem, S y r i a (Hauran) and USA are assembled i n t a b l e 8.6-1; they are main ly based on f i g u r e s ob ta ined i n t h e course o f f i e l d p r o j e c t s executed b y FAO over the years from 1954 t o 1968. The source o f power f o r t h e pumps i s e i t h e r d i e s e l o r e l e c t r i c i t y . I n most cases t h e c o s t o f t he water i s shown b o t h exc lud ing and i n c l u d i n g t h e c o s t o f t h e water d i s t r i b u t i o n system; c l e a r l y t h e c o s t o f t he d i s t r i b u t i o n system i s o f l e s s d i r e c t i n t e r e s t t o those respons ib le f o r groundwater management than a re t h e d i r e c t c o s t s o f water p roduc t ion . Cost f i g u r e s may be u s e f u l f o r purposes o f comparison; a c t u a l c u r r e n t cos ts w i l l be s i g n i f i c a n t l y d i f f e r e n t .

8.6.2 P r i c e p a i d f o r i r r i g a t i o n water. The c o s t o f groundwater produced f o r i r r i g a t i o n must be seen i n r e l a t i o n t o t h e p r i c e which farmers pay ( o r are considered as capable o f pay ing) f o r such i r r i g a t i o n water. Th i s data i s presented i n t a b l e 8.6-2. which i s ma in ly from circum-Mediterranean coun t r i es , p l u s da ta from Japan and Taiwan; i t i s based on papers by Kreutzer ( 1 9 6 7 and 1 9 7 0 ) . These f i g u r e s a re g i ven f o r t h e purpose o f comparison o f r e l a t i v e p r i c e s o f p r o d u c t i o n i n d i f f e r e n t coun t r i es .

These s tud ies showed t h a t t h e p r i c e s p a i d f o r i r r i g a t i o n water i n the circum-Mediterranean w o r l d g e n e r a l l y ranges from 0 .50 t o 1 . 5 0 cents (US) per cub ic meter a t t h e t ime o f t he s tud ies. From t a b l e 8 .6 -1 i t can be seen t h a t t h e cos ts o f p roduc ing groundwater (exc lud ing t h e i r r i g a t i o n system) ranged from 0.40 t o 1.00 cen ts (US) p e r cub ic meter. I t would t h e r e f o r e seem t h a t under average c o n d i t i o n s , groundwater can be produced a t p r i c e s which are s u i t a b l e and economic f o r i r r i g a t i o n use. K a r s t groundwaters may c o s t a l i t t l e more t o produce, and t h e maximum amount which can be p a i d when such k a r s t groundwater i s used f o r i r r i g a t i o n should be determined i n advance. The study may apply t o one k a r s t aqu i fe r i n a l i m i t e d area o f t he country; o r i t may be a more genera l study f o r a l a r g e reg ion. If produc t ion cos ts o f k a r s t ground- water are h i g h e r than the p r i c e f o r which i s can be sold, such k a r s t ground- water i s n o t commercial ly e x p l o i t a b l e f o r i r r i g a t i o n . Such a study may focus a t t e n t i o n on l i m i t e d zones where the groundwater i s shal low and where t h e r e are good i r r i g a b l e s o i l s . Since groundwater e x t r a c t i o n f o r i r r i g a t i o n may be economic i n t h i s one l o c a l i t y , s i t i n g o f development boreholes may be con- t r o l l e d by economic r a t h e r than by t e c h n i c a l f a c t o r s and cons idera t ions . Any analyses o f p r o d u c t i o n c o s t and p r i c e should consider the ex is tence o r a v a i l - a b i l i t y o f government subsid ies.

300

Tab l e 8.6-1. Cost o f producing i r r i g a t i o n water i n US cents p e r cubic meter, pumped from va r ious a q u i f e r s i n e i g h t c o u n t r i e s o f t h e wor ld, TW = tube w e l l (FAO desk study, D. B. K r a a t z ) .

Water Cost i n US C/m3

D i s t r i b u t i o n System .......................

. ....................... Nq . Country Year Power Excluded Inc luded Remarks

1.

2 .

3.

4.

5 .

6 .

7.

8.

E l Salvador II n

I n d i a

Jordan

Pakis tan (Indus Basin)

S. Yemen

Sudan

S y r i a (S.W. area)

USA

1 9 6 4 1 9 6 4

( 1 9 6 5 (

1 9 6 8

( 1 9 6 7 ( (

1 9 6 4

1 9 6 8

( 1 9 5 4 (

1 9 6 4

D E

E

D

E E D

D

D

D

E

1 .49 O .74

0 .34 t o 0.66

-- -- .

0 .482 0.343 O . 383

1 .42

-- 0.16

t o 0.86

O . 6 1

1 . 5 2 O .76

O .38 t o 0.47

1 .77 t o 2.75

-- -- -- --

1.10

-- -- --

(UNDP/FAO P r o j e c t (

IBRD Study

(UNDP/FAO P r o j e c t (

Average; P u b l i c T W Average; P r i v a t e TW Average; P r i v a t e TW

Government Study

UNDP/FAO P r o j e c t

FAO/EPTA Report

New Mexico Univ.

30.1

Table 8.6-2. P r i c e range p a i d f o r i r r i g a t i o n waters, ma in l y i n the ci rcum- Mediterranean count r ies ; i n some cases p r i c e s a re the maximum p r i c e which farmers can a f f o r d t o pay and o b t a i n a p r o f i t on use. Based on Kreutzer (FAO, 1 9 6 7 , Appendix A) and 1 9 6 9 (IAEA), p l u s da ta f rom Turkey (Kuran, 1 9 6 9 ) .

Country P r i c e o f Water o r Area US cents/m3 Notes

Canary I l s . 1.30 t o 1.60

Spain 0.33 t o 2 . 3 1

Spain 0.83 t o 4 .15

Spain 0.50 t o 0.80

Spain 1 . 0 0 t o 0.50

Spain 16 .6*

B a l e a r i c I l s . 1.10 t o 2 .60

France O .O26

France o. 805

France 1 .39 t o 2 .78

I t a l y (N.) 0.43 t o 0 .54

I t a l y ( S . ) 1.00 t o 1 . 4 0

Ma l ta 0.55*

I s r a e l 0.50 t o 2.20

I s r a e l 0.70 t o 1.30

I s r a e l 3.30 t o 13.30

Turkey 0 . 2 1

Turkey 0.28

Turkey 0.65 t o 0.80

Turkey 0.85 t o 1.00

Taiwan 1. @ O *

Japan 1 .50*

Q u a l i t y and use b o t h a f f e c t cos t /va lue

General range f o r sur face i r r i g a t i o n water

General range €or groundwater f o r i r r i g a t i o n

I n bas ins w i t h o u t a water d e f i c i e n c y

i n bas ins w i t h a water d e f i c i e n c y

Maximum p r i c e ; glasshouse crops

For h o r t i c u l t u r e and f r u i t t r e e s

O l d canals; maintenance charges on ly

New i r r i g a t i o n systems; l i n e d canals

S p r i n k l e r i r r i g a t i o n systems

L i f e o f 4 t o 1 0 meters; h i g h water use

L i f e o f 4 t o 30 meters

Maximum p r i c e which farmers can pay

Pumped groundwater

Water d i v e r t e d from spr ings and r i v e r s

Water in t roduced from ou ts ide bas in

Surface water; f l o w - o f - r i v e r o r sp r ing

Surface water f rom storage s t r u c t u r e s

Groundwater, w i t h e l e c t r i c power pumps

Groundwater, w i t h d i e s e l power

Maximum p r i c e which farmers can pay

Ma.ximum p r i c e which farmers can pay

302

8.7 Comparative cos ts o f sur face and underground water

The cos ts o f i n v e s t i g a t i n g , developing, u s i n g and managing sur face waters and underground waters va ry so much i n t ime and space t h a t i t i s n o t f e a s i b l e t o reduce genera l concepts, such as t ime o f i n v e s t i g a t i o n , r a t e o f development (step-by-step and once - fo r -a l l ) , c o n t r o l o f use, f l e x i b i l i t y and o t h e r impon- derables t o a s t r i c t o r v a l i d comparison o f cos ts except f o r d e f i n i t e ind iv id- u a l p r o j e c t s . Ins tead, some da ta on comparative cos ts o f b r i n g i n g l a n d under i r r i g a t i o n w i t h water f rom va r ious source o f supply a r e g i ven as examples o f t he type o f c o s t d i f f e r e n t i a l s f o r these va r ious systems.

An FAO survey on cos ts o f i r r i g a t i o n schemes i n A f r i c a south o f t h e Sahara, showed t h a t t h e t o t a l investments va ry w ide ly f rom p r o j e c t t o p r o j e c t as numerous v a r i a b l e s have a d i r e c t bea r ing on t h e costs . Consider ing o n l y t h e source f o r p e r e n n i a l and supplemental sur face i r r i g a t i o n w i t h . f l o o d c o n t r o l o r sur face drainage, t h e average c o s t o f i r r i g a t i o n , drainage and f l o o d c o n t r o l , exc lud ing l and p repara t i on , a re g i ven i n t a b l e 8.7-1. These c o s t f i g u r e s a re i nc luded f o r i l l u s t r a t i o n o f t h e r e l a t i v e cos ts i n v o l v e d w i t h t h e v a r i o u s schemes a n d a re n o t rep resen ta t i ve o f a c t u a l c u r r e n t cos ts .

I t may be accepted t h a t t h e methods o f c o s t e s t i m a t i o n f o r groundwater a l ready o u t l i n e d i n t h i s Guide must be fo l l owed t o determine cos ts o f k a r s t groundwater. A t t h e same t ime, standard methods o f e s t i m a t i n g cos ts o f sur face water development and supply can be done by c i v i l engineers and c o s t account- ants. Only a f t e r d e t a i l e d s tudy can t h e r e be any meaningfu l comparison f o r a s p e c i f i c case between the c o s t o f groundwater and o f sur face water.

8.8 F e a s i b i l i t y study f o r p lann ing and investment purposes

Before complet ing t h i s s e c t i o n o f t he Guide d e a l i n g w i t h "Methods o f Cost Es t imat ion" i t i s necessary t o draw a t t e n t i o n t o the end-purpose o f such c o s t es t imat ions . As t h e development a n d management o f t he water ( k a r s t groundwater inc luded) i s d i r e c t e d t o i t s p roper use, so should c o s t c a l c u l a t i o n s enable t h e p lanners t o compare d i f f e r e n t development approaches and investment o f d i f f e r - e n t amounts o f money t o a t t a i n o b j e c t i v e s o f a s o c i a l , economic and p o l i t i c a l nature.

The genera l t o o l used t o t e s t a development p roposa l i s a " f e a s i b i l i t y study" which i s made a f t e r resources i n v e s t i g a t i o n and development p lann ing have been completed, but b e f o r e investment commences. I n an FAO/IBRD p u b l i c a - t i dn "Gu ide l ine f o r t h e P repara t i on o f F e a s i b i l i t y Studies f o r I r r i g a t i o n and Drainage Pro jec ts " (Dec. 1 9 7 0 ) i n fo rma t ion i s g i ven on t h e genera l approach and on the d e t a i l e d s tud ies requ i red . Many o f t h e i tems apply as d i r e c t l y t o t h e development and management o f groundwater f rom k a r s t a q u i f e r s f o r v i l l a g e supply o r i r r i g a t i o n as they do t o t h e " i r r i g a t i o n and drainage" p r o j e c t s used i n the t i t l e .

Whi le i t i s n o t p o s s i b l e t o summarize t h e whole paper here, t h e e i g h t main themes o f an i r r i g a t i o n study, as w e l l as t h e d e f i n i t i o n o f a f e a s i b i l i t y study, a re reproduced as fo l l ows :

The o b j e c t i v e o f a f e a s i b i l i t y study i s t o demonstrate t h a t t h e p r o j e c t i s : i n conformi ty w i t h t h e coun t ry ' s development o b j e c t i v e s and immediate p r i o r i t i e s ; t e c h n i c a l l y sound, and t h e b e s t o f t h e a v a i l a b l e a l t e r n a t i v e s under e x i s t i n g t e c h n i c a l and o the r c o n s t r a i n t s ; a d m i n i s t r a t i v e l y workable; and economical ly and f i n a n c i a l v i a b l e .

I n fo rmu la t i ng (des ign ing) a p r o j e c t t h e r e should be a cons tan t e f f o r t t o min imize cos ts (but n o t a t t h e expense o f s a f e t y ) , maximize r e t u r n s and br ing about u t i l i z a t i o n o f t h e investment i n t h e q u i c k e s t p o s s i b l e t ime. The l a t t e r w i l l u s u a l l y necess i ta te a r a p i d t rans fo rma t ion

' o f t h e farming p r a c t i c e s i n t h e p r o j e c t area. From these cons idera t ions stem the main themes o f an i r r i g a t i o n p r o j e c t f e a s i b i l i t y study:

(1) A thorough study o f t h e p h y s i c a l resource base, p a r t i c u l a r l y t h e p r o j e c t area s o i l s , c l i m a t e and water supply, i n order t o ensure t h a t t he cropping p a t t e r n s proposed and t h e y i e l d s p r e d i c t e d can be mainta ined f o r a susta ined p e r i o d and i n o rde r t o determine t h e sca le of t h e p r o j e c t .

303

Table 8.7-1. Investment (US $ pe r hec tare i r r i g a t e d ) r e q u i r e d t o develop water resources f o r i r r i g a t i o n from va r ious sources o f supply i n d i f f e r e n t c o u n t r i e s o f A f r i c a South o f t h e Sahara; f i g u r e s i n b racke ts a re annual ope ra t i ng a n d maintenance cos ts a l s o i n US $ p e r hec tare i r r i g a t e d (Doorenbos, FAO, 1 9 7 0 ) .

I I

ethod o f

~~~~ ~~~

Pe renn ia l I r r i g a t i o n

Supplemental I r r i g a t i o n

Remarks

Inc ludes f l o o d contro:

I nc ludes sur face ---------------------.

drainage

Inc ludes f l o o d contro:

Inc ludes sur face drainage

---------------------.

304

A thorough examination o f t he people l i k e l y t o be i n v o l v e d i n t h e p r o j e c t i n order t o ensure t h a t t h e proposed development i s appro- p r i a t e t o t h e i r a t t i t u d e s and c a p a c i t i e s .

A thorough study o f t h e eng ineer ing a l t e r n a t i v e s f o r s e r v i n g and d r a i n i n g t h e p r o j e c t lands, and t h e i r phasing, i n o rde r t o ensure t h a t t he most app rop r ia te economical but safe s o l u t i o n i s achieved.

An adequate p r e l i m i n a r y des ign o f , and a c o n s t r u c t i o n schedule f o r t h e works, b o t h p r o j e c t works and on-farm works, i n o rde r t o demonstrate t h e i r s u i t a b i l i t y and t o es t ima te t h e i r cos ts and t h e phasing o f those costs .

The de terminat ion and schedul ing o f t h e a g r i c u l t u r a l p a t t e r n ( s i z e and t ype o f farm e n t e r p r i s e , crops and t h e i r y i e l d s ) on t h e b a s i s o f p h y s i c a l and human resources, p resen t l a n d use, market p r o j e c t i o n s and p r i c e s .

The de te rm ina t ion and phasing o f t h e v a r i o u s measures and i n p u t s necessary t o achieve t h e a g r i c u l t u r a l p lan.

The de te rm ina t ion o f t h e management and o r g a n i z a t i o n necessary t o c o n s t r u c t and implement t h e p r o j e c t t o t h e t i m e schedules p red ic ted .

The de terminat ion o f t h e economic b e n e f i t t o t h e country , t h e f i n a n - c i a l r e t u r n t o t h e farmers, t h e f i n a n c i a l r e s u l t s o f t h e o p e r a t i n g a u t h o r i t y and t h e repayment o f p r o j e c t cos ts b y b e n e f i c i a r i e s .

I t must be s t ressed t h a t t h e main themes o f t h e study a re n o t sepa- r a t e exerc ises. The f i n a l i z a t i o n o f each and i t s amalgamation i n t o t h e whole i s a process o f successive approximat ion reached a f t e r cross- cons ide ra t i on o f t he i n t e r i m r e s u l t s o f t he others. I n thus conc lud ing these g u i d e l i n e s t o t h e e s t i m a t i o n o f c o s t s o f d i f f e r -

e n t phases and aspects o f bringing k a r s t groundwater i n t o b e n e f i c i a l use, these e x t r a c t s f rom a g u i d e l i n e t o t h e p r e p a r a t i o n o f f e a s i b i l i t y r e p o r t f o r P lann in

the u t i l i z a t i o n o f t h e n a t u r a l resource o f groundwater h e l d i n k a r s t a q u i f e r s and Investment Purposes serve t o draw a t t e n t i o n t o t h e end purpose o f t h e wor

f o r t he b e n e f i t o f t h e people t o whom i t w i l l be made a v a i l a b l e as requ i red , i n q u a n t i t y , i n q u a l i t y , i n t ime, i n p r i c e and i n p lace.

305

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Yevjevich, V. (ed.) . 1976. K a r s t hydro logy and water resources. Proceedings o f t h e U.S.-Yugoslavia Symposium, Dubrovnik, 1975. F o r t C o l l i n s , Co., Water Resources Pub l i ca t i ons , v o l . 1, 4 3 9 p., v o l . 2, 4 3 4 p.

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Contributing authors

A s t i e r , Jean-Louis, Geophysician Conse i l , V i a Riccardo Zandonai-11, 00194 Roma, I t a l y .

Benson, D. J., Department o f Geology, U n i v e r s i t y o f Alabama, Tuscaloosa, Alabama, USA.

Brown, R. M., I n t e r n a t i o n a l Atomic Energy Agency, K a e r n t n e r r i n g 1, Vienna 1010, A u s t r i a .

Burdon, Dav id J., F.A.O., Ra thc la re House,Buttevant, County Cork, I r e l a n d .

Castany, G i l b e r t , 3 residence P e t i t Chambord, 9 2 3 4 0 Bourg-la-Reine, France.

G o n f i a n t i n i , R. G., I n t e r n a t i o n a l Atomic Energy Agency, K a e r n t n e r r i n g 1, Vienna 11, A u s t r i a .

Heindl , L.A., deceased, f o r m e r l y o f N a t i o n a l Research Counci l , Washington, D.C., USA.

Herak, M i lan , Geo1.-paleont. zavod, S o c i j a l . r e v o l u c i j e 8 , YU-41000 Zagreb, Yugoslavia.

Hughes, T r a v i s H., PELA, Tuscaloosa, Alabama, USA.

I s s a r , A r i e , Water Resources Center, I n s t i t u t e € o r Deser t Research, Sde Boker, I s r a e l .

Kashef, Abdel A z i z I., t r a n s l a t o r o f Castany's work, 1 1 0 4 C u r r i t u c k Dr i ve ,

Kudel in, B . I . , (deceased), U.S.S.R.

P. O. Box 1 8 4 3 2 , Raleigh, N o r t h C a r o l i n a 27609, USA.

LaMoreaux, P h i l i p E., P. E. LaMoreaux and Associates, P. O. Box 2310, Tusca- loosa, Alabama 35403, USA.

Langmuir, Donald, Department o f Chemistry and Geochemistry, Colarado School o f Mines, Golden, Colorado 80401, USA.

LeGrand, Har ry E., Hydrogeo log is t , 3 3 1 Yadkin Dr. , Raleigh, N o r t h C a r o l i n a 27609, USA.

Memon, Bashi r , PELA, Tuscaloosa, Alabama, USA.

Payne, B. R . , I n t e r n a t i o n a l Atomic Energy Agency, K a e r n t n e r r i n g 1, Vienna 1010, Aus t r i a .

Posey, S tan ley W., PELA, Tuscaloosa, Alabama, USA.

Przewlocki, Kazik, I n t e r n a t i o n a l Atomic Energy Agency, K a e r n t n e r r i n g 1, Vienna

Schoel ler , Henr i , 5 r u e Lou is Maydieu, 33200 Bordeaux - Cauderan, France.

S t r i n g f i e l d , V. T., Jr., Research H y d r o l o g i s t , 4208-50 th S t r e e t N.W., Washing-

1010, A u s t r i a .

ton, D.C. 20016.

Wilson, B e t t y M., PELA, Tuscaloosa, Alabama, USA.

Yurts&ver, Yucel, I n t e r n a t i o n a l Atomic Energy Agency, K a e r n t n e r r i n g 1, Vienna . 1010, A u s t r i a .

Zebid i , Habib, D i v i s i o n des Resources en Eau, 4 1 , r u e de l a Manoubia, Mont-

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f l e u r y , Tunis, Tunis ia .

Titles in this series

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2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14. 15.

16.

17. 18.

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22. 23.

The use of analog and digital computers in hydrology. Proceedings o f the Tucson Symposium, June 1966 /L’utilisation des calculatrices analogiques et des ordinateurs en hydrologie : Actes du colloque de Tucson, juin 1966. Vol. 1 et 2. Co-edition IASH- Unesco ICoédition AIHS-Unesco. Water in the unsaturated zone. Proceedings of the Wageningen Symposium, August 1967 / L‘eau dans l a zone non saturée: Actes dy symposium de Wageningen, août 1967. Edited by / Edité par P. E. Rijtema & H. Wassink. Vol. 1 e t 2. Co-edition IASH-Unesco / Coédition AIHS-Unesco. Floods and their computation. Proceedings of the Leningrad Symposium, August 1967 / Les crues et leur évaluation : Actes du colloque de Leningrad, août 1967. Vol. 1 et 2. Co-edition IASH-Unesco-WMO/Coédition AIHS-Unesco-OM. Representative and experimental basins. An international guide for research and practice. Edited by C. Toebes and V. Ouryvaev. Published by Unesco. (Will also appear in Russian and Spanish) / L e s bassins représentatifs e t expérimentaux: Guide international des pratiques en matière de recherche. Publié sous la direction de C. Toebes e t V. Ouryvaev. Publié par l’Unesco. (A paraître également e n espagnol et en russe). Discharge of selected rivers of the world / Débit de certains cours d’eau du monde / Caudal de algunos rios del mundo / Pacxomr B O ~ I a36pa~~brx peK Mapa. Published by Unesco/Publié par l’Unesco.

Vol. I : General and regime characteristics of stations selected / Vol. 1 : Caractéristiques générales et caractéristiques du régime des stations choisies / Vol. I : Caracteristicas generales y caracteristicas del régimen de las estaciones seleccionadas / TOM I: O6qae a pemmbie xapaKrepacreKe es6pa~mrx C T ~ H W ~ ~ .

1964) /Vol. II : Débits mensuels e t annuels enregistrés en diverses stations sélectionnées (de l’origine des obser- vations à l’année 1964) /Vol. II : Caudales mensuales y anuales registrados en diversas estaciones seleccionadas (desde e l comienzo de las observaciones hasta e l ai70 1964) / TOM II: Mecrrsmie a roaoBbie pacxor@i Boabr, ~aperacrpaposa~~b~e pasnmbrm H36paHHbIMH CT~HIOIRMM (c Hasana ~ a 6 m o ~ e m i i no 1964 roaa) .

(1965-1969) /Vol. III : Caudales mensuales medianos y caudales extremos (1965-1969) /TOM III: Cpeme-

Vol. II : Monthly and annual discharges recorded at various selected stations (from start of observations up to

Vol. III: Mean monthly and extreme discharges (1965-1969) /Vol. III : Débits mensuels moyens et débits extrêmes

MeCR’IHble li 3KClpeMâJibHbIe paCXOnb1 (1965- 1969 TI‘.).

Vol. III (part II) : Mean monthly and extreme discharges (1969-1972) /Vol. III (partie II) : Débits mensuels moyens et débits extrêmes (1969-1972) /Vol. III (parte II) : Caudales mensuales medianos y caudales extremos (1969-1972) / TOM III (sacTa II): Cpeme-Mecmbre a 3~crpe~anb~bre pacxomr (1969-1972 rr.).

Vol.111 (part III) : Mean monthly and extreme discharges (1972-1975) (English, French, Spanish, Russian). L i s t of International Hydrological Decade Stations of the world / L is te des stations de l a Décennie hydrologique inter- nationale existant dans l e monde / Lista de las estaciones dei Decenio Hidrol6gico Internacional del mundo / Crmco~ C T ~ I I , U ~ ~ MexpyHapoDHoro r~ponoresecKor0 ,qecrrmerarr 3e~Ho1-0 mapa.Published by Unesco /Publié par i’ünesco. Ground-water studies. An international guide for practice. Edited by R. Brown, J. Ineson, V. Konoplyantzev and V. Kovalevski. (4 supplements published). Land subsidence. Proceedings of the Tokyo Symposium, September 1969 /Affaissement du sol : Actes du colloque de Tokyo, septembre 1969. Vol. 1 et 2. Co-edition IASH-Unesco/ Coédition AIHS-Unesco. Hydrology of deltas. Proceedings of the Bucharest Symposium, May 1969 /Hydrologie des deltas : Actes du colloque de Bucarest, mai 1969. Vol. 1 et 2. Co-edition IASH-Unesco/Coédition AIHS-Unesco. Status and trends,of research in hydrology / Bilan et tendances de l a recherche en hydrologie. Published by Unesco/ Publié par l’Unesco. World water balance. Proceedings of the Reading Symposium, July 1970 /Bilan hydrique mondial : Actes du colloque de Reading, juillet 1970. Vol. 1-3. Co-edition IAHS-Unesco- WMO / Coédition AIHS-Unesco-OMN Research on representative and experimental basins. Proceedings of the Wellington (New Zealand) Symposium, December 1970 / Recherches sur les bassins représentatifs et expérimentaux : Actes du colloque de Wellington (N.Z.), décembre 1970. Co-edition IASH-Unesco / Coédition AIHS-Unesco. Hydrometry : Proceedings of the Koblenz Symposium, September 1970 / Hydrométrie : Actes du colloque de Coblence, septembre 1970. Co-edition IAHS-Unesco- WMO / Coédition AIHS-Unesco-OMM Hydrologic informa tion systems. Co-edition Unesco- WMO. Mathematical models in hydrology : Proceedings of the Warsaw Symposium, July 1971 / L e s modèles mathématiques en hydrologie : Actes du colloque de Varsovie, juillet 1971. Vol. 1-3. Co-edition IAHS-Unesco-WMO. Design of water resources projects with inadequate data : Proceedings of the Madrid Symposium, June 1973 /Elaboration des projets d’utilisation des ressources en eau sans données suffisantes : Actes du colloque de Madrid, juin 1973. Vol. 1-3. Co-edition IAHS- Unesco- WMO / Coédition AIHS- Unesco-Om. Methods for water balance computations. An international guide for research and practice. Hydrological effects of urbanization. Report o f the Sub-group on the Effects of Urbanization on the Hydrological Environment. Hydrology of marsh-ridden areas. Proceedings of the Minsk Symposium, June 1972. Hydrological maps. Co-edition Unesco- WMO. World catalogue of very large floods / Répertoire mondial des très fortes crues / Catilogo mundial de grandes crecidas /

Floodflow computation. Methods compiled from world experience. Guidebook on water quality surveys.

BCeM>ZpHbIfi KaTâiiOr 6onairriot HBBOAKOB.

24.

25. 26. 27. 28.

29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41.

Effects of urbanization and industrialization on the hydrological regime and on water quality. Proceedings of the Amsterdam Symposium, October 1977, convened by Unesco and organized by Unesco and the Netherlands National Committee for the IHP in co-operation with IAHS / Effets de l’urbanisation et de l’industrialisation sur le régime hydrologique et sur l a qualité de l’eau. Actes du colloque d’Amsterdam, octobre 1977, convoqué ,par l’Unesco et organisé par l’Unesco e t l e Comité national des Pays-Bas pour l e PHI en coopération avec I’AISH. World water balance and water resources of the earth. Impact of urbanization and industrialization on water resources planning and management. Socio-economic aspects of urban hydrology. Casebook of methods of computation of quantitative changes in the hydrological regime of river basins due to human activities. Surface water and groundwater interaction. Aquifer contamination and protection. Methods of computation of the water balance o f large lakes and reservoirs. Vol. 1 : Methodology. Vol. I1 : Case studies. Application of results from representative and experimental basins. Groundwater in hard rocks. Groundwater Models. Vol. I : Concepts, problems and methods of analysis with examples of their application. Sedimentation Problems in River Basins. Methods of computation of low stream flow. Roceedings of the Leningrad Symposium on specific aspects of hydrological computations for water projects (Russian). Methods of hydrological compu!ations for water projects. Hydrological aspects o f drought. (In preparation). Guidebook to studies o f land subsidence due to groundwater withdrawal. Guide to the hydrology o f carbonate rocks.

[11.96]SC.83/XX-41 / A