Environmental Hydrogeology, Second Edition

ENVIRONMENTALHYDROGEOLOGY

Second Edition

CRC Press is an imprint of theTaylor & Francis Group, an informa business

Boca Raton London New York

ENVIRONMENTALHYDROGEOLOGY

Second Edition

Philip E. LaMoreauxMostafa M. Soliman

Bashir A. MemonJames W. LaMoreaux

Fakhry A. Assaad

CRC PressTaylor & Francis Group6000 Broken Sound Parkway NW, Suite 300Boca Raton, FL 33487-2742

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v

ContentsPreface...............................................................................................................................................xiAcknowledgments .......................................................................................................................... xiii

Chapter 1 Introduction ..................................................................................................................1

1.1 Introduction .............................................................................................................................11.2 Suggestions and References ....................................................................................................5References ........................................................................................................................................ 11

Chapter 2 Geological Aspects for Assessment, Clean-up, and Siting of Waste Disposal Sites ........................................................................................................................... 13

2.1 Introduction ........................................................................................................................... 132.2 Geological Aspects ............................................................................................................... 15

2.2.1 Rock Types ................................................................................................................. 152.2.2 Candidate Sites .......................................................................................................... 192.2.3 Stratigraphy ................................................................................................................202.2.4 Structural Geology .....................................................................................................202.2.5 Physical Properties .....................................................................................................202.2.6 Hydrogeologic Considerations ...................................................................................24

2.3 Data Acquisition of Rock and Formation Fluid Testings ......................................................242.3.1 Data Obtained Prior to Drilling Potential Disposal Sites ..........................................242.3.2 Well Logs ...................................................................................................................25

2.4 Summary Site Selection ........................................................................................................26References ........................................................................................................................................26

Chapter 3 Hydrogeology .............................................................................................................29

3.1 Introduction ...........................................................................................................................293.1.1 Historical Background ...............................................................................................29

3.2 Hydrologic Cycle ...................................................................................................................303.3 Main Components of Hydrology ........................................................................................... 313.4 Watershed Hydrology ............................................................................................................ 32

3.4.1 Climatic Factors ......................................................................................................... 333.4.2 Physiographic Factors ................................................................................................ 333.4.3 Mechanism of Erosional Deposition ..........................................................................34

3.5 Hydrogeology ........................................................................................................................343.5.1 Distribution of Subsurface Water............................................................................... 353.5.2 Groundwater Flow Theories ...................................................................................... 353.5.3 Steady-State Groundwater Flow in Aquifers ............................................................. 383.5.4 Unsteady-State Groundwater Flow in Confined Aquifers ......................................... 383.5.5 Effects of Partial Penetration of Well ........................................................................ 493.5.6 Hydraulics of the Well and Its Design ....................................................................... 513.5.7 Slug Tests ................................................................................................................... 523.5.8 Groundwater Recharge ..............................................................................................54

References ........................................................................................................................................ 59

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Chapter 4 Environmental Impacts Related to Hydrogeological Systems ................................... 61

4.1 Natural and Manmade Disasters ........................................................................................... 614.2 Land Subsidence ................................................................................................................... 634.3 Causes of Subsidence ............................................................................................................65

4.3.1 Collapse into Voids: Mines and Underground Cavities .............................................664.3.2 Sinkholes .................................................................................................................... 674.3.3 Sediment Compaction ................................................................................................684.3.4 Underground Fluid Withdrawal .................................................................................694.3.5 Natural Compaction ................................................................................................... 704.3.6 Hydrocompaction ....................................................................................................... 714.3.7 Organic Soil ............................................................................................................... 71

4.4 Damage Cost and Legal Aspects of Land Subsidence .......................................................... 72References ........................................................................................................................................ 74

Chapter 5 Kinds of Waste and Physiography of Waste Disposal Sites .......................................77

5.1 Kinds and Sources of Wastes ................................................................................................775.1.1 Solid Wastes ............................................................................................................... 795.1.2 Liquid Wastes ............................................................................................................. 81

5.2 Types of Waste ......................................................................................................................845.2.1 Urban Wastes .............................................................................................................845.2.2 Municipal Wastes .......................................................................................................845.2.3 Petroleum Waste ........................................................................................................845.2.4 Mining Waste .............................................................................................................855.2.5 Industrial Waste .........................................................................................................86

5.3 Gaseous Wastes .....................................................................................................................865.3.1 Industrial Wastes ........................................................................................................865.3.2 Radon Risk .................................................................................................................875.3.3 Forest Growth Reduction by Air Pollution ................................................................885.3.4 Acid Rain ...................................................................................................................885.3.5 Mines .........................................................................................................................885.3.6 Hydrocarbons .............................................................................................................90

5.4 Hazardous Wastes .................................................................................................................905.4.1 Definition ...................................................................................................................905.4.2 Toxic Materials .......................................................................................................... 915.4.3 Soil Hazardous Wastes .............................................................................................. 915.4.4 Radioactive Wastes ....................................................................................................93

5.5 Physiography of Waste Sites .................................................................................................945.5.1 Permeable Formations (3,000–12,000 ft) Containing Connate Brine .......................955.5.2 Impermeable Formations ...........................................................................................95

5.6 Environmental Concerns on Hydrogeological Systems ........................................................975.6.1 Man-Made Earthquakes ............................................................................................975.6.2 Transport of Polluted Waters by Subterranean Karst Flow Systems .........................97

References ........................................................................................................................................98

Chapter 6 Environmental Impacts on Water Resource Systems .............................................. 101

6.1 Introduction ......................................................................................................................... 1016.2 Climatic Changes and Their Effect on Water Resources.................................................... 1016.3 Surface-Water Pollution ...................................................................................................... 102

Contents vii

6.4 Groundwater Pollution ........................................................................................................ 1046.4.1 Migration of Pollutants in Aquifers ......................................................................... 1046.4.2 Saltwater Intrusion ................................................................................................... 1096.4.3 Landfill Leachate ..................................................................................................... 115

6.5 Groundwater Monitoring .................................................................................................... 118References ...................................................................................................................................... 120

Chapter 7 Waste Management for Groundwater Protection ..................................................... 125

7.1 Primary Concept ................................................................................................................. 1257.2 Alternative of Waste Disposal ............................................................................................. 1267.3 Disposal and Control ........................................................................................................... 128

7.3.1 Types of Disposal ..................................................................................................... 1287.3.2 Disposal of Hazardous Wastes................................................................................. 1317.3.3 Salt Caverns for Disposal ......................................................................................... 132

7.4 Groundwater Protection ...................................................................................................... 1337.4.1 Damage Prevention to the Water Resource System ................................................. 1337.4.2 Remediation of Groundwater Aquifers .................................................................... 134

7.5 Risk and Legal Aspects of Waste Disposal Sites ................................................................ 1377.5.1 Definition of Risk and Risk Assessment.................................................................. 1387.5.2 Application of Risk Assessment in the Context of Waste Disposal ........................ 1387.5.3 An Outline of the Risk Assessment Process ............................................................ 141

7.6 Components of the Risk Assessment Process ..................................................................... 1427.6.1 Risk or Hazard Identification ................................................................................... 1427.6.2 Risk Estimation ........................................................................................................ 1447.6.3 Exposure Assessment: Identification of Sources of Chemicals ............................... 1477.6.4 Exposure Assessment: Chemical Releases/Environmental Fate and Transport ..... 1487.6.5 Exposure Assessment: Routes of Exposure ............................................................. 1557.6.6 Dose–Response Estimation ..................................................................................... 157

7.7 Hydrogeological Systems and Monitoring .......................................................................... 158References ...................................................................................................................................... 160

Chapter 8 Hydrogeologic and Environmental Considerations for Design and Construction in Karst Terrain/Sinkhole-Prone Areas ................................................................... 165

8.1 Introduction ......................................................................................................................... 1658.2 Investigation-Design Considerations................................................................................... 166

8.2.1 Desk Top Investigations ........................................................................................... 1688.2.2 Field Investigations .................................................................................................. 1688.2.3 Surface Geophysical Exploration ............................................................................. 1698.2.4 Borehole Geophysics ................................................................................................ 1708.2.5 Risk Assessment ...................................................................................................... 1718.2.6 Site Characterization for Planning and Design ....................................................... 171

8.3 Design and Construction Considerations ............................................................................ 1728.3.1 Distribution of Solution Features at a Site ............................................................... 1728.3.2 Site Preparation ........................................................................................................ 1738.3.3 Site Excavation and Sinkhole Activity..................................................................... 174

8.4 Remediation ........................................................................................................................ 1758.4.1 Preventive Measures to Stop Raveling and Erosion at Soil–Rock Interface ........... 1758.4.2 Overburden Dome Collapse and Repair .................................................................. 1768.4.3 Repair of Sinkhole ................................................................................................... 176

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8.4.4 Partially Supported Structure on Sinkhole-Prone Ground Structure ...................... 1778.4.5 Design Structure Resistant to Erosion-Dome Collapse ........................................... 1788.4.6 Emergency Actions .................................................................................................. 178

References ...................................................................................................................................... 179

Chapter 9 Groundwater Modelling ........................................................................................... 183

9.1 Introduction ......................................................................................................................... 1839.2 Electric Simulation Model .................................................................................................. 1839.3 Hele–Shaw Model ............................................................................................................... 1849.4 Resistance Network Model ................................................................................................. 1849.5 Simulation Technique .......................................................................................................... 187

9.5.1 Forward-Difference Simulation ............................................................................... 1889.5.2 Backward-Difference Simulation ............................................................................ 189

9.6 Resistor Capacitor Network Model ..................................................................................... 1929.7 Analog Computers .............................................................................................................. 1939.8 Digital Computer ................................................................................................................. 194

9.8.1 Model Development ................................................................................................. 1949.8.2 Groundwater Equation ............................................................................................. 1959.8.3 Digital Computer Solution ....................................................................................... 196

9.9 Finite — Element Method ................................................................................................... 1989.9.1 The General Quasi-Harmonic P.D.E........................................................................2009.9.2 Finite Element Discretization .................................................................................. 201

9.10 Groundwater Quality Models .............................................................................................2029.10.1 Quality Mathematical Model ...................................................................................2039.10.2 Basic Equations ........................................................................................................203

9.11 Difficulties and Shortcomings ............................................................................................204References ......................................................................................................................................205

Chapter 10 Case Studies .............................................................................................................207

10.1 The Nubian Sandstone Aquifer System in Egypt ...............................................................20710.1.1 Introduction ............................................................................................................20710.1.2 Geological and Hydrogeological Characteristics ..................................................20710.1.3 Hydrogeology ......................................................................................................... 21310.1.4 Regional Flow Pattern ........................................................................................... 21410.1.5 Groundwater Models ............................................................................................. 21410.1.6 Environmental Problems ....................................................................................... 219

References ...................................................................................................................................... 22110.2 Siting a Secure Hazardous Waste Landfill in a Limestone Terrane ................................... 223

10.2.1 Introduction ............................................................................................................ 22310.2.2 Topographic and Geographic Setting ....................................................................22410.2.3 Geologic Setting.....................................................................................................22410.2.4 Structural Geology ................................................................................................. 22910.2.5 Hydrogeology ......................................................................................................... 22910.2.6 Aquifer Test ............................................................................................................23410.2.7 Procedure ............................................................................................................... 23510.2.8 Conclusions ............................................................................................................240

References ......................................................................................................................................24510.3 Catastrophic Subsidence: An Environmental Hazard, Shelby County, Alabama ..............246

10.3.1 Introduction ............................................................................................................246

Contents ix

10.3.2 General Hydrogeologic Setting ..............................................................................24610.3.3 Geology of the Dry Valley Area ............................................................................24610.3.4 Water Level Decline and Catastrophic Subsidence ...............................................24810.3.5 Hydrology of Dry Valley ....................................................................................... 25110.3.6 Use of Remote Sensing Methods ...........................................................................25410.3.7 Test Drilling ........................................................................................................... 25710.3.8 Inventory and Monitoring of Subsidence ............................................................... 25710.3.9 Prediction of Induced Sinkholes ............................................................................ 25710.3.10 Southern Natural Gas Pipeline: A Case History ................................................... 258

References ......................................................................................................................................26010.4 Environmental Hydrogeology of Figeh Spring, Damascus, Syria ..................................... 261

10.4.1 Introduction ............................................................................................................ 26110.4.2 Geomorphology ..................................................................................................... 26110.4.3 Geology: Stratigraphic Sequence ........................................................................... 26310.4.4 Hydrogeology of the Figeh Area: Geologic Structural Setting and Karst

Development .......................................................................................................... 27010.4.5 Recharge, Storage, and Discharge of Groundwater ............................................... 27310.4.6 Discharge Groundwater to the Barada River ......................................................... 28310.4.7 Environmental Constraints to Future Use of Figeh System ..................................297

References ......................................................................................................................................29910.5 Collection and Disposal of Naturally Occurring Chloride-Contaminated

Groundwater to Improve Water Quality in the Red River Basin ........................................30010.5.1 Introduction ............................................................................................................30010.5.2 Geologic Setting.....................................................................................................30310.5.3 Hydrogeologic Setting ...........................................................................................30510.5.4 Field Investigations ................................................................................................30610.5.5 Induced Infiltration ................................................................................................ 31110.5.6 Drawdown in Bedrock Aquifer System and Overburden/Alluvial Aquifer ........... 31710.5.7 Effects of Pumping on Jonah Creek ...................................................................... 31810.5.8 Effects of Pumping on Brine Emissions ................................................................ 32110.5.9 Chloride Load ........................................................................................................ 32210.5.10 Collection and Disposal of Chloride Contaminated Groundwater ........................ 32410.5.11 Conclusions ............................................................................................................ 329

Bibliography ................................................................................................................................... 33110.6 Groundwater Recharge and Its Environmental Impact with Case Studies ......................... 332

10.6.1 Introduction ............................................................................................................ 33210.6.2 Purpose .................................................................................................................. 33510.6.3 Positive Impacts of Artificial Groundwater Recharge ........................................... 33610.6.4 Environmental Impacts of an Artificial Recharge ................................................. 33710.6.5 Adverse Recharge in Arid Regions of Egypt ......................................................... 33810.6.6 Artificial Recharge in Arid Regions of Egypt ....................................................... 33810.6.7 Future Role of Artificial Recharge in Egypt’s Water Management ....................... 341

References ...................................................................................................................................... 342

Appendix A: Glossary ................................................................................................................. 343

Appendix B: Conversion Tables ................................................................................................. 357

Appendix C: Math Modeling and Useful Programs ................................................................. 359

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Appendix D: Software Manual of Drawdown Around Multiple Wells .................................. 363

Index .............................................................................................................................................. 367

xi

PrefaceWhen this book was first written the world’s population was expected to grow over the next two decades by 1.7 billion, bringing the earth’s inhabitants to about 7 billion. Now the world’s population is 6.6 billion and continues to grow at an exponential pace. Regardless of the population, people must have adequate food, clothing, and shelter while minimizing additional impacts on the environment.

We have learned that there must be a readily accessible reserve of professionals, mainly geosci-entists in the governmental infrastructure, to guide research, regulation, and remediation. We have also learned that environmental problems are complex and not only of local concern, but, national and global in scope. Some of these concerns such as global warming, water pollution, acid rain, and air pollution extend beyond political boundaries and span the gaps between continents. Experi-enced professional geoscientists are needed to develop solutions and implement them.

Our environmental growing pains resulted in a great flurry of professional acquisitions. Sud-denly, experienced hydrogeologists are in great demand. Their knowledge is needed for the study of ground-water movement as influenced by geologic depositional environments and structures. Geo-physicists and geochemists help describe “the bucket” containing the water. Hydrologists and engi-neers determine its hydrologic characteristics and identify, monitor, and safely remove pollutants.

We have learned by experience that much waste of financial resources and time occurs with-out trained professional geoscientists to perform the remedial tasks. One of the biggest problems associated with future environmental programs is directly related to the availability of professional staffing to do the job. As we consider the future, how do we assess this factor? This can be mea-sured in part by the number of new courses, seminars, and training programs pertaining to the envi-ronment offered at universities, by professional associations, and by private training organizations. In the next few years these programs will provide a reserve of professionals trained in hydrogeology, environmental geology, environmental engineering, and environmental chemistry.

For the aforementioned reasons, this textbook was prepared to aid geoscientists in their under-standing of environmental hydrogeology. Chapter 1 provides an introduction. Chapter 2 is devoted to geological aspects of potential disposal sites. Chapter 3 covers surface water hydrology, ground-water hydrology, and the design of wells. Chapter 4 enlightens the professional and graduate and undergraduate students about relationships between environmental impacts and hydrogeological systems. Chapter 5 describes the types and sources of wastes and their properties, including adverse affects on the environment. Chapter 6 focuses on environmental impacts on water resource systems, and Chapter 7 gives a clear idea about waste management for ground-water protection. Chapter 8 discusses environmental considerations for design and construction in karst terrains, while Chapter 9 covers groundwater modeling. Chapter 10 contains selected case studies from around the world as examples to show some of the environmental impacts on water resource systems and what has to be done to protect those hydrogeological systems.

The final section, includes four appendices: Appendix A, a glossary of important hydrogeologi-cal terms; Appendix B, conversion tables; and Appendix C, mathematical modeling of some of the hydrogeological cases with accompanying software manual and computer diskette containing an executable file and a solved problem with its data file for demonstration. Appendix D is a software manual of drawdown around multiple wells.

Mostafa M. SolimanPhilip E. LaMoreauxBashir A. MemonJames W. LaMoreauxFakhry A. Assaad

xiii

AcknowledgmentsThe authors are grateful to the many people who helped with the preparation of this book and particularly to all reviewers of the manuscript, and especially, William J. Powell and Dr. John Moore.

Most of the graphics were prepared by the Graphics and Computer Department of P. E. LaMoreaux & Associates, Inc. (PELA).

Sincere appreciation is expressed to PELA for much of the field data concepts and graphics in the preparation of this text.

Many thanks to Gloria Hinton, manuscript manager, who was responsible for organizing and processing the manuscript.

1

1 Introduction

1.1 IntroductIon

It is not possible to read a daily newspaper or magazine—The Wall Street Journal, USA Today, News-week, or Time—without seeing the word environmental or reading about a tangential catastrophic event. We live with this constant reminder of local, statewide, national, and international issues, actions, or politics regarding our environment. The Earth Summit held in Brazil is an example.

On June 1, 1992, Newsweek blazoned headlines: “No More Hot Air, It’s Time to Talk Sense About the Environment.”1 The article described the meeting of world leaders in Rio the following week. Their mission: “To save the ship from its passengers.” The feature article was titled “The Future Is Here” and emphasized that Antarctica suffers an ozone hole; North America takes the lion’s share of world’s resources; South America is custodian of the world’s largest rain forest; Aus-tralia is overcultivated; Africa faces population density doubling; and Asia has stressed resources.

Another smaller and less pretentious example: Newsweek, July 27, 1992, with a full-page color ad illustrating a relatively complicated geologic cross section at a nuclear waste disposal facility.2 How many people 10 years ago would have known what a geologic cross section was, let alone understood it! The caption read: “To most people, it’s a complex diagram. To scientists, it’s a clear summary of safe nuclear waste disposal.” The ad implied to a supposedly rather sophisticated read-ing public the Madison Avenue concept of a very controversial scientific, social, and political issue: nuclear power and its associated waste disposal. This concept relates to world energy needs and is a major geoscience issue. Two different objectives are described; both, however, illustrate the great need for capable geoscientists.

World population is expected to grow in the next two decades, with an increase of 1.7 billion. This will bring the Earth’s total inhabitants to about 7 billion. The article describes the environ-mental situation with regard to water, air, land, trees, industry, energy, species risk, and climate change. The bottom line: this increased population must have adequate food, clothing, and shelter, with minimum additional impact on the environment. This population increase, with the corollary resource development, also clearly identifies another substantial need for expertise in geoscience.

Environmental problems are not new. About 2000 years ago, the first written religious docu-ments, the Bible and the Koran, related humans’ relationship to their environment and recognized the importance of water to their existence. Springs and wells are the subject of numerous stories of famine, migration, war, hate, greed, and jealousy. In fact, Dr. O.E. Meinzer, the father of “ground water,” in Water Supply Paper 489 remarked that parts of the Bible read like a Water Supply Paper.3

Since the 1970s, the environmental movement has progressed from an emotional adolescence to maturity. In the beginning there was a great cry of anguish from the general population, similar to the biblical wail, “There was pestilence in the land.” Symptoms included sores on children who had been playing in abandoned industrial fields, cancer in adults, and pollution in our waters. Problems ranged from minor to major, but all were given headlines. Love Canal was the “battle cry” and the beginning of “Not in my back yard!” or the NIMBY syndrome. Concern and hysteria reigned in many localities. The population was scared and was not sure of “the truth” from anyone—politician, government employee, or scientist. Confidence levels in these representatives were low. Everyone—individuals, politicians, industry, and government—agreed that “something” had to be done! Politicians responded, and the Resource Conservation and Recovery Act (RCRA) and the Comprehensive Emergency Response Compensation and Liability Act (CERCLA) resulted. There were companion bills and rules and regulations for each state. Initially, it was thought that money could solve the problem. It was soon learned it could not. Experienced professional geoscientists

2 Environmental Hydrogeology, Second Edition

were needed to implement programs and solve problems. We have learned that there must be a read-ily accessible reserve of professionals, mainly geoscientists, for the governmental infrastructure to guide research, regulation, and remediation. We have also learned these problems are complex and not only of local, county, and state concern but national and oceanwide, and include water pollution, acid rain, and air pollution. Some environmental problems extended beyond country boundaries and between continents. Saddam Hussein showed the world what one individual could do to jeopar-dize the environment that we live in.

In the late 1980s, our environmental growing pains resulted in a great flurry of professional acquisition. Suddenly, hydrogeologists were in great demand. Advertisements for hydrologists appeared in the trade and technical magazines. New jobs were created for geoscientists capable of writing and implementing regulations as well as serving in regulatory roles in local, state, and federal government and, subsequently, in remedial roles in business and industry and the consult-ing fields. Geoscientists were suddenly charged with studies to provide the basis for intelligent remediation. Experienced hydrogeologists were particularly in demand, for it was their knowledge regarding the relationship between groundwater recharge, storage, and movement as influenced by geologic depositional environments and geologic structure that was needed. Geophysicists and geologists could help describe “the bucket” containing the water, and hydrologists and engineers could determine how fast water flowed through this complicated system. Polluting constituents had to be identified, monitored, removed, and safely disposed.

A new set of industries associated with environment and environmental clean-up developed at the same time. See the “Guide to Environmental Stocks,” published monthly, or refer to lists on the New York Stock Exchange, NASDAQ, or over-the-counter stocks and compare 1960 versus 1990 to learn about the large number of new firms becoming involved in environmental activities. There are old names and new ones. Companies retreaded or new ones formed to include names such as DuPont, Westinghouse, Weston, NUS, Chemical Waste Management, Rollins, Waste Management, Inc., as well as a host of other smaller specialized firms.

To evaluate the greater financial impact from the environmental movement, review the appro-priations for environmental investigation and remediation in government. The U.S. Environmental Protection Agency (EPA), U.S. Department of Defense (DOD), and U.S. Department of Interior (DOI) are being appropriated each year to support research and remediation. To this we can add the corollary billions of dollars spent by commercial and industrial firms. This rapid injection of money into governmental and associated remediation has created a whole new set of demands on the geoscience community since the 1980s.

Our concept of the environment in the 2000s is much more comprehensive than in the 1960s. However, even with much progress, there remains much work to accomplish, including at least 20 years of greater emphasis on many complex problems. It will become necessary to quantify cer-tain types of groundwater movement through rocks, geochemical interrelationships between rocks, natural constituents in water as well as pollutants, risk assessment, and one of the biggest problems of all—adequate communication about these factors and their solution with the public.

We have learned by experience that there is much waste of financial resources and time without trained professional geoscientists to carry out the task of clean-up and that one of the biggest prob-lems associated with future environmental programs is directly related to the availability of profes-sional staffing to do the job. As we consider the future, how do we assess this factor? This can be measured in part by the numbers of new courses, seminars, and training programs pertaining to the environment offered at universities, by scientific societies, and by a very substantial number of new environmental institutes inaugurated since 1980. Newly developed academic programs and degrees are now available in environmental geology, environmental engineering, and environmental chem-istry, which in the next few years will provide a reserve of professionals. Another indicator would be the increased number of scientific papers in journals on the subject illustrating a reorientation of thought and emphasis on the environment. A search of the American Geological Institute GEOREF and Google Scholar* database provided the following:

Introduction 3

EnvironmEntal

Key words: pollution, water quality, ecology, land use, reclamation, conservation, nonengineering aspects of geologic hazards, and nonengineering aspects of waste disposal, plus the general term environmental geology.

Period citations

1785–1979 41,000 over 194 years

1980–1987 75,000 over 7 years

1988–1991 60,000 over 3 years

1992–2000 222,000 over 8 years

Concurrently, within the geoscience societies there are a number of new environmental divi-sions, activities, and journals; for example, the Institute for Environmental Education of the Geolog-ical Society of America (GSA) established in 1991, the newly organized Division of Environmental Geoscience of the American Association of Petroleum Geologists (AAPG) established at Calgary in June 1992, and a major new emphasis by the American Geological Institute (AGI) (see Earth System Science, a current series in Geotimes).

In the U.S. government there is greater environmental awareness—the U.S. Army Corps of Engineers (COE), allocation of substantial funding during construction of the Tenn–Tom Waterway (TTW), to employ an “Environmental Advisory Board” with the specific assignment to provide guidance that included changes in construction, to minimize soil erosion, loss of wetlands, attention to wildlife, protection of groundwater supplies, and many other environmental considerations. One such recommendation changed the course of the waterway to protect a famous old geologic locality at Plymouth Bluff, Mississippi. This large project required the efforts of many geoscientists. One aspect of their work included communication with the public, politicians, and government about what should be considered proper planning and construction and the adequate consideration of environmental impacts. This illustrates the need for the geoscientist to communicate, a responsibil-ity that will become more important in the future.

As we look into the future, environmental activities will exert the greatest demand for geosci-entists. Specific identity of four of these activities will illustrate the point. The first two, RCRA and CERCLA, in the 1970s and 1980s provided a whole new body of law with significance to envi-ronmental activities that affected all facets of the private, agricultural, commercial, and industrial sectors, as well as to local, state, and federal governments.

1. RCRA was created in 1976 and applied to future waste management. It included criteria for location, groundwater monitoring, operations, and contingencies. The law was converted to comprehensive regulations and criteria to be implemented in each state by legislative and legal action.

2. CERCLA was created in 1980 and applied to the clean-up of old, abandoned hazardous-waste facilities. It was a massive program of investigation of climate, geology, hydrology, biology, botany, and other environmental risks. SARA (Superfund Amendments and Reau-thorization Act), 1986, National Priority List (NPL) found in 40 CFR, Part 300, Appendix B. The last issue of list was in February 1991 (proposed listing as of March 1992) of 1179 NPL sites, and 84 sites removed from the list from 1980 to the present.

3. Environmental audits: The impact from the environmental laws of the 1970s was even more far reaching as the private sector as well as commercial and industrial activities began to need an environmental audit prior to property transfers. The EPA policy on July 9, 1986, Federal Register, recommends the use of environmental audits.4 Banks and other loaning institutions require audits. Millions of property transfers now require an audit by


a certified environmental scientist. Criteria for audits have been established by the Resolu-tion Trust, Small Business Administration, as well as by individual banks and American Society for Testng and Materials (ASTM). This represents a massive amount of work in the future.

4. LUST: To the uninitiated, LUST does not mean what you think it does. It means Leaking Underground Storage Tanks. In 1984, Congress responded to the problem by adding Sub-title I to RCRA. Subtitle I requires the EPA to develop regulations to protect human health and the environment from leaking USTs. Between three and five million underground stor-age tanks are currently being used in the United States to store motor fuels and chemical products. Nearly 80% of these tanks are constructed of bare steel. Not surprisingly, 60% of all leaks result from corrosion.

EPA UST rules are promulgated by 40 CFR Parts 280 and 281. Final rules on technical require-ments were published in the Federal Register (September 23, 1988).5 The most significant problem is the sheer size of the regulated community. Nationally, over 700,000 UST facilities account for over 3 million UST systems, an average per state of about 14,000 UST facilities and 40,000 UST systems. Estimates indicate that roughly 79% of existing UST systems are unprotected from corro-sion. In addition, because a relatively high proportion of UST facilities (10–30%) already have had a leak, or will soon leak unless measures are taken to upgrade them, the average number of leaking UST systems may range from 1,400 to 4,200 per state in the near future. The LUST problems must be handled by knowledgeable geologists, hydrologists, and engineers.

Information on the magnitude of the problems relating to waste management, acid rain, and water pollution, and nonpoint sources of pollution such as agricultural use of insecticides and pesti-cides, mining activities, oil and gas activities, and construction of all types, and even the acquisition of any property transfers in the future will require an environmental assessment. These issues will require a whole new team of sophisticated scientists over the next 20 years.

In Geotimes, January 1991, there appeared two excellent articles, “Tomorrow’s Geoscientist” by Marilyn Suiter6 and “Geoscience Careers” by Nick Claudy,7 which contain appropriate and accurate information about the demand for geoscientists in the future. Suiter makes the point that women and ethnic minorities will make up much of the human resources potential for the work force in the future. Also the demand in science and engineering for qualified workers will grow (Figure 1.1). Claudy concludes that the geosciences offer unparalleled diversity for career opportunities. He iden-tifies by percentage their major employment categories—oil and gas (50%), mining (9%), federal/state (12%), research institutions (4%), consulting (11%), and academia (14%). Claudy also identifies correctly the need for geoscientists with MS degrees for professional categories and extensive job opportunities, as well as for geotechnicians with BA or BS degrees. These articles, however, do not call attention to the major shift to be expected in demand for scientists in the broad environmental activities area. The state and federal government agencies are limited by appropriation constraints; however, the biggest demand will be in the broad area of environmental work. We predict that at least 50% of the new jobs will fall in this category and the need will be critical.

If the solid earth sciences are to meet the demands of society’s environmental problems, the profession must recruit, train, and place in the professional work force a sufficient number of well-qualified professionals to carry out the task ahead. According to a recent survey, about one half of earth scientists in the United States (about 120,000), including petroleum and mining engineers, are employed by the petroleum industry. The U.S. government employs about 14,000, and aca-demia about 9,000. The remainder are employed on environmental work related to waste manage-ment, hazardous and toxic radioactive waste permitting litigation, underground storage problems, environmental audits, and environmental impact studies. The supply of and demand for earth scientists over the past 50 years has historically been out of phase. In the early 1980s, because of the dramatic decline in petroleum prices, employment in oil and gas activities decreased by about 30%. This was also a depressed period in the mining industry, and there resulted a loss of

Introduction 5

thousands of jobs in the earth scientist categories. We are just recovering from this cycle. It was a traumatic period for the geosciences with over 4,000 laid off and geologists a glut on the mar-ket. Experienced PhDs were searching for any respectable employment. Qualified geoscientists, especially the younger generation, were unable to find jobs. This had a detrimental affect on the recruitment of geoscience majors and the production of professionals. Environmental legislation dealing with waste disposal was enacted in the early 1980s, and employment projections indicate employment in the earth sciences is growing rapidly, with emphasis on groundwater issues, the siting of waste repositories, and the need for environmental clean-ups. The down cycle in the oil industry had its detrimental impact in the decreased number of new scientists entering the field. In the future we must recognize that great opportunities exist in the environmental areas and that there will be critical needs for new vigorous members for the profession. With the recovery of the oil and gas and mining industries to produce resources for a rapidly expanding world population, the demand for earth scientists will become strong. Further, unless these reserves of competent professionals are forthcoming, the nation will face a critical situation. These are reasons for a textbook on Environmental Hydrogeology at this time.

1.2 SuggeStIonS and referenceS

Several recent publications provide important reference material for sound environmental geologic, geoscience, and hydrogeological programs. Each emphasizes the need for good communication between the scientific community and political, industrial, and private citizens.

Black men 5.7%

Black women 6.9%

Hispanicmen 8.3%

Hispanicwomen 6.8%

Asian andother (Men)

2.9%

Total = 42,832,000

Asian andother (Women)

2.6%White men 31.6%

White women 35.2%

fIgure 1.1 People entering the work force between 1988 and 2000 will be mostly women and minorities, according to the U.S. Bureau of Labor Statistics. (From Suiter, M., Tomorrow’s Geoscientist, Geotimes, Janu-ary 1991.)


Solid-Earth Science and Society, National Academy Press, 368 pp., 1993.Citizens’ Guide to Geologic Hazards, American Institute of Professional Geologists, 134

pp., 1993.Societal Value of Geologic Maps, Circular 1111, U.S. Geological Survey, 53 pp., 1993.

A special journal, Environmental Geology, is published twelve times annually by Springer-Verlag and is available by subscription. It provides many good case histories on the subject.

A modified statement is taken from the Citizens’ Guide to Geologic Hazards to illustrate the present:8

Hazardous geological processes most familiar to the public are those that occur as rapid events, i.e., over a period of minutes, hours, or days. Examples include: earthquakes produced by the pro-cess of rapid snapping movements along faults; volcanoes produced by upward-migrating magma; landslides produced by instantaneous failure of rock masses under the stress of gravity; and floods produced by a combination of weather events and land use. These events all produce massive fatali-ties and make overnight headlines. Other geologic processes, such as soil creep (slow downslope movement of soils that often produces disalignment of fence posts or cracked foundations of older buildings), frost heave (upheaval of ground due to seasonal freezing of the upper few feet), and land subsidence act more slowly and over wider regions. These slower processes, however, also take a toll on the economy. Human interaction can be an important factor in triggering or hastening these natural processes (see Table 1.1).

Lack of awareness induces human complacency, which sometimes proves fatal. It is difficult to perceive of natural dangers in any area where we and preceding generations have spent our lives in security and comforting familiarity. This is because most catastrophic geologic hazards do not occur on a timetable that makes them easily perceived by direct experience in a single lifetime. Yet development within a hazardous area inevitably produces consequences for some inhabitants. Hundreds of thousands of unfortunate people who perished in geological catastrophes such as land-slides, floods, or volcanic eruptions undoubtedly felt safe up until their final moments. In June 1991, Clark Air Force Base in the Philippines was evacuated when Mount Pinatubo, a volcano dormant for over 600 years, began to erupt and put property and lives at risk.

Geologic hazards are not trivial or forgiving; in terms of loss of life, geologic hazards can compare with the most severe catastrophes of contemporary society. Where urban density increases and land is extensively developed, the potential severity of loss of life and property from geologic hazards increases.

We are often faced with the decision about whether we can wisely live in areas where geologic forces may actively oppose otherwise pleasant living conditions. There follows some guidelines:

Avoid an area where known hazards exist. Avoidance or abandonment of a large area is usu-ally neither practical nor necessary. The accurate mapping of geologic hazards delineates those very specific areas that should be avoided for particular kinds of development. Other-wise, hazardous sites may make excellent green belt space or parks in areas zoned as flood-plains, thus avoiding placing expensive structures where flooding will cause damage.

Evaluate the potential risk for hazards. Risks can never be entirely eliminated, and the pro-cess of reducing risk requires expenditures of effort and money. Assuming, without study, that a hazard will not be serious is insufficient. Life then proceeds as though the hazard were not present at all. “It can’t happen here” expresses the view that is responsible for some of the greatest losses. Yet it is equally important not to expend major amounts of society’s resources to remedy a hazard for which the risk is actually trivial.

Minimize the effect of the hazards by engineering design and appropriate zoning. Civil engi-neers who have learned to work with geologists as team members can be solid and effec-tive contributors to minimizing effects of geologic hazards. More structures today fail as a result of incorrectly assessing (or ignoring) the geological conditions at the site than fail

Introduction 7

table 1.1economic costs of geologic hazards in the united States

geologic hazard cost in 1990 dollarsa Source(s)Hazards from materialsSwelling soils $6 to 11 billion annually Jones and Holtz, 1973, Civil Engrg. Vol.

43, n. 8, pp. 49–51; Krohn and Slosson, 1980, ASCE Proc. 4th Int. Conf. Swelling Soils, pp. 596–608

Reactive aggregatesb No estimate —

Acid drainage $365 million annually to control; $13 to 54 billion cumulative to repair

USBM, 1985, IC 9027; Senate Report, 1977, 95–128

Asbestos $12 to 75 billion cumulative for remediation of rental and commercial buildings; total well above $100 billion including litigation and enforcement. Costs depend on extent and kind of remediation doses; removal is most expensive option

Croke et al., 1989, The Environmental Professional, Vol. 11, pp. 256–263

Malcolm Ross, USGS, 1993, personal communication

Radon $100 billion ultimately to bring levels to EPA recommended levels of 4 PCi/L. Estimate based on remediating about 1/3 of American homes at $2500 each plus costs for energy and public buildings

Hazards from processesEarthquakes $230 million annually decade prior to 1989;

over $6 billion in 1989USGS, 1978, Prof. Paper 950; Ward and Page, 1990, USGS Pamphlet, “The Loma Prieta Earthquake of October 17, 1989”

Volcanoes $4 billion in 1980; several million annually in aircraft damage

USGS Circular 1065, 1991, and Circular 1073, 1992

Landslides/avalanches $2 billion/50.5 million annually Schuster and Fleming, 1986, Bull. Assoc. Engrg. Geols., Vol. 23, pp. 11–28/Armstrong & Williams, 1986, The Avalanche Book

Subsidencec and permafrostd At least $125 million annually for human-caused subsidence; $5 million annually from natural karst subsidence

Holzer, 1984, GSA Reviews in Engrg. Geology VI; FEMA, 1980, Subsidence Task Force Report

Floods $3 to 4 billion annually USGS Prof. Paper 950

Storm surgee and coastal hazards

$700 million annually in coastal erosion; over $40 billion in hurricanes and storm surge 1989–early 1993

Sorensen and Mitchell, 1975 Univ. CO Institute of Behavioral Sci., NSF-RA-E-70-014; Inst. of Behavioral Sci., personal communication

a Costs from dates reported in “Source(s)” column have been reported in terms of 1990 dollars. This neglects changes in population and land use practice since the original study was done but gives a reasonable comparative approximation between hazards.

b Aggregates are substances such as sand, gravel, or crushed stone that are commonly mixed with cement to make concrete.

c Subsidence is local downward settling of land due to insufficient support in the subsurface.d Permafrost consists of normally frozen ground in polar or alpine regions that may thaw briefly due to warm seasons or

human activities and flow.e Storm surge occurs when meteorological conditions cause a sudden local rise in sea level that results in water piling up

along a coast, particularly when strong shoreward winds coincide with periods of high tide. Extensive flooding then occurs over low-lying riverine flood plains and coastal plains.

Source: From Nuhfer, E. B., Proctor, R. J., and Moser, P. H. (Eds.), American Institute of Professional Geologists, The Citizens’ Guide to Geologic Hazards, Arvada, CO, 134 pp., 1993.


due to errors in engineering design. This fact has led many jurisdictions to mandate that geological site assessments be performed by a qualified geologist. Taking geological condi-tions into account when writing building codes can have a profound benefit. The December 1988 earthquake in northwestern Armenia that killed 25,000 people was smaller in mag-nitude (about 40% smaller) than the October 1988 Loma Prieta earthquake in California. The latter actually occurred in an area of higher population density but produced just 67 fatalities. Good construction and design practice in California was rewarded by preserva-tion of lives and property.

Academic training for civil engineers must include basic courses in geology taught by quali-fied geologists. A more comprehensive geologic education is needed for civil and environ-mental engineers. Engineers should be cognizant of the benefits of a geological assessment and be able to communicate with professional geologists.

California, in 1968, became the first state to require professional geological investigations of construction sites and has reaped proven benefits for that decision. Since then, many states have enacted legislation to insure that qualified geologists perform critical site evaluations of the geology beneath prospective structures such as housing developments and landfills. Most of these laws were enacted after 1980.

Zoning ordinances and building codes that are based on sound information and that are con-scientiously enforced are the most effective legal documents for minimizing destruction from geologic hazards. After a severe flood, citizens have often been relocated back to the same site with funding by a sympathetic government. This is an example of “living with a geologic hazard” in the illogical sense. A less costly alternative might be to zone most floodplains out of residential use and to financially encourage communities or neighbor-hoods that suffer repeated damage to relocate to more suitable ground. When damage or injuries occur from a geologic hazard in a residential area, the “solution” is often a lawsuit brought against a developer. The problem has not truly been remedied; the costs of the mistake have simply been transferred to a more luckless party—the future purchasers of liability and homeowners’ insurance at higher premiums. A solution would be a map that clearly delineates those hazardous areas where residential development is forbidden. A suitable alternative would be a statute requiring site assessment by a qualified geolo-gist before an area can be developed. Sound land use that takes geology into account can prevent unreasonable insurance premiums, litigation, and repeated government disaster assistance payments for the same mistakes.

Develop a network of insurance and contingency plans to cover potential loss or damage from hazards. Planners and homeowners need not be geologists, but it is useful to them to be able to recognize the geological conditions of the area in which they live and to realize when they need the services of a geologist. A major proportion of earthquake damage is not covered by insurance. Despite public awareness about earthquakes in California, the 1987 Whittier quake produced 358 million dollars worth of damage, of which only 30 mil-lion dollars was covered by insurance.

For the property owner—especially, the prospective homeowner—a geological site assessment may answer the following: Is the site in an area where landslides, earthquakes, volcanoes, or floods have occurred during historic times? Has the area had past underground mining or a history of production from wells? Did the land ever have a previous use that might have utilized underground workings or storage tanks that might now be buried? Does the site rest on fill, and is the quality of the fill and the ground beneath it known? Are there swelling soils in the area? Have geologic hazards damaged structures elsewhere in the same rock and soil formations that underlie the site in question? Has the home ever been checked for radon? If the home is on a domestic well, has the water quality been recently checked? Is the property on the floodplain of a stream? Is the property

Introduction 9

adjoining a body of water such as a lake or ocean where there have been severe shoreline erosion problems after infrequent (such as 20-yr or 50-yr) storms?

Insurance agents are not always familiar with local geological hazards. After risks have been assessed, the individual can then consult with insurance professionals (agents, brokers, salespersons) to learn which firms offer coverage that would include pertinent risks. Consulting with the state insur-ance boards and commissions can assist one in finding insurers who provide pertinent coverage.*

Local governments should make plans for zoning and for contingency measures such as evacu-ations with involvement from a professional geologist. The first line of help for local governments lies in their own state geological surveys. Hydrogeologists are employed for service to the public and can provide much of the available information that is known about the site or region in question and can direct the inquirer to other additional resources. Geologic maps and reports from public and private agencies are most useful in the hands of those trained to interpret them. Significant evidence that reveals a potential geologic hazard may be present in the reports and maps. If significant risks of hazards are thought to exist, then consultation with a professional geologist may be warranted.

Geologic hazards annually take more than 100,000 lives and take billions of dollars from the world’s economy. Such hazards can be divided into those that result dominantly from particular earth materials or from particular earth processes. Most of these losses are avoidable, provided that the public at large makes use of state-of-the-art geologic knowledge in planning and development. A public ignorant of geology cannot usually perceive the need for geologists in many environmental, engineering, or even domestic projects. The result is a populace prone to making expensive mis-takes, particularly in the area of public policy.

Education is one of the most effective ways of preparing to deal successfully with geologic hazards. Every state geological survey produces useful publications, distributes maps, and answers inquiries by the public. Unfortunately, lack of good earth science education leaves many citizens unaware of the resources that their geological surveys provide.

The literature of geologic hazards falls primarily under two indexed subfields of geology: envi-ronmental geology and engineering geology. Flood hazards may also be found under the subfield hydrology.

The following list provides suggested sources of references pertaining to environmental hydro-geology and geology:

American Society of Civil Engineers, 1974, Analysis and Design in Geotechnical Engineer-ing, New York, Amer. Soc. Civil Engrs.

American Society of Civil Engineers, 1976, Liquefaction Problems in Geotechnical Engi-neering, New York, Amer. Soc. Civil Engrs.

American Society of Foundation Engineers, 1975—ongoing, Case History Series: ASFE/The Association of Engineering Firms Practicing in the Geosciences, 811 Colesville Road, Suite G 106, Silver Spring, MD, 20910. A series of case studies arranged in terms of background, problems and outcomes, and lessons learned in brief one-page, two-sided formats.

Bennison, A. P. et al. (Eds.), 1972, Tulsa’s Physical Environment, Tulsa Geological Society Digest, 37. Tulsa Geol. Soc., Suite 116, Midco Bldg., Tulsa, OK, 74103.

Bolt, B. A., Horn, W. L., Macdonald, G. A., and Scott, R. F., 1977, Geological Hazards, New York, Springer-Verlag.

Bryant, E. A., 1991, Natural Hazards, New York, Elsevier.Coates, D. R., 1981, Environmental Geology, New York, John Wiley.Coates, D. R., 1985, Geology and Society, New York, Chapman and Hall.Dodd, K., Fuller, H. K., and Clarke, P. F., 1989, Guide to Obtaining USGS Information, U.S.

Geological Survey Circular 900. Our federal geological survey serves more than just other geologists. This free circular tells how to access their vast storehouse of information and how to order many of the USGS publications. Write Books and Open-File Reports Section, USGS, Federal Center, Box 25425, Denver, CO 80225.


El-Sabk, M. I., and Marty, T. C., (Eds.), 1988, Natural and Man-Made Hazards, Dordrecht, Netherlands, Reidel.

Federal Emergency Management Agency (FEMA), 1991, Are You Ready? Your Guide to Disas-ter Preparedness, FEMA, Publications Dept., P.O. Box 70274, Washington, D.C., 20224.

Foster, H. D., 1980, Disaster Mitigation for Planners: The Preservation of Life and Property, New York, Springer-Verlag.

Freedman, J. L. (Ed.), 1977, Lots of Danger—Property Buyers Guide to Land Hazards of Southwestern Pennsylvania, Pittsburgh Geol. Soc., 85 pp. This is a model publication that serves property owners and prospective property owners of southwestern Pennsylvania.

Gerla, P. J. and Jehn-Dellaport, T., 1989, Environmental impact assessment for commercial real estate transfers, Bull. Assoc. Engrg. Geologists, Vol. 26, pp. 531–540.

Griggs, G. B. and Gilchrist, J. A., 1983, Geologic Hazards, Resources, and Environmental Planning (2nd ed.), Belmont, CA, Wadsworth.

Haney, D. C., Mankin, C. J., and Kottlowski, 1990, Geologic mapping: a critical need for the nation, Washington Concentrates, Amer. Mining Congress, June 29, 1990.

Hays, W. W. (Ed.), 1981, Facing geologic and hydrologic hazards, U.S. Geol. Survey Prof. Paper 1240-B.

Henderson, R., Heath, E. G., and Leighton, F. B., 1973, What land use planners need from geologists, in Geology, Seismicity, and Environmental Impact, Assoc. Engrg. Geologists Spec. Pub., Los Angeles, CA, pp. 37–43.

Keller, E. A., 1985, Environmental Geology (5th ed.), Columbus, OH, Charles E. Merrill.Legget, R. F., 1973, Cities and Geology, New York, McGraw-Hill.Legget, R. F., and Hatheway, A. W., 1988, Geology and Engineering (3rd ed.), New York,

McGraw-Hill.Legget, R. F., and Karrow, P. F., 1982, Handbook of Geology in Civil Engineering, New

York, McGraw-Hill.McAlpin, J., 1985, Engineering geology at the local government level: planning, review, and

enforcement, Bull. Assoc. Engrg. Geologists, Vol. 22, pp. 315–327.Mileti, D. S., 1975, Natural Hazard Warning Systems in the U.S., Natural Hazards Research

and Applications Information Center, Univ. Colorado at Boulder.Montgomery, C. W., 1985, Environmental Geology, Natl. Geog., May, pp. 638–654.Palm, R. I., 1990, Natural Hazards: An Integrative Framework for Research and Planning,

Baltimore, M.D., Johns Hopkins University Press.Peck, D. L., 1991, Natural hazards and public perception: earth scientists can make the dif-

ference, Geotimes, 36 (5), 5.Rahn, P. H., 1986, Engineering Geology—An Environmental Approach, New York, Elsevier.Scheidegger, A. E., 1975, Physical Aspects of Natural Catastrophes, New York, Elsevier.Slosson, J. E., 1969, The role of engineering geology in urban planning, in Governor’s Confer-

ence on Environmental Geology, Colorado Geol. Survey Spec. Publ. No. 1, pp. 8–15.Smith, K., 1992, Environmental Hazards, New York, Routledge, Chapman & Hall.Steinbrugge, K. V., 1982, Earthquakes, Volcanoes, and Tsunamis: Anatomy of Hazards, New

York, Skandia America Group.Tank, R. W. (Ed.), 1983, Environmental Geology; Text and Readings (3rd ed.), New York,

Oxford University Press.United States Geological Survey, 1968–present, Earthquakes and Volcanoes, A magazine that

combines news reporting with journal articles. It is published bimonthly and is designed for both generalized and specialized readers. USGS, Denver Federal Center, Bldg. 41, Box 25425, Denver, CO 80225.

Wermund, E. G., 1974, Approaches to Environmental Geology—A Colloquium and Work-shop, Austin, TX, Texas Bureau Econ. Geol.

Introduction 11

Whittow, J., 1979, Disasters: The Anatomy of Environmental Hazards, University of Georgia Press.

Wiggins, J. H., Slosson, J. E., and Krohn, J., 1978, Natural hazards: earthquake, landslide, expansive soil loss models, Natl. Sci. Foundation, NTIS, PB-294686/AS.

referenceS

1. No More Hot Air: It’s Time to Talk Sense About the Environment, Newsweek, June 1, 1992. 2. Full page color illustration showing a complicated geologic cross section at a nuclear waste disposal

facility, Newsweek, July 27, 1992. 3. Meinzer, O. E., The occurrence of ground water in the United States, with a discussion of principles,

Water Supply Paper 489, 321 pp., 1923. 4. Federal Register, EPA policy on use of environmental audits, July 9, 1986. 5. Federal Register, Final rules on technical requirements, 53 (185), September 23, 1988. 6. Suiter, M., Tomorrow’s Geoscientist, Geotimes, January 1991. 7. Claudy, N., Geoscience Careers, Geotimes, January 1991. 8. Nuhfer, E. B., Proctor, R. J., and Moser, P. H. (Eds.), American Institute of Professional Geologists, The

Citizens’ Guide to Geologic Hazards, Arvada, CO, 134 pp., 1993.

13

2 Geological Aspects for Assessment, Clean-up, and Siting of Waste Disposal Sites

2.1 IntroductIon1

Geology and hydrogeology are broad-based multidisciplines developed from many different sci-ences. The development of hydrogeology required multidisciplinary concepts from mathematics, physics, chemistry, hydrology, geology, and the processes of evaporation, transpiration, and con-densation. Meinzer noted that the science of hydrogeology could not be undertaken until the basic concepts of geology were understood.

A knowledge of rock type, stratigraphy, and structure is imperative to understand groundwater, recharge, storage, and discharge characteristics. Knowledge of geology is a prerequisite to under-standing the source, occurrence, availability, and movement of groundwater. The application of quantitative methods for groundwater requires an accurate description of the container (aquifer) or geologic framework.

State and federal regulations have established restrictions for the location of hazardous waste and municipal solid waste landfills. Regulations require owners/operators to demonstrate that the hydrogeology has been completely characterized at proposed landfills and that locations for moni-toring wells have been properly selected. Owners/operators are also required to demonstrate that engineering measures have been incorporated in the design of both hazardous and municipal solid waste landfills, so that the site is not subject to destabilizing events as a result of location in unsuit-able or unstable areas.2

Proposed, new, or existing landfills are subjects of controversy and sources of continuing debate as to whether an area can provide suitable sites for construction of landfills for hazardous or nonhaz-ardous waste. Issues of concern are the potential threats to human health and the environment that could result from (1) collapse or subsidence, with the associated loss of structural integrity of the landfill; (2) release of contaminants through collapse, subsidence, or leakage from the landfill; and (3) contamination of groundwater or surface water, which may result from a release.

Conceptually, the selection of waste management sites involves collection of information neces-sary to answer a few simple questions, including: Will the natural hydrogeologic system provide for isolation of wastes, so that disposal will not cause potential harm to human health or the environ-ment? Is the site potentially susceptible to destabilizing events, such as collapse or subsidence, which will result in sudden and catastrophic release of material from the facility and rapid and irrevocable transmission to important aquifers or bodies of surface water? Are the monitoring wells in proper positions to intercept groundwater flow from the facility? If minor releases (leakages) occur, will con-taminants be readily detected in monitoring wells? If a release is detected, is knowledge of the hydro-geologic setting sufficient to allow rapid and complete remediation of release? Is the hydrogeologic system sufficiently simple to allow interception and remediation of contaminated groundwater?

Answers to the preceding questions depend on the thoroughness of geologic and hydrogeologic studies by which each site was assessed and evaluated prior to construction of a land disposal facility. In the experience of the authors, most significant environmental problems, resulting from releases from land disposal facilities, occur from facilities for which preliminary hydrogeologic studies were


inadequate to answer the aforementioned questions. In many such cases, studies designed to gain an understanding of the hydrogeologic system did not begin until after a release was detected. Compli-ance monitoring and remediation of groundwater are costly processes, all of which can be avoided by assiduous care in selection of proper sites for land disposal.

Specific regulations for siting landfills in all geologic settings have not been promulgated. How-ever, regulations for protection of groundwater and monitoring as well as other regulations3,4 require characterization of the hydrogeologic system and proper location of monitoring wells at landfills. Figure 2.1 is a conceptual hydrogeological model showing the gradient flow, geologic setting, and monitoring wells.

Consideration of candidate sites for land disposal facilities is a process that requires careful screening of many potential sites, rejection of unsuitable sites, avoidance of questionable sites, and demonstration that the selected site is hydrogeologically suitable for disposal of waste.

The screening process typically includes the following: (1) selection of a large number of candi-date sites within the geographic area of interest; (2) ranking of the candidate sites in order of appar-ent suitability for disposal of wastes; (3) rejection of areas or sites that are obviously not suitable for disposal of wastes; and (4) selection of one or more of the sites for further evaluation.

Tasks during screening typically involve review of published and unpublished engineering, geologic, and hydrologic literature, discussions with appropriate state or federal personnel, study of topographic maps, interpretation of sequential aerial photographs, and verification of studies by field reconnaissance. Most of the preliminary screening can be rapidly accomplished in the office at low cost. The stratigraphic intervals and structural anomalies, along with other geologic features, are defined in published geologic literature. General geologic maps are often available, and this knowledge can be extended to site-specific locations through use of aerial photographs, topographic maps, and fieldwork. The locations, depths, water levels, producing horizons, and rates of pumping for wells in the vicinity of the site are often available in the files of state or federal agencies.

Saturated zonetwo phase system

Unsaturated zonethree phase system

Air/Gas

SolidLeachate

LeachateSolid

Thin perched saturatedzone too thin to

effectively monitor

Leachate moves down slopeof clay lense to water table

Regionalground-waterflow direction

DNAPL unsaturated zonefour phase system

Air

DNAPL

Solid

Solid

Water

Water

DNAPL

DNAPL saturated zonethree phase system

DNAPL wastedisposal site

Unlined wastedisposal site

LNAPL storagetank leak

Backgroundwells

fIgure 2.1 Conceptual flow models for NAPL sites. (From Sara, M.N., Standard Handbook for Solid and Hazardous Waste Facility Assessments, Lewis Publishers, Boca Raton, FL, 1994, pp. 10–68.)

Geological Aspects for Assessment, Clean-up, and Siting of Waste Disposal Sites 15

A thorough review of published and unpublished literature must be done during the preliminary investigation. Older literature often contains more complete descriptions of the geology than more recent publications and should not be overlooked.

Table 2.1 illustrates concepts presented by many authors, including Hughes,6 LeGrand,7 LeGrand and Stringfield,8,9 LeGrand and LaMoreaux,10 LaMoreaux et al.,11,12 Newton,13,14 Parizek et al.,15 Sweeting,16 and White.17–19 Sara provides a comprehensive review of the site assessment process.5 His guide, Standard Handbook for Solid and Hazardous Waste Facility Assessments, is a compre-hensive manual to assist in the planning, implementation, and interpretation of investigations for the facility’s suitability for disposal of solid or hazardous waste. The manual also provides appropriate locations for groundwater monitoring and effectiveness of the landfill’s leachate collection and con-tamination system. This guide was the result of a substantial team effort that included professionals from government, industry, and academia. It is a comprehensive compilation of information on solid and hazardous waste management that all professionals involved with environmental hydrogeology should be aware of and use.

Aerial photographs have been sequentially available in many parts of the United States since the late 1930s. Sets of aerial photographs, as stereo pairs, can be used to determine if karst features have changed, if collapse features have locally occurred, or if depressions have been enlarged with time and can serve as a means of cataloging changes in land use over a period of about 50 years. In addition, the aerial photographs can be used for preliminary mapping of stratigraphic contacts, structural features, and lineaments.

2.2 geologIcal aSPectS

2.2.1 rock typEs

Rocks are classified according to their origin as igneous, metamorphic, and sedimentary, and according to their lithology, which describes the rock composition and texture.

Unfractured metamorphic and plutonic igneous rocks have maximum porosities of 2% with minute intercrystalline voids that are not inter connected. The primary permeabilities of these rocks are low because of the lack of void interconnection.20

Fractured plutonic igneous and crystalline metamorphic rocks have secondary (fracture) per-meability developed along the fracture openings that are generally more common at a depth of less than 100 ft with some occurring at a maximum depth of 200 ft. The permeability of fracture zones in the crystalline rocks decreases with depth, where the fractures tend to close because of vertical and horizontal stresses imposed by overburden loads.

Volcanic rocks are formed from the solidification of magma, which when discharged at land surface flows out as lava. The rocks that form on cooling are generally very permeable. Columnar joints and bubblelike pore spaces are formed owing to rapid cooling and escape of gases. The blocky rock masses and associated gravel deposits that are interbedded in recent basalts create a very high permeability.

Sedimentary rocks such as sandstones, carbonate rocks, and coal beds form aquifers to store and transmit groundwater. Sandstones constitute 25% of the sedimentary rocks of the world, and the permeable zones in these types of rocks form regional aquifers that contain large quantities of potable water. Friable sandstones generally have a high porosity (30–50%), which diminishes greatly with depth because of compaction and the intergranular cementing materials, mainly quartz, calcite, iron, and clay minerals. The latter are precipitated from hydrothermal solution circulating into the sandstone aquifers at depths where temperature and pressure are high.20

Carbonate-type rocks such as limestone and dolomite consist mostly of calcite and dolomite minerals with minor inclusions of clay. Dolomitic rocks, or dolostones, are secondary in origin, formed by geochemical alternation of calcite, which creates an increase in porosity and permeabil-ity as the crystal lattice feature of dolomite occupies about 13% less space than that of calcite. Geo-


Stratigraphy

(Regional and Local)

Stratigraphic column

Thickness of each carbonate unit

Thickness of noncarbonate interbeds

Type of bedding

Thin

Medium

Thick

Purity of each carbonate unit

Limestone or dolomite

Pure

Sandy

Silty

Clayey

Silicous

Interbeds

Overburden

(Soils and Subsoils)

Distribution

Origin

Transported

Glacial

Alluvial

Colluvial

Residual

Other

Characteristics and variability

Thickness

Physical properties

Hydrologic properties

Hydrology

Surface water

Discharge

Variability

Seasonal

Gaining

Losing

Groundwater

Diffuse flow

Conduit flow

Fissure flow

Recharge

Storage

Discharge

Fluctuation of water levels

Relationships of surface–water and groundwater flow

Geologic Structure

(Regional and Local)

Nearly horizontal bedding

Tilted beds

Homoclines

Monoclines

Folded beds

Anticlines

Synclines

Monoclines

Domes

Basins

Other

Fractures

Lineaments

Locations

Relationships with

Geomorphic features

Karst features

Stratigraphy

Structural features

Joint System

Joint Sets

Orientation

Spacing

Continuity

Open

Closed

Filled

Faults

Orientation

Frequency

Continuity

Type

Normal

Reverse

Thrust

Other

table 2.1Important characteristics of different geologic terrain


logically young carbonate rocks commonly have porosities that range from 20% for coarse, blocky limestone to more than 50% for poorly indurated chalk.21 At depth, the soft minerals that constitute the matrix of the carbonate rock are normally compressed and recrystallized into a more dense, less porous rock. Fractures or openings along bedding planes of carbonate beds create appreciable secondary permeability, whereas secondary openings due to stress conditions may be enlarged as a result of dissolution of calcite or dolomite by circulating groundwater.

Karst terrains have specific hydrologic characteristics and are composed of limestone, dolo-mites, gypsum, halite, or other soluble rocks. Karst landscapes that exhibit irregularities of the land surface are caused by surface and subsurface removal of rock by dissolution of limestone, calcite, or dolomite by circulating groundwater and erosion. Figure 2.2 shows the complex physical and geo-chemical processes involved in forming karst and the phenomenon of karst and karstification.22

Age of faults

Holocene

Pre-Holocene

Activities of Humans

Construction

Excavation

Blasting

Vibration

Loading

Fill

Buildings

Changes in drainage

Dams and lakes

Withdrawal of groundwater

Wells

Dewatering

Irrigation

Geomorphology

(Regional and local)

Relief-slopes

Density of drainage network

Characteristics of streams

Drainage pattern(s)

Dendritic

Trellis

Rectangular

Other

Perennial

Intermittent

Terraces

Springs and/or seeps

Lakes and ponds

Floodplains and wetlands

Karst features—active, historic

Karst plains

Poljes

Dry valleys, blind valleys, sinking creeks

Depressions and general subsidence

Subsidence cones, in overburden

Sinkholes

Roof-collapse

Uvalas

Caverns, caves, and cavities

Rise pits

Swallow holes

Estavelles

Karren

Other

Paleo-Karst

Climate

Precipitation (rain and snow)

Seasonal

Annual

Long-term

Temperature

Daily

Seasonal

Annual

Long-term

Evapotranspiration

Vegetation

Source: From Hughes, T.H., Memon, B.A., and LaMoreaux, P.E., Landfills in karst terrains, Bulletin of the Association of Engineering Geologists, Vol. 31, No. 2, 1954, p. 203.


Table 2.1 includes a list of generic categories of rock types and other relevant information that should be considered during evaluation of potential sites for land disposal. It includes broader cat-egories, an understanding of which is necessary during the preliminary screening of sites, and it provides a basis for formulating a conceptual hydrogeologic model.

Coal beds are lithologic units within sequences of sedimentary rocks formed in floodplain or deltaic environments.

Shale beds constitute the thickest semipervious units in most sedimentary basins. Shale beds originate as mud laid down in the gentle-water areas of deltas, on ocean bottoms, or in the back-swamp environments of floodplains. Clay is transformed to shale by digenetic processes related to compaction and tectonic activity. In outcrop areas, shale is commonly brittle and fractured with appreciable amounts of permeability, whereas, at depth, it is less fractured and permeability is generally very low. Unfractured shale, clay, anhydride, gypsum, and salt usually provide good seals against upward or downward flow of fluids.

Alluvial deposits are unconsolidated materials deposited by streams in river channels or on floodplains. They consist of particles of clay, silt, and sand and gravel. Alluvial deposits include alluvial cones, which consist of loose material washed down the mountain slopes by ephemeral streams and deposited at the mouth of gorges, alluvial fans that are formed by a tributary of high

Corrosion (Chemical)(1) Solution Precipitation(2) Ion exchange(3) Sorption (Adsorption Desorption)

Natural and/orby human activities

Pressure

Limestone, Dolomites, Sulphates,Chlorides, and other rocks

By Erosion(Corrosion and Corrasion)

Karst

StalactitesStalagmites

Sinkholes

CaveResidue

Travertines

Karst

Phenomena

TemperatureWater

GAS

by Processes?

fIgure 2.2 A flow diagram showing karstification and karst. (Modified from Assaad, F.A. and Jordan, P., Karst Terranes and Environmental Aspects, Vol. 23, 228–237, 1994.)


declivity in the valley of a stream, or those deposits built by rivers issuing from mountains upon lowlands. Numerous other alluvial features are associated with alluvial processes.

2.2.2 candidatE sitEs

On the basis of knowledge gained during the preliminary assessment of geologic framework, a rank-ordered list of candidate sites can be prepared. One or more of the candidate sites, which have the highest rankings, are typically selected for site-specific hydrogeologic and geotechnical studies. The additional studies may be performed on each of two or three selected sites or for one site with the highest ranking. The hydrogeologic studies should be designed to seek and discover fatal flaws, if they are present. In the absence of fatal flaws, detailed studies provide a means of completely characterizing the hydrogeology of the site, demonstrating the suitability of the site for a potential land disposal facility, and defining locations for monitoring the site.

Some conditions that may, but do not always, lead to rejection of a candidate site include the following: areas that contain well-developed karst features and recent karst activity; recharge areas for aquifers (i.e., particulate stratigraphic intervals); specific geologic structures (e.g., some folds, faults, and lineaments); areas that contain thin or geotechnically unsuitable soil; areas of wellhead protection for public water supplies; and areas of significant pumping (e.g., quarries, mines, and industrial wells).

The U.S. Environmental Protection Agency3 (EPA) has established definite landfill siting require-ments and some restrictions on location of municipal solid waste landfills, which locally may also constitute cause of rejection of proposed sites. The restrictions include proximity to airports, flood-plains, wetlands, Holocene faults, seismic impact zones, and unstable areas. When hydrogeologic conditions are unfavorable, or when costs of overcoming deficiencies of the site are too high, the site should be rejected from further consideration as a potential site for disposal of wastes to land.2

The EPA and state governments have established the following landfill siting requirements for waste disposal facilities and practices.

location restrictions

1. Fault areas: Landfills should not be located within 200 ft of the active fault zones that have undergone displacement in Holocene time.

2. Airport safety: Landfills should be located at least 10,000 ft from airports handling turbojets and 5,000 ft from airports handling piston-type aircraft to avoid bird hazard to aircraft.

EPA requires that landfills should not be located in a 100-year floodplain. Landfills shall not restrict the flow of a 100-year flood, reduce the temporary water storage capacity of the floodplain, or result in the washout of solid waste and pose a hazard to human health and to the environment. However, new MSWLFs or existing landfills, if located in a 100-year floodplain, should be designated and operated to mitigate and minimize adverse impacts on the flow of 100-year flood and water storage capacity of the floodplain.

3. Wetlands: New landfill units cannot be placed in wetlands unless the owner or operator gives specific assurances to the state that the facility will not result in “significant degrada-tion” of the wetlands.

Dredged or fill material should not be deposited or discharged into the aquatic ecosystem unless it can be demonstrated that such actions will not have an unacceptable adverse impact either individu-ally or in combination with known or probable impacts of other activities affecting the ecosystems of concern. The degradation or destruction of special aquatic sites, such as filling operations in wetlands, is considered to be among the most severe environmental impacts.


operating criteria

EPA has established operating requirements for landfills, such as application of daily cover and post-closure care, random inspections of incoming waste loads, and record keeping of inspection results.

1. Explosive gases control: The concentration of methane generated by landfills should not exceed 7.5% of the lower explosive limit (LEL) in facility structures and at the property boundary.

2. Air criteria: Air criteria prohibit the open burning of waste but allow infrequent burning of agricultural wastes, silviculture wastes, land-cleaning debris, diseased trees, and debris from emergency clean-up operations. Any of these infrequent burnings should be con-ducted in areas dedicated for that purpose and at such a distance from the landfill unit so as to preclude the accidental burning of other wastes.

2.2.3 stratigraphy

Stratigraphy is the study of the thickness, age, lithology, and chronological sequence of rocks. The lithostratigraphic column, a graphic representation of the rock units, is the basic display of data used in stratigraphic studies. Figure 2.3 is a generalized columnar section for northeast Illinois, showing a variety of rock types typical of the east-central states.

Cross sections show the sequence of stratigraphic data constructed from the material penetrated in several deep wells. The stratigraphic correlation aids in understanding the depositional environment of subsurface material. Understanding of depositional environment of subsurface material beneath the potential site for land disposal is important as the flow of groundwater and its recharge, storage, and discharge are controlled by various lithologies of stratigraphic section of the geologic column.

2.2.4 structural gEology23

Structural geology is related to folding and faulting and the geographic distribution of these fea-tures, which greatly affect the fluid flows, the physical properties of rocks, and the localization of mineral deposits and earthquakes.

Faults are fractures in the rock sequence along which displacement of two blocks took place. Such fractures may range from inches to miles in length, and displacements are of comparable mag-nitudes. Faults may act either as barriers to or as channels for fluid movement. Generally, geologists should consider any significant fault to be a potential flow path for purposes of preliminary evalu-ation of its importance. Accordingly, the fault would be an environmental hazard according to this assumption. If further investigation indicates this assumption to be true, it would be necessary to abandon potential disposal sites. Fractures that occur without any movement lead to cracks or joints, which are important to the development of porosity and permeability in some aquifers, but can be undesirable when there could be potential for draining fluids rapidly away from the disposal site. Joints can be examined from core samples obtained through drilling, by well logging, and by testing methods and evaluated on the basis of experience with other deep wells drilled in the same region.

Structural geologic data are commonly shown on maps and cross sections. Structure contour maps show the elevation of a particular stratigraphic horizon relative to a selected datum. These maps can be used to estimate the depth to a mapped rock unit, the direction and magnitude of dip, and location of faults and folds that may influence decisions concerning the location of the proposed disposal site and associated network of monitoring wells.

2.2.5 physical propErtiEs

Physical properties1 of fluid and porous media that describe the hydraulic aspects of saturated ground-water flow include density, ρ, viscosity, µ, and compressibility, β, for the fluid, whereas for the media


SYST

EM

SERI

ES

GROUP

MAQUOKETA MA.

RIC

H.

ED. CIN

CIN

NAT

IAN

GALENA

OT

TAW

A

TRE

NTO

NIA

N

ORD

OV

ICIA

N

CH

AM

PLA

INIA

N

CA

NA

DIA

N

BLA

CK

RIV

ERA

N

KN

OX

TRE

MPE

ALE

AU

AN

FR

AN

CO

NIA

N

DRE

SBA

CH

IAN

POT

S-

DA

M

CRO

IXA

N

CA

MBR

IAN

PLATTEVILLE

ANCELL

PRAIRIE DU CHIEN

FORMATION GRAPHIC COLUMN

THICK- NESS

(FEET) LITHOLOGY

Shale, red, hemotitic, oolitie

Shale, dolomitic, greenish gray

Shale, dolomitic, brownish gray

Dolomite, bull, medium grained

Dolomite, bull, red speckled Dolomite and limestone, bull Dolomite and limestone, gray mottling Dolomite and limestone, orange speckled Dolomite, brown, fine grained Sandstone and dolomite

Sandstone, fine; rubble of boce

Dolomite, sandy Sandstone, dolomitic

Dolomite, slightly sandy; oolitic chart

Sandstone, dolomitic

Dolomite, sandy; oolitic chart

Dolomite, slightly sandy at top end base, light gray to light brown; goodic quartz

Sandstone, dolomites and shale;gloucontic

Sandstone, medium grained, dolomitic in part

Sandstone, fine grained

Sandstone, shale, dolomite,sandstone, glauconite

Sandstone, fine to coarse grained1200-2900

370-575

10-100

80-130

50-200

90-220

50-150

0-15

190-250

0-35 0-67

100-600

0-80 20-50 20-50 20-40 0-50 0-15

170-210

90-100

5-50 0-100

0-15

Dolomits and limestone, coarse grained; shale, green

STA

GE

MEG

A-

GRO

UP

Eou Chore

Galeswile

Ironian

Fronconia

Polosl

Eminence

Gunter

Oneola

New Richmond Shakopee

St. Peter

Gienwood Pecotonica Mifflin Grand Detour Nachusa Guttenberg

Wise Lake- Dunleith

Scales

F1 Atkinson

Brainard Neda

MI Simon

fIgure 2.3 Generalized columnar section of Cambrian and Ordovician strata in northeastern Illinois. (From U.S. EPA 600/2-77-240, An introduction to the technology of subsurface wastewater injection, in Envi-ronmental Protection Technology Series, USEPA, Cincinnati, OH, 1977, pp. 21–47, 64–91, 329–344.)


(aquifers), they are porosity, Ø, permeability, k, and compressibility, α. These parameters are essen-tial to quantitatively evaluate the hydrogeologic conditions of the potential sites for land disposal.

Porosity

Porosity is basically grain formation dependent on grain size and degree of roundness.

Quantitatively, Porosity ( ) = Vv

Vtθ

(2.1)

where Ø = porosity (expressed as a percentage) Vv = volume of voids Vt = total volume of soil sample

Total porosity is a measure of all void space, whereas effective porosity is defined as the hydraulic properties of a rock unit, which considers the volume of interconnected voids available only to fluids flowing through the rock.23

A distinction must be made between primary and secondary porosity.24 Primary porosity is intergranular or intercrystalline. Intergranular porosity in a sandstone depends on the size distribu-tion, shape, angularity, packing arrangements, mineral composition, and cementation.23 Second-ary porosity results from fractures, solution channels, cavities or space (particularly in karst), and recrystallization processes and dolomitization.

Permeability

Permeability is expressed as the coefficient of permeability (k in cm2). It is a formation property that allows the flow of liquids within the rock under an applied potential gradient, and it is a rock parameter that influences the flow velocity. In general, the permeability is usually much lower in vertical directions than in horizontal.24

Permeability depends on the grain size. The smaller the grains, the larger will be the surface area exposed to the flowing fluid. As the frictional resistance of the surface area lowers the flow rate, the smaller the grain size, the lower the permeability. Shales, which are formed from extremely small grains, have very small permeability and are classified as confining intervals. The fracture permeability, due to fracturing, as well as the secondary permeability caused by the creation of karst in limestone and dolomite, may be significant for fracture flow.24 Intrinsic permeability is expressed as follows:

k = Q

A g dhdL

(cm )2µ

ρ i (2.2)

where k = coefficient of permeability Q = flow rate through porous medium A = cross-sectional area through which flow occurs µ = fluid viscosity ρ = fluid density L = length of porous medium through which flow occurs h = fluid head loss along L g = acceleration due to gravity


A simple form of Darcy’s law used in shallow groundwater is

K = Q

AdhdL . (2.3)

where K is the hydraulic conductivity (cm/s).

Transmissivity (or transmissibility), T, can be interpreted as the rate at which fluid of a certain vis-cosity and density is transmitted through a unit width of an aquifer at a unit hydraulic gradient. It is measured as the product of the thickness of the aquifer (b) and its hydraulic conductivity (K). Its unit is generally gallons per day per foot2 (gpd/ft2) or m/day.

compressibility

The compressibility of an aquifer, α, encompasses not only the formation or the skeleton of the aquifer but also the contained fluids. Compressibility and the coefficient of storage are combined as a function of the aquifer thickness.

Quantitatively, compressibility of an elastic medium is defined as

α

δδ

=v

V p (2.4)

where α = compressibility of aquifer (psi–1) δv = differential volume V δp = differential pressure P

The compressibility of the aquifer ranges from 5 × 10–6 to 10 × 10–6 psi–1 as compared with that of water alone, which is about 3 × 10–6 psi–1.

Storativity

The storage coefficient for a confined aquifer, which is a parameter related to compressibility, indi-cates the capacity of the formation to accept water and is defined as the volume of water that an aquifer releases from or takes into storage per unit surface area of the aquifer per unit change in the hydraulic head normal to the surface and is quantitatively expressed as follows:23

S = bØ

φγ βα

+

(2.5)

where S = storage coefficient Ø = porosity γ = pg = specific weight of water per unit area b = aquifer thickness β = compressibility of water α = compressibility of aquifer formation

Values of S are dimensionless and normally range between 5 and 10–5 to 5 and 10–3 for confined aquifers and 10–1 and 10–3 for unconfined aquifers.


Viscosity

The viscosity of the formation water in a porous rock influences the velocity of flow. As temperature increases, viscosity decreases and the velocity of flow increases.

Hydrodynamic dispersion

Hydrodynamic dispersion is a mixing process in which a liquid diffuses with another liquid on the condition that both are miscible. The coefficient of dispersion is inversely proportional to tempera-ture, porosity, and grain form, whereas an increase in grain size, grain roundness, and the degree of irregularity promotes dispersion.20–24

2.2.6 hydrogEologic considErations

The subsurface rocks are subdivided into groups, formations, and members in descending order. These terms imply mappable rock subdivisions based on mineralogy, fossil contents, or other geo-logical characteristics. However, such subdivisions may or may not be applicable to subsurface flow systems, as the geologic boundaries are not related to the physical properties (porosity and perme-ability). The following hydrogeologic terms are used to describe rock subdivisions according to their capacity to keep and transmit water:

An aquifer is a saturated permeable geological unit (i.e., a formation or part of it or a group of formations) that can transmit significant quantities of water under ordinary hydraulic gradients to wells and springs.

An aquiclude, on the other hand, stores water but does not transmit significant amounts. An aquitard, which has been used to describe the less permeable beds in a stratigraphic sequence, is in between an aquifer and an aquiclude and transmits enough water to be regionally significant but not enough to supply a well.23

A confined aquifer is confined between two aquicludes and occurs at depth. It may be under artesian conditions when the water level in a well rises above the ground surface. The water level elevations in wells that are tapping a confined aquifer are plotted and contoured to construct a potentiometric surface map that shows the hydraulic head in the aquifer and provides an indication of the direction of groundwater flow.

An unconfined aquifer, or water-table aquifer, is one in which the water table forms the upper boundary and occurs near the ground surface. A perched aquifer is a saturated lens of a formation that is bounded by a perched water table at the top and lenses of relatively low permeable material at the bottom. It is a special case of an unconfined aquifer.

An aquifuge will not transmit water. The basement rock, which is igneous or metamorphic, lies beneath the sedimentary mantle and is generally nonporous and impermeable.3 The groundwater flow theory and well hydraulics are discussed in Chapter 3.

2.3 data acquISItIon of rock and formatIon fluId teStIngS

2.3.1 data obtainEd prior to drilling potEntial disposal sitEs

Geologic data should be obtained for evaluation of the site selected for drilling a well. Surface geophysical methods, including seismic, gravity, magnetic, and electrical surveys, may provide con-siderable subsurface geological information, but because of high costs, surface geophysical surveys are not widely used for water-well site studies. Literature and logs on the basic geological formations are available through national and state geological surveys, state oil and gas agencies, state water resources agencies, and some universities. The available geologic information should be collected


and evaluated prior to field activities, including drilling wells. This exercise would help reduce the cost and efforts to study the proposed site.

2.3.2 WEll logs23

A drilling time log is a record of the rate of penetration of the rocks by the bit. Drilling time may be recorded directly on a log strip by a machine or plotted manually from the record sheets of the driller. It is usually expressed as penetration (feet) per unit time (minutes or hours). The rate of pen-etration changes with cementing material and lithologic rock type. A drilling time log may serve to indicate when the bit needs to be changed and when drill stem tests should be made, and is most useful if no electric or radioactivity test is available.

Lithologic logs are prepared by the well-site geologist after examining the cuttings recovered from drilling fluids in a normal rotary-drilling process and the core samples recovered from the res-ervoir rocks and the confining beds. All cuttings and cores should be retained for future reference.

Logging tools are used for recording the geophysical properties of the formations pen-etrated and their fluids. Some of the properties measured are electrical resistivity, conductivity, ability to transmit and reflect sonic energy, natural radioactivity, hydrogen ion content, tem-perature, and density. These geophysical properties are then interpreted in terms of lithology, porosity, and fluid content.

Table 2.2 lists current geological well-logging methods, their properties, and their practical applications.23–25

Miscellaneous logs include the following: (1) caliper logs, which measure borehole diameter needed for quantitative analyses of many geophysical logs and used for lithologic interpretation; (2) dip-meter logs, which measure the angle of dip of beds penetrated by the well and aid in the interpretation of geologic structure; (3) deviation logs, which measure the degree of deviation of the well from the vertical; deviation of boreholes from the vertical is undesirable and periodic sur-veys are made during drilling to check borehole orientation; and (4) production (or injection) logs, which run through tubing or casing after the well is completed and are mainly used to determine the physical condition of subsurface facilities such as the interval of production (or injection) zones, the quantity of fluid produced from (or injected into) a particular zone, and the results of well-bore stimulation treatment.23

table 2.2geophysical well-logging methods and practical applications

method Property application

1. Spontaneous potential (SP) log

Electrochemical and electrokinetic potentials

Formation water resistivity; (Rw) shaliness (sand or shale)

2. Nonfocused electric log Resistivity Water and gas/oil saturation; porosity of water zones; Rw in zones of known porosity; formation resistivity (Rt); resistivity of invaded zone (Ri)

3. Focused and microfocused microresistivity logs

Resistivity Resistivity of the flushed zone (Rxo); porosity; bed thickness

4. Sonic log Travel time of sound Rock permeability

5. Caliper log Diameter of borehole Without casing

6. Gamma ray Natural radioactivity Lithology (shales and sands)

7. Gamma-gamma Bulk density Porosity, lithology

8. Neutron-gamma Hydrogen content Porosity with the aid of hydrogen content

Source: From U.S. EPA 600/2-77-240, An introduction to the technology of subsurface wastewater injection, in Environ-mental Protection Technology Series, USEPA, Cincinnati, OH, 1977, pp. 21–47, 64–91, 329–344.


2.4 Summary SIte SelectIon2

Selection of a site requires thorough knowledge and understanding of the regional and local stratig-raphy; how that specific stratigraphic section has been affected by structural events; and how stra-tigraphy, structure, climate, and time have interacted to provide the present hydrogeologic system. Through such knowledge, one can develop a conceptual hydrogeologic model of the site. The model can include complex computer models of the hydrology or relatively simple hydrologic models, such as flow nets or contours of the potentiometric surface. Hydrogeologic models can be inaccurate representations of the system, if they are derived without inclusion of an intimate knowledge of the stratigraphy and geologic structure.

In practice, the conceptual hydrogeologic model will be modified and improved as studies prog-ress at the selected site. The final model should provide an accurate integration of the geologic, hydrologic, and geotechnical characteristics of the site that has been tested by installation of bor-ings, piezometers, and monitoring wells; measurement of water levels; and determination of the direction and rate of groundwater flow. The ultimate goal of the siting process is to aid in meeting the need for disposal at locations that will ensure protection of the environment.

referenceS

1. Meinzer, O. E., Outline of groundwater hydrology with definitions, U.S. Geol. Survey Water-Supply Paper 494, 1923, 71 pp.

2. Hughes, T. H., Memon, B. A., and LaMoreaux, P. E., Landfills in karst terrains, Bulletin of the Associa-tion of Engineering Geologists, Vol. 31, No. 2, 1954, p. 203.

3. U.S. Environmental Protection Agency, Solid Waste Disposal Facility Criteria, Final Rule, Federal Register, Vols. 53 and 56, 40 CFR Parts 257 and 258: U.S. Government Printing Office, Washington, DC, 1991a.

4. U.S. Environmental Protection Agency, Code of Federal Regulations, Vol. 40, Parts 260 and 299, U.S. Government Printing Office, Washington, DC, 1075, 1991b.

5. Sara, M. N., Standard Handbook for Solid and Hazardous Waste Facility Assessments, Lewis Publish-ers, Boca Raton, FL, 1994, pp. 10–68.

6. Hughes, T. H., Structure, in Guide to the Hydrology of Carbonate Rocks, LaMoreaux, P. E., Wilson, B. M., and Memon, B. A. (Eds.), UNESCO, Paris, 1984, p. 36.

7. LeGrand, H. E., Karst hydrology related to environmental sensitivity, in Hydrologic Problems in Karst Regions, Dilamarter, R. R. and Csallany, S. C. (Eds.), Western Kentucky University, Bowling Green, 1977, p. 10.

8. LeGrand, H. E. and Stringfield, V. T., Development and distribution of permeability in carbonate aqui-fers, Water Resources Research, 7, 1284, 1971.

9. LeGrand, H. E. and Stringfield, V. T., Karst hydrology—A review, Journal of Hydrology, 20, p. 97, 1973.

10. LeGrand, H. E. and LaMoreaux, P. E., Hydrogeology and hydrology of karst, in Hydrology of Karstic Terrains, International Association of Hydrogeologists, International Union of Geology Sciences, Series B, No. 3, 1975, chap. 1.

11. LaMoreaux, P. E., Wilson, B. M., and Memon, B. A. (Eds.), Guide to the Hydrology of Carbonate Rocks, UNESCO, Paris, 1984, 343 pp.

12. LaMoreaux, P. E., Hughes, T. H., Memon, B. A., and Lineback, N., Hydrogeologic assessment—Figeh Spring, Damascus, Syria, Environmental Geology and Water Sciences, Vol. 13, No. 2, 1989, p. 77.

13. Newton, J. G., Induced sinkholes—A continuing problem along Alabama highways, in Proceedings, International Associates of Hydrological Science, Anaheim Symposium, No. 21, Anaheim, CA, 1976, p. 453.

14. Newton, J. G., Development of Sinkholes Resulting from Man’s Activities in the Eastern United States, U.S. Geological Survey, Circular 968, U.S. Geological Survey, Denver, CO, 1987, 54 pp.

15. Parizek, R. R., White, W. B., and Langmuir, D., Hydrogeology and Geochemistry of Folded and Faulted Carbonate Rocks of the Central Appalachian Type and Related Land Use Problems, Geological Soci-ety of America Guidebook, 1971 Annual Meeting, Geological Society of America, Boulder, CO, 1971, 181 pp.


16. Sweeting, M. M., Karst Landforms, Columbia University Press, New York, 1973, 355 pp. 17. White, W. B., Conceptual models for carbonate aquifers, Ground Water, 7, 15, 1969. 18. White, W. B., Conceptual models for carbonate aquifers: Revisited, In Hydrologic Problems in Karst

Regions, Dilamarter, R. R. and Csallany, S. C. (Eds.), Western Kentucky University, Bowling Green, 1988, p. 176.

19. White, W. B., Geomorphology and Hydrology of Karst Terrains, Oxford University Press, New York, 464 pp., 1988.

20. Freeze, R. A. and Cherry, J. A., Groundwater, Prentice Hall, Inc., Englewood Cliffs, New Jersey, 1979, pp. 45–50, 58–61, 152–163.

21. Davis, S. N., Porosity and Permeability of Natural Materials, Flow Through Porous Media, DeWiest, R.J.M. (Ed.), Academic Press, New York, 1969, pp. 54–89.

22. Assaad, F. A. and Jordan, P., Karst Terranes and Environmental Aspects, Vol. 23, 228–237, 1994. 23. U.S. Environmental Protection Agency 600/2–77–240, An introduction to the technology of subsurface

wastewater injection, in Environmental Protection Technology Series, USEPA, Cincinnati, OH, 1977, pp. 21–47, 64–91, 329–344.

24. Aust, H. and Kreysing, K., Hydrological Principles for the Deep Well Disposal of Liquid Wastes and Wastewaters, A Contribution to the International Hydrological Program of UNESCO, IHP-II, Project A.3.6, IHP/OHP-Berichte, Sonderheft 1, Koblenz, 1985, pp. 46–54.

25. Everett, L. G., Acquisition of Subsurface Data in Groundwater Monitoring—Guidelines and Methodol-ogy for Developing and Implementing a Groundwater Quality Monitoring Program, Schenectady, New York, pp. 325–326 (Section 3), 1980.

29

3 Hydrogeology

3.1 IntroductIon

Hydrology is that part of water science that deals with water resources and their development. It comprises several specific areas that include hydrogeology, scientific hydrology, applied hydrology, operating hydrology, stochastic hydrology, and catchment hydrology and its modeling.

The general science of hydrology is considered an integral part of the hydrologic cycle. Numer-ous sciences relevant to the hydrologic cycle include astronomy, solar physics, cloud physics, meteorology, climatology, environmental sciences, geography, engineering, agriculture, biology, economics, surface-water hydrology, limnology, oceanography, soil physics, groundwater hydrol-ogy, and geology.

3.1.1 historical background

The earlier history of hydrogeology is well documented by O.E. Meinzer1 in his presidential address to the Geological Society of Washington on December 9, 1931. Subsequently, it was presented in greater detail in Two Hundred Years of Hydrogeology (Rosenshein et al., 1986).1 A more recent summary by Moore and Hanshaw appeared in Episodes (December 1987).2

Historical references to hydrogeology require a search of the early literature, for example, writ-ings by W.H. Norton (1897),3 A.C. Veatch (1906),4 O.E. Meinzer (1923, 1934, and 1942),5–7 C.F. Tol-man (1937),8 Biswas (1970),9 Burdon (1982),10 Narasinhan (1982),11 Van der Leeden (1983),12 J. Day (1986),13 J. Rosenshein (1986),14 G. White (1986),15 Meyer, Davis, and LaMoreaux (1988),16 and de Vries (1989).17 The oldest archaeologically dated well, constructed in 4000 BC using dressed field stone, was recently discovered in the submerged shallow coastal zone in Israel. “Kurker stone” had been used for casings. These early people apparently had a practical knowledge of the occurrence of fresh groundwater over saltwater in a coastal zone. Some of these wells date back to biblical times before Abraham.

The origin and early use of some terms in hydrogeology are interesting, even more so as there is still a controversy over terminology. The term hydrogeology was used in 1802 by J.B. Lamarck to mean “the study of aqueous erosion and sedimentation.” The first published use of the term with its present meaning was by the Frenchman A. Daubree in 1887 in his Textbook on Hydrogeology, vol. 3.18 It was first used in the United States by M.L. Fuller in 1906 in Water Supply Paper 160.19

The term aquifer was first used in the United States in 1896 by William Harmon Norton, a state geologist in Iowa, in a report on underground water. In this report he revived a European term first used by the Frenchman Arago in 1835.

Artesian well takes its name from the Province of Artois in France. Within the walls of an old Carthusian convent at Lillers, there is a well that was drilled in 1126 AD which still flows today. From France came the term artesium, the Latin equivalent of Artois; however, there were artesian-flowing wells long before in Egypt, China, and Persia. Probably the oldest of the big artesian wells were drilled in the Kharga Oases in the Western Desert of the Sahara using dome-palm casings to depths of over 900 ft. Ruins of some of these wells remain today as they have been covered and preserved by mounds of wind-blown sand spread over with moisture and vegetation. These wells were used to irrigate large tracts of land and were the oases described by Herodotus as “islands in the desert.”

Early work on groundwater research in the United States was done at state geological surveys and universities. For example, the New York State Geological Survey had been continually operative


since 1836—over 40 years before the founding of the U.S. Geological Survey. By the 1830s and 1840s, there were a number of state geological surveys that had published geological maps, begin-ning with Pennsylvania in 1817. Some examples are the Iowa Geological Survey, vol. VI; the reports by McCallie (1898), Artesian Well System of Georgia, and Smith (1907), Underground Waters of Alabama. Also, concurrently at universities, an interest developed in groundwater and some out-standing contributions resulted, for example, the works of Thomas Crower Chamberlain (1885), The Relevant and Qualifying Conditions of Artesian Wells, Franklin H. King (1889) of the University of Wisconsin, Principles of Movement of Groundwater, and Douglas Johnson (1905), Law of Under-ground Waters (Water Supply Paper 122).

Dr. O.E. Meinzer joined the U.S. Geological Survey (USGS) in 1906. He became Chief of the Groundwater Branch in 1913. It was at this time that “groundwater hydrology,” or hydrogeology, became recognized as a discipline in the United States. However, it is best to hear about this phe-nomenon from one of Europe’s well-known early hydrogeologists from Ireland, Dr. David Burdon, who, upon receiving the Aberconway Medal in 1982, presented an interesting history of hydrogeol-ogy, published in the British Geologist. Burdon recognized three episodes in the genesis of hydro-geology: the first episode (1846–1858) identified with publications by Darcy, Dupuit, Hagen, and Poiseuille; the second (1901–1906), with publications by Forchheimer, Theim, and Veatch; and the third (1930–1940), the Meinzer era, with publications by Meinzer, Jacob, Piper, Theis, and Wenzel.

It was Meinzer20 who first subdivided the science of hydrology, which according to his defini-tion dealt specifically with water completing the hydrologic cycle from the time it is precipitated upon the land until it is discharged into the sea or returned to the atmosphere, into surface hydrology and subterranean hydrology or geohydrology. Groundwater hydrology more or less follows the same concepts of geohydrology or hydrogeology.

Although this chapter discusses hydrological aspects generally, in brief, groundwater hydrology is covered in more detail. The following chapters are mainly concerned with industrial, municipal, and agricultural wastes as sources of pollution to groundwater resource systems and how these valu-able sources can be reclaimed and managed to reduce, as much as possible, the hazardous effects of wastes on water resource systems.

3.2 HydrologIc cycle

It is important to know how the hydrologic cycle is completed and how its various components are correlated in nature. The hydrologic cycle and its components are illustrated in Figure 3.1, which shows that water, in its three phases (gas, liquid, and solid), starting from the ocean, land, or living matter, moves into the atmosphere by evaporation and transpiration. It passes through complicated atmospheric phenomena, generalized as the precipitation process, back to the earth’s surface, upon and within which it moves in a variety of ways and is incorporated into nearly all compounds and organisms. This cycle, as demonstrated in Figure 3.1, shows the main hydrologic field of study.

One can conclude that the oceans are immense reservoirs from which all water originates and to which all water returns. This simple statement may be further explained as follows: water evapo-rates from the ocean, forms clouds that move inland, condenses, and falls to the earth as precipita-tion. From the earth, through rivers and underground, water runs off into the ocean. So far, there is no evidence that water decreases in quantity at a global level. No water is depleted, but none is generated either, according to the law of conservation of matter. For human usage, however, the physical state of water is important, and so is its quality. Whereas its available quantity is limited, the need for water is ever increasing, and consumption is bound to exceed the ceiling of supply. Therefore, water conservation and pollution abatement have become very important in today’s eco-nomic life. For this reason, environmental hydrologists or hydrogeologists should be familiar with the science of hydrology.

Hydrogeology 31

3.3 maIn comPonentS of Hydrology

The study of the hydrologic cycle in its wider sense is usually divided into three separate disciplines: meteorology, surface hydrology, and geohydrology21 or groundwater hydrology.

Meteorology or climatology comes first in the study of the hydrologic cycle. It has several aspects: composition and general circulation of the atmosphere; energy balance of the atmosphere; precipitation, rainfall and snow, and snowmelt; and evaporation and evapotranspiration. The ran-dom nature of climate results in a great amount of variability, at different levels of time and space, of precipitation, which is the first link in the chain of the hydrologic cycle.

Surface hydrology is concerned with flow in the hydrographic network. It may be studied with several aims in mind:

1. Evaluation of available resources, either in their natural state or after development (e.g., build-ing dams), and the calculation of the reservoir volume necessary to ensure a given flow.

2. Forecasting of flood risks and works required to control them, such as detention dams and channel improvement works. Very often these works have to fulfill several simultaneous and often contradictory needs; a reservoir to control floods must be emptied as fast as possible, and this is directly antagonistic to the objective of a reservoir meant to increase flow at low water; hence, the difficult management problems attached to multipurpose installations.

In hydrology, two methods are commonly used:

1. The stochastic method: Because of the variability of rainfall, streamflow is studied as a random variable.

2. The deterministic method: The process of runoff and infiltration is studied from a physical deterministic viewpoint as flow equations based on an impulse assumed to be known.

The basin may be represented as a black box in which components are lumped together and may be analyzed according to the theory of system analysis. On the other hand, one may study the watershed from a physical point of view by considering all the physiographic parameters of the medium.

Deep groundwater

Shallow groundwater

LakeRiver

Wind

Solarradiation

Evaporation

Evaporation

Cloud

CloudStormmechanism

Transpiration

Seepage

Rock

Precipitation

Ocean

SeawaterInterface

zone

Fresh water

Runoff

W.T.

fIgure 3.1 The hydrologic cycle.


Because surface-water hydrology is interrelated with environmental hydrogeology, this chapter includes the study of environmental impacts of hydrologic processing on watersheds, as the mecha-nism of erosion and deposition of sediments, and its effects on the aquifer upper boundaries.

3.4 WaterSHed Hydrology

A watershed is the drainage basin of a watercourse, which is the entire area contributing to the runoff and sustaining part or all of the flow of the mainstream and its tributaries. Strictly speak-ing, however, a watershed is the divide separating one drainage basin from another. Catchment is another term synonymous with watershed or drainage basin. However, any of these terms may be used to denote the area where the surface runoff travels over the ground surface and through chan-nels to reach the basin outlet.

Runoff is that part of precipitation, as well as any other flow contributions, which appears in surface streams of either perennial or intermittent form. This is the flow collected from a drainage basin or watershed, and it appears at an outlet of the basin. According to the source from which the flow is derived, runoff may consist of surface runoff, interflow, and groundwater discharge. The surface runoff is that part of runoff that flows over the ground surface and through streams to reach the catchment outlet. The part of surface runoff that flows over the land surface toward stream chan-nels is called overland flow. After the flow enters a stream, it joins with other components of flow to form total runoff, which is called streamflow.

The interflow, also known as subsurface flow, subsurface storm flow, or storm seepage, is that part of precipitation which infiltrates the soil surface and moves laterally through the upper soil horizons toward the streams as ephemeral, shallow, perched groundwater above the main ground-water level. A part of the subsurface flow may enter the stream promptly, whereas the remaining part may take a long time before joining the streamflow.

The groundwater runoff, or groundwater flow, is that part of the runoff due to deep percolation of the infiltrated water that has passed into the ground, become groundwater, and been discharged into the stream.

For practical purposes of runoff analysis, total runoff in stream channels is generally classified as direct runoff and base flow. The direct runoff, direct surface runoff, or storm runoff is that part of runoff that enters the stream promptly after the rainfall or snow melting. It is equal to the sum of the surface runoff and the prompt subsurface runoff, plus channel precipitation. In the arid and semi-arid regions, direct runoff contains only overland flow in small watersheds, because the subsurface flow percolates deep inside the ground and does not reach the stream channel where the channel is small. This is also true of rocky areas where seepage loss is very small.

The base flow, or base runoff, is defined as the sustained runoff. It is composed of groundwater runoff and delayed subsurface runoff. However, the base flow is completely excluded in arid zones22 for the same reason stated earlier with respect to the subsurface flow.

During a runoff-producing storm, the total precipitation may be considered to consist of precipi-tation excess and abstractions. The precipitation excess is that part of the total precipitation that con-tributes directly to the surface runoff. When the precipitation is rainfall, the precipitation excess is known as rainfall excess. The abstractions are that part of precipitation which does not contribute to surface runoff, such as interception, evaporation, transpiration, depression storage, and infiltration.

The part of precipitation that contributes entirely to the direct runoff may be called the effective precipitation, or effective rainfall if only rainfall is involved. Figure 3.2 demonstrates a flowchart identifying the various items from the total precipitation to the total runoff.

From the hydrologic point of view, the runoff from a drainage basin may be considered as a component in the hydrologic cycle, which is influenced by two major groups of factors—climatic factors and physiographic factors.

Climatic factors include mainly the effects of various forms and types of precipitation, intercep-tion, evaporation, and transpiration, all of which exhibit seasonal variations in accordance with the

Hydrogeology 33

climatic environment. Physiographic factors may be classified into two kinds: basin characteristics and channel characteristics. Basin characteristics include such factors as size, shape, and slope of the catchment area, hydraulic conductivity and recharge of groundwater, presence of lakes and swamps, and land use. Channel characteristics are related mostly to hydraulic properties of the channel, which govern the movement of streamflows and determine channel storage capacity. It should be noted, however, that the foregoing classification of factors is by no means exact because many fac-tors, to a certain extent, are interdependent. The following two sections list the major factors.

3.4.1 climatic Factors

These can be identified as follows:

Precipitation is classified as rain, snow, frost, etc., and according to type, intensity, dura-•tion, time distribution, areal distribution, frequency of occurrence, direction of storm movement, antecedent precipitation, and soil moisture.Interception includes vegetation species, composition, age, density, and season of the year.•Evaporation varies with temperature, wind, humidity, atmospheric pressure, soluble solids, •and nature and shape of evaporative surface.Transpiration is affected by temperature, solar radiation, wind, humidity, soil moisture, •and kinds of vegetation.

3.4.2 physiographic Factors

These are basin characteristics and channel characteristics. Basin characteristics include geometric factors and physical factors, whereas channel characteristics vary with the carrying capacity and storage capacity. Those factors may be itemized as follows:

1. Basin characteristics:Geometric factors: size, shape, slope, orientation, elevation, and stream density.•Physical factors: land use and cover, surface infiltration condition, soil type, geological •conditions, such as the hydraulic conductivity and capacity of groundwater formations,

Groundwater aquiferTotal runoffTotal loss

Loss byevaporation

Other abstract Precipitation excess Infiltration

Total precipitation

Depressionstorage

Surface runoff

Prompt subsurfacerunoff

Delayed subsurfacerunoff

Deep percolationSubsurface runoff

Direct runoff Base flow

fIgure 3.2 Various items from total precipitation to total runoff.


and topographical conditions, such as the presence of lakes and swamps, and artificial drainage.

2. Channel characteristics:Carrying capacity: size and shape of cross section, slope, roughness, length, tributaries.•Storage capacity: backwater effect.•

3.4.3 mEchanism oF Erosional dEposition

The main environmental effect of runoff on any catchment is the erosion and sedimentation processing. This also includes the change of the surface-water quality in some catchments, which indirectly affects the groundwater quality where there is an interchange between surface water and groundwater.

The prevention or improvement of soil erosion requires understanding of factors that affect the rate and magnitude of erosion. Soil erosion is responsible for irreversible degradation of vast tracts of arable land and sedimentation of reservoirs and harbors, which diminishes their capacity to store water and supply hydroelectric power. It also causes irreparable damage to transport systems. Even with the support of nearly a century of research data, researchers are unable to combat the erosion menace effectively. In fact, the soil erosion hazard is continuously increasing.

Although far from being fully understood, considerable progress is being attempted. Upland erosion begins with raindrop impact and its interaction with overland flow. Erosion occurs if the combined power of the rainfall energy and overland flow exceed the resistance of soil to detach-ment. Each of these processes is a complex phenomenon.

Transport and delivery of sediment from catchments are important processes for both downstream and within-catchment considerations. Sediment transported from a catchment presents an environ-mental problem and a potential hazard downstream in terms of sediment concentration and volumes.

In addition, concentrations and loadings of chemicals adsorbed by the sediment particles may also cause problems due to their toxicity and hazardous impacts. At some locations, however, agri-culture is enhanced by nutrient-laden sediments deposited in floodplains. In either case, unexpected sediment yield changes have the potential for large economic losses in the affected areas.

Knowledge of the distribution of sediment sources and sinks within a catchment is useful for recommending erosion and sedimentation controls. Sediment sources include agricultural lands, construction sites, disturbed lands, and roadway embankments. Sediment sinks include strips of vegetation, reservoirs, the bases of concave slopes, and areas of diverging flow. Such sinks occur when the load of a stream exceeds its transport capacity.

For a catchment system in the state of quasi-equilibrium, sediment yield at the outlet is directly related to sediment production on upland areas. Control of upland erosion does not always reduce the sediment load immediately, because decreasing the upland sediment load increases the erosivity of the channel flow. If sediment yield continues at a higher level until the system readjusts to upland controls, a process that may take several years, an accurate estimate of catchment sediment yield that is undergoing cultural change must consider the entire catchment drainage continuum in addi-tion to its erosion–sedimentation history.

3.5 Hydrogeology

Groundwater and surface water commonly form a linked system. Flow can be in either direction, and the rate of flow varies geographically and seasonally. The interchange is not significant for some aquifers.23 However, it has been estimated that about 30% of total flow in surface streams is supplied from groundwater, and seepage from streams is known to be a principal source of flow to some aquifers. Water withdrawn from wells along a bank of an alluvial stream can effect an appre-ciable reduction in surface flow, and the diversion of surface flow can reduce groundwater recharge. Supply for groundwater and surface water cannot be evaluated independently unless it is estab-lished that the interchange is minimal. There are two distinct types of circumstances concerning

Hydrogeology 35

the development and management of groundwater supplies. Groundwater is considered a renewable source with optimal use restricted to the average rate of recharge; mining of groundwater, however, is sometimes carried out with fixed-term objectives. Average annual recharge can, in extreme cases, be relatively insignificant, as in the major regional Nubian aquifers in northeast Africa.

The environmental impacts of groundwater withdrawal without a good management plan are land subsidence, seawater intrusion in coastal aquifers during overdraft situations, or waterlogging of an area during an excess recharge situation.

3.5.1 distribution oF subsurFacE WatEr

Water occurs underground in two zones (aeration and saturation) separated by the water table. The occurrence and movements in these two zones are markedly different. The water table exists only in water-bearing formations, which contain openings of sufficient size to permit appreciable movement of water. It is generally considered to be the lower surface of the zone of suspended water at which the pressure is atmospheric. The saturated zone extends down as far as there are interconnected openings. The lower boundary may be an impervious layer. The upper saturated zone is called an unconfined aquifer. Sometimes, the saturated zone is bounded on top by another impervious layer and is known as the confined aquifer. If one of the impervious layers leaks inward or outward, this aquifer is named a leaky aquifer (Figure 3.3).

Subsoil water is limited to the soil belt and reached by roots. Pellicular water adheres to rock surface throughout zone of aeration and is not moved by gravity but may be abstracted by evapora-tion and transpiration. Gravity or vadose water moves downward by force of gravity throughout saturated zone. Perched water occurs locally above an impervious barrier. Capillary water occurs only in the capillary fringe above the water table. Free water is known as the water that moves by gravity in the unconfined aquifer (see Figures 3.3a–e).

The vadose zone can be more difficult to characterize owing to complex localized flow condi-tions that are found in the saturated zone below the water table. It is nearer the land surface, reme-dial actions may not require complete characterization of the vadose zone flow system for certain site conditions and contaminants if the majority of the affected soils will be treated in place or removed.

3.5.2 groundWatEr FloW thEoriEs

Groundwater flow is treated in a general way as the flow of fluid in porous media. The classical hydrodynamics of viscous flow is applied. It has been seen that in addition to the equation of con-tinuity and the equation of state, the equation of motion should be considered in any hydro-dynamic problem. However, for the fluid flow through porous media, the equation of motion is

SoilHorizons

fIgure 3.3a Soil horizons.

Pellicularwater

Fractures

(ii)Gravity water(i)

fIgure 3.3b Pellicular water (i) in granular material and (ii) rock fractures.


Pore

wat

erpr

essu

re g

reat

erth

an at

mos

pher

ePore

wat

erpr

essu

re eq

ual

to at

mos

pher

ic

Saturated zone

Capillary fringeWater table

Unsaturated zone

Ground surface

Hyg

rosc

opic

w

ater

pre

ssur

ele

ss th

anat

mos

pher

e

fIgure 3.3d Distribution of fluid pressures in the ground with respect to water.

Unconfinedaquifer

Water table

Potentiometric surface

Sand

Sand

Clay

Clay

Confinedaquifer

fIgure 3.3e Unconfined aquifer and its water table; confined aquifer and its potentiometric surface.

fIgure 3.3c Perched water table ABC, inverted water table ADC, and true water table EF. (From Freeze, R.A. and Cherry, J.A., Groundwater, Prentice-Hall, Englewood Cliffs, NJ, 1979. With permission.)

Hydrogeology 37

replaced by Darcy’s law to obtain the groundwater flow equation in a simple manner. Darcy’s law for flow through medium is given as follows:

V=-K

dhdl (3.1)

where V is the groundwater flow and K is the hydraulic conductivity. However, the actual fluid motion can be subdivided on the basis of the components of flow parallel to the three principal axes:

u Khx

v Khy

w Khz

x

y

z

=−

=−

=−

δ

δδ

δ

δ

δ (3.2)

where h (the hydraulic head) = hp + z, where hp is the pressure head and z the potential head Kx, Ky, Kz = hydraulic conductivities with components in the x, y, and z directions, respectively u, v, w = velocity of flow in x, y and z directions, respectively

∂h∂xi

= hydraulic gradient (xi = x, y, and z directions)

The negative sign (−ve) means that water is flowing in the direction opposite to increasing hydrau-lic potentials.

Combining Equation 3.2 with both the continuity equation and the equation of state, the ground-water flow equation, in general form, can be given as follows:

∂

∂xK

∂h

∂x+∂

∂yK

∂h

∂y+∂

x y

∂∂z

K∂h

∂z= S

∂h

∂tz s

(3.3)

or

K

∂ h∂x

+K∂ h∂y

+K∂ h∂z

= S∂h∂tx y z s

2

2

2 2

2 (3.3)

where Ss represents a specific storage, defined as the volume of water a unit volume of saturated aquifer releases from storage for a unit decline in hydraulic head, per unit depth. Three-dimensional flow in aquifers of essential uniform thickness B:

T∂ h∂x

+T∂ h∂y

+T∂ h∂z

= S∂h∂tx

2

2 y

2

2 z

2

2

(3.4)

where Tx, Ty, Tz are the transmissivities in x, y, and z directions, and T = BK (m2/s), where B is the aquifer thickness. S = Ss × B, which is the storage coefficient, defined as the volume of water released from or taken

into storage per unit cross-sectional area of the vertical column of aquifer per unit change in head. For the unconfined aquifer, S is taken as the specific yield (Sy).

For well problems with radial flow, Equation 3.4 in polar coordinates becomes


∂ h∂r

+1r∂h∂r

=ST∂h∂t

2

2 (3.5)

The coefficients S and T may be regarded as empirical values to be determined principally by the pumping-test technique.

Two cases are considered for groundwater flow toward wells drilled in aquifers: the steady-state and the unsteady-state flow.

3.5.3 stEady statE groundWatEr FloW in aquiFErs

Dupuit (1863)24 was the first person who combined Darcy’s law with the continuity equation to derive an equation for well discharge. Dupuit assumed complete axial symmetry, steady flow through an infinitely extending aquifer.24a He deduced as follows for a confined aquifer (Figure 3.4a):

Q=2πKm(h -h )

r /r2 w

2 wln (3.6)

and for an unconfined aquifer (Figure 3.4b):

Q=πK(h -h )

r /r22

w2

2 wln (3.7)

where Q is the discharge, K is the hydraulic conductivity, and h2 and hw are the head levels above the impervious bed at radial distances r2 and rw, respectively.

3.5.4 unstEady statE groundWatEr FloW in conFinEd aquiFErs

If there is no replenishment, the area of influence of a well increases and the potentiometric head declines in such a manner that the water released from storage equals the well discharge. The dif-ferential equation governing such unsteady flow to an axially symmetrical well is shown in Equa-tion 3.5.

For the artesian case, this water is released by consolidation and compression effects associated with release of pressure. For the water table case, the water originates as a result of recession of the water table, and S equals the specific yield. Theis25 applied a solution of Equation 3.5 to the case of constant discharge from an infinitely extending artesian aquifer. For this case, the drawdown D and ho, …, h, at any radial distance r and time of pumping t is given by (Figure 3.5)

D=

Q4πT

eudu

-u

u

∞

∫ (3.8)

where

u =r S4Tt

putting w(u) =eudu

2

-u

u

∞

∫ (3.9)

Therefore,

Hydrogeology 39

D=

Q4πT

W(u) (3.10)

The graphical method could be used to solve Equation 3.10. This is called the matching procedure. A curve such as that shown in Figure 3.6 can be used. This figure shows W(u) plotted as a function of u.

From Equations 3.8 and 3.9, for any specific well test, u is proportional to r2/t and D to W(u). By plotting D as the ordinate and r2/t as the abscissa on transparent paper to the same scale as the Theis type curve (Figure 3.6), a field data curve similar to the type curve will be obtained. A portion of the field data curve will be superimposed and matched to the type curve keeping coordinates paral-lel when matching. Choose a specific match point on the matching portion of the curve and record

Observationwells

Pumping well

Position ofpiezometric

surface beforepumping begins

Position of piezometricsurface duringequilibrium pumping H

mhwh1h2 Kaquifer

hr

r

r1

r2

dhdr

R

QL

aquiclude

c

a

Observationwells

Pumping well

Position of water tablebefore pumping begins

Position of water tableduring equilibriumpumping H

K

hwh1h2

aquifer

hR

r

r

r1

r2

dhdr

QL

aquiclude

c

b

fIgure 3.4 Drawdown curve around well in (a) confined aquifer and (b) unconfined aquifer. (From Wal-ton, W.C., Groundwater Resource Evaluation, McGraw-Hill, New York, 1970.)


values of u, W(u), D, and r2/t for this point. Substitute these values for D and W(u) into Equation 3.8 and solve for T. Using this value of T and substituting values for u and r2/t into Equation 3.9, solve for S.

Theis’ nonequilibrium equation is of fairly general applicability to artesian wells tapping con-fined aquifers and also to wells tapping the water table aquifer, if the drawdown is a small percent-age of the saturated thickness of the aquifer. In a number of special cases, however, it can be greatly simplified with negligible loss in accuracy. Probably the most important of the modified forms of Theis’ nonequilibrium equation are the basic modified equation, the rate of drawdown equation, and the recovery equation.

0.011.00.10.010.001

0.0

1.0

B &

C S

cale

s

10.0 0.001 0.01 0.3 = AC = 0.03

1.0 10.01.0

0.1A

Sca

le

A Scale

W (u

)

B Scale

B

C

C Scale

A

fIgure 3.6 Theis curve.

Observationwells

Pumping well

Position of piezometricsurface before pumping begins

Position of piezometricsurface during pumping

D

S

Krrw

aquifer

aquiclude

aquiclude

m

Q

fIgure 3.5 Transient flow toward a well in a confined aquifer. (From Walton, W.C., Groundwater Resource Evaluation, McGraw-Hill, New York, 1970.)

Hydrogeology 41

the basic modified equation

The basic modified equation26,27 is the least modified. It is the basic modification in that through it all other equations are nearly derived. For its derivation and limitations, consider Figure 3.7, which is the same as Figure 3.6 except that the ordinate scale is linear. The solution of Equation 3.8 is an infinite series that can be expressed in the form

W(u) = (−1.00)(ln u) + a = (−2.30)(log u) + a (3.11)

where a is nearly constant for small values of u, approaching (−0.5772) as u approaches zero. The type curve is therefore asymptotic to the straight line.

W(u) = (−2.30[log u]) −0.57722 (3.12)

For small values of u the type curve nearly parallels the asymptote with slope = −2.30. Thus, the type-curve equation, written in two points, becomes

(y2 − y1) = m(x2 − x1)

which becomes

W(u )–W(u ) = –2.3(logu logu ) = 2.3 log

uu2 1 2 1

1–22

Replacing u and W(u) with their equivalents according to Equations 3.8 and 3.9, assuming S1 = S2 and simplifying,

D D =2.3Q4πT

logr /tr /t

2 112

1

22

2

– (3.13)

Equation 3.11 is the basic modified equation. The choice between the two numbering systems is a matter of convenience.

At a constant radial distance, r, the rate of drawdown is given by the following equation:

∆D=D D =

2.3Q4πT

logtt2 12

1

– ⋅ (3.14)

54

log u

321–1–2–3–4–5

Asymtote equationw(u) = (–2.3 log u) –.577

0

1

2

3

4

5

6 W(u)

fIgure 3.7 Semilog-type curve.


The values of drawdown (D1 and D2) are taken per log cycle of time, t

log

tt

= 12

1

Thus, Equation 3.14 becomes

∆D=

2.3Q4πT (3.15)

where ∆D = drawdown per log cycle of time (such as t1 = 2, t2 = 20) when D is plotted versus t on semilog paper forming a straight line relation, and T can be calculated from Equation 3.15.

By projecting this line to meet the horizontal axis where D = 0 and t = t0, S can be calculated using Equation 3.12 as follows:

S ≈

2.25Ttr

o2

(3.16)

adjustment of the modified equations for free-aquifer conditions8

In the case of free-water table conditions, the saturated thickness B is reduced by the drawdown D, so that T = KB is replaced by

K(B − Dave) = Kyave = K(y1 + y2)/2

where y1 and y2 are the two drawdown curve ordinates corresponding to the two times and/or radial distances and Dave = average drawdown. Then, because D2 − D1 = y1 − y2, the quantity (D2 − D1) T is replaced by:

(y y )Kx(y +y )/2 = ((y y )/2)K1 2 1 2 12

22– –

For example, the basic modified Equation 3.12 then becomes

y y =2.3Q2πK

logr /tr /t

12

22 1

21

22

2

– (3.17)

Care must be used in applying a free-aquifer equation that has been derived from artesian well equations by replacing KB by K(yave) as illustrated previously. The artesian equations are derived on the basis that all streamlines are horizontal, so that the hydraulic gradient in the Darcy equation is equal to dy/dL = dy/dx, and equipotential surfaces representing area in the Darcy equation are vertical cylinders. In the case of free-aquifer flow, the upper streamlines slope downward toward the well, so that their head losses vary with the sloping flow distance, and hydraulic gradient is not equal to dy/dx. Furthermore, in the case of a free-aquifer well, the equipotential surface represent-ing areas in the Darcy equation are not vertical cylinders but semicylindrical surfaces that curve inward at the top as indicated by the curvature of the equipotential lines. No adjustment is made for these factors, so that the resulting free-aquifer equations are applicable only to computations where y represents the height of the hydraulic grade line (P/w) + Z along nearly horizontal stream-lines representative of the main flow. This includes all bottom streamlines, a large part of the flow at intermediate elevations where the flow is nearly horizontal, and water table streamlines at such radial distances such that the water table is nearly horizontal. Such equations are applicable also in terms of the water level in the pumping well, because the point (re, dw) (re = effective radius or radius of the borehole; dw = drawdown in the well) is a point on the hydraulic grade line for all streamlines except those that enter the well along the seepage surface.

Hydrogeology 43

If the pumping drawdown in the pumping wells is large, the free-aquifer equations may be inap-plicable in terms of the free-surface drawdown curve for radial distances as great as 1.5B or 2B. In such cases, the values of water table drawdown closer to the well can be computed on the basis of empirical relationships.

As Q is proportional to T:

Q artesianQ free

=KB

K(B–D )=

BB–Dave ave

where B is the saturated thickness.Thus, failure to adjust such modified equations as Equations 3.14 and 3.8 for free-aquifer condi-

tions by replacing KB with K(B − Dave) gives

Q computed =

BB–D

Q trueave

Computed values of K and (D2 − D1) are in error to a similar degree.

the recovery equation

Suppose, as shown in Figure 3.8, the pumping rate Q is suddenly changed to a new rate Q′. The additional drawdown Z caused by the additional discharge (Q′ − Q) may be expressed in terms of the Theis nonequilibrium equation as follows:

Z =

(Q –Q)4πT

W(u )′

′ (3.18)

where

′′′

′

′

u =r S4Tt

S = new storage coefficient

t =

2

time with reference to the start of Q .′ (3.19)

tt´

Z´

D´ D

Discharge = Q

Q = Q´

Q = 0

Q´Q

Z

fIgure 3.8 Hydrographs illustrating drawdowns during change in rate and recovery conditions.


However, in the recovery condition the drawdown is called the residual drawdown and Q′ = 0; there-fore, Equation 3.18 becomes

′ ′Z =

Q4πT

W(u ) (3.20)

and the residual drawdown D′ becomes

′ ′D =D-Z =

Q4πT

(W(u)-W(u )) (3.21)

For small values of u and u′, the modified condition can be used as

′ ′D =

Q4πT

(-2.3 log u+a)-(-2.3 log u +a) (3.22)

or

′ ′′

D =

2.34πT

log t / t - logSS

Q (3.23)

If S/S′ is taken as a constant, D′ and t/t′ can be plotted on semilog paper giving a straight line rela-tion. The line need not pass through the origin where t/t′ = 1, as it will do so only when S′ = S. Often S′<<S owing to imperfect elastic recovery and, in the case of free aquifers, owing to air pockets and capillary log or land subsidence.

drawdown equation for Water-table conditions

Boulton29–32 was able to derive an equation to solve for the hydrologic factors for a water table aquifer with a fully penetrating well. It was assumed in his solution that the gravity drainage to the water table due to lowering of the water level (dz) between the times T and T + dT since pumping commenced consisted of two parts:

1. A volume (S dz) of water instantaneously released from storage per unit horizontal area, at any time from the start of pumping

2. A delayed yield from storage, at t(t ≥ T) from the start of pumping

dz ∝ S′ e − α(t − T) + and n = 1 + S′/S,

where α is an empirical constant and S′ is the total volume of delayed yield from a storage per unit drawdown per unit horizontal area

With this assumption, Boulton derived the following equations:

D=

Q4πT

W(U , r/ )a,b β (3.24)

U =

Sr4T

=1Øa

2

t (3.25)

Hydrogeology 45

u =

S r4Tt

=(r/ )4 t

=1Øb

2 2′′

βα (3.26)

The values of W(uabr/β) are plotted against values of 1/Ua and 1/ub on logarithmic paper to construct type curves as shown in Figure 3.9. The type curves that lie to the left of the values r/β are termed type A curves. The type curves that are shown to the right of the values are termed type B curves.

The method of using type curves is briefly described as follows: The observed values of draw-down, D, at a given distance, r, from the pumped well are plotted against the values of time, t, on the same logarithmic scale as that used for the type curves to prepare a graph designated as time-drawdown field-data curve. Placing the time-drawdown curve (on transparent paper) first over the type A curves and then over the type B curves, and keeping the respective coordinate axes parallel, a value of r/β is determined from the type curve that gives the best fit. Two cases may arise:

1. If the time-drawdown curve becomes horizontal after the early-time drawdown, a “match point” is chosen on this segment and, with the time-drawdown curve fitted to the appropri-ate type A curve, corresponding values of D, W(u), t, and 1/ua are read off at the match point. The time-drawdown curve is then fitted to the appropriate type B curve, and the value of 1/ub noted for the match point. (Being on the horizontal segment of the type curve, the match point will give the same value of W [ua, ub] as before.) The formation constants (T, S, S′, t, and α) are calculated from Equations 3.24, 3.25, and 3.26, respectively.

2. If the early-time-drawdown curve never becomes horizontal, the early-time-drawdown time segments of the time-drawdown curve may be fitted, respectively, to the type A curve and type B curve having an r/β that gives the best fit. Choosing a match point in each of these segments, values are read from curves and substituted into Equations 3.24 to 3.25 to compute the hydrogeologic characteristics (T, S, and α).

For case 1, it is evident that type A and type B curves, though strictly for situations in which n equals infinity, are applicable when n has a large finite value because they both have zero slope at their

Nonequilibrium type curve

10–1

Nonsteady-State Water-Table Type Curves

10–2

3.0

W (U

a, r/β)

W (U

b, r/β)

2.52.0

1.51.0

0.60.4 0.3

(I/Ua)

(A)

0.2= 0.1

10–310–40.01

0.1

1

10

10010–1 1 10 102 103 104 105 106 107

100

10

1

0.1

0.011

I/ub10 10–2 10–3 10–4

rβ

0.8

Nonequilibriumtype curve

(B)

fIgure 3.9 Delayed yield type curves.

pjw

stk|

4020

64|1

4354

3251

2


intersection. For case 2, however, type curve B for finite n is generally required. However, if the intermediate slope of the time-drawdown curve is not large, the complete type curve is obtained with sufficient accuracy by joining the appro-priate type A and type B curves (plotted on 1/ua and 1/ub base) by a straight line tangential to both curves. In this case, the match points on the type A and type B curves must be chosen so as to lie on segments of these curves that are clear for the sloping tangent. If the value of S is not required, the constants T, S′, and α may be directly obtained from the type B curves, in which case the type A curves are not needed.

After a relatively long period of pumping, the effects of delayed yield are negligible and aquifer characteristics may be computed using the Theis solution or its approximation as men-

tioned earlier. Boulton10 developed a curve that can be used to estimate the time, t0, when the effects of delayed yield become negligible (Figure 3.10). The figure gives α t0 as a function of r/β, where α is an empirical coefficient, T−1, α = T/β2S′ and r is the radial distance from the pumping well.

Neuman33–37 gave another solution for the average drawdown Dav in an observation well at a distance r at time t after pumping from a fully penetrating well in an unconfined aquifer with satu-rated thickness m.

D =

Q4πT

(Wt , , )av s σ β (3.27)

where

W(ts, σ, β) is the new well function

t =

TtSr

s 2 (3.28)

σ = S/S′ (3.29)

β =r Km K

2z

2r (3.30)

Kz and Kr represent, respectively, the vertical and horizontal hydraulic conductivity.On the basis of the preceding equations, the aquifer properties Kr, S′, and Kz can be obtained simply by plotting the drawdown D versus t. The procedure is as follows:

1. Plot D versus log t. 2. Fit a straight line to the late portion of the data. The intersection of this line with the hori-

zontal axis where D = 0 is denoted by t0. The slope of this line is the change in drawdown over one log cycle, denoted by ∆D.

3. Equation 3.27 can be approximated on the assumption that S<<S′ and σ ≈ 0:

321Values of r/β

Valu

es o

f αt 0

00

2

4

6

8

10

fIgure 3.10 Curve for estimating time, t0, when delayed yield ceases to influence drawdown.

Hydrogeology 47

D=

Q4πT

W(t , ) =Q4πT

(2.3 log 2.25 t )y yβ (3.31)

and

T=

2.3Q4π D∆ (3.32)

using this equation to solve for transmissivity (T), then compute horizontal hydraulic con-ductivity as Kr = T/m.

4. The specific yield S′ can be computed using

′S =

2.25Ttr

o2

(3.33)

5. Using the computed values of T and S′, solve for the dimensionless time ty from the equation

t =

TtS r

y 2′ (3.34)

The following equation36 can give β provided that 4.0 ≤ ty ≤ 100 (otherwise, Figure 3.11 may be used):

β = 0.195/(ty)1.1053 (3.35)

Equation 3.28 can be used to solve for KZ as follows:

K =

Krmr

Z

2

2

β

1001010.10.1

1

10

100

1000

ty

0.1951.1053ty

β =1β

fIgure 3.11 Logarithmic plot of 1/β versus ty.


Because the value of S, which is the storativity of the early time of pumping, is of no impor-tance, only S′, Kr, and KZ will be considered.

unsteady State flow in Semiconfined aquifer30,31

The drawdown in a semiconfined aquifer can be described by the Huntush and Jacob formula as follows:

D=

Q4πT

1ue du-(y)

u

∞

∫ (3.36)

or

D=

Q4πT

W(u, r/L)

where

u =

r S4Tt

2

(3.37)

and

y = u + r2/4L2u (3.38)

L = TC , where C=D /K′ ′ (3.39)

D′, K′ = thickness and hydraulic conductivity, respectively, of semipervious aquifer.Walton23 developed a group of curves defining the value of r/L for the application of both methods (see Figure 3.12).

Lai and Su38 gave a solution for the drawdown in the leaky aquifer for large wells:

D=

Q4πT

F(u, , r / , p)wα β (3.40)

where

u =

r S4Tt

2

(3.41)

α = r S/rw2

c2

(3.42)

where rw = effective radius of the well bore or open hole and rc = radius of the pumping well casing within the range of the water level fluctuation

r = r / T/D /Kw wβ ′ ′ (3.43)

Because many assumptions need to be satisfied for a solution in regard to the last condition of Equa-tion 3.38. Equation 3.36 may be considered for its simplicity and the approximate solution obtained for field problems.

Hydrogeology 49

3.5.5 EFFEcts oF partial pEnEtration oF WEll

Muskat39 discussed this problem in detail and presented methods for determining the flow pattern. He succeeded also in deducing a satisfactory approximate formula for the discharge. However, this formula is too complicated for practical application. Muskat later suggested another formula, obtained by Kozenys, as an approximation to his own (p. 274, Muskat39) for steady state conditions in a confined aquifer, as follows:

Q=2πDln

kmm(r /r )

1+7r

2mmcos

πm2e w

w′

′⋅

′

(3.44)

where m′ is the ratio of the depth penetrated by the well to the thickness of the aquifer, m.It must be noted that the effects of partial penetration are only apparent in drawdown data col-

lected within an approximate radial distance r of the pumping well:

r < 1.5m K /Kr z

where m = thickness of aquifer Kr = horizontal hydraulic conductivity Kz = vertical hydraulic conductivity (beyond this distance groundwater flow is essentially

horizontal)

102

w(w

, r/l)

101

100

10–1

10–2

10–3

6

642

6

6

4

4

2

2

642

642

10–4

10–5

10–1 100 1012 4 6 2 4 6 2 4 6 102 2 4l/u

6 103 2 4 6 104 2 4 6 105 1062 4 6

642

42

5.0

5.0

4.0

3.0

2.0

1.0

0.50

0.100.0500.001

0r/L

fIgure 3.12 Family of Walton’s type curves W(u, r/L) versus I/u and different values of r/L.


In case the flow is unsteady, Huntush42 gives an equation for the drawdown (D) at any point in an

observation well, as follows:

D=

Q4πK m

[W(u)+f(u, x, d/m, l/m, z/m)]r (3.45)

where

u =

r S4K mt

2

r (3.46)

W(u) =Theis well function and

f =2mπ(l-d)

1n

sinnπlm

-sinnπdmm

cosnπzm

W(u,

xx)

n=1

∞

∑ (3.47)

where

W(u, x) =

eydy

c

u

∞

∫ (3.48)

c =-y-x4y

2

(3.49)

x =

rm

K /Kz r (3.50)

The rest of the variables are as shown in Figure 3.13.

Pumping well

Q

Position ofpiezometric surfaceduring pumping

ddo

Kz

Kr lo

r

D

z

l

aquifer

m

m

aquiclude

Position ofplezometric surface

before pumping beginsObservation well

s

fIgure 3.13 Partially penetrating well in a confined aquifer.

Hydrogeology 51

3.5.6 hydraulics oF thE WEll and its dEsign

The foregoing discussion has treated the flow of fluid through the aquifer under an energy gradi-ent created by a well. The water must also be transferred through the screen and casing or pump column to the point of discharge. Under some circumstances, the energy expended in moving the water through the well structure may exceed that used in moving it through the aquifer. A better understanding of hydraulic principles involved in this latter mechanism should lead to improved well design. Some of the considerations are outlined in the following discussion.

Specific capacity

Engineers have designated specific capacity as the ratio of discharge to drawdown. If the hydraulic head losses through the screen and casing were zero and the time effect of storage depletion were ignored, the discharge of an artesian well could be expected to be directly proportional to drawdown. This would lead to a constant value of specific capacity corresponding to all values of discharge of an artesian well—a condition usually assumed. For wells in unconfined aquifers, an increase in drawdown decreases the effective thickness of the aquifer. Thus, even discounting energy losses at the well, the specific capacity would decrease with discharge for the water-table case.

The hydraulic losses through the well cause further nonlinearity in the relationship of discharge to drawdown. As mentioned by Jacob,26 flow through the screen and casing usually occurs in the turbulent regime and the resulting head losses are thus proportional to Q2. Aquifer losses under conditions of laminar flow should be proportional to Q for an artesian well.

Thus, one may write as follows:

D = BQ + CQ2 (3.51)

where D is the total drawdown in the well and B and C are constants.Equation 3.51 can be evaluated approximately by performing pumping tests at two different

discharge rates, Q1 and Q2, measuring the respective values of drawdown, D1 and D2; substitution successively into Equation 3.51 provides simultaneous equations in B and C. The difficulty with this procedure is that it is based on the assumption of steady flow and does not take into account the effect of time depletion of storage.

effective radius

The effective radius of a well, as it is used in the formulas of flow, may not be the same as the radius of the screen or hole, especially for wells in unconsolidated sediments. Development of the well or use of gravel envelopes increases the permeability of the formation immediately surrounding the casing. This effect is the same as increasing the radius. The effective radius is defined by Jacob as the distance, measured radially from the axis of the well, at which the theoretical drawdown based on the logarithmic head distribution equals the actual drawdown just outside the screen. In the ref-erence previously cited, Jacob43 gives a procedure for determining this quantity using the results of field tests.

Well Screens

Frequently, a large part of the energy imparted through a well is expended in transferring the water through the screen and pump. For this reason, attention should be given to the hydraulic perfor-mance of the well structure. Although considerable progress has been made, collection of data, especially in the field, is difficult because of rapidly changing flow conditions near the well. Labo-ratory experiments that simulate field conditions are expensive and arduous. Nevertheless, more attention should be given to this important aspect of the problem of well hydraulics.


An important part of the well structure is the screen. Screens of some kind are always required except in consolidated sediments. They may range from a rough, haphazard, perforation in a steel casing to highly engineered and carefully manufactured screens of specially selected material. The function of a screen is to exclude the natural sediments while allowing the greatest possible flow of water into the well. The factor of longevity influences the choice of screen.

The hydraulic performance of the well screen was ably treated by Peterson et al.40 Water enters the interior of a screen in the form of a radial jet at relatively high velocities. The energy of these jets is dissipated, and the flow accelerated in the axial direction. From a theoretical consideration of the mechanics involved, these investigators deduced:

∆hv /2g

=coshcosh

(CL/D+1)(CL/D-1)2

(3.52)

where ∆h is the hydraulic head loss involved in the screen and v is the first average velocity along the screen axis (Q/A, where Q is the well discharge and A the cross-sectional area of the screen). L is the axial length of the screen, and D the screen diameter. C is defined as the screen coefficient.

C = 11.31CcAp (3.53)

In Equation 3.53 Cc is the orifice coefficient of discharge applying to the screen opening and Ap is the fractional ratio of screen opening to total screen surface.

The loss coefficient ∆hv /2g2 in Equation 3.52 approaches 2 for values of CL/D exceeding about 6.

Velocity distribution

The velocity distribution around the well screen was taken constant along its length. This was proved later by Soliman44 to be curvilinear having the following relations:

U = UoeKL/D (3.53)

where K is a constant depending on the well screen and the rest of the values are shown in Figure 3.14.

These relations should be considered in the designing of screen length.

3.5.7 slug tEsts48

The slug test considered in this subsection is a test for determining the hydraulic conductivity (K) of unconfined or leaky aquifers connected to completely or partially penetrating wells (Figure 3.15). For other cases of confined aquifers, data collected from the pumping tests can be used to determine the hydraulic conductivity and storage coefficient.

The equations describing flow are based on a modified form of the Thiem (Dupuit) equation (Equation 3.6). The rate of groundwater flow, Q, from a well screen between the depths d and L for a specified water level in the well, Hw is

Q=2πK(l-d)Hln(R/r )

w

w (3.54)

where R is the radius of influence of the injection well and rw is the effective radius of the well bore; also

r = r (1-n) + nrw i

2o2

Hydrogeology 53

if the water level is falling within the screen length of the well and the hydraulic conductivity of the filter material or developed zone is much larger than the hydraulic conductivity of the aquifer, and n is the porosity of the filter:

ri = inside radius of well screenro = outside radius of filter materialrc = effective radius of the well casing over which the water level in the well changes.

To develop a simple equation, the following assumptions are given:

D

L

Uo

U

Q

fIgure 3.14 Velocity distribution around the well screen.

Aquiclude

Aquifer

Filter material

Position of water tablebefore injection

Position of water tableduring recovery

Injection well

Km

Ss = 0

rc

Hw

V

Water level inwell at t = 0

Ho

rw

d

l

fIgure 3.15 Slug test in an unconfined aquifer.


1. The aquifer is homogeneous and isotropic. 2. A volume of water, V, is injected instantaneously at time t = 0. 3. Head losses through the well screen, filter material, and developed zone (if present)

are negligible.

The rate of fall of the water level in the well is equal to the flow rate divided by the effective cross-sectional area of the well casing:

dHwdt

= -Qπrc

2

. (3.55)

Combining Equations 3.54 and 3.55 and integrating, K can be given as follows (refer to Figure 3.15 for limits):

K =

r ln(R/r )ln(Ho/Hw)2(l-d)t

c2

w

(3.56)

Bouwer and Rice48 determined the radius of influence, R, for different values of rw, (L − d), Hw, and m in using measurements made with an electrical resistance analog model. From their experiments, the following empirical equation was developed for estimating R:

ln(R/r ) =1.1

ln(l/r )+A+Bln[(m-l)/r ]

2(l-dww

w

))/rw

-1

(3.57)

where A and B are dimensionless coefficients that are functions of (l – d)/rw as shown in Figure 3.16.

If (Ln(m − L)/rw) > 6, then Equation 3.57 becomes

ln(R/r ) =1-1

ln(l/r )+

A+6B(l-d)/rw

w w

--1

(3.58)

Also, if the injection well fully penetrates the aquifer, the following equation is used:

ln(R/r ) =1-1

ln(l/r )+

C(l-d)/rw

w w

-1

(3.59)

where C can be interpolated from Figure 3.16.

3.5.8 groundWatEr rEchargE

Groundwater recharge may be obtained by artificial or natural means. Artificial groundwater recharge is a planned operation of transferring water from ground surface into aquifers. Natural groundwater recharge is a phenomenon in which water reaches aquifers, without human interven-tion from surface sources such as streams, natural lakes, or ponds.

The factors affecting natural groundwater recharge are thickness and properties of soil forma-tion and stratification, surface topography, vegetative cover, land use, soil moisture content, depth to water table, duration, intensity and seasonal distribution of rainfall, air temperature and other meteorological factors (humidity, wind, etc.), and influent and effluent streams.

Groundwater recharge45 may occur by infiltration, injection, or induction. The infiltration pro-cess is the entry of water into the saturated zone at the water table surface (Figure 3.17). The injec-tion method is the introduction of water into confined or unconfined aquifers by the injecting wells

Hydrogeology 55

(Figure 3.18). Recharge by induction is the entry of water into aquifers from surface-water bodies due to extraction of groundwater (Figure 3.19). Ground water recharge by infiltration could be natu-ral or artificial, whereas recharge by injection or induction is artificial.

The objectives of artificial groundwater recharge may be given as follows:

1. To serve as water-conservation mechanisms by subsurface storage for local or imported surface waters, supplement the quantity of groundwater available, and reduce the cost of pumping.

2. To prevent, reduce, and correct adverse conditions such as seawater intrusion, lowering of the water table, land subsidence, and unfavorable salt balance (Figure 3.20).

100000

1

B

B

A

C

2

3

10001001010

2

4

6

8

A &

C

10

12

14

(l – d)rw

fIgure 3.16 Values of the coefficients A, B, and C for use in estimating the radius of influence, R. (From Bouwer, H. and Rice, R.C., Water Resources Research, 1976, p. 426.)

Unconfined aquifer

Water table afterrecharging

Infiltration pond

fIgure 3.17 Infiltration from ponds.


Unconfinedaquifer

Water table

hw

ro

2rw

Qr

Ground surface

ho

fIgure 3.18 Water injection by recharge well.

Impermeable

River

Pumping well Ground surfaceWater table

fIgure 3.19 Induced recharge resulting from a well extraction.

Fresh waterSalt water

Ocean

Recharge wellGround surface

Piezometric surface

Aquifer

fIgure 3.20 Control of seawater intrusion by recharge well.

Hydrogeology 57

3. To allow heat exchange by diffusion through ground to conserve or extract heat energy. 4. To obtain suspended solid removal of infiltration through ground and storage of reclaimed

wastewater for subsequent use.

The sources of water for groundwater recharge may be storm runoff that could be collected in ditches, basins, or reservoirs; a distant surface water that might be imported into a region by pipe-line or aqueduct; and treated wastewater.

Depending on source and quality of water, type of aquifer, type of soil, topographical and geological conditions, and economic considerations, there are various artificial groundwater recharge methods.

These include water-spreading methods—basins, stream channel, ditch furrow, flooding, and irri-gation (see Figure 3.21); the pit method (Figure 3.22); and the recharge well method (Figure 3.23).

Recent interest has been focused on the reuse of municipal wastewater to recharge groundwater aquifers. Almost all uses of this are nonpotable, e.g., irrigation or industrial purposes, because of questionable health effects.

Interbasin control structure

Recharge basin

Maintenance roads onlevees as required

Sedimentretention

basin

Intakestructure

Diversion structureStream

Fence, as requiredOutlet

12

2

2

2

2

2

2

2

1 11

1

1 1

×

× × ×

×

××

fIgure 3.21 Multibasin recharge method.

Vertical scale, metersHorizontal scale, meters

Bedrock

15-cm gravel layer 30-cmpipe

40-cm pipe

ValvesRecharge pit

Sand andgravel

Top of levee

Control tower

River orCanal

Water table

201003020100

fIgure 3.22 Cross section through a recharge pit.


Recharge of wastewater (usually after secondary treatment) improves its quality by removal of physical, biological, and some chemical constituents.

Storage is provided until subsequent reuse reduces seasonal temperature variations and dilutes the recharged water with native groundwater. Land application practices involve irrigation, spread-ing overland flow, and recharge wells. Selection of a given system is governed by soil and subsurface conditions, climate, availability of land, and intended reuse of the wastewater.

Groundwater recharge by infiltration from ponds depends on rate of infiltration, which in turn depends on the soil characteristics. The infiltration rate of any soil can be measured by a double-ring infiltrometer. The total volume of water infiltrating the soil per unit of surface area can be deter-mined by integrating Horton’s equation46,47

f = fc + (fo − fc)e–Kt (3.60)

and by integrating Equation 3.60 the total volume of water (F) infiltrating the soil until time t

F = f t+

1K(f –f )(1–e )c o c

–Kt

. (3.61)

where f is the rate of infiltration of water into soil at time t, fo the initial infiltration rate, fc the final infiltration rate, and K a rate constant; fo, fc, and K can be given for any soil from the infiltration tests.

On the other hand, groundwater recharge by injection or by induction depends on the hydraulic conductivity of the aquifer to be recharged. Hydraulic conductivity of aquifers can be determined by pumping tests as mentioned earlier or by using slug tests.

Porous lavaformation

Sludge

Septic tank

Surface casingSoil

Lid

W.L.Inlet

Ground surface Disposal well

fIgure 3.23 Recharge well for disposal of septic tank effluent into a lava formation.

Hydrogeology 59

referenceS

1. Rosenshein, Moore, and Lohman, Two Hundred Years of Hydrology, 1986. 2. Moore, and Hanshaw, Episodes, December 1987. 3. Norton, W. H., 1897. 4. Veatch, A. C., 1906. 5. Meinzer, O. E., 1923. 6. Meinzer, O. E., 1934. 7. Meinzer, O. E., Hydrology, Dover, NY, 1942, p. 4. 8. Tolman, C. F., 1937. 9. Biswas, 1970. 10. Burdon, 1982. 11. Narasinhan, 1982. 12. Van der Leeden, 1983. 13. Day, J., 1986. 14. Rosenshein, J., 1986. 15. White, G., 1986. 16. Meyer, Davis, and La Moreaux, 1988. 17. de Vries, 1989. 18. Daubree, A., Textbook on Hydrology, Vol. 3, 1887. 19. Fuller, M. L., Water Supply Paper 160, 1906. 20. Wenzel, L.K., Local overdevelopment of groundwater supplies, with special reference to conditions at

Grand Island, Nebraska, USGS Water Supply Paper 836, Washington, D.C., 223, 1940. 21. De Wiest, R. J., Geohydrology, John Wiley, New York, 1965. 22. Soliman, M. M., Environmental Effects on the Arid Coastal Water Sheds in Egypt, International Sym-

posium of Arid Region Hydrology, San Diego, CA, 1990. 23. Walton, W. C., Groundwater Resource Evaluation, McGraw-Hill, New York, 1970. 24. Dupuit, 1863. 24a. Freeze, R. A. and Cherry, J. A., Groundwater, Prentice Hall, Englewood Cliffs, NJ, 1979, pp. 45–50,

58–61, 152–163. 25. Theis, C. V., The Relation Between the Lowering of Piezometric Surface and the Duration of Discharge

of a Well Using Groundwater Storage, Am. Geophysical Union Trans., 1935. 26. Jacob, C. E., On the Flow Water in an Elastic Artesian Aquifer, Trans. American Geophysical Union, 1954. 27. Soliman, M. M., Groundwater Management in Arid Regions, Vol. 1, Ain Shams University, 1984. 28. Todd, D. K., Groundwater Hydrology, John Wiley, New York, 1959. 29. Boulton, C. A., The drawdown of the water table under non-steady conditions near a pumped well in an

unconfined formation. Proceedings, Institute of Civil Engineers, 3, 3, 1954, pp. 564–579. 30. Boulton, N. S., Analysis of data from nonequilibrium pumping tests allowing for delayed yield from

storage. Proceedings, Institute of Civil Engineers, 26 (6693), 1963, pp. 469–482. 31. Boulton, N. S. and Streltsova, T. D., New equations for determining the formation constant of an aquifer

from pumping test data, Water Resources Research, 11, 1, 148–153, 1975. 32. Boulton, N. S. and Streltosova, T. D., The drawdown near an abstraction well of large diameter under

non-steady conditions in an unconfined aquifer, Journal of Hydrology, 30, 1976, pp. 29–265. 33. Neuman, S. P., Theory of flow in unconfined aquifers considering delayed response of the water table,

Water Resources Research, 8, 4, 1031–1045, 1972. 34. Neuman, S. P., Supplementary comments on theory of flow in unconfined aquifers considering delayed

response of the water table, Water Resources Research, 9, 4, 1102–1103, 1973. 35. Neuman, S. P., Calibration of distributed parameter groundwater flow models viewed as a multiple-

objective decision process under uncertainty, Water Resources Research, 9, 4, 1006–1021, 1973. 36. Neuman, S. P., Analysis of pumping test data from anisotropic unconfined aquifers considering delayed

gravity response. Water Resources Research, 11, 2, pp. 329–342, 1975. 37. Neuman, S. P., Perspective on delayed yield, Water Resources Research, 15, 4, 899–908, 1979. 38. Lai, R. Y. S. and Su, C. W., Nonsteady flow to a large well in a leaky aquifer, Journal of Hydrology, 22,

333–345, 1974. 39. Muskat, M., The Flow of Hogeneous Fluids through Porous Media. McGraw-Hill, New York, 1937. 40. Luthin, I., Drainage of Agricultural Lands, American Society of Agriculture, Madison, WI, 1957.


41. Huntush, M., Nonsteady Flow to Well Partially Penetrating an Infinite Leaky Aquifer, Proceedings, Iraqi Science Society, 1956.

42. Huntush, M. S., Hydraulics of Wells, Advanced Hydroscience, Vol. I, 1964. 43. Jacob, C. E., Notes on determining permeability by pumping tests under water table conditions, U.S.

Geological Survey, Open File Report, 1944. 44. Soliman, M. M., Boundary flow consideration in the design of wells, ASCE Journal of Irrigation and

Drainage, March 1965. 45. Lerner, D. N., Arie, S. I., and Ian, S., Groundwater Recharge, International Association of Hydrogeolo-

gists, Vol. 8, 1990. 46. Horton, R. E., Analysis of runoff plate experiments with varying infiltration capacity, Trans. Am. Geo-

phys. Union, 1939, pp. 693–711. 47. Green, I. R. A., An explicit solution of the modified Horton equation, Journal of Hydrology, 83,

23–27, 1987. 48. Bouwer, H. and Rice, R. C., A slug test for determining hydraulic conductivity of unconfined aquifers

with completely or partially penetrating wells, Water Resources Research, 12, 3, 423–428, 1976.

61

4 Environmental Impacts Related to Hydrogeological Systems

4.1 natural and manmade dISaSterS

During the past decade, geologists have been requested to participate in an ever-expanding role of responsibility regarding the evaluation and protection of the environment. The earliest geologists described and catalogued rocks, fossils, and minerals. Subsequently, they used this knowledge to develop mineral, water, and energy resources. During the past 20 yr, there has been an increasing demand to use the same expertise to bring about remedial actions on “endangered environments” and to aid environmental planning and development. Geologists are now requested to provide solu-tions to properly manage hazardous, toxic, and radioactive wastes, as well as to cope with problems of catastrophes, both natural and manmade. With this responsibility, there has evolved a need for risk assessment and guidance for the development of insurance programs that will protect individu-als against disaster. What are the risks, what are the chances for a reasonable risk assessment, and what are the limits of liability?

Ancient man must have looked upon a volcano such as Santorini (an island volcano in the Medi-terranean), or would have looked upon the recent hurricanes such as Katrina or Ivan in the United States as totally unfathomable calamities. In prehistoric times, disasters of this magnitude were the basis for a belief in gods’ venting their wrath upon mankind. These were similar to the biblical flood of Noah’s day, caused by a storm of such large magnitude that the entire Tigris and Euphrates valleys were inundated, and life was destroyed over a very extensive area. These were the kinds of natural disasters that formed the basis of legends handed down by word of mouth over hundreds of years.

Natural catastrophes do take place today; however, civilization has become more knowledge-able, and information is collected with regard to the causes and effects of these natural phenomena. For example, during the last few years, the scientific community has predicted, with considerable accuracy, hurricanes, earthquakes, volcanic eruptions, and tsunamis. Effective warning systems have been developed that save thousands of lives through emergency planning for evacuation from danger zones. Special construction of buildings has been mandated in the event that one of these natural catastrophes should take place in a populated area. Modern civilization, however, still has not been able to cope with certain types of catastrophic phenomena. Worldwide, nearly 3 million people have died in natural disasters during the past 10 years, and some 820 million more have been injured, displaced, or otherwise affected; property damage from individual catastrophes has been in the order of billions of dollars. Hugo’s damage was in excess of 2 billion dollars; the October 19, 1989, San Francisco earthquake damage exceeded 10 billion dollars, and the more recent hurricane Camille caused damage to Florida and Louisiana in excess of 13 billion dollars.

In 1980 the eruption of Mt. Saint Helens in the state of Washington awakened many to the impact of volcanic hazards, and in December 1987, the United Nations General Assembly desig-nated the 1990s as the International Decade for Natural Disaster Reduction. One of the first reports from this effort is “Reducing Disasters’ Toll,” by the United States National Research Council.1 This is one of a series of publications that have been and will continue to be published in the future as a result of cooperative international programs to reduce the impact of natural hazards. Man is now evaluating more carefully these natural phenomena and measuring their worldwide impact.

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From 1650 to 1450 BC, major eruptions of Santorini caused such damage to the natural environ-ment that climate around the world was affected; billions of tons of fine ash were thrown into the air, and day turned into night over much of the Eastern Mediterranean. Ocean tidal waves lashed against the shores of all the Greek islands, Asia Minor, and North Africa. Therefore, even though this catastrophe was not studied and recorded as are those of today, a record remains of the event over 3500 years after it occurred. From a hydrogeologist’s perspective, the environmental impact was so great, even in a relatively unpopulated world, that it left indelible historical evidence. The eruption was recorded by geological, chemical, and biological time clocks. There is no written record, at least none discovered to date; however, all available data from a great variety of sources can be pieced together to interpret the size of this historical event. If this event were to happen in a relatively populated area today, such as the Mediterranean, the Gulf Coast of the United States, Japan, or Indonesia, the loss of life and damage to property from the tragedy would be on a scale unknown to modern civilization.

The Santorini event was so violent that it has never been equaled in the memory of humankind. The eruption of Krakatau, the only natural event with gaugeable force, could not equal its violence. It was one of the most spectacular natural environmental events of all time.

Another Santorini could happen, and the hydrogeologist, geophysicist, and seismologist could predict, with some accuracy, where it would happen and, sometimes, with adequate data, approxi-mately when. But how can such a catastrophe be insured? What type of environmental planning must be carried out in these critically sensitive spots of the world?

The benefits from investments in geoscience pay enormous dividends. The U.S. Geological Sur-vey reports predicting the eruption of Mt. Pinatubo in the Philippines resulted in the safe evacuation of more than 100,000 people and billions of dollars in United States military equipment. Imagine the impact of a volcano in today’s world that would disrupt an area the size of the Mediterranean with tsunamis 100 ft high and with a poisonous ash fallout over 1,000 square miles. Similar catas-trophes would be another major earthquake along the San Andreas Fault through San Francisco, California, or a repeat of Hurricane Andrew (1992) in the United States that killed 17 and caused over $17 billion in damage.

There are many natural catastrophes for which hydrogeologists or other earth scientists have been able to identify and provide risk factors; locate potential areas of occurrence; and determine frequency, severity, and potential damage to property and life. These include landslides, mudslides, tsunamis, earthquakes, hurricanes, tornadoes, and catastrophic subsidence or sinkhole collapse.

Many of these catastrophes can be predicted with substantial accuracy using present-day scien-tific knowledge, methodology, techniques, and instrumentation. Funding for research, and therefore accuracy of results, depends to a great extent on the perception of the public and its willingness to support financing of necessary research that will allow the most accurate modeling and predictions of these natural events.

In Japan and the United States, extensive research in the area of volcanology has allowed rather accurate predictions of volcanic events. Predictions of impending activity in Mt. Saint Helens allowed the removal of populations and minimized damage of many types and the loss of life. The U.S. Geological Survey of the Department of the Interior has an excellent record of research effort. In addition to its responsibility for the assessment of energy, minerals, water, and topographic mapping, it carries on a detailed study program, as well as monitoring and prediction programs on volcanoes.*

Earthquake phenomena have also been the subject of extensive research in the Soviet Union, China, Japan, the United States, and certain other areas of the world that are impacted by frequency of earthquakes. In the United States, the U.S. Geological Survey and National Oceanic and Atmo-spheric Administration (NOAA) carries on extensive programs of research, including a comput-

* Information is available from the Branch of Distribution, USGS, 604 South Pickett Street, Alexandria, VA, 22304, or USGS Center, Menlo Park, CA.

Environmental Impacts Related to Hydrogeological Systems 63

erized maintenance of records of epicenters over the world and periodic earthquake probability maps rating the areas by frequency of earthquakes. This subject has received so much attention in the past that there are now textbooks and regular scientific journal publications, for example, the NOAA earthquake frequency map and epicenter determination reports, regular articles in Episodes, an international geoscience journal, annual summary of the American Geological Institute, and a monthly summary of geologic phenomena in Geotimes.

One of the best summaries on earthquakes is available from the U.S. Geological Survey Infor-mation in a 1991 pamphlet titled “Earthquakes.”2

Predicting earthquakes, though improved in recent years, has not attained quite the accuracy as predicting volcanic eruptions. However, in the case of both volcanoes and earthquakes, the detailed knowledge of the geology of the earth and its geologic structure and plate tectonics, in addition to recent information from satellite research on natural phenomena, have provided tools that have made predictions far more accurate in recent years. Information on earthquake research in the United States can be obtained from the Branch of Distribution, U.S. Geological Survey.

Earthquakes and volcanoes are related to major tectonic features of the earth’s crust and can be of such a minor impact as an unobservable deep-seated intrusion of magma on the ocean floor or a quake of a fraction of 1 on the Richter scale that could occur unknown to the population. These incidents, however, are in sharp contrast to a large eruption such as a Santorini or a Krakatau, or an earthquake of the magnitude of the 1909 San Francisco catastrophe. These are monitored in much detail by today’s scientific community and are being used to gain more accurate knowledge of natural phenomena, some of which will affect the insurance industry much more in the future. There will come a time when all of these events will be the subject of insurance programs that will require risk assessments.

4.2 land SubSIdence

There are a number of other natural phenomena that scientists can predict with a substantial degree of accuracy as to where, why, and when hazards may occur and the frequency and size of the haz-ard. These would include landslides, mudslides, and sinkhole collapse or catastrophic subsidence. Let us analyze problems associated with land subsidence.

More than 44,000 km2 of land in 45 states in the United States has been lowered by the types of subsidence considered in this report. Underground mining of coal, groundwater withdrawal, and drainage of organic soils are the principal causes of subsidence with approximately 8,000, 26,000, and 9,400 km2 of land having subsided from each of these causes, respectively. In addition, about 18% of the conterminous United States is underlain by cavernous limestone, gypsum, salt, or marble, and is locally susceptible to catastrophic collapse into sinkholes.

Annual costs resulting from flooding and structural damage are in the billions of dollars.3 Although these costs are small relative to those of many other earth-science hazards, their geo-graphic distribution is not uniform. Thus, localized areas bear disproportionate shares of these costs. In addition to this uneven cost distribution, parties damaged by subsidence associated with resource exploitation commonly are stymied from reimbursement by legal recovery systems that are in conflict with doctrines that establish rights to resource exploitation.

Many examples are available of successful efforts at the federal, state, and local levels to mitigate specific subsidence problems. The efforts include public information programs, mapping programs, regulation of resource development, land-use management and building codes, market-based meth-ods, and insurance programs. Despite these successes, continued mitigation of subsidence requires action in three additional areas.

First, basic earth-science data and information on the magnitude and distribution of subsid-ence are needed to recognize and assess future problems. Such data include geodetic, geologic, hydrogeologic, and hydrologic inputs as well as information on soils and land use. These data, in both map and tabular formats, help to not only address local subsidence problems but also identify


national problems. Collection of these data in general should be overseen by earth-science agencies, particularly state geological surveys and the U.S. Geological Survey. Channels of communication should be developed to designate levels of government and interest groups advising them of the availability of this information.

Second, research on subsidence processes and engineering methods for dealing with subsid-ence is needed for cost-effective damage prevention and control. Although general understanding of subsidence processes is well developed, prediction of subsidence magnitudes, rates, and location is commonly impeded by incomplete understanding of specific details of the relevant processes and the inability to adequately determine subsurface conditions and physical properties of the deform-ing earth materials. Even when a specific subsidence occurrence is well understood, experience of the United States with engineering design to accommodate ground deformation, and with methods to control it, is modest. New funding is needed to support research on subsidence processes by the U.S. Geological Survey, Bureau of Mines, Bureau of Reclamation, and Agricultural Research Service, and on engineering methods by the Federal Highway Administration, Corps of Engineers, Bureau of Reclamation, Federal Housing Administration, and Soil Conservation Service.

Third, although many types of mitigation methods are in use in the United States, studies of their cost effectiveness would facilitate choices by decision makers. Such studies should be funded by the Federal Emergency Management Agency, National Science Foundation, and industrial and professional organizations.

Catastrophic subsidence takes place in areas underlain by limestone that is sufficiently mas-sive, pure, and has been subject to certain erosional conditions that resulted in dissolution of large segments of the rock (limestone carried away by solution) so as to leave a Swiss-cheese appearance in the rock itself. For example, beneath Orlando, Florida, the Floridan Aquifer is made up of three major formations:

1. The Suwannee—limestone 2. The Ocala—limestone 3. The Avon Park—limestone/dolomite

These formations include preferential flow zones that have been extensively dissolved. Large solu-tion openings, cavities, and caves have developed in the rocks over millions of years. Subsequently, during the Pleistocene or Glacial periods, these rocks in the peninsula of Florida have periodically been invaded and covered by the sea and overlaid by sediments of clay, sand, silt, gravel, and some limestone. This is a general geologic setting for catastrophic subsidence. Subsequently, to the pres-ent day, the solution cavities have become filled with water, and now this groundwater functions as a buoyant effect on the overlying sediments. Mother nature places things in balance. Evidence of the many solution cavity features occurs in the form of thousands of sinkholes that are filled with water, which can be seen when flying over this region.

Natural phenomena, such as extensive periods of drought followed by heavy rains from tropi-cal storms, however, can trigger catastrophic subsidence. The downward movement of the water table from shortage of rainfall over a long period and the loss of buoyant support of the water to the sediments, with subsequent torrential rain, may act as a lubricant for the unconsolidated material, causing it to collapse into the solution system. Where this happens, in an area of farms, commercial buildings, highways, and airports, big holes in the land surface can develop with substantial damage to property, animals, and humans. This situation is not unique to Florida but exists in many other parts of the United States, Europe, Southeast Asia, and the Middle East, in fact, in approximately 25% of the area of the earth’s landmass where limestones occur.

Extensive studies of this type of catastrophic event by many different scientific groups have provided substantial literature on the subject. Scientific groups involved in such studies include the Panel on Subsidence of the Commission on Engineering and Technical Systems, Committee on Ground Failure Hazards of the National Academy of Sciences, and the Karst Commission of


the International Association of Hydrogeologists. Results have been published in textbooks and volumes of symposia papers. Extensive work has been done by the U.S. Geological Survey, and the phenomenon is so well known in Florida that catastrophic subsidence insurance is available there. This is possible because of predictability, on the basis of research regarding this phenomenon, and the perception of the public and the government that it represents enough of a source of damage to warrant insurability. Some states, through cooperative programs with the U.S. Geological Sur-vey have mapped in detail the areas where catastrophic subsidence can take place. The triggering effects that cause catastrophic collapse include:

1. Heavy withdrawals of groundwater by pumpage for industrial, agricultural, and municipal use

2. Diversion of drainage in a karst area 3. Excavation or use of heavy equipment 4. Mine dewatering (for example, in South Africa, where sinkholes caused the collapse of a

three-story building, in which 29 men lost their lives) 5. Earthquakes 6. Use of explosives

A substantial amount of work is now being done on natural risk phenomena using past model-ing and predicting. The reader’s attention is called to an interesting article in the Electric Power Research Institute Journal titled “Measuring and Managing Environmental Risk.”4

4.3 cauSeS of SubSIdence

Subsidence is caused by a diverse set of human activities and natural processes, including min-ing of coal, metallic ores, limestone, salt, and sulfur; withdrawal of groundwater, petroleum, and geothermal fluids; dewatering of organic soils; pumping of groundwater from limestone; wetting of dry, low-density deposits, which is known as hydrocompaction; natural sediment compac-tion; melting of permafrost; liquefaction; and crustal deformation. This diversity and the broad range of impacts from subsidence are probably the major causes of a lack of national focus on subsidence. Instead, many industries, professions, and federal, state, and local agencies are inde-pendently involved with aspects of subsidence. Most occurrences of subsidence in the United States, however, are induced by human activity. Resource development and land-use practices, particularly underground mining of coal, groundwater and petroleum withdrawal, and drainage of organic soils, are the primary causes.

Land subsidence, the loss of surface elevation due to removal of subsurface support at rates that are of practical significance to manmade structures, affects most of the United States. It is one of the most varied forms of ground failure affecting the country, ranging from broad regional lowering of the land surface to local collapse. Its practical impact depends on the specific form of the surface deformation. Regional lowering may either aggravate the flood potential or permanently inundate an area, particularly in coastal or river settings. Local collapse may damage buildings, roads, and utilities, and either impair or totally destroy them. Fortunately, subsidence is more hazardous to property than to life because of the typically slow rates of lowering. It has caused few casualties, but it increases the potential for loss of life in flood-prone areas by increasing the magnitude and size of areas susceptible to flooding.

Table 4.1 shows the types of land subsidence that affect parts of at least 45 states (Figure 4.1).5

More than 44,000 km2 of land, an area equal to half the state of Maine, has been lowered.The common association of land subsidence with either the exploitation of natural resources or

land development practices is an important aspect of subsidence. These activities have economic ben-efits. Problems often arise because those who benefit from the activity that causes subsidence may not bear the full cost. In fact, some parties who incur damage may not profit at all from the activity


causing the subsidence. In addition to the equity issue, specific subsidence problems may be aggra-vated by legal and institutional barriers that prevent legal recourse to injured parties. Legal recovery theories conflict in some states with other doctrines that establish rights to resource recovery.

4.3.1 collapsE into voids: minEs and undErground cavitiEs5

Collapse of surficial materials into underground voids is the most dramatic kind of subsidence. Buildings and other engineered structures may be damaged or destroyed, and land may be removed from productive use by such ground failure.

Underground excavations have been constructed in the United States since the early 1700s. Most of the voids with which subsidence has been associated in the United States were created by coal mining. Abandoned tunnels and underground mining of metallic ores, limestone, and salt con-tribute to a much smaller extent, although associated problems may be severe in some regions.

In general, coal-mine subsidence is caused by collapse of the mined-out or tunneled void. It occurs as both steep-sided pits (Figure 4.2) and broad, gentle depressions.5 Subsidence depends on the number, type, and extent of the voids. For example, it is a planned consequence of the longwall mining method for coal, in which most of the coal seam is removed along a single face, the long-wall. By this method, the roof above the mined-out seam is allowed to collapse when the longwall advances laterally as mining progresses. Subsidence above longwall mines is rapid, generally end-ing within a few months after the removal of subsurface support. Subsidence above mines with par-tial extraction is usually unplanned. By this method, only parts of the coal, the rooms, are removed. The unmined portions, the pillars, are left to provide support. Collapse into the rooms occurs when the pillars, floors, or ceilings deteriorate. Subsidence resulting from collapse into rooms may take years to decades to manifest itself. Examples of collapse occurring 100 yr after mines were aban-doned have been documented.

Coal is found in 37 states and mined underground in 22 states of approximately 32,000 km2. Approximately 8,000 km2 of the undermined area, most of which is in the eastern United States, already has experienced subsidence.5 The U.S. Bureau of Mines estimates that 1,600 km2 of land in urban areas is threatened.6 Seventy-one percent of this area is in Pennsylvania, Illinois, and West Virginia.5

table 4.1types of land subsidenceCollapse into voids

Mining

Sinkhole

Compaction

Underground fluid withdrawal

Natural compaction

Hydrocompaction

Liquefaction

Drainage of organic soils

Melting of permafrost

Crustal deformation

Volcanism

Seismic

Aseismic

Postglacial deformation

Source: From Panel on Land Subsidence, National Research Council, National Academy Press, Washington DC, 1991.

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4.3.2 sinkholEs5

The sudden formation of sinkholes—catastrophic subsidence—is usually caused by movement of overburden into underlying cavities in soluble bedrock (Figure 4.3). Failure of the bedrock is rarely believed to be a major factor in catastrophic subsidence. Most catastrophic subsidence in the United States is associated with carbonates such as limestone, but occasionally it is associated with evapo-rites such as gypsum and halite (Figure 4.4). Although most historical collapses are artificially induced, the cavities in the bedrock usually antedate human activities. This is particularly true of carbonates because the rates of solution are so low. Cavities in halite can be an exception because of its high solubility. For example, several dozen sinkholes have formed in the last 30 yr in Kansas as a result of solution of salt beds by leaks through the casings of brine disposal wells. A recent example is a 60-m-wide and 33-m-deep sinkhole that formed in the summer of 1988 near Macksville, Kan-sas.7 Catastrophic subsidence is most commonly induced by water-table lowering, rapid water-table fluctuation, diversion of surface water, construction, use of explosives, or impoundment of water.

A. Mining

C. Underground fluid withdrawal

E. Hydrocompaction F. Drainage of organic soils

D. Natural compaction

B. Sinkholes

LegendCosts

<$1 million $1–10 million $10–100 million >$100 million

fIgure 4.1 National distribution of subsidence problems by state. Costs were compiled from published and unpublished sources for the purpose of providing an order-of-magnitude, state-by-state comparison. Only relative importance is suggested by maps because the time periods on which estimates are based vary by state, and costs were not converted to constant dollars. In general, costs are conservative estimates. (From Panel on Land, Subsidence, National Research Council, National Academy Press, Washington DC, 1991.)


Davies et al. indicate that more than 1.4 million km2 of land in 39 states is underlain by cavern-ous limestone and marble.8 More than 30,000 km2 of this area lies beneath standard metropolitan statistical areas inhabited by 33 million people. Fortunately, only a small portion is actually under-lain by voids and at risk. Newton estimates that more than 6,000 collapses have occurred in the east-ern United States since about 1950.9 The states with the largest number of active sinkholes include Alabama, Florida, Georgia, Indiana, Missouri, Pennsylvania, and Tennessee.

4.3.3 sEdimEnt compaction5

Sediment compaction typically causes broad regional subsidence. Exceptions include ground rupture and hydrocompaction. Rates of subsidence usually are low, ranging from a few millimeters to centi-meters per year, but total subsidence may reach several meters as it accumulates over decades.

fIgure 4.3 Catastrophic subsidence caused by collapse of overburden into voids in limestone near Bastow, Florida, which destroyed two houses. (Photograph courtesy of Florida Sinkhole Research Institute.)

fIgure 4.2 Oblique aerial view of subsidence pits above abandoned coal mines in the Sheridan, Wyoming, area. The diameter of the pits ranges from 5 to 50 m. (From Panel on Land Subsidence, National Research Council, National Academy Press, Washington DC, 1991. Photograph courtesy of C. Richard Dunrud.)


4.3.4 undErground Fluid WithdraWal5

The weight of the overburden above underground fluid reservoirs is supported by both fluid pres-sures and stresses transmitted through the solid framework of the reservoir soil or rock. When flu-ids are withdrawn, fluid pressures decline and support of the overburden is transferred to the solid framework. If the reservoir soil or rock is compressible, large and permanent loss of pore volume or compaction will occur as it adjusts to the new stresses. In geothermal reservoirs, significant thermal contraction also may occur as the reservoir cools during exploitation.

Most of this type of subsidence in the United States is caused by pumping of groundwater and petroleum. More than 31 areas in seven states have subsided. The two largest areas are in the San Joaquin Valley, California, and Houston, Texas, where 13,500 and 12,000 km2, respectively, have subsided because of groundwater withdrawal. Maximum elevation loss from this type of subsidence has been 9 m in the San Joaquin Valley.

Two coastal areas in California and Texas where subsidence caused or threatened inundation and increased flooding potential have suffered the most from this type of subsidence. Petroleum withdrawal in Long Beach, California, caused parts of the city’s harbor facility to subside almost 9 m from 1937 to 1966. Groundwater withdrawal in Houston, Texas, has caused some coastal areas to subside by more than 2 m. About 80 km2 of land has been inundated, and several hundred square kilometers, including the 500-unit Brownwood subdivision in Baytown, which was abandoned in 1983, have been added to the area susceptible to flooding by storm surges.

Inland areas are not immune to damage from subsidence. Changes of surface gradients can affect either the design or operation of canals. For example, canals in the State Water Project and the Central Valley Project in California and the Central Arizona Project have been affected. Other causes of damage in inland areas include subsurface deformation and ground rupture. Subsurface deformation shears or crushes well casings and diminishes the productivity of water and oil wells. Ground rupture, including faults and earth fissures, is particularly devastating to manmade struc-tures. Faulting has damaged hundreds of houses in Houston, Texas, and in California in 1963 that caused by the catastrophic failure of the Baldwin Hills reservoir, claiming five lives. Earth fissures (Figure 4.5) are an increasingly common occurrence as groundwater withdrawals increase in allu-vial basins in the desert parts of the Sun Belt.5

fIgure 4.4 Catastrophic subsidence over the Boling salt dome, Texas, August 11, 1983. Diameter of the depression is about 75 m. (Photograph courtesy of Boyd V. Dreyer.)


4.3.5 natural compaction5

Sediments compact naturally as they are buried under younger sediment. Probably nowhere in North America does natural subsidence occur more rapidly than in the Mississippi River Delta area of southern Louisiana, where about 3900 km2 of land is subsiding, at least in part, through natural compaction. Estimated average rates of subsidence range from 8 to 11 mm per century.10 Maximum rates measured by geodetic surveys are about 12 mm per year. The abandoned town of Balize, approximately 130 km southeast of New Orleans, on the tip of the delta, is an example of the long-term implication of this subsidence. Balize, which was abandoned during a yellow-fever epidemic in 1888, was more than 1.2 m below marsh level in 1934.11 Today the abandoned town sits more than 3 m below sea level.

Increased flooding potential is the principal impact of this type of subsidence because affected areas commonly are low lying and naturally subject to flooding. Thus, subsidence exacerbates a preexisting problem. The flood problem is particularly acute in coastal areas where long recurrence intervals between large storm surges and tidal floods diminish public perception of the problem. Documenting subsidence problems in coastal areas may be difficult if other types of subsidence are occurring and sea level is changing. For example, subsidence caused by drainage of organic soil and withdrawal of underground fluids is common in many deltaic areas. A well-studied example of this complexity is Venice, Italy, where increases in the incidence of tidal flooding prompted an investigation, which discovered that the mean elevation above sea level had decreased from 130 to 110 cm since the turn of the century. About 14, 41, and 45% of the 20-cm average elevation loss was attributed to natural compaction, sea level rise, and withdrawal of groundwater, respectively.12

Another very important impact from this subsidence is the destruction of productive estuarine marsh and coastal wetlands by either inundation or erosion. Thousands of hectares of low-lying coastal land along the Gulf of Mexico are converted each year to open water by natural subsidence (Figure 4.6). This process, referred to as coastal land loss, results in a significant loss of habitat for birds, fish, crustaceans, and reptiles, and has a profound impact on the commercial fishing, shrimp-ing, oystering, and fur-trapping industries. In addition, salt water intrusion into these areas destroys agricultural usage.

The most severe land-loss problem in the United States is in southern Louisiana (Figure 4.6).5 Channelization of the Mississippi River has caused riverborne sediment, which normally offsets land loss by replenishing beaches and wetlands, to discharge directly offshore into the Gulf of Mex-ico. The rate of land loss in southern Louisiana currently is about 130 km2 per year; approximately

fIgure 4.5 Tension crack in southcentral Arizona that has been enlarged by erosion into 1-m-wide gully. (Photography courtesy of Thomas L. Holzer.)


3,200 km2 of land has been lost in the last 80 years. Nationally, more than 150,000 km2 of coastal marsh has been lost since 1954.13

4.3.6 hydrocompaction5

Dry, low-density, fine-grained sediment may be susceptible, when wetted, to a loss of volume known as hydrocompaction (Figure 4.7). These sediments, known as collapsible soils, generally are of two types: mudflow deposits in alluvial fans, and wind-deposited, moisture-deficient silt called loess. Most collapsible soils have anomalously low densities because they remained moisture deficient throughout their postdepositional history. When water percolates through the root zone into this type of sediment, the soil structure collapses and the soil compacts. Very localized subsidence, typically 1 to 2 m, may result.

Damaging hydrocompaction has been reported in 17 states. The three largest affected areas are the alluvial slopes of the western San Joaquin Valley and loess-covered areas in the Missouri River basin and the Pacific Northwest. The major impact has been on design and operation of hydraulic structures—canals and dams. Locally significant impact has been incurred by build-ings and highways. Irrigation for agriculture also has caused differential subsidence that required releveling of fields.

4.3.7 organic soil5

Drainage of organic soil, particularly peat and muck, induces a series of processes, including biological oxidation, compaction, and desiccation, which reduce the volume of the soil. Biological oxidation usually dominates in warm climates (Figure 4.8). The principal areas of organic soil subsidence in the United States are the greater New Orleans, Louisiana, area; the Sacramento–San Joaquin River Delta, California; and parts of the Florida Everglades. Maximum observed subsidence is 6.4 m in the Sacramento–San Joaquin River Delta. About 9,400 km2 of land under-lain by organic soil has subsided in the United States because of drainage. An even larger area is susceptible to subsidence. About 101,000 km2 of the conterminous United States is covered by peat and muck soils;14 more than 26,000 km2 of organic wetlands is in standard metropolitan statistical areas.

A motorboat’s wakein dredged channelscontributes to theloss of 60 sq. mi. ofwetlands annually

GULF OFMEXICO

MississippiR.New Orieans

PLAQUEMINESPARISH, L.A.

fIgure 4.6 Regional land subsidence and diversion of sediment carried by the Mississippi River directly to the Gulf of Mexico contribute to the disappearance of more than 130 km2 of wetlands annually in southern Louisiana.


4.4 damage coSt and legal aSPectS of land SubSIdence5

The average annual damage cost from all types of subsidence is conservatively estimated to be at least $125 million (Table 4.2). The costs are dominated by subsidence from underground mining of coal, drainage of organic soils, and withdrawal of underground water and petroleum. These costs consist primarily of direct structural and property losses and depreciation of land values, but they also include business and personal losses that result during periods of repair. Although the total annual damage cost of subsidence to the United States is small relative to the United States nation’s economy, subsidence imposes substantial costs on individual cities and neighborhoods.

fIgure 4.8 Concrete monument set on rock beneath organic soil in Belle Glade, Florida, an active subsid-ence area. Elevation painted on the monument is feet above mean sea level. Dates show former elevation of land surface. The photograph was taken October 1987. (Courtesy of George H. Synder.)

fIgure 4.7 Hydrocompaction of test plot in San Joaquin Valley, California. Water has infiltrated from pond and caused collapsible soils to compact as they become wet. Note extensive ground cracking in the background around the margin of subsidence depression. Poles were used to measure compaction at different depth intervals. (Photograph courtesy of California Department of Water Resources.)


The dollar value of economic losses from subsidence shown in Table 4.2 reveals only part of the United States’ subsidence problem. Inequitable aspects of both economic incentives and the American legal structure are major factors in the nation’s subsidence problem, particularly where subsidence is caused by resource extraction or land use. Often, existing legal or market incentives do not encourage the developer of a resource to consider the costs imposed on others who do not receive the benefit of development. These are termed external costs.

External costs cause misallocation of society’s resources. Social costs, the costs to society as a whole, are greater than private costs when there are external costs. Thus, a mine operator who has caused subsidence on land that he does not own receives all of the benefits of ore production, but he pays only the private cost, a portion of the social cost. The surface property owner affected by subsidence, however, receives none of the benefits and bears the external costs from the actions of the mine operator. This misallocation of resources is corrected when the mine operator pays all of the social costs, private and external, of the mine operation.

In evaluating external costs, several dimensions are worth noting. External costs from sub-sidence can stem from past activities, as in the case of abandoned mines. These activities can be viewed as a one-time imposition of some level of external costs on the future. Alternatively, past and current activities can cause a continuing subsidence problem. These types of external costs are direct. External costs from subsidence also may be indirect. These include situations where subsid-ence increases the potential for economic damage from other natural events. Increased susceptibil-ity to flooding from storm surges of low-lying coastal areas is an example.

Another category of external costs potentially presents a special dilemma. This involves situ-ations in which the external cost is borne in perpetuity by future generations. For example, con-sider an area in which drainage of organic soil causes land to subside below sea level or alters the freshwater–saltwater balance. In such cases, land may simply disappear because of inundation, or the ecology may change; thus, a permanent loss is passed on to future generations.

In common law, the principal means to prevent externalities by transferring external costs to the actor who created them is the tort system. It generally has a twofold purpose: (1) to compensate worthy victims for damages they have suffered by the negligence of others (thus imposing the costs of the damage on the actor who created them) and (2) to act as a deterrent to negligent activity, that is, to encourage the actor to decide not to engage in an activity if it creates a cost that can be trans-ferred back to that actor in a tort or lawsuit.

There are at least three reasons the legal system does not provide an adequate mechanism for transferring subsidence costs onto the actors that create them.18 First, in many states, such as those applying the English common law doctrine of absolute ownership of groundwater, the legal system

table 4.2estimated annual losses from land subsidence (in millions of dollars)Mines 30

Sinkholes 10

Underground fluid withdrawal 35

Natural compaction 10

Hydrocompaction Not available

Organic soils 40

Total 125

Source: From Jones, L.L., External Costs of Surface Subsidence: Upper Galveston Bay, Texas, International Association of Hydrological Sciences Publication No. 121, 1977; Newton, J.G., Natural and Induced Sinkhole Development in the Eastern United States, International Association of Hydrological Sciences Publication No. 151, 1986; Prokopovich, N.P. and Marriott, M.J., Cost of Subsidence to the Central Valley Project, California, Association of Engineering Geologists Bulletin, 20(3), 1983, pp. 325–332; HRB-Singer, Inc., Technical and Economic Evalua-tion of Underground Disposal of Coal Mining Wastes, Report prepared for U.S. Department of the Interior, Bureau of Mines, Contract No. J0285008, 1980.


does not allow a party injured by subsidence to recover from the person causing the subsidence. Similarly, the legal system may not provide a recovery mechanism for a surface owner injured by subsidence caused by underground mining. Second, even in those jurisdictions that allow recovery of subsidence damage, lack of public understanding about the causes and effects of subsidence may prevent members of the public from recognizing their damages and the identity of those who caused them. Even if some members of the public can successfully recover their losses, those who do not, or cannot, recover their losses will leave external costs that are not internalized. Third, because many of the damages caused by subsidence are indirect, the full cost of subsidence may not be recog-nized. For example, a flood may inundate 1000 ha when it would have inundated only 500 ha in the absence of subsidence. The owners of the property whose inundation was caused by the subsidence may not recognize the role played by subsidence in expanding the flooded area. From an economic point of view, these indirect costs are as significant as direct costs and, if they are not recognized and recovered, they will not be internalized.

When traditional legal mechanisms fail to provide adequate control over external economic costs, governments may create statutory or regulatory controls to compensate for the deficiencies in common law. These are not always limited to recovery for negligent performance of an activity. Legislation can remove the element of negligence by establishing strict liability for surface damages. Alternatively, administrative regulation may be used to address local subsidence problems by either imposing taxes that internalize the external costs or regulating resource exploitation or usage.18

Given that subsidence commonly is a phenomenon characterized by imposed external cost due to legal conflicts or market failure, what are the barriers to mitigating external costs? At least three barriers inhibit the design of appropriate public policy measures. First, a significant barrier is sim-ply the lack of availability and public understanding of scientific literature; it is difficult to mitigate the unknown. Second, subsidence is not typically viewed as a catastrophic event or even necessarily the primary cause of large economic damages. As such, on the agenda of preparations for natural hazards, subsidence is low. Third, the potential for long delays in the observance of phenomena causes significant problems for public policy response.

referenceS

1. National Research Council, Reducing Disasters’ Toll, National Academy Press, Washington, DC, 1989. 2. USGS, Earthquakes, U.S. Geological Survey Information pamphlet, 1991. 3. Sprigg, W. A., Weather and Outbreaks of Disease, in WSTB, a newsletter from the Water Science and

Technology Board, National Research Council, 13, 2, April/May 1996. 4. EPRI, Measuring and managing environmental risk, Electric Power Research Institute, July/August 1985. 5. National Academy of Sciences/National Resource Council Committee on Ground Failure Hazards

Mitigation Research, Mitigating Losses from Land Subsidence in the United States, National Academy Press, Washington, DC, 1991, 58 pp.

6. Johnson, W. and Miller, G. C., Abandoned Coal-Mined Lands: Nature, Extent, and Cost of Reclama-tion. U.S. Bureau of Mines Special Publication 6-79, 1979.

7. Kansas Sinkholes, Geotimes, 33(11), 1988, p. 15. 8. Davies, W. E., Simpson, J. H., Ohlmacher, G. C., Kirk, W. S., and Newton, J. G., Map Showing Engineer-

ing Aspects of Karst in the United States, U.S. Geological Survey (USGS) Open-File Report 76-625, 1976, 1:7,500,000 scale.

9. Newton, J. G., Natural and Induced Sinkhole Development in the Eastern United States, International Association of Hydrological Sciences Publication No. 151, 1986.

10. Penland, S., Ramsey, K. E., McBride, R. A., Mestayer, J. T., and Westphal, K. A., Relative Sea Level Rise and Delta-Plain Development in Terrebonne Parish Region, 1988, Louisiana Geological Survey, Coastal Geology Publication Technical Report No. 4, 1988.

11. Russell, R. J., Howe, H. V., McGuirt, J. H., Dohm, C. F., Hadley, W., Kniffen, F. B., and Brown, D. A., Lower Mississippi River Delta, Reports on the Geology of Plaquemines and St. Bernard Parishes, Loui-siana Geological Survey Bulletin, No. 8, 1936.


12. Gatto, P. and Carbognin, L., The Lagoon of Venice: Natural Environment Trend and Man-Induced Modification, Hydrological Science Bulletin, 16, 4, 1981, pp. 379–391.

13. Gosselink, J., Tidal Marshes: The Boundary Between Land and Water, U.S. Fish and Wildlife Service, Office of Biological Services, 1980.

14. Stephens, J. C., Allen, L. H. Jr., and Chen, E., Organic soil subsidence, in Man-Induced Land Subsid-ence, Holzer, T. L., Ed., Geological Society of America, Reviews in Engineering Geology, Vol. VI, 1984, pp. 107–122.

15. Jones, L. L., External Costs of Surface Subsidence: Upper Galveston Bay, Texas, International Associa-tion of Hydrological Sciences Publication No. 121, 1977.

16. Prokopovich, N. P. and Marriott, M. J., Cost of Subsidence to the Central Valley Project, California, Association of Engineering Geologists Bulletin, 20(3), 1983, pp. 325–332.

17. HRB-Singer, Inc., Technical and Economic Evaluation of Underground Disposal of Coal Mining Wastes, Report prepared for U.S. Department of the Interior, Bureau of Mines, Contract No. J0285008, 1980.

18. Amandes, C. B., Controlling land surface subsidence—A proposal for a market based regulatory scheme, University of California at Los Angeles, Law Review 31, 6, 1984, pp. 1208–1246.

77

5 Kinds of Waste and Physiography of Waste Disposal Sites

5.1 kIndS and SourceS of WaSteS

All kinds of wastes—solid, liquid, and gaseous—have affected the safety and use of our water resources. Some of these wastes are hazardous to humans and wildlife. The different kinds of wastes and their main sources are given and discussed briefly in this chapter.

The United States currently faces a very large groundwater contamination problem. Although the total number of contaminated sites is unknown, estimates of the total number of waste sites where groundwater and soil may be contaminated range from approximately 300,000 to 400,000. Recent estimates of the total cost of cleaning up these sites over the next 30 years have ranged as high as $1 trillion.1

Several recent studies have raised troubling questions about whether existing technologies are capable of solving this large and costly problem. As a result of these studies, there is almost univer-sal concern among groups with diverse interests in groundwater contamination—from government agencies overseeing contaminated sites to industries responsible for the clean-ups, environmental groups representing affected citizens, and research scientists—that the nation might be wasting large amounts of money through ineffective remediation efforts. At the same time, many of these groups are concerned that the health of current and future generations may be at risk if contami-nated groundwater cannot be cleaned up to make it safe for drinking.

Theoretically, restoration of contaminated groundwater to drinking water standards is possi-ble. However, clean-up of contaminated groundwater is inherently complex and will require large expenditures and long time periods, in some cases, centuries. The key technical reasons for the dif-ficulty of clean-up include the following:1

Physical heterogeneity• —The subsurface environment is highly variable in its composition. Very often, a subsurface formation is composed of layers of materials with vastly differ-ent properties, such as sand and gravel, and even within a layer the composition may vary over distances as small as a few centimeters. Because fluids can move only through the pore spaces between the grains of sand and gravel or through fractures in solid rock and because these openings are distributed nonuniformly, underground contaminant migration pathways are often extremely difficult to predict.Presence of nonaqueous-phase liquids• (NAPLs)—Many common contaminants are liq-uids that, like oil, do not dissolve readily in water. Such liquids are known as NAPLs, of which there are two classes: light NAPLs (LNAPLs), such as gasoline, are less dense than water; dense NAPLs (DNAPLs), such as the common solvent trichlorethylene, are more dense than water. As an NAPL moves through the subsurface, a portion of the liquid will become trapped as small immobile globules, which cannot be removed by pumping but can dissolve in and contaminate the passing groundwater. Removing DNAPLs is further complicated by their tendency, due to their high density, to migrate deep underground,

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where they are difficult to detect and remain in pools that slowly dissolve in and contami-nate the groundwater.Migration of contaminants to inaccessible regions• —Contaminants may migrate by molecular diffusion to regions inaccessible to the flowing groundwater. Such regions may be microscopic (for example, small pores within aggregated materials) or macroscopic (for example, can serve as long-term sources of pollution as they slowly diffuse back into the cleaner groundwater).Sorption of contaminants to subsurface materials• —Many common contaminants have a tendency to adhere to solid materials in the subsurface. These contaminants can remain underground for long periods of time, and then be released when the contaminant concen-tration in the groundwater decreases.Difficulties in characterizing the subsurface• —The subsurface cannot be viewed in its entirety but is usually observed only through a finite number of drilled holes. Because of the highly heterogeneous nature of subsurface properties and spatial variability of con-taminant concentrations, observations from sampling points cannot be easily extrapolated and, thus, knowledge of subsurface characteristics is inevitably not complete.

Both the complex properties of the subsurface environment and complex behavior of contaminants in the subsurface interfere with and retard the ability of conventional pump-and-treat systems to meet drinking-water standards for contaminated groundwater.

At hazardous waste sites nationwide, industries and government agencies are spending millions of dollars trying to clean up contaminated groundwater. These clean-ups are required by federal and state laws passed in the last two decades—mostly in response to public concern that drinking contaminated groundwater may affect public health and the environment. The laws require that, in most instances, the contaminated groundwater be restored to a condition that meets state and federal drinking-water standards.

Recently, some have begun to question the current approaches to groundwater clean-up. Evi-dence suggests that restoring contaminated groundwater to drinking-water standards poses con-siderable technical challenges that may sometimes be insurmountable. For example, at one New Jersey site, a computer manufacturing company spent $10 million for removing toxic solvents from groundwater, but not long after the clean-up system was shut down, the solvent concentrations in some locations returned to levels higher than before the clean-up began. This company’s efforts and other similar attempts have raised concern about whether the amount spent to clean up the ground-water is proportionate to the benefits society receives. Businesses and government agencies paying for the clean-ups are calling for reconsideration of whether returning all contaminated groundwater to drinking-water standards is a realistic goal.

In 1980, prompted by the Love Canal incident, Congress, for the first time, made groundwater clean-up a high national priority with the passage of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), commonly known as the Superfund Act. CERCLA established a $1.6 billion federal fund (which has subsequently grown to $15 billion), the Superfund, to pay for cleaning up abandoned hazardous waste sites.2 CERCLA also provided an authority for the Environmental Protection Agency (EPA) to sue parties responsible for the contamination to recover clean-up costs. These groups have since become known as potentially responsible parties.

In 1984, Congress broadened the nation’s groundwater clean-up program by amending the Resource Conservation and Recovery Act (RCRA) to require clean-up of contamination at active facilities that treat, store, or dispose of hazardous waste. To continue handling wastes, operators of active RCRA site must agree to clean up existing pollution. RCRA also covers clean-up of con-tamination from leaking underground storage tanks containing petroleum products and other organic liquids.

Since the passage of CERCLA and the 1984 RCRA amendments, virtually all states have enacted laws granting them authority to require clean-up of sites with contaminated groundwater.3

Kinds of Waste and Physiography of Waste Disposal Sites 79

CERCLA and RCRA have strongly influenced the state laws, although some state laws are more stringent than the federal versions.

The primary type of groundwater contamination of concern in the United States today is con-tamination from hazardous chemicals. The use of such chemicals is ubiquitous: substances iden-tified in contaminated groundwater are used in everything from lumber treating to electronics manufacturing, fuels, food production, and agricultural chemical synthesis. When used as storage or disposed of on land, these chemicals may eventually migrate to the groundwater.

Common causes of groundwater contamination are accidental spills; intentional dumping; and leaks in storage tanks, industrial waste pits, and municipal or industrial landfills. In addition, signif-icant quantities of contaminants may be released through routine activities such as washing engines and rinsing tanks. Standard application of agricultural chemicals is also a source of groundwater contamination. The EPA estimates that about 1% of all drinking-water wells in the United States exceed a health-based limit for pesticides.4 Although pesticide application is a potentially important source of contamination, this report focuses on the point sources of contamination found at hazard-ous waste sites and other sites where hazardous chemicals have leaked or spilled into the environ-ment. Because point sources affect only a limited area, they present a more manageable problem than contamination of large areas of land with agricultural chemicals, which might far exceed the limits of clean-up technologies. Table 5.1 ranks chemicals found at hazardous waste sites in order of prevalence and gives common sources for these chemicals.

Because of the widespread use and disposal of hazardous chemicals on land, the groundwater contamination problem is potentially very large. However, estimates of the total number of con-taminated sites have varied.

Table 5.2 shows estimates of the number of sites in each of these categories as compiled from three different sources. As this table shows, the total number of sites where groundwater may be contaminated is likely to be in the range of 300,000–400,000. However, it is extremely important to recognize that the magnitude of the contamination problem varies widely at these sites. Ground-water contamination from a single leaking underground storage tank at a gas station may affect a relatively small area. On the other hand, contamination of CERCLA sites and at major Department of Energy (DOE) installations may be widespread and very difficult to clean up. The differences between these types of sites are illustrated by the costs of cleaning them up. According to recent EPA data, the average cost of cleaning up a leaking underground storage tank is $100,000, whereas the average cost of cleaning up a Superfund site is $27 million.5 According to the EPA (1993),5 the cost of cleaning up underground storage tank leaks varies widely and may be as low as $2000 for some sites and as high as $1 million for others. By far the bulk of the sites listed in Table 5.2 are contaminated from leaking underground storage tanks. The larger sites posing the greatest hazard to public health and the environment represent a relatively small portion of the total potential num-ber of sites.

5.1.1 solid WastEs

It is expected that by the end of this century, the solid wastes produced by the United States alone will approach 475 million tons.6 This is equivalent to 17 lb/capita/d. Table 5.3 shows the sources of this waste in percentages.

The solid wastes produced by sewerage systems are not included in this section but are incor-porated with liquid waste in the following section. Table 5.3 shows that the daily waste production from nonindustrial and municipal sites is over 50% of the total waste generated. Urban dwellers produce more waste than their rural counterparts. Table 5.4 shows the material components of this waste stream.

Most of this refuse has been disposed of in landfill sites within or near the community generat-ing the waste or by incineration. In the past, most landfill sites were little more than open dumps,


and the incinerators produced ash and hazardous and noxious gases, which were introduced into the atmosphere.

Future solid waste generation in industrial and institutional sectors is dependent upon the types of industry located in the urban areas and the number of employees they bring into these areas. Large-scale industrial development could greatly increase quantities of waste, and the population associated with these industries will also increase quantities of waste from hospitals, schools, and other institutions.

The main sources of solid wastes in industry are wood factories; paper mills; steel and alumi-num factories; all kinds of packing companies; glass factories; and industries that deal with metal-lurgy, food, and chemicals.

Urban areas generate a variety of solid waste materials from households, hospitals, and clinics, which may include bottles, syringes, toxic materials, radioactive substances, and dressings.

Agricultural solid wastes may be produced in rural areas as crop wastes, agricultural-processing wastes, animal manure, and hazardous pesticide containers. Some crop wastes are disposed of by being plowed back into the soil, burned on site, or used as feed. However, in all instances, the waste moves in a continuous cycle and eventually into the air, soil, or water. Returning the wastes to the

table 5.1the 25 most frequently detected groundwater contaminants at hazardous waste sites

rank compound common sources

1 Trichloroethylene Dry cleaning, metal degreasing

2 Lead Gasoline (prior to 1975), mining, construction material (pipes), manufacturing

3 Tetrachloroethylene Dry cleaning, metal degreasing

4 Benzene Gasoline, manufacturing

5 Toluene Gasoline, manufacturing

6 Chromium Metal plating

7 Methylene chloride Degreasing, solvents, paint removal

8 Zinc Manufacturing, mining

9 1,1,1-Trichloroethane Metal and plastic cleaning

10 Arsenic Mining, manufacturing

11 Chloroform Solvents

12 1,1-Dichloroethane Degreasing, solvents

13 1,2-Dichloroethene Transformation product of 1,1,1-trichloroethane

14 Cadmium Mining, plating

15 Manganese Manufacturing, mining, occurs in nature as oxide

16 Copper Manufacturing, mining

17 1,1-Dichloroethene Manufacturing

18 Vinyl chloride Plastic and record manufacturing

19 Barium Manufacturing, energy production

20 1,2-Dichloroethane Metal degreasing, paint removal

21 Ethylbenzene Styrene and asphalt manufacturing, gasoline

22 Nickel Manufacturing, mining

23 Di(2-ethylhexyl)phthalate Plastics manufacturing

24 Xylenes Solvents, gasoline

25 Phenol Wood treating, medicines

Note: This ranking was generated by the Agency for Toxic Substances and Disease Registry using groundwater data from the National Priorities List of sites to be cleaned up under CERCLA. The ranking is based on the number of sites at which the substance was detected in groundwater.


soil is a low-cost method that returns organic matter and nutrients to the land. Burning crop wastes is an effective method of controlling plant diseases and weeds, and it eliminates excessive crop wastes detrimental to the soil if plowed under. However, burning crop wastes creates problems of air pollution.

Abandoned transformers, batteries, vehicles, large appliances, and furniture are considered solid wastes, and are produced in both urban and rural areas.7

Dumping these solid wastes in disposal sites8 or landfills may affect water resource systems. If they are near streams or above groundwater aquifers, the leachate produced from these sites will move into the subsurface9 and groundwater resources. A more complete analysis of this subject is given in Chapter 7.

5.1.2 liquid WastEs

Liquid wastes are the main sources that contaminate water resource systems, either through the sur-face-water networks such as rivers, canals, and drains or into groundwater aquifers because they can easily migrate downward into the porous soils and fractured rocks to the groundwater reservoirs.

Some principal waste sources contaminating water resource systems include the following:10

1. Industrial wastewater that is contained in surface impoundments (lagoons, ponds, pits, and basins)

2. Liquids derived from municipal and industrial solid refuse and sludge that are disposed of on land

table 5.2number of hazardous waste sites where groundwater may be contaminated

Site category

Source of estimate

ePa, 1993russell et al.,

1991office of technology

assessment, 1989

CERCLA National Priorities List 2,000 3,000 10,000

RCRA corrective action 1,500–3,500 NA 2,000–5,000

Leaking underground storage tanks 295,000 365,000 300,000–400,000

Department of Defense 7,300 (at 1,800 installations) 7,300 8,139

Department of Energy 4,000 (at 110 installations) NA 1,700

Other federal facilities 350 NA 1,000

State sites 20,000 30,000 363,000–466,000

Total 330,150–332,150 NA 363,000–466,000

Note: The numbers presented in this table are estimates, not precise counts. In addition, at some of these sites, groundwa-ter may not be contaminated. For example, the EPA (1993) estimates that groundwater is contaminated at 80% of CERCLA National Priorities List sites. There is also some overlap in site categories. For example, 7% of RCRA sites are federal facilities, and 23 DOE sites are on the CERCLA National Priorities List (EPA, 1993). NA indicates that an estimate comparable to the other estimates is not available from this source.

table 5.3Percentage of solid wastes generated in the u.S. per day

Residential 34

Commercial 14

Bulky wastes 4

Industrial 48

Total 100


3. Sewage waste from urban areas that is discharged to septic tanks and cesspools 4. Storm water runoff in rural and urban areas that is collected, treated, and discharged to the

land 5. Brine from petroleum exploration and development that is injected into the ground or

stored in evaporation pits 6. Solid and liquid wastes from mining operations that are disposed of in tailing piles or

lagoons or discharged to land 7. Domestic, industrial, agricultural, and municipal wastewater that is disposed of in wells 8. Animal feed lot waste that is disposed of on land and in lagoons

The sources of potential contaminants and their various routes to water resources systems are shown in Figure 5.1. Table 5.5 lists the waste disposal sources and their relative impact on the water resources environment.

Industrial wastewater impoundments11 are a serious source of groundwater contamination because of their large number and their potential for leaking hazardous substances that are rela-tively mobile in the groundwater environment. In some heavily industrialized sections, regional problems of groundwater contamination have developed where the areal extent and the toxic nature of the contaminants have prevented the use of groundwater from shallow aquifers. Contaminated groundwater originating from impoundments at industrial establishments can be even more impor-tant because of the potential for migrating to local water supply wells.12

Solid waste disposal sites can be sources of groundwater contamination because of the gen-eration of leachate caused by water percolating through the bodies of refuse and waste materials. Precipitation falling on a site either becomes runoff, returns to the atmosphere via evaporation and transpiration, or infiltrates the landfill that produces leachate. This leachate is a highly mineralized

table 5.4Sources and percentage of refuse by weight of an average municipal refuse from studies made by Purdue university

component rubbish Percentage of all refuse by weightPaper 42.0

Wood 2.4

Grass 4.0

Brush 1.5

Greens 1.5

Leaves 5.0

Leather 0.3

Rubber 0.6

Plastics 0.7

Oil, paints 0.8

Linoleum 0.1

Rags 0.6

Street sweepings 3.0

Dirt 1.0

Unclassified 0.5

Total 64.0

Food wastes 12.0

Noncombustibles (metals, glass, and ashes) 24.0

Total 100.0

Source: From REA, Modern Pollution Control Technology, Vol. II, Staff of Research and Education Association (REA), 1980.


Surface waterGround water

Ocean

Disposalwell

Landspread

Land disp.effluent

Municipallagoon

Industriallagoon

Tailingpipe

Brinepipe

Feed lotlagoon

Injectionwell

Mininglagoon

pit or basin

Industrialtreatment

plant

Municipaltreatment

plantSludge

Septictank

Urban Industrial Mine Oil & Gas Rural

Liquid LiquidSolid Solid Liquid LiquidSolid LiquidSolid

Sewer Landfill

fIgure 5.1 Waste disposal routes of contaminants from solid liquid wastes.

table 5.5

Waste disposal sources and their impactsWaste disposal practice frequency

reportedPrincipal

contaminantstypical

hazard to health

typical size of affected area

Land disposal of solid waste C, I, Hm, P

Municipal I I b

Industrial III I b

Municipal wastewater N, C, Hm

Sewer system III II a

Treatment lagoons III II b

Petroleum exploration and development S, C, O

Wells and pits II III b

Mine waste Sa, I, Hm

Coal III III b

Others III II b

Agricultural N

Cattle and other III III c

Note: I = high; II = moderate; III = low; A = acid; B = bacteria; C = chloride; Hm = heavy metals; I = iron; M = MBAS; N = nitrate; O = oil; P = phenols; S = sodium; Sa = sulfuric acid; T = temperature; a = small area but can be regional due to high density of individual sources; b = can affect adjacent properties; c = contained one property.

Source: Modified from Shuckrow, A.J., Pajack, A.P., and Touhill, C.J., Hazardous Waste Leachate Management Man-ual, Noyes Data Corporation, New Jersey, 1982.


fluid containing such constituents as chloride, iron, lead, copper, sodium, nitrate, and a variety of organic chemicals. Where manufacturing wastes are included, hazardous constituents are often present in the leachate (e.g., cyanide, cadmium, chromium, chlorinated hydrocarbons, and PCB). The composition of the leachate is dependent upon the industry using the landfill or dump.

5.2 tyPeS of WaSte

5.2.1 urban WastEs

Septic tanks and cesspools13 rank highest in total volume of wastewater discharged directly to groundwater and are the most frequently reported sources of contamination. However, most prob-lems are related to individual homesites or subdivisions where recycling of septic fluids through aquifers has affected the private wells used for drinking water. Except in locations where such recycling is so quick that pathogenic organisms can survive, the overall health hazard from on-site domestic waste disposal is only moderate, with relatively high concentrations of nitrate representing the principal concern.

5.2.2 municipal WastEs

Municipal wastewater follows one of three routes to reach groundwater: leakage from collecting sewers, leakage from the treatment plant during processing, and land disposal of the treatment plant effluent. In addition, there are two indirect routes: effluent disposal to surface-water bodies, which recharge the aquifers, and land disposal sludge, which is subject to leaching. The volume of waste-water entering the water resources systems from these various sources is substantial. There have been many documented cases of hazardous levels of constituents of sewage or storm water affecting well-water supplies.14,15

Municipal and industrial sludge is the residue remaining after treatment of wastewater.16 Sludge may be a product of physical, biological, or chemical treatment or a combination thereof. Groundwater quality degradation can be caused by land spreading of sludge because organisms (such as viruses), chemical ions, and compounds can be leached by precipitation and percolate to groundwater.

5.2.3 pEtrolEum WastE

Disposal of brine from oil and gas17 production activities has been a major source of groundwater contamination in areas of intense petroleum exploration and development. Most oil-field brines today are disposed of through injection into oil-producing zones or deep saline aquifers by utilizing old production wells or brine injection wells. Many of these wells are poorly designed for injec-tion, however, and allow saltwater to enter the freshwater formations through ruptured or corroded casings.

As the American economy expanded during the 1950s and 1960s, industries sought new meth-ods for managing wastes. The toxic effects of many chemicals were recognized and industries required an inexpensive method of management that would isolate the chemicals from the environ-ment. Deep-well injection was a disposal method that had developed in the oil industry during the 1930s. This technology was soon adopted by petrochemical industries.

During the 1960s and 1970s, the deep-well injection industry grew until there were at least 209 wells injecting industrial waste in 1974. Even though the industry experienced no major operations problems or contamination incidents during this time, the American public had become quite con-cerned with both air and water pollution by the late 1960s. Consequently, environmental laws to control air and water were passed in the early 1970s.18

In 1984 and 1985, two publications were released that brought deep-well injection to the fore-front of the hazardous waste debate. In the first publication, waste generators and managers were surveyed, and the quantities of hazardous waste produced and managed were estimated. The survey


revealed that deep-injection wells received almost 60% of the hazardous waste disposed. The second publication contained a negative assessment of the technology and history of deep-well injection.

When the Safe Drinking Water Act (SDWA) was enacted in 1974, the law required the EPA to set minimum standards that the states were to adopt in their Underground Injection Control (UIC) Programs. These new regulations, adopted in 1980, contained a classification system for injection wells. This classification system (Table 5.6) is based on three factors: the industries involved, the fluid being injected, and the location of the injection zone in relation to potable water.18,19

5.2.4 mining WastE

All forms of mining can result in products and conditions that may contribute to groundwater con-tamination. The patterns of groundwater recharge and movement responsible for the distribution of contaminants are highly variable and inherently dependent upon the mining practice itself and local conditions of geology, drainage, and hydrology.

Associated with both surface and underground mining, refuse piles20 and slurry lagoons are prob-ably the major potential sources of groundwater contamination. Where aquifers underlie these sources, water with a low pH and an elevated level of total dissolved solids can percolate to groundwater.

The importance of resource development to the world economy demands a full understanding of the impact from the extraction of natural resources to the human environment as a basis for deci-sion making on the part of government as well as the extraction industry. Complete protection of the environment is sometimes impossible; thus, the implementation of decisions to mine balanced against the benefit to be gained is important.

Minerals are the basis for materials upon which civilization depends. The environmental impact of mining is complex and involves geographic, geologic, technical, and socioeconomic parameters.

A recent text, Environmental Effects of Mining, by Ripley, Redmann, and Crowder21 provides an excellent background on environmental hydrogeology as a further reference. The book charac-terizes the sequential stages of mining activities:

table 5.6

classification of injection wellsClass I Wells used by generators of hazardous waste, or owners or operators of hazardous waste management

facilities to inject hazardous wastes beneath the lowermost formations containing, within one-quarter (1/4) mile of the well bore, an underground source of drinking water. Class I includes other industrial and municipal disposal wells that inject fluids beneath an underground source of drinking water.

Class II Wells that inject fluids: (1) which are brought to the surface in connection with conventional oil or natural gas production, (2) for enhanced recovery of oil or natural gas, and (3) for storage of hydrocarbons that are liquid at standard temperature and pressure.

Class III Wells that inject for extraction of minerals including (1) mining of sulfur by the Frasch process, (2) in situ production of uranium or other metals (but only from ore bodies that have not been mined conventionally), and (3) solution mining of salts or potash.

Class IV Well used to dispose of hazardous or radioactive wastes into or above formations that, within one-quarter (1/4) mile, contain an underground source of drinking water.

Class V Wells not covered under the other classes. These include air conditioning return flow wells; certain multiple use cesspools; cooling water return flow wells; drainage wells; dry wells; recharge wells; saltwater intrusion barrier wells; sand or other backfill wells; multiple use septic systems; subsidence control wells; radioactive waste disposal wells (other than Class IV); wells associated with recovery of geothermal energy; wells for solution mining of conventional mines (such as stope leaching); wells for injection of spent brine after the extraction of halogens or their salts; injection wells used in experimental technologies; wells used for in situ recovery of lignite, coal, tar sands, and oil shale.

Source: From 40 CFR 146.5.18


1. Exploration, which may involve geochemical or geophysical techniques, followed by the drilling of promising targets and the delineation of ore bodies.

2. Development, i.e., preparing the minesite for production by shaft sinking or pit excavation, building access roads, and constructing surface facilities.

3. Extraction, i.e., ore-removal activities that take place at the minesite itself, namely, extrac-tion and primary comminution (or crushing).

4. Beneficiation (or concentration), which takes place at a mill usually not far from the mine-site; at this point (except in the case of coal), a large fraction of the waste material, or gangue, is removed from the ore.

5. Further processing, which includes metallurgical processing and one or more phases of refining; it may be carried out at different locations.

6. Because every ore body is finite, a final decommissioning stage is required through which the disturbed area is returned to its original state or to a useful alternative.

As the authors state, these stages are generally not discrete but may overlap or take place simultaneously. In subsequent chapters of the book, however, each is discussed in its context of environmental effects.

5.2.5 industrial WastE

Industrial waste, sewage effluent, spent cooling water, and storm water are discharged through wells into fresh- and saline-water aquifers in many parts of the world. The greatest attention in existing literature has been given to deep disposal of industrial and municipal wastes through wells normally drilled 1000 ft or more into saline aquifers.

Some environmental impacts associated with subsurface injection through wells are as follows:22

1. Groundwater contamination 2. Surface-water pollution 3. Alternation of hydraulic conductivity 4. Land subsidence or earthquakes 5. Contamination of mineral resources

The generation and disposal of large quantities of animal waste at locations of concentrated feeding operations is another environmental problem. There are three primary mechanisms of groundwater contamination from animal feed lots23 and their associated treatment and disposal facilities: (1) run-off and infiltration from feed lots, (2) runoff and infiltration from waste products collected from the feed lots and disposed of on land, and (3) seepage or infiltration through the bottom of a waste lagoon. The principal contaminants are phosphate, chloride, nitrate, and, in some cases, heavy metals.

Figure 5.1 illustrates the sources of liquid contamination and the different activities involved in disposing of them into different environmental sites.

5.3 gaSeouS WaSteS

5.3.1 industrial WastEs

Industrial activities produce two classes of contaminants or pollutants into the atmosphere. The first includes solid and liquid particles that may be designated as particulate matter, e.g., dusts found in the smoke of combustion and as droplets of cloud and fog. The term aerosol describes the entire system of particles of colloidal size (of a maximum of 1 µm) together with the gas in which they are suspended. The second class includes the compounds in the gaseous state that are known as chemi-cal pollutants. One group of chemical pollutants of industrial and urban areas, produced directly from a source on the ground (of primary origin), includes the following gases: nitrogen oxides (NO,


NO2, NO3), CO, SO2, and hydrocarbon compounds. In polluted air, certain chemical reactions take place among the components injected into the atmosphere, generating a secondary group of pol-lutants; e.g., SO2 may combine with oxygen to produce SO3, which in turn reacts with suspended droplets of water to yield sulfuric acid, that is both irritating to organic tissues and corrosive to many inorganic materials.

Also, isolated industrial activities can produce pollutants far from urban areas, e.g., processing of sulfide ores, by heating in smelters close to the mine, leads to the release of enormous concen-trations of sulfur compounds that can be destructive to vegetation. Another example of industrial wastes that leads to “Bergkrankheit” (a mountain disease that causes mortality from lung cancer among pitchblende miners in Austria) is the radioactive gas radon, which emits alpha particles.24

The ozone layer (11–15 mi) is a region of concentration of ozone molecules (O3), which is pro-duced by the action of ultraviolet rays upon ordinary oxygen atoms. The ozone layer serves as a shield, protecting the earth’s surface from most of the ultraviolet radiation found in the sun’s radia-tion spectrum. If excessive ultraviolet radiation reaches the earth’s surface, it will destroy all the exposed bacteria and severely burn animal tissues and plants. Therefore, the presence of the ozone layer is essential in the environment of the biosphere. Conversely, the ozone, which produces a toxic and destructive gas by the action of sunlight upon nitrogen oxides and organic compounds (e.g., photochemical reactions brought about by the presence of sunlight on hydrocarbon com-pounds), may lead to a toxic product known as ethylene.25a, 25b

Nuclear test explosions inject a wide range of particulates into the atmosphere, including many radioactive substances capable of traveling thousands of miles in the atmospheric circulation. Some of these pollutants belong to a very special and dangerous class as they are the sources of ionizing radiation, which is capable of tearing off electrons from atoms that intercept radiation.25

5.3.2 radon risk

Radon is a cancer-causing radioactive gas. It comes from the natural (radioactive) breakdown of uranium in soil, rock, and water and gets into the air that we breathe. High levels of indoor radon are found in every state of the United States and are estimated to cause many thousands of deaths each year.

Radon gas is found in nearly all soils, and it typically moves up through the ground to the air above and into our homes through cracks and other holes in the foundation. Although radon from soil gas is the main cause of radon problems, it sometimes enters the house through the well water and can be released into the air when the water is used for showering and other household uses.

The geology of the site and its radon potential may give an idea about the radon in a house and if it has an indoor radon problem. Scientists evaluate the radon potential of an area and create a radon potential map by using a variety of data that includes the uranium or radium content of the soils and underlying rocks, and the permeability and moisture content of the soils. The amount of radon in the air is measured in “picocuries per liter of air,” or pCi/L. Sometimes it is expressed in working levels (WLs) rather than picocuries per liter (pCi/L).

Because the level of radioactivity is directly related to the number and type of radioactive atoms present, a house having four picocuries of radon per liter of air (4 pCi/L) has about eight or nine atoms of radon decaying every minute in every liter of air inside the house. A 1000 ft2 house with 4 pCi/L of radon has nearly 2 million radon atoms, decaying in it every minute.

Radon levels in outdoor air, indoor air, and groundwater can be very different. Radon in outdoor air averages about 0.2 pCi/L, indoor air averages about 2 pCi/L, and soil air ranges from 20 to more than 100,000 pCi/L. The amount of radon dissolved in groundwater ranges from about 100 to nearly 3 million pCi/L. Testing for radon in homes is easy and can be carried out by radon test kits, which are available at hardware stores and other retail outlets.

Many publications provide information on radon gas. Most recent publications on this subject include the following: Measurement and Determination of Radon Source Potential by Allan B.


Tanner;26 “Development of EPA’s Map of Radon Zones” by White, Gundersen, and Schumann in the 1992 International Symposium on Radon and Radon Reduction Technology;27 and “Radon in the Geological Environment” by Reimer and Tanner.28

5.3.3 ForEst groWth rEduction by air pollution29

Little is known about the influence of ozone gas on forest growth although it is the most widespread gaseous air contaminant that influences U.S. forests today. Photosynthetic response to ozone shows a certain reduction in carbon dioxide assimilation following exposure to ozones for a certain time.

Elevated atmospheric fluoride can reduce the growth of trees contaminated from industrial sources as indicated by research conducted in the western United States. Also, the influence of SO2 exerts on plant photosynthesis has received more research attention than any other air pollutant, because it may cause, together with other factors, large reductions in the photosynthetic rate of the alfalfa plant.

5.3.4 acid rain30,31

The world’s total fossil fuel reserve is estimated to contain about 10 trillion tons of carbon. The temperature of the lower atmosphere is estimated to increase from 2.5 to 3°C for every doubling of CO2 in the atmosphere.

The acidified wet (acid rain) and nonacidic precipitation leads to acid disposition. The former is enriched in sulfuric, nitric, carbonic, chloride, fluoride, and organic acids, and may react with soils and surface waters in such a way as to increase leaching of metals and nutrients.

The quantification of corrosion of limestones carried by acid precipitation depends on many factors, namely, the amount of precipitation and its pH value, temperature, global radiation, effec-tive catalysts, buffer capacity of the soil, soil moisture, and geological features of the saturated zones. The hydrogen ion concentration is greatly affected by climatic and meteoric influences in space and time. Figure 5.2 illustrates the impacts of acid rain.

5.3.5 minEs

There are several environmental impacts of mineral and fuel extraction processing. A few of these are as follows:

acid mine drainage32,33

Acid mine drainage (AMD) is one of the earliest-recognized water pollution sources and has been the focus of research activity for decades. It causes pollution problems for the coal industry as well as for other mining industries. Several methods of treatment and ways of controlling surface water drainage were considered to mitigate or minimize acid drainage.

Neutralization of AMD water with lime or limestone results in the generation of a waste slurry (sludge) containing the precipitates from the neutralization reactions as well as unreacted reagents. The main constituents of the solid sludge are iron, aluminum, sulfates and hydroxides, and unused calcium carbonate or hydroxide.

Several factors are to be considered prior to applying of spray irrigation of neutralization sludge:

1. Erosion of the sludge during high- and medium-intensity rainfall is readily apparent and undesirable.

2. No gross pollution is observed in the runoff from sludge-irrigated areas during mild pre-cipitation events.

3. Flat topography on sites proposed for spray irrigation of neutralization sludge is essential to prevent erosive loss of sludge during precipitation events.


4. Sludge application appears to have a slight beneficial effect on the establishment and main-tenance of a vegetative cover.

Studies on the use of drying beds of AMD sludge indicated that the drainage rate through the sludge and sand averaged 26 L/d−1 m−2 (0.6 gal/d−1 ft−2), whereas the sludge solids appeared to stabilize near 20% within 20 d drying time when using lime-neutralized coagulant-treated sludge in summer operations.

AMD may be controlled by (a) air sealing of the underground mine to prevent oxygen from entering the mine, which would stop the oxidation of pyrite in the mine and reduce the produc-tion of iron and acidity; (b) reducing the amount of pollution source, rechanneling streams to establish drainage away from the mines, and constructing solid “dry” seals in portals through which water could not pass; and (c) revegetating disturbed areas to prevent erosion and stabilize the backfills.

Aquifer: Saturated

Zone

KARST TERRANE

Geologic Substrata

gypsum, sulfates and chlorides

To Karst River or Outflow

Output (discharge)

Soil: unsaturated

zone

EVAPORATION Organic matter

ABOVE GROUND BIOMASS

TRANSPIRATION SOx NOx

Wet and dry deposition (washout and fallout)

COx CFCs

GASEOUS EXHALATION

(CO2, H2S, etc.)

Zone of Maximum Limestone Corrosion

Water Table

MaximumBiochemical activity

Inorganic acidic medium

Washout rom

foliage

REC

HA

RGE

GLOBAL CHANGE OF TEMPERATURES

(ozone disruption andgreenhouse effect)

CLOUD

fIgure 5.2 A flow diagram of acid rain. (From Kramer, J.R. et al., Streams and lakes, in committee on monitoring assessments of trends in acid deposition, Long Term Trends, National Academy Press, Washing-ton, DC, 1986, pp. 231–249.)


coal mining

The mining of coal has a strong environmental impact on the land and water of the coal fields and on the miners. It has caused a terrifying record of death and injury from explosion, fires, and cave-ins. Another hazard lies in the inhalation of coal dust produced in mines causing the prevalent black lung disease—pneumoconiosis.

An explosion that killed 78 employees in the Farmington, West Virginia, mine in 1968 triggered an angry reaction from coal miners across the nation, who marched to Charleston, West Virginia, and Washington, DC, demanding protection at both the state and federal levels. Within months, the U.S. Congress passed the Coal Mine and Health Safety Act, which took effect on March 30, 1970.

America’s mining community celebrated the 25th anniversary of the Coal Mine Health and Safety Act on March 30, 1996, with special ceremonies and remembrances. “Coal miners were almost five times as likely to be killed in the mines in 1969 as they are today,” J. Davitt McAteer, assistant labor secretary for mine safety and health, told the audience at Department of Labor head-quarters in Washington, DC.

Before the law, about 250 workers died each year in coal-mining accidents. Between 1992 and 1994, the average number of coal-mining deaths dropped to fewer than 50 a year. Incidences of black lung disease, caused by exposure to respirable dust in coal mines, has been reduced during the past quarter century by an average of 75%, and the prevalence of the disease among miners has declined by more than two-thirds.34

mining of radioactive ores

A comparatively new environmental hazard is the ionizing radiation that is derived from the min-ing and milling of uranium ores. Very high radiation doses (of 5600 mrem/yr) measured in the uranium mines may be considered about 50 times as much of the average radiation dose from all sources. Besides the direct gamma radiation from the uranium ore, there is a radiation hazard in the inhalation of radon gas, a radioactive product of uranium decay. The gas produces other radioactive derivative products that lodge in the lungs and cause cancer; for example, some 50% of the miners of pitchblende (an ore of uranium and radium) died of lung cancer due to radiation exposure.

5.3.6 hydrocarbons

Marine oil pollution events have frequently occurred in the recent years with detrimental effects on the ecosystem of the shore zone, polluting beaches and damaging marine life of the coast. Evidence of widespread marine oil pollution comes from the collection of floating oil–tar lumps over wide reaches of the oceans. These lumps represent the nonvolatile residue of crude oil spilled in oil transportation.

Together with the major marine oil pollution to the seas and oceans, mention should be made of the tremendous number of oil wells (~ 800 wells) in the state of Kuwait that were set on fire by the Iraqis at the end of the Gulf Crisis in January 1991. A firm decision should be taken by the Security Council of the United Nations to avoid such dangerous and irresponsible action towards humans, animals, and plants, as well as to the living organisms in the sea.

5.4 HazardouS WaSteS

5.4.1 dEFinition

Hazardous wastes are defined as “Any waste material or a mixture of wastes which is toxic, cor-rosive, flammable and irritant; a strong sensitizer, which generates pressure through decomposi-tion, heat or other means; such a waste or mixture of wastes may cause substantial personal injury, serious illness or harm to wildlife during or as a proximate result of any disposal of such waste or mixture of wastes.”35 Hazardous wastes, which are the residues of normal industrial processes, can-


not be prevented but must be controlled by industry. The Environmental Protection Agency (EPA) estimates that, every year, 30 million tons of hazardous wastes are being generated in this manner.

One of the most interesting recent summaries on hazardous and radioactive waste management appeared in the August 1996 issue of Geotimes.36 These three articles: “Why Have Earth Scientists Failed to Find Suitable Nuclear Waste Disposal Sites,” by John B. Robertson, “Unsaturated-Zone Characterization for Low-Level Radioactive Waste Disposal in Texas,” by Bridget R. Scanlon, and “Beneath the Surface: Geophysical Aspects of Radioactive Waste Disposal,” by Don W. Steeples highlight some of the serious problems faced by environmental geoscientists in managing wastes of all types but particularly those of hazardous or radioactive nature.

Management of hazardous waste requires an understanding from many scientific disciplines: geography, geology, hydrology, hydrogeology, and biology. In addition to the scientific knowledge required, there must be an understanding of technical regulations, economics, permitting, and insti-tutional and public policy issues, for example, RCRA of 1976 and CERCLA of 1980. These statutes, plus others passed at federal level by Congress, must also be implemented with appropriate regula-tions and legislation by state statutes.

In addition, new techniques for waste management are evolving, and must be understood and implemented as they become acceptable practices, for example, state-of-the-art treatments in chemi-cal, physical, and biological treatments. Incineration has become an effective technique for destroy-ing certain types of hazardous wastes.

Another problem relates to the storage and transport of waste. One of the most difficult prob-lems in waste management relates to temporary storage and the generation of waste products and leachates that pollute the environment.

Finally, a major problem with regard to waste management practices of all types relates to the contamination of surface water, soil, and groundwater. Groundwater waste problems can be of the most insidious types.

In a recent text, Hazardous Waste Management Engineering by Martin and Johnson (1987),37 a table is presented that provides some sample alternatives for waste management at an individual site (see Table 5.7).

5.4.2 toxic matErials

Thompson et al.38 studied the sources of hazardous industrial wastes and stated that many industrial processes involve the use of materials that are potentially toxic if released into the environment. These materials are usually concentrated by waste treatment systems into a semisolid or sludge that should be disposed of without degrading the surrounding environment. Many of the most danger-ous waste products are organic chemicals. Incineration or other techniques are generally applied for oxidizing organic materials to produce nontoxic or less toxic compounds. Inorganic contami-nants that cannot be destroyed must also be disposed of in a way that limits their migration to the environment. Table 5.8 lists examples of industries that produce large amounts of hazardous inor-ganic wastes containing high concentrations of toxic metals, for example, cadmium, chromium, mercury, and lead. Although these materials are present in most industrial sludges as insoluble hydroxides or sulfides, changes in the pH or oxidation conditions of the environment can lead to their mobilization.

5.4.3 soil hazardous WastEs

Vegetables grown in areas with contaminated soils have proved to have high concentrations of lead (10–100 ppm in the ash). The development of highly sophisticated analytical techniques, such as the atomic absorption spectrophotometer that permits rapid microchemical studies of cells, soil, and water, facilitates investigation into the sources of trace elements and their actual role in physi-ological function. Trace elements, which are usually but not always present in the body in parts per


table 5.7the black-box approach

management option effluent X1 air emission X2 residue X3

Incinerator 0 Fugitive stack, PICa Ash and scrubber water

Secure L.F. Leaks (leachate) Air emission Remainder after lifetime

Land treatment Leachate and runoff Air emission Remainder on land

Storage tanks Leakage Air emission Pump out

Piles Leaching and runoff Air emission Pile residue

S.I. Leaching Air emission Residue in impoundment

Containers Leakage and spillage 0 Container contents

Treatment removal

Effluent + PITb Air emission Residue

Effluent + PITb Air emission Residue

Destruction Effluent + PITb Air emission Residue not destroyed

Fixation/stabilization Leachate Air emission Fixed solids

Encapsulation Leachate 0 Fixed solidsa PIC = Products of incomplete combustion.b PIT = Products of incomplete treatment.

Source: From Martin, E.J. and Johnson, J.H. Jr., Eds., Hazardous Waste Management Engineering, Van Nostrand Rein-hold, New York, 1987, p. 3.

table 5.8examples of major industries that produce major amounts of hazardous industrial wastes and their toxic constituents

Industry type of waste typical hazardous components

Electroplating and metal finishing Plating wastes and spent liquors Chromates, copper, nickel, phosphate

Metal refining and smelting Slags Aluminum fluoride, zinc, copper, lead

NiCad battery industry Production sludges Nickel, cadmium, lead

Leather production Tanning liquors Chromium, sulfide

Electronics industry Spent etching solutions and solder Copper, nickel, cadmium, lead

Dyestuff, petrochemical Spent catalysts Cobalt

Metallurgical industry Mine tailings, sludges Most heavy metals, selenium, antimony, arsenic

Dye manufacturer Dye liquors Sulfide, polysulfides

Chemical industry Effluent treatment sludges Copper, iron, nickel, fluoride, chromium, lead

Gas purification Spent oxide and sulfur residues Arsenic, antimony, sulfides, polysulfides

Power generation Flue gas cleaning sludges, fly and bottom ash

Heavy metals, calcium sulfite, and sulfate

Source: From Thompson, D.W. et al., Survey of available stabilization technology, in Toxic and Hazardous Waste Dis-posal, Pojasek, R.B., Eds., Ann Arbor Science Publishers, Ann Arbor, MI, 1, 1979, pp. 9–11.


million, may cause pathological conditions when found in a slight deficiency or in a slight excess of a particular element, as in the case of selenium and fluorine.

However, the fact that an element is present in soil does not mean that it is necessarily avail-able to plants or that it will dissolve in water, as its physical state and mineralogical criteria may determine its availability. Various soil waste sources include animal wastes, fertilizers, pesticides, plant residues, and saline waste waters. LeGrand39 discussed the movement of agricultural pollut-ants in groundwater and concluded that there were sufficient safeguards to minimize groundwater pollution. The unsaturated zone above the water table reduces almost all of the foreign bodies that are potential pollutants of the underlying groundwater. Fertilizers used to improve crop productivity may result in leaching of nitrogen and phosphorous to the groundwater.

The groundwater contamination of silica and nitrate may have resulted from the percolation of nitrate fertilizer and the leaching of silica through water-logged soil. Factors that tend to reduce the pollution of groundwater from wells and springs may be summarized as follows:40

1. A deep water table that allowed adsorption-slowed subsurface movement of pollutants and facilitated oxidation

2. Sufficient clay in the path of pollutants to favor retention or sorption of pollutants 3. A gradient beneath a waste site away from nearby wells 4. A great distance between wells and wastes

Pesticides contribute significantly to improve crop productivity, but they pose risks to humans and the environment. Two pesticides discovered in 1979 and 1982 in groundwater in certain areas of the United States were dibromochloropropane (DBCP) and ethylene dibromide (EDB), respectively. By 1986, a total of 19 different pesticides had been detected in groundwater in 24 states. The health effects of chemicals may be classified as follows:

1. Acute effects resulting from contact with high levels of a chemical over a short period of time are usually easier to identify because they occur soon after exposure, for example, nausea, skin irritation, etc.41

2. Chronic effects, which generally occur as a result of long-term exposure to low levels of a chemical, are harder to document, particularly because of the long-term interval between exposure and outcome.

Concentrations of pesticides in groundwater have been found at low levels; therefore, most of the concern has been focused on the potential for chronic effects such as cancer, mutations, birth defects, and immunological changes. However, there are great variations in the chemical properties of pesticides that control their tendency to leach to groundwater.

Local agricultural practices that may affect the potential for pesticides to contaminate ground-water vary greatly across the United States depending on the crops grown, local pest control needs, and the preferences of the grower.41 Also, animal wastes in soil, which lead to groundwater contami-nation with nitrates, are a result of leaching from livestock-feeding operations.

5.4.4 radioactivE WastEs

Holcomb42 states that the nuclear power and radioisotope industry in the 20th century have devel-oped greatly and presented a continuous problem in dealing with the management of radioactive waste materials. Natural decay is the only means of destroying radioactivity and, as the various waste radionuclides have decay rates ranging from days to thousands of years, treatment and processing (such as solidification techniques) become an important factor in radioactive waste management. The main two classes of radioactive wastes (radwastes) for which solidification techniques have been developed are high-level and low-level wastes. The high-level wastes are


those of fission products with a high level of penetrating radiation and high rates of heat genera-tion, and they include the liquids of high-activity radioactive wastes or their solidified products. Because of their high hazard and long decay times, considerable money and effort have been devoted to the removal of high-level wastes from solution and their solidification and shipping to centralized repositories for permanent emplacement. The danger and expense of handling these wastes can be reduced by allowing them to decay before final disposal, thereby reducing radio-activity and heat production in the waste. Present policy allows 10 yr of interim storage before final disposition.

The low-level wastes include a variety of materials with low levels of radiation or those radio-actively contaminated wastes that are generated from nuclear fuel cycle operations and facilities not specifically designated high level. The majority of these wastes are generated by nuclear power plants and are usually in the form (prior to solidification) of processed wastewater, evaporator concentrates, sludges, and filter aids. These wastes include a broad spectrum of materials varying widely in chemical and radioactive content.

5.5 PHySIograPHy of WaSte SIteS43,44

In the early 1970s, a period that has been termed “a decade of environmental action,” the subject of radioactive waste management continued to be of increasing public concern. Extensive research and development have been supported by the Atomic Energy Committee (AEC) to safely store certain types and quantities of solid and liquid radioactive waste materials in the deep underground formations (1,000–3,000 ft for the deep hydrologic environment, and about 3,000–12,000 ft for the petroleum industry).

There are many types of injection wells that are used to dispose of different forms of liquid wastes. The geological and hydrological criteria must be considered in siting wells used for the disposal of hazardous wastes. For siting a hazardous waste injection well, attention should be given to the nature of the host interval into which wastes will be injected and the adequacy of the confining units that separate the wastes in the host interval from the environment and drinking water supplies. Site-specific geologic, hydrologic, and structural conditions are to be considered for the selection of a site for a hazardous waste disposal injection well. Stratigraphically, the injection zone should be bounded at the top and bottom by a low-permeability confining zone that prevents the upward and downward migration towards freshwater aquifers. Both the injection and confining zones should have enough thickness and extend laterally far enough so that wastes remain in the injection zone and do not reach the discharge areas. Lithologically, the permeability and porosity parameters should be determined for both the injection and confining intervals to decide the best-suited rock type for each interval. The injection intervals that receive and house the wastes (without artificial fracturing by high pressure) should have high porosity and a permeability value in the order of ≈ 0.1–1.0 cm/s. For acidic wastes, which must be neutralized after injection in order to render them nonhazardous, a carbonate-rich injection zone is desirable because the reaction generates CO2 gas, which is generally dissolved in the groundwater of the injection zone. In contrast, the confining zone must be of very low permeability, in the order of 10−6–10−9 cm/s, for example, clay, shale, anhydrides, and possibly dense and unfractured carbonates (except for acidic wastes). Structurally, the hazardous waste injection sites are considered to be safe if faults and fractures represent pathways for waste migration through the injection zone but not into and through the confining units. Faults can also represent barriers to the migration of groundwater (and wastes) sealed with secondary materials, but generally they are considered as potential pathways.

Prewaste injection hydrofracturing should be avoided as it may extend into the confining units and create pathways out of the injection zone. Also, faults and other fractures should be avoided because, when a faulted injection horizon is under stress, the fluids enter the fault system, thus facili-tating movement and seismic activity. A full investigation of structural and tectonic complexities is recommended during the siting of disposal wells, especially in areas of tectonic activity.


The hydrochemical criteria deals with the compositions of the groundwater in the injection interval as well as in the confining units and is important because (1) reactions may occur between the wastes and the formation water in the injection zone, and (2) the composition of groundwater may reflect the history, age, and mixing of groundwater. Age dating of groundwater could be deter-mined by using radioactive isotopes such as C14 or Cl36.

The hydrologic aspects mainly include the hydrophysical characteristics of the injection zone and the hydrologic characteristics of the confining units. The former deals with the aquifer geom-etry parameters (e.g., thickness, areal extent, and form), the hydrophysical parameters of the host formations (e.g., permeability, k; porosity, Ø; pressure, P; temperature, T; and saturation, S), and its physiochemical parameters such as chemistry (including total dissolved solids, TDS), pressure, temperature, density, and compressibility.

Structural, physical, and hydraulic parameters of the confining and semiconfining formations adjacent to the host formation determine the boundary conditions of the host hydraulic system, that is, the degree of waste confinement. The host hydraulic system, which includes the aquifer and con-fining units, may be an open or a closed system. Larger amounts of waste can generally be injected into open hydraulic systems because the liquid within the aquifer can be displaced, but contamina-tion can occur at the open boundaries with adjacent hydraulic systems and should be avoided for injection of highly persistent and refractory wastes. Injection into more closed systems requires the use of relatively high injection pressures to compress subsurface materials and create storage space. Excessive injection pressures can fracture confining units and open the system boundaries, allowing uncontrolled contaminant migration.

5.5.1 pErmEablE Formations (3,000–12,000 Ft) containing connatE brinE

Disposal of large volumes of waste in porous beds, which are interstratified with impermeable beds in a synclinal structure, is of particular interest. Deep disposal wells have been utilized by the chemical, petrochemical, and steel industries. The application of deep-well injection for certain types of radioactive wastes needs more caution and precise studies from the reservoir engineer-ing point of view, in order to determine if there should be sufficient porosity or permeability in the receiving strata to receive “x” number of gallons of waste per day, if the well and the pumping equivalent should be properly protected against corrosion, or if the disposal well is properly cased and cemented from the surface to the disposal zone.43

Hydrogeologic information of the receiving formation is also required to define the rate of movement and direction of flow and, in short, to understand the effects of disturbing the hydro-logic system by injecting the wastes, for example, the potential effects of increasing the forma-tion pressure, such as fracturing confining beds and changing the hydraulic gradients. Continuing surveillance is quite necessary for all toxic waste injection wells to avoid any accidental contamina-tion of overlying freshwater aquifers.

5.5.2 impErmEablE Formations

Hydraulic fracturing in Shale formations

In the petroleum industry, the technique of hydraulic fracturing is widely used to increase oil recovery in reservoir rocks of low permeability. For waste disposal purposes, a well is drilled into a shale forma-tion rather than into an oil reservoir rock, and the aqueous wastes are mixed with preblended dry solids (principally containing cement). Then, the resulting slurry is pumped down the well and out into a con-formable, horizontal fracture in the thick shale formation at depths usually on the order of 1000–1500 ft. The well, which is cased by a strong steel casing, is prepared for the injection by perforating the casing at the desired depth and pressurizing the well with water. This pressure induces a fracture in the rocks into which the waste slurry is pumped, causing the fracture to extend. After the completion of the pumping phase, the cement slurry is allowed to harden under pressure to form a thin horizontal grout sheet. This procedure is then repeated successively up the well, creating a stack of horizontal grout sheets.44


Storage in crystalline bedrock44

Storage in deep impermeable basement rocks is sometimes found necessary for the disposal of high-level wastes below a site. For example, high-level radioactive liquid wastes at a chemical reprocess-ing plant in South Carolina are stored in the crystalline rock where it is separated from the overlying unconsolidated sediments (at a depth of approximately 1000 ft) by a clay bed known as saprolite, which is a residual weathered product of the crystalline rock. A long-term disposal facility that con-sisted of a concrete-lined vertical shaft (≈15 ft in diameter) would pass through the unconsolidated sediment and about 500 ft into the crystalline rock where six tunnels (each approximately 3500 ft long with a cross section of 26 ft wide × 28 ft high) were constructed. Waste feed and instrument lines from the surface would go into each of the tunnels through separately drilled service shafts.

Prior to repository in crystalline rocks, an exploratory drilling program should be conducted to determine the hydraulic and physical characteristics of the basement rock and the overlying sedi-mentary aquifer. These hydraulic and physical characteristics can be determined by obtaining con-tinuous rock-core samples from the overlying sediments. Hydrologic studies, including drill stem testing (DST) to calculate the bottomhole pressures (BHP), pumping tests of packed-off sections of the hole, and piezometer measurements of the several main aquifers that overlie the bedrock, can be conducted. From these tests, the permeabilities of the rock and the regional permeability of the fractured-rock zones can be estimated together with the hydraulic gradient, and extensive tritium tests can also be made.

Storage in basalt flows44

At the AEC Hanford Plant in Richland, Washington, approximately 25% of the tank-stored high-level wastes were in the form of salt cakes and sludges. This form was the result of Hanford’s in-tank solidification that reduced the high-salt-content waste to this form by successive passes from the tank through an evaporation cycle.

The bulk of the high-level wastes could be immobilized as salt cakes in the existing under-ground tanks and safely isolated in the underground concrete-tank structures for hundreds of years. The principal protection needed would be from erosion, requiring minimal surveillance. However, the salt cakes are retrievable, and their storage in underground tanks is considered an interim mea-sure until the long-term safety of this method is determined to be acceptable.

The AEC has started investigating the structure, stratigraphy, and hydrology of the basalt flows underlying the Hanford site for possible consideration as a long-term storage environment for the Hanford wastes. The information collected shows that more than 100 basalt flows, some as much as 200 ft in thickness separated by weathered basalt zones, are present to a depth greater than 10,000 ft in the center of the site.

Storage in Salt mines

The AEC’s ground disposal research and development program was directed in the past 30 years to use the underground salt formations for the isolation of high-level solidified radioactive wastes. Salt beds are generally located in areas of low seismic activity and widely separated from flowing aqui-fers. They are normally dry and impervious to water and have considerable compressive strength, being similar to concrete in this respect.

It may be interesting to mention that salt movements and diapirism of salt bodies penetrating younger beds are characterized by two phenomena: halokinesis and halotectonics.45 Halokinesis leads to the formation of salt domes or to piercing diapirs when there is a continuous supply of mother salt or where there are pressure contrasts. Halokinematics was proposed to define salt move-ments more precisely according to their cause.46 Because of the plasticity of salt, fractures seal or close rapidly.


In locations where salt dome structures exist, large spaces can be mined out and, even at depths of 1000 ft, two-thirds of the salt can be removed with only slight deformation of the support pillars.

5.6 enVIronmental concernS on HydrogeologIcal SyStemS

5.6.1 man-madE EarthquakEs47,48

There is a close relationship between humans and the surrounding physical environment, which is actually a dynamic system accommodated by human activities. The living or biological systems of the earth are progressively changing, as well as the nonliving physical aspects of the earth, which undergo change at an equal or greater rate. As a matter of fact, a dynamic system is more difficult to adopt human activities to a constantly changing situation than to an unchanging or static system. Human activities have made great physical and chemical changes to our planet in the past 50 years.

Earthquake activity can be explained by the theory of plate tectonics, which states that the earth’s crust is made up of rigid plates floating on an underlying layer and moving relative to each other in response to convection currents and resulting in the formation of subduction and rift zones. Human-made earthquakes may also result from pumping of waste fluids into deep-disposal wells as it is believed that this injection raises the fluid-level pressure in the reservoir (or the injection interval) for some distance from the well borehole and during the shutdown. This elevated pressure equalizes throughout the reservoir and at increasing distance from the well where the fluid pres-sure reduces the frictional resistance in fractures, and eventually, movement takes place and small earthquakes result.

5.6.2 transport oF pollutEd WatErs by subtErranEan karst FloW systEms

In karst regions, the water flow may be partially or totally turbulent and leads to the contamination process with little or no filtration or precipitation taking place, and it also leads to the ionic retarda-tion processes of adsorption or desorption of pollutants. As hydraulic conductivity and water-flow velocity are high in karst regions, the flow velocity of pollutants is also high, and therefore, karst water can be polluted very quickly in different pathways and directions in different velocities. The fluid movement and the pollutant migration depend greatly on the spatial distribution of faults and fissures. There is little contact between rock matrix and water in karstic aquifers where the water flow takes place through the solution channels (of irregular dimensions and directions).

In karst terrains, the passage of rainwater into the subterranean cavities normally carry polluted materials without being filtered as in other rocks. The velocity of flow of the groundwater is high in the karst in the order of several hundreds or thousands of meters per day, whereas outside the karst regions, they are usually of several meters per day.

Emili49 discussed the transport of intestinal pathogenic germs by subterranean karst systems and stated that the subterranean water courses are one of the characteristics of the karst that are of interest to geologists, hydrogeneticists, and also to epidemiologists. It concerns the question of whether the intestinal pathogenic bacteria, which are the main causative agents of typhoid, can be transported by karst rivers over large karst areas. Subterranean connections between sinkholes and springs have been proved in several occasions by the use of dyes. Emili also established the earlier-known rule that the waters of karst at points of observations (sources) are less polluted with bacteria of the coliform group than the waters at the sites of the sinkholes. This is clear proof that, in the subterranean course of karst rivers, there occurs a retention of bacteria that are much more resistant in an open environment than intestinal pathogenic germs. His opinion was that the transport of intestinal germs over greater distances by subterranean rivers in the karst area did not come into consideration practically. If, however, hydric epidemics of typhoid fever in the karst region are so frequent, such pollution of drinking water with pathogenic germs occurs as a rule in the vicinity of the water supply plants.


referenceS

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2. EPA, Superfund Fact Sheet: Who Pays for Superfund? EPA, Washington, DC, 1990. 3. EPA, An Analysis of State Superfund Programs: 50-State Study—1993 Update, EPA, Office of Emer-

gency and Remedial Response, Washington, DC, 1994. 4. EPA, National Pesticide Survey, Update and Summary of Phase II Results. EPA 570/9-91-020, EPA,

Office of Pesticide Programs, Washington, DC, 1992. 5. EPA, Cleaning Up the Nation’s Waste Sites: Markets and Technology Trends, EPA 542-R-92-012, EPA,

Office of Solid Waste and Emergency Response, Washington, DC, 1993. 6. REA, Modern Pollution Control Technology, Vol. II, Staff of Research and Education Association

(REA), 1980. 7. Klickat Regional Council, Klickat County Solid Waste Management Plan, unpublished report, 1977. 8. Blebs, R. T. and Scaro, E. C., Cost Accounting for Landfill Design and Construction Past and Present,

Proceedings of Waste Tech 85, Boston, October 28, 1985. 9. Prothro, M. G., An Overview Status of the Surface Water Toxic Control Program, Proceedings of the

Industrial Waste Symposium, San Francisco, 1989. 10. Shuckrow, A. J., Pajack, A. P., and Touhill, C. J., Hazardous Waste Leachate Management Manual,

Noyes Data Corporation, New Jersey, 1982. 11. Miller, D. W., Waste Disposal Effects on Groundwater, Premier Press, New Jersey, 1980. 12. U.S. Environmental Protection Agency, Handbook for Monitoring Industrial Waste Water, EPA, Wash-

ington, DC, 1973. 13. Patterson, J. W. et al., Septic Tanks and the Environment, Illinois Institute for Environmental Quality,

Chicago, 1971. 14. Soliman, M. M., Groundwater Quality Model of Greater Cairo, Research Report presented to the Egyp-

tian Academy of Science, 1982. 15. Soliman, M. M., Environmental Impacts of Irrigation by Sewage Water, P.P. International Conference

on Advances in Groundwater Hydrology, Tampa, FL, November 1988. 16. Page, A. L., Fate and effects of trace elements in sewage sludge when applied to agricultural lands, U.S.

EPA 670/2-74-005, 97. 17. American Petroleum Institute, Annual statistical review, American Petroleum Institute, Washington,

DC, 1975, p. 79. 18. Moffett, T. B., LaMoreaux, P. E., Smith, J. Y., and Dismukes, M. B., Management of Hazardous Wastes

by Deep-Well Disposal, The University of Alabama Environmental Institute for Waste Management Studies, Tuscaloosa, AL, Ch. 3, 1987.

19. LaMoreaux, P. E. and Vrba, J., Eds., Hydrogeology and Management of Hazardous Waste by Deep-Well Disposal, International Association of Hydrogeologists, a report of the Commission on Hydrogeology of Hazardous Wastes, Vol. 12, University of Alabama Press, 1990.

20. Martin, J. F., Quality of Effluents from Coal Refuse Piles, First Symposium on Mine and Preparation Plant Refuse Disposal, Washington, DC, 1974, pp. 26–37.

21. Ripley, E. A., Redmann, R. E., and Crowder, A. A., Environmental Effects of Mining, St. Lucie Press, Delray Beach, FL, 1996.

22. Stallman, R. W., Subsurface waste storage—the earth scientist’s dilemma, in American Association of Petroleum Geologists Memoir 18, Underground Waste Management Implications, Tulsa, OK, 1972, pp. 6–10.

23. Anderson, R. K., Feedlot wastes, System Management Division, Office of Solid Waste Management Programs, U.S. EPA, unpublished report, 1975.

24. Strahler, A. N. and Strahler, A. H., Environmental Geoscience—Interaction between Natural Systems and Man, Hamilton Publishing, Santa Barbara, CA, 1973, pp. 46–54, 151–154, 255–256.

25a. Spencer, J. M., Geological influence on regional health problems, in The Environmental Geology—Text and Readings, Tank, R.W., Ed., Oxford University Press, New York, 1983, pp. 459–460.

25b. Kramer, J. R., Andren, A. W., Smith, R. A., Johnson, A. H., Alexander, R. B., and Ochlent, G., Streams and lakes, in committee on monitoring assessments of trends in acid deposition, Long Term Trends, National Academy Press, Washington, DC, 1986, pp. 231–249.

26. Tanner, A. B., Measurement and Determination of Radon Source Potential: A Literature Review, U.S. Natl. Inst. Standards and Technology Report, NISTIR-5399, 1994, 190 pp.


27. White, S. J., Gundersen, L. C. S., and Schumann, R. R., Development of EPA’s map of radon zones, in The 1992 International Symposium on Radon and Radon Reduction Technology, U.S. Environmental Protection Agency, Research Triangle Park, NC, paper VIII-4, 1992, 14 pp.

28. Reimer, G. M. and Tanner, A. B., Radon in the geological environment, in Encyclopedia of Earth Sys-tem Science, Nierenberg, W. A., Ed., Academic Press, San Diego, CA, 1991, pp. 705–712.

29. Smith, W. H., Air Pollution and Forests—Interactions between Air Contaminants and Forest Ecosys-tems, Springer-Verlag, New York, 1981, pp. 44–50, 204–210.

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32. Grube, E., Jr. et al., Disposal of Sludge from Acid Mine Drainage Neutralization, EPA, Paper present at the NCA/BCR Coal Conference & Expo III, Louisville, KY, October 1976, pp. 1–18.

33. Hill, R.D., Elkins Mine Drainage Pollution Control Demonstration Project, paper presented at the 3rd Symposium on Coal Mine Drainage Research, Pittsburgh, PA, May 20, 1970.

34. LaMoreaux, P.E., Twenty-fifth anniversary of the Coal Mine Health and Safety Act, Environmental Geology, 27, 1996, pp. 71–72.

35. Doyle, R. D., Use of an extruder/evaporator to stabilize and solidify hazardous wastes, in Toxic and Hazardous Waste Disposal, Pojasek, R. B., Ed., Ann Arbor Science, Ann Arbor, MI, Vol. 1, 1979, pp. 65–66.

36. News & Features, Geotimes, 41, 8, August 1996, pp. 16, 22, and 26. 37. Martin, E. J. and Johnson, J. H. Jr., Eds., Hazardous Waste Management Engineering, Van Nostrand

Reinhold, New York, 1987, p. 3. 38. Thompson, D. W. et al., Survey of available stabilization technology, in Toxic and Hazardous Waste

Disposal, Pojasek, R. B., Eds., Ann Arbor Science Publishers, Ann Arbor, MI, 1, 1979, pp. 9–11. 39. LeGrand, H. E., Movement of Agricultural Pollutants with Groundwater, Agricultural Practices and

Water Quality, Willrich and Smith, Eds., Iowa State University Press, Ames, 1970, pp. 303–313. 40. Todd, D. K. and McNulty, D. E. O., Agricultural pollution, in Polluted Groundwater—A Review of the

Significant Literature, A Water Information Center, Huntington, NY, 1976, pp. 48–51. 41. EPA, Pesticides in groundwater: The concern, in Agricultural Chemicals in Groundwater: Proposed

Pesticide Strategy, U.S. Environmental Protection Agency, Office of Pesticides and Toxic Substances, 1987, pp. 21–29.

42. Holcomb, W. F., An overview of the available methods of solidification for radioactive wastes, in Toxic and Hazardous Waste Disposal, Pojasek, R. B., Ed., Ann Arbor Science Publishers, Ann Arbor, MI, 1, 1979, pp. 23–25.

43. Belter, W. G., Deep disposal systems for radioactive wastes, in Underground Waste Management and Environmental Implications, Cook, J. D., Ed., Proceedings of the Symposium, Houston, TX, 1971, pp. 341–347.

44. Stow, S. H. and Koleju, V., Geologic and hydrologic criteria for design of a deep disposal system, in Hydrogeology and Management of Hazardous Waste by Deep Well Disposal, a report of the Hydroge-ology of Hazardous Waste Commission of the International Association of Hydrogeologists, Vol. 12, 1990, pp. 21–38.

45. Assaad, F. A., A further geologic study on the Triassic formations of North Central Algeria with special emphasis on halokinesis, J. Petro. Geol. London, 4, 2, 1981, pp. 163–176.

46. Assaad, F. A., An approach to halokinematics and interplate tectonics (North Central Algeria), J. Petro. Geol. London, 6, 1, 1983, pp. 83–88.

47. U.S. Department of Energy, Geothermal energy and our environment, in Environmental Geology, Text and Readings, Tank, R. W., Ed., Oxford University Press, New York, 1983, pp. 35–82, 532–540.

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49. Emili, H., Possibility of transport of intestinal pathogenic germs by subterranean karst rivers, in KRS Jugoslavic Carsus Iugoslaviae, Zagreb, Petrik, M., Zagreb, 1969, pp. 465–467.

101

6 Environmental Impacts on Water Resource Systems

6.1 IntroductIon

As the world’s population continues to grow, it is evident that we must think very carefully in terms of development that meets the needs of the present without compromising the ability of future generations to meet their own needs and aspirations, i.e., truly sustainable development. It is clear, however, that some quite unsustainable development policies and practices, particularly concerning water management, have been followed. Economic and social change necessitate develop ment of water resources based on sound environmental principles. A sound scientific understanding should form the foundation upon which rational decisions regarding water resources management should be made.

The essential role of science in continued socioeconomic development, an area in which water resources are essential, is not a simple one. In managing our resources, it is evident that not only does nature affect humans, human activities can also have devastating results on nature. It has become evident now, for example, that some human activities appear to be leading to possible major climate changes. The probable consequences are not yet known with certainty, but it is clear that climate change would result in a redistribution, in time and space, of our water resources. To understand this change and be able to cope with it, we must have a much stronger scientific understanding of the processes involved. The approaching problems, coupled with the many existing environmental stresses (including, for example, land and water pollution, erosion and sedimentation, and natural and artificial hazards), emphasize the need for continued development of human potentials, educa-tion, training, and public understanding as essential elements in a major international effort.

The responsibility of water scientists and engineers, then, must be, with full consideration of the changing environment, (1) to develop and maintain information on the availability of water resources; (2) to assess, monitor, and predict the resulting quality of water bodies and water-related environment; (3) to develop a better scientific understanding of the effects of human activities that influence hydrological regimes (especially those resulting from climate change); and (4) to provide decision makers with the necessary information in properly constructed formats so that they realize the problems and the importance of the hydrological sciences as a basis for proper environmental management—especially of water resources—and react appropriately.

6.2 clImatIc cHangeS and tHeIr effect on Water reSourceS

The climatic changes1 foreseen and the probable consequent changes in the physical environment show that our present understanding of water resources and of the hydrological cycle is not suffi-cient. Prediction of new hydrological regimes will require a better understanding of the systems and a better capability for quantitative analysis than is now available. More than ever before, decision makers must be made aware of the importance of water problems, and they must be given recom-mendations for action based on sound scientific rationale.

Hydrology and the study of water resources for sustainable development in a changing environ-ment open a new era in the development of water sciences and management, and are designed to provide an international focal point for a broad coordinated effort in hydrology and the scientific


bases for water management. They represent the combined efforts of national, regional, and inter-national governmental organizations.

6.3 Surface-Water PollutIon

The water quality aspects of water resources are becoming increasingly important. During the last decade, attention was focused on many new problems and approaches for their prediction. Besides the pollution from point and nonpoint sources such as agriculture and deforestation, we must also consider the problem of pollutant precipitation from the atmosphere. Simply adding water quality parameters to classical hydrological formulas is no longer sufficient. Detailed small-scale hydro-logical investigations of a different nature are needed to predict pollution pathways. It is necessary to research the ways in which polluting substances, under certain conditions, are transformed, com-bined with other substances, temporarily retarded somewhere, and then suddenly released. Non-point pollutant transport and transformation processes are greatly influenced by vegetation, land use, and soil processes, including snowmelt aspects, and these continue in unsaturated and saturated zones of soils, in rivers and lakes, and, finally, in the estuaries in the brackish interface between the river and the sea.

Flow patterns on hill slopes and within the soil profile depend on the interactions between the modified rainfall inputs described previously and the drainage basin geology, pedology, and topog-raphy. The nature of these interactions determines the division of hill slope outputs into quickflow and baseflow streams, and, thus, has important implications for the form of the storm hydrograph and sediment and solute losses from arid and forest catchments. There is a fundamental distinction between infiltration-excess overland flow and the subsoil and subsoil-related processes, which are highly dependent on site-specific soil moisture and moisture-retention characteristics.

The next important hydrological division is at the soil surface. If rainfall intensities exceed the infiltration capacity of the soil, the unabsorbed water (minus any losses from evaporation of surface-water stores), once the surface detention capacity has been exceeded, runs off downslope via the hydrological process known as infiltration-excess overland flow (Figure 6.1). In forest areas, however, infiltration rates are usually high owing to the high hydraulic conductivity of the forest

Unsaturated Unsaturated

Unsaturated

Saturated Saturated

Unsaturated

SaturatedSaturated

QoQt

Qp

P DP

P

CP

Qp

Qo(s)

Qo(s)

Qg

Qg

Qp

P

Qt

B

AP

fIgure 6.1 Flow paths2 of streamflow sources and changing contributions to streamflow through the storm hydrograph (From Ward, R. C., Journal of Hydrology, 79, 1984).

Environmental Impacts on Water Resource Systems 103

litter layer,3 good soil aggregate structure, and the presence of macropore channels formed by roots and soil fauna activities.4 Thus, infiltration-excess overland flow is a relatively limited phenom-enon, occurring only where litter dynamics produce ephemeral patches of bare ground,5 where soil becomes exposed through tree fall, and where landsliding exposes the regolith,6 such as on steep slopes under high rainfalls or seismic triggering. Elsewhere, surface wash and associated soil losses are usually insignificant. However, in some localities, the interactions between rainstorm inputs and soil properties may induce natural surface flow, as in a location7 where highly transmissive surface soils (saturated hydraulic conductivity K = 20 m/d) are underlain at shallow depths by a relatively impermeable subsoil (K = 0.02–0.16 m/d). With prolonged and heavy storm rainfall, a perched water table rises to the surface, and saturated overland flow results (Figure 6.2).8 Similar natural occurrences of overland flow have been recorded from the Ivory Coast.9 Clearly, such settings pose a high erosion risk.

Further, hydrological processes interact with sediment transport effects, as small-scale land-slides in saturated stream head hollows in humid temperate environments appear to lead to channel-network extensions.

Different flow routes clearly have different residence times and, therefore, might be expected to show different solute concentrations (Figure 6.3). In particular, macropores create preferred paths along which water moves as channelized flow, thus bypassing the soil matrix. This biphasic flow regime (where water flows rapidly through the large pores, while remaining relatively immobile in the fine pore spaces) is important as it restricts leaching of solutes from the soil matrix.11 At Reserva Ducke, Amazonas, Nortcliff and Thornes12,13 have suggested that the low solute concentrations of stream water (wet and dry season mean: (ΣCa + Mg + Na + K = 0.03 meg/L) represent rapid filling and emptying of the macropore system, masking the smaller contribution in terms of flow volume of the longer-residence-time/higher-solute-concentration (ΣCa + Mg + Na + K = 0.3 meg/L) water within the meso- and micropores. It follows from this study that an understanding of hydrological pathways is unlikely to be gained through measure of variations in through flow chemistry obtained simply by sampling streamflow outputs from instrumented catchments. Further, such outputs are unlikely to give a correct picture of nutrient availability to plant rooting systems. Finally, as organic matter decomposition rates are controlled, at least in part, by the degree of saturation, there are likely to be linkages between soil organic matter dynamics and fluctuations in the extent of stream-side and floodplain saturated areas.13

Surface-water pollution by human activities has been covered by many books, articles, and research papers. As the main objective of this book is to cover the geohydrologic part related to its environmental impacts, the surface-water pollution issue is confined to this scope.

Clay/Silt

Silty sand

Thin humus layer

RunoffLand surface

Saturated zone50 cm

100 cm

fIgure 6.2 Runoff draining a surface and soil horizons at one of the tropical rain forest sites.

pjw

stk|

4020

64|1

4354

3253

6


6.4 groundWater PollutIon

The movement of contaminants in groundwater is a particularly active area of research. Models have been developed to study saltwater intrusion as well as leachate migration from waste disposal sites. Groundwater pollutants can be categorized as bacteria, viruses, nitrogen, phosphorus, met-als, organics, pesticides, and radioactive materials. This section covers information on subsurface transport in a general way.

6.4.1 migration oF pollutants in aquiFErs

Movement of contaminants in groundwater occurs not only by advection but also by dispersion. Advection (also referred to as convection) refers to the transport of a solute at a velocity equivalent to that of groundwater movement.14 It is considered to be the movement of the solute at a rate equal to the average pore water velocity due to the hydraulic gradient, which has the form

Fc = q · c (6.1)

where Fc = mass flux (M/T/L2) q = average pore water velocity (L/T) c = concentration (M/L3)

Dispersion refers to the mixing and spreading caused in part by molecular diffusion and in part by the variations in velocity within the porous medium. For many field problems, dispersion caused by molecular diffusion and by flow around grains in the porous medium is negligible in comparison to the dispersion caused by large-scale heterogeneities within the aquifer. It can simply be defined

Extremey highVery highModeratelyhigh

Low

Topsoil depthpermeabilityand water-holding capacity

LowSubsoilpermeability

Widespreadsaturation

Localized saturation overland flow/throughflow model

Rapid throughflowmodel

Allophanepodzolics

AllophanelatosolicsKaolinMontmonllonite

Wet-and-drytropics A0 mm

Ever-wet tropicswith no/weak dry

season andmoderate rainfall2000–3500 mm

Perennially very& wet tropics

3500 mm

Climate

Perenniallyextremely wet

7000

High Very high Very low

fIgure 6.3 Relationships between climate, soil type, and hydrological model. (From Burt, T. P., Solute Processes, Trudgill, S. T., Ed., Wiley, Chichester, 1986, pp. 193–249.)


as the movement of solute due to varying velocity from pore to pore at high velocities, and then the dispersive mass flux in the x direction:

F =-D

∂c

∂xx L

(6.2)

where Fx = dispersive flux in x direction (M/T/L2) DL = dispersion coefficient in the longitudinal direction; it has the dimension (L2/T).

Also, the dispersive mass flux in y direction becomes

F =-D

∂c∂yy T

(6.3)

where Fy = dispersive flux in y direction (M/T/L2) DT = dispersion coefficient in the transverse direction (L2/T)

Experiments have demonstrated that, in an isotropic medium, the longitudinal and transverse components of dispersion (See Equations 6.2 and 6.3) are linearly dependent on the average speed of groundwater flow. For a uniform flow field with an average linear velocity Vx,

DL = aLVx (6.4)

and

DT = aTVx (6.5)

where aL = dispersivity in the longitudinal direction (L) aT = dispersivity in the transverse direction (L)

Equations 6.2 and 6.3 are equivalent to Fick’s law. The solute transport governing the equations can be obtained in the same way as the governing equation of groundwater flow was obtained. The equation governing solute transport can be developed by utilizing the conservation of mass approach and Fick’s law of dispersion. The equation in statement form is as follows:

Net rate of change of mass of solute within = flux of solute out of the element – flux of solute into the element ± loss or gain of solute mass due to reactions

The one-dimensional form of the equation for a nonreactive, dissolved constituent in a homoge-neous, isotropic aquifer under steady-state, uniform flow is as follows:

D∂ c∂x

-u∂c∂x

=∂c∂t

2

2 (6.6)

where D = coefficient of dispersion in x direction (L2/T) u = average linear groundwater velocity (L/T) c = concentration (M/L3)

The two-dimensional equation for a nonreactive, dissolved chemical species in groundwater flow becomes


∂∂x

D∂c∂x

+∂∂y

D∂c∂y

-qL T

xx y

∂c∂x

-q∂c∂

±Qc =∂c∂ty

′

(6.7)

where

DL and DT = the hydrodynamic dispersion coefficients in x and y directions, respectively.

c′ = concentration of the solute of a source/sink of strength Q (assumed to be known).

qx, qy = effective pore water velocities in x and y directions, respectively,

generally q =Vine

where Vi is the flow per unit area and ne is the effective porosity.

Equation 6.6, for the case in which the solute transport problem is a one-dimensional flow, was

solved15 for a soil column of length (see Figure 6.4). The boundary conditions represented by the

step function inputs are described mathematically as

C ,o =o ≥o

C(o,t)=Co t≥o

C(∞,t)=o

ε ε( )

t≥o

The analytical solution derived16 is shown in Equation 6.8:

Outflow with tracerat concentration C

after time t´(a)

(b)Time

Effect ofdispersion

Breakthrough, t2

Firstappearance tI

to

to

Continuous supplyof tracer atconcentration Coafter time to

0

0

1

1

C/Co

C/Co

(c)Time

×

fIgure 6.4 Longitudinal dispersion of a tracer passing through a column of porous medium; (a) column with steady flow and continuous supply of tracer after time to; (b) input of tracer; (c) relative tracer concen-tration in outflow from column (dashed line indicates plug-flow condition and solid line illustrates effect of mechanical dispersion and molecular diffusion). (From Shamir, V. and Harleman, D. R. F., Water Resources Research, 3, 2, 1967, pp. 557–581.)


C=Co2

expuxD

erfcx + ut

2 D tL L

+ erfc

x - ut

2 D tL

(6.8)

where u = average linear velocity DL = longitudinal dispersion DT = o, because the problem is for one-dimensional flow, and

erfc z =2

πe du-u

2

2( ) ∫-∞

(6.9)

Soliman and Hassan17 applied the finite element methods18 to solve both the groundwater equation and the solute transport equation for two-dimensional flow. The finite element model was applied to two aquifers. The first aquifer is located in the Ruehn Valley in Germany (Figure 6.5). The model area was discretized into 1450 elements and 780 nodes (Figure 6.6). The model was constructed to simu-late the propagation of a contaminant plume created by injection at a point in the middle of the aquifer thickness and within the zone of influence of a group of wells. The rate of injection was 10 kg/h for a total time of 2 h. Figure 6.7 shows the computed concentration isolines 3 weeks after the injection.

The second aquifer is located east of the Nile Delta in Egypt (Figure 6.8). The model area is about 4750 km2. The delta aquifer is composed generally of unconsolidated sand and gravel with occasional clay lenses. The aquifer thickness varies between 200 and 700 m. The upper boundary

RA40

RA79

RA9

RA74RA78

N

TIDI/II

RA75

RA11

RA13RA12 RA2

R65 RA1

R66

EBXV

R27 R30

R31R21R19

EBII

EBIII

EBXIIIRA4

R33R32 R24

R22R23

EBXIV

Parsauer Gr.

RA5

RA8R71

R51R50

R72EBVIIRA42

R55RA41

RA43

R57

R60R59

R52

R53

R54

Durchhaugraben

RA6

R62R61

R63

R6

R76

R67

R15R16R29R18

R17R28EBI

Fanggrahon

Millellandkanal

Zwan

zigru

nGr

aben

R64

R58

R51

R48EBR 6

R4 RA7EBX R70

R46R26

R69R25 R44

R45EBIV

EBXI

EBXII

EBVI

RA10

Landgraben

Sech

zehn

fune

rG

rabe

n

Grenzgroben

0 0.5

R BeobachtungsbrunnenEntnahmebrunnenNetzbegrenzung

E

1.0 1.5 2.0 km R38

R20

RA14

RA3

Parsau

Croya

EBVIII

fIgure 6.5 General layout of Ruehn region, Germany.


DISP. COEFF. EXP. (NACL CONC. ISOLINES IN G/M’3)21.000

50100

500

13

10

fIgure 6.7 TDS contour map after 21 days (in gm/m3).

14000120001000080006000400020000

2000

4000

6000

8000

10000

0

fIgure 6.6 Finite element network of Ruehn model.


of this formation is a clay cap aquitard with a variable thickness ranging from 0.0 m up to 15 m. The model area was discretized into 543 elements and 310 nodes (Figure 6.9). The same grid was used for both groundwater flow and solute transport models. Figure 6.10 illustrates the simulated field sit-uation in the form of concentration isolines. For each run, the computed concentration values were compared with the observed values at some points where data was available. The calibrated values of the model—longitudinal dispersivity (northward) and lateral dispersivity (eastward)—amount to 100 and 10 km, respectively. Figure 6.11 shows the result of the computation in isolines form.

6.4.2 saltWatEr intrusion

Saltwater intrusion along sea coasts creates a region that separates the freshwater from saltwater. For simplicity, this region is sometimes taken as a separating surface and, therefore, may be con-sidered an interface between the freshwater and saltwater, which is stable only underground. It is broken up in open basins by diffusion and mixing due to motions resulting from very small potential gradients. The source of the freshwater is either rain water or irrigation water, which seeps through the ground surface.

0

Cairo

201

34

32 50 3126206

209

532716

344

346282

207

205

2821449

30 51

2556

57 58

211

E-4 219 100

224 220

232222

220

22567226

231

Port Said

Ismailia

Bounia C.

N

Suez Canal

210

60

66

117

Damietta

MEDITERRANEAN SEA

Lake Manzala

110120

237

229119

6364

230

337228351350

156156 Tanah

65

6162

22722

54 55

Bahe

r Mou

so

208

35

10 20 30 km

Ismalla canal measurement station

Nile W.L. measurement station

Plezometric level data+ chemical data

Plezometric level data

Chemical data

Kalyoubla M

.O

Danile

a Bran

ch

Ismailia Canal

122

fIgure 6.8 Map of the eastern region of the Nile Delta.


Recently, a great deal of emphasis has been placed on the law of Ghyben–Herzberg. Each of these authors independently made the discovery that in wells near the seacoast, saltwater was not encountered at sea level, as they had expected, but at depths below sea level on the order of 40 times the height of the freshwater above sea level. For this phenomenon, each author deduced the same explanation, namely, that a static equilibrium existed between the freshwater and the saltwater. Fol-lowing this reasoning, we should have19 (see Figure 6.12) the following equation:

H =

ee -e

hsf

s f (6.10)

where Hs = depth of freshwater flow below sea level ef and es = freshwater and saltwater density, respectively h = freshwater depth above sea levelFor, es = 1.025 gm/cm3 and ef = 1 gm/cm3, Equation 6.10 becomes

Hs = 40 h (6.11)

The assumption on which Equation 6.10 is derived is that we are dealing with a case of hydrostatic equilibrium, and to the extent that this assumption is valid, the equation is correct.

In groundwater problems, however, the assumption is not valid at all, because the freshwater is not at a constant potential but is in a state of continuous motion. If no additional water were added by precipitation or as irrigation water, the flow of the freshwater continues until it has all been dissi-pated, and only saltwater with a water table at sea level would remain. Therefore, the potential flow theory should be applied to define the dynamic depth of freshwater. Following this procedure,19 the actual depth (H) accordingly becomes (Figure 6.13)

140000130000120000110000100000

The finite element netI..7 Code no. of the transmissivity class

9000080000700006000050000400003000010000

10000

20000

30000

40000

50000

60000

70000

80000

90000

200000

fIgure 6.9 Finite element network of the Nile Delta model.


H=

eeH + zs

s ∆ (6.12)

and

∆ ∆z = -e

e -eh

s (6.13)

where ∆z = difference between potentials at the interface ∆h = difference between water levels

Equation 6.12 can also have the form,

H = HF + ∆Z (6.14)

This means that the difference between the dynamic depth, H, and the static depth, Hs, is ∆Z.

Cairo

320

320

320

1280

10000 15000 20000 25000 30000

40000

Damiatte

Lake Manzaia

Suez Canal

Ismailia

TDS contours in ppm

0 10 20 30 km

Ismailic Canal

Port Said

Bouhia C. Ba

her M

ousa

Tanah

Damiet

ta Bran

oh

45000

fIgure 6.10 TDS field data in isolines form (in ppm).


A number of investigations have been carried out over the past few years, most of them based on the Ghyben–Herzberg relationship, in which freshwater and saline water are considered to be immiscible fluids. In fact, they are miscible, and the sharp interface is not realistic, especially when the width of the dispersion zone is considerable. Henry20 was one of the first investigators who solved the coupled flow and mass transport equation for steady-state idealized confined aquifers. Henry21 also developed the first analytical solution that included the effect of dispersion in confined coastal aquifers under steady-state conditions. Shamir and Harleman22 presented a finite difference method for the solution of dispersion problems in a steady three-dimensional potential flow field in porous media, in which the miscible fluids had the same density and viscosity. Pinder and Cooper23 determined the movement of the saltwater front in confined coastal aquifers, including the effect of dispersion. The method of characteristics was used to solve the solute transport equation. Pinder

4000.003000.00

1290.00690.00

320.00

310.00

TDS CONTOURS IN PPM

fIgure 6.11 TDS from numerical solution (in ppm).

Salt water

Seah

HsFresh water

Transition zone

m.s.l.

Water table

G.S.

fIgure 6.12 Ghyben–Herzberg freshwater body.


and Frind24 used Galerkin’s procedure in conjunction with the finite element technique to simulate seawater intrusion into confined coastal aquifers.

Lee and Cheng25 formulated a finite element model using stream functions to obtain a steady-state solution for the convective-dispersive transport equation. Segol and Pinder26 applied the finite element technique to the solution of the transport equation. Frind26 studied the case of a fully con-fined aquifer overlain by an aquitard that extends out under the sea. He applied the Galerkin finite element technique with linear rectangular elements. The solution was based on a linear interpola-tion for the potential heads and the concentration between nodal points. Kawatani27 presented a two-dimensional model for the behavior intrusion in layered coastal aquifers. He addressed the instability problems that occurred when the convective terms exceeded a certain criterion related to the dispersion coefficients and the size of the finite elements. Kawatani took the longitudinal dis-persion coefficient as a constant to avoid the instability and other numerical problems. Pandit and Anand28 did a parametric study on an idealized confined aquifer with the same boundary conditions as applied by Henry. Their results indicated that the depth of the aquifer influenced the extent of saline water intrusion into the aquifer. It was also concluded that cyclic flow existed when the char-acteristic velocity at the seaward boundary was bigger than the longitudinal dispersivity. Huyakorn et al.29 developed a three-dimensional finite element model for simulation of saltwater intrusion in single and multiple coastal aquifers with either a confined or phreatic top aquifer. The model employed the Picard sequential solution algorithm with special provisions to enhance convergence of the alternative solution.

Some of the preceding studies have reported the existence of cyclic flows near the sea bound-ary (Figure 6.14). Because of its higher density, seawater migrates to the bottom of the aquifer and mixes with the freshwater. This mixed water is of lower density, and it finds its way back again to the sea from the upper part of this boundary.

The finite element model, 2D-FED, was designed by Sherif30 for the saltwater intrusion problem north of the Nile Delta in Egypt.

The Nile Delta groundwater reservoir extends over 6 million acres and is naturally bounded northward by the Mediterranean Sea and eastward by the Suez Canal (Figure 6.15). The western boundary extends well into the desert. The Nile Delta aquifer, is a complex groundwater system. It is a leaky one, with an upper semipermeable boundary (clay cap) and lower impermeable boundary.

Dynamic interfaceStatic interface

W.T.

H8

S.L.H

Hf

∆Z

∆h

G.S.

fIgure 6.13 Static and dynamic interfaces.


The Nile Delta aquifer is subjected to the problem of saltwater intrusion from both the Mediter-ranean Sea to the north and the Suez Canal to the east. As with any coastal aquifer, an extensive saltwater wedge has intruded into the coastal part of the Nile Delta aquifer, forming the major con-straint against aquifer exploitation.

The 2D-FED model is applied to the longitudinal geological cross section A-A given in Fig-ure 6.16. The depth and length of the domain are given in Figure 6.17 on the basis of some field data. A calibrated value of the hydraulic conductivity, K, of 100 m/d is considered representative of the aquifer medium. The vertical hydraulic conductivity for the upper semipervious layer, Kz, is set equal to 0.05 m/d.

CAIRO

OSIM

SMATHMUF0 10 20 30 km

EL BASOUR MINIA EL-KAMHABU SULTAN

ABU-KIBIR

SAN EL-MAGAN

EL-ABADIYA

BALTIM

KAFR EL-SHEIKH

TANTA

ZIFTAKOM HAMMAD

DILINGAT

ETAY EL-AYUD

EL-MAHMUDYA

LAKE BURULLUS

ALEXANDRIA

MEDITERRANEAN SEA

RAS EL-BARR

L. MANZALLAEL-MATARIYA

DITARBNIGM

ABU-MAMMAD

A

A

fIgure 6.15 The Nile Delta in Egypt.

Impermeable

ConfinedAquiffer

Seawater0.5 Isochlor

Seawater

MSL

Freshwater

Watertable aquifer

WatertableShore

Potentiometricsurface

Aquitard

fIgure 6.14 Cyclic flow near the sea side.


The piezometric head at the land boundary is 14.0 m above sea level. A piezometric level of 0.6 m was observed near the sea boundary. The free water table level is given for some stations and is assumed linear between them. The longitudinal and transverse dispersivities aL and aT are assumed 100.0 and 10.0 m, respectively.

The domain is divided into five subdomains; each subdomain is divided into a number of tri-angular elements with smaller areas in the regions where variation in the concentration gradient is relatively high. An intensive grid is adopted near the sea boundary. The domain is finally repre-sented by a nonuniform grid with 4020 nodes and 7600 triangular elements. The solution converges to an accuracy of 10–5 after 14 iterations.

It can be concluded from the shape of the equipotential lines that the depth of the window at the seaside is about 350 m (Figure 6.17). There is some upward flux of the mixed water through the upper semipervious layer within a distance of 22.0 km from the sea boundary. Strong cyclic flows in the Nile Delta aquifer occur at the sea boundary.

6.4.3 landFill lEachatE

Solid wastes deposited in a landfill degrade chemically and biologically to produce solid, liquid, and gaseous products. Ferrous and other materials are oxidized; organic and inorganic wastes are utilized by microorganisms through aerobic and anaerobic synthesis. Liquid waste products of microbial degradation, such as organic acids, increase chemical activity within the fill. Food wastes degrade quite readily, whereas other materials, such as plastics, rubber, glass, and some demolition wastes, are highly resistant to decomposition.

Clay

HOR SCALE

0

720680640600560520

Elev

atio

n In

Met

ers

480440400360320280240200160120

804000

EL M

AN

AWAT

OSI

M

NIL

E

SHAT

AN

UF

TAN

TA

KAT

R EL

SH

EIA

ARA

DIY

A

SEA

A´

A

10

CAIROOSIN

DAGURTANTAIM

PERMEABLE

20 30 40 50 km

SandSand & Clay Sand & Gravel

KAFREKSHEMH

fIgure 6.16 Lithological cross section (A-A) normal in the shore in the Nile Delta aquifer.


Some factors that affect degradation are the heterogeneous nature of the wastes; their physi-cal, chemical, and biological properties; the availability of oxygen and moisture within the fill; temperature; microbial populations; and type of synthesis. Because solid wastes usually form a heterogeneous mass of nonuniform size and variable composition, and other factors are complex, variable, and difficult to control, it is not possible to accurately predict contaminant quantities and production rates.

Biological activity within a landfill generally follows a set pattern. Solid waste initially decom-poses aerobically, but as the oxygen supply is exhausted, facultative and anaerobic microorganisms predominate to produce methane gas, which is odorless and colorless. Temperature rises to the high mesophilic–low thermophilic range (15–66˚C) because of microbial activity.

60016.014.012.010.0

2.04.0

6.0

8.0

500

400

300

200

100

SEA

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.

0

110.

0

120.

0

130.

0

140.

0

km 150.

0

m(b)

10.012

.014.0

600

500

400

300

200

Seawater

Fresh water 100

SEA

10.0

20.0

30.0

40.0

50.0

60.0

70.0

1.0 5.0

10.0

20.0

35.0

80.0

90.0

100.

0

110.

0

120.

0

130.

0

140.

0km 15

0.0

SHAT

AN

OF

TAN

TA

OM

SIN

KA

FR E

L-SH

IKH

m(a)

fIgure 6.17 (a) Equiconcentration lines (∞ 1000 ppm); (b) equipotential lines from the model in Nile Delta aquifer.


Characteristic products of aerobic decomposition of waste are carbon dioxide, water, and nitrate. Typical products of anaerobic decomposition of waste are methane, carbon dioxide, water, organic acids, nitrogen, ammonia, and sulfides of iron, manganese, and hydrogen.

Leachate percolating through the soil underlying and surrounding the solid waste is subject to purification (attenuation) of the contaminants by ion exchange, filtration, adsorption, complexing, precipitation, and biodegradation. It moves either as unsaturated flow, if the voids in the soil are only partially filled with water, or as a saturated flow, if the voids are completely filled. The type of flow affects the mechanism of attenuation, as do soil particle size and shape, and soil composition.

Attenuation of contaminants flowing in the unsaturated zone is generally greater than that in the saturated zone because there is more potential for aerobic degradation, adsorption, complexing and ion exchange of organics, inorganics, and microbes. Aerobic degradation of organic matter is more rapid and complete than anaerobic degradation. Because the supply of oxygen is extremely limited in saturated flow, anaerobic degradation prevails. Adsorption and ion exchange are highly dependent on the surface area of the liquid and the solid interface.

Leachate travel in the saturated zone is primarily controlled by soil hydraulic conductivity and hydraulic gradient, but a limited amount of capillary diffusion and dispersion do occur. The leachate is diluted very little in groundwater unless a natural geologic mixing basin exists.

Bouwer31 notes that landfills behave essentially as point sources of pollution. When leachate from a landfill reaches the groundwater, it travels in the general direction of the groundwater move-ment. A high chloride ion concentration usually provide an early indication of the presence of a leachate in groundwater.32

The shape and areal extent of a leachate contaminant plume for a thoroughly characterized landfill are shown by contours in Figure 6.18.

Figure 6.19 shows the progress of the movement of leachate in an anisotropic aquifer system with significant variation in hydraulic conductivities of the subsurface geologic material. This figure shows the time sequence of the movement of the plume and the network of the monitoring system.

The movement of the plume in saturated carbonate rocks is controlled by fracture and solution channels. The movement of the contaminated groundwater (plume) is generally directional along discontinuities and dissolution-widened joints. Figure 6.20 illustrates the movement of groundwater and plume in a fractured and karstified carbonate rock.

Additional examples as related to aquifer degradation, landfill leachate, and industrial contami-nants’ plume, configuration, and movement are covered in Chapter 7, the appendices, and the diskette.

235230225220215210205200195

Met

ers A

bove

Sea

Lev

el

Clay

mg/IStandpipe TipPiezometer TipMulti-level

Sampling Point

Chloride50640

660

680

700

720

740

760 Landfill

Feet

Abo

ve S

ea L

evel

200

200 100

0

0 m

Horizontal Scale200 400 ft.

1025

50100

200

300400 200

fIgure 6.18 Example leachate water quality, plume-field determined. (From Sara, M. N., Standard Hand-book for Solid and Hazardous Waste Facility Assessments, Lewis Publishers, Boca Raton, FL, 1994, pp. 10–68.)


6.5 groundWater monItorIng

Water quality characteristics must be established and trends observed. A comprehensive investiga-tional program for evaluation of these factors is essential. Groundwater should be sampled regularly on a continuing basis. Sampling points should include both shallow and deep wells, selected with due consideration to areal distribution, geologic and hydrologic influences, pattern of pumpage, and waste disposal. Practice samples should be obtained at the peak of the pumping season, when water levels are at their lowest and also, if possible, during the period of replenishment when levels are high.

In areas vulnerable to seawater intrusion, particular attention should be given to changes in chloride concentration. Total dissolved solids content is significant when salt balance problems exist. Phenols, boron, and heavy metals are usually critical when large volumes of industrial waste are involved. Domestic sewage disposal particularly influences nitrate, phosphate, and detergent

“Upgradient”wells

“Downgradient”wells

B C DRiverUnlined landfill

A

Sink

hole

fIgure 6.20 Movement of leachate plume in karstified carbonate rock. (From Sara, M. N., Standard Handbook for Solid and Hazardous Waste Facility Assessments, Lewis Publishers, Boca Raton, FL, 1994, pp. 10–68.)

630

670

690 Silty sand

Gravel

Silty clay

Bedrock

Potentiometriclevel710

730FT

Strong downwardgradients

Unlined waste disposal

Strong downward gradientsA1A2 A3

B1B2B3

650

YEAR 5Year 4

Year 3Year 2Year1

fIgure 6.19 Progress of leachate plume in anisotropic aquifer. (From Sara, M. N., Standard Handbook for Solid and Hazardous Waste Facility Assessments, Lewis Publishers, Boca Raton, FL, 1994, pp. 10–68.)


content. For these water quality observations to be properly evaluated and interpreted, they must be augmented with adequate information on geology, hydrology, rate and pattern of extractions, and sewage disposal practices.

In general, a groundwater management program should be used to indicate potential problems so that timely corrective action can be taken. The collection of basic data should not become an end in itself, but should be an integral part of a comprehensive, balanced program of continuing examination and interpretation of all factors involved in protection of the aquifer and maintenance of groundwater quality.

The adequacy of a groundwater-monitoring program33 hinges, in large part, on the quality and quantity of the hydrogeologic data used in designing and implementing the program. For example, sites with more heterogeneous subsurfaces will require more hydrogeologic information to provide a reasonable assurance that well placements will intercept contaminant migration pathways. Like-wise, investigating techniques that may be appropriate in one setting (given certain waste charac-teristics and geologic features) may be inappropriate in another.

Once contaminant leakage in any site has been detected via detection monitoring efforts, a more aggressive groundwater program, called assessment monitoring, must be undertaken. Specifically, researchers must determine the vertical and horizontal concentration profiles of all the hazardous waste constituents in the plumes escaping from waste management areas, besides establishing the rate and extent of contaminant migration.

There are a number of elements that the researchers should include in their assessment monitor-ing plan:

1. Description of hydrogeologic conditions 2. Description of the detection monitoring system 3. Description of a short-term statistical analysis of detection monitoring data 4. Description of the approach for conducting the assessment as direct or indirect methods of

investigation, or as mathematical modeling of contaminant movement 5. Discussion of number, location, and depth of wells 6. Information on well design and construction 7. Description of sampling and analysis procedures 8. Determinations of the rate of migration and the extent and hazardous constituent composi-

tion of the contaminant plume 9. Specifying a schedule of implementation of the assessment plan

There are several different t-tests that can be used to analyze the interim status detection monitoring groundwater data. Because of its simplicity and reliability, a t-test termed the averaged replicate (AR) t-test is presented in this section.

In AR t-test, the background mean and variance must be calculated for the first year. This is done by first averaging the replicate measurements and then using these replicate averages to calcu-late the background mean and variance as described here:

Background mean:

Xu= (X )g/nij

K=1

n

∑ (6.15)

X = (X /M)b d

2=t

n

1=t

n j1

∑∑ (6.16)

where


n = the number of replicate measurements; n1 and n2 are the number of wells and the num-ber of sampling periods, respectively; and M is equal to n1 times n2

Xb = background mean

Background variance:

S - X /(M-1)b2

ij b2= (X )

j=1

n

i=1

n j1

∑∑ (6.17)

The data for every parameter from each monitoring well, and from each sampling event (upgradi-ent and downgradient wells from the site) after the first year, must be compared individually with the background data collected during the first year. At least four replicate measurements should be taken from each well for every indicator parameter (IP) during every quarter to semiannual sam-pling event. These monitoring data are used to calculate a mean and variance for every IP at every monitoring well each time the well system is sampled.

The mean (Xm) for monitoring well m for the AR t-test is

X = X /Nm km m

k=1

Nm

∑ (6.18)

where Xkm = the K-th replicate measurement from the m-th monitoring well, where K = 1 to Nm

Nm = number of replicate measurements from the monitoring well m

The AR t-statistic is calculated as follows

t =X -X

S 1 -1/Mm b

b2

∗

(6.19)

The critical t-statistic (tc) is obtained directly from Table 6.1. The value tc from Table 6.1 corre-sponds to M − 1 degrees of freedom (Note: If pH is being tested, use the two-tailed critical values; otherwise, use the one-tailed critical values).

The t* value is then compared with tc using the following decision rules:

If the total organic carbon (TOC) and total organic halogens (TOX) are being evaluated, •and if t* is less than tc, then there is no statistical indication that the IP concentrations are larger in the well under comparison than in the background data. If t* is larger than tc, there is a statistical indication that IP concentrations are larger in the well under comparison.If pH is being evaluated, and if |t*| (which is the absolute value of t*) is less than t• c, then there is no statistical indication that pH has changed. If |t*| is larger than tc, there is an indication that pH has changed statistically. If t* is negative, then pH has increased; if t* is positive, then pH has decreased.


table 6.1one- and two-tailed critical t values at the 0.1 level of significance

degrees of freedom one-tailed two-tailed

1 31.821 62.657

2 6.965 9.925

3 4.541 5.841

4 3.747 4.604

5 3.365 4.032

6 3.143 3.707

7 2.998 3.499

8 2.896 3.355

9 2.821 3.250

10 2.764 3.169

11 2.718 3.106

12 2.618 3.055

13 2.650 3.012

14 2.642 2.977

15 2.602 2.947

16 2.583 2.921

17 2.567 2.898

18 2.552 2.878

19 2.539 2.861

20 2.528 2.845

21 2.518 2.831

22 2.508 2.819

23 2.500 2.807

24 2.492 2.797

25 2.485 2.787

26 2.479 2.779

27 2.473 2.771

28 2.467 2.763

29 2.462 2.756

30 2.457 2.750

40 2.423 2.704

60 2.390 2.660

120 2.358 2.617

∞ 2.326 2.576

Source: Adapted from Table III: Statistical Tables for Biological, Agricultural, and Medical Research, RCRA, Ground-Water Monitoring Technical Environment Guidance Doc-ument, EPA, Washington, DC, August 1985.


referenceS

1. UNESCO, Hydrology and water resources for sustainable development in a changing environment, 1990. 2. Ward, R. C., On the response to precipitation of headwater streams in humid areas, Journal of Hydrol-

ogy, 79, 1984. 3. Walsh, R. P. D. and Voigt, P., Vegetation litter, an underestimated variable in hydrology and geomor-

phology, Journal of Biogeography, 4, 1977, pp. 253–254. 4. Lal, R., Tropical Ecology and Physical Edaphology, Wiley, London, 1987. 5. Spencer, T., Douglas, I., Greer, T., and Sinun, W., Vegetation and fluvial geomorphic process in South-

east Asian tropical rain forests, in Vegetation and Erosion, Thornes, J. B., Ed., Wiley, Chichester, 1990, pp. 451–469.

6. Garwood, N. C., Janos, D. P., and Brokaw, N., Earthquake-caused landslides: A major disturbance to tropical forest, Science, 205, 1979, pp. 997–999.

7. Bonell, M. and Gilmore, D. A., The development of overland flow in a tropical rain forest catchment in Northeast Queensland, Earth Surface Processes and Landforms, 8, 1983, pp. 253–272.

8. Douglas, I. and Spencer, T., Environmental Change and Tropical Geomorphology, Allen and Unwin, London, 1985, pp. 39–73.

9. Wierda, A., Veen, A. W., and Hughes, R. W., Infiltration at the Tai rain forest (Côte d’Ivoire): Measure-ments and modelling, Hydrological Processes, 3, 1989, pp. 371–382.

10. Burt, T. P., Runoff and denundation rates on temperate hillslopes, in Solute Processes, Trudgill, S. T., Ed., Wiley, Chichester, 1986, pp. 193–249.

11. Solins, P. and Radulovich, R., Effects of physical structure on solute transport in a weathered tropical soil, Journal of the Soil Science Society of America, 52, 1988, pp. 1162–1173.

12. Lal, R. and Russell, E. W., Tropical Agricultural Hydrology, John Wiley, New York, 1981, pp. 37–57. 13. Nortclif, S. and Thorns, J. B., The dynamics of a tropical flood plain environment with reference to for-

est ecology, Journal of Biogeography, 15, 1988, pp. 49–59. 14. Roberts, P. V., Reinhard, M., and Valocchi, A. J., Movement of organic contaminants in groundwater:

Implications for water supply, Journal of the American Water Works Association, August 1982, pp. 408–413.

15. Bear, J., Hydraulics of Groundwater, McGraw-Hill, New York, 1979, chap. 8. 16. Canter, L. W., Knox, R. C., and Fairchild, D. M., Groundwater Quality Protection, Lewis Publishers,

Boca Raton, FL, 1987, chap. 6. 17. Soliman, M. M. et al., Groundwater quality model with applications to various aquifers, Environmental

Geology Water Science, 17, 3, Springer-Verlag, New York, 1991, pp. 201–208. 18. Huyakorn, P. S. and Pinder, G. F., Computational Methods in Subsurface Flow, Academic Press, New

York, 1983. 19. Soliman, M. M., Groundwater Management in Arid Regions, Vol. 1, Ain Shams University Press, 1984,

pp. 179–187. 20. Henry, H. R., Saltwater Intrusion in Coastal Aquifers, International Association of Scientific Hydrology

Publication, 52, 1960, pp. 478–487. 21. Henry, H. R., Effect of Dispersion on Salt Encroachment in Coastal Aquifers, U.S. Geol. Surv., Water

Supply Paper, 1613–C, 1964. 22. Shamir, V. and Harleman, D. R. F., Numerical solution for dispersion in porous media, Water Resources

Research, 3, 2, 1967, pp. 557–581. 23. Pinder, G. F. and Cooper, H. H., A numerical technique for calculating the transient position of the salt-

water front, Water Resources Research, 6, 3, 1970, pp. 875–882. 24. Pinder, G. F. and Frind, E. O., Application of Galerkin’s procedure to aquifer analysis, Water Resources

Research, 8, 1, 1972, pp. 108–120. 25. Lee, C. H. and Cheng, R. T., On seawater encroachment in coastal aquifers, Water Resources Research,

10, 5, 1974, pp. 1039–1043. 26. Frind, E. O., Seawater intrusion in continuous coastal aquifer-acquired system, Proceedings of the 3rd

International Conference on Finite Elements Water Resources, University of Mississippi, Oxford, 1980. 27. Kawatani, T., Behavior of seawater intrusion in layered coastal aquifers, Proceedings of the 3rd Inter-

national Conference on Finite Element Water Resources, University of Mississippi, Oxford, 1980. 28. Pandit, A. and Anand, S. C., Groundwater flow and mass transport by finite elements—A parametric

study, Proceedings of the 5th International Conference on Finite Elements Water Resources, University of Vermont, 1984.


29. Huyakorn, P. S., Anderson, P. F., Mercer, J. W., and White, H. O., Saltwater intrusion in aquifers: Devel-opment and testing of a three-dimensional finite element model, Water Resources Research, 23, 2, 1987, pp. 293–312.

30. Sherif, M. M., Singh, V. P., and Amer, A. M., A two-dimensional finite element model for dispersion (2D-FED) in coastal aquifers, Journal of Hydrology, 103, 1988, pp. 11–36.

31. Boumer, H., Groundwater Hydrology, McGraw Hill, New York, 1978. 32. Freeze, R. A. and Cherry, J. A., Groundwater, Prentice-Hall, Englewood Cliffs, NJ, 1979. 33. RCRA, Ground-Water Monitoring Technical Environment Guidance Document, EPA, Washington,

DC, August 1985. 34. Sara, M. N., Standard Handbook for Solid and Hazardous Waste Facility Assessments, Lewis Publish-

ers, Boca Raton, FL, 1994, pp. 10–68.

125

7 Waste Management for Groundwater Protection

7.1 PrImary concePt

Environmental effects are considered the major problem with groundwater management1-2 and pro-tection. The major factors in considering the suitability of a water supply are water quality require-ments and limitations associated with its uses. Various criteria have been developed covering all categories of water quality, including bacterial characteristics and chemical constituents.

The removal or neutralization of undesirable chemical characteristics is often both difficult and expensive. Criteria of general application for use in evaluating the chemical aspects of water qual-ity should be generally considered as guides and indicators of desirable water quality and not as absolute standards for all applications.

The U.S. Public Health Service has developed standards for physical, chemical, and bacterial quality of drinking water as shown in Table 7.1. These standards have been widely adopted. Bacte-rial standards are expressed in a complex relationship between the number of samples to be ana-lyzed and the allowable number of coliform organisms in these samples. In effect, average monthly coliform is limited to a most probable number (MPN) of 1/100 mL of sample.

General specifications further provide that there shall be no objectionable odors or tastes; turbid-ity shall not exceed 10 ppm (silica scale), and color shall not exceed 20 ppm (platinum–cobalt scale). In addition to these standards, concentration of nitrate shall not be in excess of 10 ppm, as nitrogen (44 ppm as NO3) in domestic water supplies has been determined to be harmful to infants.

Although hardness does not ordinarily affect the provision of drinking water, it is important, in general, for industrial water usage. Excessive hardness causes increased consumption of soap and induces the formation of scale in pipes and fixtures. The following standards have been formulated by the U.S. Geological Survey:

class range of hardness (in ppm)Soft 0–55

Slightly hard 56–100

Moderately hard 101–200

Very hard 201–500

The suitability of water for irrigation use depends upon such factors as soil texture and composi-tion, crop types, irrigation practices, and chemical characteristics of the water supply. Sodium can be a significant factor in evaluating irrigation water quality because of its potential effect on soil structure. A standard of classification based upon the total salinity and the relative proportion of sodium in irrigation water has been developed by the salinity laboratory of the U.S. Department of Agriculture (USDA). The classification makes use of the sodium adsorption ratio (SAR) of soil solution, which is defined as

SAR=Na

(Ca +Mg )/2

+

2+ 2+

(7.1)

in which Na, Ca, and Mg are expressed in meg/L.


There are many environmental effects on groundwater quality. These effects are due to waste disposal such as sewage, industrial waste, cooling water, radioactive wastes, dump sites, watershed influences, connate waters, and seawater intrusion. In formulating an effective plan for control and recovery of groundwater quality, full consideration must be given to geology, hydrology, and cul-tural development within the area of the groundwater reservoir.

7.2 alternatIVe of WaSte dISPoSal

Environmental protection has taken its place beside efficient manufacturing and other human activi-ties. Pressures to handle wastes properly arise from several sources:

Legislative and regulatory actions•Concerns over known or suspected effects of a specific material, which is as yet unregulated•Process economics improvement through waste reduction•Conservation of resources, including water•Protection of workers’ health•

Responses by all concerned people to these pressures largely demonstrate a high degree of respon-sibility. However, the concern to all parties is a comparison of the cost of the environmental protec-tion measures versus their true benefits to the environment.

Alternatives of waste disposal are to provide practical technology useful in selecting and designing various environmental protection operations and processes that economically and reli-ably fill identified needs. The achievement of cost-effective means of disposing of liquid and solid wastes3 involves the systematic consideration of a range of alternative approaches. Table 7.2

table 7.1limiting concentrations of mineral constituents for drinking water

constituent limits (in ppm)

mandatory limits

Fluoride (F) 1.0

Lead (Pb) 0.1

Selenium (Se) 0.05

Hexavalent chromium (+6Cr) 0.05

Arsenic (As) 0.05

nonmandatory (but recommended) limits

Iron (Fe) and manganese (Mn) together 0.3

Magnesium (Mg) 125

Chloride (Cl) 250

Sulfate (SO4) 250

Copper (Cu) 3.0

Zinc (Zn) 15

Phenols 0.001

Total solids, desirable 500

Permitted 1,000

Source: From Langer, M., Rheological behaviour of rock masses, Int. Association of Rock Mechanics Engineers, Proceedings of the 4th International Congress on Rock Mechanics, Montreaux, France, Vol. 3, 1979, pp. 29–96.

Waste Management for Groundwater Protection 127

table 7.2treatment technologies

Physical treatment chemical treatment

Sedimentation Neutralization

Centrifugation Chemical precipitation

Flocculation Chemical hydrolysis

Oil or water separation Ultraviolet photolysis

Dissolved air flotation Chemical oxidation (chemical reduction)

Heavy media separation Oxidation by hydrogen peroxide (H2O2)

Evaporation Ozonation

Air stripping Alkaline chlorination

Steam stripping Oxidation by hypochlorite

Distillation Electrolytic oxidation

Soil flushing/soil washing Catalytic dehydrochlorination

Chelation Alkali metal dechlorination

Liquid/liquid extraction Alkali metal/polyethylene glycol (A/PEG)

Supercritical extraction

Filtration

Carbon adsorption biological

Reverse osmosis Aerobic biological treatment

Ion exchange Activated sludge

Electrodialysis Rotating biological contractors

Bioreclamation

Anaerobic digestion

fixation/stabilization White-rot fungus

Lime-based Pozzolan processes

Portland cement Pozzolan process

Sorption

Vitrification thermal destruction

Asphalt-based (thermoplastic) Liquid injection incineration

Microencapsulation Rotary kiln incineration

Polymerization Fluidized bed incineration

Pyrolysis

Wet air oxidation

Potential source Industrial boilers

control strategies Industrial kilns (cement, lime, aggregate, clay)

Recycling Blast furnaces (iron and steel)

Resource recovery Infrared incineration

Materials recovery Circulating bed combuster

Waste-to-energy conversion Supercritical water oxidation

Encapsulation Advanced electric reactor

Waste segregation Molten salt destruction

Codisposal Molten glass

Leachate recirculation Plasma torch


provides various technologies available for treatment or disposal of waste. Figure 7.1 shows tech-nologies used for 70 sites in 1989 to either treat or dispose of the waste. Figure 7.2 depicts an over-view of the available alternative means of wastewater disposal. A comprehensive list of treatment alternatives for dilute and concentrated wastes is presented in Table 7.3. A treatment/disposal schematic for solid wastes4 is shown in Figure 7.3.

7.3 dISPoSal and control

This section covers the disposal and control of wastes that have an unfavorable impact on the groundwater aquifers. Liquid wastes can easily migrate through soils, causing contamination to the aquifers. Therefore, this section is restricted to the disposal and control of all wastes that may produce contaminants in liquid state.

7.3.1 typEs oF disposal

Manufacturing is the leading source of controllable manmade water pollutants; domestic waste is second. Industrial wastes are more likely to contain substances that will resist the normal treatment procedures. However, except for the types of industries that generate large amounts of incompatible wastes, many industries take advantage of the local municipal treatment facilities for some or all of their waste waters. It is often necessary to pretreat some of the industrial wastes before introducing them into the municipal treatment facility, but, most of the time, there is no difficulty in handling

Source: EPAAugust 14, 1990

10.6%

5.3%

4.3%

Bioremediation(10)In-situ

soil flushing(3)

Vacuum/Vapor extraction

(17)

Chemicalextraction

(5)

Soilwashing

(4)

13.8%

13.8%

Solidification/Stabilization

(20)

Thermaldesorption (3)

In-situvitrification (2)

Other(4)

Off-siteincineration

(13)

On-siteincineration**

(13)

Fiscal Year 1989

21.3%

3.2%2.1%

4.3%

18.1%

3.2%

**Also includes sites where location of incineration is to be determined

*Sources include solids, soils, sludges and liquid wastes; waste sources do not include ground water or surface water

fIgure 7.1 Treatment technologies for 70 sites.4


Manufacturingunit

Processwastewaters

Physicaltreatment

Product recovery Water reuse Treatment processresidue

Incinerationor pyrolysis

Deep wellinjection

Deep oceandisposal

Landdisposal

Municipalcollectionsystems

Dilution infreshwater

orestuaries

Chemicaltreatment

Biologicaltreatment

Washwater

Coolingwater

Stormwater

Spills &upsets

Low BTUgas

fIgure 7.2 General strategies in wastewater disposal.

table 7.3alternative treatment for water wastesPhysical

Equalization, adsorption, sizing, phase change, ion exchange, membrane process, force-field separation, surface methods (foaming, skimming, etc.), and extraction

Biological

Activated sludge (completely mixed, oxygen-based, etc.), fixed film processes (trickling, etc.), aerated stabilization, anaerobic (lagoons, etc.), algae stabilization ponds, balanced ecosystems (aquatic plants, animals), enzyme conversions (immobilized enzymes/cells)

Chemical

Acid–base treatments, chemical precipitation (coagulation, flocculation, etc.), oxidations (chlorination, ozonation, etc.), reduction reactions, complexation, photochemical reactions, hydration and clathrates, electromotive displacement, and thermal decomposition

Electrical and electromagnetic

Ultraviolet irradiation, electrolysis, magnetic separation, electrodialysis, and electron beam radiation

Acoustical

Ultrasonic

Nuclear

Irradiation

Source: From Conway, R. A. and Ross, R. D., Handbook for Industrial Waste Disposal, Van Nostrand Reinhold, New York, 1980, chap. 1.


industrial wastes by the normal municipal technologies. Industrial wastes frequently constitute a large percentage of the volume treated by municipalities. Even if the industry has its own treatment facility, it usually operates on the same principles and employs many of the same techniques as the municipal systems.

There are three broad classes of treatment methods that are employed:

1. Primary treatment: Primary treatment removes from the wastewater those substances that float or settle out. All processes in this category focus on removing the pollutants by physical means; hence, this is the mechanical treatment stage. Techniques included are grit removal, screening, grinding, and sedimentation.

2. Secondary treatment: This is based on biological oxidation; thus, it is the reproduction of the degradation processes that occur in nature. The major purpose is to remove the soluble BOD (biological oxygen demand), as well as the suspended solids that were not removed in the primary treatment. BOD is the amount of oxygen required to biologically oxidize the water contaminants to carbon dioxide. The three common methods used are activated sludge, trickling filters, and oxidation ponds (lagoons). All these are based on having vari-ous microorganisms feeding on the organic impurities in the presence of oxygen at a favor-able temperature and for a sufficient period.

3. Tertiary treatment: This primarily includes the various chemical treatments of wastewater.

Most treatment facilities include primary and secondary treatments. Some of them, particularly those associated with an industry, also include certain forms of advanced treatment. Figure 7.4 shows a typical system component for treating dilute process wastes. There have recently been many projects devoted to studying the effects of using municipal sludge as a soil conditioner and as a liquid, dewatered or dried.

Landfilling is the most common method used for sludge disposal. Usually, before the sludge can be landfilled, digestion is required to avoid odors, insects, and water pollution. All types of dewa-tered sludges can be disposed of by landfill similar to many other types of solid wastes. The sludges can be transported to the landfill site by truck, train, pipelines, or barges.

Severe measures have recently been taken for disposing and discharging the primary treated industrial wastes and sewage to deep-ocean outfalls. This is done to prevent any undesirable impacts on the marine environment.6

ReuseSteamAchSoilbuilder

Landreclamation

Landfill

Shredding Grinding Compaction

Solid waste

Wet pulping Materialrecovery

Composting Incineration Boilers Pyrolysis

Low BTUgas

Deep oceandisposal

fIgure 7.3 Treatment/disposal sequence for solid waste.


7.3.2 disposal oF hazardous WastEs

There has been much interest in hazardous waste disposal since the early 1960s. Hazardous wastes are those that are ignitable, corrosive, chemically reactive, or toxic.7 Radioactive wastes are consid-ered to be the most dangerous of hazardous wastes. Recently, the catastrophe caused by a nuclear power plant in the former USSR8 had a disastrous impact on the environment. This includes the environmental impacts on water resources and even the hydrological cycle.

In the past, hazardous wastes were often simply drummed and then disposed of in a landfill area. This was generally an unsatisfactory method. Several approaches are currently being made toward evolving appropriate disposal techniques. Secured landfills are available in some locations and can be used to dispose of toxic wastes. These landfills are located in thick natural clay depos-its or engineered with various layers of specially designed liners and leachate collection systems (Figure 7.5). Often, however, appropriate sites are too far from the plant that generates the waste to make them a logistically and economically viable disposal method. Therefore, other methods such as incineration are to be investigated and used for disposal of toxic waste.

Secondary leachatecollection and removal

Primaryleachate

collection andremoval system Low permeability soil

Lowercomponent

(compacted soil)

Uppercomponent

Bottom compositeliner

Top liner

Filter medium

Protectivesoil or cover

Drainage

Drain

material

Drainagematerial Pipes

DrainPipes

fIgure 7.5 Linear leachate collection system for landfill. (From Environmental Institute for Waste Man-agement Studies, Disposal of Solvents and Solvent-Contaminated Wastes to Land—A Position Paper, Univer-sity of Alabama, Tuscaloosa, December 1985.)

Drainageditch

Setling Biologicalsystem

Neutralization

Acidbase

Landfill orincinerator

Centrifugation

ClarificationCollection Equalization

fIgure 7.4 Typical system components for treating dilute process wastes.


The liquid waste incinerator is one that generally consists of a waste-fed system to deliver the liquids, slurries, sludges, and solids of thermal destruction chambers. There are usually two ther-mal chambers: one for oxidation and a separate one for gasification. Typical incinerators operate at 540–1400°C with residence times of the waste of 1–3 s or perhaps longer. Inclusion of heat recovery units can make the systems more economically feasible.9

Another potentially useful disposal technique for hazardous wastes consists of combined sta-bilization and solidification of these wastes. If properly done, the hazardous waste can then be disposed of in any well-designed landfill. The technique used is dependent upon the nature of the waste. In the future, it is likely that processes will be changed to generate fewer toxic wastes, and more wastes will be converted to useful by-products, or recycling may be increased.

7.3.3 salt cavErns For disposal

Use of salt caverns for disposal of hazardous wastes has proved to be feasible in some locations worldwide. The solution mining method11 provided the means for the creation of large storage capacities at economical costs. Moreover, underground sites in salt are safer from an environmental point of view when compared to conventional shallow disposal sites.

Rock salt is practically impermeable to gas and liquids. This impermeability is due to the tight-ness of the structure and the absence of open natural joints and fissures that exist in many other types of rocks. Moreover, the high plastic deformation of rock salt hinders the development of arti-ficial fissures through which liquids and gases could leak out. The safe sealing of liquids leaks in a cavern in a rock-salt formation has two geochemical aspects:12–14 the stability of the cavern, and the tightness of the closure and surrounding formations.

The stability of a cavern at a particular depth and with predefined geometrical dimensions is decisively affected by the geological situations and the geological properties of the rock salt, rock mass temperature, in situ stress, and pressure conditions in the cavern. Thus, the engineer or scien-tist has access to all the data required for prediction models, which allow realistic statements to be made and the time-dependent, load-bearing behavior of caverns for storage and waste disposal.15,16

To seal off a liquid-filled cavern from the biosphere for a long period of time, the following points should be noted:

1. Demonstration that a cavern will be permanently sealed. This is primarily an engineering problem involving the sealing material.

2. Demonstration that the natural increase of pressure in the sealed cavern will not cause cracking in the surrounding rock formation.

3. The size of the critical pressure determined in the frac test depends on natural conditions such as the mechanical properties of the surrounding halite and existing stress patterns, and on the test method itself, specifically on the time at which the test is performed and the rate of pressure increase.

4. The results obtained from frac tests in boreholes cannot be directly applied to the case of a closed cavern with a natural pressure increase.

5. The previously permitted maximum pressure gradient for closed caverns should be sub-jected to extensive testing.

6. Regarding a permanently sealed cavern, an accompanying computer analysis is urgently needed to correctly interpret the results of the frac tests and correctly evaluate the danger of fractures in the surrounding salt formation.

One example of hazardous waste disposal in salt caverns is the Waste Isolation Pilot Plant (WIPP) located in Southwestern New Mexico, which was selected by the Department of Energy (DOE) for deep geologic depository for permanent disposal of radioactive wastes in the United States. The repository is located in bedded salt of Permian Age at a depth of 2150 ft below groundwater. Bedded


salt is a preferred medium for permanent emplacement of wastes because of the favorable physical, thermal, and mechanical properties of halite. However, bedded salt does undergo different degrees of dissolution; therefore, it is necessary to have a thorough evaluation and understanding of the horizontal and vertical extent as well as the time and rate of salt dissolution.

The WIPP site has been investigated over a period of 8 years to achieve a desirable level of assurance about its integrity and to ensure that there will not be a breach and leakage of the waste to either freshwater aquifer or the nearby Pecos River.

Prior to depositing hazardous wastes in salt caverns, it is important to have a complete knowl-edge and thorough understanding of the geologic and hydrogeologic characteristics of the site that relate to the transport of waste to the biosphere in the event of a breach.

7.4 groundWater ProtectIon

7.4.1 damagE prEvEntion to thE WatEr rEsourcE systEm

The prevention of damage to water resources is preferable and less costly than treatment. This applies only to human activities such as mining and other constructions that affect the environment. However, many practical problems arising from dewatering by mines have been observed in differ-ent parts of the world.17 Some of them are degrading of water and aquifer quality, reduction in yield or drying of wells, additional pumping costs for water supplies as a result of deeper pumping levels, intrusion of sea water, pollution of surface water by degraded groundwater, and land subsidence, especially sinkhole development.

Aquifers can be contaminated directly from mining wastes or as a result of rerouting of degraded waters because of mining activities. Contaminated surface streams may also affect local aquifers, especially where heavy mine pumping has lowered the water table, which encourages recharge from the contaminated stream.

The extent of the problem is highlighted by the U.S. Geological Survey Water Summary for 1984,18a 1988,18b 1991,18c and 1993.18d Streamwater and groundwater quality were studied in 52 states; 32 states had surface-water problems from sources such as toxic contaminants, pesticides, herbicides, acid precipitation, and bacteria; 30 states showed groundwater pollution from causes such as hazardous waste sites, seepage from septic systems, landfill leachates, intensive pumping at coastal regions, and high concentrations of salt because of recirculation from irrigation water. Of these, 17 states showed both surface and groundwater problems from acid mine drainage and other mining activities.

Because mining is the most prevalent means of deteriorating the hydrogeological system, the prevention of damage to water resources due to mining is discussed in more detail. There are dif-ferent methods to prevent this damage:

1. Premining studies should investigate the impact of the proposed mine on the hydroenviron-ment and provide detailed baseline studies of the district to: (a) identify all aspects of the proposed mining activities liable to cause damage to water resources, (b) draw up plans to deal with the identified problems using the best approved methods, (c) make provisions for ongoing impacts that may occur after the mine has started working and also after mining operations have ceased, and (d) prepare advanced plans to deal with the main types of possi-ble accidents during mining, which are likely to seriously damage the hydroenvironment.

2. A monitoring program should be carried out to provide adequate data on all relevant aspects of water quality in the existing mine area and in the district of the proposed mine. The monitoring system should be designed to provide an early warning system in the event of unforeseen changes in conditions that would be harmful to water resources.


3. Movement of polluted water from old workings should be controlled. It can be reduced by grouting of old boreholes, shafts, and fissures. Subsurface dams and grout curtains are also used to contain polluted waters.

4. Rehabilitation of the site by remedial action can reduce damage to water. Compaction and landscaping with gently sloping topography can reduce the polluting potential of mining wastes to the hydroenvironment. Highly acidic waste heaps may be moved to an unex-posed location. Revegetation by covering with metal-tolerant gases and plants can help stabilize old tips and tailing ponds. It helps bind the surface and reduces both wind and water erosion. Various patent coagulants are also used to try to bind and stabilize tips and tailings. In many sites, a combination of different types of actions may be required to achieve maximum benefit.

5. If water resources are being polluted by mine waters, and no ready means is available to prevent it at source, treatment may be necessary. The most commonly used methods of treating mine waters include neutralization, coagulation, and aeration.

Limestone and its derivatives are the most frequently used substances for neutralizing acid mine waters. Unslaked lime, hydrated lime, and, most recently, limestone have been widely used, primar-ily because of their low cost.19,20 Besides adjusting the pH, the increased alkalinity also enables other methods of treatment to work more effectively, especially with regard to the removal of metals from solution in the water.

A number of standard water treatment procedures involving the addition of chemicals, such as aluminum sulfate, are used to help remove fine particles. The coagulant binds together minute particles, which then settle or can be filtered out.

The addition of oxygen is particularly helpful in facilitating the precipitation of the soluble forms of iron and manganese. Other polluting substances, including hydrogen sulfide and cyanide, found in mine and industrial waters can also be removed by aeration.

Several other methods of treatment have been tried in different countries but are more limited in application, of less certain effectiveness, or controversial because of side effects. Methods for waste control in industry include minimizing use of water, controlling losses in processes, extraction by recycling water and recovery of products, fine-tailings filtration in mineral industry, floatation in mineral industries, bioremediation/biological treatment, air stripping, and carbon bed adsorption.

7.4.2 rEmEdiation oF groundWatEr aquiFErs

Groundwater contamination by petroleum hydrocarbons, organic solvents, and other toxic nonaque-ous phase liquids poses a serious threat to groundwater resources worldwide. The processes that govern the behavior and fate of contaminants have been investigated by many researchers through mathematical models with varying degrees of complexity.21,22

The goal of site remediation is to restore soil and groundwater quality to precontamination conditions as much as possible. The remedial or clean-up standards are based on numerous criteria, including site information, contamination type and extent, potential threat to human health, and protection of future soil and groundwater quality.23

Costs for site remediation can quickly escalate into large sums. Considerable progress has been made recently in regulation, engineering practice, environmental awareness, source control, and waste management procedures. This progress enables more reasoned decisions to be made regard-ing contaminant migration and threat to human health.

Numerous technologies to remediate sites exist, and new technologies are being developed and tested. A brief review of some of the more common technologies follows:


1. Excavation: This involves the removal of contaminated materials for disposal at a hazard-ous waste or other disposal landfill site. Newer regulations favor alternative waste treat-ment technologies at the contaminated site; however, municipal refuse will continue to be placed at landfills for some time to come despite its containing small quantities of hazardous materials. Attempts must be made to remove these from domestic refuse to keep the sanitary landfills from becoming hazardous waste landfills. Excavation projects must include determination of the volume of material to be removed, equipment to be used, source and type of clean backfill, compaction specifications, and sidewall stability. Finally, postexcavation sampling and testing are required to determine the effectiveness of the excavation clean-up. Even though the cost is high, excavation is still the most effective way of site remediation.

2. Air stripping: This utilizes the volatilization characteristics of the contaminant to separate it from groundwater. The contaminated water is pumped into a tank filled with a packing material to enhance aeration and slow the water movement. Air is blown into the hose of the tank as the water moves through it, and the volatile compounds are stripped and entrained to the atmosphere. This technology requires the contaminant to be highly vola-tile (such as solvents or light hydrocarbon fuels).

3. Bioremediation: There are several methods for bioremediation of groundwater. These include those used by Hazen et al.,24 who injected methane mixed with air into the con-taminated aquifer via a horizontal well, and extraction from the vadoze zone via a parallel horizontal well (Figure 7.6). The indigenous microorganisms were stimulated in situ to degrade trichloroethylene (TCE), tetrachloroethylene (PCE), and their daughter products. Hazen et al. recorded in their test that all of the wells in the zone of effect showed signifi-cant decreases in contaminants in less than 1 month. Four of five vadose zone piezometers (each with three sampling depths) declined from concentrations as high as 10,000 ppm to less than 5 ppm in less than 6 weeks. A variety of other microbial parameters increased with methane injection, indicating the extent and type of stimulation that had occurred.

Savannah river technology center

O2 CH2

Contaminated zone

Water table

Groundsurface

Heating elementsVacuumblower

Injection point for air/methane

Compressednatural gas

Compressor

Catalytic oxidizer

Catalyst

CO2 HCl

Slotted liner

Wat

er sa

tura

ted

zone

Vado

se zo

ne

HCl + CO2

TCE

Extraction of air containing volatile compounds

fIgure 7.6 In situ bioremediation via horizontal well. (From Hazen, J. C. et al., In-Situ Bioremediation Via Horizontal Wells, Int. Symp. on Engin. Hydrology Proc. ASCE, 1993, p. 862.)


Bioremediation using a recirculation well is still in practice. Lang et al.25 designed and showed that their model of in situ bioremediation can be fairly cost effective. Bioremediation requires recirculating contaminated groundwater with a treatment that uses oxygen (such as peroxide) and nutrients. This delivers nutrients that allow biologic action to react on contaminants, cleaning the aquifer matrix. The groundwater is pumped by extraction wells, moving the treated waste through the contaminated zone and allowing biological respira-tion of the indigenous microfauna to further metabolize remaining contaminants. The con-taminant plume must not move offsite, and the site geology must be acceptable (sandy, using methanotrophic bacteria for degradation of volatile organic compounds). Methanotrophic bacteria produce the enzyme methane monooxygenase (MMO) so that microorganisms can utilize the supplied electron donor (methane). Lang’s work investigated the use of a vertical recirculation well (Figure 7.7) to promote co-metabolic transformation of vinyl chloride (VC) using methanotrophic bacteria. The vertical recirculation well recirculated the target contaminants, thus increasing their contact time with the biologically active zone and allow-ing a greater extent of contaminant removal. The benefit of using recirculation wells is the elimination of the cost of pumping groundwater to the surface for aboveground treatment.

Site remediation can be compromised based on the applicable regulations, hydrogeo-logic data, data interpretation, final clean-up concentrations of contaminants, negotiation of the remedial action plan alternatives, cost, and remediation plan execution. The ability to estimate the safety risk and cost–benefit ratio of the remediation effort must be used.

Problems still exist with these methods because the release of the contaminant into the atmosphere is being discouraged in some areas, and a second treatment is often required to capture the airborne contaminants (such as carbon adsorption).

4. Carbon bed adsorption: This is an established technology used to treat contaminated groundwater. The contaminant becomes adsorbed to the carbon, which removes weakly polar molecules. The concentration of the contaminated influent directly affects the reten-tion time of carbon adsorption before all the absorption sites are filled and break through. The spent carbon can then be replaced with unused carbon, and the adsorption process repeated. Carbon is versatile and can be used for many organic contaminants. Costs can become high, depending on how often the carbon must be regenerated or replaced.

Aquitard

Pump

Ground waterRecirculation unit

Seal

Vadose zone

MethaneOxygen

fIgure 7.7 In situ bioremediation using a recirculation well. (From Lang, M. M. et al., In-Situ Bioremedia-tion Using a Recirculation Well, Int. Symp. on Engin. Hydrology, Proc. ASCEP, 1993, p. 880.)


7.5 rISk and legal aSPectS of WaSte dISPoSal SIteS26

Chemical solvents are potential threats to human health and the environment. The sequence of activities that can lead to releases of chemical solvents into the environment is shown in Figure 7.8. This section focuses on the human health effects that can occur at the point of ultimate disposal as related to landfills as the final disposal method.

In the past, landfilling has been a major disposal option for solvents. The U.S. Environmental Pro-tection Agency (U.S. EPA) has estimated that about 22.4 million metric tons of hazardous waste are disposed of on land each year.27 The risks from land disposal of chemicals originate from the potential for chemicals to migrate into water supplies or soils and to evaporate into the atmosphere. Because of these problems, landfilling of solvents has become a major public issue. The Hazardous and Solid Waste Amendments of 1984 (P.L. 98-1134, Section 201 (e)) prohibit the land disposal of certain liquid hazardous wastes unless the EPA can demonstrate that there is no threat to human health.

Risk assessment is used widely to evaluate environmental health risks. The application of risk assessment to the land disposal of organic solvents has been done to a limited extent in con-nection with site investigations or remedial clean-up actions under the Comprehensive Environ-mental Response Compensation and Liability Act (CERCLA or “Superfund”). The application of risk assessment to evaluate which chemicals should be disposed of on land and in what concen-trations has received less attention. The procedures for risk assessment, the application of these

Generation of chemicalsdue to migration atdisposal site

Generation of chemicalsthrough product orservice use

Generation of wastechemicals throughspillage, disposalof excess material

Generation of wastechemicals throughaccidents, washingoperations fortransport vehicles

Dermal absorptionfrom contact withcontaminated soil,water, clothes,objectsInhalation ofparticles andvapors (workersand the public)

Ingestion of con-taminated soiland dustIngestion throughdrinking water

Ingestion through contam-inated food products

Generation of wastechemicals throughspillage, disposalof excess material

Source of WastesPotential

Health EffectsActivity

MANUFACTURE OF CHEMICALS

TRANSPORT OF CHEMICALSTO SECONDARY MANUFACTURERS

USE OF CHEMICALS BYSECONDARY MANUFACTURING

OPERATIONS

CHEMICAL USAGE THROUGHCONSUMPTION OF GOODS AND

SERVICES

DISPOSAL OF CHEMICALS

fIgure 7.8 Generalized framework for the origins of risks from organic chemical solvents.


procedures to chemical disposal decisions, and the uncertainties that occur in the assessment process are outlined with emphasis on the effect that these uncertainties can have on the level of risk that is calculated.

Risk assessment techniques are used to evaluate the use of land disposal for 24 organic solvents. Risk acceptability, risk evaluation, and risk management are important dimensions of the use of risk assessment, and perception literature and the public’s perception and acceptability of the risks from organic solvents in landfills must be determined. A framework follows for translating physical, chemical, biological, and health-related attributes of the solvents into dimensions of public percep-tion of risks from organic solvents.

7.5.1 dEFinition oF risk and risk assEssmEnt

Risk has been defined as “the potential for realization of unwanted, negative consequences of an event”28 and as “the complete description of possible undesired consequences of a course of action, together with an indication of their likelihood and seriousness.”29 Risk also has been defined in more quantitative terms as follows:

The probability per unit time of the occurrence of a unit cost burden represents the statistical likeli-hood of a randomly exposed individual being adversely affected by some hazardous event. Thus, risk involves a measure of probability and severity of adverse impacts.30

Quantitative risk assessment is a procedure for estimating the probability of an adverse health effect occurring in a population from some event and the probability of the occurrence of the event. A level of risk associated with the use of a chemical solvent is calculated as the combined probability (or product of the probabilities) of the hazard existing, the chemical’s release into the environment occurring, population exposure, and potential health effects.31,32

Risk assessment is most accurate when decision situations, causative events, and effects are specific. In the context of siting a waste disposal facility, it means that the accuracy is greatest for a site where geological, hydrological, and meteorological characteristics of proposed sites, as well as the physical, chemical, and biological characteristics of the waste material, are known. When risk assessment is used to evaluate an existing waste disposal facility, results are most accurate when applied to the behavior of individual chemicals known to produce, or suspected of producing, adverse health effects.

7.5.2 application oF risk assEssmEnt in thE contExt oF WastE disposal

Risk analysis or assessment has received attention from the scientific community for more than two decades. Between 1973 and 1982, a number of federal agencies proposed carcinogen assessment policies or guidelines that incorporated risk assessments. Risk assessment was used extensively by the EPA in 1980 for the development of water quality guidelines. Its importance for the hazardous and toxic waste legislation of the late 1970s and early 1980s has been recognized by regulatory agencies.33,34 Regulations were proposed by the EPA to establish and systematize methods for con-ducting risk assessments for a variety of its environmental programs. In the regulations, risk assess-ment is a method of quantifying the carcinogenic, mutagenic, and developmental effects of toxic substances35–37 and the health effects associated with complex chemical mixtures.38

Risk assessment can be applied to several kinds of waste disposal situations, including aban-doned waste disposal sites, operation and maintenance of an existing facility, closure of an existing facility, and the siting and construction of a new disposal facility. In each of these four situations, risk assessment can be used for the following purposes (some of these have been suggested by Anderson et al.39 and by Russell and Gruber):40


Setting priorities among existing waste sites or potential waste disposal site locations as a •basis for regulatory action (e.g., the hazard ranking system used to establish the National Priorities List under CERCLA)Setting standards or guidelines for the release of contaminants to air, water, and land in •both the general environment and occupational settingsEvaluating the residual risk to human health and the environment of alternative technologies•Evaluating the suitability of alternative sites for waste disposal•

Of these uses of risk assessment, the most common use is for the development of environmental standards. Many existing environmental standards are directly applicable to assessing the impacts of solvent disposal in landfills. In fact, regulations for the National Contingency Plan under CERCLA require that, at least for remedial action for uncontrolled waste sites, these standards be reviewed prior to undertaking a formal risk assessment.41 A summary of programs under which standards are developed is given in Table 7.4 for the chemicals under review here:

Drinking water standards: The EPA’s Office of Drinking Water makes extensive use of risk assessment in the development of “Recommended Maximum Contaminant Levels” (RMCLs) for drinking water under the Safe Drinking Water Act.42 The most recent ver-sion of these RMCLs for the organic solvents under study is given in Table 7.4. Prior to the EPA’s work, the National Academy of Sciences (1977 and ongoing) published the extensive drinking water limits based on risk assessments in its Drinking Water and Health series. A number of states, such as New York, have also been active in the area of developing drink-ing water standards using risk assessment techniques.

Ambient water quality standards: One of the earliest applications of risk assessment to stan-dards development was for water quality criteria. In November 1980, the EPA proposed water quality criteria in the form of water concentrations, assuming risk levels ranging from 10–5 to 10–7. These levels are given in Table 7.5 for the solvents under review.

Air quality standards: The EPA is drawing upon risk assessments in the development of National Emission Standards for Hazardous Air Pollutants (NESHAPs) under the Clean Air Act. These risk assessments are appearing in health assessment documents conducted on a chemical-by-chemical basis by the EPA Office of Health and Environmental Assess-ment. Health effects assessments have been conducted for many of the solvents covered in this study: acetone; carbon tetrachloride; tetrachloroethylene; toluene; 1,1,1-trichloro-ethane; trichloroethylene; and xylene. The EPA has issued “intent-to-list” notices under NESHAPs for the following solvents under review here: carbon tetrachloride; trichloro-ethylene; methylene chloride; and 1,1,1-trichloroethane.43 Decisions have been made not to regulate toluene and chlorobenzenes. Xylenes are currently undergoing a preliminary health screening under NESHAPs. States are also taking the lead in using risk assessments for the development of emission limits (called performance standards) for new sources of air pollutants under the Clean Air Act. As of mid1986, 17 states had developed air toxic programs, and 19 more were in the process of doing so. Many of the chemicals selected for state action are organic solvents. Fourteen of the states use or plan to use risk assessments in the evaluation of air toxic pollutants.43

Occupational health standards: The Occupational Safety and Health Administration (OSHA) and its research division, the National Institute of Occupational Health and Safety, develop criteria and standards primarily for air pollutants in occupational settings under the OSHA Act. Risk assessments are used in the development of many of these guidelines. Some of the pollutants are organic solvents.

Consumer protection standards: The Consumer Product Safety Commission and the Food and Drug Administration (FDA) also set limits for contaminants, including some solvents, in cer-tain settings that affect the general public. Risk analyses are used for some of these limits.

140 Environmental Hydrogeology, Second Editionta

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7.5.3 an outlinE oF thE risk assEssmEnt procEss

Risk assessment is a useful tool for evaluating the potential threats that chemical solvents pose to human health and the environment. It provides a unified analytical framework that integrates the sources of chemical releases, environmental fate and transport, exposure, and health effects of such solvents. A risk assessment provides an estimate of the lifetime risk to an individual or to a population of the exposure to a hazard. Individual risk is the probability that an individual will experience a risk of death or disease in the course of a lifetime. Population risk is the number of excess cases of disease or death that could appear as a result of lifetime exposure of the population to a particular hazard.

Because the concept of risk assessment is straightforward, its application depends upon a variety of complex models whose mathematical formulations are far from refined and whose data require-ments can be enormous. Although debates exist about the definition of the overall process of risk analysis or risk assessment, several components are generally accepted as critical to the process. These components include the following:

1. Risk or hazard identification: A qualitative identification of the likelihood that hazards can result in risk and the nature of the risk agents

2. Risk estimation: A quantification of the types and magnitudes of the risks to humans, that is, how bad they are and the probability of the risks occurring

3. Risk acceptability: A determination of the acceptability of risk levels to society and to individuals, taking into account perceptions of and attitudes toward risks

4. Risk evaluation: An evaluation of the economic and social ramifications of the risks asso-ciated with an activity including, but not limited to, an assessment of the costs and benefits of the risks

table 7.5concentrations for selected organic solvents equivalent to a 10–5 risk level

chemical

concentrations in µg/l

ambient water quality criteriaa

drinking water concentrations

equal to 10–5 riskb

naS cag rmclsc

Trichloroethylene 27 45 26 5

Tetrachloroethylene 8 35 6.7 NA

Carbon tetrachloride 4 45 2.7 5

1,2-Dichloroethane 9 7.0 3.8 5

Vinyl chloride 20 10 0.15 1

1,1-Dichloroethylene 0.3 NC 0.61 7

Benzene 7 NC 13 5

1,1,1-Trichloroethane 200

p-Dichlorobenzene 750a From Anderson et al. (1984, p. 288), updating U.S. EPA Federal Register (November 28, 1980, pp. 79318–79379).b Cited in Federal Register 50 (November 13, 1985, p. 46883). Abbreviations: CAG, Cancer Assessment Group in the

EPA; NAS, National Academy of Sciences; NC, Not calculated.c RMCLs or Recommended Maximum Contaminant Levels are from U.S. EPA (November 20, 1985).

pjw

stk|

4020

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4354

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0


5. Risk management: The design and implementation of a management and decision-making system that unites analytical elements of the risk assessment process with judgmental and institutional factors

A schematic illustration of the risk-assessment process is shown in Figure 7.9. This overall process has been called by various names: risk analysis or assessment, risk control, and risk management. Alternative frameworks for the process have been proposed by Lowrance,44 Rowe,28 and Lave.45 The concept of risk control was discussed by Davies.46 The term risk assessment will be used primarily to characterize the risk identification and estimation process as it applies to chemical solvents.

7.6 comPonentS of tHe rISk aSSeSSment ProceSS

7.6.1 risk or hazard idEntiFication

(Note: Hazard identification should not be confused with hazard assessment. Hazard assessment is a term often used to describe dose–response estimation.)

Behavioral,personal

experientialfactors

Communication,problem

structuring

RISK ACCEPTABILITY DETERMINATIONInputs

OutputsRisk perceptions

Attitudes toward risk

RISK EVALUATION

Social and economic impacts

Standards and normsRISK MANAGEMENT

Decision outcome

Perceivedchemicalattributes

RISK OR HAZARD IDENTIFICATIONInputs

Structure-activity relationshipsexisting standards and criteriahealth effects data

Outputs

RISK ESTIMATIONInputs

Physical, chemical & biologicalproperties or attributes

of chemical solvent

Environmental Fata/TransportToxicity assessment: Dose-

response relationships

Degree of exposure (Dose)Sensitivity of population at risksocio-economic characteristics

of those exposedOutputs

Quantitative risk assessment:Probability and magnitude ofoccurrence and consequences

Identification of chemicals and their hazards

*

*

*

*

fIgure 7.9 A risk assessment and management framework for chemical solvents.


Hazards are threats to human health, and risks are the probability of harm occurring from such hazards. The first step in risk assessment is to identify hazards and risks through a qualitative or semiquantitative screening process. Hazard identification is a form of problem identification. In this step, a potential linkage between a risk agent and an adverse effect is identified.47 Those substances are identified that have a high probability of being harmful to human health. The decision-making process might never conclude if the sources and consequences of risks are not identified adequately at the beginning of a risk assessment. In fact, decision making could proceed incorrectly.

methods for Hazard Identification

Lave45 identified five methods for hazard identification that are applicable to chemical solvents. These methods have also been incorporated in the proposed federal regulations for risk assess-ment35 and developed at the National Academy of Science.47

1. The identification of abnormal disease patterns through an analysis of case clusters 2. The identification of structural and toxicological similarities (known as structure–activity

relationships) among chemicals through structural toxicology 3. The use of data from experimental tests of chemicals on simple organisms whose response

time is rapid 4. The use of data from experimental tests through animal bioassays 5. The creation of inferences from epidemiological studies

Many of these methods have been incorporated into hazard identification procedures for uncon-trolled hazardous waste or Superfund sites under CERCLA and analogous state legislation. The guidance document for conducting public health assessments at Superfund sites, for example, uses hazard identification procedures to obtain a list of “indicator” chemicals. These indicators are con-sidered representative of a larger number of chemicals found in a particular landfill. The physical, chemical, and biological attributes of chemicals are used to identify and select these indicator chem-icals and determine their health risks. Once the chemicals are identified, the chemical attributes are used as a basis for quantifying risks more precisely.

The output of hazard identification for an existing landfill is an identification and ranking of chemicals likely to be found in the vicinity of the landfill. According to the EPA health assessment manual, the ranking of the chemicals is based upon the product of two chemical attributes: the toxicity and concentration of each chemical found at a particular landfill site.48 The concentration is either measured directly or estimated from a wide range of chemical attributes such as solubil-ity, permeability in soil, and volatility. The set of indicator chemicals is considered representative of different chemical groups. In the case of Superfund sites, these indicator chemicals are used as the basis for analyzing the relative risks from alternative remedial actions. An important input into the toxicity component for the ranking of chemicals is a “weight of evidence” determination. Such a determination rates the quality of the toxicity data from high to low. The criteria developed by the International Agency for Research on Cancer (IARC) are commonly used to characterize the weight of evidence for carcinogens. The IARC categories are sufficient evidence, limited evidence, inadequate evidence, no evidence, and no data. This is used to group carcinogens into five catego-ries: human carcinogens, probable carcinogens, possible carcinogens, not classified carcinogens, and no evidence carcinogens.35,49

Because the parameters and methodologies used in hazard identification are similar to those used for certain steps in risk estimation, they will be discussed in detail in Section 7.6.2. The major difference between the two steps is that hazard identification uses data qualitatively, whereas risk estimation uses data more quantitatively. The objective of hazard identification is to obtain a subset of chemicals for more detailed investigation.


uncertainties and errors in Hazard Identification

These can adversely affect the accuracy of identifying chemicals that have a high potential for entering the environment from a landfill. When sampling data is used to identify chemicals and their prevalence in a landfill, a number of potential sources of error can occur. First, analytical techniques can miss chemicals. These techniques used under the Superfund (CERCLA) program, for example, are designed to analyze for a number of compounds simultaneously. They rely on scan-ning devices that do not spend enough time to identify particular chemicals. It is, therefore, not an optimum technique when the detection of individual compounds is important. Isaacson, Eckel, and Fisk51 recently reanalyzed 3000 samples from Superfund sites known to contain both organic and inorganic compounds. They detected 28 organic compounds that had been undetected in a previous analysis oriented toward identifying multiple compounds simultaneously.

A second source of error can be the choice of an improper indicator chemical to character-ize the risks from a group of chemicals. Often, the most toxic compounds in a group are used to characterize the group. This can cause an overestimation of risk. Sometimes, a chemical is chosen to characterize a group of chemicals with risks ranging over several orders of magnitude. In such cases, additional chemicals should be chosen to characterize the group.

Errors can result from exclusive reliance on tests with lower organisms as screens for potential carcinogens. Evidence of mutagenicity is often used as an indicator of potential carcinogenicity because the two often show strong correlations. There have been significant exceptions; that is, false negatives occur. For example, carbon tetrachloride is a chemical that has not been shown to be mutagenic in bacteria or cultured liver cells, yet it is carcinogenic in animals.51

7.6.2 risk Estimation

Once chemicals and their hazards are identified, estimates of the magnitude of risks from those hazards and the consequences of the risks can be made. The estimation procedure consists of the following steps:

1. Exposure assessment is “the determination of the estimation (qualitative or quantitative) of the magnitude, frequency, duration, and route of exposure.”52 Exposure assessment includes a knowledge of the following:

The sources of the chemical.•The rates of release of the chemicals into the environment and their fates and transport •in the environment. The rates are related to the physical, chemical, and biological attributes of the chemicals and the way in which these attributes are transformed under environmental conditions.The routes or pathways of exposure from environmental endpoints to human organ-•isms via oral, inhalation, and dermal pathways.

2. Health effects assessment primarily uses health data to determine the likelihood that, once exposed, a given individual or population will actually experience the risks. Where health data are available, socioeconomic characteristics of the population would be used as an indirect measure of health sensitivity, but these relationships are not well established. The assessment consists of the following:

Estimation of intake levels•Absorption by the body•Toxicity of the risk agent, once in the body•State of health of the organism (though it is usually not feasible to include this)•

3. Dose–response relationships (or toxicity assessment) are expressed as the responses of different organisms to varying doses of the chemicals. These responses are a function of


the health-related characteristics of the chemicals (for example, chronic or acute toxicity, carcinogenic potential).

4. Risk calculation (or risk characterization), the output of a quantitative risk assessment, is expressed as a risk to an individual or population for a lifetime of constant exposure. The individual risk is the chance of contracting a disease or dying from it. The population risk is the increased number of disease cases or deaths resulting from the exposure. Once that risk level is known, measures can be designed to reduce the level of exposure to some acceptable level.

These steps are portrayed in a simple form in Figure 7.10. To envision the interrelation of the forego-ing steps, one can begin at the end of the risk-estimation process: risk calculation.

risk calculation

The formulation of the equations for risk calculations depends on whether: (1) the risk agent is a carcinogen and (2) a threshold exists; that is, a dose of the chemical exists, below which no health effect is observed. Carcinogens are considered to have no threshold, and most noncarcinogens are assumed to have a threshold.

carcinogens (no threshold)

A simplified version of the calculation of the individual lifetime risk of exposure to a carcinogen (assuming no threshold) is as follows:

Ti = Ri · Di (7.2)

where i = the specific chemical or chemicals.

Excess number of cases in apopulation

Probability of excess riskto an individual **

Unit riskestimate

Dose

Dose-responseestimate

Hazard and Risk Identification

Subset of chemicals

Risk estimation

Populationat risk

estimates

Concentration

Environmental fateand transport

Release rates

fIgure 7.10 Elements in risk estimation and their relationships to risk calculation.


T = the probability that a human response such as the development of cancer will occur over a lifetime of exposure to a constant dose, D, of a chemical, i.

R = the unit risk factor in terms of number of excess cases of cancer that develop in a given population after a lifetime exposure to a chemical. It is expressed as the inverse of a milligram (mg) of the chemical consumed per kilogram (kg) of body weight per day (d).

D = the dose of the chemical in terms of mg/kg/d.

The risk, Z, to an entire population, P, is

Zi = Ti · P = Ri · Di · P (7.3)

The simplicity of the equation conceals a number of complexities. The mathematical formulation in Equation 7.2 is based on the assumption that a linear relationship exists between the dose and the response. This assumption is often made for low doses or concentrations of a substance at which no dose–response data exists. This assumption may not always be valid. At higher doses, common formulations have the probability, T, of increasing exponentially with dose. Such an exponential relationship could also be occurring at low doses.

The dose, D, is the end result of the exposure assessment and is derived from one of the outputs of environmental fate and transport modeling for air, water, and soil concentration. The unit risk factor, R, is derived from experimental work relating chemical doses to responses in test organisms (dose–response curves). The unit risk factor for carcinogens is the response level associated with a dose of 1 mg/m3 (via inhalation) and 1 mg/L (via water ingestion) for an adult whose body weight is 70 kg when exposed over a 70-year lifespan. When using a linearized multistage model to extrapo-late potency of chemicals down to low doses, the unit risk is the upper bound of the 95% confidence limit of the maximum linear term derived from the dose–response data, that is, the steepest slope.

To obtain acceptable concentrations as a goal for mitigation, one can use Equation 7.2 to back calculate to a desired concentration reflecting some desired risk level (e.g., 1 ∞ 10–6 chance of get-ting cancer). To do so, some response or “acceptable risk” level must be defined.

Utilizing assumptions about human body weight and the amount of a given chemical consumed per day (Table 7.6), one can calculate the “acceptable” concentration from the dose that corresponds to the acceptable risk level. For a body weight of 70 kg and a consumption rate of 2 L of water per day, Equation 7.3 is

Ci = Di · 70 kg/2 L/d (7.4)

where C = the concentration in mg/L.This “acceptable” concentration can then be compared with measured concentrations, at a dis-

posal site, or with concentrations from a series of environmental fate and transport models for water,

table 7.6daily ingestion rates

adult child

Water 2 L 1 L

Air 20 m3 5 m3

Fish 6.5 g —

Note: The average body weight of an adult is assumed to be 70 kg, and the average weight of a child is assumed to be 10 kg. There is some variation in the rates used for quantitative risk assessments. For example, air intake rates of 17 m3 have been used rather than 20 m3 (U.S. EPA, December 27, 1985, p. 26).

Source: Summarized in ICF (1985, p. 75) from water-quality criteria and National Academy of Sciences, Drinking Water and Health series.


soil, and air. Alternatively, it can be used as an input into environmental fate and transport models to obtain an acceptable discharge of the substance into the environment.

noncarcinogens

Acceptable risk levels for noncarcinogens are generally expressed in terms of acceptable daily intake (ADI) levels. The expression for ADIs usually takes the following form:

ADI = (B/U) · (A/C) (7.5)

where ADI = acceptable daily intake (in mg/L/d). A = the weight of the consuming organism (e.g., 70 kg for humans). B = the amount sufficient to produce an unwanted health effect, which has been deter-

mined empirically (expressed in mg/kg of body weight). Lethal doses that will kill 50% of a population (LD50) could be used as one extreme. Concentrations at which no effect is observed (No Adverse Effect Levels or NOELs) could be used as the other extreme.

U = an uncertainty factor that for drinking water, has ranged from 10 to 1,000 to introduce conservatism into the risk estimate.

C = the amount of water/air/food consumed daily (e.g., the consumption of 2 L of water per day or inhalation of 20 m3/d by humans).

ADI and B are usually subdivided into subchronic and chronic effects. Chronic levels are preferable to acute levels when chronic estimates are available. Equation 7.5 can be reformulated with B as the dependent variable. This allows one to calculate a targeted dose once an acceptable level has been established.

Figure 7.10 above illustrates the relationship among the parameters in the risk calculation. If the doses needed to compute the risk level, T, are not available from reliable monitoring data, they can be calculated from the amounts of a given chemical released into the environment and from environmental fate and transport models. Unit risk estimates are obtained from dose–response rela-tionships. The product of doses and unit risk estimates gives the excess risk to an individual. Multi-plying this product by total population gives the risk level in terms of the number of excess cases in a population expected from exposure to the given dose of the chemical.

7.6.3 ExposurE assEssmEnt: idEntiFication oF sourcEs oF chEmicals

There are a number of ways of defining the source of chemical solvents in landfills. On the broadest level, the source can be defined in terms of the origin of the chemical in the economy. It can also be defined as the mixture of chemicals that enter, or are inputs to, a landfill.

This is a difficult task even though, for operating landfills, it is required that incoming wastes be documented and controlled through a manifest system. A large variety of chemicals arrive at a landfill in widely varying concentrations. Solvents, for example, typically arrive at landfills in drums. An analysis of solvents in over 1200 drums nationwide revealed that the mean and maxi-mum concentrations of organic solvents in the drums often differed by several orders of magni-tude.52-53 The mean concentration of carbon tetrachloride was 342 parts per million (ppm), and the maximum was 400,000. The mean concentration for chlorobenzene was 85 ppm, and the maxi-mum was 57,000. Once the solvents are dispersed in a landfill, their concentrations can become even more variable. This uncertainty is particularly acute for existing landfills. Operators of new landfills are required by RCRA permit to determine the correlation of effluent in incoming wells prior to accepting the waste, thereby controlling this source of uncertainty. Operators are also required to categorize waste to prevent their liability from accepting questionable or banned waste.


New landfills can presumably control this source of uncertainty by sampling incoming wastes and adjusting the amounts accepted for disposal.

A third definition of the source is in terms of the outputs from the landfill (i.e., the chemical mixtures that leave the landfill). This probably has a greater degree of variation than estimates from sources.

7.6.4 ExposurE assEssmEnt: chEmical rElEasEs/EnvironmEntal FatE and transport

general considerations

Release or emission estimates are the first step in evaluating the fate and transport of chemicals in the environment. Releases of chemicals into the air, land, and water occur in a variety of ways. Releases to water occur via leaching (or percolation) and runoff. Releases to the air occur via direct air emissions from soil, fugitive dust emissions, and evaporation from land and water surfaces. The amount of material stored in a landfill is a major factor in predicting discharges from the landfill. As discussed earlier, uncertainties occur in estimating these amounts because the quantity of materials in landfills is highly variable. This can cause emission and effluent rates to vary by several orders of magnitude.

The transformation and migration of released chemicals can be estimated via mathematical models. These models are specific to the particular medium in which chemicals are found. The media are soil, groundwater, surface water, air, foods (vegetables, fish, shellfish), and objects with which humans come into contact. Some of the major input parameters to models used to characterize the fate and transport of chemicals in the environment are listed in Table 7.10. The values assigned to many of these parameters for organic solvents are given in Tables 7.7, 7.8, and 7.9.

Onishi54 distinguished between primary and secondary release mechanisms of contaminants. A primary release, he noted, is directly from the contaminant source. A secondary release occurs from a location or a source that has become contaminated from the primary source. For example, a primary source would be a spill or discharge of chemicals to soils surrounding a factory. The secondary source would be the release of those chemicals to groundwaters or surface waters driven by flood waters. This aspect of environmental fate and transport is often ignored. Monitoring data used as a basis for calculating doses often does not include a record of the weather conditions at the time of the sampling. Heavy rains and floods can substantially affect chemical detection in both soil and water.

An important aspect of the fate of organic chemicals in the environment is the extent at which they disappear altogether. Processes of degradation are hydrolysis, reduction, oxidation, photolysis, or biodegradation. A measure of the resultant of all of these forces is persistence. It is measured in terms of the “half-life” of a chemical. The half-life of a chemical is the amount of time it takes for half of the chemical to disappear, regardless of the mechanisms of degradation. Although this is an extremely useful measure, data are not always available for every chemical, and values vary with environmental conditions.

air

Evaporation is a major mechanism by which organic chemicals leave landfills. A recent review of the literature on organic chemical emission rates at landfills was conducted by Bennett.55 Experi-ments and models that estimate air emissions from landfills reveal that the rate of air emissions is a function of the following (often interrelated) variables:55,56

Environmental conditionsWind speedWind directionAtmospheric stability


TemperaturePrecipitation, moisture

Landfill attributes and surrounding conditionsGeneral rate of methane gas (if it is present, it can physically drive chemicals out of a landfill)Surface areaSoil typeSoil moistureType of soil coverDepth of soil coverSoil disturbance (vehicles, other human activity, and animals)Soil porosity or permeability

table 7.7environmental release/transport potential into air

Ignitability explosivity limits (% by volume) relative volatility

(evaporation ratea)flash point °f

Vapor pressure mmHg @ 20°c lower upper

Chlorobenzene 82 8.8 1.3 7.1 1.07b

o-Dichlorobenzene 160 0.348 2.2 9.2 0.15b

Cresol, cresylic acid 86 0.15

Ethylbenzene 20 7.1 1.0 6.7

Nitrobenzene 88 0.15

Pyridine 20 18.00 1.8 12.4

Toluene 45 38 1.2 7.0 1.5b

Xylene 80 9.5 1.0 7.0 0.75b

Cyclohexanone 129 7.0 1.1 8.6 0.31

Acetone −4 185.0 2.6 12.8 7.7

Methyl ethyl ketone 16 70.6 1.8 10.0 4.6

Methylisobutylketone 60 16.0 1.2 — 1.6

N-Butyl alcohol 97 4.39 1.2 10.9 0.46

Isobutyl alcohol 85 8.8 1.45 11.25 0.63

Methanol 54 96 6.7 36.0 3.5

Carbon disulfide –30 300

Carbon tetrachloride — 90.0 — — 6.0b

Ethyl acetate (99%) 24 76 2.2 11.0 4.1

Diethyl ether –45 440

Methylene chloride — 340 — — 14.5b

Tetrachloroethylene — 13.0 — — 2.1b

Trichloroethylene — 59.0 8.0 10.5 4.46

1,1,1-Trichloroethane 100

Chlorofluorocarbons c 284–502 — — c

a Given for acetone = 1 unless indicated otherwise.b Given for n-butyl alcohol = 1.c No flash points or explosive limits are available for most chlorofluorocarbons; practically all evaporation rates are

unspecified.

Source: From ChemCentral. Physical Properties of Common Organic Solvents and Chemicals. Chicago, IL: ChemCen-tral, 1980. The reader is referred to these tables for detailed notes.


Chemical attributesAmount of the chemical (its concentration in soil pores and at the air–soil interface)Vapor pressure of the chemicalDiffusion rate of the chemicalSolubility

Emission rates are negatively correlated with the amount of soil moisture, depth of soil cover, the solubility of the chemical in water, and the weight of the chemical. Emissions are positively cor-related with the diffusion rates of the chemicals, porosity and permeability of the soil, amount of

table 7.8environmental release/transport potential through soil and water

mobility in soil, based on koc

a

dielectric constant, 25°c

Solubility, mg/l, 30°c in waterb

Chlorobenzene 2 5.65 448 L

o-Dichlorobenzene 1 6.83 150 L

Cresol, cresylic acid 4 11.8 (m) 21,800 (m) VS

11.5 (o) 24,500 (o) VS

9.9 (p) 19,400 (p) VS

Ethylbenzene 1 2.41 150 L

Nitrobenzene 3 34.8 2,000 MS

Pyridine 4 12.3 CM

Toluene 2 2.44 500 S

Xylene 1,2 2.44 (m) 2.57 (o)

2.27 (p) 175 SS

Cyclohexanone 4 18.3 50,000 VS

Acetone 4 20.7 CM

Methyl ethyl ketone 4 18.5 270,000 VS

Methylisobutylketone 4 15.0 19,000 VS

N-Butyl alcohol 4 17.7 70,800 VS

Isobutyl alcohol 4 17.9 87,000 VS

Methanol 4 32.6 CM

Carbon disulfide 3 2.64 2,940 MS

Carbon tetrachloride 2 2.205 800 L

Ethyl acetate 4 6.02 85,300 VS

Diethyl ether 4 4.2 60,050 VS

Methylene chloride 4 9.1 13,200 VS

Tetrachloroethylene 2 2.35 150 L

Trichloroethylene 2 3.42 1,000 MS

1,1,1-Trichloroethane 2 7.1 700 L

Chlorofluorocarbons 1,2,3,4 7.1 700 LaKoc scale: 1 = low mobility; 2 = medium mobility; 3 = high mobility; 4 = very high mobility.bSolubility scale: L = low; SS = slightly soluble; S = soluble; MS = moderately soluble; VS =

very soluble; CM = completely miscible.

Source: Summarized from R.A. Griffin and W.R. Roy, Interaction of Organic Solvents with Satu-rated Soil-Water Systems. Open File Report, University of Alabama, Environmental Insti-tute for Waste Management Studies, Tuscaloosa, AL, 1985.


exposed surface area, vapor pressure, Henry’s Law constant, temperature, the velocity of the meth-ane gas (if it is present), and wind velocity.55

The quantification of atmospheric concentrations of organic chemicals via air quality monitor-ing is limited by several factors. First, the scope of existing air-quality-monitoring networks is lim-ited in terms of the coverage of organics and the quality of the data. Only 368 chemicals are covered by the EPA’s National Emissions Inventory, and adequate monitoring information is available for only about 10% of these.43

Second, chemical transformations in the atmosphere are not easy to capture through a monitor-ing network. The fates and ultimate concentrations of emissions into the atmosphere are usually estimated via a variety of air-quality simulation models. These models tie together many of the variables listed in the preceding text. They have been developed by or under the auspices of the EPA

table 7.9environmental release/transport potential: biodegradability

% removed

rate of degradation (mg cod/g · VoS-hr)

Half-life in soilb bioconcentration bioaccumulation

Chlorobenzene H 2 450

o-Dichlorobenzene H 2 89

Cresol, Cresylic acid 95–96 54–55 H

Ethylbenzene

Nitrobenzene 98 14 M 1 15

Pyridine H 0

Toluene H 1 15–70

Xylene

Cyclohexanone 96 30

Acetone

Methyl ethyl ketone M 1

Methylisobutylketone M

N-Butyl alcohol 99 84

Isobutyl alcohol

Methanol

Carbon disulfide L 1

Carbon tetrachloride L 17–30

Ethyl acetate

Diethyl ether

Methylene chloride MH 1

Tetrachloroethylene MH 3c 49

Trichloroethylene L 3c

1,1,1-Trichloroethane 1 9

ChlorofluorocarbonsaFrom W.W. Eckenfelder, Jr., Principles of Water Quality Management, pp. 279–281.bKey to half-life in soil: H = High, less than 7 d; MH = Moderately high, 1–4 weeks; M = Moderate, 1–5 months; ML =

Moderately low, 5–9 months; L = Low, greater than 9 months. From Berkowitz, J.B., Harris, J.C., and Goodwin, B., Identification of hazardous waste for land treatment research, in Proceedings of the 7th Annual Research Sym-posium, Schultz, D.W. and Black, D., Eds., U.S. EPA, Philadelphia, 1981, pp. 168–177.

cBioconcentration in marine life. Source of bioconcentration and bioaccumulation data: GCA Corp., Disposal Alternatives for Certain Solvents, U.S. EPA, Washington, DC, January 1984, p. 77.


for compliance with the requirements of the Clean Air Act. The most popular series of models is the User’s Network for Applied Modeling of Air Pollution (UNAMAP). These models use emissions and meteorological data as inputs and provide concentrations of selected air pollutants as outputs. The applicability of any given model to landfill emissions depends upon the terrain, physical setting of the facility, type and frequency of the emissions, and distance of the receptors. For the purpose of model-ing emissions from landfills, landfills are generally treated as emitters located at ground level.

A major factor in determining the degree of model accuracy in reflecting the dispersion and deposition of emissions from a given source to a given receptor is the choice of coefficients that represent how fast a plume will rise and fall. Another major factor is the source emission rate.

table 7.10Summary of input parameters for risk estimation for chemical solvents

release rates

Amount of surface exposed or disrupted

Chemical and environmental factors enhancing release rates (see the following parameters)

environmental fate and transport

Environmental factors

Generation rate of methane gas (if it is present)

Wind speed

Wind direction

Atmospheric stability

Temperature

Precipitation, moisture

Surface area

Gradients or slope

Soil type

Soil moisture

Type of soil cover

Depth of soil cover

Soil density and porosity

Water flow rate

Hydraulic conductivity

Chemical factors

Soil

Soil adsorption (Koc)

Persistence (biodegradability)

Amount of the chemical (concentrations in soil pores and at the air–soil interface)

Vapor pressure of the chemical

Diffusivity of the chemical

Water

Solubility

Kow

Henry’s Law constant

Air

Vapor pressure

Flash point

Explosivity


Caravanos and Shen57 have demonstrated that wind speed is a major factor in influencing the rate of emissions of carbon tetrachloride and trichloroethylene from landfills. Emissions vary more accord-ing to wind speed than they do by soil types. When estimated and actual emission rates are com-pared, the variation often ranges between 50% and 150%, unless corrections are made using wind speed data.57 Thus, both of these factors can cause outputs to vary by several orders of magnitude.

groundwater Soil/Surface Water

The parameters that influence the migration of organic chemicals into groundwater are

Landfill or environmental conditionsHydraulic conductivity (water flow rate)Net infiltration from precipitation, runoff, and evapotranspirationSoil density and porosityThickness of soil layerOrganic content

Chemical attributesSoil–water partition coefficient or organic carbon–water partition coefficient (Koc)Persistence (biodegradability)SolubilityOctanol–water partition coefficient (Kow)Henry’s Law constant

Empirical work indicates that leaching to groundwater is inversely proportional to the Henry’s Law constant, diffusion rate, organic content of the soil, soil adsorption rates, runoff of water over land surfaces, and evapotranspiration. Leaching is directly proportional to infiltration and rainfall, soil permeability, solubility of the chemical in water, and the size of the site.

Four parameters to estimate the mobility of nonpolar organic solvents in soils covary with one another.58 These parameters are the octanol–water partition coefficient, Kow; the organic carbon–water partition coefficient (or the ability of chemicals to adsorb to organic carbon), Koc; solubility; and the retardation factor.48,58 Because each of these four parameters represents the mobility of a chemical in soil in approximately the same manner, any one parameter can be used to represent chemical mobility in soil. This is only plausible if there is roughly a linear correlation among them.

The advantage of using Koc is that it is available for specific chemicals. There are several draw-backs, however, to the use of Koc as an indicator of chemical mobility. A first drawback is that the value of Koc varies with the organic carbon content of the soil (especially when the organic carbon content is less than about 0.1%). Organic content in soils is often difficult to estimate and is known to vary between 0.1 and 3%.59,60 Second, the prediction is unreliable for soils with large particles (greater than 50 µm in diameter). Third, adsorption rates for organic solvents to clay and soil change because of interaction or reaction effects between the chemical and the soil or clay; that is, the pres-ence of chemical solvents can change the affinity of the soil or clay for the solvent. Affinity is not necessarily linearly proportional to the concentration of the solvent.58 Fourth, adsorption is influ-enced by the rate of flow of water through the soil; that is, nonequilibrium conditions may exist at fast flow rates. Finally, the value of Koc varies from one to one million.61 Other variables have wide ranges as well. Vapor pressure, for example, ranges from 0.001 to 760 mmHg for liquids. Any error or variability of these parameters could distort computations in which the parameter is used by sev-eral orders of magnitude unless an index with a narrower range is constructed from those values.

The mobility of organic chemicals in soil is inversely proportional to Koc; however, there are several qualifications. A compound that normally has a high affinity for soil has low mobility, but it can still migrate due to runoff or soil erosion.


The variation in the range of parameter values (other than Koc) used to estimate the migration of contaminants in groundwater can be quite substantial. For example:

Groundwater flow velocities can range from 1 to 100 m/year• 62 with a velocity of 9,000 m/year, representing an extreme situation (glacial outwash conditions).63 A velocity range of 10 to 100 m is typical.Retardation factors affect the flow of chemicals relative to groundwater. Retardation fac-•tors for organic solvents (e.g., 1,1,1-trichloroethane; trichloroethylene; and tetrachloroeth-ylene) range from 1 to 10. Thus, the estimate of the velocity of the solvent relative to groundwater flow ranges from 10 to 100%.62

The storage capacity of an aquifer is another parameter that has a considerable range of •variation. McKown, Schalla, and English64 quote a range of 0.05 to 0.25 for storage in porous unconfined aquifers. The range they quote for confined aquifers is even greater: 0.00001 to 0.001.

There are many groundwater models that can be used to predict the patterns and rates of movement of groundwater and associated chemicals.65 A series of groundwater models is commonly com-bined to estimate the movement of contaminants through the saturated and unsaturated zones. For a review of these models see Sternberg;66 Onishi;65 and Javandal, Doughty, and Tsang.67 The model that the EPA has recommended for estimating movement in the saturated zone is the Vertical–Horizontal Spread (VHS) model. A source of uncertainty in the modeling of the transport of landfill contaminants in groundwater arises from assumptions about whether the zone of subsurface con-tamination beneath a landfill is portrayed as a single plume or many plumes.62 Mackay et al. noted that plumes are often delineated with inorganic nonreactive tracers. Organic contaminants, which are reactive, do not follow the same pattern. In fact, they estimated that plumes of trichloroethylene and 1,1,1-trichloroethane arrive sequentially rather than simultaneously. Arrival times are much sooner than predicted from groundwater velocity and retardation factors alone.

A back calculation can be used to derive the concentration of chemicals in groundwater from their concentration in soil using the following simple model.68

Cwater = Csoil/[Koc · (OC)] (7.6)

where Cwater = concentration in water (µg/L) Csoil = concentration in soil (µg/kg) Koc = adsorption coefficient (µg/kg organic carbon/µg/L water) OC = fractional organic carbon content (grams of carbon per gram of soil)

The rate of movement of water into the soil can be estimated from the product of the area and the infiltration rate of water. Infiltration, in turn, is computed by subtracting runoff, evapotranspira-tion, and evaporation from precipitation.61

The concentrations of chemicals in surface water can be estimated from surface-water flow rates and the rate of seepage of contaminants into the surface waters. Many of the same parameters that influence the migration of pollutants into groundwater also affect their migration into surface water. In addition, the following variables influence surface-water migration of contaminants:

Sewage or leaching rate from soil or groundwater into surface water•Surface-water flow•Distance or distances from point of seepage•

Ultimately, the outputs from water-resource modeling that are used as inputs into risk-assessment models are the steady-state concentrations of contaminants at the following locations:61


Within the landfill•Under the site•At the boundary of the site•In adjacent streams•In aquifers•In environmentally sensitive areas, such as wetlands and floodplains, that are hydrologi-•cally contiguous with the landfill

food

The characteristics that relate water concentrations of chemicals to concentrations in biota consum-able by humans are bioaccumulation, bioconcentration, and biomagnification. Bioconcentrations in foods are estimated in a variety of ways. For fish and shellfish, bioconcentration factors usually are derived from concentrations of the chemicals in the water. Thus, the concentration in micrograms per kilogram weight of fish (kg) of a particular chemical in fish or shellfish (in µg/kg) is calculated as the product of the bioconcentration factor and the concentration (µg/L) in water.68 The tendency of chemicals to accumulate in the food chain is directly correlated with Koc. Bioaccumulation is more likely to occur at higher values of Koc.48

areas of uncertainty in fate and transport estimates

Areas of uncertainty in environmental fate and transport estimates occur anywhere between the initial measurement of parameters characterizing chemical transport and the underlying assump-tions and simplifications in the models. Of the many examples given in the preceding text, a few are particularly significant.

One of the most important parameters is the estimation of the tendency of a chemical to migrate in soil and water, Koc. There are also several related parameters that describe similar tendencies. Errors in both laboratory and field measurements for these parameters can be substantial (several orders of magnitude). The range in the value of Koc for chemicals can be as large as six orders of mag-nitude. Because Koc is used directly in risk estimation, this error becomes a part of the risk estimate.

The rate of flow of groundwater is another parameter with a high degree of uncertainty. Errors of a few orders of magnitude can result from improper field measurements alone, for example, where monitoring wells have been improperly drilled or installed.64

In environmental fate and transport modeling, uncertainties exist in the structure of both air- and water-quality models. Estimates of the deposition and emission of materials can be a source of considerable error in air-quality models. The accuracy of both deposition and emission esti-mates depends on the accuracy of estimates for wind speed and direction. Deposition estimates are affected further by the existence of barriers to uniform dispersal and by chemical degradation and transformation processes in the atmosphere.

7.6.5 ExposurE assEssmEnt: routEs oF ExposurE

Exposure pathways are the routes by which chemicals come into contact with human receptors. The importance of the route depends on the type of waste disposal activity that is being conducted and the type and magnitude of population exposed (e.g., the general population versus workers).

The exposure pathways typical of land-disposal facilities for hazardous wastes are inhalation, ingestion, and dermal adsorption:

Inhalation of airborne soil particles or chemical vapors as they volatilize from soil•Ingestion of soil particles directly or from clothing, skin, animals, or plants•Dermal absorption (and absorption by other body fluids such as blood or tears) from direct •contact with contaminants in soil particles and water or airborne vapors and particulates


Ingestion of foods that have become contaminated via the air or water such as fish, shell-•fish, vegetables, and dairy productsIngestion of drinking water that is obtained from contaminated surface or groundwaters•Inhalation, dermal contact, and ingestion from bathing in waters that are contaminated•

The importance of each of these routes of exposure varies by type of chemical, type of environ-mental condition, and proximity of individuals to the land-disposal facility. For example, contact through ingestion of soil particles that become airborne from the land or from the movement of vehicles is a common route of exposure for workers at a landfill.

exposure Points

Exposure points are locations where human contact occurs with the contaminants. One can iden-tify exposure points from the routes by which people can be exposed to a chemical from a landfill. Although exposure points are unique to specific sites, the following general categories of exposure routes for chemicals from landfills can be identified:

Groundwater: ingestion of water from a well•Surface water: dermal contact from swimming or ingestion of water from a surface-•water supplySoil: ingestion of or dermal contact with windblown soil•Air: inhalation at points of population concentration, such as a school, shopping center, or •office building

Uncertainties that can occur in identifying routes of exposure include omission of important routes of exposures and overemphasis or underemphasis of routes of exposure that have been identified. These uncertainties result because human behavior cannot be predicted exactly. For example, not all private wells in use can be identified; children might be playing in contaminated areas where such activity is prohibited.

Health effects

Human health effects from chemicals are related to doses of the chemicals that are taken into the body (intake rates), the amounts that are absorbed or retained by the body, the size and nature of the population at risk, the state-of-health or resistance of individuals to the effects, and the effects that the absorbed chemicals are likely to have on health (dose–response relationship).

dose estimation

Dosage is a function of the amount of air, water, and food and the concentration of a chemical that is taken into the body. Typical intake rates are given in Table 7.6. Considerable variation in rates obviously exists. These variations result from differing assumptions about the sizes and weights of individuals, their levels of activity, and their tastes and preferences for food and water.

Given these intake rates, daily human doses can be calculated per unit of body weight according to the following equation:

D = (C · R)/W (7.7)

where D = daily intake in mg/kg/d C = concentration of the chemical in mg/L (water) or mg/m3 (air) R = daily intake rate in units comparable to C, i.e., L/d (water) or m3/d (air) W = body weight in kg


absorption

Absorption of a substance by the human body is one component of the effect of exposure. The level of exposure (in mg/day) is equivalent to the product of the concentration (in mg/L) of the chemical taken in, the weight of the medium by which it is taken in (e.g., food), and the rate of absorption. The amount of a substance that is actually absorbed by the human body (as distinct from the exposure to the substance) is dependent upon the route by which the substance enters the body, the length of exposure, type of species exposed, and the behavior of the substance in general and relative to the body’s chemistry. In addition, the rate depends on the state of health of the individual, degree of starvation, and whether the individual is exercising during exposure. When information is lacking on absorption rates, the ratio of the concentration of substances absorbed to the concentration of the substance in the exposure medium is often set equal to one.39

The variation in absorption rates of organic solvents is illustrated by some empirical findings reported by the EPA for a few selected chemicals. For trichloroethylene, absorption ranged from about 50–65% in humans via inhalation, and 95–98% in rats and mice via ingestion.69 For carbon tetrachloride, absorption ranged from 65–85% in rats via inhalation, and 30–60% via ingestion.50 For xylene, absorption via ingestion was 85–90% and 55–70% via inhalation.70 Toluene exhibited approximately 100% absorption via ingestion, and 30–55% via inhalation.

State of Health

The health of individuals in a population can determine the actual toxic effect that is felt. Animal and human experimental data giving the effects of doses under varying health states is an important input into these determinations. In reality, such information is rarely available. Most experiments used as the basis for establishing dose–response curves are conducted on healthy organisms.

Size and nature of the Population at risk

The degree to which sectors of the population are at risk depends on the proximity of people to the chemical releases, time spent near sources, level of physical exertion, resistance to the effects of exposure, and the extent to which chemicals are transported to people via wind, water flow, etc. One can work back from an acceptable dose level and the behavior or migration of the chemical along each of the routes of exposure to obtain a radius from the source within which populations can be considered at risk. However, the populations at risk may not always be easily defined as a direct function of distance from a source of chemical emissions. Various concentration effects that are not linear with distance can occur. For example, dispersed chemicals can be concentrated in water through entrainment in sediment and through turbulence, in air from downwash effects and eddys, and in soil.

The sectors of the population that are typically considered to be at higher risk from chemi-cal exposures than other sectors of society are defined in terms of age, activity, or state of health. The higher risk groups typically are children at play or in school, nursing mothers, the infirm and chronically ill, the elderly, athletes, trespassers, workers in proximity to the chemical dis-posal site (e.g., landfill operators, truckers), and persons that typically spend a lot of time outdoors (e.g., maintenance workers and the homeless). Certain populations defined by environmental or behavioral factors (e.g., smoking) may experience greater toxicity once exposure has occurred.

7.6.6 dosE–rEsponsE Estimation*

Experimentally derived data on the responses of bacteria, animals, or humans to doses of a par-ticular chemical are used to create dose–response curves. These curves can only be constructed in

* Dose-response estimated is considered a distinctly separate step from exposure assessment.


ranges where chemical concentrations and the responses are easily measured. The dose–response relationship is used to develop the unit risk estimate (R in Equation 7.2). The unit risk estimate is defined as “the increased individual lifetime risk” for an individual of a given weight (usually 70 kg) exposed continuously to a unit amount of a chemical (e.g., 1 µg/m3 in air, or 1 mg/L in water) over a lifetime (usually 7 years).39 Unit risk is computed for acute and chronic toxicity and for more long-term health effects such as carcinogenesis.

7.7 HydrogeologIcal SyStemS and monItorIng71–74

Acceptable waste management for groundwater protection must be based on an adequate and detailed monitoring system. It must be representative of the geology, stratigraphy, structure, deposi-tional environment, and water-bearing beds. It must provide adequate information about base-level conditions in the aquifer or aquifers involved with regard to recharge, storage and discharge condi-tions, and water quality parameters. The monitoring system must reflect the conditions of contami-nation or pollution as well as the dynamic aspects of these conditions, e.g., the natural impacts of climate, rainfall, snowfall, freezing, and evaporation/transpiration.

A list of federal laws and regulations has been provided in Table 7.4; however, six of those are of the utmost importance regarding groundwater protection and should be emphasized as follows:

1. The Clean Water Act of 1972 gives the EPA authority to protect surface and groundwater. 2. The Safe Drinking Water Act of 1974 sets drinking-water standards that are used to pro-

tect groundwater. A provision of the act allows the EPA to designate an aquifer as the sole source of drinking water for an area and denies federal money to water projects that threaten to contaminate the aquifer. The EPA has set maximum-contaminant-level stan-dards for public drinking-water supplies.

3. The Federal Insecticide, Fungicide, and Rodenticide Act of 1974 (FIFRA) assigns to the EPA control over availability and use of pesticides that may leach into groundwater.

4. The Toxic Substances Control Act of 1976 gives the EPA authority to limit certain uses of chemicals, require warning labels, and reduce risks from chemicals that have the potential to contaminate groundwater.

5. The Resource Conservation and Recovery Act of 1976 gives the EPA authority to set up programs to prevent hazardous wastes from leaching into groundwater from landfills, sur-face impoundments, and underground tanks.

6. The Comprehensive Environmental Response, Compensation, and Liability Act of 1980 is called the Superfund bill because it set up a fund to support federal and state responses to hazardous-waste problems. The law gives the EPA authority and money to clean up haz-ardous waste sites that are a threat to human health and the environment.

It must be recognized that federal regulations and rules must in turn be implemented at the state level; therefore, within each state in the United States there is a companion organization to the Public Health Service and EPA. In Alabama, it is the Alabama Department of Environmental Man-agement, and in Georgia, the Department of Environmental Regulations and Department of Envi-ronmental Resources. The state of Florida passed legislation to be applied to the development of groundwater. These regulations require strict adherence to defining the impact on surface water, shallow surficial aquifer, and deeper intermediate and Floridan aquifers. Regulations require the Development of a Regional Impact Statement or DRI. Extensive pumping tests; surface-water and groundwater studies; and monitoring for discharge, water levels, and quality of water are required to identify these impacts.

The Southwest Florida Water Management District (SWFWMD), in its Code Section 16, CR—0.15 (5) (A) states, “The water crop, in the absence of data to the contrary, is 1,000 gallons per day per acre.” The cooperative’s project tract is 7810 acres, and the water crop established legally


for the acreage involved is more than needed for the projected mining operations that have been proposed. However, “the 5–3–1 criteria,” which also applies, requires that a determination be made to show that there will not be more than a 5-ft average decline in water level in the Florida aquifer at the boundary of the property, not more than a 3-ft decline in the Surficial aquifer at the boundary, and not more than a 1-ft decline in the nearest water body (pond, lake, etc.). In addition, surface-water flow in streams of the area must not be decreased more than 5% unless a variance to the rule is obtained.

Surface-water flow is affected by differences in soils, geology, vegetation cover, altitude, eleva-tion, and precipitation intensities for the various surface-water basins within the tract. Each year, within the project area, streams recede to low flows from April to June. Therefore, a seasonal distribution of average monthly flow must be determined. The annual minimum instantaneous or daily flow is subject to alterations by transient, natural, or manmade causes; therefore, the lowest 7-d average flow each year is used as the reference period for low flows. The yearly minimum 7-d low flows are determined from the data collected by the U.S. Geological Survey at gauging stations strategically located over the state. One or more of these long-term gauging station records provide the 7-d minimum flows. Regression models are used to obtain a site-specific extension of the annual flows to an equivalent 40-year period.

The environmental monitoring strategy must achieve goals established by a great variety of governmental legislation and regulations pertaining to a wide diversity of uses. Specifications for monitoring are contained in a series of federal laws that address the need for protection of ground-water quality.

Table 7.4 lists the laws enacted by Congress and summarizes the applicable groundwater activi-ties associated with each law. Of the 16 statutes listed in Table 7.4, 10 statutes have regulatory programs that establish groundwater-monitoring requirements for specific sources of contamina-tion. Table 7.5 summarizes the objectives and monitoring provisions of the federal acts. Acts may mandate that groundwater-monitoring regulations be adopted, or they may address the need for the establishment of guidelines to protect groundwater. Further, some statutes specify the adoption of rules that must be implemented uniformly throughout the United States, whereas others authorize the adoption of minimum standards that may be made more stringent by state or local regulations.

Specific groundwater-monitoring recommendations can be found in the numerous guidance documents and directives issued by agencies responsible for the implementation of the regulations. Examples of guidance documents include the Office of Waste Programs Enforcement Protection Agency, the Office of Solid Waste Documents SW-846 and SW-611 (U.S. EPA), and CERCLA and RCRA documents.

The purpose and importance of proper groundwater-monitoring well installation must have as a primary objective a monitoring well that will provide an access point for measuring groundwater levels and permit the procurement of groundwater samples that accurately represent in situ ground-water conditions at the specific point of sampling. To achieve this objective, it is necessary to fulfill the following criteria:

1. Construct the well with minimum disturbance to the formation. 2. Construct the well of materials that are compatible with the anticipated geochemical and

chemical environment. 3. Properly complete the well in the desired zone. 4. Adequately seal the well with materials that will not interfere with the collection of repre-

sentative water quality samples. 5. Sufficiently develop the well to remove any additives associated with drilling and provide

unobstructed flow through the well.

In addition to appropriate construction details, the monitoring well must be designed in concert with the overall goals of the monitoring program. Key factors that must be considered include the following:


1. Intended purpose of the well. 2. Placement of the well to achieve accurate water levels and/or representative water quality

samples. 3. Adequate well diameter to accommodate appropriate tools for well development, aquifer-

testing equipment, and water-quality sampling devices. 4. Surface protection to assure no alteration of the structure or impairment of the data col-

lected from the well.

There are many excellent references for well construction, spring development and sampling, well testing and sampling, and systematic monitoring programs. Each, however, must be based on a detailed knowledge of the geology, stratigraphy, structure, and depositional environment, as well as all the manmade factors involved.

referenceS

1. American Society of Civil Engineers, Manual on Groundwater Management, ASCE Mann (40), 1972. 2. APHA, Standard Methods for the Examination of Water and Waste Water, 14th ed., American Public

Health Association, New York, 1976. 3. Panoni, J. L., Heer, J. E., Jr., and Hagerty, D. L., Handbook of Solid Waste Disposal: Materials and

Energy Recovery, Van Nostrand Reinhold, New York, 1975. 4. Hazardous Waste, Proposed guidelines and regulations and proposal on identification and listing, Fed-

eral Register, 43, 243, 58945–59028. 5. Conway, R. A. and Ross, R. D., Handbook for Industrial Waste Disposal, Van Nostrand Reinhold, New

York, 1980, chap. 1. 6. Sell, N. J., Industrial Pollution Control: Issues and Techniques, Van Nostrand Reinhold, New York,

1981, chap. 5. 7. Hazardous Waste Disposal, Science News 114, 26, December 23 and 30, 1978, p. 440. 8. Chernobyl, Special Programs of United Nations System Organizations Relating to the Aftermath of the

Accident at the Nuclear Power Plant, UNESCO, 25 October 1990. 9. The fire next time, Environmental Science and Technology 12, 2, February 1978, p. 134. 10. Environmental Institute for Waste Management Studies, Disposal of Solvents and Solvent-Contaminated

Wastes to Land—A Position Paper, University of Alabama, Tuscaloosa, December 1985. 11. Kozlovsky, E. A., Ed., Geology and the Environment: An International Manual, 3 Vols., UNESCO–

UNEP, 1989, pp. 100–120. 12. Langer, M., Geotechnical Investigation Methods for Rock-Salt, Paris, Bull. I AEG, 25, 1982, pp.

155–164. 13. Lux, K. M., Gebirgsmechanischer Entwurf und Feldefahrungen in Salzkavernenbau, Enke-Verlag,

Stuttgart, Germany, 1984. 14. Schmidt, M. W. and Quast, P., Disposal of MLW and LLW in Leached Cavern, Braunschweig, Report

GSF-T, 166, 1984. 15. Langer, M., Rheological behaviour of rock masses, Int. Association of Rock Mechanics Engineers,

Proceedings of the 4th International Congress on Rock Mechanics, Montreaux, France, Vol. 3, 1979, pp. 29–96.

16. Hardy, H. and Langer, M., The Mechanical Behaviour of Salt, Proc. 1 Conference, Penn State Univer-sity, Trans Tech Publ. Clausthal, 1984.

17. Libby et al., The Taa Mines Story, Transactions of the Institute of Mining and Metallurgy, London, 1985. 18a. U.S. Geological Survey, National Water Summary, Hydrologic Events and Issues, Water Supply Paper

2250, 1984, pp. 79–239. 18b. U.S. Geological Survey, Hydrologic Events and Groundwater Quality, Water Supply Paper 2325, 1988,

pp. 143–546. 18c. U.S. Geological Survey, Hydrologic Events and Floods and Droughts, Water Supply Paper 2375, 1991,

pp. 163–582. 18d. U.S. Geological Survey, Hydrologic Events and Stream Water Quality, Water Supply Paper 2400, 1993,

pp. 155–576.


19. Williams, R. E., Waste Production and Disposal in Mining, Milling, and Metallurgical Industries, Miller Freeman, San Francisco, 1975, pp. 38–83.

20. Down, C. G. and Stocks, L., Environmental Impact of Mining, Applied Science Publishers, London, 1977, p. 131.

21. Tyagi, A. K. and Turner, W., Underground Storage Tanks: Spill Prevention and Clean Up, Engineering Extension, OSU, Stillwater, OK, 1987.

22. Tyagi, A. K. and Martell, J., Fate/Transport Modelling of Imissible LNAPL in Unsaturated Aquifers, Int. Symposium on Engineering Hydrology, Proc. ASCE, 1993, pp. 701–705.

23. Palmer, C. M., Principles of Contaminant Hydrogeology, Lewis Publications, Boca Raton, FL, 1992, p. 161. 24. Hazen, J. C. et al., In-Situ Bioremediation via Horizontal Wells, Int. Symp. on Engin. Hydrology Proc.

ASCE, 1993, p. 862. 25. Lang, M. M. et al., In-Situ Bioremediation Using a Recirculation Well, Int. Symp. on Engin. Hydrology,

Proc. ASCEP, 1993, p. 880. 26. Zimmerman, R., Risk Assessment Procedures for Organic Solvent Disposal in Landfills (Procedures

and Their Uncertainties), Open File Report prepared for the Environmental Institute for Waste Manage-ment Studies, University of Alabama, June 1987.

27. Office of Technology Assessment, Superfund Strategy, Washington, DC, OTA, 1985. 28. Rowe, W. D., An Anatomy of Risk, John Wiley, New York, 1977. 29. Vlek, C. and Stallen, P., Rational and personal aspects of risk, Acta Psychologica, 45, 1980, pp.

273–300. 30. Sage, A. P. and White, E. B., Methodologies for risk and hazard assessment: A survey and status report,

IEEE Transactions on Systems, Man, and Cybernetics, 10, August 1980, pp. 425–446. 31. Sloan, A., III and Sepesi, J. A., Public health: A quantitative way of determining threat, Proceedings

of the Management of Uncontrolled Hazardous Waste Sites, Hazardous Materials Control Research Institute, Silver Spring, MD, 1984, pp.

32. Ess, T. and Shih, C. S., Perspectives of risk assessment for uncontrolled hazardous waste sites, Pro-ceedings of the Management of Uncontrolled Hazardous Waste Sites, Hazardous Materials Control Research Institute, Silver Spring, MD, 1983.

33. Ruckelshaus, W. D., Science, risk, and public policy, Science, 221, September 9, 1983, pp. 1026–1028. 34. U.S. Environmental Protection Agency, Risk Assessment and the U.S. EPA, Washington, DC, Decem-

ber 1984. 35. U.S. EPA, Guidelines for carcinogen risk assessment, Federal Register, 51, September 24, 1986a,

33992–34003. 36. U.S. EPA, Guidelines for mutagenicity risk assessment, Federal Register, 51, September 24, 1986b,

34006–34012. 37. U.S. EPA, Guidelines for the health assessment of suspect developmental toxicants, Federal Register,

51, September 24, 1986d, 34028–34040. 38. U.S. EPA, Guidelines for the health risk assessment of chemical mixtures, Federal Register, 51, Septem-

ber 24, 1986c, 34014–34025. 39. Anderson, E. L. et al., Quantitative approaches in use to assess cancer risk, Journal of Risk Analysis, 3,

1983, pp. 277–295. 40. Russell, M. and Gruber, M., Risk assessment in environmental policy-making, Science, 236, April 17,

1987, pp. 286–290. 41. U.S. EPA, National oil and hazardous substances pollution contingency plan: final rule, Federal Regis-

ter, 50, November 20, 1985, pp. 47912–47979. 42. U.S. EPA, National primary drinking water regulations; volatile synthetic organic chemicals; final rule

and proposed rule, Federal Register, 50, November 13, 1985, pp. 46080–46933. 43. Cannon, J. A., The regulation of toxic air pollutants—A critical review, Journal of the Air Pollution

Control Association, 36, 5, May 1986, pp. 562–573. 44. Lowrance, W. W., Of Acceptable Risk, William Kaufman, Los Altos, CA, 1976. 45. Lave, L. B., Methods of risk assessment, in Quantitative Risk Assessment in Regulation, Lave, L.B.,

Ed., Brookings, Washington, DC, 1982. 46. Davies, J. C., Science and policy in risk control, in Risk Management of Existing Chemicals by the

Chemical Manufacturers Association, Government Institutes, Rockville, MD, June 1984. 47. National Academy of Sciences, Risk Assessment in the Federal Government: Managing the Process,

National Academy Press, Washington, DC, 1983.


48. ICF, Inc., Draft Superfund Public Health Evaluation Manual, U.S. Environmental Protection Agency, Office of Emergency and Remedial Response and Office of Solid Waste and Emergency Response, Washington, DC, December 18, 1985.

49. International Agency for Research on Cancer (IARC), IARC Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans, Supplement 4, IARC, Lyon, France, 1982.

50. U.S. EPA, Drinking Water Quality Criteria Document for Carbon Tetrachloride (Final Draft), National Technical Information Service, Springfield, VA, January 1985a.

51. Isaacson, P. J., Eckel, W. P., and Fisk, J. F., Low occurrence compounds: Analytical problem or environ-mental process?, Proceedings of the Management of Uncontrolled Hazardous Waste Sites, Hazardous Materials Control Research Institute, Silver Spring, MD, 1985, pp. 130–135.

52. U.S. EPA, Guidelines for exposure assessment, Federal Register, 51, September 24, 1986e, pp. 34042–34054.

53. Blackman, W. C., Jr. et al., Chemical composition of drum samples from hazardous waste sites, Pro-ceedings of the Management of Uncontrolled Hazardous Waste Sites, Hazardous Materials Control Research Institute, Silver Spring, MD, 1984, pp. 39–44.

54. Onishi, Y., Chemical transport and fate models, in Principles of Health Risk Assessment, Ricci, P., Ed., Prentice-Hall, Englewood Cliffs, NJ, 1985, pp. 155–234.

55. Bennett, G. F., Fate of Solvents in a Landfill, Open File Report of the University of Alabama Environ-mental Institute for Waste Management Studies, Tuscaloosa, AL, August 1985.

56. Thibodeaux, L. J., Estimating the air emission of chemicals from hazardous waste landfills, Journal of Hazardous Materials, 4, 1981, pp. 235–244.

57. Garavanos, J. and Shen, T. T., The effect of wind speed on the emission rates of volatile chemicals from open hazardous waste dump sites, Proceedings of the Management of Uncontrolled Hazardous Waste Sites, Hazardous Materials Control Research Institute, Silver Spring, MD, 1984, pp. 68–71.

58. Griffin, R. A. and Roy, W. R., Interaction of Organic Solvents with Saturated Soil-Water Systems, Open File Report, University of Alabama Environmental Institute for Waste Management Studies, Tusca-loosa, AL, August 1985.

59. Tucker, W. A., Gensheimer, G. J., and Dickinson, R. F., Coping with uncertainty in evaluating alterna-tive remedial actions, Proceedings of the Management of Uncontrolled Hazardous Waste Sites, Hazard-ous Materials Control Research Institute, Silver Spring, MD, 1984, pp. 306–312.

60. Freeze, R. A. and Cherry, J. A., Groundwater, Prentice-Hall, Englewood Cliffs, NJ, 1979. 61. ICF-Clement, Risk Assessment of the Tyson’s Dump Site, Montgomery County, PA, Final Report, ICF-

Clement, Arlington, VA, February 21, 1986. 62. Mackay, D. M., Roberts, P. V., and Cherry, J. A., Transport of organic contaminants in groundwater, ES

and T, 19, 1985, pp. 384–392. 63. Guven, O., Mo, F. J., and Melville, J. G., An analysis of dispersion in a stratified aquifer, Water Resources

Research, 20, 10, 1984, pp. 1337–1354. 64. McKown, G. L., Schalla, R., and English, C. J., Effects of uncertainties of data collection on risk assess-

ment, Proceedings of the Management of Uncontrolled Hazardous Waste Sites, Hazardous Materials Control Research Institute, Silver Spring, MD, 1984, pp. 283–286.

65. Onishi, Y., Chemical transport and fate in risk assessment, in Principles of Health Risk Assessment, Ricci, P., Ed., Prentice-Hall, Englewood Cliffs, NJ, 1985, pp. 117–154.

66. Sternberg, Y. M., Mathematical Models of Contaminant Transport in Ground Water, Open File Report, University of Alabama Environmental Institute for Waste Management Studies, Tuscaloosa, AL, 1985.

67. Javendal, I., Doughty, C., and Tsang, C. F., Groundwater Transport: Handbook of Mathematical Mod-els, American Geophysical Union, Washington, DC, 1984.

68. Little, A. D. Inc., Quantitative Risk Assessment for Bloody Run Capping and Excavation Options, Little, A. D. Cambridge, MA, October 5, 1984.

69. U.S. EPA, Drinking Water Quality Criteria Document for Trichloroethylene (draft), National Technical Information Service, Springfield, VA, January 1985b.

70. U.S. EPA, Drinking Water Criteria Document for Ethylbenzene (final draft), National Technical Infor-mation Service, Springfield, VA, March 1985a.

71. Aller, L. et al., Handbook of Suggested Practices for the Design and Installation of Ground-Water Monitoring Wells, National Water Well Association, Dublin, OH, EPA 600/4-89/034, 1989.

72. National Research Council, The Management of Radioactive Waste at the Oak Ridge National Labora-tory: A Technical Review, Panel for Study of the Management of Radioactive Waste at the Oak Ridge National Laboratory, National Academy Press, Washington, DC, 1985.


73. Davis, S. N. and DeWiest, R. J. M., Hydrogeology, John Wiley, New York, 1966. 74. Meinzer, O. E., The Occurrence of Ground Water in the United States, with a Discussion of Principles,

Department of the Interior, U.S. Geological Survey Water Supply Paper 489, Washington, DC, 1923.

165

8 Hydrogeologic and Environmental Considerations for Design and Construction in Karst Terrain/Sinkhole-Prone Areas

8.1 IntroductIon

The occurrence of subsidence and sinkholes is reported and documented each year in parts of the United States and many other countries in the world underlain by carbonate rocks. Despite frequent land subsidence, road collapses, stream disappearances, and other karst manifestations, subsidence and sinkhole education and management have only recently been addressed. Karst is frequently characterized by karrens, dolines (sinkholes), shafts, poljes, caves, ponors (swallow holes), cav-erns, estavelles, intermittent springs, submarine springs, lost rivers, dry river valleys, karst plains, irregular surfaces with pinnacles, cutters, and collapses. Karst geology, exacerbated by mining, construction practices, and storm water drainage, is a source of havoc and humor.1–4 Hundreds of sinkholes and thousands of landscape depressions (i.e., including sinkhole forming or filling) may occur within a band of carbonate bedrock. Great potential for damage exists when any structure including buildings (residential, office blocks, commercial, and industrial), pipelines, roads, rail-roads, airports, lakes, waste lagoons, stockpiles, and landfills are built in areas of karst terrain. Sinkhole-related failures not only can cause significant property and environmental damage but also pose serious threats to the lives and economic and emotional well-being of those involved.5,6

Karst terrain and sinkhole-prone areas present special problems, mining difficulties, and man-agement concerns of the pits, as well as challenges for the design and construction of a development because of the variable and changeable nature of the soil and rocks that may support the structure.6 Concern related to subsidence and sinkhole occurrence must also be considered, and preventive measures taken to mitigate or minimize the natural and anthropogenic forces that drive the mecha-nisms of sinkhole formation.

To select a suitable location and design for a project, a thorough understanding of regional hydrogeologic conditions, geologic structure, patterns and interconnection of fractures and joints, stratigraphic sequence, cavities and solution features, and subsidence or collapse triggering factors is essential. It is also important to investigate the degree of dissolution, slot and pinnacle geom-etry, the extent of karst-related features, and the potential for their further development. A full understanding of karst morphology, careful evaluation of subsurface data along with comprehensive planning, and engineering design can overcome sinkhole-related problems and avoid or minimize damage due to development of induced sinkholes and future sinkhole collapses.

Environmental issues that may be exacerbated by the presence of sinkhole-prone carbon-ate formations need to be addressed at the planning and design stage. Periodically, however, most of the problems develop or are realized in the overlying residuum (regolith) or deposited


soils that cover rock solution features (voids and cavities). To address these problems, includ-ing inherent defects and weaknesses of the soil and rock, it is important to understand and characterize the rock and any overlying soil as well as their interaction to physical changes. A fundamental understanding of karst processes and 3-D conceptualizations are an integral part of the engineering required for the project. Structures whose failure could cause significant environmental damage or impact human health and safety must be designed to withstand sub-sidence or sinkhole development. A realistic model has to be developed that represents typical conditions as well as the extremes that are likely to occur at each site. The model should focus on the peculiar features of the carbonate terrain that will influence design and performance of the proposed project.4,7

8.2 InVeStIgatIon-deSIgn conSIderatIonS

Development of a site in a karst terrain or sinkhole-prone area requires multidisciplined efforts.8,9 A professional team at a minimum consists of competent and experienced geologists/hydrogeologists, geotechnical engineers, civil engineers, and assorted specialists on an as needed basis. Team mem-bers with demonstrable experience in karst can bring invaluable perspectives to the design process. Data gathered and facts uncovered during each phase of an investigation provide design guidelines that enhance the quality of design efforts.

Karst conditions present special challenges for foundation engineering and construction because of the variable and changeable nature of the soil and rock that may support structures. The primary difficulty with foundations in karst terrains is the nonuniformity and potentially changing nature of the soil and rock profile. The rock is generally hard and the rock surface is typically irregular due to differential weathering along joints and bedding planes. Deep soil-filled slots that form between pinnacles of hard rocks are typically common. These conditions pose potential differential settle-ment problems for shallow foundations unless full support of the foundation on the rock is or can be established.

Voids or cavities may also be present in the soil and rock in a karst area. If the voids are not detected during the investigative or construction phase and addressed, foundation placed above them can be damaged and may fail when the voids eventually collapse. Additionally, the continuing process of weathering and percolation of water through the soil into solution cavities in the rock may cause soil particles to migrate. This raveling of soil may form sinkholes and cause settlement or collapse of foundations above the migrating soil.10–13

Selection of a suitable location and design for a facility requires a thorough understanding of hydrogeologic conditions, geology and geologic structure, patterns and interconnection of fractures, cavities and solution features and their aerial extent, slot and pinnacle geometry, and the potential for further development and triggering factors of subsidence and sinkhole formation.

The prevalence of underground drainage in the area is indicated by many losing and disappear-ing streams as well as extensive cave(s) and conduit systems. These conditions need to be evaluated before development and considered during the design phase of the project.

Existing groundwater conditions and potential changes that occur naturally or by anthropogenic activities are to be evaluated so that steps can be taken to minimize adverse effects.

Conduits carrying water can exist in a variety of forms: along deeply penetrating geologic faults, joints, and fractures or following the path of preferentially eroded bedding. Preferential structural deformation along faults, joints, and fractures or eroded bedding planes can enhance dissolution during subsequent interaction with groundwater.10,14 The resulting conduit may be a complex combination of many geologic features, making the exploration and remediation of the pathway difficult.

Subsidence and sinkholes at a project site can occur within several contexts. The changes in groundwater level in the vicinity of a project area due to dewatering of a nearby quarry may be

Hydrogeologic and Environmental Considerations for Karst Terrain/Sinkhole-Prone Areas 167

a triggering mechanism for subsidence and sinkhole collapse.10,15 Modification of existing drain-age pattern, vegetative stress, ponding of water, removal of stumps, land disturbance, grubbing, development of radial cracks, fissures and fractures, and subsequent enhancement of infiltration of surface water may cause subsidence and development of sinkholes.10,16

Preexisting subsidence structures can reactivate and subside further, forming a new collapse sinkhole within soil directly overlying the conduit.

Experience has shown that karst is unavoidable in most of the limestone terrains and that remediation of collapse damage in karstic zones is extremely expensive. As a result, the most cost-effective way to approach this issue is through integration of engineering design of the structure (facility, roads, industrial plants, etc.) or mine planning with an evolving understanding of local geologic and hydrogeologic conditions.

A thorough understanding of the subsurface in karst terrain will provide for the design and remediation of problematic conditions. As with any geotechnical problem, investigation costs, remedial design, and risk must be evaluated and balanced, so that the karst project can be under-taken in an enlightened manner.

Karst regions prone to subsidence can cause sewer problems in urban areas. A decision–logic framework comprises: (a) identification of casual mechanisms, (b) construction and evaluation of conceptual models, and (c) evaluation and parameterization of fundamental processes and develop-ment of a management strategy to tackle the problem.17

A predevelopment site investigation phase identifies the degree of dissolution, pattern, and extent of hazards such as subsidence, sinkholes, soil raveling and erosion domes, and the potential for their further development. The thickness and strength profile of soil overburden, particularly the soft zone over rock, location of rock collapses, or the potential for soil dome collapse, all influence design and use of shallow foundations. Adding fill on the top of rock or on the soil overburden, as well as excavating soil and rock, alter the present and future integrity of the karst system because these activities change the stress in the underlying formations.10,18

Mining limestone and dolomite can encounter solution features in rock on some scale at all locations. These features may range from micro-scale stylolitic seams to groundwater-filled cav-ern systems with the potential to shut down operations and threaten the extraction of significant valuable resources (tens of millions of dollars). Although blasting and groundwater management associated with mining may appear to cause sudden and catastrophic development of sinkholes and other karstic features, in all cases it is the karst and its underlying geologic and hydrogeologic conditions which came first. Mining, groundwater extraction, and other activities associated with quarrying merely serve to enhance these features and encourage their expression at the surface or in the pit.

Existing groundwater conditions and potential changes that occur naturally or by human activities must be evaluated so that steps can be taken to minimize adverse affects. Evaluation of topographic maps, aerial photography, subsurface geology (stratigraphy, structure), hydro-geology (occurrence, movement, and storage of groundwater), hydrologic (surface drainage), geophysical data (resistivity, dipole–dipole, microgravity, seismic), and the physical changes that effect solutioning rock or soil dome collapses (along with comprehensive planning and engineering design) will assist to solve sinkhole- and subsidence-related problems, and prevent or minimize damage. Understanding and evaluating these factors, including karst processes, aid in conceptualization and developing realistic models representing typical conditions as well as extremes that are likely to occur at a site. Such evaluation also assists in designing structures to be antikarst and insensitive to the occurrence of subsidence and sinkhole development, and abet in estimating the risks involved with long-term land uses such as construction (domestic, office complex, and industrial) or mining to extract valuable resources for aggregate or other purposes.


8.2.1 dEsk top invEstigations

Investigations typically start with the collection and detailed review of existing fundamental data, including published and unpublished reports and files; data on files, raw information, graphics, maps (topographic, geologic, structure, soil, land use, property tax, etc.) obtainable from federal and state agencies (U. S. Geological Survey, Bureau of Mines, U.S. Department of Agriculture, U.S. Environmental Protection, U.S. Corps of Engineers, U.S. Fish and Wildlife Services; NOAA, State Geological Surveys, Soil Conservation Service, Land Management), county and local agencies, consultant reports, and theses from universities on relevant topics.

Features on topographic maps (lineaments and sinkholes) must be located as they typically signal risk of ground failure and potential for flooding. Such features include lineaments, existing depressions, sinkholes, surface-water impoundments, creeks or streams flowing across the prop-erty, etc. Geologic maps provide information on geologic contacts, lithology, and structure. Geo-logic records from existing borings (drilling logs) provide information to locate karst zones and the water table (or potentiometric surface) and also aid to construct a conceptual model of the site.

Black and white as well as color and false-color infrared sequential historical aerial photogra-phy, satellite imagery of the project site and adjacent areas are used to identify lineaments, traces of sinkholes, chronologic development of surface expressions, structural features, interconnected joints and fractures, stressed vegetation, potential locations of sinkholes, seeps, springs, surface-water bodies, depressions, and drainage features (shallow erosion gullies, wet weather streams, etc.). Geomorphic features are studied to identify karst terrains as well as identify locations that are most likely to become water-related (quarry dewatering) or engineering problems related to carbonate solution features (sinkholes and solution depressions). Review of subsurface geophysical information for the site under consideration, if available, can delineate distributions and depths of caverns in the underlying bedrock.19

Intensive land use may mask potential surface expressions of buried paleokarsts or the effects of a growing void in the residuum. It also quickly erases traces of sinkholes in the landscape. More-over, the bedrock may be overlain by a thick cover in most of the area. For these reasons, the study of the ground surface is often of little help as a straight link does not exist between paleokarsts and existing surface relief. It is therefore not surprising that, in these areas, aerial photographs and remote sensing techniques show little results in delineating collapse hazard zones.

Identification of causal mechanisms, construction and evaluation of conceptual models, evalu-ation and parameterization of fundamental processes, and development of a management strategy helps to modify design plans according to evolving site specific conditions and to tackle problems during construction in an efficient and cost-effective manner.

Understanding the potential for environmental changes that affect solutionization of limestone/dolomite rock and soil dome collapse is necessary in estimating the risks involved with long-term use of the project site. The economics of investigation, and preventive and corrective work, as well as the impacts on the environment, must be considered before starting field activities.19

It is also important to perform a field reconnaissance survey to ground truth the features iden-tified on topographic maps, sequential aerial photographs, and satellite imagery during desk top investigations. Particularly, suspicious or problematic karst terrain details that are difficult to iden-tify from review of aerial photography and maps because of (a) tree and vegetative cover as well as overhangs and other obstructions, and (b) their small size or low relief, are to be investigated during field activities.

8.2.2 FiEld invEstigations

Review of information during the desktop investigation will provide a framework and timetable for field investigations that will include both direct and indirect procedures for detection and delineation


of subsurface geologic hazards during development, laying the foundation, and construction of the project area.

Field investigations include vertical and horizontal test borings, rock coring, test pits or test trenches, collection of representative soil samples of (regolith) and overburden, rock, and fill mate-rial in rock cavities. Vertical borings are drilled to assist in defining the shape, size, and orientation of voids, if present, in regolith and overburden, and fractures, openings, and cavities in bedrock. Horizontal and directional borings may be used to identify and explore the solution enlargement of vertical fractures, fissures, and joints, their width, and fill material.

Direct procedures such as test borings, test pits, ditches, and probes provide information related to (1) distribution and dimensions of rock cavities and soil voids, (2) depth and configuration of the rock surface, (3) variation in physical characteristics of the subsurface soils (regolith and overbur-den) and rock, (4) clay-filled seams, (5) stained joints, (6) drilling fluid losses at various depths, and (7) falling of drill rods into open or soft clay-filled cavities. Air-trac probes are valuable, particu-larly when used in conjunction with test borings, because of the mobility, speed of drilling, and the relative economy of operation.

Test pits and trenches are dug to the rock surface to delineate the orientation and extent of cavi-ties and slot and pinnacle formation, and to gain information that cannot be obtained by boreholes. The size and depth of trenches and pits may be limited by the availability and capability of equip-ment, strength of soil overburden, extent of soft zones, and depth to water.

Many indirect methods include borehole geophysics, video imaging of borehole walls, and appropriate noninvasive geophysical exploration. The host of geophysical techniques include seismic reflection and refraction, electrical resistivity and conductivity, self-potential, ground-penetrating radar (GPR), and dipole–dipole and gravity surveys that can be performed to characterize the con-figuration of the bedrock surface, randomly oriented fissures, large-size voids, cavities, and other solution features.19

A down-hole color camera is a direct means to (1) evaluate a borehole with closely fractured rock that produced no core recovery, (2) determine if fissures, fractures, and joints are open or clay-filled, and (3) determine if the voids encountered are isolated, enlarged fractures and joints, or large continuous caverns.

A geographic information system (GIS), which is a collection of computer hardware and soft-ware, may be used to manage and analyze spatial data. A GIS provides the ability to organize, visu-alize, and merge spatial data sets from different sources and allows quantitative spatial analysis and predictive modeling of these data. The GIS techniques are used to investigate natural hazards. New remotely sensed data sets and computer-based techniques developed during the 1980s and 1990s have opened the opportunity for more synoptic study of sinkhole hazard. These data sets also offer potential for understanding the hazards of sinkhole collapse by permitting spatial analysis within a GIS of such related factors, as topography, hydrology, and land use.20

8.2.3 surFacE gEophysical Exploration

Geophysical surveys are used to explore shallow (± 30 m) subsurface conditions. Geophysical meth-ods are used to determine indirectly the extent and nature of geologic material beneath the surface. The thickness of soil (residuum and overburden), probable void zones or cavities, and depth to the bedrock and groundwater can also be determined.

Geophysical exploration involves measuring a force system (geophysical properties) in the Earth and inferring boundaries between zones of similar responses to those forces and the patterns of force change, known as anomalies. The force system can be natural (gravity and the Earth’s mag-netic field) or induced (electrical current and electromagnetic or shock wave).21

Geophysical exploration involves making measurements at many different locations, either in traverses or grid patterns. Results are interpreted from the variation of the geophysical proper-ties relative to location and, in some cases, with the spacing between the sensing points. Various


geophysical methods are employed to determine the depth to rock, configuration of rock surface and probably void zones, cavities, solution features, etc. Successful interpretation of the subsurface using noninvasive geophysical procedures occurs only under ideal conditions. In general, the inter-pretation of geophysical methods can be misleading unless used in conjunction with other data from the exploratory drilling of bore holes, test trenches, and test pits for confirmation or correlation.

gravity Survey

Measurement of the gravimetric fields of the Earth is a standard geophysical method used to study the structure and composition of the Earth. Gravity exploration is useful in the early stages of site investigations to locate areas that are likely to exhibit significant near-surface dissolution features or where there are large shallow raveling erosion domes in the soil. An anomaly in a gravity survey data may indicate the presence of dissolution features, thus warranting additional invasive investigation.

ground-Penetrating radar

Ground-penetrating radar (GPR) is based on the transmission of repetitive pulses of electromagnetic waves into subsurface materials. These pulses are reflected back to the surface when the radiated waves encounter an interface between two materials of differing dielectric properties.

The depth of penetration of electromagnetic energy varies in different lithologies. In sandy materials above the water table, penetration of more than 30 m is possible, whereas in clay below a water table, penetration of only 3–6 m may be possible. The data are analyzed and interpreted to determine the depth and the lateral extent of change in subsurface material.21

electrical resistivity

This method measures the electrical conductivity (inverse of resistivity) of soil and rock. The extent and resolution of material tested depends on the spacing and patterns of electrodes or induction arrays compared to the geometry of the high and low conductivity strata or lenses. The depth and geometry of zones of different conductivities are deduced by empirical or mathematical analysis of data. Cavities filled with air have no conductivity; cavities filled with clay or mud are relatively more conductive than cavities with water. Electrical resistivity methods are useful in estimating the average depth to rock, and usually, the depth to groundwater.

Seismic refraction

Seismic refraction involves the measurement of velocity of a compressive shock wave induced at the ground surface or in a borehole by a hammer blow or a small explosion. The wave velocity depends on the density, modulus of elasticity, and Poisson’s ratio of the soil or rock. The type of soil or rock sometimes can be inferred from the shock wave velocity, particularly if the geophysical results are correlated empirically with soil and rock test data from a nearby boring. Interpretation of data is subjective in solutioned limestone with irregular boundaries. This method seldom can detect large cavities in the overburden because shock waves through the subsurface soil travel faster than through the cavity. It cannot define cavities in rock because the higher wave velocity in solid rock above cavities obscures the slower wave return of the cavity. The ability of the method to sense irregularities decreases with increasing depth below the surface.

8.2.4 borEholE gEophysics

Borehole geophysics senses the response of rock and soil in the walls of a borehole. Multiple instru-ments, stacked in a single probe, test the borehole walls. These techniques are utilized to determine


detailed variations in lithologies of soil and rock and their properties more or less continuously at greater depth below the ground surface.

The various downhole probes which provide useful information for geotechnical work are:18

logs Information

Caliper log: borehole diameter Fracture, solution openings, voids, and cavities detection. Identify very soft soil, unstable closely fractured rock or cavity intersected by borehole

Self-potential log: voltage Detect permeable beds, determine formation water resistivity. The magnitude of the SP deflection is due to the difference in resistivity between mud filtrate (Rmf) and formation water (Rw). Correlate strata from one bore to another by voltage pattern comparisons

Resistivity log (R) Determine resistivity, porosity, and specific permeable zones. The formation’s resistivity close to the borehole is used to determine porosity in a water-bearing zone

Gamma ray log Used for identifying lithologies and for correlating zones. Locate clay seams, clay or shale content, relative sand-shale content

Induction log, IP log Clay or shale content

Neutron log Measures liquid-filled porosity, moisture content of soil and rock. Locate porous media, estimate percentage of porosity, bulk density

Computer-assisted tomography (CAT)

Grain size/pore size distribution; total porosity/bulk density, moisture content

Acoustic televiewer Cavity detection, sedimentary structure orientation, fracture orientation

Acoustic velocity Compressibility/stress–strain properties bed thickness

Uphole/downhole seismic cross-hole seismic

Compressibility/stress-strain properties

8.2.5 risk assEssmEnt

It should be acknowledged that the risks of development in karst terrain (sinkhole-prone areas) involve unforeseeable site conditions that may need specialized geotechnical investigations to mini-mize additional construction costs and future problems. A thorough understanding and differentia-tion between observed facts and interpretation of data is necessary to facilitate decision-making processes regarding technical remedial measures.

The factors that should be included in risk assessment are both the natural and anthropogenic conditions that drive failure mechanisms. Natural conditions to be considered are climate, geology, and groundwater. Human activities include regional or local environmental disturbances such as excessive groundwater pumping, quarry dewatering, diversion of natural drainage, and other con-struction activities.

Land surface damages may range from subtle movement and subsidence to fissure development and sudden collapse. The results of these occurrences range from minor inconvenience to cata-strophic loss and environmental disaster.

8.2.6 sitE charactErization For planning and dEsign

To develop a single realistic model for the deterministic analysis of bearing capacity and potential settlement in karst/carbonate regions is usually difficult because of the variability of dimensions of features typical to karst terrains and the changes in the soil and rock profile from location to loca-tion. A model therefore needs to be developed for each project area representing the typical condi-tions, as well as the extremes that are likely to occur in that area. The model focuses on the peculiar features of carbonate terrain that influence foundation design and performance: the depressions, sinkhole(s), soil raveling–erosion domes, the inverted soil strength profile, the slot and pinnacle


rock surface geometry, and the cavities in the rock. Design concerns as related to karst terrains are to be evaluated and resolved before consideration of foundation characterization related to bearing capacity and consolidation settlement.19

8.3 deSIgn and conStructIon conSIderatIonS

Planning, design, and construction considerations focus on overcoming difficulties inherent in karst terrain. These difficulties include features and weaknesses of the soil and rock such as sinkholes, solution depressions, troughs and pinnacles in the soil-rock interface, dome cavities in the soil over-burden, and collapse-prone caverns in the underlying rock. Existing karst-related problems can be aggravated by changes and activities such as frequent significant seasonal changes in groundwater level, excavation, stockpiling, impoundment, dewatering, poor surface-water drainage, improper project management during construction, poor maintenance and waste management, and leaking pipes during and after completion of the construction. Off-site activities such as groundwater level fluctuations or excessive groundwater withdrawal, or excessive soil erosion could act as triggering mechanisms for subsidence or sinkhole development. Therefore, planning, design, and construction in a karst terrain must involve all activities that influence the conditions that aggravate a karst ter-rain, including the carbonate rock and related overburden voids on project site and adjacent property controlled by others.

Site preparation in karst terrain also includes remedial activities to improve and fix any existing sinkhole or solution-related problems, such as voids or cavities or erosion domes that might impact construction, as well as measures to minimize the future development of karst features during the lifetime of the project.18,22

Additional investigations are warranted before construction operations commence to identify erosion domes, depressions, sinkhole throats, and openings in the rock surface, and collect infor-mation so that remedial steps can be taken before construction. Also the potential for collapse of an existing cavity or cavities under the weight of equipment that could delay construction, damage equipment, and, more importantly, injure workers, should be thoroughly investigated.

Altering the surface topography and surface drainage by construction activities such as excava-tion can redirect water flow, thereby concentrating it and aggravating downward seepage. Conse-quently, raveling erosion and dome development or reactivation of sinkholes can cause project delay and added cost, or development of karst features on adjacent properties.

It is often necessary to make changes in design and construction in karst terrain because of sig-nificant fluctuations of water levels, or the occurrence of irregular but abrupt soil–rock interfaces, or inverted residual soil strength profiles. These changes may result in additional project costs and, consequently, become a “point of contention” among owner–sponsor, designer, and contractor.

These conflicts essentially end up in delaying the project and adding expenses, and may jeop-ardize the entire project. Thus, it is prudent to promptly identify, evaluate, and correct potential problem areas.

8.3.1 distribution oF solution FEaturEs at a sitE

Air photos and topographic maps are used to identify karst features (solution depressions, sink-holes) and total areas of these features per unit of land area. A field survey is performed to identify small sinkholes or solution features and to prepare maps showing areas of similar drainage align-ments or drainage density and solution feature densities. These maps are used to define similarities, patterns, and delineate lineaments (the alignment of features along straight or somewhat curved lines). Typically, lineaments are better defined and more closely spaced parallel to the strike in dipping beds. The intersections of lineaments are more susceptible to the formation of depressions and development of sinkholes. If there is no depression at an intersection and conditions in the area


are favorable for sinkhole or depression development, the chances of occurrence of new ones (sink-holes) at the intersection are relatively more favorable than elsewhere.

A solution pattern approach needs to be used to delineate the most suitable areas for devel-opment of large industrial complex offices, buildings, hospitals, etc., in karst areas that include some of the most closely spaced, well-developed solution depressions and sinkholes. Based on this approach, areas with only minor solution development could be identified for the construction and successful completion of a large structure without facing or dealing with large problems related to karst hazards.

Areas where carbonate formations, particularly solution features, are covered with regolith (residuum), a site exploration program must be planned, designed, and developed to determine the extent and intensity of geologic hazards. The exploratory work includes geophysical surveys and borings in a regular pattern. The information generated by field activities and desk studies, such as review of aerial photos, topographic, geologic, and lineament maps, are compiled and interpreted tentatively in terms of defects or problems for the use of the site for a planned purpose. Based on the results of this investigative work, the following alternatives are considered: (a) the conditions are not suitable or are bad enough that there is little chance of completing the project without extraordinary costs; (b) the conditions appear so favorable that no problems are likely; or (c) some blanks in the data and drawbacks in the findings require collection of additional information before utilization of the site for the proposed purpose. The last alternative could cause substantial delay and require more investigative work to be performed, which translates into additional time and funding requirements before decisions can be made to either proceed with the project or select another site.19

There are only a few owners or developers who are willing to invest time and money to develop needed data for prudent decisions. Most of the time, it is assumed that sinkhole problems can be easily overcome and will not affect project costs or the schedule. This kind of thinking and attitude to the problems related to sinkhole development and subsequent subsidence cost very dearly in terms of both monetary and time consequences.

It is prudent for both prospective developers and contractors, before committing to a compre-hensive contract for planning design and construction, to have desktop studies and field investiga-tions performed in sufficient detail to adequately understand and evaluate the subsurface conditions in karst terrain where limestone is known to exist, or where solution features are hidden by regolith or deposited soil. In such areas, the site exploration required to determine possible problems is far more extensive and intensive than areas with visible solution features such as depressions and sinkholes. A contract for construction typically entails a rigid time for completion, a penalty for delays, and a fixed lump sum price for all work, including site investigation for estimating founda-tion costs.

The reliance on limited or incomplete data to make plans of unprecedented scale that do not allow flexibility for changes warranted in areas underlain by subsurface karst conditions would result in substantial financial and development costs and may also incur penalties, significant legal fees, and expenses.

The detailed investigation, however, would indicate potential risks and allow formulation of alternative designs to fit the various solution features and cavity conditions at sites underlain by karstified carbonate rocks that are to be developed. This approach would also allow development of a range of costs and construction approaches and a schedule of completion for the project without frustration on the parts of the parties involved and with a savings of millions of dollars in penalties and litigation costs.

8.3.2 sitE prEparation

Sites in karst terrain involve solution depressions, sinkholes, dome cavities in the regolith (over-burden), pinnacle and slot zones in the overburden bedrock interface, and sinkhole-prone, col-lapse-prone caverns in the underlying bedrock (Figure 8.1). Development of a site and design and


construction of foundations warrant efforts to overcome the inherent flaws and weaknesses of the soil and rock. Raveling and erosion in the overburden soil and the erosion of cavity filling in the rock can change during construction and alter greatly within the expected life of most structures. These carbonate-rock-related deficiencies can be further exacerbated by environmental modifications or changes as a result of construction activities such as large amplitude of groundwater fluctuations; changes in surface-water drainage pattern; poor water control; cut and fill; excavations; movement of heavy equipment; and imprudent project management. These defects can also be exaggerated by adjacent off-site withdrawal of large quantities of groundwater and excessive drawdowns. Also groundwater pollution influences both soil erosion and bedrock dissolution. Thus, the foundation design and construction entails: (a) installation of a foundation structure, and (b) considerations, control, and abatement measures of all environments that influence the processes that aggravate the carbonate bedrock and related overburden deficiencies on site and adjoining off-site property.

Preparation of a site underlain by carbonate rock includes: (1) excavation and filling and (2) remedial measures to improve or fix any solution-related drawbacks that might impact the con-struction and the future structure, and to mitigate or minimize the development of solution features during the lifetime of the project.

8.3.3 sitE Excavation and sinkholE activity

Overburden soil and rock profiles are investigated before excavation for installation of foundations. The overburden soils are explored by test pits, trenches, and drilling of exploratory boreholes to iden-tify erosion domes, sinkhole throats, and openings in the rock surface to gather information needed to plan remedial actions and perform required mitigative work for installation of sound foundations.

In karst terrains the soil strength is typically higher near the surface but declines with depth. The soil–rock interface is typically uneven due to pinnacle-slot irregularities and soft wet zones, different water-level elevations within overburden and bedrock fractures, and cavities. The solution domes within the overburden could collapse and reactivate the formation of sinkholes because of construction activities and alteration of surface-water drainage. This could interrupt construction activities, worsen repair work, endanger workers and equipment, and cause expensive delays.

During exploratory work, it is important to (1) have excavation slopes sufficiently flat to avoid toppling and sliding; (2) maintain the stability of the bottom of excavation against heave and boiling from excessive groundwater pressure; (3) remove boulders and pinnacles; and (4) manage the effects of excavation and filling on the overall site environment, such as (a) surface drainage, (b) rainfall and surface-water infiltration, (c) groundwater movement, and (d) water chemistry and pressure.18

Removal of overburden soil above the carbonate bedrock during excavation has an impact on the development of sinkholes because it (1) reduces the vertical stress in the remaining soil, (2)

Limestone

Residualgravelly

clayRavelling

domesThroat

Loos

eso

il

Fill

Floor

Dome-shapedcavity In

clay

fIgure 8.1 Sinkhole beneath.


increases the vertical stress in the remaining soil owing to weight of the new structure on the ground surface, and (3) reduces the seepage path from the ground surface to the soft zone.

Reduction in vertical stress could cause localized heave of the soil due to increase of potentio-metric pressure and may prove detrimental to the project, halt construction, and seriously damage the site. When heave or boil occurs it is prudent to stop further excavation until water pressure is relieved by pumping from nearby wells that tap underlying carbonate aquifers containing fracture systems or cavities. The potential of raveling erosion, dome development, and foundation settlement from relieving groundwater pressure must be weighed against the need for deeper excavation. It is also judicious to install piezometers into underlying fracture systems/cavities to monitor the fluctua-tion of groundwater levels in bedrock during excavation and construction activities. Water level data will serve as an indicator for taking necessary corrective measures, if required, to prevent heave and boiling, before it occurs and therefore help to avoid taking costly emergency procedures during or in the middle of excavation.

The removal of the densest, most impervious soils in the upper part of soil profile could enhance seepage erosion in the soil. If the water pressure in the bedrock drops sufficiently from excava-tion drainage, downward seepage is accelerated, resulting in the development of erosion domes, increased settlement, and occurrence of sinkhole activity.

Deep excavation exposes relatively smaller erosion domes near the rock surface which could be dealt with and remediated before construction. Geophysical exploration after excavation will be prudent if high structural loads are to be imposed on the remaining overburden soil.

8.4 remedIatIon

8.4.1 prEvEntivE mEasurEs to stop ravEling and Erosion at soil–rock intErFacE

Numerous small erosion domes and soft zones, where there are few or no pinnacles, are repaired and further development of domes can be avoided by injecting viscous and quick-settling grout or high-slump sandy fly ash cement mortar through grout holes laid out in a grid pattern to form a quasicon-tinuous grouting cap on the top of the rock (Figure 8.2). This grouting is called cap grouting. The spacing of holes depends on the estimated space between the larger openings or voids in the rock surface and any soft zones in the soil–rock interface. The grout pressure should be enough to force the soft soil into open rock voids below the top of rock and replacing the soft soil with the grout. The grout pressure should be monitored to avoid or forestall occurrence of ground surface heave.

In some cases where there is no well-defined soft zone, it is possible to grout some cavities in the upper few feet of the underlying bedrock to inhibit downward erosion. Some of the fractures and cavities in the rock may not get grouted by this method because the locations of the cavities cannot be determined accurately from the ground surface. Even closely spaced grout holes may not find a particular cavity that might be responsible for further erosion. Filling the near-surface cavities in the underlying bedrock, however, can stop further erosion and raveling development.18,23

Soil dome

Closely spacedgrout holes

Groutcap Soil

fIgure 8.2 Grouting of small cavities and slots.


8.4.2 ovErburdEn domE collapsE and rEpair

Erosion domes that are either identified or suspected during preparation of the site can be treated and repaired in a similar way as sinkholes. Erosion domes, which are sometimes drilled through its roof and the cavity including the throat of the sinkhole at the soil–rock interface, are filled with high-slump concrete to stop erosion and enlargement of cavity and provide required support.

Erosion domes are sometimes collapsed by high impact compaction (dynamic compaction). This is done by having heavy construction equipment or sheepsfoot rollers repeatedly traverse between the sites or by repeatedly dropping a weight of tens of tons from a height varying 50–75 ft, during site preparation. This way the erosion domes are collapsed and filled with collapsed soil with vary-ing degrees of compaction; however, the process does not correct the underlying soil erosion and raveling problem. The formation of an erosion dome can begin again if the environmental condi-tions are favorable, but at a reduced rate because of the densification of undisturbed loose soil and reduction in soil permeability owning to compaction. This method is considered to be most effective in sandy soils to retard but not necessarily prevent development of sinkholes.

8.4.3 rEpair oF sinkholE

Sinkholes and erosion domes (boils) exposed during excavation are to be repaired before instal-lation of foundations. The sinkhole is to be excavated to the narrowest point of the bottom, called throat, to expose carbonate rocks and pinnacles surrounding the throat for installation of a concrete plug across the opening. Clay adhering to the rock should also be removed to provide better rock surface for bonding between rock and concrete or reinforcement plug(s). Both the plain and rein-forcement concrete plugs have proved to be effective in preventing further erosion at those locations, thus providing support to the structure being built on the top of the cavity or cavities covered by overburden (Figure 8.3).

Blocking or prevention of downward water seepage in areas where a structure is being built, in some cases, may aggravate raveling and erosion and cause sinkholes to be developed in the vicinity of the project site. Under these circumstances, it is advisable to fill open sinkholes with coarse rock, followed by smaller rock fragments, forming a graded filter. Finally, sand–cement mortar is placed on the top of rock fragments to build an arch across the bottom opening (Figure 8.4). The holes are

filled with coarse or large blocks of rock until the surface of the fill material is above the narrow throat at a height of approximately two-thirds the width of the opening. The coarse material is followed by gravel, sand, and finally fluid sand–cement mortar so as to penetrate the large voids and bond the rock pieces and fragments together for a depth equal to the rock fill height above the narrowest point of the natural opening. If an impervious plug is required, it is necessary to completely fill the void.

Dumping of crushed stones to repair sinkholes may cause some problems because of measurable settlement. This situation can be avoided by vibrat-ing and densifying the fill material, even in narrow openings.

In areas with a significant amount of anticipated surface infiltration, a pervious plug is installed to permit downward seepage and drain water from the overburden. In some cases short pipes, with top ends at the source of water, are inserted through

Rim

Throat

Backfill

Concreteplug

fIgure 8.3 Plugging sinkhole throat with concrete.


the fill rock before grouting to facilitate infiltra-tion downward. In this way, a gradual filter pre-vents downward erosion of soil from overburden materials.

Compaction grouting can often form relatively impervious plugs in areas where excavation into the throat and cleaning of the rock is not practical. Compaction grouting uses pumped cement, sand, and pea gravel mortar with a slump of approxi-mately 70–120 mm at a pressure ranging from 250 to 500 psi. The compact grout at a high pressure typically displaces soft soil in narrow openings (fractures, voids, etc.) and develops a generally stable and watertight plug.6,13,24

Compaction grouting for the plug followed by low-pressure grouting of the remainder of the open-ing is used to minimize ground settlement in areas where working space for sinkhole filling is restricted because of the location of the sinkhole either in between buildings or under existing structure.

Erosion domes are filled by grouting under con-trolled conditions to avoid the occurrence of heave of the ground surface from the grout pressure. Grouting is stopped at the first sign of heave or when the grout pressure rises above the limiting pressure during continuous pumping.

Jet grouting is used to repair sinkholes where the throat of the sinkhole is too stiff to displace. The jet erodes soil, stiff clays, and soft erodable rock into small gravel and boulder-sized pieces. The grout mixes with the coarse particles of soil and sand and gravel from drilling and forms a mixed-in-place concrete to plug the throat. The jetting pressure (4000–7000 psi) dissipates rapidly within the soil and does not cause heave when the volume of the grout is properly controlled.13,18,24

8.4.4 partially supportEd structurE on sinkholE-pronE ground structurE

As long as the foundation pressure does not exceed the safe bearing capacity of the residuum (stiff clay), the subsidence or settlement of the structure is largely controlled or balanced by pinnacle punching and relatively low compressibility of the residual soil. The structure design, therefore, should minimize excavation that removes a stiff residual soil. Design should also include remedia-tion or repair of any nearby solution depressions or sinkholes that can be corrected in addition to detailed exploration to identify hidden erosion domes near the ground surface.

A structure at the ground surface impedes or minimizes infiltration of rainfall into the underly-ing soil and, therefore, limits the opportunity for the enlargement of an existing raveling erosion dome and formation of a new dome. This same structure, however, could aggravate dome develop-ment by allowing infiltration of surface water from leaking pipes and poorly designed drainage. It is important that design emphasizes minimization of surface-water infiltration into the residual soil. Thick stiff residual soil, small structural loads, and avoidance of impounding or channeling water towards structure are good and helpful to foundations supported by the residual soils. Environmen-tal controls are necessary to minimize further deterioration and development of solution features in the underlying carbonate rock.

A structure or design of a structure is modified to adapt to poor soil and rock conditions, and making it resistant to potential dome collapse. Even if dome collapse is only a remote possibility it might be prudent to design the structure to be tolerant to the usually small differential settlements that occur from overburden sag and pinnacle punching.

Rim

Sand cementmortar

fIgure 8.4 Plugging of sinkhole with graded material.


In spite of taking all appropriate measures to identify soil defects or potential soil defects and testing them properly before installation of foundations, there is always some risk that soil or ero-sion dome collapse could develop in the future. Some of these risks arise from the design and construction of the structure. These include improper surface-water drainage and leaking water pipes and sewers. The risk can be increased by off-site changes such as lowering the groundwater level. In most karst areas, the risk of sinkhole collapse and catastrophic failure is infrequent and the public usually ignores the potential hazard. Ignorance of the risk of sinkhole collapse is illustrated by the many developments in karst areas.

8.4.5 dEsign structurE rEsistant to Erosion-domE collapsE

Power plants, communication systems, as well as hospitals and buildings used for public-related ser-vices, have to function without short interruptions despite some catastrophic events. It is, therefore, prudent to minimize even very small risks by designing structures to sustain a large dome collapse that could occur randomly at any critical location beneath the structure.

A sinkhole resistant structure is to be designed to prevent any failure of such structure, should there be a sudden catastrophic loss of foundation support because of collapse of an erosion dome; structural deformation and structural damage could be tolerated without compromising overall sta-bility of the structure. The functionality of the structure or remainder of the structure should not be significantly impaired until the affected zone is repaired.

The foundation and the upper part of the structure are to be designed to withstand the affects of a potential erosion dome failure and a dropout. Mat foundations are well suited for local loss of support design. The mats are reinforced and thickened so they become raftlike.

The diameter of a potential erosion dome—a zone of no support for foundation at the time of collapse—is typically larger than the initial dropout at the ground surface with its overhanging rim, but less than the ultimate funnel-like opening of a sinkhole after its rim has caved (Figures 8.3 and 8.4). The diameter of potential collapse of the erosion dome can be estimated from the size of nearby sinkholes in the same type of carbonate rocks with similar thickness of overburden or residual soil. When there is no sinkhole in the vicinity of the area where the structure is to be built, the diameter (width) of potential erosion domes in both cohesionless soil and cohesive stiffer clayey residual soil will be different.

The estimated effective diameter or width of erosion domes in cohesive soil will typically be greater than one half, but less than or equal to the thickness of the residual soil overburden. In cohesionless (sandy) soil, the diameter of erosion dome will be narrower and is estimated to be less than 10 ft.18

It is also important to put in place a system to monitor the structure and soil beneath it regularly for the development of subsidence or erosional dome. If signs of dome development or subsidence features (radial fractures, change in elevations at measuring points, soil movement) are apparent or discovered, remedial measures are to be taken before severe distortion and deformation in the structure develops and eventually catastrophic failure occurs. By having detection monitoring in place, significant foundation failure or damage to the structure as a whole or part could be prevented without severe interruption necessary to life-saving and important public services.

8.4.6 EmErgEncy actions

Emergency steps are to be taken to protect public and property, particularly when a sinkhole occurs in populated areas or in the vicinity of a structure that becomes hazardous. Structures typically inhibit failure of erosion domes or sinkhole development because they eliminate or reduce rainfall infiltration. The structure, however, could also aggravate the erosional dome and subsequent forma-tion of a sinkhole by improper disposal of surface drainage or wastewater. The concentrated load


of a surface foundation can develop failure by increasing the stress on an undetected erosion dome underneath the structure.

The following remedial measures should be considered regardless of the cause of the develop-ment of subsidence or a sinkhole:

1. Put a barricade or fence around the immediate affected area. 2. Fill in the bottom of the depression or sinkhole. 3. Repair the structure as soon as is possible and practical. 4. Repair or demolish the structure, fill in the hole, and make the site an asset rather than a

hazard or liability. 5. Prevent further activity in that sinkhole. The throat of the sinkhole must be closed or filled

despite the obstruction of the work space by any damaged structure. Once the throat of a sinkhole has been closed, the remainder of the hole is filled with a stable fill material.

6. Steps should be taken to minimize the site conditions that were responsible for the sinkhole.

referenceS

1. Berg, T. M. et al., Geologic Map of Pennsylvania, Pennsylvania Geological Survey, 4th Series map, scale 1:280,000, 1980, 3 sheets.

2. Buskirk, Jr. et al., Education about and management of sinkholes in karst aeas: Initial efforts in Lebanon County, Pennsylvania, in Hydrogeology and Engineering Geology of Sinkholes and Karst, Beck, B. F., Pettit, A. J., Herring, J. G. (Eds.), Balkema, Rotterdam, The Netherlands, 1999, pp. 263–266.

3. Beck, B. F., Herring, J. G. (Eds.), Geotechnical and environmental applications of karst geology and hydrology, Proceedings of the Eighth Multidisciplinary Conference on Sinkholes and the Engineering and Environmental Impacts of Karsts, Louisville, Kentucky, 2001, p. 437.

4. Kaufman, O., Quinif Y., Cover-collapse sinkholes in the “Tournaisis” area, Southern Belgium, in The Engineering Geology and Hydrogeology of Karst Terrains, Beck, B. F., Stephenson, J. B. (Eds.), 1997, pp. 41–47.

5. Reith, C. M. et al., Engineers challenged by mother nature’s twist of geology, in Hydrogeology and Engineering Geology of Sinkholes and Karst, Beck, B. F., Pettit, A. J., Herring, J. G. (Eds.), Balkema, Rotterdam, The Netherlands, 1999, pp. 149–155.

6. Knott, D. L. et al., Foundation engineering practice for bridges in karst areas in Pennsylvania, in Applied Karst Geology, Beck, B. F. (Ed.), Balkema, Rotterdam, The Netherlands, 1993, pp. 235–241.

7. Siegel, T. C. et al., The importance of a model in foundation design over deeply weathered pinnacled carbonate rock, in Karst Geohazards, Beck, B. F. (Ed.), Balkema, Rotterdam, The Netherlands, 1995, pp. 375–382.

8. Benson, R. C., LaFountain, L. J., Evaluation of subsidence or collapse potential due to subsurface cavi-ties, in The First Multidisciplinary Conference on Sinkholes, Beck, B. F. (Ed.), Balkema, Rotterdam, The Netherlands, 1984, pp. 201–216.

9. Wilson, W., Beck, B. F., Evaluating sinkhole hazards in mantled karst terrain, in Geotechnical Aspects of Karst Terrains, Sitar, N. (Ed.), Special Volume, 1988, pp. 1–24.

10. Newton, J. G., Development of sinkholes resulting from man’s activities in the Eastern United States, U.S. Geological Survey Circular 968, Denver, 1987, 54 pp.

11. Beck, B. F. (Ed.), Applied karst geology, Proceedings of the Fourth Multidisciplinary Conference on Sinkholes and the Engineering and Environmental Impacts of Karst, Panama City, Florida, Balkema, Rotterdam, The Netherlands, 1993, p. 437.

12. Tolmachev, V. V., Reuter, F., Engineering Karstology (in Russian). Moscow, Nedra, 1993, 151 pp. 13. Siegel, T. C. et al., Compaction grouting versus cap grouting for sinkhole remediation in East Tennessee,

in Hydrogeology and Engineering Geology of Sinkholes and Karst, Beck, B. F., Pettit, A. J., Herring, J. G. (Eds.), Balkema, Rotterdam, The Netherlands, 1999, pp. 157–163.

14. Beck, B. F. (Ed.), Sinkholes: Their Geology, Engineering and Environmental Impact. Florida Research Institute. Balkema, Rotterdam, The Netherlands, 1984, 429 pp.

15. Lolcama, J. L. et al., Deep karst conduits, flooding and sinkholes: Lesson for the aggregates industry, in Hydrogeology and Engineering Geology of Sinkholes and Karst, Beck, B. F., Pettit, A. J., Herring, J. G. (Eds.), Balkema, Rotterdam, The Netherlands, 1999, pp. 51–55.

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16. DeStephen, R. A., Wargo, R. H., Foundation design in karst terrain, Bulletin Association of. Engineer-ing Geologists, 39(2), 165–173, 1992.

17. Lamont-Black, J. et al., Hydrogeological monitoring strategies for investing subsidence problems poten-tially attributable to gypsum karstification, in Hydrogeology and Engineering Geology of Sinkholes and Karst, Beck, B. F., Pettit, A. J., Herring, J. G. (Eds.), Balkema, Rotterdam, The Netherlands, 1999.

18. Sowers, G. F., Building on Sinkholes, ASCE Press, New York, 1996, 202 pp. 19. Memon, B. A. et al., Site selection and design consideration for construction in karst terrain/sinkhole-

prone areas, in Hydrogeology and Engineering Geology of Sinkholes and Karst, Beck, B. F., Pettit, A. J., Herring, J. G. (Eds.), Balkema, Rotterdam, The Netherlands, 1999, pp. 107–110.

20. Whitman, D. et al., Applications of GIS technology to the triggering phenomena of sinkholes in Central Florida, in Hydrogeology and Engineering Geology of Sinkholes and Karst, Beck, B. F., Pettit, A. J., Herring, J. G. (Eds.), Balkema, Rotterdam, The Netherlands, 1999, pp. 67–73.

21. Memon, B. A. et al., Control of naturally occurring brine springs and seeps in an evaporite karst setting, in The Engineering Geology and Hydrogeology of Karst Terrains, Beck, B. F., Stephenson, J. B. (Eds.), Balkema, Rotterdam, The Netherlands, 1997, pp. 137–150.

22. Sowers, G. F., Introductory Soil Mechanics and Foundation Engineering, Macmillan, New York, 1979.

23. Kannan, R. C., Nettles, N. S., Remedial measures for residential structures damaged by sinkhole activ-ity, in Hydrogeology and Engineering Geology of Sinkholes and Karst, Beck, B. F., Pettit, A. J., Herring, J. G. (Eds.), Balkema, Rotterdam, The Netherlands, pp. 135–139.

24. Fischer, J. A., Fischer, J. J., Karst site remediation grouting, in Karst Geohazards, Beck, B. F. (Ed.), Balkema, Rotterdam, The Netherlands, 1995, pp. 325–334.

25. Barner, W. L., A geologic evaluation: The first step in land use planning in Stone County, Missouri,in The Engineering Geology and Hydrogeology of Karst Terrains, Beck, B. F., Stephenson, J. B. (Eds.), Balkema, Rotterdam, The Netherlands, 1995, pp. 389–393.

26. Beck, B. F., Herring, J. G. (Eds.), Geotechnical and environmental applications of karst geology and hydrology, Proceedings of the Eighth Multidisciplinary Conference on Sinkholes and the Engineering and Environmental Impacts of Karsts, Louisville, Kentucky.

27. Currens, J. C., Ray, J. A., Karst atlas for Kentucky, in Hydrogeology and Engineering Geology of Sink-holes and Karst, Beck, B. F., Pettit, A. J., Herring, J. G. (Eds.), Balkema, Rotterdam, The Netherlands, 1999, pp. 85–89.

28. George, S. et al., Karst system characterization utilizing surface geophysical, borehole geophysical and dye tracing techniques, in Hydrogeology and Engineering Geology of Sinkholes and Karst, Beck, B. F., Pettit, A. J., Herring, J.G. (Eds.), Balkema, Rotterdam, The Netherlands, 1999, pp. 225–242.

29. Heath, W.E., Drilled pile foundations, in Karst Geohazards, Beck, B. F. (Ed.), Balkema, Rotterdam, The Netherlands, 1995, pp. 371–375.

30. Jennings, J. E., Brink, A. B., Louw, A., Gowan, G. D., Sinkhole and subsidences in the transvaal dolo-mite of South Africa, Proceedings of the 6th International Conference on Soil Mechanics and Founda-tion Engineering, University of Toronto Press, Toronto, Canada, 1965, pp. 51–54.

31. Kaufmann O., Quinif, Y., Geohazard map of cover-collapse sinkholes in the “Tournaisis” area, South-ern Belgium, in Hydrogeology and Engineering Geology of Sinkholes and Karst, Beck, B. F., Pettit, A.J., Herring, J. G. (Eds.), Balkema, Rotterdam, The Netherlands, 1999.

32. Schmertmann, J. H., Henry, J. F., A design theory for compaction grouting, grouting, soil improve-ment and geosynthetics, Proceedings of the Geotechnical Division, ASCE, New Orleans, LA, 1992, pp. 215–228.

33. Sitar, N. (Ed.), Geotechnical Aspects of Karst Terrains, Geotechnical Special Technical Publication No. 14, ASCE, New York, 1988.

34. Sowers, G. F., Correction and protection in limestone terrain, Proceedings of the First Multidisciplinary Conference on Sinkhole, Florida Sinkhole Institute, University of Central Florida, Orlando, FL. Also published in Environ. Geol. Water Sci., 8(1/2), 77–82, 1988.

35. Sweeting, M. M., Karst Landforms, Macmillan, London, 1971, 362 pp. 36. Terzaghi, K., Peck, R. B., Soil Mechanics in Engineering Practice, 2d ed. John Wiley & Sons, New

York, 1967, 729 pp. 37. Tolmachev, V. V., Evaluation of antikarst protection efficiency, in Sinkholes and the Engineering and

Environmental Impacts of Karst, Beck, B. F. (Ed.), Balkema, Rotterdam, The Netherlands, 1967, pp. 371–373.


38. Warner, J., Schmidt, N., et al., Recent advances in compaction grouting technology, Grouting, Soil Improvement and Geosynthetics, Proceedings of the ASCE Conference, New Orleans, Louisiana, 1992, pp. 252–264.

39. Welsh, J. P., Sinkhole rectification by compaction grouting, Proceedings of Geotechnical Aspects of Karst Terrains, ASCE National Conference, Nashville, TN, 1988, pp. 115–132.

40. White, W. B., White, E. L., Thresholds for soil transport and the long-term instability of sinkholes, Karst Geohazards, Beck, B. F. (Ed.), Balkema, Rotterndam, The Netherlands, 1995, pp. 73–79.

41. White, W. B., Geomorphology and Hydrology of Karst Terrains, Oxford University Press, Oxford, 1988.

42. Wohlford, T., Important Considerations for Bed Rock Fracture Analysis for the Placement of Bedrock Water Supply Wells, The Professional Geologist, September/October 2003, pp. 2–5.

183

9 Groundwater Modelling

9.1 IntroductIon

Many types of models have been used for simulating groundwater distribution and flow conditions in water-bearing materials. Scale models and direct analogy models of physical systems include simple scale models, such as sandboxes,1 electrical conductivity sheets, Hele — Shaw and resis-tance network models.

The sand tank or hydraulic model can simulate both confined and unconfined systems under both steady state and dynamic conditions. This type of model has been used in studying seepage through dams, groundwater movement, seawater intrusion, and flow to and from wells. Due to the creation of air bubbles, however, many problems may arise that make sand models difficult to use.

9.2 electrIc SImulatIon model

Electrical conductivity models are restricted to steady-state solutions. The simpler types apply to homogeneous, isotropic aquifers. Solid, liquid, and gelatin conductors have been used. Electrolytic models are adapted for seepage analysis and flow net construction.

Early use of electrical analog simulation techniques resulted from similarity between Darcy’s law and Ohm’s law. Darcy’s law can be written:

V K dhds

= − (9.1)

in which V = velocity of flow for a specific discharge, K = hydraulic conductivity, h = total head, and S = distance along the direction of flow.

Ohm’s law can be expressed as

i dEdx

= −σ (9.2)

in which i = electric current, and σ an electric conductivity per unit length of conductor in the

direction of flow, E = Electric potential or voltage, and x = length of conductor in the direction of current flow.

The similarity between the last two equations is not an accident. The analogy is based on the laws of conservation of mass and conservation of energy. The translation of these laws into a mathematical expression results in a differential equation which is applicable to mechanical as well as electrical systems, hence the similarity. The flow of groundwater resulting from gravitational forces can be expressed by the same differential equation as those described in current flow and in an electrodynamic system. Electric potential distribution in a conductive sheet or liquid is directly analogous to groundwater elevation or head in two-dimensional aquifers.


i.e E analogous to h ) σ ______________K ) (9.3) i ______________V )

This similarity has led to several types of electric analog models. These include conductive liquid analogs, conductive solid sheet analogs, resistance-capacitance network analogs, and complex ana-log computer models.

Flow nets can be drawn properly using conductive sheets or electrolytic tanks, where as a resis-tance-capacitance network can be used with the finite difference techniques discussed later.

9.3 Hele–SHaW model

Viscous flow models frequently known as Hele-Shaw models are being applied as a good tool for various groundwater flow problems. Drainage problems are examples of problems that can be solved using such models.

The average velocity of a viscous flow between closely spaced parallel plates is represented as

Vav. = – Km ∂∂

hx

(9.4)

where

Km = b y2

12 µ (9.5)

in which Vav is the average velocity, µ is the dynamic viscosity of the fluid, y is the specific weight and ∂h / ∂x is the hydraulic gradient.

9.4 reSIStance netWork model

Steady state problems can be solved numerically using the finite-difference method.Using a combination of resistance network and finite-difference methods, problems can be

solved easily and rapidly. The continuity Eq. (9.6) for the steady state two-dimensional flow can be solved numerically as follows.

∂∂

+∂∂

=2

2

2

2 0hx

hy

(9.6)

The piezometric heads, h1, h2, h3, h4 and h0, in an aquifer, which is divided into a grid system (see Figure 9.1), then,

∂∂

≈−h

xho h

x1

∆ from 0 to 1 (9.7)

or

∂∂

≈−h

xh

xh2 0

∆ from 2 to 0 (9.8)

if ∆ x ≈ ∆ y ≈ a (9.9)

Groundwater Modelling 185

∂∂

≈−h

xh

ah0 1 (9.10)

and ∂∂

≈− − −2

22 0 0 1h

xh

ah a h h a/ ( ) /

(9.11)

= h

ah h1 2 0

22+ −

(9.12)

also

∂∂

=+ −2

23 4 0

22h h h

yh

a (9.13)

Therefore

∂∂

+∂∂

=2

22

2h

x yh

0 (9.14)

and in matrix notations,

h i J h i j h i J h i J h i J( , ) ( , ) ( , ) ( , ) ( , )+ + − + + + − −1 1 1 1 4

aa2 = 0 (9.16)

where i, j are letters representing x and y directions, respectively.

2

4aa

a

a

x

y

3

01

fIgure 9.1 Grid system.

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Alternatively, three-dimensional well problems can be solved using the same technique.

∂∂

+∂∂

+∂∂

=2

2

2

21 0h

r rhr

hz

(9.17)

Using the finite difference method, the last equation becomes.

a h h h h h h n h h2 21 2 3 4 0 2 44 1 2 0∆ ≈ + + + − + − =( / ) ( ) (9.18)

where n = r/a

1

21 2 4

2rhr n a

h h

( )∂∂

=−

(9.19)

The last arrangement can be simulated in a resistance network where each node is surrounded by four resistances as shown in Figure 9.2 Recalling Kirchoff’s Law.

Σ I = 0 (9.20)

I I I I1 2 3 4 0+ + + = (9.21)

where I is the current passing through any branch and

IV V

R11 0

1=

− … etc. (9.22)

in which V1 and VO are the voltage at the terminals of a resistance R. Eq. 9.21therefore becomes

3

1

02 4

R2

R3

R4

R1

I4I2

I3

I1

fIgure 9.2 Resistance network model.


V V

R

V V

R

V V

R

V

R1 0

1

2 0

2

3 0

3 40−

+−

+−

+ =V4 - 0

(9.23)

if R1 = R2 = R3 = R4,

Eq. 9.23 is analogous to Eq. 9.18 if the following relationships correspond =

h h V V1 0 1 0− ≡ −

h h V V2 0 2 0− ≡ −

h h V V3 0 3 0− ≡ −

h h V V4 0 4 0− ≡ −

9.5 SImulatIon tecHnIque

The simulation technique is suitable for the numerical solution of unsteady state problems. Recall-

ing the unsteady state differential equation,

∂∂

+∂∂ =

∂∂

22

22

hx

hy

ST

ht

(9.25)

Two methods of approximating the time derivative in the last equation exist in finite difference

simulation. One of these is termed the forward difference approximation, and one the backward

difference approximation. Figure 9.3 shows a plot of head versus time. The time axis is divided into

intervals of length ∆ t. The head at the end of the nth interval is termed hn ; at the end of the preced-

ing interval is termed hn −1 ; and at the end of the subsequent interval is termed hn h t+ ∂ ∂1. /

at the end of the nth interval, n ∆ t can be approximated.

If one utilizes the head difference over the subsequent time interval, it is possible to employ the

difference approximation to the time derivative; if the head difference is utilized over the preceding

interval, it is preferred to employ the backward-difference approximation. The forward-difference

approximation is given by:

( / )∂ ∂ = + −h t hn hnt

1∆

(9.26)

The backward-difference approximation is given by

( / ) ( )∂ ∂ → − −h t hn hn

t1

∆ (9.27)


9.5.1 ForWard-diFFErEncE simulation

(Time = (n+1) ∆†) h i,j, n+1

h i,j n+1

h i+1,j,n

h i,j,n

h i,j–1,n

h i–1,j,n

(Time = n ∆†)

fIgure 9.4 Forward – difference techniques.

Head (h)

n–1 n+1n time

h n+1

h n

h n–1

fIgure 9.3 Head versus time for the unsteady state problems.


The forward-difference simulation of Eq. 5.25 is

hi J n hi J n hi J n hi J n h i J n− + + + − + + −1 1 1 1 4, , , , , , , , , ,aa

ST

hi J n hi J nt

2

1= + −, , , ,∆ (9.28)

where a is the node spacing, S is the storativity, and T is the transmissivity.The main objective is to know the new value of head at the time (n + 1) ∆ t for the point i, J.

Figure 9.4 shows the computation sketch for this simulation; the head at node i, J at the time (n+1) ∆ t depends on the head in a five node array at the preceding time, n ∆ t. The five values of h at the time n ∆ t are all known. We need only to rearrange the equation, solving for hi, J, n + 1 and to insert the known values of hi J n hi J n hi J n h J n and hi J− + − +1 1 1 1 1, , , , , , , , , , , , , nn. . There is no need to use simultaneous equations; the head at each node is computed explicitly, using the head at that node and the four neighboring nodes from the preceding time. The sequence, in which we move through the x y plane, calculating new values of head, is immaterial. The solution at one point does not require information on the surrounding points for the same time, only for the preceding time, For all these reasons, the forward difference technique is computationally simpler than the backward-difference technique.

As noted earlier, the forward-difference method does suffer from a serious drawback. Unless the ratio ∆ t a/ 2 is kept sufficiently small, errors, which grow in magnitude with each step of the calculation, may appear in the result. More exactly, let us suppose that an error of some sort does arise, for whatever reason, at a certain node at a particular time step.

Unless the ratio ∆ t a/ 2 is sufficiently small, this error will increase in magnitude at each succeeding time step in the calculation until eventually the error completely dominated the solu-tion. The term “error” as used here, refers to any difference between the computed head at a node i, j and time n ∆ t, and the actual value of head that is the value which would be given by the exact solution to the differential equation at that point and time. Such errors are inevitable in the normal application of finite-difference methods; they generally appear throughout the mesh in the first steps of the calculation. If the restriction on ∆ t a/ 2 is satisfied, these errors will tend to die out as the computation sequence continues; the solution is then said to be stable. If the restriction is not suc-ceeding time step, then it will eventually destroy any significance which the solution might have; in this case, the solution is said to be unstable.

9.5.2 backWard-diFFErEncE simulation

Due to the limitation of the forward-difference approach, attention has been given to a variety of alternative methods. One of these is simulation of the differential Eq. 9.25 through use of the backward-difference approximation to the time derivative as given in Eq. 9.25. The resulting finite-difference equation is

h j n h j n h j n h j n h ni i i i i− + + + − + + −1 1 1 1 4 1, , , , , , , , , ,aa

S T h j n h j nt

i i

2

1=

− −/ , , , ,∆ (9.29)

Figure 9.5 shows a diagram of the computation arrangement for Eq. 9.29. The time derivative is simulated over an interval that precedes the time at which ( / ) ( / )∂ ∂ + ∂ ∂2 2 2 2h x h y is simulated; the equation incorporates five unknown values of head, corresponding to the time n ∆ t, and only one known value of head, corresponding to the time (n-1) ∆t. Clearly, an explicit solution

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cannot be obtained to a single equation of the form of Eq. 9.28; however an equation of the form of Eq. 9.29 can be written for each node in the x, y plan. Then since there is an unknown value of head (for the time t =- n ∆ t) at each node in the plane, a system will exist in which the total number of equations is equal to the total number of unknowns. It should be possible, therefore, to solve the entire set as a system of simultaneous equations, obtaining the new value of hi j n, , at each node. The only draw-back to this approach is that a great deal of work may be involved in solving the set of simultaneous equations; offsetting this drawback is the advantage that the technique is stable regardless of the size of the time step-that is, that errors tend to diminish rather than to increase as the computation proceeds, regardless of the size of ∆ t relative to a2 .

The work required in utilizing the backward-difference technique depends upon the size of the problem, that is, upon the number of equations in the simultaneous set. If this number becomes large as it does in most groundwater problems, the work entailed becomes substantial, particularly when the standard direct methods of solving simultaneous equations are used. For this reason it is worthwhile to look for efficient methods of solving these sets of equations. Iiteration or relaxation, in connection with solution of the steady-state equation, provides us with a reasonably efficient approach, which is

14 1 1( ), , , , ,h h h h hl l j l l j l j l j l j− + − ++ + + = (9.30)

This equation states that the head at the node i, j should be the average of the heads at the four sur-rounding nodes. The method is to move through the x, y plane, replacing the head at each node by the average of the heads at the four surrounding nodes. This process is not continued until the head changes become negligible, that is, until the head at each node remains essentially unchanged after each traverse through the plane indicating that Eq. 9.30 is satisfied throughout the plane.

In applying iteration to non-equilibrium problems, the idea is to carry out a similar series of traverses of the x, y plane at every time step using Eq. 9.29 rather than Eq. 9.30 as the basis of the calculation at each node.

Thus to compute heads for the time n ∆ t Eq. 9.29 should be rearranged as follows:

(Time = (n–1) ∆†)

(Time = n ∆†)

h i+1,j,n

h i,j+1,n

h i,j,nh i–1,j,n

h i,j n–1

h i,j–1,n

fIgure 9.5 Backward – difference simulation.


h i j n

aS

T t

hi j n hi j na

hi j

, , ( ) , , , ,

,

=+

− + +

+ −

14

1 1

2

2

∆

11 1 12, , , , , )n hi j n

aS

T thi j n+ + + −∆ 9.31

Try an x, y plane for the time n ∆ t, initially containing specified values of hi j n, , , at a few nodes, corresponding to the boundary conditions, and trial values of hi j n, , , at the remaining nodes. Write an equation of the form of Eq. 9.31 for every node not controlled by a boundary condition, and write equations expressing the boundary conditions for the nodes at which these conditions apply. In Eq. 9.31 the value of hi j n, , , are expressed in terms of the head at the four surrounding nodes for the same time, and the head at the same node for the proceeding time. In solving the set of equations for values of hi j n, , , the values of hi j n, , ,−1 actually constitute known or constant terms, determined in the preceding step of the operation. Thus, Eq. 9.31 related the head at each node to the head at the four surrounding nodes, in terms of a set of constants or known quantities. The equation is a little more cumbersome than Eq. 9.30 in that instead of multiplying the sum of the heads at the heads at the surrounding nodes by 1/4, the equation is now multiplied by

1 42

2/( )

aS

T ta+

∆

and adding the known term

( / ( ) ) , , ,ST t a

ST t

hi j n∆ ∆

4 12 + −

on the right side. These changes, however, do not make the equation appreciably more difficult to solve. It is still possible to use the process of iteration; that is, move through the x, y plane, replacing each original trial value of hi j n, , , by a new value, calculated from the four surrounding values by Eq. 9.31. At each node note the difference between the value of hi j n, , , which have been calcu-lated, and the trial value which have been calculated, and the beginning trial value. If this difference turns out to be negligible at every node, it may be concluded that the starting values already satisfied Eq. 9.31, and that further computation of new value is not necessary. More commonly, however, a measurable change in the value of h at each node may be noted indicating that the initial values did not satisfy Eq. 9.31, and that the iteration procedure is producing an adjustment toward new values which will satisfy the equation. In this case transverse the x, y plane again, repeating the procedure; each value of hi j n, , , calculated in the first step (or iteration) is replaced by a new value calculated from the heads at the four surrounding nodes by Eq. 9.31. Again, the difference is small enough to indicate that the new array of head values approximately satisfies Eq. 9.31. The process is continued until the difference between newly computed and preceding values is negligible throughout the array, indicating the Eq. 9.31 is essentially satisfied at all points.

The technique described above is often referred to as the Gauss-Seidel method. It is an example of a relaxation technique — a method of computation in which the difference between the two sides of an equation are successively reduced by numerical adjustment, until eventually the equation is satisfied. There are a number of varieties of relaxation techniques in use, differing from one another in the order or sequence in which the x, y, plane is transversed in the calculation and in certain other respects. It has been found that the number of calculations required to solve the set of finite-


difference equations can frequently be reduced by the inclusion of certain “artificial” terms in these equations. These terms normally take the form λ ( , , , , ).hi j n m hi j n m+ −1

The superscripts m and m + 1 indicate levels of iteration; that is hi j n m, , , represents the value of hi j n, , , after m transverses of the x, y plane in the iteration process, and hi j n m, , , + 1 repre-sents the value of hi j n, , , obtained in the following calculation, after m+1 traverses. The term λ is an “iteration parameter”; it is a coefficient which, either on the basis of practical experience or theoretical analysis, has been shown to produce faster rates of solution. As the iteration process approaches its goal at each time step, the difference between the value of hi j n, , , obtained in one iteration and that obtained in the next iteration becomes negligible. In other words the term ( , , , , , )hi j n m hi j n m+ −1 approaches zero, so that the difference equation appears essentially in its original from, without the iteration parameter term; and the solution obtained applies to the orig-inal equation. In some cases, λ is given a sequence of different values in successive iteration, rather than a single constant value. Again, the particular sequence of values is chosen, either through theo-retical analysis or through practical experience, in such a way as to produce the most rapid solution. When an iteration parameter or sequence of iteration parameters is utilized, the relaxation process is termed “successive over relaxation” and is frequently designated by the initials SOR.

9.6 reSIStor caPacItor netWork model2, 3, 4

The electric characteristics are resistance and capacitance, which are used to simulate the distribu-tive qualities and storage factors of the aquifer. Two- or three-dimensional networks can be con-structed with uniform or non-uniform properties in the various directions. The aquifer properties within the sub-area are averaged in the value of the network components at a node. The transmis-sivity of the aquifer is designated by the value of resistance connecting a particular node with an adjacent node. The storage factor of the aquifer within the particular area is designated by the value of capacitance between the node and the ground. Leaky boundaries between an aquifer and an aquitard or to adjacent basins are simulated by resistance values to ground. Impervious boundaries are simulated by open circuits, The recharge and discharge of various points within an aquifer are simulated by current sources or sinks connected to various nodes in the network.

The replacement of disturbed parameters by lump parameters is compatible with a finite-differ-ence system of equations, which are solved without the need for differential equation techniques.

The resistance-capacitance network simulates a two-dimensional aquifer. A third (vertical) dimension can be added to this network by another set of resistors and capacitors in a direction nor-mal to existing elements. In operation, the resistance-capacitance network representing the ground-water basin is connected to a time varying current generator representing water inflow and current sinks representing outflow. Output from the simulator is a voltage-time response analogous to a watershed a history that is displayed on an oscilloscope. The simulated water levels are compared to historic water levels and capacitors adjusted to obtain the best fit of the coefficients of transmissivity and storativity until adequate plausibility is achieved.

The analog simulator is both an engineering tool and an educational device. The output from the simulation can be readily understood, as the model concept and the relationship between the model and the prototype.

The finite-difference of the equation for two-dimensional non-equilibrium ground-water flow is

h h h h h Sa hoT t1 2 3 4 0

24+ + + − =

∆∆

,

while the equation for resistance-capacitance network is

Ø Ø Ø Ø - 4Øo RC dØodt1 2 3 4+ + + = (9.32)


Comparison of these equations illustrates that resistance, R, may be considered to be analogous to the term 1/T; voltage, Ø, is analogous to head, h; and capacitance, C may be considered analogous to the term Sa2.

In the answer, voltage is treated as analogous to transmissivity, in that the procedure calls for increasing voltage in areas of high transmissivity.

(See current diagram in Figure 9.6.)

9.7 analog comPuterS

Analog computers are general-purpose devices, which employ laws of physics for performing math-ematical operations. The electronic differential analyzer is so named because of its application in solving ordinary differential equations. The analog computer is similar in construction to the analog model. The electric analog model, however, is a special-purpose tool and not capable of handling a wide variety of problems.

Although the analog computer can be operated as a direct analog with passive elements, more generally it uses amplifiers, active elements, and a variety of other electronic devices, such as func-tion generators and electronic multipliers for adding and multiplying voltages.

The analog computer gives the impression of complexity because of numerous knobs, dials, and indicators, which tend to confuse, however, it is simple to operate and serves as a good general purpose computer to solve mathematical equations describing the problem. These equations are set up on a patch panel and wired into the computer.

For a simple problem, there may be some advantages in using the analog computer rather than the analog model. First, the analog computer components are connected to a central patch panel, which facilitates operations. Moreover, the different elements used to simulate the storativity and transmissivity characteristics of the aquifer are variable; hence, the adjustments are performed more easily than in a direct analog model, where it is necessary to replace fixed resistors and capacitors.

I3

I4I5

C

I2

I1

Ø3 Ø0 Ø4

Ø2

Ø1

fIgure 9.6 Resistor – Capacitor Network Model.


Another advantage of the analog computer is that the output hydrographs can be recorded graph-ically by pen plotters rather than on an oscilloscope, providing a permanent record. Multi-channel pen plotters on the analog computer produce output graphs of several nodes simultaneously.

9.8 dIgItal comPuter

Because of the availability of powerful digital computers with large memory banks, using sophis-ticated programming languages such as FORTRAN, the digital computer has become an attractive device for groundwater basin modeling. Particularly attractive features of the digital approach are that a special device does not have to be constructed nor does an expensive differential analyzer need to be maintained or patch panel stored for future use of the model. Using a digital system, the model consists of a deck of software that can be used at any time on various digital computers that utilize the FORTRAN language. The wide availability of digital computers means that a solution for a particular analysis can be obtained on relatively short notice.

The groundwater basin model is not the end point of a study; it is only a tool for use in further evaluation. Much additional evaluation is done through the use of supplementary computer pro-grams that use the water level output from the groundwater model.

The digital computer approach to the solution of the groundwater storage and flow problems has evolved from the analog simulator and analog computer models. The computer solution of the system of finite difference equations is based on a relaxation method. Relaxation methods are defined as a col-lection of numerical techniques for solving, approximately, large numbers of simultaneous equations.

A particular relaxation method used to solve the system of finite difference equations within each iteration and time interval typically consists of the following procedure. The computed net deep percolation or source flow rate is determined for each time increment and for each control point. This computation involves an interpolation of known yearly source flow rates to obtain values of source flow for each simulated time interval, which may be from 1/50 yr to 1/4 yr. Transmis-sivity (the factor affecting the flow between any two nodes) is a function of the flow path cross-section area, the permeability of the aquifer, and the flow path length. This computation is further complicated by the fact that the cross-section area is not a constant in an unconfined aquifer, but depends on a saturated depth of the aquifer material. To handle this non-linearity, maximum value of transmissivity is computed for a fully saturated aquifer. During each iteration cycle, the value of transmissivity is modified by the actual depth of the saturated portion of the aquifer. This is done by straight-line approximation between the higher water table elevation and the bottom elevation. Flow rates are computed in accordance with Darcy’s law. Flow into or out of storage is also computed for each time increment. For each node, a summation is performed to account for the external flow rate, the subsurface flow rate, and the storage flow rate. The result of this summation is a residual error, or unaccounted flow rate. Iterations continue until the total residual flow rate error for the entire network is acceptably small, that is, all nodal residual flow rates are summed and compared with some predetermined error criteria. If the flow rates are in excess of the error criteria, adjustments are made in the water level elevations and the process is repeated. If the error is equal to or less than the appropriate criterion, then the mass balance for the network is acceptable for the current time interval and the next increment of time is undertaken. This procedure is repeated until the entire study period has been completed (refer to forward or backward simulation or the general ground-water equations given below).

9.8.1 modEl dEvElopmEnt

The steps for preparing a groundwater basin model are as follows:


1. The groundwater basin is subdivided into a mesh. 2. Geologic data are analyzed and transmissivity factors between zones and storativity fac-

tors within each zone or sub-area are determined. 3. Historical surface hydrologic data are analyzed and the net deep percolation for a given

time increment for each polygonal sub-area is determined for a study period preferably 10 years or more.

4. For each sub-area, the historical water levels during the study period are tabulated. A uni-form water level is assumed across each sub-area.

9.8.2 groundWatEr Equation

In preparing any model, a generalized groundwater equation that defines the storativity, trans-missivity is developed. Combining Darcy’s law and the law of conservation of mass gives: (see Figure 9.7):

∇⋅ ( )∇

T x y h, – S (x, y)

∂∂ht

– Q (x, y, t) = 0 (9.33)

where T (x, y) = transmissivity; h = elevation of water leve l S = storativity; t = time; and Q = net inflow of water.

A finite difference form of the last equation is:

Σ∆

yi hi j hB j AB SBt

hB j hB j[ ( ) ( )] [ ( ) ( )]+ − + = + − +1 1 1 hhB QB j( )+ 1 (9.34)

in which h = water table height, AB SB = Storativity for the polygonal area (Theissen method); AB SB = net external inflow for the polygonal area, i, B = contiguous node and node in question,

In Extraction

Is Os

G.S.

W.T.

fIgure 9.7 Definition sketch of a polygonal aquifer.


respectively; and Y is a conductance factor made up of transmissivity, T, boundary width W, and flow path length, L, linear (see Figure (9.8).

Yi BWiB TiB

LiB, = (9.35)

and nonlinear

Yi BWiBLiB

TiB Saturated thicknessTotal thic

, ( )=

kkness

9.8.3 digital computEr solution

The last system of equations is solved on the general purpose digital computer by an implicit numerical integration technique. The procedure is as follows: initial values hB ( )0 are impressed at the terminals labeled h (J) (B) = 1, 2 ....N; N = number of interior nodes)B . Then for a given of coef-ficients, Yi and SB, and currents Q JB ( ),+ 1 the values hB (J + 1) are implicitly determined at the end of a step in time ∆ t. Once determined these values become the initial water elevation for the next succeeding step in time.

To facilitate the writing of the Fortran program it is useful first to assign consecutive numbers to all the nodes. Consecutive numbers are also given to the line segments (branches) connecting the nodes. These assignments are illustrated in Figure 9.8. The flow chart of the program is shown in Figure 9.9.

11

12

4

310

9

2

3

5

6

7

1

8

Wh–3

fIgure 9.8 Polygonal model elements.


Note, for simplicity in writing, the amount of computer time spent on each time step.Next a suitable formula must be found for the relaxation coefficient (Relax). Since the product

of the residual term (RES) and the relaxation coefficient results in a change in water level elevation, h, and since the residual term is a flow rate, the relaxation coefficient must be an impedance of the branches joining a node to its neighbors.

RELAXB Y A S ti B B B=

+1

, / ∆

fIgure 9.9 Simplified flow chart for digital computer solution of groundwater problem.


9.9 fInIte — element metHod

A given region D may be two-dimensional, three-dimensional, or multidimensional (depending on the number of independent variables). For our purpose, it will be sufficient to take D as two dimen-sional in space.

a. The region is divided by imaginary lines into a number of finite elements. b. The elements are encountered by lines closing at a discrete number of nodal points situ-

ated on their boundaries. The value (s) of some variable (s) at those nodal points will be the basic unknown (s) of the problem.

c. A function (s) is chosen to define uniquely the state of the variable (s) within each “finite element” in terms of its nodal value (s). In this treatment it is supposed that the single function Ø (x, y) is the function to be determined and that it will be determined by the minimization of a certain function.

Let the triangle with vertices labeled i, j, k be a typical element numbered p. Suppose that 0 is given as a linear function of the coordinates (see Figure 9.10).

Ø p alp a2px a3p y= + + (9.37)

where, of course, the ‘a’s will differ from element to element.

Then the nodal values of Ø p, i.e., Ø pi, Ø pj, Ø pkare

y

y

xx

0

K

j

iØ

fIgure 9.10 Linear coordinates of an element.


Ø pi alpa2pxi a3pyi= + +

Ø pj alp a2pxj a3pyj= + + (9.38)

Suppose these nodal values were known, it could then be possible to evaluate

a p a p a p giving1 2 3, ,

[a p

a p

a p

i i

j j

k k

x y

x y

x y

1

2

3

1

1

1

=

−

1 Ø

Ø

Ø

pi

pj

pk

(9.39)

=

12∆

ai aj ak

bi bj bk

ci cj ck

piØ

Ø

Øpj

pk

(9.40)

where

ai xj yk xk yj

bi yj yk

ci x xk j

= −

= −

= −

(9.41)

and 2

1

1

1

2∆ =

=det (

xi yi

xj yj

xk yk

areaa of ijk∆( ) (9.42)

Therefore

Ø Ø pi (aj bjx cjy) Ø pj (akp ai bix ciy= + + + + + + +1 2/ ( )∆ bbkx cky) Ø pk+

giving the value of Ø at any point of the A in term of its values at its vertices, i.e., the nodal values. We write

Ni ai bix ciy= + +( ) / 2 ∆

Then


Ø p Ni ØiØjØk

= =

Nj Nk N Ø

(9.43)

9.9.1 thE gEnEral quasi-harmonic p.d.E.

The general quasi-harmonic equation governing the behavior of some unknown physical Ø can be written as

∂∂

∂∂

+

∂∂

∂∂

+

∂∂

∂x

kxx

kyz

kzØ Ø Øx y ∂∂

+ =

zQ 0 (9.44)

where kx, ky, kz, and Q are known functions of x, y, z, e.g., steady state heat conduction with kx, ky, kz, as anistropic conductivity coefficients, the function Q as the rate of heat generation and Ø the temperature, or in an electrical or hydrodynamic context, specific conductivities current influx and potential respectively. The physical conditions, will impose certain boundary conditions. The two most commonly encountered are those in which

a. The value of ∅ is specified on the boundary

Ø ØB= (9.45)

or

b. 1 1 1 0xkx x yky y zkz z

q a∂∂

+∂∂

+∂∂

+ + =Ø Ø Ø Ø

(9.46)

on the boundary in which lx, 1y, lz, are the direction cosines of the outward normal to the boundary surface. If Kx, Ky, Kz, are all equal and both a and q are zero this reduces to the well known condi-tion applicable to non-conducting boundaries

∂∂

=Øn

0 (9.47)

In a conduction, problem q represents the heat flux per unit of surface area and a Ø the convection loss. Now, we know from our variational methods that this differential equation would be obtained by minimizing the functional

U Kx x Ky y Kz z Q= ∫ ∫ ∫ ∂ ∂ + ∂ ∂ + ∂ ∂ −1 2 2 2 2/ [ ( ) ( / ) ( / )Ø/ Ø Ø ØØ ] dx dy dz (9.48)

subject to Ø obeying the same boundary conditions.The simultaneous imposition of the boundary conditions (a) or (b) on the assumed function form

is, however, impractical in this mailer though (a) is much easier to implement than (b).To overcome this it is best not to constrain the boundary values on the part where condition

(b) is to be satisfied, but to add to the right hand side of Eq. (48) another integral pertaining to the boundary surface which on minimization automatically yields the boundary condition. This inte-gral is


∫ +s q a ds( )Ø Ø1

22

in which S is the surface where condition (b) applies. The integral is added as described and on minimization, it will be found that the boundary condition (b) is automatically satisfied.

9.9.2 FinitE ElEmEnt discrEtization5,6

In the two-dimensional case with which this started, volume integrals become surface integrals and surface integrals become contour integrals.

If the unknown function Ø is defined element by element in the manner already described

Ø [ Ni, Nj,...] Øi

Øj

.

Ø}e=

= [ ]{N

(9.49)

where Øi etc. are the nodal parameters, approximate minimization can be carried out,

∫ ∂∂

=∂∂

∂∂

∂∂

+∫Uex x

Se

ØiØ Kx

ØØi

Ø KKy

Qds q

Ce

∂∂

∂∂

∂∂

−

∂∂

+

∂∂

+∫

Øy Øi

Øy

ØØi

ØØi

aa dsØ ØØi

∂∂

where the second integral only applies if the element has a part of its boundary on the boundary of the problem on which conditions of type (b) are specified.

Noting that ∂∂

=∂∂

∂∂

{ }Ø Øe

xNix

Nix

etc, . . . .

and that ∂

∂

∂

∂=

∂∂Øi

Øx

Nix

∂∂

=ØØi

Ni etc. (9.50)

We have immediately for the whole element

∂∂

= +Ue

Oeh e[ ] { Ø } e { F } e (9.51)

in which the stiffness matrix’ he is obtained from equations (9.49) and (9.50)


hiej eS

Kx Nix

Nix

Ky Niy

Nix

d= ∫∂∂

∂∂

+∂∂

∂∂

ss

Fei eS

QNi dS eC

qNi ds eS

N aNi ds= − ∫ + ∫ + ∫[ [ ] ] { Ø } e

Assembly of the whole set of minimizing equations follows thus for the whole region.

∂∂

= = +

=

U HØ

Ø} {F}

with Hij hije , Fi

0 [ ]{

Σ Fie= Σ (9.52)

summation over all elements.

9.10 groundWater qualIty modelS 7, 8

In the past, water quality has often not received the attention it deserved in connection with water planning. Recently, engineers have recognized that water quality can exert a significant effect on water resources management.

A management plan in which quantity alone is considered does not provide the information needed, because water quality may limit the use of some water so that the amount assumed available to meet demand may be unsuitable for use.

Furthermore, water quality problems may affect the economics of the alternative management plans to such a degree that what is supposedly the most economical plan might prove to be the most expensive because of special water treatment required.

To make a complete economic evaluation of alternative management plans, and assessment of the magnitude of economic consequences due to changes in water quality is essential. This assess-ment requires determination of the magnitude of water quality changes under various alternative water management plans.

Surface water systems are comparatively simple and accessible, and many reliable investiga-tions have been conducted for the purpose of predicting future surface water quality. However, the development of a groundwater quality predication device has progressed more slowly.

Conceptually, the predications of water quality in groundwater basins may be accomplished by developing a mathematical model that integrates all physical characteristics, surface and subsurface of the groundwater basins to simulate physical characteristics. Such a model requires sufficient knowledge of the various influences on water quality, comprehensive data concerning these influ-ences, and a computational tool.

Many attempts have been made in the past to develop water quality predication procedures. These have resulted in the basin wide salt balance approach that is still widely used.

The salt balance procedure is a form of quality model in which entire groundwater basins are treated as a unit. It takes into account all salts percolated from the ground surface to the saturated zone and extractions therefrom.

Salts percolated to the saturated zone are not solely attributable to the salinity of water sup-ply to a basin. Other sources include: (1) Salts leached from fertilizer and manure. (2) agricultural wastewater whose salinity has been raised by evaporation and transpiration; (3) municipal waste-water whose salinity has been increased by a few hundred parts per million due to domestic and commercial uses and ion-exchange water softeners; and (4) stream flow, precipitation, and imported


recharge water. Further, phyreatophytes may increase groundwater salinity by extracting and trans-piring water without effecting aproportionate removal of salts from the groundwater.

The basin salt balance approach is of a general nature and should be used only for general short-term projections (less than 20 to 30 yr) arid small areas less than 2,000 acres (8,100,000 m2

to 12,100,000 m2). In the case of large basins, the quality picture presented by a salt balance is too broad for meaningful interpretation.

A basic assumption usually made in the salt balance procedure is that mineral content of a given groundwater basin is equally distributed, and that any addition of salts is immediately dispersed in equal density throughout the groundwater basin. Analysis of physical laws indicated that this assumption of complete dispersion is erroneous and misleading.

9.10.1 quality mathEmatical modEl9,10,11

The model can be defined as a set of equations that describe the flow and storage of salts in ions in the groundwater basin. Given the necessary input data and the equations, the behavior of the system is computer-simulated to provide, as output, the water quality at specific areas and at specific times.

It is helpful in the development of a water quality model if a quantity model has already devel-oped. In a quantity model, the basin is normally divided into polygons, nodes, and paths. The polygon surrounds the node and represents the boundary of the area pertaining to the node. The same network is used pertaining to the node. The same network is used for the quality model. Such a model, however, will not forecast water quality at individual water wells.

Data requirements: Data required for the verification and application of a groundwater quality mathematical model are the following:

1. Precipitation, percolation, and its salt. 2. Surface water percolation and its salt. 3. Percolation of return irrigation water and its salt. 4. Sources of water supply, including imported water and its salt. 5. Wastewater discharges and their salt. 6. Groundwater extractions and their salt content. 7. Initial groundwater quality. 8. Boundary surface and subsurface water inflows, outflows, and their quality. 9. Exported water and its salt. 10. Imported wastewater and its salt. 11. Exported wastewater and its salt.

9.10.2 basic Equations

Two equations are necessary to describe the quality system: one to describe the additions and sub-tractions of salt from each node, and another to describe the transfer of salt between nodes. For the first equation, the relationship that is based on conservation of mass-change in the mass of salt, is equal to the difference between addition and subtraction of salt to the basin.

The basic equation for salt concentration in water flowing from one node to the other, such as from node to node j along a single path, is

Cij ci cj= ∂ + −∂( )1

in which Ci = salt concentration in node i, Cj = salt concentration in node j, and ∂ = interpolation factor.It was found 8,10 by experimentation that an interpolation factor of 0.75 was a fair compromise

to be applied.The following assumptions were made in model development:


Minerals contained in water move with the water in accordance with Darcy’s law.

1. Groundwater pumped from a well is a composite of all water from the water table, or potentiometric surface, to the bottom of the well. The quality of the water is a composite.

2. The saturated zone comprises two different layers, an upper layer from the water table to the well depth, and a lower layer which, is only slightly affected by pumping or replenish-ment. The first layer is referred to as the “the zone of mixed layer” and the second layer as the “zone of native water.”

3. The water in the zone of mixed yield can be treated as if the quality were uniform within the zone in each sub-area.

4. Unsaturated zone sediments have no influence on the quality of water that percolates through them.

5. The geochemical characteristics of the saturated zone have no significant influence on the quality of water. Ion-exchange reactions, causing exchange of equivalent ionic concentra-tions, will have a small effect on the overall total dissolved solids (TDS).

6. Percolated water through the surface reaches the zone of saturation within a short period, a year.

7. The effect of diffusion arid dispersion of salt in the aquifer is negligibly slow. 8. All salt applied on the ground surface, except that portion taken up by plants, from fertil-

izers, percolates to the zone of mixed yield. 9. The total uptake of nutrients by plants is from the applied fertilizers. 10. TDS in precipitation percolation is approximately l00 ppm. 11. TDS pick-up due to domestic use is 300 ppm. 12. TDS concentrations of subsurface outflow from boundary polygons are the same as those

within the polygons.

9.11 dIffIcultIeS and SHortcomIngS

The development of a mathematical groundwater quality model, or prediction procedure, is more difficult to achieve than a mathematical quantity model for the following reasons:

1. There is no agreement as to what is the best water quality parameter to use in describing the suitability of water for different beneficial uses. Some authorities prefer total dissolved solids (TDS, sometimes called “Filterable residue’); others electrical conductivity; and still others, specific ionic constituents, however, there is general agreement on the parameters for defining groundwater recharge.

2. TDS includes many ionic constituents of significant weight. Given changes in TDS may not necessarily reflect the same changes in ionic constituents although, in some cases, there may be relationships between TDS and some significant ions.

3. The extent of knowledge of quality is much less than that of quantity. Equations have long been available describing the dynamic behavior of the hydrologic system; and in the mathematical quantity models. Such, however, is not the case with quality. Studies of the movement of salt from one area to another are few and of limited application. For that rea-son, most quality investigations describe either a salt balance or else general groundwater quality conditions.

4. The hydrologic balance is an adequate check on groundwater quantity calculations. The salt bal-ance, though similar, is not in itself an adequate check on groundwater quality calculations.

5. A static water level measure at a well is indicative of an area’s general groundwater level. The quality of a water sample from a pumping well is indicative only of the quality of mixed waters from the section of the aquifer yielding water to that particular well.


6. Micro-gradients exist in a water table where recharge or extraction occurs; they vary with time, especially when pumps are started and stopped. Such micro-gradients are important in the transport of salts in the saturated zone, but the detailed data required for evaluation of their influence are unavailable.

7. If the groundwater basin contains clay lenses of unknown thickness and extent, the water level represents the summation of the water pressures in all the sediments tapped by the well. Hydraulic continuity, therefore, may be safely assumed. In the case of quality, the aquifer above the clay may only be subject to degradation from direct percolation.

8. Aquifer tests and well core samples yield useful information for determining an aquifer’s hydraulic properties. For the study of water quality, data on an aquifer’s mineral proper-ties and their variations, by area and with depth, are essential for a precise understanding of variations in water quality from one area to another. Such data are difficult to obtain because mineralogical analyses of core samples are virtually nonexistent.

9. The quality of water changes while it is moving either vertically through the zone of aera-tion or laterally through the zone of saturation. Mechanisms of this modification of qual-ity may include oxidation, reduction, absorption ion exchange solution, and precipitation. Rainwater percolating through the soil profile and into deeper substrata will dissolve sol-uble salts and minerals and transport them to the aquifer. On the other hand, concentrated percolating down may precipitate salts in the unsaturated zone. Salts of limited solubility may be dissolved, transported, and subsequently re-precipitated in either the saturated or the unsaturated zone. The extent of these reactions, their relationships, and their quantita-tive effect on water quality are not known. The combined effect of these chemical reac-tions determines the quality of water at any point.

10. Data are unavailable on the transit time of water and salt from the ground surface to the zone of saturation.

11. Quality data are generally not closely associated with extraction data. Knowledge of such data is important in determining the seasonally or annually weighted quality of pumped water, especially if seasonal quality variations are marked.

12. Precise data are not available on fertilizer rates, their consumption by crops, and the amounts leachable from the root zone to the zone of saturation.

13. Salts move from areas of higher concentration to areas of lower concentration. Data are insufficient to permit modeling this molecule diffusion mechanism.

There is still a vital need to develop a more comprehensive, and hence more reliable water quality model, based less on assumptions and more on facts. The model to be developed should take into consideration, for example, local water quality changes; significant parameters other than TDS; reactions of water and aquifer materials; and surface, as well as groundwater. Construction of such a model requires input data more accurate than any assumed data. To accomplish this, more research on soil-water reactions and a better mathematical representation of quality relations are required, since the model depends on a mathematical formulation of the dynamic natural system being mod-eled. When the dominant controls and the cause-and effect relationships of the natural system are known, an accurate mathematical formulation of the water quality system may be possible.

The governing equation for any solute transport model can be based on the mathematical pro-cedure given in Appendix C.

referenceS

1. Soliman, M. M. “Groundwater flow toward partially penetrated wells” Ph. D. thesis, Utah State Univer-sity, Utah, USA 1959.

2. Salem, M.H. Study of the hydraulic parameters of the Nubian Sandstone Aquifer with reference to the productivity of pattern for well development in Kharga Oasis, Egypt 1970.


3. Baretti, M., and Karanjac, J. Kharga and Dakhla Oasis, determination of hydrogeological and hydraulic parameters, Reports, presented by INDUSTROPPOJECT, Zaghreb, Yugoslavia, 1968.

4. Ezzat, M. A. et. al., South QaHara area groundwater model, General Petroleum Company, Cairo, 1977. 5. Soliman, M. M. et al., Groundwater quality model with applications to various aquifers, Environmental

Geology Water Science 17, 3, Springer- Verlag, New York, 1991, pp. 201–208. 6. Soliman, M. M. Groundwater Management in Arid regions, Aim Shams University Press Volume 1,

1986, pp. 179–187. 7. Sherif, M. M. Singh, V.P. and Amer, A.M., A two-dimensional finite element model for dispersion (2D

— FED) in coastal aquifers, Journal of Hydrology, 103, 1988 pp. 11–36. 8. Soliman, M. M., Mostafa, I., and Nour, M. Groundwater quality three dimensional Model, Ill Interna-

tional Symposium on Environmental Hydrology, Cairo, Egypt, 2002. 9. Anderson M. P. Movement of contaminants in groundwater transport a direction and dispersion in

groundwater contamination, Washington D.C. National Academy Press, pp. 37–35, 1984. 10. Anderson, M. P. and Woessner, W. W. Applied groundwater modeling simulation of flow and advective

transports, Academic Press, New York, 1992. 11. Prikett, T. A. Naymik, T. G. Lanquist, C. G. A ”Random Walks” Solute Transport Model for selected

Groundwater Quality Evaluations, Illinois State Geological Survey, Bulletin 65, 1981.

207

10 Case Studies

10.1 tHe nubIan SandStone aquIfer SyStem In egyPt

10.1.1 introduction

The Nubian Sandstone aquifers in Egypt are mostly located in the Western Desert of Egypt (Fig-ure 10.1), an area of 750,000 km2, representing 75% of the whole area of Egypt. Groundwater of good chemical quality occurs in this aquifer system in the Western Desert. The Nubian aquifers also occupy a vast area in the northern region of Africa. This system extends from northeastern Sudan and Chad, through eastern Libya and Egypt west of the Nile River, nearly to the Mediterranean Sea. It covers an area of 2 million square kilometers, of which about one-third lies in the Egyptian territories.

Although the tableland areas in the Western Desert are characterized as low productivity soils, the depression areas have proved to contain arable land resources. Agricultural development activi-ties have been started in the last 20 years in the two southern depressions, Kharga and Dakhla, as pilot development projects. These projects included the drilling of a prolific system of deep wells, originally flowing. The outflow of the wells has been decreasing year after year, with a continuous decline of water levels. The majority of the wells in Kharga Oasis have ceased flowing and have been pumped. Figures 10.2 and 10.3 show the general physical features of the study area. The West-ern Desert consists of large plateaus that rise 300–700 m above the mean sea level. From south to north, these are the southern El-Gilf El-Kebir Sandstone Plateau, the central Eocene-Cretaceous Plateau, and the northern Miocene Marmaricau Plateau. These plateaus are interrupted by a series of low-lying depressions, namely, from south to north, the South Kharga, Kharga, Dakhla, Farafra, Bahariya, Siwa, and Qattara depressions. The southern plateau extends from the Nile River in the east to the Tibesti and Ennedi highlands (Chad Republic) in the west and from the highlands of Kordofan (Sudan) in the south to the Eocene-Cretaceous Plateau in the north. The land surface is mainly underlain by the Nubian Sandstone series with some inlands of pre-Cambrian crystalline basement complex. The central plateau covers an extensive area west and east of the Nile, with Eocene limestone underlying its land surface. In the south, it is defined by a steep escarpment overlooking the sandstone lowlands and is interrupted by the Nile Valley in the middle part. The northern boundary is characterized by a steep scarp on the northern side of Siwa Oasis and the Qat-tara depression. The plateau is covered on its western side by the Great Sand Sea.

The northern plateau extends from the bold escarpment at Siwa and Qattara depressions north-ward to the coastal plain along the Mediterranean Sea and from the Nile Delta westward to Cyra-naica (Libya). The lithologic character of the formations of the plateau are limestone and sandstone of the Miocene age.

In the Western Desert, the maximum temperature ranges from 48°C during summer to about 7°C during winter nights. The rainfall is sparse in these regions (annual average of 9.6 mm at Siwa and 0.3 mm in Kharga Oasis). The average humidity ranges 30–60%.

10.1.2 gEological and hydrogEological charactEristics

10.1.2.1 the basement complex

The total sedimentary successions in the Western and Eastern Deserts have been deposited on the eroded surface of the crystalline basement complex of the pre-Cambrian age. The basement complex, largely crystalline rocks, crop out in the Eastern Desert, where they form the backbone


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fIgure 10.1 Location map of the study area.

of the elevated Red Sea mountains, extending continuously from latitude 28° to Sudan. The base-ment surface dips progressively from the Red Sea mountains belt toward the west, to an elevation of −1600 m near El-Monya and −4000 m east of Assuit, and increases in elevation to the north of Aswan.

In the Western Desert, basement rocks are prominently exposed in the southwest in Gebel Oweinat, whereas smaller exposures occur in the area between Oweinat and Aswan and to the south of Kharga Oasis in the vicinity of Abu-Bayan.

pjw

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Case Studies 209

Figure 10.4 shows a compiled basement relief map. A series of structural trends affecting the basement surface were traced (Ministry of Land Reclamation in Egypt, 1979), forming discontinui-ties in its general north-dipping trend. The map indicates that, in the area south of latitude 25°N, shallow basement occurs at elevations ranging between −500 and −1000 m, but some occur at mean sea level.

The elevation of the top of the basement ranges from −500 m at the southern periphery of Kharga Oasis to −1000 m in northern Kharga, −2000 m in Baharia, −3300 m at Sirva, and −4000 m to the east of Assuit.

The sandstone system consists of alternating beds of sandstone, shale, and clay. Shaley and clayey beds occurring within the sandy sequence of the system is of minimum proportion in the southern part of the Western Desert, but their frequency increases to the north. Analysis of the drilled wells’ records indicates that the proportion of sandstone averages between 40 and 90%, with the grain size ranging from fine to coarse-grained.

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fIgure 10.2 Physical features of the study area.


Figure 10.5 is an isopach map of the sandstone system from the upper Cretaceous to the base-ment. It indicates that the minimum thickness occurs in the south and increases toward the north and northwest.

The thickness of the sandstone system ranges 500–1000 m near the Sudanese borders and the El-Gilf El-Kebir area (with some exception of reduced thickness in the vicinity of basement out-crops), 500–1000 m in regions north of Kharga Oasis, 500–2000 m in Farafra, and 500–3500 m in regions south of Sirva Oasis, where it forms the most conspicuous, thick sedimentary basin.

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fIgure 10.3 Schematic geological map of the study area.

Case Studies 211

In the Eastern Desert east of the River Nile, the sandstone system forms a north–south elon-gated belt of outcrops directly overlying the basement that plunges westward. It forms the eastern continuation of the immense pre-Cretaceous sandstone system of the Western Desert. The sand-stone system in the Eastern Desert attains a maximum thickness of 1000 m in regions east of Assuit, and the thickness decreases gradually toward the Red Sea mountains, where it is 100 m.

The sandstone system is overlain by the upper Cretaceous-Eocene shale–carbonate complex in the northern part of the study area, but it crops out in the southern part (south of latitude 25°30′N), Toshka Basin, and the central part of the Eastern Desert. Basement uplifts in the southern and southeastern parts of the Western Desert are at elevations higher than the water table and are con-sidered as the lateral boundary of the system.

The top of the sandstone system is capped by a thick sequence of low-permeable shale-carbonate complex from the Cretaceous-Eocene age in the north and central parts of the Western Desert. Under these “cap rocks,” the aquifer system is highly confined. In the southern part of the study area and the central part of the Eastern Desert, where the sandstone system crops out, water table conditions prevail.

The intercalated shale and clay beds within the sandstone system are lateral extensions. Although individual beds or groups of beds may be continuously traced in some local areas within the system, on a regional basis, the entire sandstone aquifer system is to be hydraulically regarded as one single aquifer system.

The geologic framework of the area was described in early publications of Zittle,1 Beadnell,2 Little,3 Ball,4 Hellstrom,5 Little and Altia,6 Caton-Thompson,7 Murray,8 Paver and Pretorious,9

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fIgure 10.4 Structure contours on the surface of the basement complex.


Shulkri,10 Shazly et al.,11 Shata,12 Ghobrial,13 Barakat and Milad,14 Grandic and Koscec,15 Jacob,16 Borelli and Kararyac,17 Hamad,18 and FAO.19 Many additional studies include reports on gravity and magnetic surveys for most of the oasis and provide valuable information on the surface of the underlying crystalline basement rock.

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fIgure 10.5 Isopach map of sandstone aquifer system.

Case Studies 213

10.1.3 hydrogEology

The Nubian aquifer system (Figure 10.6), one of the largest groundwater systems of the Sahara, is formed by two major basins—the Kufra Basin in Libya, northeastern Chad, and northwestern Sudan, and the Dakhla Basin of Egypt. The aerial extent of the aquifer includes the southernmost strip of the Northwestern Basin of Egypt and the Sudan Platform. The total area is about 2 million square kilometers.

The aquifer mainly consists of continental sandstone and intercalations of shale and clays of shal-low marine and deltonic origin. To the south, east, and west, the aquifer is limited by basement out-

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sti

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fIgure 10.6 Location map of the Nubian aquifer system.


crops. In the southwest, the sandstone layers crop out at the rim of the Chad Basin. In the northwest, the sandstones are connected to the Sirte Basin. In the north, the possible groundwater movement is limited by the freshwater–saltwater interface. North of the 25th parallel, the aquifer is confined under thick marine shale.

In spite of the hyperarid climate, there are huge groundwater reserves. In the center of the basin, where the average precipitation is < 5 mm/year, there are several thousand meters of saturated sand-stones. Obviously, there is no recent groundwater recharge in most parts of the system.

For the origin of the groundwater, two concepts have been under discussion. The first and older one is based on observations of groundwater levels and postulates a large-scale flow from mountain-ous recharge areas in the southwest (Tibesti and Ernedi) to discharge areas in the northeast. Present recharge and a more or less steady state prevail. Thus, groundwater can be considered a renew-able resource. According to the second concept, which is based on investigations of groundwater isotopes, groundwater had been formed locally in the surroundings of the present discharge areas during a more humid climate that prevailed all over the present desert. If so, groundwater extraction must be regarded as mining of a nonrenewable resource under unsteady conditions.

In order to clarify this point, several groundwater models were constructed. A brief description of each model is given herein together with its achievement.

10.1.4 rEgional FloW pattErn

Piezometric mapping began with the earliest data collected on water levels from wells and springs in the oases. The first areal water level maps providing the earliest concepts of groundwater move-ment were made by Ball (Figure 10.7),4 Hellstrom (Figure 10.8),5 and then by the Ministry of Land Reclamation in 1960 (Figure 10.9). The flow lines give evidence of some eastern flow.

Ezzat et al.20 estimated the total groundwater inflow rate to the Western Desert sandstone sys-tem to be about 1306.3 × 106 cu m3/year. Groundwater outflow mainly occurs through natural springs and drilled well discharges as well as natural losses by evaporation and/or evapotranspira-tion. Ezzat et al.,21 in their model study on the sandstone aquifer system south of the Qattara area, concluded that the belt of the topographically low lands of Al-Eng, Bahrein, and Sitra, located at the southern periphery of the Qattara depression, represent the only northern natural discharging area for the aquifer system. Groundwater natural losses were estimated differently by several investiga-tions (Barber and Carr22 and Ezzat21).

10.1.5 groundWatEr modEls

Several models of both analog and digital types have been constructed for the regional sandstone aquifer system in the Western Desert and for the Kharga–Dakhla Oases area.

Salem23 constructed two regional one-layer R-C analog models for the sandstone aquifer sys-tem of the Western Desert. The first model was set to simulate the artesian condition, whereas the second one represented the water table condition, with a vertical, low hydraulic conductivity value so that a period of time will elapse between the earlier artesian effect and the development of water table conditions. Cause–effect response of the aquifer system was studied under both the artesian and water table conditions as a result of the two pumping programs at the different oases areas for a period of 50 years.

Borelli et al.,17 who made the two-layer model of the Kharga-Dakhla area, described the results of this R-C analog model where a regional one-layer model of the Western Desert was represented to define the boundary conditions. Steady-state simulations were achieved by invoking various con-ditions, both geometrically and hydraulically, that violate present understanding of the systems’ hydraulic features.

Ezzat et al.21 reported on a regional groundwater one-layer model of the Western Desert and a semidetailed model of the Kharga-Dakhla Oases area. The models were carried out using the

Case Studies 215

Honeywell ECAP program. The regional model output was used to control boundary conditions on the semidetailed one with a very simplified system geometry. Steady-state simulation for the piezometer in the Kharga-Dakhla area was achieved with fair accuracy. Time-controlled calibra-tion proved impossible; therefore, the forecasts of the system response to future extractions are questionable.

In the framework of the United Nations Development Program technical assistance to the New Valley project, Western Desert, evaluation of groundwater resources in the Kharga-Dakhla Oases area was carried out.22 A detailed numerical model, based on the integrated finite difference method,

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fIgure 10.7 Contours of underground static water levels. (From Ball, J., Problems of the Libyan desert, Geog. J., London, 1927.)


was made. The objective of the model was to determine the economic quantities of groundwater to be extracted to support long-term development of irrigated agriculture in the area. The model simulated a two-layer aquifer system connected by vertical leakage. However, the drawbacks of the simulated input data were a unique average value for the horizontal hydraulic conductivity all over the modeled area and the setting of an arbitrary flow line outside the two oases areas as the western and northern boundaries of the model. These boundaries were treated as no-flow boundaries in the steady-state condition and step-down boundaries in the transient stage. Figure 10.9 shows the output of that assumption.

A regional numerical two-dimensional model, simulating the pre-upper Cretaceous sandstone aquifer system in the Western and Eastern Deserts as a one-layer system, was made by Amer et al.24 using the finite element technique. The model was prepared to forecast the aquifer system’s hydrau-lic response to future foreseen water extractions at the different development desert areas. Amer

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fIgure 10.8 Stream lines of equal pressure in the Libyan desert. (From Hellstrom, B., Sartreyte Geogr. Annater., 34, 1940, pp. 206–239.)

Case Studies 217

considered the sandstone aquifer system as nonhomogeneous and anisotropic, with essentially hori-zontal flow. The model output for a steady-state condition is given in Figure 10.10. The final water balance of the aquifer system was also obtained from the model study, as given in Table 10.1.

Heinl and Brinkmann (1989)25 constructed a two-dimensional horizontal finite element model for the simulation of the Nubian aquifer system. The finite element grid covered an area of 2 million

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fIgure 10.9 Regional steady-state potentiometric surface of sandstone aquifer system. (From Egypt Min-istry of Land Reclamation, 1960.)


square kilometers. Thus, a large distance flow from the Chad to the Qattara depression was mod-eled, with a transition of several thousands of years from a semiarid climate to the present hyperarid conditions and a corresponding flow distance. The model was designed as a closed system, where reliable zero-flow boundary conditions could be identified at the outcrops of the basement, i.e., the natural boundaries of the system. All groundwater flow, recharge, and discharge occurred within the model.

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fIgure 10.10 Simulated steady-state potentiometric surface (with oases permeability and natural loss value adjustments—Run 8).

Case Studies 219

The confined part of the system in the north was considered as a leaky aquifer, allowing vertical water exchange between the Nubian aquifer and overlying sediments, i.e., exfiltration to the large Egyptian depressions, such as Kharga or Dakhla, and possible infiltration from the highlands. The hydrogeological system parameters, viz., transmissivity, storage coefficients, and leakage factors, were deduced from field data.26

The simulated extraction plans in Egypt and Libya are compiled in Figure 10.11. The total assumed extraction plan is 2800 × 106 m3/year in Egypt and 2200 × 106 m3/year in Libya. The total extraction imposed on the Nubian aquifer is 5 km3/year. The groundwater flow pattern at the begin-ning of the new projects in 1990 is still marked by natural flow to the oases.

In 2070, after 80 years of additional extraction, deep drawdown cones will have been formed (Figure 10.12). In the unconfined part of Egypt, the new Farafra projects are now in the center of a common drawdown cone between Bahariya and Dakhla. It will also include Sirva and Kharga and a small part of Libya. The model predicts a maximum drawdown of 130 m in Bahariya and Farafra. The extraction of E-Oweinat and Qena-Lagita will cause separate drawdown cones, also exceeding 100 m.

Heinl and Brinkmann25 concluded that infiltration supporting equilibrium conditions stopped some 8000 years ago, but continued on a minor scale in different areas and time intervals. The pres-ent recharge in Wadi Howar on the Tibesti mountains is relevant only for natural flow conditions in geological time scales; for artificial extraction, it is negligible. The River Nile, acting as a drainage channel, does not recharge the system. Heinl and Brinkmann also concluded that groundwater extraction in the Nubian aquifer is groundwater mining of a limited and nonrenewable nature. Its costs and gains have to be carefully evaluated.

10.1.6 EnvironmEntal problEms

Two environmental problems can occur from using the groundwater of the Nubian aquifer without good water management plans. The first problem is rapid groundwater depletion, and the second is increasing the existing water supply with eventual salinization of the soils.

table 10.1final simulated steady-state inflow–outflow groundwater pattern sandstone aquifer system, egypt

total outflow (m m3/year)

area by wells natural lossesoutflow through

boundaries total

total inflow through boundaries (m m3/year)

Kharga 51.80 54.12 105.92 —

Kakhla 114.20 36.73 150.93 —

Farafra 0.84 5.77 6.61 —

Bahariya 25.50 29.41 54.91 —

Siwa 54.03 15.00 69.03 —

South Qattara — 87.25 87.25 —

Western front — 114.92 114.92 489.23

Southern front — 32.86 32.86 133.20

Total 622.43 622.43


1914

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

3319 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4

33

32

KHARTUM

DONGOLA

+ 1200E-OWEINAT

SE-SARRA

NW-OWEINAT

SE-KUFRA

KUFRASW-KUFRA

S-BISHARA

TAZERBO

S-SARIR

SIWA + 140

BAHARIYA+ 143

FARAFRAWADI QENA

WADI LAQITADAKHLA

ZAYAT + 10ABU TARTUR

KHARGA ± 0

CAIRO

BENGHAZI

+ 290

+ 14

+ 203

+ 30

+ 75

+ 75+ 140

+ 39

315

315

315

409315

315

376

220

20 21 22 23 24 25 26 27 28 29 30 31 32 33 34

FAYA

fIgure 10.11 Proposed future extraction in Libya (total) and Egypt (additional) at 106 m3/year.

Case Studies 221

referenceS

1. Zittle, A. K., Beitrage Zur Geologic and Palaontologic der Libyschen Wuste und der Angrezenden gabi-ete von Aegypten, Paleotographica, 30, 1983, pp.

2. Beadnell, H. J. L., Flowing wells and subsurface water in Kharga Oases, Geological Magazine, 5, 524, 1908, pp. 49–57.

3. Little, O. H., Preliminary Report on the Water Supply of Kharga and Dakhla Oases, Egyptian Survey Dept, 1931.

4. Ball, J., Problems of the Libyan Desert, Geographical Journal, London, 1927.

3433323130292827262524232221201914

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

3319 20 21

BENGHAZI

22 23 24 25 26 27 28 29 30 31 32 33 3433

32

31

30

29

28

27

26

25

23

24

22

21

20

19

18

17

16

15

14

80

DATTAHA BIEN

BENGHAZI

DESOURI

AMMONITE

10

40

3020

70

10

10GILF HEBIRBIR

TERFAVI

70

SELINA

LAQITA

DONGOLANUKHEILA

10

10

30

30 40

50

10

15040

10

40BISHARA

TIBESTI

HERFONA

HOZETHA

IHZERRO

20

SNARA

AIRUN

VADI HOWAH

HORDI DEPRENNEDI

EADI

UNTANGA

FATA

BIR HURRIOSHKA

IAKIHLA

140

EDAN

30

10

HEBALA

fIgure 10.12 Drawdown after 80 years of additional extraction (1990–2070).


5. Hellstrom, B., The subterranean water in the Libyan Desert, Sartreyte Geogr. Annater., 34, 1940, pp. 206–239.

6. Little, O. H. and Attia, M. I., The Deep Bores in Kharga and Dakhla Oases: Cairo Geological Survey, Report, 1942, 58 pp.

7. Caton-Thompson, G., Kharga Oases in Prehistory with a Physiographic Introduction by Gardner, E. W., University of London, Athlone Press, London, 1952.

8. Murry, G. W., The Artesian Water of Egypt: Survey Dept., Ministry of Finance and Economy, Paper No. 52, 1952, 20 pp.

9. Paver, G. L. and Pretorius, D. A., Hydrogeological investigation of Kharga and Dakhla Oases, Bulletin of Egyptian Desert Institute, 4, 1954, pp.

10. Shulsri, N. M., Remarks on the geological structure of Egypt, Bulletin de la Société Géographie d’Egypte, 27, 1954, pp. 65–82.

11. Shazly, M. M. et al., Contribution of the study of the stratigraphy of el-Kharga Oasis, Bulletin de l’Institut du Désert d’Egypte, 10, 1, 1959, pp.

12. Shatta, A., Remarks on the regional geological structure of the groundwater reservoir of El-Kharga and Dakhla Oases, Bulletin de la Société Géographie d’Egypte, 34, 1961, pp. 177–186.

13. Ghorbrial, M. G., The Structural Geology of the Kharga Oasis, Cairo, Geol. Survey, and Min. Research Dept., Paper No. 43, 1967.

14. Barakat, M. G. and Milad, G. S., Subsurface geology of Dakhla Oasis, Journal of Geology, 10, 2, 1966, pp. 145–154.

15. Grandic, S. and Koscec, B., Geological characteristics of sedimentary complex of the Nubia Formation: Report of Egyptian general desert development organization, INDUSTROPROJECT, Zagreb, Yugosla-via, 1968.

16. Jacob, C. E., Geology and Hydrology of Kharga Oasis, in Water Well Design, Western Desert, Egypt, Rosscoe Moss Company, Report to Egyptian E.G.D.D.O., 1964.

17. Borelli, M. and Karanjac, J., Kharga and Dakhla Oases, Determination of Hydrogeological and Hydrau-lic Parameters: Reports, presented by INDUSTROPROJECT, Zagreb, Yugloslavia, 1968.

18. Hammad, H. Y., Groundwater Potentialities in the African Sahara and the Nile Valley, Beirut Arab University, Beirut, 1970.

19. FAO, Development of the New Valley Region in the Western Desert, Fact-finding Mission’s Report, Draft: Rome, EGY/8903 Terminal Report, 1970.

20. Ezzat, M. A., Abuer, and Atta, A., Regional hydrogeological conditions, Groundwater Series in A.R.E. Part I, Ministry of Land Reclamation, Cairo, 1974.

21. Ezzat, M. A., Nour, S. E., Morshed, T., and Mishriki, M., South Qattara Area Groundwater Model, General Petroleum Company, Cairo, 1977.

22. Barker, W. M. and Carr, D. P., Groundwater Model of the Kharga-Dakhla Area: Working Document No. 7, UNDP/FAO, AGON:EGY 71/561, 1976.

23. Salem, M. H., Study of the Hydrologic Parameters of the Nubian Sandstone Aquifer with Reference to the Productivity of Pattern for Well Development in Kharga Oasis, Egypt, 1970.

24. Amer, A. M., Nour, S. E., and Mishriki, M. F., A Finite Element Model of the Nubian Aquifer System in Egypt, Groundwater Seminar, Egyptian Ministry of Land Reclamation, 1979.

25. Heinl, M. and Brinkmann, P. J., A groundwater model of the Nubian aquifer system, Journal of Hydro-logical Science, 34, 4, 1989, p. 8.

26. Hesse, K. H., Hissene, A., Kheir, O., Schnacher, E., Schneider, M., and Thorweike, U., Hydrogeological investigations in the Nubian aquifer system, Berliner Geowissen-Schaftliche Abhandlungers (A), 75, 2, 1987, pp. 397–464.

Case Studies 223

10.2 SItIng a Secure HazardouS WaSte landfIll In a lImeStone terrane

10.2.1 introduction

This study describes the geologic and hydrologic settings for a secure hazardous waste landfill in a limestone terrane in New York.

The site is located in a part of the Niagara River corridor, which occurs adjacent to the Niagara River, from the northern part of Buffalo to Lewiston, New York (Figure 10.13). The Niagara River corridor, in the town of Niagara and the city of Niagara Falls in the southwestern part of New York state, is highly industrialized as a result of the abundant water supply available for industrial pro-cessing, waste assimilation, and power generation. There are numerous disposal sites in the area (Figure 10.13).

The area was investigated to determine site suitability for a hazardous waste landfill. In line with the results of geological and hydrological investigations, proper design and engineering of the site, installation of a double liner with leachate collection, and adequate pre- and postmonitoring systems developed this site as suitable for a landfill.

BERGHOLTZ

CAYUGA CREEK

CREE

KSI

BUFFALO

RESERVOIR

CREEK

HYDERESERVOIR

PARK

BURIED

GIL

L

CONDUITS

NIAGARA FALLS

FISH CREEK

SmcOq

78° 58' 30''79°

43°

06'

10'

00''

30''

43°03'00''

STUDYAREA

LEWISTON NIAGARACOUNTY

NEW YORK

LOVE CANAL

102nd ST.

S-AREA

AMERICAN FALLS

CANADA

WHIRLPOOL

CANADIANFALLS

NIAGARA RIVER

Ss

0 8000

20000

FEET

METERS

Modified from U.S. Geological SurveyNiagara Fails.

Hazardous Waste Disposal SiteWaste Site Administered by USEPANiagara EscarpmentNiagara Gorge

1948 1:62.500

EXPLANATIONContact between Geologic Formation or Group:

Ss Silurian Salina GroupSl Silurian Lockport GroupSmc Silurian Medina and Clinton GroupsOq Orcovician Queenston

fIgure 10.13 Major geographic features and geologic settings of Niagara Falls area and location of haz-ardous waste sites.


10.2.2 topographic and gEographic sEtting

Niagara Falls is within a lowland bordered on the north by the Lake Ontario plain and to the south by the Lake Erie plain. The Niagara escarpment, which crosses the area along an east–west line, forms a 200-ft high cliff north of the Niagara River, and then diminishes to a broad, sloping incline toward the south (falls). The Niagara River declines by about 320 ft along its 30-mi length between Lake Erie and Lake Ontario, including the 160-ft drop at the Canadian falls.

The topography of the site is relatively flat, with the exception of the artificial mounds created by landfills in the area. The natural ground surface elevation ranges 574–584 ft above sea level. Sur-face drainage is relatively poor due to the apparently undersized culverts immediately downstream of the site that cannot accommodate the high volumes of runoff. The runoff is in turn caused by the clayey glacial soils.

10.2.3 gEologic sEtting

Unconsolidated glacial deposits of till and lacustrine clay, silt, and sand overlie gently dipping sedi-mentary rocks throughout the Niagara Falls area.

Middle Silurian Lockport Dolomite directly underlies the northern part of the area, and the younger Upper Silurian Salina Group underlies the southern part, owing to the bedrock’s southward dip of about 30 ft/mi. In the Niagara Falls area, the Lockport Dolomite ranges 130–160 ft in thick-ness and consists of five members that have been differentiated on the basis of lithologic character-istics and fossil evidence.

The overburden, Lockport Dolomite, and Rochester Shale, considered to be the most important geologic units, are described in the following text. Figure 10.14 is a schematic block diagram show-ing the geologic setting.

SOURCES1. AMERICAN FALLS INTERNATIONAL BOARD, 1974, PRESERVATION AND ENHANCEMENT OF THE AMERICAN FALLS AT NIAGARA, APPENDIX C–GEOLOGY AND ROCK MECHANICS: FINAL REPORT TO THE INTERNATIONAL JOINT COMMISSION, JUNE, 71 P.2. JOHNSTON, R.H., 1964, GROUND WATER IN THE NIAGARA FALLS AREA, WITH EMPHASIS ON THE WATER-BEARING CHARACTERISTICS OF THE BEDROCK: STATE OF NEW YORK, CONSERVATION DEPARTMENT WATER RESOURCES COMMISSION BULLETIN GW 53, 93 P.3. MILLER, T.S., AND KAPPEL, W.M., 1987, EFFECT OF NIAGARA POWER PROJECT ON GROUND WATER FLOW IN THE UPPER PART OF THE LOCKPORT DOLOMITE, NIAGARA FALLS AREA, NEW YORK: U.S.G.S. WATER-RESOURCES INVESTIGATIONS REPORT 86–4130, 31 P.4. WOODWARD-CLYDE CONSULTANTS, 1987, DRAFT GEOLOGIC REPORT NECCO PARK, NIAGARA FALLS, NEW YORK: V.2, DECEMBER.5. ZENGER, D.H., 1965, STRATIGRAPHY OF THE LOCKPORT FORMATION (MIDDLE SILURIAN) IN NEW YORK STATE: NEW YORK STATE MUSEUM AND SCIENCE SERVICE BULLETIN, NO. 404, 210 P.

fIgure 10.14 Schematic block diagram.

Case Studies 225

overburden

The overburden materials in the Niagara Falls area consist of predominantly natural sand, silt, clay, and man-deposited miscellaneous fill.

A 1–5 ft thickness of glacial till generally occurs at the base of the overburden. Glacial till contains very poorly sorted sands, silts, clays, and gravels. The till in the Niagara Falls area was deposited near the end of the Wisconsinan Glaciation during the Pleistocene epoch. The tills are characteristically stiff red clays with varying amounts of sand, silt, and gravel. Above the till, there is usually a variable thickness of glaciolacustrine lake sediments consisting of sand, silt, and clay deposited about 12,000 years ago as the continental ice sheets retreated north-ward. These sediments, commonly represented as varved (banded) silt and clay, were deposited in temporary lakes that formed at the ice front (preglacial lakes). Additional sediments were later deposited when a large postglacial lake formed on the flatland between the Niagara and Onon-daga escarpments. This lake (Lake Tonawanda) stretched for over 50 mi to the east of the Niagara Falls area.1 A 1–2 ft thickness of topsoil overlies the glaciolacustrine sediments in undisturbed regions. Because much of the Niagara Falls area has been disturbed by human activities, many areas exist where sections of natural overburden have been removed and/or replaced with miscel-laneous fill material.

lockport formation

The Middle Silurian Lockport Formation, consisting of approximately 140 ft of relatively competent dolomite, lies beneath the overburden in the Niagara Falls area. This unit thickens to the southeast and thins to the west toward the Niagara Gorge and to the north toward the Niagara Escarpment. The Lockport Formation, which has also been referred to as the Lockport dolomite (or dolostone), is subdivided into five principal members: the Oak Orchard, Eramosa, Goat Island, Gasport, and DeCew members.2

The Lockport Formation is primarily dolomitic and characterized generally by a brownish-gray to dark gray color; medium granular; medium to thick bedded; with stylolites, carbonaceous part-ings, vugs, and poorly preserved fossils. The Lockport is subdivided into five principal members based on variations within this general description.2 A stratigraphic column showing the Lockport Formation is provided in Figure 10.15. Figure 10.16 shows the locations of geologic cross sections; Figure 10.17 shows the northeast–southwest geologic cross section; and Figure 10.18 shows the northwest–southeast geologic cross section.

oak orchard member

The Oak Orchard Member, the uppermost and thickest member of the Lockport Formation, ranges approximately 80–120 ft in thickness in the Niagara Falls area. It is brownish-gray to dark gray, fine to medium grained, thin to thick bedded, saccharoidal, bituminous dolomite with stylolites, carbonaceous partings, vugs, minor occurrences of stromatolites, oolites, and tabulate coral fossils. The Oak Orchard exhibits the greatest degree of variability of the Lockport Formation members, being shaley and thin bedded in some sections and massive in other sections.

eramosa member

The Eramosa Member is 16–18 ft thick and underlies the Oak Orchard Member. This unit is gener-ally medium to dark gray, fine grained, and thin to medium bedded, argillaceous and bituminous dolomite, with many shale partings, gypsum vugs, and some stylolites.2 The contact between the Oak Orchard and the Eramosa Member is characteristically sharp.


goat Island member

The Goat Island Member, occurring beneath the Eramosa, is generally 19–25 ft thick in the Niagara Falls area. It is light olive gray to brownish-gray, medium grained, thick bedded, saccharoidal dolomite, with abundant chert nodules near the top, stylolites, carbonaceous partings, and some vugs containing gypsum, calcite, and sphalerite.2 The contact between the Eramosa and the Goat Island Members is conformable and is characterized by a gradual lightening in color over a 2-ft thickness.

0 FT

10 FT

20 FT

30 FT “OOLITE”BED

40 FT

50 FT

60 FT

70 FT

80 FT

90 FT

100 FT

110 FT

120 FT

130 FT

140 FT

150 FT

160 FT

170 FT

180 FT

190 FT

200 FT

DECEWMEMBER

MODIFIED FROMZENGER, 1965.

GASPORTMEMBER

GOAT ISLANDMEMBER

ERAMOSAMEMBER

OAK ORCHARDMEMBER

LACUSTRINECLAY

EXPLANATION

GLACIAL TILL

DOLOMITE

DOLOMITICLIMESTONE

ARGILLACEOUSDOLOMITE

SHALE

BIOHERM

BIOSTROME

ENTEROLITHICDOLOMITE

OOLITES

STROMATOLITES

INFRAFORMATIONALOR EDGEWISECONGLOMERATE

CHERT

CRINOIDS

210 FT

220 FT

LACUSTRINE CLAY

GLACIAL TILL

LOCKPORTDOLOMITE

ROCHESTERSHALE

fIgure 10.15 Stratigraphic column.

Case Studies 227

gasport member

The Gasport Member occurs below the Goat Island Member and is approximately 15–30 ft thick. Because the Gasport occurs as a complex of different facies, this member tends to exhibit a high degree of variability between geographic localities. The Gasport is predominantly olive-to-brownish gray, coarse-grained, and medium-to-thick bedded fossil, fragmental and crinoidal limestone, or dolomite.2 However, owing to localized facies changes, this member can appear as dark gray, fine grained, and argillaceous dolomite with sporadic crinoid fragments. The contact between the Goat Island and Gasport Members is conformable.2 Because of local facies, the relationships between the top of the Gasport and the bottom of the Goat Island are often difficult to identify. The combined thickness of the Goat Island and Gasport Members, however, is generally constant.

100

LOCATIONS OF GEOLOGIC CROSS SECTIONS

87-136-2

87-135-2

87-134-287-134-3

87-128-2

87-127-287-128-3

422424

420

413

401402400 RB-51s

RB-51iRB-51d

RB-34 sRB-34 iRB-34 d

PC-1PC-2

86-120-2 60086-120-3

RB-63iRB-63d

RB-29sRB-29iRB-29d

86-103-286-103-3

87-104-186-104-2 86-121-2

86-121-3 86-114-287-114-1

L-2L-1

87-106-186-106-286-106-3

86-104-3VAR630

630

Dup-11

Dup-4 Dup-2Dup-1

Dup-8Dup-7

88-150-1

D-18 D-19D-20

Dup-3

Dup-6Dup-5

Dup-10Dup-9

Dup-12Vf

VH-143AVH-143BVH-143C

VH-115B

VH-116BVH-111B

D-12 31SR20SR350

360711SZR

83 359358

VH-116C



VH-145B VH-145A

VH-120BVH-114B

VH-119BVH-129C

10354353355

18SR600

18ASR52

3528

351

630

33AVH-145C

88-141-288-140-2

VH-153A

VH-154A

88-139-2

88-138-2

N

88-137-2

VH-154C

VH-153BVH-153C

81R

VH-117AVH-127C

VH-117CVH-118B

VH-141BVH-141CVD

PELA-4

87-110-187-142-1

87-112-1

PELA-568PELA-3 PELA-6

PELA-2

630

PW-B

38

35794

630

660

660

600

327326

305304303A

335336

86-112-2

86-114-386-125-286-125-387-125-1

86-112-3

87-142-287-142-3

86-110-286-110-386-110-4

VdVH-142AVH-142B

356

87-105-186-105-286-105-3

74

600

7576

86-118-386-118-2

PELA-7SE

SW

600

173171

P1 P2P7

169170414

416

404405403

418

630

406 7879

425172260

87-133-2

600

88-132-288-132-3

87-136-3

SCRF. NO. 6

NW

PACKARD ROAD

EXPLANATION

TOP OF CLAYTOP OF ROCK

PELA COREHOLEPC-186-108-386-108-2

LOCATION OF GEOLOGICCROSS SECTION

SW

NE87-108-1

BEDROCK

200 0 200

SCALE IN FEET

400

411412410302301300

323325324

320

310309

317

314316315

307306308312

313311340329

339328

88-143-188-143- 288-143-3

319318

414

NE -129-1-129-2

630

TO GRAND IS

LAND (BUFF

ALO)

fIgure 10.16 Location of wells and coreholes.


HORIZONTAL SCALE 1 INCH EQUALS 100 FT.

EXPLANATION

CORE EXTENDS TO TOPOF ROCHESTER SHALE

540

550

560

570

580

VH-141

86-108-2

RB-38RB-31RB-24

NO VERTICAL EXAGGERATION

LAND SURFACE

PROJECTED BOUNDARIES OF SCRF 6

RB-54

RB-10

630

620

610

600

SCA

LE IN

FEE

T A

BOVE

MEA

N S

EA L

EVEL

590

580

570

560

550TD 40.0 FT. TD 43.5 FT.

TD 163.9 FT.

TD 73.2 FT.CORE EXTENDS TO TOPOF ROCHESTER SHALE

“OOLITE’’ BED

“MASSIVE’’DOLOMITE

GLACIAL TILL REEF BED

LACUSTRINECLAY

SLAG ANDLIME FILL

STROMATOLITICDOLOMITE

TD 65.0 FT.

SOILSOIL

TD 63.7 FT. TD 61.6 FT.

TD 59.5 FT.

540

550600650

87-128-287-128-3 PC-1

LAND SURFACE 590

600

610

620

630550600650

TD 162.0 FT.

VERTICAL EXAGGERATION: 10X

SCA

LE IN

FEE

T A

BOVE

MEA

N S

EA L

EVEL

SOIL

PROJECTEDONTO LINE OF

CROSS SECTION

fIgure 10.17 Northeast–southwest geologic cross section.

REEF ZONE

530

540

550

560565570575580

590

600605610RB-34d

RB-54d

RB-8d

RB-1RB-11

530HORIZONTAL SCALE: 1 INCH EQUALS 100 FEETVERTICAL EXAGGERATION: 20X

540

550

560

SCA

LE IN

FEE

T A

BOVE

MEA

N S

EA L

EVEL

570

SOIL580

590

600605610615620625630

NW

565

575

585

595

535

545

555

SCRF 6

615620625630

SE

595

585

545

555

535

DOLOMITE

STROMATOLITICDOLOMITE

“MASSIVE’’DOLOMITE

“OOLITE’’BED

GLACIALTILL

LACUSTRINECLAY

SOIL AND FILL

SCA

LE IN

FEE

T A

BOVE

MEA

N S

EA L

EVEL

EXPLANATION

TD 79.0 FT.

TD 21.8 FT.

TD 73.2 FT.

TD 78.2 FT.

fIgure 10.18 Northwest–southeast geologic cross section.

Case Studies 229

decew member

The DeCew Member underlies the Gasport Member and overlies the Rochester Shale. The DeCew is described as medium gray to medium dark gray, fine grained, thin to thick bedded, and massive argillaceous dolomite. The thickness ranges 8–10 ft in the Niagara Falls area. The contact between the DeCew and the Gasport Members is characteristically abrupt in the Niagara Falls area, marked by a change from the massive crinoidal basal conglomerate of the Gasport Member to the fine-textured, argillaceous dolomite of the DeCew.2 Tesmer1 separates this unit from the Lockport For-mation on the grounds that a nonconformity exists between the DeCew and the Gasport, indicating a break in sedimentation. However, Zenger2 notes that the nonconformity occurs locally and that the contact between the DeCew and Gasport is conformable at other localities.

rochester Shale

The Rochester Shale Formation lies below the DeCew Member and is typically 55–65 ft thick in the Niagara Falls area. It is considered to be the fifth principal marker horizon within the study area. It is described as dark bluish- to brownish-gray, calcareous shale, with occasional argillaceous limestone layers. The upper Rochester Shale tends to be more dolomitic than the lower, especially at the con-tact with the DeCew. This contact, although gradational at most locations, tends to be more abrupt and undulating in the Niagara Falls area. This has been attributed to localized channeling at the top of the Rochester Shale in the Niagara Falls area prior to the deposition of the DeCew Member.1

10.2.4 structural gEology

A south-dipping homocline, which affects the Paleozoic rocks of western and southern New York, is the dominant structural feature in the Lockport Formation and in the sedimentary formations beneath it. Bedding dips are characteristically gentle. Local deviations in the dominant regional structure do occur and may be attributed to monoclinal flexures and faulting. A large-scale, tectoni-cally related, structural pattern is believed to affect the rocks of western New York.3

Joints—high angles to vertical fractures related to regional stress patterns—are common in the Lockport Formation. These joints are probably most open or developed in the upper part of the Lockport Formation, where a relatively high degree of weathering has occurred.4 Where dissolu-tioned, these joints may serve as conduits for the vertical and horizontal movement of groundwater between bedding plane fractures. The prominent sets of vertical joints in the Niagara Falls area are oriented N65°E and N30°W.4 Near the bedrock surface, the joints tend to be open and well developed; however, they become relatively tight and poorly developed at depths.5 The incidence or frequency of vertical fractures may vary with depth between the areas. Studies conducted by the U.S. Geological Survey suggest that vertical fracture frequency may increase along regional structural lineaments.3 These lineaments are related to the large-scale structural pattern mentioned previously.

Bedding plane fractures near the horizontal fractures parallel to the bedding formation tend to lie within particular stratigraphic intervals. Bedding plane fracture zones transmit the majority of the groundwater flow in the Lockport Formation.3–5 Water-bearing bedding plane fracture zones develop due to variations in lithology, differential weathering, solutioning, and tectonic or isostatic rebound related to stress release.

10.2.5 hydrogEology

The Lockport Dolomite is the principal aquifer in the Niagara Falls area, but it is not heavily pumped because the Niagara River is the major source of water supply. Well production not affected by induced infiltration commonly ranged 10–100 gallons per minute (gpm), but production as high


as 950 gpm has been developed. Near the river, induced infiltration augments yields from the Lock-port to industrial wells, some of which produce more than 2000 gpm.4

The Lockport Dolomite has been divided into two zones on the basis of water-transmitting properties. The upper zone is 10–25 ft thick and has well-connected horizontal and vertical frac-tures. The horizontal hydraulic conductivity of the upper permeable zone is estimated to be 3 ft/d (1.76 × 10−5 cm/s).4 The lower zone contains the separate water-bearing bedding planes, which gen-erally are poorly connected by vertical joints.

The distribution of well production from the Lockport Dolomite indicates areas of high trans-missivity that may be related to fractures within the bedrock. The average production of a well in the area is estimated to be 30 gpm.4 An analysis of the distribution of wells producing more than 50 gpm shows that yields from the water-bearing zones are highest near the Niagara River, probably as a result of induced river infiltration. Johnston4 states that the most productive of these wells are within a narrow zone that trends northeastward from about 2 mi east of Niagara Falls.

The high production along the conduits (950 gpm) and from a more recently installed well 5 mi to the northeast (370 gpm) supports Johnston’s4 hypothesis that a band of high transmissivity exists in the Lockport and is possibly caused by fracturing within the horizontal bedding planes.

Groundwater in the Niagara Falls region generally flows southwestward from recharge areas near the escarpment toward the Niagara River (Figure 10.19), the major discharge zone. Near the city of Niagara Falls, however, the direction of flow has been altered by manmade structures. The Niagara Power Project Reservoir is a source of additional recharge to the Lockport Dolomite, and the buried conduit system, which carries water from the Niagara River to the power plant, is a point of groundwater discharge. Groundwater also discharges to the Falls Street Tunnel, which crosses the conduit system. Water level data were collected from wells, tapping separately top-of-clay and top-of-rock data. The data were converted, tabulated as water surface elevation, and plotted (Fig-ures 10.20 and 10.21). The top-of-clay flow of groundwater is to the south–southeast; the top-of-rock flow of groundwater is also to the south–southeast.

Groundwater flow through the Lockport Formation in the area occurs through horizontal water-bearing bedding plane fracture zones. This was reported by Johnston,4 based on observations along the exposed walls of the New York Power Authority (NYPA) conduits that cut through the Lockport Formation west of the study area. Johnston4 identified seven water-bearing zones, each consisting of either a single open bedding plane or an interval of rock layers containing several open bedding planes. Although the concept of separate and hydrologically distinct fracture zones has been an issue of dispute in the past, the U.S. Geological Survey (USGS) concurs with Johnston.5

A series of bedding plane fracture zones were identified during site investigations. The identifi-cation of water-bearing fracture zones was based on field observations, circulation fluid losses dur-ing drilling (expressed as percent water loss), bedrock core examination, and hydraulic conductivity test results greater than 10−4 cm/s. Over 200 core observations were used to verify the depth of a fracture zone. A weathered fracture or series of fractures were observed at approximately the same depth as the noted circulation fluid losses. Moderate-to-high hydraulic conductivity test results greater than 1 × 10−4 cm/s usually corresponded to water-bearing fracture zones where water loss was observed. Low hydraulic conductivity values less than or equal to 1 × 10−4 cm/s usually cor-responded to intervals where no circulation loss occurred. For the purpose of identification and discussion, the water-bearing fracture zones in the area are designated the 7-through-1 zones (see Figure 10.22).

7-Zone. The uppermost water-bearing bedding plane fracture zone in the Lockport Forma-tion within the area is designated as the 7-zone. It generally exists approximately 4 ft below the top of the rock and 10 ft above the C-zone. The 7-zone dips mainly southeast at an average angle of 0.6°. The 7-zone subcrops northwest of the area of investigation and is recharged through vertical fractures. Similar subcrop areas may exist for fracture zones 6 through 3 further northwest of the area of investigation.

Case Studies 231

6-Zone. The 6-zone generally occurs approximately 10 ft below the 7-zone. This zone dips to the southeast with bedding at an angle of approximately 0.7°. This zone was not observed within the southeastern half of the area. Hydraulic conductivity results in the range 10−5 to 10−6 cm/s support observations during drilling and core inspection.

5-Zone. The 5-zone generally occurs approximately 30 ft below the 6-zone. This zone is well represented in the northern half of the area but is poorly represented in the southern half.

NIAGARA RIVER

INTAKES

FEET

Adapted from U.S. Geological Survey, 1980. 1:25,000

400020000HORSESHOE FALLS

ISLAND

AMERICAN FALLSGOAT

NFB-6 NFB-7.7A

NFB-12 NFB-13

CON

DU

ITS

NFB-9

NEW YORK

TWIN CONDUITS(COVERED)

PUMP-STORAGERESERVOIR

N

RESERVOIR PUMP-GENERATING PLANT

ROBERT MOSESHYDRO-POWERPLANT

LEGENDPotentiometrio contour at10' intervals of the LockportDolomite. Arrows show directionof groundwater flow.Major Industrial pumping centre.Well used for cross-section ofFalls St. tunnel.

POWER CANAL

NIAGARA RIV

ER

570 560550

570580590

NFB-10NFB-11

NFB-8

570

560

550 560

570

580

600

560550

580590600610

570

550

530

550

540

490

510

500

520

530

540

550

560

590

550FALLS ST. TUNNEL

City of NiagaraFalls

ONTARIO

NIA

GARA

RIV

ER

NFB-5.5A

NFB-1.2

flow

NFB-3.4

fIgure 10.19 Potentiometric surface of the upper Lockport (approximate contours).


The approximate dip angle is 0.7° to the southeast. As the 5- and 4-zones tend to be very close to one another, 5 to 10 ft, discretion is used when assigning a zone designation to either of these fractures. In locations where both of these zones are present, indications are that they may be hydraulically connected based on proximity and similar hydraulic heads.

4-Zone. The 4-zone usually occurs 5–10 ft below the 5-zone. The E-zone has not been observed in the southwestern corner of the area. It is inferred that the presence of this water-bearing zone, although widespread throughout the area, tends to be locally discon-tinuous. The approximate dip angle of this fracture zone is 0.4° to the southeast.

CONFIGURATION OF THE WATER SURFACE FOR THETOP OF ROCK WELLS, NIAGARA FALLS, NEW YORK.

582.

5 577.5 57

5

580

572.5

570

567.5TO G

RAND ISLA

ND (BUFF

ALO)

572.5

575

567.5

570 200 200

SCALE IN FEET

4000

DIRECTION OF GROUNDWATER FLOW

TOP OF CLAYTOP OF ROCKBEDROCKPELA COREHOLEPC-1

575 86-108-386-108-286-108-1

575.05LOCATION OF WELLAND WATER SURFACEELEVATION

CONTOUR OF GROUNDWATER SURFACE IN FEET

EXPLANATION

572.5

575

577.5

582.5

585

587.5

587.

5

585

580

580

PACKARD ROAD

SCRF. NO.6


Case Studies 233

3-Zone. The 3-zone occurs approximately 17 ft below the 5-zone and/or 7 ft below the 4-zone. This zone dips toward the southeast at approximately 0.7° and has not been observed in the southwest and southeast sections of the area.

1- and 2-Zones. A fracture zone, given the designation 1- and 2-zones, was identified through test drilling as existing approximately 60 ft below the 3-zone and 30 ft above the top of the Rochester Shale. Three water-bearing fracture zones exist within this zone in the Lock-port Formation below the bottom of the Oak Orchard Member and above the top of the Rochester Shale.

LOCATION OF WELLAND WATER SURFACEELEVATIONCONTOUR OF GROUNDWATER SURFACEIN FEET 575

570

EXPLANATION

TOP OF CLAYTOP OF ROCKBEDROCKPELA COREHOLE

DIRECTION OF GROUNDWATER FLOW

572.5

567.5

570

572.5

575

577.5

575

575

580

577.5

582.5585587.5

592.5590

595 SCRF. NO. 659

7.5

595

590 57

5

592.

5 587.

558

5

582.5

582.

558

057

7.5

597.5PACKARD ROAD

580

572.

557

0

567.5

TO GRAND IS

AND (B

UFFALO

)

TOP OF CLAY WELLS, NIAGARA FALLS, NEW YORK.CONFIGURATION OF THE WATER SURFACE FOR THE

N

200 200 4000SCALE IN FEET



10.2.6 aquiFEr tEst

The distribution of drawdowns produced by an aquifer test provides direct information on hydrauli-cally significant features within the area affected by the test. The orientation of these features is determined by computing directional transmissivities between the pumped well and observation wells by the method of Papadopulos6 as modified by Maslia and Randolph.7 In two dimensions, a Poler plot of directional transmissivity in relation to the azimuth of the observation well* for a homogeneous, isotropic, confined aquifer forms a circle. If the aquifer is homogenous and anisotro-pic, the plot approximates an ellipse with major and minor axes parallel to the principal directions

* The location of the production well is defined as the origin.

LACUSTRINECLAY

EXPLANATION

GLACIAL TILL

DOLOMITE

DOLOMITICLIMESTONE

ARGILLACEOUSDOLOMITE

SHALE

BIOHERM

BIOSTROME

ENTEROLITHICDOLOMITE

OOLITES

STROMATOLITES

INFRAFORMATIONALOR EDGEWISECONGLOMERATE

CHERT

CRINOIDS

LEGEND

GASPORTMEMBER

DECEWMEMBER

GOAT ISLANDMEMBER

ERAMOSAMEMBER

OAK ORCHARDMEMBER

#7

#6

#5

#4

#3

#2

#1

#1 APPROXIMATE POSITIONS OF WATER BEARINGZONES IN NIAGARA FALLS AREA

MODIFIED FROM JOHNSTON, 1964,ZENGER, 1965.

“OOLITE”BED

20 FT

30 FT

40 FT

50 FT

60 FT

70 FT

80 FT

90 FT

100 FT

110 FT

120 FT

130 FT

140 FT

150 FT

160 FT

170 FT

180 FT

190 FT

200 FT

210 FT

220 FT

10 FT

0 FT

APPROXIMATE POSITIONS OF WATER BEARING ZONES

LACUSTRINECLAY

GLACIALTILL

LOCKPORTDOLOMITE

ROCHESTERSHALE


Case Studies 235

of transmissivity. If the aquifer is heterogeneous, any discrete fracture is indicated by a much larger value of transmissivity along the azimuth of the well, which intersects the fracture.

A production well and observation wells were installed to perform a constant-rate aquifer test. The major groundwater zone penetrated during drilling of the production well and the observation wells was a horizontal interval of solutioning and fracturing occurring at 3–5 ft below the top of the bedrock. The interval was consistent laterally and was penetrated in all the wells installed.

The purpose of the test was to determine the hydraulic characteristics of the water-bearing zones, the degree of isotrophy, the vertical and lateral extent of the interconnection of the fracture system, and the existence of any geologic and hydrogeologic boundaries.

10.2.7 procEdurE

The design of the pumping test included the selection of the location of the pumping well and 56 wells that were used as observation wells during the test (Figure 10.23). The selection of the 56 observation wells was based on the review of the design and construction details of these wells and the areal distance of each observation well from the pumping well (production well) to cover sufficient areal extent and obtain as much hydrogeologic information for the site as possible. The observation wells were selected for all three transmissive zones, top-of-clay, top-of-rock, and bed-rock wells (see Figure 10.24).

Prior to performing the test, additional steps were taken to determine the natural trend of the groundwater and also the impact of ongoing activities at the site and at adjacent sites, such as drill-ing and grouting. Based on the evaluation of the data, it was decided that the test should be per-formed during a weekend to eliminate any impact of ongoing activities.

The selected wells were equipped with instruments that included Stevens recorders, in-situ meters, and a data logger to obtain a continuous recording of the fluctuations of water level to determine the water level trend, the impact of drilling and construction of wells at the site, and the grouting activities at adjacent sites. Continuous water level data were also collected during the pumping test.

A recording barograph was used to continuously monitor barometric pressure before and dur-ing the test. Because the top-of-rock zone is confined, it was anticipated that barometric pressure changes would cause water level fluctuations that would need to be accounted for when interpreting the data.

At the beginning of the test, the water level increased when barometric pressure was declining and decreased later in the test when barometric pressure was rising. It is possible that the water level rises at the beginning were at least partially due to infiltration of rainfall, but the timing of the water level changes corresponded closely with barometric pressure changes.

Before pumping, the groundwater levels in the well clusters were 5.65–11.86 ft higher in the top-of-clay zone than in the top-of-bedrock zone. The water level difference between the top-of-bedrock zone and bedrock zone was less than 1 ft. Therefore, the potential for vertical movement was downward during nonpumping conditions.

A step-drawdown test was performed on August 12, 1988, using four steps, pumping at rates of 8, 22, 30, and 45 gpm, to determine the rate at which the pumping well could be pumped during the 72-h test. The step-drawdown test was also performed to determine the extent of the impact so that the locations for the observation wells could be modified to collect all critical water level data during the test. The step-drawdown test was performed for approximately 6 h. The pumping well was equipped with an in-situ meter for continuous recording of the changes of water level during the test.

Based on the results of the step-drawdown test, it was determined that the rate at which the 72-h pumping test could be performed was 14–15 gpm. The layout of the location of the observation wells was modified as necessary, and additional observation wells were added in the monitoring program.


The 72-h pumping test was started on August 13, 1988, and run until August 16, 1988. During the test, the well was pumped at an average rate of 14 gpm, and 56 observation wells were moni-tored to determine the impact of the pumping on water levels. After termination of the pumping, water level recovery data were collected for a period of 48 h from all the observation wells and the pumping well. Data from the tests were corrected for pressure fluctuations using the barometric efficiency. The water level data were tabulated, plotted, and analyzed using standard aquifer evalu-ation methodologies.

EXPLANATION

TO GRAND IS

LAND (B

UFFALO

)

TOP OF CLAY WELLAND NUMBERTOP OF ROCK WELLAND NUMBERBEDROCK WELL ANDNUMBER

200 200 4000

N

SCALE IN FEET

PACKARD ROAD

SCRF NO. 6

fIgure 10.23 Location of wells monitored during pumping test.

Case Studies 237

Graphical plots of log time versus log drawdown and log time versus log recovery were made for each of the observation wells (Figure 10.25). These plots were matched against the standard type curves presented in Lohman,8 for nonleaky confined aquifers using the Theis method, for leaky confined aquifers using the Hantush–Jacob method,9 and for leaky confined aquifers, where storage in the confining bed is accounted for, using the Hantush modified method.10 These three methods were chosen to cover the possible groundwater conditions in the top-of-rock zone. These methods were used to calculate the transmissivity, storativity, and leakance.

The leakance factor was used to calculate permeability of the confining bed (K′). In this situa-tion, water level measurements in the three zones would indicate that the majority of the vertical flow is between the bedrock and top-of-rock zones with relatively minimal flow between the top-of-clay and top-of-rock zones. The head difference between the top-of-clay and top-of-rock zones ranges 5–12 ft, whereas that between the top-of-rock and bedrock zones ranges 0–8 ft. Thus, the leakance calculation is assumed to be representative of the flow between the top-of-rock and bedrock zones, a thickness of 10 ft. The calculated vertical H-conductivity ranges 0.02–6 gpd/ft2 (9 × 10−7 to 3 × 10−4 cm/s). The summaries of the results of the aquifer test are contained in Tables 10.2a–c.

The drawdown was computed and plotted in the form of contour maps for various time peri-ods ranging 1–72 h for the top-of-rock to determine the extent and configuration of the cone of depression, degree of anisotropy, associated geological structural features, and solution channels and trends, and to graphically portray the impact on the water level. A similar set of drawdown contour maps was prepared for the bedrock.

ATOP-OF-CLAY

CBEDROCK

BCONSENT ORDER

TOP-OF-ROCKPUMPING WELL

FILL

TILL

“B” FRACTURE

“C” FRACTUREOPEN BOREHOLE INTO BEDROCK

LOCKPORT DOLOMITE

CLAY

PUMP TESTTOP-OF-ROCKPIEZOMETER

fIgure 10.24 Aquifer pumping test monitoring system.


Isotropy is the condition of a medium that has hydraulic properties uniform in all directions. Anisotropy, or nonisotropy, is the condition of a medium that has nonuniform hydraulic properties in different directions.

The results of the pumping test determined that the permeability of the top-of-rock zone in the area of the test ranges 10−2 to 10−3 cm/s and that of the bedrock ranges 10−2 to 10−3 cm/s. The storage coefficient in the area of the test generally ranged 10−3 to 10−6 for the top-of-rock and 10−2 to 10−5 for bedrock zones. The other result obtained from the pumping test was the indication of the lateral

114.6 × Q × w(u)sT2 =

114.6 × 14 × 11.2

T2 =

T2 = 1337.0 gpd/ft

114.6 × Q × w(u)

PUMP ON @ 9:45 A.M.ON 8-13-88

PUMP OFF @ 10:00 A.M.ON 8-16-88

PUMPING TEST (DRAWDOWN)PUMPING WELL = PW-B

TIME DRAWDOWN10.0

1.0

0.1Dra

wdo

wn

in F

eet (

s)

0.011 10 100 1,000 10,000

w(u) = 11/u = 1

s = 1.20t = 4.1

sT3 =

T3 =

T3 = 1419.82 gpd/ft

114.6 × Q × w(u)sT1 =

MP-2

w(u) = 10–1

1/u = 1s = 0.113t = 5.1

MP-3

w(u) = 10–1

1/u = 10s = 0.062t = 10.7

MP-1

TIME “t” IN MINUTES

114.6 × 14 × 10–1

0.062T1 = 114.6 × 14 × 10–1

0.113T1 = 2587.74 gpd/ft

114.6 × Q × w(u)s´

T2 =

114.6 × 14 × 11.1

T2 =

T2 = 1,458.55 gpd/ft

114.6 × Q × w(u)

PUMP OFF @ 10:00 A.M.ON 8-16-88

RECOVERY TESTPUMPING WELL = PW-B

TIME RECOVERY10.0

1.0

0.1Reco

very

in F

eet (

s´)

0.011 10 100 1,000 10,000

w(u) = 11/u = 1

s´= 1.1t = 3.65

w(u) = 11/u = 1

s´= 1.70t = 6.3

s´T3 =

T3 =

T3 = 943.76 gpd/ft

114.6 × Q × w(u)s´

T1 =MP-2w(u) = 1

1/u = 1s´= 0.60t = 1.6MP-1

MP-3

w(u) = 10–1

1/u = 10s´ = 0.103t = 8.2

MP-4

TIME “t” IN MINUTES

114.6 × 14 × 10.60

T1 =

114.6 × 14 × 11.7

114.6 × Q × w(u)s´T4 =

T4 =

T4 = 1,557.67 gpd/ft

114.6 × 14 × 10–1

1.1

T1 = 2,674 gpd/ft

fIgure 10.25 Time-drawdown and time-recovery plots for pumping well PW-B.

Case Studies 239

and vertical extents of the cone of depression (cone of influence). Figures 10.26 to 10.29 show the extent of the cones of depression in the top-of-rock wells and the bedrock wells for a period of 24 and 72 h, respectively. Plots of the cone of depression depict the total drawdown for periods of 24 h and 72 h. These cones were drawn separately to show the extent of the impact of the test at different time periods throughout the test and the degree of anisotropy. Evaluation of the cones of depression, which are in, general circular, indicates little degree of anisotropy and nonhomogeneity. The data further indicate that there is a well-developed fracture system in a particular direction and, there-fore, no preferential flow system.

table 10.2acalculated aquifer parameters, niagara falls

t S v b′ k′

Welltransmissivity

(gpd/ft) Storativityleakance

factor

thickness of leakance zone (ft)

Permeability of leakance zone

gpd/ft2 cm/s

P1 5900 5 × 10–4 0.05 10 0.02 9 × 10–7

P2 2200 2 × 10–4 0.2 10 0.6 3 × 10–5

P8 4500 6 × 10–4 0.15 10 0.1 7 × 10–6

170 4000 1 × 10–4 0.15 10 0.1 6 × 10–6

table 10.2bSummary of pumping test results for top-of-rock wells

t t k S

Well numbertransmissivity

(gpd/ft)transmissivity

(cm2/s)Permeability

(cm/s)coefficient of

storage

88-143-2 1725 2.48 1.63 × 10−2 8.86 × 10−6

PELA 4 2766 3.97 2.60 × 10−2 2.56 × 10−5

DUP-7 4062 5.84 3.83 × 10−2 4.12 × 10−5

PELA 3 2891 4.15 2.72 × 10−2 8.08 × 10−5

PELA-2 2139 3.07 2.01 × 10−2 2.02 × 10−4

86-114-2 1420 2.04 1.34 × 10−2 2.00 × 10−2

PELA 7 1472 2.11 1.38 × 10−2 4.73 × 10−5

402 1744 2.51 1.65 × 10−2 2.44 × 10−4

86-116-2 1637 2.35 1.54 × 10−2 1.80 × 10−4

PW-B 2057 2.96 1.9 × 10−2 —

PELA-1 3085 4.43 2.91 × 10−2 2.96 × 10−4

86-112-2 3630 5.22 3.41 × 10−2 8.31 × 10−8

87-142-2 1445 2.08 1.36 × 10−2 5.91 × 10−5

86-125-2 2084 2.99 1.96 × 10−2 1.70 × 10−4

86-110-2 1866 2.68 1.76 × 10−2 9.80 × 10−5

PELA-5 2198 3.16 2.07 × 10−2 7.32 × 10−5

86-121-2 3913 5.62 3.69 × 10−2 2.37 × 10−5

86-108-2 2487 3.57 2.34 × 10−2 9.79 × 10−5

RB-54i 3145 4.52 2.97 × 10−2 3.91 × 10−4

335 1163 1.67 1.10 × 10−2 1.42 × 10−5

PELA-6 2139 3.07 2.01 × 10−2 1.62 × 10−4

86-123-2 1689 2.43 1.59 × 10−2 6.58 × 10−5


Facts learned from the pumping test included the following:

1. Water levels in the monitoring wells tapping from the top-of-clay zone did not show impact from pumping, which means that there is no measurable hydraulic communication between the top-of-clay and top-of-rock.

2. Water levels in some of the wells tapping the bedrock show drawdown, indicating restricted hydraulic communication between top-of-rock and bedrock.

3. The cone of depression is almost circular showing little degree of anisotropy in a discrete water-bearing zone, the top-of-rock.

4. The configuration of the cone of depression indicates that there is no hydraulic boundary that would be indicative of faulting or the fracturing associated with faulting.

10.2.8 conclusions

Review of technical reports, on-site investigations, and observations made during the drilling and construction of the piezometers and wells, and analyses of the data collected during the step-draw-down and aquifer tests were used to characterize the top-of-rock transmissive zone in the vicinity of the site.

1. The major groundwater bearing zone determined during drilling was a porous interval of solutioning and fracturing in the dolomite occurring 3–5 ft below the top-of-bedrock zone. This interval was penetrated in all the piezometers and wells installed and in nearby exist-ing monitoring wells.

2. The site is underlain by a fractured water-bearing zone, top-of-rock, that comprises a flow system connected hydrologically beneath the site. It is sufficiently homogeneous to be sys-tematically monitored and, if necessary, effectively remediated.

3. The general direction of groundwater flow in the top-of-clay zone is south–southwest. The flow in both the top-of-rock and bedrock zones is south–southeast.

table 10.2cSummary of pumping test results for top-of-bedrock wells

Well numbertransmissivity

(gpd/ft)transmissivity

(cm2/s) Permeability (cm/s)coefficient of

storage

88-143-3 3775 5.42 1.18 × 10−2 2.94 × 10−4

87-110-4 1472 2.12 4.64 × 10−3 1.10 × 10−3

D-18 4336 6.23 1.36 × 10−2 1.52 × 10−3

336 7640 10.98 2.40 × 10−2 2.41 × 10−4

86-123-3 5942 8.54 1.87 × 10−2 5.16 × 10−4

86-110-3 4650 6.68 1.46 × 10−2 3.41 × 10−4

86-142-3 5093 7.32 1.60 × 10−2 2.36 × 10−4

312 8444 12.13 2.65 × 10−2 1.62 × 10−4

87-114-3 3913 5.62 1.23 × 10−2 1.10 × 10−1

86-118-3 6418 9.22 2.02 × 10−2 2.36 × 10−3

400 1371 1.97 4.31 × 10−3 2.48 × 10−4

86-118-3 5014 7.21 1.58 × 10−2 2.21 × 10−3

D-20 4011 5.75 1.26 × 10−2 1.72 × 10−5

400 1371 1.97 4.31 × 10−3 2.48 × 10−4

86-103-3 3414 4.91 1.07 × 10−2 8.80 × 10−4

RB-63-d 9274 13.33 2.91 × 10−2 7.43 × 10−4

Case Studies 241

4. Under nonpumping conditions, a south-southeast trending water level depression is present in the top-of-rock zone, indicating localized groundwater interflow between the top-of-rock and bedrock zones.

5. Barometric pressure changes cause water level fluctuations in the top-of-clay, top-of-rock, and bedrock zones, indicating confinement in all the three zones.

6. The barometric efficiency of the top-of-rock zone appears to be on the order of 25–50%.

DRAWDOWN IN FEETBEDROCK WELL ANDNUMBER

DRAWDOWN DETERMINED FROMTIME-DRAWDOWN CURVE

DRAWDOWN CONTOUR,CONTOUR INTERVAL IS 0.5 FOOTEXCEPT WHERE INDICATED

TOP OF ROCK WELLAND NUMBER

TOP OF CLAY WELLAND NUMBER

EXPLANATION

1.0787-142-3

87-142-2

87-142-1WELL WITH NO OR THINSEDIMENTS

POST CONSENT ORDER WELL

CONSENT ORDER WELL

NOTE: BASE MAP MODIFIED FROM DRAWING SHEET1, 2, AND 3, DEWBERRY AND DAVIS. 1987.

SCALE IN FEET

200 200

N

TO GRAND IS

LAND (B

UFFALO

)0 400600

630

600

600

Dup-3

D-18 D-20

Dup-5 0.24

0.5 1.0 1.50.14Dup-1

600

PELA-286-121-20.54

630

630

PACKARD ROAD

CONFIGURATION OF DRAWDOWN - TOP OF ROCK WELLS AFTER PUMPING FOR 24 HOURS.

630

660

660

630

2.00600

0.02

0.02

86-103-286-103-3

0.01

0.1

600 600

630

600

600

190

190

312 600

–0.41 0.47

3.40

86-114-3

5.58

RB-541

0.12400402401

87-142-387-142-287-142-1

1.52.0

1.01.52.02.53.03.5



7. The hydraulic conductivity of the top-of-rock zone ranges 10−2 to 10−3 cm/s and the bed-rock ranges 10−2 to 10−3 cm/s. The storage coefficient ranges between 10−3 to 10−6 for top-of-rock and 10−2 to 10−5 for bedrock. The vertical hydraulic conductivity between the top-of-rock and bedrock zones is 0.2 gpd/ft2 (5.28 × 10−4 cm/s).

8. Pumping at a rate of 14 gpm from the top-of-rock zone caused drawdown in all directions at a distance in excess of 500 ft away from the test pumping well. Elongation of the cone of depression indicates that this zone is somewhat anisotropic.

CONFIGURATION OF DRAWDOWN–TOP OF ROCK WELLS AFTER PUMPING FOR 72 HOURS.

PACKARD ROAD

TO GRAND IS

LAND (B

UFFALO

)

EXPLANATIONDRAWDOWN CONTOUR,CONTOUR INTERVAL IS 0.5 FOOTEXCEPT WHERE INDICATED


CONSENT ORDER WELLPOST CONSENT ORDER WELL

DRAWDOWN IN FEET

WELL WITH NO OR THINSEDIMENTS

TOP OF ROCK WELLAND NUMBERBEDROCK WELLAND NUMBER


200 200 4000

N

SCALE IN FEET

SCRF NO. 6


pjw

stk|

4020

64|1

4354

3259

6

Case Studies 243

9. Analysis of the aquifer test data indicates localized linear (nonradial) flow conditions in the top-of-rock zone coinciding with the orientation of prominent jointing in the top-of-the Lockport Dolomite zone in the Niagara Falls area. The groundwater conditions in this zone are somewhat anisotropic, but influence of pumping was observed in all directions away from the pumping well. Vertical fracturing contributes to the groundwater conditions as a secondary control to the flow.

10. A groundwater monitoring plan will detect any potential release from the site. The detec-tion monitoring wells are to be properly located along the boundary of the site. If any

CONFIGURATION OF DRAWDOWN–BEDROCK WELLS AFTER PUMPING FOR 24 HOURS.

PACKARD ROAD

TO GRAND IS

LAND (B

UFFALO

)

SCRF NO.6

EXPLANATIONDRAWDOWN CONTOUR,CONTOUR INTERVAL IS 0.5 FOOTEXCEPT WHERE INDICATED


CONSENT ORDER WELLPRE-CONSENT WELLDRAWDOWN IN FEETTOP OF ROCK WELL

AND NUMBERBEDROCK WELLAND NUMBER


200 200 4000

N

SCALE IN FEET



release of contamination occurs, then contamination would be detected. Remedial plans for the site can be prepared and remedial action taken during this period.

11. Based on understanding of the design of the site, there should be no appreciable change in the groundwater flow if the facility is constructed as planned. In the unlikely event of release occurring from the site, the facility could be remediated by implementing a reme-dial plan.

CONSENT ORDER WELL

PRE-CONSENT WELL

DRAWDOWN IN FEET

BEDROCK WELL ANDNUMBER 87-142-3

87-142-20.31

87-142-1

TOP OF ROCK WELLAND NUMBER


EXPLANATIONDRAWDOWN CONTOUR,CONTOUR INTERVAL IS 0.5 FOOTEXCEPT WHERE INDICATEDDRAWDOWN DETERMINED FROMTIME-DRAWDOWN CURVE

CONFIGURATION OF DRAWDOWN- BEDROCK WELLS AFTER PUMPING FOR 72 HOURS.

PACKARD ROAD600

630

630

600

600

630190

190

TO GRAND IS

LAND (B

UFFALO

)

N

200 4002000

SCALE IN FEET

86-103-286-103-3

RB-63i

86-120-2 600

0.

4014024000.41

86-120-3

RB-63d

0.12

600

600

560

660

630

630

600

Dup-3 Dup-1

Dup-7Dup-5

D-18 D-20 PELA-40.19

600

630

600

2.17

86-108-2

L-4

SCRF NO.6

0.14

0.32

0.71 86-118-286-118-3

0.10

NOTE: BASE MAP MODIFIED FROM DRAWING SHEET1, 2, AND 3, DEWBERRY AND DAVIS. 1987.

600

6301.29 329

339 312

327335336

88-143-188-143-288-143-3

87-142-387-142-286-110-4

1.12 86-110-386-110-287-110-1

87-142-10.31


Case Studies 245

The results of geologic and hydrologic investigations characterize this site to be suitable for a haz-ardous waste landfill provided the landfill is properly designed and engineered, including installa-tion of double liner, effective leachate collection, and adequate pre- and postmonitoring systems.

This study illustrates that proper knowledge of geology, structural controls, and hydrogeology is the key and best way to understand groundwater flow regimes and watershed, and select, as well as possible, locations for landfills. The understanding of subsurface geologic conditions further aids to mitigate and/or minimize potential problems, including capturing of leachate by leachate collection systems, postmonitoring, and protecting groundwater resources.

referenceS

1. Tesmer, I. H., Colossal Cataract—The Geologic History of Niagara Falls, State University of New York Press, Albany, 1981.

2. Zenger, D. H., Stratigraphy of the Lockport Formation (Middle Silurian) in New York State, New York State Museum and Sciences Geological Survey, Bulletin 404, 1962.

3. Yager, R. M. and Kappel, W. K., Detection and Characterization of Fractures and Their Relation to Groundwater Movement in the Lockport Dolomite, Niagara County, New York, U.S. Geological Survey Water Resources Division, 1987.

4. Johnston, R. H., Groundwater in the Niagara Falls Area, New York, with Emphasis on the Water-Bearing Characteristics of the Bedrock, New York State Conservation Department, Bulletin GW-53, 1964.

5. Miller, T. S. and Kappel, W. M., Effect of Niagara Power Project on Ground-Water Flow in the Upper Part of the Lockport Dolomite, Niagara Falls Area, New York, U.S. Geological Survey Water Resources Investigations Report 86–4130, 1987.

6. Papadopulos, I. S., Non-steady flow to a well in an infinite anisotropic aquifer, Proceedings of the Dubrovnik Symposium on the Hydrology of Fractured Rock, International Association of Scientific Hydrology, 1965, pp. 21–31.

7. Maslia, M. L. and Randolph, R. B., Methods and Computer Program Documentation for Determining Anisotropic Transmissivity Tensor Comments of Two Dimensional Groundwater Flow, U.S. Geological Survey Open-File Report 86–227, 1986, 64 pp.

8. Lohman, S. W., Ground-Water Hydraulics, U.S. Geological Survey Professional Paper 70B, 1972. 9. Hantush, M. S. and Jacob, C.E., Nonsteady radial flow in an infinite leaky aquifer, American Geophysi-

cal Union Transactions, 36, 1, 1955, pp. 95–100. 10. Hantush, M. S., Modification of the theory of leaky aquifers, Journal of Geophysical Research, 65, 11,

1960, pp. 3713–3725. 11. Cooper, H. H., Jr., Type curves for nonsteady radial flow in an infinite leaky artesian aquifer, In Short-

Cuts and Special Problems in Aquifer Testing, Bentall, R. (Ed.), U.S. Geological Survey Water-Supply Paper 1545–C, 1963, pp. C48–C55.

12. Jenkins, D. N. and Prentice, J. K., Theory for aquifer test analysis in fractured rock under linear (nonra-dial) flow conditions, Ground Water, 20, 1, 1982, pp. 12–21.


10.3 cataStroPHIc SubSIdence: an enVIronmental Hazard, SHelby county, alabama

10.3.1 introduction

The sudden formation of sinkholes, or “catastrophic subsidence,” in recent years has focused atten-tion on a little-understood geologic hazard. Few people realize that thousands of sinkholes have formed in the United States since 1950. Costly damage, some accompanied by injuries and loss of life, has resulted from sudden collapses beneath highways, railroads, bridges, buildings, dams, reservoirs, pipelines, vehicles, and drilling operations. Perhaps one of the most spectacular was the “Golly Hole” collapse on December 2, 1972, in Shelby County, Alabama; another was the surface collapse of part of a city block in Winter Park, Florida, in 1981.

Sinkholes can be separated into categories described as “induced” and “natural.” Induced sink-holes are those caused or accelerated by human activities, whereas natural ones occur in nature. Recognition of induced sinkholes or catastrophic subsidence, the subject of this study, and their investigation have been confined mainly to this century. Almost all the investigations dealing with the triggering mechanisms or processes have been made since 1950.

The purpose of this section is to present mechanisms triggering the development of induced sinkholes resulting from water level declines, identify predictive capabilities relating to sinkhole occurrence, and describe techniques used in a case history of relocating a gas pipeline in a highly vulnerable karst setting.

10.3.2 gEnEral hydrogEologic sEtting

The karst terrain chosen to illustrate catastrophic sinkhole development is Dry Valley, Shelby County, Alabama (Figure 10.30). It is a youthful basin that contains a perennial or near-perennial stream. Water is stored in underlying carbonate rocks and moves through interconnected open-ings along bedding planes, joints, fractures, and faults, some of which are enlarged by solutioning. Recharge from precipitation, in response to gravity, moves downward into this system of openings or toward the stream channel, where it discharges and becomes streamflow. A schematic cross sec-tion illustrating the conditions described is shown in Figure 10.31.

Water in rocks underlying the basin occurs under water table and artesian conditions; how-ever, this study is concerned with water table conditions only. The configuration of the water table conforms to that of the topography, but is also influenced by precipitation, geologic struc-ture, and water withdrawal. Bedrock openings underlying lower parts of the basin are water filled, and those underlying upland areas north of County Highway 16 (see Figure 10.30) are air filled.

A mantle of unconsolidated deposits resulting from the solution of the underlying rocks consists chiefly of residual clay (residuum). This clay commonly contains chert debris and covers most of the bedrock surface. Alluvial or other unconsolidated deposits often overlie the clay adjacent to streams. The contact between residuum and the underlying bedrock is highly irregular because of the differential solution of the bedrock. Unconsolidated deposits commonly fill openings in bedrock to depths of 30 ft or more.

10.3.3 gEology oF thE dry vallEy arEa

Dry Valley is within the Cahaba Valley District of the Valley and Ridge physiographic province, which is characterized by northeast–southwest-trending valleys and ridges. The Cahaba Valley was formed by differential erosion of folded and faulted rock formations composed primarily of chert, limestone, and dolomite (Figure 10.32).

Rock formations in the Dry Valley area outcrop in northeast–southwest-trending parallel bands. The rocks dip to the southeast at 20–60˚ and range in age from Cambrian to Mississippian. From

Case Studies 247

northwest to southeast, the rock formations include the Copper Ridge Dolomite of Cambrian age; the Chepultepec Dolomite, Longview Limestone, Newala Limestone, Lenoir Limestone, and Ath-ens Shale of Ordovician age; the Chattanooga Shale of Devonian age; and the Fort Payne Chert and Floyd Shale of Mississippian age (Figure 10.32).

The Copper Ridge and Chepultepec dolomites form the western boundary of Dry Valley and support a stream-dissected ridge, which is locally more than 100 ft above Dry Creek. The valley of Dry Creek is underlain by the Longview, Newala, and Lenoir Limestones. The Newala is mined from recessed quarries and underground mines in the valley as a source of raw material for the manufacture of cement. The Athens Shale and Fort Payne Chert outcrop in a sinuous, narrow ridge that forms the eastern boundary of the valley.

30

SHELBY COUNTYAIRPORT 2927 26

35

3634

1011

1415

MONTEVALLO

MOORESCROSSROADS

22

23 24

12

5

8

6 4

9

32

103

13Rerouted

SNGpipeline

CALERA

NEWALA

DRY

CREEK

SPRIN

G

7119

25

16

3

31

R 13 ER 12 ET

21S

T22

ST

24N

28 27

333

DARGIN

BRANCH

CAM

P3431

31

32

3

4

5

8

65

22

fIgure 10.30 Location of study area.


A mantle of unconsolidated material consisting of residual clay covers the bedrock in the area, obscuring surface exposures of geologic contacts and faults. This unconsolidated material, or residuum, has resulted from the solution of underlying carbonate rocks. It commonly contains varying amounts of insoluble chert debris. Some of this unconsolidated material fills solutionally enlarged fractures and solution openings in the bedrock underlying the valley floor. Because of dif-ferential solution, pinnacles of bedrock extend in places upward into the residuum, and boulders of “floating” rock occur within the residuum. These can easily be mistaken for the bedrock surface.

10.3.4 WatEr lEvEl dEclinE and catastrophic subsidEncE

Sinkholes resulting from water level declines are not unique to the Dry Valley area. Foose,2 in a study in Pennsylvania, first identified sinkhole activity associated with pumping and a decline in the water table. He determined that these sinkholes were confined to areas in which a drastic lowering of the water table had occurred and that the sinkhole occurrence ceased when the water table recovered. He stated that the shape of the collapses indicated the lowering of the water table and withdrawal of support. Robinson et al.3 added that sinkhole occurrence in a cone of depression was related to the increased velocity of groundwater. Spigner4 attributed intense sinkhole development near Jame-stown, South Carolina, to a water level decline resulting from pumpage and provided descriptions indicating loss of support and downward movement of unconsolidated deposits due to piping. Sin-clair5 attributed similar activity in Florida to loss of support and water level fluctuations.

Cited reports have described only in part the geologic and hydrologic impacts from a decline of the water table that cause the downward migration of unconsolidated material. It is important to understand, that in almost all instances, only the unconsolidated overburden becomes unstable and flows downward causing a collapse or failure, whereas the bedrock remains stable (Figure 10.33). The most common cause of induced subsidence is the decline of the water table as a result of groundwater withdrawal from wells or from underground mines and quarries. This occurred in Dry

Air-filledOpening

Spring

Water-filledOpening

Carbonate Rock

WaterTable

UnconsolidatedDeposits

PerennialStream

fIgure 10.31 Schematic cross section characterizing geologic and hydrologic conditions in a youthful karst terrain.

Case Studies 249

Valley. Similar problems are documented in published reports for other areas of Alabama (Powell and LaMoreaux,7 Newton and Hyde,8 and Newton et al.9), Pennsylvania, Florida, South Africa, Europe, and elsewhere in the karstic areas of the world (Newton10).

The following processes or activities are generally recognized as causing or accelerating subsid-ence following a decline of the water table.

1. The loss of buoyant support exerted by groundwater to unconsolidated materials overlying bedrock. Based on comparative specific gravities, for instance, this support to an unsatu-rated clay overlying a bedrock opening would amount to about 40% of its weight.

2. An increase in the velocity of groundwater movement resulting from an increased hydraulic gradient toward a discharge point. This water velocity results in the flushing of sediments, filling openings in the cavity system, which, in turn, results in the downward movement of overburden into bedrock openings that form a sinkhole.

–Cr

Otv

Oa

–Cbf

–Ccr

–Cbf

–Ck

–Ck –CcrOn Mf

OlOn

Oc

Olv OnOl OaMfp–Cbf–Cr

A

–Cc

–Cc

–Cb

–Cr

–Cb

6 5

8

17

3

16

19

5

46

2063

OnOl

Dc

Dc

On

OaOl

OlOlv

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k Faulf

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line

Mfp

A´

A´

Mfp

7

12

13

23

25

1 0

03000

Vertical Exaggeration 10x

Modified from Butts, 1940.3000

feet

1

Calera

Anticline

mile1/2

24

16 12

R3W R2W

ReroutedSNG Pipeline

Oc

84

Anticline

Fault

Geologic Contact

Tuscaloosa Group

Floyd Shale

Fort Payne Chert

Chattanooga Shale

Athens Shale

Longview Limestone

Chepultepec Dolomite

Copper Ridge Dolomite

Bibb Dolomite

Ketona Dolomite

Brierfield Dolomite

Conasauga Formation

Rome Formation

Odenvile and NewalaLimestones(undifferentiated)

Lenoir and MoshemLimestones(undifferentiated)

Southern NaturalGas Company Pipeline

Kt

Mt

Mfp

Dc

Oa

Ol

On

Oc

–Ccr

Olv

–Cc

Camp Branch Anticline

–Cb

–Ck

fIgure 10.32 Geologic map and cross section of the Dry Valley area (modified from Butts, 1940).1


3. The weakening of unconsolidated bridging materials, the downward erosion of these mate-rials caused by alternate repeated addition and subtraction of buoyant support, and alter-nate wetting, drying, and lubrication brought about by water level fluctuations.

4. Induced recharge to previously water-filled bedrock cavities by infiltrating surface water passing through and eroding overlying unconsolidated material downward. This process, most active during periods of heavy or prolonged rainfall, is the same process described by many authors as piping or subsurface mechanical erosion.

5. Grading, ditching, or other human-related disturbances, which result in thinning of over-burden, or concentrations of drainage at the surface or in the subsurface. These activities induce more water to move more rapidly along preferential flow patterns through soils or overburden and into bedrock. Triggering mechanisms are piping, saturation, and loading.

B. Vertical and lateral enlargement and resulting collapse.

A. Vertical enlargement and resulting collapse.

EXPLANATION

Unconsolidated depositsWater-filled opening

in limestoneDirection of water movementLimestone

Boundary designatingcavity growth

WTP - Water table prior to declineWTA - Water table after decline

WTP

WTA

WTA

WTP

WTA

WTPWTP

WTA

fIgure 10.33 Development of induced sinkholes (modified from Newton, 1976).6

Case Studies 251

Other examples include leaking pools, pipes, gutters, irrigation, and broken lined canals or ditches. Collapses resulting from leakage from underground pipes are well documented in the literature. Such a collapse in a gold mining district in South Africa resulted in the loss of a three-story building and the lives of 29 men.

6. Heavy construction, traffic, or explosives that disturb the soil or overburden and trigger its downward movement into solution openings in bedrock.

7. Removal of vegetation or the planting of large, deep-rooted trees that increases recharge by creating avenues for more rapid movement of water from the land surface through soils and overburden to bedrock.

8. Drilling, augering, or coring by which surface water gains access to uncased or unsealed holes. These activities cause erosion of overburden into underlying openings in bedrock, which result in collapses at and near the drill rigs or holes created.

9. Impounding of water results in saturation of overburden and loss of cohesiveness of uncon-solidated deposits overlying bedrock openings. This, accompanied by loading caused by the weight of impounded water, results in the collapse of unconsolidated material into a bedrock opening. Similar collapses beneath impoundments are also caused by piping. This occurs where the water table has declined below the top of bedrock and where openings at the surface are interconnected with those in the bedrock. Collapses resulting from satura-tion and loading have been described by Aley et al.,11 and those resulting from saturation and piping have been described by Warren.12 Collapses resulting in draining of impound-ments in cones of depression are not uncommon.

10.3.5 hydrology oF dry vallEy

Present conditions

Hydrologic conditions in Dry Valley are characterized by a water table that has been lowered by extensive groundwater withdrawals by mines and wells. The approximate decline has been illus-trated by Warren.13 Natural surface water drainage patterns in the Dry Creek area have been exten-sively modified by road construction and mining operations. Dry Creek is now intermittent north of Shelby County Highway 16 all year because of the small drainage area and rapid downward infiltration of water from the main channel to the lowered water table in the bedrock. A tributary of Dry Creek, originating from Simpson Spring and an impoundment on the Floyd Shale east of the rerouted pipeline (Figure 10.32) has appreciable flow over the shale during the “dry season.” How-ever, this flow disappears into induced sinkholes near the contact between the Athens Shale and Lenoir Limestone. This water, and that from the upper reach of Dry Creek Valley, move southward in the subsurface to a mine, where it is pumped back into a downstream reach of Dry Creek. It then flows southwestward to Spring Creek (see Figure 10.30).

Discharge measurements made by the U.S. Geological Survey in October 1973 (low-flow period) indicated the runoff from Simpson Spring and the impoundment at 0.07 cubic feet per sec-ond (cfs). A discharge measurement made downstream by the U.S. Geological Survey at Dry Creek on Shelby County Highway 23 (see Figure 10.30) in October 1973 indicated that the discharge was about 32 cfs. At the time of this measurement, Dry Creek north of Highway 16 was dry.13 There-fore, all natural runoff originating in the Dry Valley drainage basin did not flow through this part of the basin as surface water. Stream flow in the area immediately north and south of Highway 16 discharges directly into sinkholes. For example, runoff from the Simpson Spring tributary of approximately 5 cfs on March 4, 1977, was discharging into a recent collapse near County High-way 16 in the SE 1/4 NW 1/4, s. 18, T. 22 S., R. 2 W. On April 3, 1977, a runoff of about 6 cfs was observed to be flowing into a second collapse farther upstream (Figure 10.34).

Surface water discharging into sinkholes in the area enters the solution cavity system in the underlying carbonate rocks and, from this part of the karst system, is pumped by dewatering wells


into a downstream reach of Dry Creek that is south of Highway 16. Groundwater withdrawals in October 1973 amounted to about 14,000 gpm or about 32 cfs.13 This is approximately the same dis-charge measured in Dry Creek at Shelby County Highway 23 during the same period.

Water table decline in the area is the result of extensive groundwater pumping from wells, recessed quarries, and underground mines. Water level at the center of the cone of depression is more than 400 ft below land surface. The center of the cone of depression corresponds closely with the location of the deepest underground mine in the area (Figures 10.35 and 10.36).

A schematic cross section of a cone of depression (Figure 10.37) superimposed on a youthful terrain (Figure 10.31) illustrates the downward migration of unconsolidated deposits, the creation of cavities in overburden, and “catastrophic sinkhole” development. The creation of a cone of depres-sion in an area of large water withdrawal results in the loss of buoyant support to overburden and an increased hydraulic gradient toward the point of discharge. Both can cause sinkhole development. The increased gradient results in increased velocity of groundwater movement. Erosion caused by this movement of water through a system of openings such as joints, fractures, faults, or solution cavities, partly filled with clay or other unconsolidated sediments, results in the creation of cavities that enlarge toward the surface and eventually collapse (Figures 10.33 and 10.37).

Variations in pumpage and recharge result in water level fluctuations far greater in magnitude than those occurring under natural conditions. The repeated movement of water through openings in bedrock against overlying unconsolidated deposits causes repeated addition and subtraction of buoyant support to them and repeated saturation and drying. This triggers the downward migration of the deposits that creates or enlarges cavities in the overburden (Figure 10.33).

The inducement of recharge through openings in unconsolidated deposits interconnected with openings in bedrock also results in the creation of cavities in the unconsolidated deposits. The material immediately overlying the bedrock openings is eroded to lower elevations. The water table, previously located above the top-of-bedrock zone (Figure 10.31), is no longer in a position to dissipate the mechani-cal energy of the downward moving recharge. Repeated rains result in the progressive enlargement of this type of cavity. A corresponding thinning of the cavity roof due to its enlargement toward the surface eventually results in collapse. The position of the water table below the unconsolidated deposits and openings on the top of bedrock favorable to induced recharge is illustrated in Figure 10.37. The creation and eventual collapse of cavities in the deposits by induced recharge is described as piping.

Where the cone of depression is maintained by constant pumpage, all mechanisms described are active. Any one or all mechanisms may be responsible for the development of a collapse at a specific site. For example, in an area near the outer margin of the cone, the creation of a cav-

fIgure 10.34 Stream discharging into sinkhole on April 3, 1977.

Case Studies 253

16

450

400

350

250

450

300

200

300

350450

400

200

150

350

400 100

R3W R2W

T22ST24N

12

84

EXPLANATION

Contour of top of watertable, Oct. 1973 (Datumis mean sea level.Contour interval = 50 feet)

Southern natural gascompany pipeline

Approximate limits ofquarry operations

Line of cross-sections

Approximate location ofunderground mine (1971)

23

B

B´

1 003000 3000 feet

1 mile1/2

63

A

A

A´

A´

25

16

12

1

7 8

17N

13 1814

24

6 5 4 3

19 2023

6 52

11

fIgure 10.35 Water table map of the Dry Valley area.

State Hwy 25A600

400

200

–200

600

400

200

Elev

atio

n (fe

et)

Elev

atio

n (fe

et)

MSL

MSL

Co. Hwy 23

Water table

SNG PipelineCo. Hwy 16

Land surface

Approximate limits ofunderground mine (1971)

(Oct. 1973)

A´

B´B´

State Hwy 25

Land surface

Water table (Oct. 1973)

Approximate limits of underground mine (1971)

SNG PipelineCo. Hwy 23

Vertical exaggeration 10%

3000 3000 feet0

00.51 1 mile

Horizontal scale

fIgure 10.36 Hydrologic cross sections of the Dry Valley area.


ity and its collapse can result from all mechanisms. It can originate from a loss of support, can be enlarged by water level fluctuations, can be enlarged by increased velocity of water move-ment against sediment that originally filled the openings, and can be enlarged and collapsed by induced recharge.

Many induced sinkholes in Dry Valley are near the center of the cone of depression, and their locations are controlled by the decline in the water table. The number of sinkholes and related features such as “pipes” or fractures has increased since 1967. The number to date is estimated to exceed 2000.

10.3.6 usE oF rEmotE sEnsing mEthods

A broad definition of remote sensing includes all methods of collecting information about an object without being in physical contact with it. If a more restrictive definition is used, it could include only those methods that employ electromagnetic energy, including light, heat, and radio waves, as a means of detecting and measuring target characteristics.14 The major types of remote sensing used in carbonate hydrology are aerial photography, satellite imagery, thermography, and radar. Remote sensing techniques or surveys used on the land surface include sonar down-hole geophysical logging and television cameras, and seismic resistivity, gravity, and magnetic radar.15

Satellite Imagery

The determination of the optimum satellite imagery or remote sensing band or band ratios (i.e., range of detected wavelengths) and the type of other remote sensing techniques to be employed depend on the objectives of the study and the features that are sought to be enhanced. This optimum band or band ratio selection can be done by statistical methods (which generally require the use of a computer) or by manual techniques such as the coincident spectral plot methods described by Shourong.16 This method was used to map regional and site-specific geologic features and linea-

Water-filledOpening

Carbonate Rock

Water Table

Air-filledOpening

UnconsolidatedDeposits

PumpDischarge

CementPlug

fIgure 10.37 Schematic cross section showing changes in geologic and hydrologic conditions resulting from groundwater withdrawal in a youthful karst terrain.

Case Studies 255

ments. These results, in turn, were integrated with findings obtained from aerial photography. They were then used to interpret regional and local geology and geologic structures; this provided an understanding of subsurface karstification trends and preferential flow paths (Figure 10.38). Similar investigations have been made in Alabama by Powell et al.17 and elsewhere.

aerial Photography

Sequential high- and low-altitude color infrared and black-and-white aerial photographs were obtained and analyzed to determine drainage patterns and geomorphic trends and to define lin-eaments. Other information on soil, vegetation, and rock outcrops was defined. The photographs were also used to locate and monitor induced sinkholes and to define trends in their develop-ment. This information was used to interpret the regional and local geologic structure and to identify potential preferential groundwater flow patterns. Findings and data were then integrated with those from the satellite imagery studies (Figure 10.38). Similar work utilizing photography has been accomplished in Alabama by Newton et al.,9 in Pennsylvania by Lattman and Parizek,18 and elsewhere.

Landsat Black and White Infrared

U-2 Color Infrared

Low Level Black and White Scale In Feet

2000 0 2000 4000

Black and White LineamentTrend South End of Valley

S

E

N

W

Black and White LineamentTrend North End of Valley

S

E

N

W

19

8

Dry Cree

k

16

1212

7

Sprin

g Cree

k

24

N

fIgure 10.38 Lineaments interpreted from aerial photographs.


Seismic Survey

Seismic refraction profiling was selected to provide a rapid and accurate definition of the bed-rock surface trends and depths, and the thickness of unconsolidated material overlying the bedrock (Figure 10.39).

A total of 130 seismic profiles were completed from May 17 to July 21, 1977, along the exist-ing pipeline route and along possible alternate routes. After the final pipeline route was selected,

Chep

ulte

pec

dolo

mite

Long

view

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ne

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ale

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ulte

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olom

ite

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ock

surfa

ce

New

ala l

imes

tone

Long

view

limes

tone

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line

SPRING

New

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fIgure 10.39 Geologic map and cross section, Shelby County, Highway 16.

Case Studies 257

an additional 47 seismic profiles were completed between August 22 and August 30, 1977, to obtain greater detail. An additional 10 profiles were completed along Shelby County Highway 16 in response to a request from the County Highway Department to identify areas of potential future subsidence for highway planning purposes.

10.3.7 tEst drilling

To verify and provide increased definition of the bedrock surface, 29 holes were augered in the study area on June 7 and 8, 1977, and an additional 48 holes were augered between September 12 and 15, 1977. A Central Mine Equipment Model 55 rig equipped with 4-in. auger flights was used to deter-mine the depth to bedrock. All holes were augered to refusal. Samples of cuttings were described and geologic logs were prepared and correlated with the geophysical data to define the top of the bedrock and overburden thickness along Alternate Route 1 and County Highway 16 (Figure 10.39).

10.3.8 invEntory and monitoring oF subsidEncE

Catastrophic sinkholes within the study area were mapped using aerial photography and field investigation by LaMoreaux and Associates.19 The area was field inspected on a monthly basis to detect subsidence occurrence and growth. Over 100 new subsidence features were identified and described. During dry weather and relatively stable hydrologic conditions, the land surface was sta-ble. After prolonged dry periods followed by rainfall, a substantial increase in subsidence occurred. For example, during a monitor run on February 13, 1980, there were 13 active subsidence features. Rains preceding this inspection followed a dry period from October to December 1979.

Low-level black-and-white infrared and color photography was used to identify points of proba-ble subsidence correctly. The criteria used included changes in drainage patterns, ponding of water, vegetation stress, lineament and geologic structural features, and construction activity. One such collapse was predicted and observed as it happened.

Monthly monitoring findings were plotted on a base map showing Shelby County Highway 16, the existing Southern Natural Gas pipeline, and Alternate Route 1 across Dry Creek Valley. These monthly maps were used to determine the pattern, size, and trend of the subsidence features with respect to geo-logic and dynamic hydrologic conditions that, in turn, provided a basis for the choice of the location for an alternate pipeline route.

10.3.9 prEdiction oF inducEd sinkholEs

Induced sinkholes are predictable in the context that they will occur within the area impacted by activities such as dewatering. Also predictable, in some instances, are their alignment with other sinkholes and their shape, size, and depth. Predictive capabilities would be most significant in the type of terrain described in this article and would be dependent on the amount of geologic and hydrologic data available.

The most predictable induced sinkhole development is that which results from water level declines due to dewatering by subsurface mines, recessed quarries, and wells. This occurs where the water level, previously above the top of bedrock during all or most of the year (Figure 10.31), is maintained below it by pumping (Figure 10.37). All mechanisms that trigger sinkhole development in unconsolidated deposits are activated by the decline.

Conversely, the unconsolidated deposits are not impacted and sinkholes will not occur in the zone where the water level fluctuations are located below the top of the bedrock prior to dewatering. Determining the position of the water table in relation to the top of the bedrock aids in predicting whether sinkholes will or will not occur at a given site.

Where and when will sinkholes occur in a dewatered area is also predictable to a limited degree. Many occur where concentrations of surface water are greatest, such as streambeds, natural drains, or poorly drained areas. Large numbers occur where natural drainage has been altered and where


natural recharge has been increased as a result of activities such as ditching and timber removal. Most of the sinkhole activity occurs during or immediately after rains, especially deluges, when hydrologic stresses to overburden are greatest.

Prediction of size, shape, and depth is based on a knowledge of the character of the bedrock; the extent, orientation, and size of the solution features; the thickness and stability of the overburden; and the mechanisms triggering overburden erosion. Induced recharge in an area prone to flooding, for instance, would assure maximum subsurface erosion of overburden.

10.3.10 southErn natural gas pipElinE: a casE history

Active subsidence (catastrophic collapse) in Dry Valley had presented a danger to highways, rail-road, buried telephone cables, personal property, farm animals, and oil and gas pipelines, includ-ing the Southern Natural Gas 10-in. Bessemer-to-Calera pipeline. Many collapses had occurred along the pipeline’s right-of-way. Some collapses directly underneath the pipeline had exposed it (Figure 10.40).

Geologic, geophysical, and hydrologic surveys along the pipeline identified the areas where sinkholes could occur. Extensive collapse sinkholes could result from a combination of factors, including groundwater withdrawal, modification of surface drainage, construction activities, and heavy and prolonged rain. Catastrophic collapse in the area will continue indefinitely until these conditions change. Therefore, an alternative pipeline route had to be chosen to anchor the pipeline to the bedrock with anchor points not more than 20 ft apart because of the strength of the pipe.

fIgure 10.40 Collapse exposing pipeline.

Case Studies 259

Determining the geographic distribution, frequency, and probability of catastrophic sinkhole occur-rence was accomplished as follows:

1. Preparation of a detailed map of the geology and structure along the pipeline in the critical areas of subsidence (Figure 10.39).

2. Mapping of exposures of bedrock limestone in quarries, road cuts, and sinkholes to deter-mine the dip and strike of bedding and joints and fault trends to relate to preferential solu-tion zones and groundwater flow patterns.

3. Acquisition and analysis of satellite imagery and high- and low-altitude aerial photog-raphy (black-and-white, black-and-white infrared, color infrared, and color). The result-ing regional and local geological structural trends, lineaments, and sinkhole and drainage alignments were studied to project preferential groundwater flow patterns and solution zones in bedrock limestone (Figure 10.38).

4. Use of seismic geophysical studies and test drilling to define the top of the bedrock and overburden thickness along the alternate pipeline route (Figure 10.39).

5. Determination of the geology along the new pipeline route before construction (which was ver-ified during its construction to ensure that the pipeline was securely connected to bedrock).

6. Monitoring of sinkhole-subsidence occurrence on a monthly basis over a period of 38 months. Each month, photographs from an overflight were analyzed and located subsid-ence features were checked in the field and documented.

Based on the various studies, two alternate pipeline routes were delineated that would reduce the danger from catastrophic subsidence beneath the pipeline. Alternate Route 1, the final route chosen, was the best and most direct route across Dry Valley. It followed shallower bedrock; had less over-burden thickness, fewer sinkholes, and undisturbed drainage; and crossed an area underlain by less limestone and a larger area underlain by Athens Shale (Figure 10.39).

Construction of the new pipeline route involved opening the ditch line twice. The ditch was first dug to remove all bedrock float and pinnacles. The ditch was backfilled and dressed at the end of each day to prevent rainfall and surface runoff from entering. During excavation, it was noted that bedrock was shallower and pinnacles were more frequent beneath Dry Valley than previously iden-tified. Construction was redesigned to obtain maximum bedrock support for the pipeline.

The ditch was then reopened to lay the pipes. Fractured bedrock zones were grouted wherever necessary. Supports of steel piling driven to the bedrock with a crossbar were erected in areas of deep unconsolidated overburden and large solution features. A steel casing was placed beneath a railroad and Shelby County Highway 16 to protect the pipeline from excessive weight. These sup-ports were tied directly to the bedrock.

The new pipeline was cleaned, tested, and tied into the old pipeline. Valves were placed on both the old and the new pipelines so that the old line could be reactivated if necessary. The original pipeline across Dry Valley was purged with nitrogen.

Tree roots and logs were removed from the overburden, and a clay lining was placed in high subsidence-risk areas adjacent to the pipeline to prevent downward migration of water into the ditch. After the pipe was laid, the ditch was backfilled, and a clay crown was spread over it. The right-of-way was then graded and restored to the approximate original land surface. It was then properly ter-raced to control surface drainage and seeded with grass, and all fences previously crossing it were replaced. Natural drainage was left unobstructed.

Subsequently, the right-of-way has been monitored through a period of rains during which cata-strophic subsidence could be expected. No subsidence has been recorded to date along the right-of-way, and the area is now completely reclaimed and vegetation recovered.


referenceS

1. Butts, C., Description of the Montevallo and Columbiana Quadrangles (Alabama), U.S. Geological Sur-vey Atlas Folio 226, 1940.

2. Foose, R. M., Ground water behavior in the Hershey Valley, Pennsylvania, Geological Society of Amer-ica Bulletin, 64, 1953, pp. 623–645.

3. Robinson, W. H., Ivey, J. B., and Billingsley, G. A., Water supply of the Birmingham area, Alabama, U.S. Geological Survey Circular, 254, 1953, 53 pp.

4. Spigner, B. C., Land Surface Collapse and Ground-Water Problems in the Jamestown Area, Berkley County, South Carolina: South Carolina Water Resources Commission Open-File Report No. 78–1, 1978, 99 pp.

5. Sinclair, W. C., Sinkhole Development Resulting from Ground-Water Withdrawal in the Tampa Area, Florida, U.S. Geological Survey Water Resources Investigations 81–50, 1982, 19 pp.

6. Newton, J. G., Early Detection and Correction of Sinkhole Problems in Alabama, with a Preliminary Evaluation of Remote Sensing Applications, Alabama Highway Department, Bureau Research and Development, Research Report No. HPR–76, 1976, 83 pp.

7. Powell, W. J. and LaMoreaux, P. E., A problem of subsidence in a limestone terrain at Columbiana, Alabama, Alabama Geological Survey Circular, 56, 1960, 30 pp.

8. Newton, J. G. and Hyde, L. W., Sinkhole problem in and near Roberts Industrial Subdivision, Birming-ham, Alabama—A reconnaissance, Alabama Geological Survey Circular, 68, 1971, 42 pp.

9. Newton, J. G., Copeland, C. W., and Scarbrough, L. W., Sinkhole problem along proposed route of Interstate 459 near Greenwood, Alabama, Alabama Geological Survey Circular, 83, 1973, 53 pp.

10. Newton, J. G., Natural and induced sinkhole development—Eastern United States, International Asso-ciation of Hydrological Sciences Proceedings, Third International Symposium on Land Subsidence, Venice, Italy, 1984.

11. Aley, T. J., Williams, J. H., and Masselo, J. W., Groundwater contamination and sinkhole collapse induced by leaky impoundments in soluble rock terrance, Missouri Geological Survey and Water Resources Engineering Geology Series, 5, 1972, 32 pp.

12. Warren, W. M., Retention basin failures in carbonate terranes, Water Research Bulletin, 10, 1, 1974, pp. 22–31. 13. Warren, W. M., Sinkhole occurrences in western Shelby County, Alabama, Alabama Geological Survey

Circular, 101, 1976, 45 pp. 14. Sabins, F. F., Jr., Remote Sensing, Freeman, W. H., San Francisco, 1978, 426 pp. 15. LaMoreaux, P. E., Wilson, B. M., and Memon, B. A., Eds., Guide to the Hydrology of Carbonate Rocks,

UNESCO, 1984, 354 pp. 16. Shourong, S., The coincident spectral plot method for selecting the remote sensing bands of carbonate

rocks, Carsologica Sinica, 1, 2, 1982, pp. 158–166. 17. Powell, W. J., Copeland, C. W., and Drahovzal, J. A., Delineation of linear features and application to

reservoir engineering using Apollo 9 multispectral photography, Alabama Geological Survey Informa-tion Series, 41, 1970, 37 pp.

18. Lattman, L. H. and Parizek, R. R., Relationship between fracture traces and the occurrence of ground water in carbonate rocks, Journal of Hydrology, 2, 1964, pp. 73–91.

19. LaMoreaux, P. E. and Associates, Inc., Unpublished reports to the Southern Natural Gas Company, Tuscaloosa, Alabama, 1982.

20. Remote-sensing techniques and the detection of karst, in Bulletin of the Association of Engineering Geologists, XVI, 3, 1979, pp. 383–392.

21. Environmental aspects of the development of Figeh Spring, Damascus, Syria, in Proceedings of the Third Multidisciplinary Conference on Sinkholes and the Engineering and Environmental Impacts of Sinkholes and Karst, St. Petersburg Beach, Florida, Oct. 2–4, 1989; Beck, F. F., (Ed.), Balkema, A. A., Rotterdam, The Netherlands, pp. 17–23.

22. Environmental planning for karst areas, in Proceedings of the International Symposium and Field Semi-nar on Hydrogeologic Processes in Karst Terranes (abs.), UKAM, Antalya, Turkey, in preparation, 1990.

23. LaMoreaux, P. E., Assaad, F. A., and McCarley, A. E., (Eds.), Annotated Bibliography of Carbonate Rocks, Vol. V, Karst Commission IAH, Verlag, Heinz, Heise, Hannover, Germany, Vol. 14, 1993, 425 pp.

24. LaMoreaux, P. E. and Newton, J. G., Catastrophic subsidence: An environmental hazard, Shelby County, Alabama, In Environmental Geology and Water Sciences, Vol. 8, No. 1/2, Springer-Verlag, New York, 1986, pp. 25–40.

25. LaMoreaux, P. E., Wilson, B. M., and Memon, B. A., (Eds.), Guide to the Hydrology of Carbonate Rocks, United Nations Educational, Scientific and Cultural Organization 7, place de Fontenoy, 75700 Paris, 1984, 345 pp.

Case Studies 261

10.4 enVIronmental Hydrogeology of fIgeH SPrIng, damaScuS, SyrIa

10.4.1 introduction

A hydrogeological assessment and a stress pumping test at Figeh Spring were performed to deter-mine groundwater flow paths; recharge, storage, and discharge characteristics; and the maximum reliable yield. The project was designed to augment low-season flows from the spring and to supple-ment the water supply for the city of Damascus, Syria. The evaluation was directed toward install-ing permanent pumping facilities at the spring (Figure 10.41). Work included a detailed analysis of published literature on the geology and hydrology of the area, as well as a review of data from the files of Figeh.

Before any modification to the spring could be made, it was necessary to understand, in detail, the recharge, storage, and discharge, as well as the preferential groundwater flow patterns in the karst limestone system. Evaluation included studies of satellite imagery, sequential aerial photog-raphy, geomorphology, stratigraphy, and geologic structure (folding, faulting, and jointing). The studies were performed to determine the relationships among geologic control, karstification, pref-erential groundwater flow patterns, and storage characteristics of the aquifer system.

Interpretation of remote-sensed data, including satellite imagery and high- and low-level air photography, was verified by field studies. Geologic and geomorphic parameters controlling dis-charge and preferential flow were described. A well and spring inventory, streamflow measure-ments, and sequential sampling and analyses of surface- and groundwater provided water quality parameters, which were correlated with natural geologic phenomena and stress pumping from wells and springs. The final phase of work included a series of synchronized pumping tests at Figeh Spring, Side Spring, Ain Harouch, and the PELA test wells (Figure 10.42).

10.4.2 gEomorphology

The geomorphology of the recharge area is the result of Jurassic to recent deposition, tectonics, and vulcanism. Sporadic uplift along with compressive folding and faulting at shallow depths has resulted in a variety of surface forms and geologic structures in the Anti-Lebanon range in the area of Figeh Spring. Dominant ridges of the area are anticlines, questas, or hogbacks, which have resulted from folding and/or faulting. Major wadis (valleys) follow synclinal structures, occur as strike valleys parallel to hogbacks, or are the result of Pleistocene erosion along normal faults of significant displacement. Immediately north of the Barada River near Deir Qanoun, even minor anticlines form ridges, and small wadis follow synclinal axes. Structural features in the recharge area can easily be recognized on aerial photographs and in the field.

Synclinal valleys often contain the trunk of consequent trellis drainage. Wadis of the trellis system most frequently follow transverse fractures, which are either perpendicular to or across fold axes at angles of 30–40°. The fractures can be easily observed on a drainage map of the Zebdani quadrangle and depicted on rose diagrams of the Arrsal quadrangle. In the Zebdani quadrangle, east–west trending normal faults become the loci of major wadis with consequent tributaries that are controlled by minor fractures, which have prevailing north-to-northwest trends. Reverse faults appear to have remained tight during landscape development.

Paleokarst features had their origin along bedding planes in the Cenomanian and Turonian lime-stone during Paleocene and Eocene at a time of major structural movement. During Pliocene and Pleistocene, major changes in groundwater base level occurred and karstification was accentuated.

Paleokarst features have been preserved since Pleistocene and are abundant. However, of major significance to the Figeh karst system is the presence of extensive solution cavity systems and caves in the Turonian limestone and dolomite, as well as collapse features in the Senonian strata, which have been buried by Pleistocene alluvial deposits of the Barada River. The most significant karst

pjw

stk|

4020

64|1

4354

3261

7


feature of the area is the cave, which serves as the conduit for discharge of groundwater at Ain Figeh. The cave was formed by groundwater discharge that rises subparallel to the Khadra anticlinal axis in Turonian dolomite. The cave floor is underlain by as much as 70 m of breccia, which indicates that the cave has migrated upward through the dolomite by a process of roof collapse. Continuation of cave evolution, through roof collapse, will provide changes in position of the discharge point of Ain Figeh with time. For this reason, any construction or development of the spring must be care-fully planned and carried out with extreme caution.

CYPRUS

NABK

MEDITERRANEANSEA

BEIRUT

ZEBDANI

DAMASCUS

20 15 10 10 20

N

5 0

KILOMETERSAREA OF RECHARGEFOR FIGEH SPRING

U.S.S.R.BLACK SEA

TURKEY

CRETE

MEDITERRANEANSEA

CASPIAN SEA

LEBANON

SYRIABEKKA VALLEY N41

3

EM1

EM5

N11

3

N110

ANTI-LEBANON BARGE

LEBA

NON RA

NGE

ME7

ME2ME2

ME7 EM5

FIGEHSPRING

BLOUDANTAKEYE

BARADA

RIVER

IRAN

ISRAEL

JORDAN

SAUDIARABIA

EGYPT

KUWAIT

PERSIAN GULFKILOMETERS

RED SEA

NILE

0 500

IRAQ

EUPHRATES

SYRIALEBANON

TIGRIS

50°40°30°

30°

40°

fIgure 10.41 Regional location map.

Case Studies 263

10.4.3 gEology: stratigraphic sEquEncE

cretaceous System

Essentially all exposed rock units in the area of recharge for Figeh Springs belong to the Cretaceous System and include important aquifers and aquicludes (Figures 10.43 and 10.44). The most com-plete and continuous section of these Cretaceous rocks, more than 1800 m thick, is exposed between Bloudan and Wadi Hubeidi (Figures 10.45 and 10.46).

The Cretaceous system was subdivided and described by Dubertret.1 Later work under Pon-ikarov2 provided extensive information about the Cretaceous system, but resulted in only minor modification to the stratigraphy. The present study included interpretation of aerial photographs and field mapping to verify the distribution of lithostratigraphic units of the Cretaceous System (Figure 10.45).

Dubertret1 distinguished the lower and upper Cretaceous series and divided them into stages as follows:

Lower Cretaceous seriesPre-Upper AptianUpper Aptian stageAlbian stage

Upper Cretaceous seriesCenomanian stageTuronian stageSenonian subseries

Y 60 350

Y 60 400

Y 60 450

Y 60 500

Y 60 550

Y 60 600

Y 60 650

Y 60 700

Y 60 750

Y 60 800

N

Y 60 850METERS

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EXISTING WELLSCALE IN METERS0 1000 2000

WELL WITH RECORDER

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F-2PL-4

F-1

F-4

AFREE

F-3X-7

PL-3

G-2

fIgure 10.42 Ain Figeh location map—Ain Figeh wells and springs.


Maastrichtian stageCampanian stageSantonian stageConiacian stage

lower cretaceous Series

Pre-Upper AptianPre-Upper Aptian rocks unconformably overlie rocks of the Tithonian (Jurassic) age. They consist of a basal, cross-bedded, quartz sandstone with ferruginous cement, with a basal conglomerate being present locally. The sandstone is coarse to medium grained and attains a total thickness of about 50 m, and basalt flows locally overlie the basal sandstone. Where present, the basalt may be as thick as 120 m. The upper part of the pre-Upper Aptian unit is composed of argillaceous sand-stone, clays, lignites, and sandy clays. The maximum thickness of pre-Upper Aptian rocks in the Figeh recharge area is about 200 m; however, the thickness of the unit is variable, depending on the thickness of the basalt. These rocks are not resistant to weathering and are exposed on lower slopes or in valleys. Springs may be associated with the lower sandstone. Clay beds near the top of the pre-Upper Aptian sequence act as the lower confining unit for the overlying Cretaceous aquifers and the Figeh karst system.

Upper Aptian StageThe upper part of the Upper Aptian strata consists of ferruginous, quartz sandstones that have a total thickness of up to 100 m. The sandstones are similar to those of the pre-Upper Aptian strata.

Rocks of the Upper Aptian stage conformably overlie the pre-Upper Aptian strata and are divided into two distinct lithologic units. A basal unit consists of about 50 m of well-cemented, yellowish-white, compact limestone and marl. The limestones are light gray, fossiliferous, lumpy

PLIESTOCENE-RECENT

EOCENE-PLIOCENE SENONIAN SYNCLINE

ANTICLINE FAULTSSCALE IN METERS

1000 1000 20000TURONIAN

fIgure 10.43 Significant geologic features along the Barada River.

Case Studies 265

grain stones, and contain about 50% clay. The limestone forms cliffs, which are easily identified (“la muraille de Blance” of Dubertret). Solution pits, karren, and karst features are present. These limestone beds are intensely fractured; springs may occur near the base of the unit.

AlbianLimestones, argillaceous limestones, and marls conformably overlie the Upper Aptian sandstones. Limestones have a characteristic yellowish-green color and lumpy structure. They are fossiliferous and oolitic, and are interbedded with argillaceous limestones. The argillaceous limestones are thin bedded and platey, and may contain marls. The Albian strata have a total thickness of about 120 m in the recharge area. They are compact and indurated and have primary and secondary porosity. In outcrop, they are a source of recharge for water and do not appear to be aquicludes. Albian strata have not been tested by drilling or by pumping tests in the Figeh area.

upper cretaceous Series

The Upper Cretaceous series includes the Cenomanian, Turonian, and Senonian strata, with an aggregate thickness of about 1000 m.

PLIOCENE

EOCENEPALEOCENE

SENONIAN

TURONIAN

CENOMANIAN

ALBIANUPPERAPTIAN

PRE-UPPERAPTIAN

TITHONIAN

LIMESTONE

DOLOMITE

BASALT

SANDY CLAY

CROSS-BEDDEDSANDSTONEMARL

CONGLOMERATECONFORMABLE CONTACTUNCONFORMABLE CONTACT

JURA

SSIC

CRE

TAC

EOU

STE

RTIA

RY

MAXIMUMTHICKNESSIN METERS

250

250

80

600

120

10050

50

80120

fIgure 10.44 Geologic column of the recharge area for Figeh Spring.


Cenomanian StageRocks of the Cenomanian age conformably overlie the Albian strata and are the most extensively exposed strata in the recharge basin. A rhythmically alternating sequence of rocks characterize the Cenomanian strata, and lithologies include massive compact limestone at the base; gray, fos-siliferous limestone; platey, argillaceous limestone and yellowish lumpy marl; and marls at the top. Alternating sequences typically contain two or more of the lithologic units and may include layers of dolomite limestone.

The maximum thickness of the Cenomanian strata is about 600 m. The unit thins to about 400 m near the crest of the Hassiya Anticline. Closely spaced fractures are present in the Cenomanian strata

TertiaryCretaceous

TQl

Ks SenonianKt TuronianKcm CenomanianKal Albian

QuaternaryHORIZ. 1:42, 500

Ks

TQl

KtKsKcm

Kal

--

K----

-

Elev

atio

n (m

eter

s)

NW

Kcm

Kcm

1800160014001200

Kal

KtKs Kt Kt

?

WA

DI

HU

RAIR

E

WA

DI E

L IM

AN

E

WA

DI A

BOU

FIG

EH S

PRIN

GS

BARA

DA

RIV

ER

SALE

M

ASEA´

fIgure 10.45 Geologic cross section A–A .

TertiaryCretaceous

T

Ks SenonianKt TuronianKcm CenomanianKal Albian

HORIZ. 1:42, 500

KsKt

T

Kt KsKs

KcmKcm

Kal

Kal

-K-

---

-

Elev

atio

n (m

eter

s)

NE

Kal

Kcm180019002000

170016001500 Kal

KsBASALT ?

Kt

BLO

UD

AN

JABE

L A

IN A

NSO

UR

JABE

L EL

HA

SSIY

A

WA

DI H

URA

IRE

WA

DI E

D D

ICH

ARE

HA

LBO

UN

BSEB´

fIgure 10.46 Geologic cross section B–B .

Case Studies 267

throughout the area of recharge. Karst features (solution pits, caves, etc.) are limited to exposures of massively bedded limestones and dolomitic limestone, which rarely exceed a thickness of 20 m. Infiltration and movement of groundwater are controlled by the density of the fractures and solution openings and the relatively thin-bedded nature of the rocks. The groundwater flow is in the direction of the dip of the strata and along the orientation of fractures.

Turonian StageGray, massive-bedded, unfossiliferous, dolomites and dolomitic limestones, as much as 80 m thick, are present along the flanks of the El Hassiya Anticline and the Dome of Figeh. The unit is absent in all other parts of the recharge area. The rocks are fine- to medium-grained and massively bed-ded. The Turonian dolomites and dolomitic limestones contain karst features in the vicinity of Figeh Spring including the cave systems at the outlet of the spring. This is the only unit exposed in the recharge area of sufficient thickness, competence, and aerial extent to support extensive cavern systems in the subsurface.

Disagreement exists about the age of the massively bedded dolomitic limestone. Dubertret1 and Ponikarov2 describe the unit as Upper Cenomanian. However, others3–5 place the unit in the Turo-nian stage. This report has complied with this more recent classification.

Overlying the dolomites is a light gray to white, thin-bedded, shaley limestone containing some marl. These beds are aquicludes and impede the flow of groundwater.

Senonian Strata SubseriesRocks of the Senonian subseries include the Coniacian, Santonian, Campanian, and Maastrich-tian stages and constitute the lower portion of a thick sequence of confining beds that overlie the principal Cenomanian and Turonian aquifers of the Figeh aquifer system. The Senonian consists predominantly of marl and has a total thickness of 225–250 m. This strata are conformably overlain by about 200 m of lithologically similar marls of Paleocene and Eocene age.

Geologic mapping of the Senonian strata is facilitated by the presence of dolomitic sandstone in rocks of the Coniacian Stage, gray-brown flint beds in rocks of the Campanian Stage, and massive chalk beds in the Maastrichtian strata.

Figeh Spring is near the downstream exposure of the Cenomanian–Turonian aquifer system. The contact between these systems has been penetrated by cores for test holes in the Figeh Spring area and observed in the spring during scuba diving exercises. It occurs about 755 m msl or 30 m below land surface in the Figeh cave system. Senonian strata in this locality are locally fractured and karstified and act as a semiconfining series of beds that restrict lateral and vertical movement of groundwater in the Figeh system.

geologic Structure

The recharge area for Figeh Spring includes a northeast-trending part of the Anti-Lebanon Range, which is bounded on the northwest by the Bekka Valley rift system and by the Barada River to the south; the southeastern boundary is marked by the limits of large tertiary basins (Figure 10.47).

The dominant structure of this portion of the Anti-Lebanon Range is the southeastward dipping homocline. The homocline originates along faults of the Bekka Valley or its branches, such as the Serghaya Fault system. The homoclinal form of the Anti-Lebanon Range is disrupted by anticlines and synclines that trend subparallel to the regional strike of the homocline (northeast). The most complex folding of the recharge area occurs in the area immediately north of the Barada River and Figeh Spring, and includes about one-third of the recharge area (approximately 200 km2 of the total 700 km2 in the recharge area).

Dominant folds of the area include the Huraire Syncline, the Hassiya Anticline, the Khadra Anticline, and the Dome of Figeh (Figure 10.47). The Huraire Syncline and Hassiya Anticline are northeast-trending, subparallel folds, which have been intermittently active since late Cretaceous (Cenomanian). The Huraire Syncline and Hassiya Anticline are dominant structural features for a


distance of about 20 km north of the Barada River. The syncline is nearly symmetrical with a dip of 45–60° on each limb. However, the anticline is asymmetrical with a dip of 45–60° on the northwest limb. The southeast limb has a dip of 15–20° (Figures 10.45 and 10.46). Both folds plunge gently toward the southwest, except near their southern limits where the plunge steepens and cross folding causes the axes to trend almost toward south.

The Huraire Syncline is terminated by faulting at its southern end near the Village of Huraire. Cenomanian, Turonian, and Senonian strata, exposed in the syncline, terminate abruptly at the fault. South of the fault, approximately 300 m of the Pliocene conglomerate is exposed in the down-thrown block. The Pliocene conglomerate extends approximately 5 km to the Barada River. Minor folds of low amplitude occur on the flanks of the Huraire Syncline and the Hassiya Anticline. The minor folds are seldom coaxial with the major folds.

The Khadra Anticline has a total exposed length of 12 km. The axis of the fold plunges 11° in north and 78° west direction. The anticline is asymmetrical with a near vertical southern limb, the fold being well exposed north of Ain Khadra (Figure 10.47). The Khadra Anticline is one of the most recent folds (Pliocene–Pleistocene) in the recharge area and is transverse to the dominant folds of the Anti-Lebanon Range.

The intersection of the northwestern-trending Khadra Anticline with the northeastern trend-ing structures of the Anti-Lebanon Range has created the Dome of Figeh, has refolded the Hassiya Anticlines and the Huraire Syncline, and has created southeastern-plunging minor folds exposed west of the Dome.

4000

LOCATION OF CROSS-SECTIONSYNCLINE

ANTICLINE

JURASSIC

APTIAN AND ALBIAN

CENOMANIAN

TURONIAN

SENONIAN SUBSERIES

CRETACEOUSKHADRA

ANTICLINE MOICENE (?) BASALT

TERTIARY

QUATERNARY

EXPLANATION

A

A

KHADRAANTICLINE

B´

A

DOME OFFIGEH

A

BBLOUDAN

SERG

HAY

A FA

ULT

FIGEH SPRINGBARADA RIVER

HALBOUN

0

SCALE IN METERS

4000 8000

fIgure 10.47 Geologic structural features of the Figeh Spring system.

Case Studies 269

The path of the Barada River is controlled by faults parallel to the Khadra Anticlinal axis. At the southeast end of the fold axis, faults controlled deposition in the Neogene basin, marginal to the Anti-Lebanon Range.

faults and fractures

The northwest boundary of the recharge basin occurs along a branch of the major rift system that forms the Bekka Valley. The branch fault system is well exposed near Serghaya and will be referred to as the Serghaya fault zone. The zone itself is 1–3 km wide; however, intense fracturing of adjacent Jurassic and Cretaceous rocks has occurred. The Serghaya fault zone behaves as a hinge fault with normal, left-lateral movement. Stratigraphic throw increases to the northeast. Maximum throw in the Zebdani quadrangle is over 1000 m.

The structural configuration strongly suggests the presence of major bounding faults hidden beneath sediments of the Paleogene and Neogene age along the southeastern and southern margins of the recharge area. The rectangular path of the Barada River provides strong indication of fault control along the southern border of the recharge area. The structural control of the Barada has been verified south of Zebdani, near Takeye, and near Souk Wadi Barada. The east–west segment of the Barada Valley suggests control by faults, which also serve as the boundary of the large Neogene basin south of Figeh Spring.

The southeastern border of the recharge area is coincident with a major lineament (Jarajir lin-eament), which is subparallel to the Serghaya and Bekka rift faults. The Jarajir lineament extends more than 100 km northeast from Halboun. The Jarajir lineament is presumed to be the surface expression of a major fault system at depth.

The Jarajir lineament serves as the boundary between the Cretaceous rocks, exposed in the recharge area for Figeh Spring, and the large Tertiary-Quaternary basin (13 by 50 km), where Assal el Ward is located. Northeast of the Assal el Ward basin, the Jarajir lineament appears to bifurcate. One branch follows the central axis of the Tertiary-Quaternary basin in the vicinity of Jarajir and Quara. The other branch follows the western margin of the basin.

Within the recharge area, faults and joints are numerous, and no exposure of rock is devoid of fractures. The major faults in the southern part of the recharge area strike northwest, almost perpendicular to the fold axes, and consist of both normal and reverse faults, some of which have a right-lateral component of movement. North, northeast, and east–west trending normal faults may have significant displacement but are not as numerous as the northwest-trending faults.

Orientation of fractures, joints, and faults measured in the field (in the northern part of the Zebdani Quadrangle) between Bloudan and Figeh are illustrated on a rose diagram in Figure 10.48. In order of decreasing importance, the dominant fracture orientations are nearly perpendicular to the fold axes (23.7% of the fractures), cross the fold axes at angles of about 40° (18.6% of fractures), or are almost parallel to the fold axes (13.6% of fractures). The fracture systems are open and, in conjunction with the southeastward stratigraphic dip, can readily transport groundwater toward Figeh Spring.

In the central part of the recharge area (northern part of the Assal El Ward Quadrangle), domi-nant fractures are oriented more nearly in a north–south direction. Groundwater flow in this area is controlled by the southeastern dip of the strata; the nearly north–south orientation of dominant, open fractures; and subsurface faults associated with the Jarajir lineament, all of which provide components of the flow toward Figeh Spring.

North of the recharge area (in the NABK Quadrangle), the stratigraphic dip is toward the south-east. The trend of the most abundant fractures is northwestward (Figure 10.48). Groundwater in the area moves along the bedding planes and fractures in a southeast direction toward Jarajir, Nebek, and Quara. The area cannot be considered as a source of recharge to Figeh Spring.

The northern two-thirds of the recharge area has a more simple homoclinal form than that near Figeh Spring. Strata undulate, but north to northeast strikes prevail; the dip of the strata becomes

pjw

stk|

4020

64|1

4354

3260

6


progressively more gentle in the northern part of the recharge area. Minor anticlines and synclines occur but have small amplitudes and appear to have little effect in diverting the flow of groundwa-ter. The dominant trend of fractures in the central portion of the recharge area is approximately north–south, whereas the orientation of the most abundant fractures rotates progressively toward the northwest in the northern part of the recharge area.

Straight segments of wadis have characteristically developed along faults or joints. Fracture patterns can be accurately interpreted from aerial photographs or from drainage maps. Fracture-controlled surface morphology is characteristic of the northern two-thirds of the recharge area. Groundwater infiltration and groundwater flow in the central part of the recharge basin is controlled by the south-to-southeastern stratigraphic dip, southward-dipping normal faults in valleys, and north–south trending minor fracture systems. The Cenomanian and Turonian strata are intensely fractured, thus causing these beds to be porous and permeable. The significant directional compo-nent of the flow is toward Figeh Spring.

10.4.4 hydrogEology oF thE FigEh arEa: gEologic structural sEtting and karst dEvElopmEnt

For karstification to develop and solution action to progress to form caverns, it is necessary that

1. Water rich in carbon dioxide be available to recharge the system 2. Sufficient permeability (in the form of fractures or bedding plane or both) be available for

water to move in the rocks 3. Water be able to discharge from the system

A fourth criterion, which expedites the process, is a steady source of recharge water, such as from snow melt, or an overlying blanket of sediments. Under water table conditions, a zone of higher per-meability tends to develop in the zone of greatest circulation and solution, which is commonly at or just below the water table. Topography and the position of belowground carbonates are important;

59 DATA POINTS

10.2%8.5%

13.6%11.9%

18.6%

5.1%

23.7%

3.4%

5.1%W E

S

N

fIgure 10.48 Rose diagram of faults and joints between Bloudan and Figeh.

Case Studies 271

carbonates that allow at least moderate circulation and are entrenched by perennial streams tend to develop solution openings and increase circulation. Some circulation of water and, to a certain extent, solution cavities may locally occur at a depth of several hundred meters below the level of the major stream of a region provided that a good discharge system and well-established gradient are available and the water is chemically aggressive. This is true in the case of the Barada River Valley, which flowed at a lower elevation during the late Pleistocene.

The relation of the recharge to the discharge area in a karst region determines, to a large extent, the patterns of the lateral solution channels or openings. The size and frequency of these channels will depend on many factors involving the conditions in the recharge area, the volume of water that enters the recharge area, the solubility of the karst rocks, and the rate at which the base level is lowered as perennial streams entrench.

Where the discharge area is along a more or less straight line, such as the Barada River Valley, the lateral solution channels tend to be more or less parallel to each other and at right angles to the line of discharge. Discharge is therefore, in the line of springs such as Figeh, Ain Harouch, and Ain Kadra, into the Barada. The direction of the movement of water between the recharge and discharge areas is affected by faulting, folding, jointing, and other geologic structures. Cave passages may occur at more than one level.

Water level behavior in space and time is a primary consideration for interpreting karst hydrol-ogy. The position of the water table is important because:

1. The water table defines generally the zones of greatest circulation and solution. 2. The configuration of the water table aids in identifying the general direction of flow, the

hydraulic gradient, and the areas of recharge and discharge. 3. Information about the water table provides general information about the permeability of

the aquifer system. 4. The position of the water table locally indicates the extent to which caverns are filled with

air or water.

Carbonate aquifers often have seasonal variation in water levels ranging 20–80 m, and the effects of recharge in the recharge area from isolated rains are nearly instantaneous. Large seasonal varia-tions in water level beneath the carbonate uplands may cause the movement of groundwater to one basin in dry weather and to another in wet weather. A controlling factor in the range of seasonal groundwater levels is the great infiltration capacity of karst terranes. Large volumes of water from heavy storms infiltrate into the air-filled caverns of karst lands, reaching the level of saturation quickly and causing the water table to rise rapidly. From a single storm or snow-melt event, the rise in the water table in relatively impermeable parts of the saturated carbonate rocks can be as much as 10 or more meters, whereas the rise of the water table in permeable zones of the same carbonate rocks can be less than a meter.

Big springs, such as Ain Figeh, the third largest spring in the world, rather than small springs and diffuse seepage, are the general rule in karst regions, and often emerge from underground streams or caves. Most groundwater flow, however, occurs in large solution openings near the top of the saturated zone, which carry much of the groundwater to the springs. Zones of solution openings may tend to branch upgradient, along fractures, which in arterial fashion represent the more perme-able, upper parts of the saturated zone. The water table is depressed along the arterial system so that groundwater discharge meets the surface stream almost at grade.

In karst areas, the distribution of permeability beneath streams causes loss or gain of water depending on the position of the water table with reference to the stream level. A surface stream may lose water where bedrock in the losing stretch is very permeable and the water table is low, and it will gain water where the water table is above stream level. For example, the Barada River gains water where it crosses an area immediately south of the Wadi Huraire Syncline and loses water in the reach west of Deir Moukarren.


An understanding of the geologic history and paleokarstification is critical in the Figeh karst system in the vicinity of Ain Figeh where the fractured limestone and dolomites dip toward the Barada River Valley. Karstification of these rocks began during the Pleistocene along fractures and bedding of the more pure limestone. These beds were subsequently folded and fractured during the tectonic uplift in the area. During the Pleistocene, the Barada River near Ain Khadra became impounded, probably by a landslide, and the base level of the river was raised. Erosion subsequently took place, dropping the base level to the present level of the Barada River. At Figeh, alluvial depos-its extend to as much as 45 m below the present land surface (Figure 10.49). These beds of sand, gravel, and boulders fill a buried Paleokarst feature at Ain Figeh and comprise an important seg-ment of the Karst aquifer storage system.

Excellent plan views and cross sections of three major solution features in the immediate vicin-ity of Figeh Spring (Gallery Cave, Cheikh Cave, and the Karst Cavity) have been mapped and surveyed in detail.5 Each cave is subparallel to the bedding of the Turonian rocks; however, each contains small openings associated with fractures. The lower elevation of each cave is 835 m above the mean sea level and corresponds to elevations of late Pleistocene to recent river terraces. The presently active karst system of Figeh, Gallery Cave, and Cheikh Cave were originally paleokarst features of the late Pleistocene and the recent age.

The Gallery and Cheikh caves differ from the Figeh Karst Cavity as they occur at higher eleva-tions than the Figeh Karst Cavity; also, the floors of these two caves are underlain by solid bedrock, whereas the lower part of the Figeh Karst Cavity is filled with breccia.

830

825

820

815

810

800

795

Elev

atio

n in

Met

ers A

bove

Mea

n Se

a Lev

el

790

830

785

775

770769.4

773.9

792.7795.1

799.2

794.3

SCALE 1:200 meters

CAVITY

TURONIAN

SENONIAN

QUATERNARY

X-6 X-33 X-34 X-36 X-39X-40

PROJECTED

X-37

fIgure 10.49 Geologic cross section of Ain Figeh.

Case Studies 273

The developmental history of the Figeh Karst Cavity is more complex than that of the Gallery and Cheikh caves. This is because two different, but interrelated, karst features are associated with the Figeh Karst Cavity. The primary feature is the Karst Cavity itself; above the Karst Cavity is a depression in the top of the bedrock; the depression is filled with breccia, overlain by soil and/or allu-vial deposits, as demonstrated in the logs for test wells X-6, X-33, X-34, and X-8 (Figure 10.49).

The Karst Cavity is overlain by Turonian strata. Although the overlying beds are fractured, they have not been significantly displaced from their stratigraphic position except where overlying depres-sions occur. However, drill holes that penetrated the bottom of the Karst Cavity have tapped underly-ing karst breccia. For example, well X-40 penetrated 27 m of karst breccia beneath the cavity.

A theory of the origin of the Figeh Karst Cavity incorporates the upward movement of ground-water along fractures connecting the Cenomanian and Turonian strata: Groundwater in the Turo-nian strata, under artesian pressure, eroded, by dissolution and mechanical action, a cave system subparallel to the bedding of the Turonian strata. Figure 10.54 (see later) indicates a progressive evolution of the cave system by which the physical cavity migrated upward through the Turonian rocks due to intermittent collapse of the cave roof and backfilling of the cave floor with karst brec-cia. The stratigraphic interval during which the cave system originated is unknown, as drilling has not penetrated the base of the breccia in the karst.

Filled depressions are present in the immediate vicinity of the Figeh Spring, which are paleokarst features, and are connected to and associated with development of the main Figeh cavity. Wells X-6, X-33, and X-34 (Figure 10.49) have penetrated the margin of one depression filled with karst breccia and connected to a cavity penetrated by well X-6. The deepest known part of this depression was penetrated in test well X-8; the breccia extended to a depth of 30 m and was overlain by alluvial sediment representing an ancient, higher stage of the Barada River. A similar and apparently large alluvial-filled depression was penetrated in well E-3. Karst breccia and alluvial fill is also present in the surrounding drill holes X-12, E-1, X-31, and X-10. These depressions are not expressed at the surface and were probably created and filled during the Pleistocene age. The karst breccia in the depressions serve as zones for groundwater movement and storage in the present Figeh system.

10.4.5 rEchargE, storagE, and dischargE oF groundWatEr

Photogeologic and surface geologic methods were used to identify boundaries of the recharge area (Figure 10.47). For modeling and quantitative analysis, it was necessary to have a thorough under-standing of recharge, storage, and discharge features in the groundwater system. The criteria for identifying the recharge area were as follows:

1. The contact of the Turonian rocks with overlying confining beds or with faults of significant displacement was used to identify the southern and southeastern limit of the recharge area.

2. The western and northwestern limits were defined by the surface water drainage divide in the Anti-Lebanon mountains, or by the stratigraphic contact with underlying confining beds where structural control allows groundwater to cross the surface water divides.

The recharge area for Figeh has boundaries influenced by the location of the surface water divides, geologic structures (fractures and folds), and stratigraphic relationships. Results from these studies were confirmed by field work that included geologic structural analysis.

The recharge storage zone within which groundwater may flow toward Figeh Spring is complex and varies depending on the porosity, permeability, structure, and season of the year.

Groundwater in the system is typically unconfined at higher elevations and becomes confined or semiconfined near the points of discharge along the Barada River, such as at Figeh Spring and Ain Harouch. The confining beds consist of upper Cretaceous to Eocene marls that overlie the Turonian strata.


groundwater movement in the recharge area

Groundwater movement in the portion of the Anti-Lebanon Range, which serves as the recharge area for Figeh Spring, is structurally and stratigraphically controlled. The homoclinal form of the Anti-Lebanon Range allows general groundwater movement in a southeastern direction by per-colation along bedding planes in the thinly bedded, Cenomanian limestones. Secondary porosity is provided by open fractures, while allowing vertical movement of groundwater. The orientation of dominant fracture systems and a dip of strata (in the central and northern parts of the recharge area) provide a directional component of groundwater flow toward Figeh Spring. The southwest-plunging Huraire Syncline, Hassiya Anticline, and associated fracture systems control the direc-tion of groundwater movement in the southern one-third of the recharge area.

Groundwater in the Huraire Syncline does not discharge at Figeh Spring. A portion of this water is confined beneath the Senonian strata and should be available by drilling wells northeast of the faulted terminus of the syncline near the village of Huraire. A portion of groundwater moves toward the south and southeast to discharge as springs along the Barada River west of Figeh Spring. These springs include Ain Habil, the springs near Souk Wadi Barada, and Kfer el Aquamid, as well as Ain Harouch. Some groundwater underflows or discharges to the Barada River.

Groundwater on the eastern flank of the Hassiya Anticline flows in a southerly direction and becomes confined beneath the Senonian strata. The groundwater moves around the eastern side of the Dome of Figeh and rises to the surface by an upward flow parallel to the axis of the Khadra Anticline to discharge at Ain Figeh. Faults beneath the Barada Valley appear to restrict the amount of water that underflows the Barada River.

Groundwater and surface water in the northern part of the Anti-Lebanon Range flow either toward the Bekka Valley or toward the Tertiary basin near Jarajir and Quara.

Movement of groundwater along the border between the recharge area and the Assal el Ward basin is less certain owing to limited information. The Assal el Ward basin is a large tertiary-quaternary synclinal basin. Faults associated with the Jarajir lineament may restrict groundwater movement from the recharge area into the basin. Alternatively, groundwater may flow across the fault zone, be confined beneath the Senonian strata in the basin, and be directed toward Figeh Spring because of the southwestern plunge of the syncline.

recharge–discharge relationships

Climatological factors effecting discharge include the following:

1. Rainfall, evaporation, and transpiration 2. Discharge into or under the Barada River, and discharge or pumping from wells and springs 3. Seepage along the southeastern boundary of the basin due to the stratigraphic dip and the

trend of fracture 4. Leakage of groundwater through fractures crossing the northwestern boundary of the

recharge area 5. Losses along the southern border of the system as spring flow

Over historical times, beginning with the Romans, Figeh Spring experienced a variety of different attempts to capture water. Evidence of this early development remain in the opening to the cavity of Figeh Spring and the aqueducts leading south toward the city of Damascus. The discharge from Figeh Spring, the water obtained from the Pilot Development Project, is mainly from the karst system. Water discharging from Side Spring has two sources—the Figeh Karst System and the alluvial deposit in an old stream channel that is recharged from the Barada River. Ain Harouch and Deir Moukarren represent discharge points from the karst system. Shallow large-diameter wells

Case Studies 275

obtained water from alluvial deposits in an old meander of the Barada River and moved it toward the sump at Side Spring.

climate—evaporation and transpiration

The climate of most of the recharge areas of Figeh is classified as Mediterranean by the widely recognized Koppen climatic classification system. The Mediterranean climate is one of dry, hot summers and wet, cool winters. A part of the recharge area rises over 2500 m above the mean sea level, almost certainly causing average monthly winter temperatures to be below freezing in the highest elevations.

The normal vegetative response to the Mediterranean climate ranges from grassland to forest; however, in the Figeh recharge area, the response is xerophytic vegetation. Thornbush and cacti of several varieties proliferate as a sparse ground cover. The area is characterized by rubbly bedrock, thin top soil, and man-induced soil and vegetation changes caused by overgrazing, agriculture, and gathering of firewood. Rapid infiltration of moisture, combined with the long, dry summers, results in low soil moisture retention. Therefore, natural vegetation plays a minimal role in the amount of moisture available for the recharge area.

There are three operative weather stations in the recharge area, all with elevations of 1540–1560 m above the mean sea level. The Bloudan and Huraire stations appear to be well maintained and the data recorded with minimal transferral error. Data for the Afre station are not reliable and were not used. Table 10.3 shows the mean monthly precipitation for Bloudan and Huraire for hydro-logic years 1971 through 1978. Figure 10.50 shows the mean monthly temperature and humidity for Bloudan and Huraire, respectively, for hydrologic years 1971 through 1978.

Moisture generally decreases eastward across the recharge area for any given elevation. This is a consequence of the increasing distances from the principal source of water vapor, the Mediter-ranean Sea, and the increasing effectiveness of a rain-shadow effect as the moisture is carried east-ward across the Anti-Lebanons by winter storms. This decrease in precipitation from west to east across the recharge area appears to be approximately 10%. The precipitation decreases dramatically in the Syrian Desert to the east of the Anti-Lebanons. Higher elevations should receive more pre-cipitation than lower elevations from a combined effect of orographic causes and cyclonic storms. In addition, evaporation should be less at higher elevations in response to lower temperatures and consequent higher relative humidities. This should result in the availability of more net moisture for recharge at higher elevations than at lower elevations. There appears to be little north–south varia-tions in precipitation in the recharge areas at any given level.

Humidity generally increases with a decrease in temperature in the area. Figure 10.50 shows the relationship between relative humidity and temperature for the hydrologic years 1971 through 1978. The hydrologic year utilized by the Figeh system is from September 1 to August 31. Precipitation occurs predominantly during the late fall, winter, and early spring. The average annual precipitation at Bloudan and Huraire for the period from September 1971 through August 1978—by hydrologic year—was 611.10 and 632.08 mm, respectively, with the wettest month of January averaging 140.09 and 155.46 mm, respectively. Summer months of June, July, and August are very dry, averaging less than 1.0 mm. Figures 10.51 and 10.52 generalize the data from Bloudan and Huraire, respectively, into climographs, to show the months of moisture surplus and deficit for a hydrologic year. The stations show a moisture surplus (for potential recharge) from November through February and a deficit for the remainder of the year.

What is significant is the fact that over 88% of the Figeh recharge area of approximately 735 km is higher than 1500 m above sea level, and therefore, it is higher in elevation than the weather stations of Bloudan and Huraire and Afre (Table 10.4). Seventy-six percent of the total area is higher than 1900 m above mean sea level.


tab

le 1

0.3

mea

n m

onth

ly p

reci

pita

tion

for

blo

udan

(a

) an

d H

urai

re (

b),

Sep

tem

ber

1971

–aug

ust

1978

, hyd

rolo

gic

year

s

mon

thSe

ptem

ber

oct

ober

nov

embe

rd

ecem

ber

Janu

ary

febr

uary

mar

cha

pril

may

June

July

aug

ust

ann

ual

aver

age

a. b

loud

an (

1560

m a

bove

msl

)

Rai

nfal

l (m

m)

0.20

13.4

368

.80

90.4

294

.09

71.1

378

.27

47.4

110

.54

0.96

——

475.

25

Mon

thly

per

cent

0.04

2.83

14.4

819

.03

14.9

716

.47

9.98

2.22

0.20

——

—10

0.00

Snow

fall

equi

vale

nt (

mm

)a—

—4.

5717

.64

46.0

028

.64

36.0

03.

00—

——

—13

5.85

Tota

l pre

cipi

tatio

n0.

2013

.43

73.3

710

8.06

140.

0999

.77

114.

2750

.41

10.5

40.

96—

—61

1.10

Perc

ent o

f pr

ecip

itatio

n as

sn

owfa

ll—

—6.

2316

.32

32.8

428

.71

31.5

05.

95—

——

—22

.23

b. H

urai

re (

1540

m a

bove

msl

)

Rai

nfal

l (m

m)

1.24

8.70

73.6

789

.24

88.9

682

.11

69.7

445

.73

8.11

0.61

——

468.

11

Mon

thly

per

cent

0.26

1.86

15.7

419

.06

19.0

017

.54

14.9

09.

771.

730.

13—

—10

0.00

Snow

fall

equi

vale

nt—

—11

.57

9.21

66.5

037

.00

37.9

01.

79—

——

—16

3.97

Tota

l pre

cipi

tatio

n1.

248.

7085

.24

98.4

515

5.46

119.

1110

7.64

47.5

28.

110.

61—

—63

2.08

Perc

ent o

f pr

ecip

itatio

n as

sn

owfa

ll—

—13

.57

9.36

42.7

831

.06

35.2

13.

77—

——

—25

.94

a C

onve

rted

fro

m c

entim

eter

s of

sno

w to

mill

imet

ers

of m

eltw

ater

(ba

sed

on s

tand

ard

conv

ersi

on r

ate:

10

to 1

).

Case Studies 277

S024681012141618202224

AJJJDNOS20

30

40

50

60

70

Rela

tive H

umid

ity %

Tem

pera

ture

(°C

)

80

90

100RELATIVE HUMIDITY RELATIVE HUMIDITY

BLOUDANHURAIRE

MMMonths

F A

fIgure 10.50 Mean monthly temperature and humidity, Bloudan and Huraire, 1971–1978.

AJJMAMFJMonths of Hydrologic Year

MOISTURE AVAILABLE FOR INFILTRATIONAND/OR EVAPORATION

DNOS0

20

40

60

80

100

120

140

160

180

Moi

stur

e in

Mill

imet

ers

200

SEASONAL MOISTURE DEFICIT

STATION: BLOUDAN

AVERAGE ANNUAL PRECIPITATION:

POTENTIAL EVAPORATION: 1840.75 mm

AVERAGE ANNUAL MOISTURE DEFICIT:

PRECIPITATIONPOTENTIAL EVAPORATION

611.10 mm

1229.76 mm

33.43 N, 30.07 E, 1560ABOVE MSL

220

240

260

280

300

320

360

SEASONAL MOISTURESURPLUS

fIgure 10.51 Climograph for Bloudan by hydrologic years, 1971–1978.


AJJ

PRECIPITATION

–1557.47 mm.

632.08 mm.

ABOVE MSL33.40 N, 36.07 E, 1570 m.

AVERAGE ANNUAL MOISTURE DEFICIT:

POTENTIAL EVAPORATION:

AVERAGE ANNUAL PRECIPITATION:

STATION: HURAIRE

2189.55 mm.

POTENTIAL EVAPORATION

MAMFMonths of Hydrologic Year

MOISTURE AVAILABLEFOR INFILTRATION

AND/OR EVAPORATION

SEASONALMOISTURE

SURPLUS

SEASONAL MOISTURE DEFICIT

JDNOS

20

40

60

80

100

120

140

160

Moi

stur

e in

Mill

imet

ers

180

200

220

240

260

280

300

320

340

360

fIgure 10.52 Climograph for Huraire by hydrologic years, 1971–1978.

table 10.4elevation of recharge area by quadrangle (km2)

elevations (m) 1000

1000–1300

1300–1600

1600–1900

1900–2200

2200–2500 2500+ total Percent

Zebdani 3.15 37.93 42.78 73.18 64.80 2.05 — 223.89 30.44

Damas Nord — — 0.30 18.18 1.20 — — 19.68 2.68

Rijak — — — 0.33 27.43 17.68 — 45.44 6.18

Assal El Ward — — — — 167.70 84.15 — 251.85 32.24

Aarsal — — — — 25.08 95.68 2.75 123.51 16.79

Nabk — — — — 46.03 25.10 — 71.13 9.67

Total 3.15 37.93 43.08 91.69 322.24 224.66 2.75 735.50 —

Percent 0.42 5.16 5.85 12.47 45.17 30.55 0.37 — 100.00

pjw

stk|

4020

64|1

4354

3261

0

Case Studies 279

To estimate the availability of moisture for recharge of the Figeh system, several models were attempted, using data from the weather stations at Bloudan and Huraire. The five principal variables utilized in the evolution of the final model were:

1. Seasonal variations in precipitation 2. Elevational differences in temperature 3. Evaporation 4. Snowfall and moisture storage as ice 5. Infiltration

The mean precipitation for the hydrologic years September 1971 through August 1978 for Bloudan and Huraire was used in calculating the potential moisture availability for recharge in the study area. A 0.6 infiltration rate was determined based on lysimeter data from the Bloudan and Huraire weather stations. This rate is representative of only the lower portion of the recharge area. In other words, based on the assumptions that precipitation will be higher and evaporation rates lower at higher elevations, the infiltration rates should increase with increasing elevations.

Over the 7-year period from the hydrologic year 1971 through 1978, annual snowfall, con-verted to meltwater, accounted for 22.23% of the total precipitation at Bloudan and 26% at Huraire, although average annual snowfall amounts were approximately the same at both stations. Gener-ally, the variability in amounts of annual snowfall was slightly greater at Huraire than Bloudan (Table 10.5). Also, 1 cm of fresh snow is equal to 1 mm of meltwater.

To estimate the snowfall in the recharge area, some rough calculations were made using only the data from Bloudan and Huraire (Table 10.6):

1. Using an adiabatic rate of 0.8°C/100 m (dry adiabatic cooling rate of 1°C/100 m less the dew point lapse rate of 0.2°C/100 m), the estimated average monthly elevation of dew point (the temperature at which the air becomes saturated or at which relative humidity becomes 100%) was calculated for the recharge area (Table 10.6).

2. Further, the elevation at which the average monthly air temperature should theoretically reach 0° was calculated, representing an approximately monthly snow line, or, in other words, where precipitation should occur mostly as snow or ice.

3. The relationships between the elevations of the recharge area and those of the estimated mean monthly 0°C were analyzed to determine how much of the recharge area was above the snow line for each month (see Figure 10.53). Table 10.6 illustrates the significance of these relationships by elevation. Precipitation occurring above the snow line (0° elevation) is assumed to be in the form of snow.

Over the recharge area, an estimated average of 74% of the precipitation from December to March may have occurred as snowfall during the hydrologic years 1971 through 1978. Much of this snow represents a snowpack being stored over the period, and it appears to be released as meltwater over a snowmelt period from mid-March through April.

The length of time during which the release of snowmelt becomes available for infiltration (plus any precipitation that might occur simultaneously) is approximately 45 d. The total amount of melt-water was 398 mm over the 45 d; the amount available for infiltration in the model, after evapora-tion, was 239 mm, or 5.3 mm/d. This was calculated as follows:

Y = [P )Sp]+R

TIr4+5+6+7 ⋅


tab

le 1

0.5

esti

mat

ed m

ean

snow

fall

equi

vale

nt (

mm

), S

epte

mbe

r 19

71–a

ugus

t 19

75m

onth

Sept

embe

ro

ctob

ern

ovem

ber

dec

embe

rJa

nuar

yfe

brua

rym

arch

apr

ilm

ayJu

neJu

lya

ugus

t

bas

ed o

n da

ta fo

r b

loud

an

Elev

atio

n (m

)

Abo

ve 2

500

——

73.4

108.

114

0.1

99.8

114.

350

.4—

——

—

2201

–250

0—

—73

.410

8.1

140.

199

.811

4.3

38.4

——

——

1901

–220

0—

—50

.410

8.1

140.

199

.888

.326

.6—

——

—

0°C

Ele

vatio

na (sn

ow li

ne)

1601

–190

0—

—27

.562

.914

0.1

64.2

62.2

14.8

——

——

1301

–160

0—

—4.

617

.646

.028

.636

.03.

0—

——

—

1001

–130

0—

——

——

——

——

——

—

Bel

ow 1

000

——

——

——

——

——

——

bas

ed o

n da

ta fo

r H

urai

re

Elev

atio

n (m

)

Abo

ve 2

500

——

85.2

98.5

155.

511

9.1

107.

647

.5—

——

—

2201

–250

0—

—67

.498

.515

5.5

119.

110

7.6

36.6

——

——

1901

–220

0—

—48

.898

.515

5.5

119.

184

.325

.0—

——

—

0°C

Ele

vatio

na (sn

ow li

ne)

1601

–190

0—

—30

.254

.015

5.5

78.5

61.1

13.4

——

——

1301

–160

0—

—11

.69.

266

.537

.037

.91.

8—

——

—

1001

–130

0—

——

——

——

——

——

—

Bel

ow 1

000

——

——

——

——

——

——

a A

bove

the

snow

line

, mon

thly

pre

cipi

tatio

n sh

ould

be

mos

tly a

s sn

ow o

r ic

e bu

t is

show

n as

mel

twat

er (

mm

).

Case Studies 281

tab

le 1

0.6

esti

mat

ed d

ew p

oint

and

sno

wl i

ne b

ased

on

data

for

blo

udan

(15

60 m

) an

d H

urai

re (

1540

m),

Sep

tem

ber

1971

–aug

ust

1978

, hy

drol

ogic

yea

rsm

onth

Sept

embe

ro

ctob

ern

ovem

ber

dec

embe

rJa

nuar

yfe

brua

rym

arch

apr

ilm

ayJu

neJu

lya

ugus

t

a. b

loud

an

Rel

ativ

e hu

mid

ity (

%)

34.9

042

.79

74.8

077

.40

70.1

762

.59

53.7

944

.70

37.1

334

.21

36.6

7

Mon

thly

tem

pera

ture

(°C

)20

.30

15.7

79.

163.

501.

863.

676.

4010

.68

15.1

718

.92

21.1

621

.74

App

roxi

mat

e de

w p

oint

(°C

)3.

02.

32.

4–5

.0–2

.1–2

.0+

2.0

+2.

4+

4.0

4.0

5.0

Subt

otal

a17

.313

.56.

88.

54.

05.

88.

48.

712

.814

.917

.216

.7

Ele

vatio

n of

dew

poi

nt (

m)

3723

3248

2410

2623

2060

22.8

526

1026

4831

6034

2337

1036

47

Ele

vatio

n at

0°C

4097

b35

35b

2710

b19

9717

9220

1923

6028

95b

3498

b39

23b

4210

b42

73b

b. H

urai

re

Rel

ativ

e hu

mid

ity (

%)

50.8

057

.91

70.7

084

.76

84.8

679

.96

75.2

470

.51

63.0

156

.71

49.8

747

.37

Mon

thly

tem

pera

ture

(°C

)19

.815

.88

9.56

3.58

2.00

4.01

6.50

10.8

115

.78

19.6

022

.30

21.9

0

App

roxi

mat

e de

w p

oint

(°C

)8.

07.

52.

51.

6–1

.81.

62.

06.

09.

010

.010

.97.

5

Subt

otal

a11

.011

.47.

12.

03.

82.

44.

54.

86.

89.

611

.414

.4

Ele

vatio

n of

dew

poi

nt (

m)

2915

2965

2426

1790

2015

1840

2103

2140

2390

2740

2965

3340

Ele

vatio

n at

0°C

4015

b35

28b

2735

b19

9017

9020

4025

3528

901

3515

b39

90b

4328

b42

78b

a To

tal d

egre

es (

C)

air

tem

pera

ture

mus

t be

low

ered

for

dew

poi

nt to

be

reac

hed.

b T

hese

ele

vatio

ns a

re h

ighe

r th

an a

nd n

ot in

clud

ed in

the

rech

arge

are

a.

It is

ass

umed

that

win

ter

prec

ipit

atio

n re

sult

s m

ostl

y fr

om o

rogr

aphi

c co

ndit

ions

and

an

adia

bati

c ra

te o

f 0.8

°C p

er 1

00 m

ade

quat

ely

repr

esen

ts c

lim

atic

con

diti

ons

upsl

ope

from

th

e w

eath

er s

tati

ons

to th

e el

evat

ions

of t

he d

ew p

oint

and

sno

w li

ne.


where

y = moisture available for infiltration P 2 + 3 + 4 + 5 = precipitation for December, January, February, and March (471 mm) Sp = snowfall as a percent of total precipitation (74%) R = rainfall in April (49 mm) T = 45-d snowmelt period Ir = infiltration rate (0.6)

Therefore, an impulse equivalent to 239 mm of moisture, or 38% of the annual precipitation, should enter the recharge system of Figeh during the snow melt period in March and April. This impulse should cause a response in the discharge at Figeh in a predictable manner.

These calculations are approximations used to estimate the combined effect of five climatologi-cal variables on annual groundwater recharge within the recharge basin. The calculations are based on established examples, but are no more than estimates because the existing climatological data represent only two stations, both at similar elevations. These estimates, however, have scientific merit and must await better and more geographically dispersed data bases before being refined.

The size and scope of the snow melt impulse on the recharge area of Figeh are critical to understanding the dimensions and durations of not only high flows but also low flows within the Figeh system. The importance of accurately measuring the climatological variables and using

0

0

Below1000

1001–1300

1301–1600

1601–1900

1901–2200

2201–2500

Above2500

50 100 150 200 250 300 350

8009001000110012001300140015001600170018001900200021002200230024002500260027002635 METERSAPRIL

AREA (km2) BY ELEVATION

ESTIMATED ELEVATION OF MEANMONTHLY 0°C (SNOW LINE)

2500 METERSNOVEMBER

MARCH

FEBRUARY

2205 METERS

1945 METERSDECEMBER 1910 METERSJANUARY 1765 METERS

5 10 15 20 25Percent of Total Area

Area (km)

30 35 40 45 50

Estim

ated

Ele

vatio

n of

Mea

n M

onth

ly 0

°C A

bove

MSL

(m)

Elev

atio

n of

Rec

harg

e Are

a Abo

ve M

SL (m

)

fIgure 10.53 Elevations of recharge area and estimated monthly means of 0°C (or snow line).

Case Studies 283

them to determine the recharge impulses and time windows of recharge cannot be overstressed as a long-term water management tool, particularly, as the basis for safe and efficient low-flow augmentation.

10.4.6 dischargE groundWatEr to thE barada rivEr

Increase in the discharge of groundwater to the Barada River was recognized by Burdon6,7 and sub-sequently by Dr. Meir,8,9 Department of Irrigation and Hydraulic Work, in his studies made during the fall of 1982. The interpretation of a conductivity traverse of the Barada indicated changes in chemical quality due to mixing that may be from spring discharge not discernible in the river bed. Ain Harouch and several springs are reported to emerge in the bottom of the Barada River between Ain Harouch and Side Spring. A reconnaissance survey of springs along the Barada River indicates that several springs occur between the villages of Takeye and Khadra.

The discharge of the Barada River was measured at six locations by the Department of Irriga-tion and Hydraulic Power. The measurements were performed during the period from October 13 to October 30, 1982, at Ain Habib, Takeye Hydroelectric Power Plant, Kfer el Aquamid, Deir Moukar-ren, Ain Khadra, and Hemeh.

The study was designed to provide data to determine whether the Barada River gains or loses water through communication with the groundwater system and to allow the determination of spe-cific river reaches in which water is gained or lost. The study provided data indicating groundwater discharge from the karst system.

Data in Table 10.7 indicate losses of water from the Barada River in the two reaches between the Takeye Power Plant and Deir Moukarren (Figure 10.54). These measurements indicate loss of large quantities of groundwater to the Barada River that would be potentially available for the water supply of Damascus. The water losses are due to the recharge to the groundwater system.

During the period of measurement, the Barada gained 0.4–0.9 m3/s flow between Deir Mou-karren and Ain Khadra. Much of this significant water gain must be a result of the recharge from groundwater of the Figeh karst system in the area where Turonian strata are exposed in proximity to the river.

Of even greater significance is the discharges of the Barada River and from the Figeh karst system are hydrologically connected. Any future long-term development of water supplies from the Figeh karst system, particularly any extensive augmentation of low flow, must take this into account from environmental as well as water supply aspects.

Data in Table 10.7 indicate loss of water from the Barada River in the reach between Ain Tak-eye and Hama. Fourteen water samples were collected from the Barada River, and six from springs adjacent to the river. The pH, specific conductance, and temperature of each sample was measured in the field.

table 10.7discharge of barada river (m3/s)

10/13 10/16 10/20 10/27 10/30

Dam at Takeye — — — — — —

Habib Spring 0.165 0.131 0.131 0.135 0.172 0.152

Takeye Discharge Hydroplant

1.968 2.362 2.120 1.706 1.929 1.70

Kfer el Aquamid 1.740 — 2.045 1.613 1.663 1.432

Deir Moukarren 1.108 1.568 1.532 — 1.325 1.373

Ain Khadra — 2.303 2.249 — 1.994 1.603

El Hama — 1.383 1.505 — 1.474 1.602

Source: From Dr. Meir, 1982.


NU

MBE

RD

IVER

SIO

N O

F W

ATER

CA

PAC

ITY

OF

DIV

ERSI

ON

LITE

RS P

ER S

ECO

ND

80

11SC

ALE

IN M

ETER

S

1000

2000

HA

MEH

GAG

ING

STA

TIO

NS

1000

0

fIgure 10.54 Sites of measurements of discharge of the Barada River.

Case Studies 285

Temperature and conductivity for each of the 14 water samples from the Barada River and each of the 6 from the springs were obtained. In addition, profiles are shown for the ten locations where pH was measured. A deflection of the plots for temperature, conductivity, and/or pH occurs at each location where significant additions of water from springs enter the Barada River, as for example, at Ain Habib, at the springs at Souk Wadi Barada and Kfer el Aquamid, at Ain Harouch, at Side Spring, and at Figeh Spring. Based on this information, PELA inferred that additional springs are present in the reach of the Barada River between Kfer el Aquamid and Deir Qanoun. More detailed studies are needed on stream flow. To determine relationships—as a basis for the management and development of these water supplies—the studies should also include correlation with changes in water quality.

Pumping test Studies

Extensive stratigraphic and structural geologic studies were a prelude to a series of pumping tests at critical points in the Figeh Spring area. Interpretation of pumping tests must be based on a knowledge of the stratigraphic sequence of rocks, their lithology, fracturing, karstification, and the recharge area, as well as their storage and discharge characteristics, to properly interpret quantita-tive results from pumping tests.

Geologic mapping during the summer of 1981 led to the opinion that karstification of the Cenomanian strata acts as the principal aquifer to the Figeh system. Groundwater movement is controlled by the dip of strata, plunge of folds, location of faults, and intensity and orientation of fractures. The presence of marls in the Cenomanian rocks retard the vertical movement of water.

Intersection of the anticlinal axes of the Hassiya and Khadra folds created an interference struc-ture, the Figeh Dome. These three structures control the outcrop pattern of the Turonian rocks and, along with faults and fractures, the location of Figeh Spring.

The structural and stratigraphic setting dictates that groundwater in the system must be divided into two different, but interrelated, flow systems. Both systems flow southward, but part of the water is diverted around the western side of the Figeh Dome. This water rises at Ain Harouch, and some discharges directly to the Barada, or is lost as underflow beneath the Barada River. The second major system allows water to move around the eastern side of the Figeh Dome and to rise at Ain Figeh. A portion of this water moves southeastward along the Khadra axis and may underflow the Barada River. The Side Spring at Figeh receives water from both the flow systems as well as from the groundwater that moves downgradient in Pleistocene alluvial deposits along the Barada River.

The hydrologic system of Figeh10 represents a system where numerous losses occur and have been observed. Losses include seasonal evapotranspiration, perennial springs, seeps, evaporation, underflow to the Barada River, and, possibly, underflow to other systems outside the area.

Another major loss from the system is due to withdrawals of groundwater from wells for irriga-tion or urban use. One example is at Deir Moukarren, 3 km west of Figeh Spring, where a large well and pumping station have been constructed on the southwest side of the Figeh Dome.

A series of carefully planned pumping tests were also performed to quantitatively delineate the aerial extent and the boundaries of the karst system supplying water to the Figeh Spring. It was recognized that such series of pumping tests would also be required to properly assess the inter-relationship between Figeh Spring, Side Spring, the Pilot Development Project, Ain Harouch, and groundwater movement in the Deir Moukarren area.

Pumping tests11 have to be carefully planned with representative monitor wells in all possible impacted water sources. They were performed on the following sources:

1. Figeh cavity opening 2. Pilot Development Project 3. Side Spring 4. Ain Harouch, PELA test wells PL-4, PL-5C, and PL-5D 5. Wells in the vicinity of Deir Moukarren


The pumping tests and monitoring carried out during the project at Figeh documented the following:

1. The extent of the cone of depression (dewatering) in the Quaternary deposits above bedrock 2. Changes in turbidity of samples from pilot development wells 3. Changes in turbidity in discharge samples from Figeh 4. Rapidity of changes in water level in Quaternary deposits 5. Changes in water level in the underlying cavities (limestone) in the aquifer system 6. Changes in turbidity of select samples from observation wells tapping the cavity system

and from spring discharge points 7. Record of barometric pressure 8. Change in land surface elevation at selected points around Figeh Spring 9. Change in groundwater temperature from Main Spring, Side Spring, and selected wells in

the surficial aquifer and the cavity system 10. Change in discharge from Figeh and Side Spring 11. Change in discharge from springs discharging to the Barada River 12. Change in water level in five piezometers along the south and north sides of the Grout Curtain 13. Area of impact as related to the potential for pollution of water from the Spring

main cavity—figeh Pumping test

A monitoring network, with systematic collection of data using a combination of water level record-ers, manual measurements, and stream gauging, was an important part of test results during pumping and recovery (Figure 10.55). The following summarizes the results of these tests (see Table 10.8):

FIGEHSPRING

SCALE IN METERS0 500 1000

AFREE

OBSERVATION WELL(MANUALLY RECORDED)

OBSERVATION WELL EQUIPPEDWITH A RECORDER

X-13

PL-1

AFG-10

X-1

E-1

X-14

X-44

X-21X-32

X-19

X-9

Y-1

Y-11

CB-9CB-7

CB-13E-2

X-12X-3

X-42X-47

X-53X-52

X-5

SIDESPRING

FIG

EH R

IVER

BARADA RIVER

CB-3

RIVER

BARADA

HAROUCHSPRING

S-3

F-1

F-3F-2

X-7G-2

INSETENLARGED

AREA

FIGEHSPRING

HAROUCHSPRING

DIERMOUKARREN

0 10 30 50METERS

N

fIgure 10.55 Location of observation wells for the cavity pumping test.

Case Studies 287

1. The pumping test at Figeh Spring was conducted using a step-drawdown procedure. Dis-charge was increased in three steps to stress the aquifer gradually but avoid any potential for collapse at the spring due to subsidence. The pumping test was performed for a period of 7 days, and recovery data were collected for a period of 3 days, i.e., until the system stabilized.

2. Observation wells X-9, X-32, X-53, CB-9, X-35, PELA-1, and F-3 were equipped with recorders; Figeh Spring was monitored by reading an in-place staff gauge. Wells X-1, X-3, X-5, X-12, X-13, X-14, X-21, X-42, X-44, X-52, X-55, X-47, AFG-10, Y-11, E-1, E-2, CB-3, CB-13, and S-3 were manually monitored (Figure 10.55).

3. The measured drawdown data, after adjusting for change in barometric pressure, were plotted against time on double logarithmic paper of the same scale as the type curve (time was plotted on the abscissa, and drawdown on the ordinate). The time-drawdown plots of data from the wells showed steps or segments (a, b, c, and d) caused by gradual increase in pumping rate.

table 10.8results of main cavity pumping test

observation well number ra (m) qb (m3/d) tc (m2/d)

leakance ((m/d)/m) Sd

graphical plot

Cavity 21772.8 140935 — — t-d

29946.2 119213 — — t-d

51321.6 145933 — — t-d

51321.6 181605 — — t-R

X-32 168 29946.2 851518 1.207 × 10−4 9.22 × 10−5 t-d

51321.6 68102 6.03 × 10−5 4 × 10−5 t-R

X-42 28.5 21772.8 31518 3.88 × 10−1 1.185 × 10−1 t-d

29946.2 170304 6.58 × 10−1 5.24 × 10−3 t-d

X-44 19 21772.8 99057 6.86 × 10−1 1.29 × 10−1 t-d

51321.6 81722 4.5 × 10−2 4.4 × 10−4 t-d

X-53 64 21722.8 222244 1.356 × 10−3 2.86 × 10−3 t-d

51321.6 302675 2.05 × 10−4 t-d

X-55 50 21772.8 22224 3.55 × 10−1 8.89 × 10−3 t-d

29946.2 50729 8.11 × 10−3 2.87 × 10−2 t-d

51321.6 56752 — 4.73 × 10−3 t-d

34732.8 691337 2.765 × 10−4 2 × 10−4 t-R

E-2 131 51321.6 120180 — 1.17 × 10−1 1-R

Scattered data — — t-d

CB-9 113 29946.2 72250 — 9.7 × 10−1 t-d

51321.6 329525 2.58 × 10−3 1.7 × 10−1 t-d

PL-1 53 21772.8 101971 — 3.4 × 10−1 t-d

29946.2 70125 — 4.2 × 10−1 t-d

31622.4 62943 8.96 × 10−3 3.1 × 10−1 t-d

51321.6 74923 1.05 × 10−3 8.2 × 10−1 t-d

51321.6 37147 5.29 × 10−1 6.6 × 10−1 t-R

X-1 15 38102.4 195718 — 9.7 × 10−1 t-R

X-13 120 34732.8 74739 8.3 × 10−1 9.4 × 10−1 t-R

Note: r = Distance from pumping well to observation well (m). Q = Discharge rate (m3/day). T = Coefficient of transmis-sivity (m2/day). S = Coefficient of storage (dimensionless).


4. Some irregular variation in the time-drawdown plot may have been caused by an irregular distribution of fractures that act as recharge or barrier boundaries. The fractures, filled with water, contribute water and thus reduce the rate of drawdown, whereas empty frac-tures act as a barrier that increases the rate of drawdown.

5. Characteristics of the drawdown curve indicate that pumping at the cavity during the early period had a point impact on the system and the cone of depression deepened relatively more than the lateral expansion. After pumping for a longer period, with a higher rate of withdrawal, the cone began to gradually expand outward. Pumping at a rate of 51,321.6 m3/d did not affect the regular flow of Figeh Spring. The spring continued to flow at a rate expected for that particular time of the year.

The time-drawdown and time-recovery plots (Figures 10.56–10.59) show a decrease in the time rate of drawdown and recovery, which, based on available hydrogeological data, can be attributed to the effects of leakage. The deviation of the time-drawdown plots from the nonleaky artesian-type curve (Theis curve) indicates that the hydrologic system at Figeh is a semiconfined system.

Side Spring Pumping test

A pumping test on Side Spring of 10 days duration was performed during the period September 5–16, 1982. Well Z-1 was used as one of the points of discharge, and wells X-1, X-2, X-3, X-5, X-13, X-19, X-20, X-21, X-26, X-32, X-53, X-54, X-55, E-1, E-2, AFG-10, CB-1, CB-2, CB-3, CB-6, CB-7, CB-9, CB-11, CB-13, Y-1, Y-2, Y-3, Y-6, F-1, F-3, PL-4, F-2, Figeh Spring, and Side Spring were used as observation points. Observation wells X-9, X-32, X-52, X-55, CB-9, F-3, and PL-4 were equipped with recorders. The staff gauges in Figeh and Side Springs were read throughout the test, and the remainder of the observation wells were manually measured (Figure 10.60).

Sa =

Sa =

4Ttu

MATCH POINT (c)Q = 31622.4 m2/d.W(u, r/D) = 101/u = 102

r/D = 0.02s = 40 cm.t = 500 minutes

MATCH POINT (a)Q = 21772.8 m3/d.W(u) = 101/u = 10s = 17 cm.t = 33.5 minutes

MATCH POINT (b)Q = 29946.2 m3/d.W(u) = 101/u = 10s = 34 cm.s = 40 cm.t = 61 minutes

MATCH POINT (d)Q = 51321.6 m3/d.W(u, r/D) = 101/u = 102

r/D = 0.02

p´/mc =

p´/mc =

p´/mc = 8.96 ×103 (m/d)/mr2

r2

Ta =

Ta =

Ta =

Tb =

Tb =

Tb =Sb =

Sb =

Sb =

W(u)Q4πs21772.8 × 10

4 × 3.14 × 0.17101971 m2/d

Sa = 3.4 ×10–1

4 × 101971×33.5 × 10–1

(53)2 × 1440 s = 55 cm.t = 1115 minutes

FIELD DATA

Td =

LEAKY ARTESIANTYPE CURVE TRACEr/D = 0.02

LEAKY ARTESIANTYPE CURVE TRACE r/D = 0.0

Q4πs W(u, r/D)

4Ttur2

Tc =Q

4πs

Q

29946.2 × 10 4 × 3.14 × 0.3470125 m2/d

4πs

W(u, r/D)

W(u)

Tc =Sc =

4 × 62943 × 500 × 10–2

3.1 × 10–1(53)2 × 1440

Tc =31622.4 × 10

62943 m2/d4Ttu

Td =

Td =

Sd =

4 × 74293 × 1115 × 10–2

Sd = 8.2 × 10–1

51321.6 × 10

74293 m2/d4 × 3.14 × 0.55

(53)2 × 1440

4 × 3.14 × 0.4

DEVIATION DUETO LEAKAGE

(r/D)2 T

(0.2)2 × 62943

p´/md =

p´/md =

p´/md =

(r/D)2 Tr2

(53)2

(0.02)2 × 7429(53)2

1.05 × 103 (m/d)/m

DEVIATION DUE TO LEAKAGE

r2

Sc =

Sc =

+

+

+

+

FIELD DATA

4Ttu

4 × 70125 × 61 × 10–1

4.2 × 10–1

102101

10

Dra

wdo

wn

(s) i

n C

entim

eter

s

NON-LEAKY ARTESIANTYPE CURVE TRACE

102

103 1810 min.PUMP 2 OFFVALVE OPEN

1640 min.PUMP 3 ON

3500 min.PUMP 2 ON

104200 min.

PUMP 2 ON

Time (t) in Minutes

(53)2 × 14402

r2(a)

2690 min.VALVE COLSED


(b)

(d)(c)

Sd =

fIgure 10.56 Time-drawdown plot for observation well PELA-1 (cavity pumping test).

Case Studies 289

Q = 21772.8 m/sec.W(u, r/D) = 101/u = 102

r/D = 0.2S = 78 cm.t = 36 minutesQ = 29946.2 m3/sec.

W(u, r/D) = 101/u = 10r/D = 0.02s = 47 cm.t = 51 minutes

r = 50 meters

Q = 51321.6 m3/sec.W(u, r/D) = 101/u = 102

r/D = 0.01S = 72 cm.t = 75 minutes

MATCH POINT (d)

MATCH POINT (b)

MATCH POINT (a)




LEAKY ARTESIAN TYPECURVE TRACE


LEAKY ARTESIANTYPE CURVE TRACE

r/D = 0.01

Time (t) in Minutes

Dra

wdo

wn

(s) i

n C

entim

eter

s

FIELD DATAFIELD DATA

FIELD DATADEVIATION DUE TO LEAKAGE



P´/md =

P´/md =

P´/md = 2.27 × 103 (m/d)/m

(r/D)2T

(0.01)2 × 56752(50)2

r2

Q4πs´ W(u, r/D)Ta =

Ta =

Sa =

Sa =

Ta = 22224 m2/d

Sa = 8.89 × 10–3

4Ttur2

21772.8 × 104 × 3.14 × 0.78

4 × 22224 × 36 × 10–2

(50)2

Sd =

Sd =

Sd = 4.73 × 10–21810 min.

PUMP 2 OFFVALVE OPEN

3500 MIN.PUMP 2 ON

2000 min.Valve Closed

1640 min.Pump 3 ON

200 min.Pump 3 ON

1010210

10

102

11

10

4Ttur2

4 × 56752 × 76 × 10–2

Q4πs W(u, r/D)Tb =

Tb =

Sb =

Sb =

Tb = 50729 m2/d

Sb = 2.87 × 10–2

4Ttur2

29946.2 × 104 × 3.14 × 0.47

4 × 50729 × 51 × 10–2

(50)2 × 1440

(50)2 × 1440

Q4πs W(u, r/D)Td =

Td =

Td = 56752 m2/d

51321.6 × 104 × 3.14 × 0.72

P´/ma =

P´/ma =

P´/ma = 3.55 × 10–1 (m/d)/m

(r/D)2T

(0.2)2 × 22224(50)2

r2

P´/mb =

P´/mb =

P /mb = 8.11 × 10–3 (m/d)/m

(r/D)2 T

(0.2)2 × 50729(50)2

r2

(b)

(a)

(d)

fIgure 10.57 Time-drawdown plot for observation well X-55 (cavity pumping test).

Q = 34732.8 m3/dW(u, r/D) = 102

1/u = 105

r/D = 0.001s´ = 40 cms.t = 27 minutesr = 50 meters

Q4πs´ W(u, r/D)T =

T =

S =

S =

T = 691337 m2/d

S = 2 × 10–4

102

10

11 10 102 103

4Ttur2

34732.8 × 102

4 × 3.14 × 0.4

4 × 691337 × 27 × 105

(50)2 × 1440

MATCH POINT



Time (t) in Minutes

Reco

very

(s´)

in C

entim

eter

s (cm

s)

DEVIATION DUETO LEAKAGE

P´/m´ =

P´/m´ =

P´/m´ = 2.765×10–4(m/d)/m

(r/D)2T

(0.001)2 × 691337(50)2

r2

FIELD DATA

fIgure 10.58 Time-recovery plot for observation well X-55 (cavity pumping test).


MATCHPOINT

10

Reco

very

(s´)

in C

entim

eter

s (cm

s)



Q = 51321.63 m/dW(u, r/D) = 11/u = 1r/D = 0.2s´ = 11 cms.t = 18 minutesr = 53 meters


FIELD DATA

T = Q

P´/m´ =

P´/m´ =

P´/m´ = 5.29 × 10–1 (m/d)/m

(r/D)2T

51321.6 × 14 × 3.14 × 0.11

T = 37147 m2/d

W(u, r/D)4πs´

4Ttu

4 × 37147 × 18 × 11440 × (53)2

S =

S =

S = 6.6 ×10–1

Time (t) in Minutes

101

102 103 104

r2

T =

r2

(0.2)2 × 37147(53)2

fIgure 10.59 Time-recovery plot for observation well PELA-1 (cavity pumping test).

AFREE

OBSERVATION WELL (MANUALLYRECORDED)

OBSERVATION WELL EQUIPPED WITH ARECORDERSTAFF GAGEF-4

F-1F-3

F-2PL-4

INSETENLARGEDAREA

FIGEHSPRING

DIERMOUKARREN

HAROUCHSPRING

S-3

X-20X-19

Y-1Y-3

X-32 X-21

X-2X-3

X-26

X-1 X-5

X–13

X-55

X-53X-9

CB-1CB-2CB-3 CB-6 CB-7

SIDESPRING

BARADA RIVER

FIGEHSPRING

FIG

EH R

IVER

CB-9CB-11 CB-13

N

0 10 5030

METERS

E-2

E-1

Z-1

AFG-10

RIVER

BARADA

HAROUCHSPRING

fIgure 10.60 Location of observation wells for the Side Spring pumping test.

Case Studies 291

Owing to difficulties in determining instantaneous discharges, the total average discharge rates during different periods of the test were calculated. The rate was 1.546 m3/s (133,574.4 m3/d) for the first 200 min of pumping; it then increased to 2.04 m3/s (176,256 m3/d) until 2,000 min of pumping. Then the discharge rate increased to 2.218 m3/s (191,695.7 m3/d) and remained almost the same until 10,000 min of pumping. During the final stages of pumping, the rate of discharge increased to 2.227 m3/s (192,412.8 m3/d) until termination of pumping. Discharge rates had to be calculated precisely because of the following factors:

1. There was no method for the direct instantaneous measurements of discharge rates from the Side Spring.

2. Failures of the pumps during test period. 3. Power surges caused by uncontrollable voltage and power failure. 4. Extracted water was not fully contributed by the aquifer, but came from three different

sources: a. Source I—The contribution of Figeh Spring increased exponentially with time, as the

hydraulic gradient reversed because of pumping. b. Source II—A volume of water was contributed by the subsurface drainage (alluvial

water) to the Side Spring. This contribution was due to the lowering of water level in Side Spring caused by pumping.

c. Source III—Water was contributed from fractures in the limestone at a higher eleva-tion than the Side Spring. These fractures initially contributed to Figeh Spring, but pumping diverted the flow of groundwater toward Side Spring.

The quantity of water contributed by these various sources to pumping appears to be more than what could be directly from the aquifer; so the impact of pumping from Side Spring on the aquifer system during the earlier period of pumping is on localized storage as it is not recorded at distant observation wells (r = +100 m). The transmissivity values determined in this test must be evaluated carefully; computations of the coefficient of storage are not included in the time-rate drawdown of each of the observation wells (Table 10.9).

The time-drawdown graphs show, in general, that the steps of the time-drawdown curve are due to different rates of discharge. Some of the data points do not fall on the curves, indicating either sudden increases or declines in the rate of discharge, thereby causing the variation in time-rate drawdown. Some of the variations in the time-drawdown are the result of a single or collective effect of various factors previously described and must be evaluated as a part of the interpretive process.

The effects of pumping of Side Spring were observed within the first 10 min of pumping. The water levels in observation wells X-19, X-21, Y-1, Z-1, and CB-6 show direct hydraulic connections between Side Spring and the water-bearing zones tapped by these wells. But in the remaining obser-vation wells, X-1, X-2, X-5, X-13, X-20, X-26, X-32, X-53, CB-2, CB-3, CB-7, CB-9, CB-11, CB-13, E-1, and E-2, the impact of pumping was not recorded or measured until after 100 min of pumping, indicating a more indirect hydraulic connection of Side Spring with the water-bearing zones tapped by these wells. Thus, the aquifer at these wells is either independent of the main cavity system, or the cone of depression does not extend deep enough, until after 100 min of pumping, to affect these wells and establish a hydraulically connected system between the Side Spring and water-bearing zones tapped by these observation wells. A similar situation was observed during the cavity pump-ing test (Table 10.9).

The computation and analyses of time-drawdown graphs for the one observation well is given in Figure 10.61. The summary of results are given in Table 10.9.


Pilot Pumping test

The design of the pilot pump test involved the construction of a caisson containing 20 wells of 12 1/4 in. diameter, penetrating the main cavity at Figeh Spring (see Figure 10.62). The caisson was connected to the pump intakes in the central control center via a tunnel of 1.5 m in diameter. The total discharge from the spring and caisson was about 4.0 m3/s.

The objective of the test was to determine the feasibility of augmenting the flow from Source Figeh during the periods of stable low flow without seriously impacting the flow from Figeh or adversely affecting the hydrologic system supplying Figeh Spring.

table 10.9results of Side Spring pumping testobservation well

number r (m) q (m3/day) t (m2/day)leakance (m/

day)/m graphical plot

X-1 84 176256 44550 — t-d

191695.7 141318 — t-d

192412.8 38299 — t-d

X-2 30 133574.4 42534 4.72 × 10−1 t-d

176256 44550 1.23 × 10−1 t-d

191695.7 30573 — t-d

X-19 286 133574.4 2955414 144 × 10−1 t-d

176256 25059 2.75 × 10−2 t-d

191695.7 4489 — t-d

X-21 78 133574.4 42202 6.24 × 10−1 t-d

176256 66823 2.74 × 10−2 t-d

192412.8 56739 — t-d

X-26 78 133574.4 59082.8 2.4 × 10−2 t-d

176256 444086 1.82 × 10−1 t-d

Y-1 153 133574.4 129694 2.216 × 10−1 t-d

176256 55032 2.35 × 10−2 t-d

191695.7 20082 — t-d

192412.8 16297 — t-d

Z-1 133574.4 128131 — t-d

192412.8 64367 — t-d

CB-1 133574.4 66468 — t-d

176256 48390 — t-d

192412.8 19149 — t-d

CB-2 104 133574.4 50642 1.87 × 10−1 t-d

176256 45524 4.208 × 10−9 t-d

192412.8 25528 — t-d

CB-3 84 133574.4 46239 2.62 × 10−1 t-d

176256 43179 6.12 × 10−2 t-d

192412.8 55707 — t-d

E-1 79 133574.4 393885 6.31 × 10−1 t-d

Note: r = Discharge from pumping well to observation well (m). Q = Discharge rate (m3/day). T = Coefficient of transmis-sivity (m2/day). S = Coefficient of storage (dimensionless).

Case Studies 293

102

103 MATCH POINT (a)Q = 133574.4 m3/dW (u, r/D) = 101/u = 102

s = 250 cm.t = 1.57 × 103 minr = 30 meters

MATCH POINT (b)Q = 176256 m3/dW (u, r/D) = 10r/D = 102

s = 315 cm.t = 8.8 × 103 minr = 30 meters

MATCH POINT (c)Q = 191695.7 m3/dW (u) = 101/u = 102

s = 500 cm.t = 1.78 × 103 min

(r/D)2 T

(r/D)2 T

r2

r2

(0.1)2 × 42534

(0.05)2 × 44550

(30)2

(30)2

Time (t) in Minutes104103103

10105




FIELD DATA LEAKY ARTESIAN TYPECURVE TRACEr/D = 0.05

Ta =

Ta =

Ta = 42534 m2/d

Tc = 30573 m2/d

Tb = 44550 m2/d

176256 × 10

191695.7 × 104 × 3.14 × 5

133574.4 × 104 × 3.14 × 2.5

4 × 3.14 × 3.15

W(u, r/D)

W(u, r/D)

4πs

4πs

Q

Q

LEAKY ARTESIAN TYPECURVE TRACEr/D = 0.1

Dra

wdo

wn

(s) i

n C

entim

eter

s P/ma = 4.72 × 10–1 (m/d)/m

P/mb =

P/mb = 1.23 × 10–1 (m/d)/m

P/mb =

P/ma =

P/ma =

Tc =

Tc =

Tb =

Tb =

W(u, r/D)4πsQ

fIgure 10.61 Time-drawdown plot for observation well X-2 (Side Spring pumping test).

Total capacity of 3 Pump =3 Cubic meters per second

Elevation826 meters

Elevation827 meters

Cluster of 20 wells

Pump platform

Surface elevation825 meters

TunnelConcretewall

GroutInto figeh

cavern system Severed casing

Elevation 817.5meters

PumpPump intake

elevation 818.75meters

Elevation 817.0

Discharge

Limestone

20 meters thick

Fractures

Potentiometric

827 Meters

1.5 m

10 m

fIgure 10.62 Schematic pilot pumping installation.


The specific objectives were to

1. Augment flow from Figeh during periods of low flow 2. Determine the impact of pumping on the discharge from Figeh 3. Determine the impact of pumping on the hydrologic system supplying water to Figeh 4. Determine the areal extent of the cone of depression caused by pumping the pilot develop-

ment facility 5. Determine the most effective rate of pumping from the system 6. Determine any changes in land surface (subsidence features) caused by the pumping

Pumping from the pilot project was from the flow discharged to the pumps through tunnels 1.5 m in diameter. The head on the system, at the time of the test, was at an elevation of 825 m. The minimum elevation in head at which the pumping was performed was 818.75 m. The elevation of the pump intake provided for a maximum drawdown in potentiometric head of 6 m. A schematic diagram of the pilot pumping installation is shown in Figure 10.62. The geologic setting of the well is shown on the geologic cross section.

The limestone underlying the site is at a depth of 10 m and forms a semiconfining bed for the under-lying artesian system. The semiconfining bed of limestone is extensively fractured, and these fractures serve as avenues for limited hydraulic connection and flow of water from the Figeh aquifer system upward to the unconsolidated Quaternary alluvial deposits. Water was observed entering the well dur-ing drilling operations at the site of test hole X-37 after 1 m of limestone had been penetrated.

The geologic setting at the pilot development test site was of concern, because the limestone on which the pilot development caisson was set was fractured and the bearing strength was unknown. During test drilling and pumping, there was substantial potential for collapse caused by the drilling activities and vibration from pumping. A collapse of any portion of the underlying limestone would have an adverse effect on the hydrologic system supplying water to Figeh. As a part of the pumping test, therefore, a detailed monitoring program was implemented to detect changes in the surface features and the hydrologic system (e.g., muddying and change in water temperature or quality) that would be indicative of changes within the system during withdrawal.

The monitoring program during pumping from the pilot development project at Figeh included the determination of the following items:

1. Close monitoring of the extent of cone of depression (dewatering) in the alluvial deposits above bedrock

2. Changes in turbidity of samples from the pilot development wells 3. Changes in turbidity from samples from Figeh discharge 4. Rapidity of changes in water level in Quaternary deposits 5. Changes in water level in the underlying limestone aquifer system 6. Changes in turbidity of selected examples from observation wells tapping the cavity sys-

tem and at the spring discharge points 8. Changes in land surface elevation at selected points around Figeh Spring 9. Changes in groundwater temperature in samples from Figeh Spring, Side Spring, and

selected wells in the surficial aquifer and the cavity system 10. Changes in discharge from Side Spring 11. Changes in discharge from springs discharging to the Barada River

The pilot pump test was performed using the step-drawdown procedure (Table 10.10). Three pumps were installed near the caisson to pump at a rate of 1 m3/s each. Four pumps were installed in Main Spring. The collective discharge rate from these four pumps was 1.00 m3/s. During the test, the rate of discharge was increased in four steps at a rate of 1 m3/s.

Case Studies 295

table 10.10results of pumping test analysis (pilot test) time-drawdown

Well number

r(m) distance from cavity

(main Spring)transmissivity

t1 (m2/day)transmissivity



t4 (m2/day)leakance (m/

day/m)

PL-2A 83 295,000 980,000 1 × 10−1

Y-7 155 84,000 299,000

Y-9 185 79,000 785,700

Y-11 165

Ain Harrouch 570 206,200 190,000

X-5 35 245,550 8 × 10−2

PL-5D 580 199,000

PL-5B 582 305,500

S-3 540 172,000

X-18 38 283,000

X-13 120 81,000

X-11 78 134,000

X-8 23 149,000 1.12 × 10−1

X-14 14 150,000

X-55 48 150,000

PL-7 90 225,000

PL-9 138 335,000

F-2 150,000

X-20 445 166,000

Caisson (Ca-2) 27 153,000 172,000

Sh-3 15,000 275,000

CB-13 148 270,000

X-21 135 550,000

X-46 47 230,000

PL-2C 60 190,000 196,440

PL-1 55 180,000 151 × 10−1

E-2 142 40,000

X-26 93 392,000

F-3 86,000 38,000

Y-6 200 86,000 60,000

E-1 78 120,000 190,000

Main spring 180,000 200,000

PL-3 37,000 200,000

X-52 75 10,000 50,000

X-50 52 170,000 180,000

X-44 35 90,000 150,000

X-9 205 230,000 5.5 × 10−2

JZ-1 114 355,000 480,000

Cassion (Ca-1) 25 67,000 140,000

X-1 20 145,000 9 × 10−1

X-2 80 625,000

X-32 170 720,000 500,000

X-43 36 197,000 3.7 × 10−3

Note: Q = 3 m3/d, or 259200 m3/d, Q2 = 4 m3/s or 345600 m3/d.


The test was initiated at 10 a.m. on October 12, 1983, by starting pump number 1 at a rate of 1 m3/s. The pumping continued for 60 min, and then a second pump was started. The total discharge rate was 2 m3/s. The third pump was turned on after 120 min of pumping. The total discharge rate was 3 m3/s for a period of 180 min. Then the four cavity pumps were started one by one. The total pumping rate after 240 min of pumping was 4.00 m3/s and remained stable until the termination of the test at 10:45 a.m. on October 17, 1983. Recovery data were collected until 10 a.m. on October 21. The test was performed for a period of 5 d and recovery data collected for a period of 4 d until the system stabilized.

The observation wells X-55, PL-7, PL-9, X-32, X-26, X-9, F-2, and F-3 were equipped with recorders, and Main Spring, Side Spring, and Ain Harouch were maintained by reading in-place staff gauges. Two shallow wells, Sh-1 and Sh-2, were penetrating the unconsolidated upper aqui-fer; wells, X-1, X-2, X-5, X-7, X-8, X-11, X-13, X-14, X-18, X-20, X-21, X-26, X-43, X-44, X-46, X-50, X-51, X-52, X-54, X-55, Y-1, Y-2, Y-6, Y-7, Y-9, Y-11, CB-1, CB-5, CB-6, CB-10, CB-11, CB-13, E-1, E-2, F-1, F-3, Z-1, PL-2A, PL-2C, PL-3, PL-4, PL-5B, PL-5D, and PL-6 were manu-ally monitored.

The time-drawdown or time-recovery plots for water levels of the wells were obtained from location map recorders or carefully monitored manual measurements to show the current changes in spring flow and water levels caused by gradual increases in pumping rates. The results of the pumping tests are summarized in Tables 10.10 and 10.11.

The water level in the shallow wells Sh-1 and Sh-2 did not show significant response to the pumping, indicating minimum direct hydraulic connection with the underlying karst system. The responses measured in the observation wells during the test demonstrate that the karst system at Figeh responds heterogeneously and that the spring is supplied by interconnected or preferential flow paths within the area of the observation wells. Barada River, which flows south of Figeh Spring, acts as a hydrologic boundary. The surficial and alluvial deposits occurring on the top of the bedrock constitute a water table aquifer that is in a delicate hydraulic balance with the underlying Figeh karst aquifer.

The karst system at Deir Moukarren has a poor hydraulic connection with Figeh Spring, and an additional volume of 2 m3/s could be developed from the Deir Moukarren Basin in the general vicinity of PL-5 wells. The water temperature data collected during the test indicate the presence of a deeper karst fissure system that contains water at a higher temperature than the water discharging from the upper part of the Figeh system.

In conclusion, the pumping of the cavity at the mouth of Figeh and from the Pilot Development Project at a total rate of 4 m3/s increased the yield from the system about 0.6 m3/s (600 L/s). This pumpage could be safely increased to a rate of 1 m3/s, which would result in an additional drawdown of 2 cm at Main Spring during low-season flows. The maximum drawdown at the cavity, below the caisson, at Side Spring, and at Ain Harouch, with pumping rates of 1 m3/s from the spring and 3 m3/s from pumping caisson, was 1.17, 1.83, 0.27, and 0.29, respectively.

The discharge at Ain Harouch is, in part, hydraulically connected with the Barada River and the overlying alluvial aquifer. It is also hydraulically connected with the irrigation ditches that recharge the karst aquifer in the vicinity of Ain Harouch (well X-19).

Pumping test results indicate that, with proper control and managed modifications at Figeh Spring, flow augmentation in the amount of 4 m3/s is available to support the needs of Damascus during the low-flow season. The reduction in storage will be replaced by the rains during the early part of the recharge period.

Case Studies 297

10.4.7 EnvironmEntal constraints to FuturE usE oF FigEh systEm

1. The Cenomanian and Turonian strata comprise a karst aquifer system through which water is conveyed from recharge to storage and ultimately to discharge at the springs at Ain Figeh and Ain Harouch. There are many additional springs along the Barada River, which are points of discharge. There is, likewise, a substantial upward flow from the Turonian rocks through fractures and solution cavities into the Barada, which maintains its base flow.

2. The overlying Senonian marls act as aquitards, which restrict discharge to the land surface where they occur.

table 10.11results of pumping test analysis (pilot pumping test) time-recovery

Well number

r (m) distance from cavity

(main Spring)transmissivity t1

(m2/d)transmissivity t2

(m2/d)transmissivity t3

(m2/d)leakance (m/d/m)

Sh-3 213,000

X-9 205 327,400

PL-5B 582 370,000 1,145,900

PL-3 92,000

Main Spring 1,835,500 4,9297,000

E-2 142 30,000

Z-1 114 226,000 598,000 1,262,000

Caisson (Ca-2) 27 125,000

Caisson (Ca-1) 125,000 8 × 10−2

Y-6 200 1,300,000

X-52 75 110,000 125,000 610,000

X-50 52 275,000 1.02 × 10−4

X-43 36 240,000

X-44 35 250,000 8.16 × 10−4

X-20 445 197,000

Ain Harrouch 810,000

PL-7 90 382,000 1.2 × 10−5

Cb-3 55,000

Y-7 155 130,000 292,000

PL-2C 60 371,000 2.6 × 10−5

X-1 20 370,000 170,000 420,000

E-1 78 3,055,775 1.25 × 10−3

X-2 80 177,500 723,000 1,146,000

X-8 23 180,000 1.3 × 10−1

X-5 35 275,000

PL-1 55 275,000 352,500

X-14 14 83,000 1.7 × 10−1

X-18 38 177,400 3.07 × 10−1

X-11 78 125,000 2 × 10−1

X-13 120 88,700

X-46 47 289,500 1.31 × 10−4

PL-9 138 491,100 2.57 × 10−1

Note: Q = 4 m3/s or 345600 m3/d.


3. Detailed photogeologic and ground-truth studies have established that virtually the entire recharge area of the Figeh Spring system is underlain by rocks of the Cenomanian Age, which are fractured and karstified in this area, and a major source of the recharge is from the snow fields and snow accumulation at altitudes above 1500 m upgradient from the springs.

4. Geologic mapping and hydrogeologic studies during the summers of 1981 and 1982 showed that the Cenomanian strata also contains a complex karstified aquifer system that supplies large quantities of water to the Figeh system. Groundwater movement is from the outcrop of these rocks into interconnected openings along bedding and fractures, and locally in solution cavities, to the underlying storage system. The specific movement of water is con-trolled by the dip of bedding, plunge of folds, location of faults, and the system and inten-sity of fracturing.

5. Major structural features influence the direction of groundwater movements from recharge to storage and to discharge. Intersections of the anticlinal axis of the Hassiya and Khadra folds create an interference structure (the Figeh Dome). These three structures control the outcrop pattern of the Turonian rocks in the area, and along with the faults and fractures, the present location of the Figeh and other springs that discharge into the Barada River.

6. Interpretations of the structural and stratigraphic settings have indicated that groundwater in the area should be divided into two different flow paths, both regimes flowing south-ward. Part of the water is diverted around the western flank of the Figeh Dome. Some of this water rises at Ain Harouch; some is believed to be lost as underflow beneath the Bar-ada River. The second major flow regime consists of the water that moves around the east-ern side of the Figeh Dome and rises at Ain Figeh. A portion moves southeastward along the Khadra fold axis, and some of the water may underflow the Barada River. The Side Spring at Figeh receives water from both flow regimes as well as from the flow through the alluvial beds of an ancient Barada River channel, now parallel and adjacent to the Barada River.

7. Flow directions of groundwater are shown in the map. Points of discharge are shown by the location of the springs (see Figure 8.54 and Table 10.7). Figeh Spring discharges near a Pleistocene meander of the Barada River. Figeh Spring during Roman occupation (63 bc to 633 ad) discharged at a lower elevation than it does today. At present it discharges through an opening in the Turonian rocks. At this point, a reservoir system has been developed, diverting the water into the channels that supply the city of Figeh. There is also withdrawal of groundwater from sump pumps that have been installed at the spring. This water is under semiartesian pressure.

8. The importance of understanding the reservoir system from which the water flows, the flow direction, and the rate of water withdrawn allows determination of the area around the spring in which environmental restraints should be imposed on development. These are (as shown in Figure 10.63):Area A: In the closest semicircular area around Ain Harouch, Side Spring, and Figeh, two

karst flow systems are involved. Maximum security must be imposed here to limit development that could cause physical (discharge) or chemical change, or cause pol-lution to access areas near surface solution cavities and rock fractures that are con-nected to the water in the spring. This area has been designated a Maximum Security Area. No development other than that associated with the production of water from the spring should be undertaken.

Area B: A second semicircle delineates an upgradient area in the spring flow system in which development such as housing, agriculture, grazing, and other activities should be restrained. There should be no placement of landfills of hazardous, toxic, or radio-active waste, and all construction or other development should be carefully reviewed and approved by representatives of Figeh Spring.

Case Studies 299

Area C: The third outlying semicircular area shown in the map is an area that would be safe and proper for development of light agriculture and light grazing with minimum use of pesticides, insecticides, and fertilizers. Minimum housing, urban development, and construction should be allowed by approval of Figeh city officials. Hazardous, toxic, and radioactive waste should be banned.

referenceS

1. Dubertret, L., Carte Geologique au 50,000 du Liban. Feuille de Zebdani et Notice Explicative, Bey-routh, 1949.

2. Ponikarov, V. P., (Ed.), Vinogradskey, A. V., Trans, The Geological Map of Syria, Scale 1:50,000, with Explanatory Notes, Ministry of Industry, Syriani Arab Republic, 1968, 120 pp.

3. Bazin, F. (SOGREAH), Etude hydrologique et hydrogeologique de la Source Figeh, rapport final, A. Cartes; R. 11.422, 1973.

4. Bazin, F. (SOGREAH), Etude hydrologique et hydrogique de la Source Figeh; R. 11.343, 1973. 5. Bazin, F. (SOGREAH), 1973, and others, Etude hydrologique et hydrogeologique de la Source Figeh,

rapport final; R. 11.422, 1973. 6. Burdon, D. J., Geological features of the Barada Valley in relation to the proposed storage reservoirs,

Technical FAO United Nations Report No. 337 to the Government of Syria, 1954. 7. Burdon, D. J., The Groundwater Resources of the Damascus Basin—A Preliminary Report, Department

of Irrigation and Hydraulic Power, Ministry of Public Works, Government of Syria, 1959, 19 pp. 8. Burdon, D. J., Groundwater Development and Conservation in Syria, Expanded Technical Assistance

Plan Rept. No. 1270, FAO, United Nations, Rome, 1961, 84 pp. 9. Burdon, D. J. and Safadi, C., Ras-El-Ain (the great karst spring of Mesopotamia), Journal of Hydrology,

7, 1, 1963. 10. LaMoreaux, P. E., Remote-sensing techniques and the detection of karst, Association of Engineering

Geologists, 16, 3, 1979. 11. LaMoreaux, P. E. and Associates, Assessment of pilot development project report, 28 July–8 August,

1982, with a section on Calculation of stability of boreholes at the project Al-Fije Spring, by Walid Kanaan, Establissement Public des Eaux de Figeh, P. E. LaMoreaux and Associates, Tuscaloosa, AL, 1982, 22 pp.

B

C

A

fIgure 10.63 Map of environmental protection zones: (A) total protection—maximum security; (B) per-mit housing and other development; (C) permit proper development and light agriculture.


10.5 collectIon and dISPoSal of naturally occurrIng cHlorIde-contamInated groundWater to ImProVe Water qualIty In tHe red rIVer baSIn

10.5.1 introduction

Naturally occurring brine emissions via seeps and springs in the Red River basin contribute an average of 3600 tons of chloride daily to the Red River. Eight areas in the river basin in Arkansas, Louisiana, Oklahoma, and Texas (U.S. Corps of Engineers) were identified as the main contributors to the chloride contamination in the Red River (Figures 10.64, 10.65, and 10.66). Separate method-ologies for the control of chloride for each area were developed. One that was implemented included

TEXAS

LOUISIANA

ARKANSAS

OKLAHOMA

RED RIVER BASIN

EMISSION AREA

FortWorthDallas

Modified from US Army Corps of Engineers Tulsa District (US GPO: 1993-769-606)

Shreveport

Amarillo

fIgure 10.64 Regional map.

Collingsworth

Harmon OklahomaJackson

Wilbarger

Vicinity MapLEGEND

Foard

Texas

Hardeman

Cottle

King

Modified from Red River Authority of Taxas

Knox

Motley

Childress

Hall AREA XIII & XIV

AREA VIII

AREA V

Graphic Scale in Miles

AREA VIII

AREA IX

AREA X

AREA V

Wichita

Archer

Baylor

Clay

Greer

AREA VIDonley

0 5 10 15S

E

N

W

20 25

fIgure 10.65 Main identified chloride sources.

Case Studies 301

the construction of a ring dike around Estelline spring (Area V). The height of the dike was more than the head of the groundwater discharging from the spring; subsequently the spring ceased to discharge. Another was the construction of Truscott Brine Lake, a large evaporation basin. Surface water, high in chlorides, was collected from Area VIII and pumped 35 km to the manmade Lake Truscott to evaporate. The method selected for Upper Area XIII was the collection of chloride-contaminated groundwater through a series of shallow collection wells and the disposal of brine through a series of deep injection wells.

Investigations described herein are related to Upper Area XIII. Brine emissions through seeps and springs enter the tributaries of the Red River in Area XIII at an average of 145 metric tons of chloride per day. Area XIII is located in Childress County, Texas, about 16 km west of the south-west corner of Oklahoma (Figure 10.67). The chloride load from brine emissions in this area is transported to the Prairie Dog Town Fork of the Red River via Jonah Creek (Figure 10.65). Jonah Creek is located in Upper Area XIII (Figure 10.68), and drains into the adjacent subbasins. Springs and seeps in Jonah Creek contribute a total of 145 t/d of chloride to the Prairie Dog Town Fork of the Red River.

Brine from Areas XIII (left) and XIV (right) carries 570 tons of salt per day into tributaries of the Red River. About 88% of this will be collected in shallow wells before it reaches the surface It will be disposed of by deep well injection into the Ellenburger Formation 5,800 feet below the surface.

At Area VI emissions containing 510 tons of salt per day occur in three canyons within a half-mile area; 82% will be collected and piped to Salt Creek Brine Lake.

Area XIII & XIV Area IV

Area V

Area IX

Area VII

Area X Area VIII

Salt Creek Brine Lake Crowell Brine

Lake

Amarillo

Vernon Wichita Falls

Fort Worth

Dallas

Truscott Brine Lake

Area VIII springs contribute almost 195 tons of salt pollution daily. A low-flow dam has been constructed which traps 85% of the brine. The brine is pumped to the Truscott Brine Lake.

Area X daily contributes 48 tons of salt to the Wichita River. The spring area extends for about 6 miles, with the brine emerging from the base of vertical cliffs. An inflatable dam will stop the flow of 84% of the brine which will be pumped to Truscott Brine Lake.

Area VII will have an inflatable dam to stop 84% of the flow of 186 tons of salt per day. The brine will be pumped to Crowell Brine Lake.

MODIFIED: FROM US ARMY CORPS OF ENGINEERS, TULSA DISTRICT

The plan for Area IX will capture 60% of the 340 tons of brine per day coming from two pollution sources along the Pease River. The brines at the southern location will be collected by a surface structure. The northern location is for future study. The brine will be pumped to Crowell Brine Lake.

The ring dike around Estelline Springs is preventing 240 tons of salt contamination per day

Red River

Shreveport

fIgure 10.66 Brine emission areas.


SaltCreek

Creek

AREA XIII & XIV

AREA V

AREA IX

AREA VLEGEND

Modified from Red River Authority of Texas

Childress

Cottle

Texa

s

Oklahom

a

Jonah

RED RIVER

Childress

Graphic Scale in Miles0 5 10 15 20 25

Identified Chloride Sources

LakeChildress

BaylorLake

fIgure 10.67 Vicinity map.

B4 B5

PIEZOMETERBOREHOLECORE HOLETEST WELL BOREHOLE

LOCATION OF CROSS–SECTION

PARSHALL FLUMESPRING

SCALE IN FEET

400 200 0 400 800

A´

A

TW214–81

P–7

B3

P3

P6P4SP1S

B1

TW2TW1PW95

B2

A´

B´

P7

P2P5

11–70

12–70

5–70

P4DP1D

A

fIgure 10.68 Site map, Upper Area XIII.

Case Studies 303

The purpose of this investigation was to evaluate hydrogeologic conditions in Upper Area XIII for the optimal design of a shallow well system that controls natural brine discharges into the creek and for installing a treatment system to treat the water, along with a deep injection well system for the disposal of collected and treated brines. Investigations included a detailed reconnaissance survey to locate visible seeps and springs, and test drilling in emission areas; installation of pump-ing wells and monitoring piezometers; and installation of Parshall flumes to measure creek flow. Aquifer tests were performed to determine hydraulic characteristics of the bedrock aquifer system in Upper Area XIII, which included hydraulic communication between the alluvial and bedrock aquifers and the creek bed, and by collection and analyses of water samples from the pumping wells, creeks, and selected piezometers to provide water quality information for design of a treat-ment facility and a deep injection well system.

10.5.2 gEologic sEtting

Area XIII is east of the High Plains subdivision of the central lowland physiographic province at the base of the Texas Panhandle. During the Permian Period (270 million years ago), a shallow inland sea became isolated, and interbedded shale and evaporites that currently cover these areas were deposited. The evaporites include dolomite, gypsum, and halite. The Flowerpot Formation overlies the San Angelo Formation and consists of shale interbedded with gypsum in the upper portion. Overlying the Flowerpot Formation is the Blaine Formation, 76 m thick, which consists of numer-ous evaporite cycles of gypsum and dolomite separated by thin shale beds. Approximately 90% of the Blaine Formation is evaporites. The lower member, the Elm Fork Member of this formation, has three evaporite cycles. The Acme Dolomite, part of the sixth evaporite cycle, is the thickest dolomite of the Van Vactor Member and is the main saturated zone of the bedrock aquifer system, which provides groundwater flow and brine discharge through seeps and springs to the creek. Fractures and cavities formed by dissolution of the underlying carbonate rocks and evaporites are filled with alluvial deposits consisting of clay, silty clay with rock fragments, and gravel. The alluvial deposits facilitate discharge of brine as seeps. Figure 10.69 is a stratigraphic column of the units underlying the area of investigation.

The thickest section, about 18 m of the overburden/alluvium replacement or fill material, was penetrated by the boring for piezometer P1 (Figure 10.69). This area represents the bottom of a solu-tion feature that has been draped by the overlying, more competent Acme Dolomite. As the bedrock units underlying the Acme went through dissolution, the Acme slumped onto the underlying units, forming an intermittent unit composed primarily of large blocks of the Acme lying on relatively competent bedrock.

The dolomite units throughout the Upper Area XIII are typically light gray to olive gray, very finely crystalline, fractured along bedding planes, vuggy in places, and weathered. Gypsum units are typically white to light gray, finely crystalline, and massively bedded to interbedded with thin layers of dolomite. Cavities were penetrated in either dolomite and/or gypsum in numerous bore-holes in the Upper Area XIII. Some of the cavities were open with no fill material, whereas some were filled with clay, sand, and gravel. Shale in the Upper XIII Area is variable in color from moder-ate reddish brown to light to dark gray.

The overburden/alluvium is primarily composed of alternating deposits of silt, sand, and gravel. Typically the silt is moderate reddish brown with variable amounts of clay and sand. The sand is typically moderate to dark reddish brown, with some yellow or gray lenses, fine- to medium-grained, rounded quartz. Gravel is typically white quartz or brown chert, with occasional gypsum or dolomite pieces, subrounded to round, and less than 1 in. in diameter. Thickness of the overbur-den/alluvium or fill material within the salt flats range 8–12 m. Figure 10.70 illustrates the hydro-geologic cross section in Area XIII.

The brine discharge areas along Jonah Creek (Upper Area XIII) are generally broad, relatively flat and bowl shaped, and cover about 36 ha. The dissolution of the underlying carbonate rocks and


SYSTEM SERIES GROUP OR FORMATION SURFACE EL 1723

GYPSUM, DOLOMITE, AND SHALE

SHALE AND SOME GYPSUMAND DOLOMITE

SHALE AND HALITE (UPPERCLEARFORK SALT)

SHALE AND ANHYDRITE

SHALE

SHALE

DOLOMITE, LIMESTONE, ANDSHALE

SHALE, LIMESTONE, AND SOMESANDSTONE

ELEV

ATIO

N

SHALE AND REEFY LIMESTONE

LIMESTONE, SANDSTONE, ANDSHALE

DARK SHALE AND LIMESTONE

LIMESTONE AND SHALE

MASSIVE CRINOIDAL LIMESTONEWITH SOME DOLOMITE AND CHERT

DOLOMITE WITH SOMELIMESTONE

SHALEY LIMESTONE, DOLOMITE,AND GLAUCONITIC SANDSTONE

BOH EL –6117

–6000

–5000

–4000

–3000

–2000

–1000

0

1000

GYPSUM AND DOLOMITESANDSTONE AND SHALE

BLAINE

FLOWERPOTGUADALUPIAN

LEONARDIAN

PERMIAN

CHOZA

CIMARRONANHYDRITETUBB ZONE

CLEAR FORKEVAPORITES

RED CAVE

WICHITA

WOLFCAMPWOLFCAMPIAN

VIRGILIAN

MISSOURIAN

DES MOINESIAN

MORROWAN MORROW

CHESTERIAN

MERAMECIANTO

OSAGIAN

CAMBRO–ORDOVICIAN

CAMBRIAN

TD

MISSISSIPPIAN

PENNSYLVANIAN

CISCO

CANYON

STRAWN

CHESTER

MERAMEC–OSAGE

ELLENBURGER

UPPER CAMBRIAN

DOLOMITELIMESTONE

SHALESANDSTONE

CHERTGAMMA LOG (LEFT)RESISTIVITY LOG (RIGHT)CEMENTED CASINGLOCK SET PACKER AT BASE OF4–1/2 INCH INJECTION TUBING

HALITEGYPSUM

1000´

2000´

3000´

4000´

DEP

TH

5000´

6000´

7000´

7840´

SOURCE: COE DM 27

0´


Case Studies 305

subsequent collapse of land surface and deposits of alluvium in these features resulted in the broad bowl-shaped areas. Thick alluvial deposits consisting primarily of sand, with some gravel lenses, underlie the central portion of the area. At the boundaries of the brine discharge areas, bluffs are gen-erally 1 m high and goes up to as high as 5 m where bedrock is exposed at the southern boundary of the emission areas. From the crest of the bluffs, the land surface slopes gently upward, east and west, away from the brine emission area, to the hills that form the boundaries of the drainage basin.

10.5.3 hydrogEologic sEtting

The drainage basin of Jonah Creek (Area XIII) covers approximately 16,000 ha. Its flow, most of the year, is maintained by groundwater (base flow) that, in places (emission areas), migrates through naturally occurring salt beds within the Blaine Formation. The bedrock aquifer system at the site is under semiartesian conditions, having partial hydraulic connection with the overlying overburden/alluvial aquifer. Salt-laden groundwater moves through bedrock with a relatively high hydraulic conductivity in conduit or fracture flow. It intersects the emission areas comprised of weathered bedrock with fractures and cavities filled with alluvium, which has relatively low hydraulic conduc-tivity. Thus, groundwater, under artesian conditions, moves from the higher conductivities of the alluvium-filled fractures and cavities and daylights as seeps and springs forming emission areas. Seeps flow from alluvium, and springs flow from fractures in pinnacles at the base of each spring. Salt crust or emission areas are formed by the upward movement of salt-laden groundwater through fine-grained alluvial deposits by capillary action and the subsequent evaporation of water, leaving a fine-grained salt deposit (salt crust) in an area known as a salt flat. The entire salt flat area is devoid of vegetation, and under most climatic conditions there is a crust of salt 1–2 mm thick covering the entire area. In the vicinity of the seeps, the salt crust attains a thickness of 7–8 cm. During rain storms, the salt crust is dissolved, and the upper portion of the alluvium is flushed with freshwater, which sends the salt downstream.

Naturally occurring springs that are a direct conduit from the underlying bedrock range in size from 5 cm to 1 m in diameter and depth. The larger springs form spring pots in the alluvial deposits. Discharge from relatively large springs erodes the alluvial deposits, typically contains boiling sand, and is continuous. Discharge from small springs forms mounds of fine-grained sand and silt around the openings (throats) of springs.

Numerous springs and seeps are visible within the salt-encrusted depressions (salt flats) in Jonah Creek (Figure 10.68). The major source of saltwater, a number of small springs with a west-

LEGENDSAND

GYPSUM

CLAY/GYPSUM

1600

1620

1640

1660

ELEV

ATIO

N (F

EET

NG

VD

)

1680

1700

1720

1740XIII–U–B3

A

XIII–U–P3

XIII–U–B2

XIII–U–P4

XIII–U–12–70A´

XIII–U–11–70

400 800D

SCALE IN FEET

0

20

SILT CAVITY

GRAVEL SILTY CLAY

CLAY SHALE

DOLOMITE

fIgure 10.70 Geologic cross-section XIII-U-AA’.


to-east orientation, is along the southern boundary of the emission area, about 305 m upstream of a USGS weir. These springs range in size from 5 mm to 90 cm in diameter and depth. The larger springs in the salt flat, some distance from Jonah Creek, typically form spring pots in the alluvial deposits. Discharge from these larger springs in the salt flats erodes the alluvial deposits, typically contain boiling sands, and is continuous. Discharge from the smaller springs of the salt flats forms small spring mounds of fine-grained sand and silt. Discharge from these springs is variable. Springs within Jonah Creek are more potlike and are a direct conduit to the underlying bedrock. The salt flat area is devoid of vegetation and, under most climatic conditions, there is a thin crust of salt, 1–2 mm thick, covering the entire area. Capillary action brings saltwater to the land surface, and the evaporation rate of the area precludes any accumulation of water at the surface for runoff.

10.5.4 FiEld invEstigations

Field investigations were performed to identify seeps and springs, which aided in the selection of locations for drilling of stratigraphic borings and construction of piezometers and wells. Locations of these borings were also selected based on a review of the literature, aerial photography, and site interpretation of geologic and structural features observed during the detailed reconnaissance. Six stratigraphic borings were completed in the Upper Area XIII by coring overburden and bedrock at depths ranging from 9 to 30 m below land surface (bls). Stratigraphic borings were drilled to gather information about the lithology, geometry, structure, changes in orientation of fractures and bed-ding characteristics of the bedrock and overlying alluvium, and potential water-bearing zones. After coring, each of the boreholes was geophysically logged (natural gamma, caliper, and electric logs). Lithologic information obtained from the boreholes, geophysical logging of boreholes, and observa-tions made during drilling were used to select the screened intervals of the piezometers.

Seven piezometers, using 3 meters of schedule 40 PVC screen (0.25-mm slot) in each of the piezometers, were constructed in the bedrock aquifer. A filter pack of 20–40 size sand was placed around and 60 cm above the top of the slots of the screen through tremie pipe in each piezometer. A bentonite seal was placed from the top of the filter pack to the land surface to make sure that the annular space above the sand pack was properly sealed. Two shallow piezometers were installed at selected locations in Upper Area XIII to monitor groundwater in the overburden/alluvial aquifer and the underlying bedrock aquifer system. A concrete antipercolation collar (120 × 120 cm) was placed around each piezometer.

Additionally, one piezometer was installed in Upper Area XIII to collect water samples during the tests for groundwater quality determinations. These piezometers were developed by bailing or air compressor to measure water levels, determine the relationship between groundwater and sur-face water, and serve as observation points during aquifer (pumping) tests.

Two 30 cm diameter pumping wells (TW-1 and TW-2) were constructed to perform aquifer tests. Each of these wells were constructed by drilling a small-diameter pilot hole at each location in the bedrock. The pilot holes were tested to ensure that each location provided abundant water to perform the tests and there was impact on brine emissions in Area XIII during pumping. Subse-quently, the boreholes were reamed and constructed as 30 cm diameter pumping wells (test wells). Each of the test wells was constructed of a Schedule 40-PVC, 30 cm diameter screen (18 mm slot). A filter pack of 6–9 size filter sand was placed around the screen. The filter pack was added directly from bags to a minimum of 1 m above the top of the slotted screen. Bentonite chips were placed from the top of the filter pack to the land surface. A concrete pad (2 m × 2 m) was constructed around each well. Table 10.12 provides construction information for the pumping wells used in the pumping test performed in Upper Area XIII. The locations of piezometers and pumping wells are shown in Figure 10.68.

Two Parshall flumes were installed in Jonah Creek to measure streamflow—one upstream flume located 425 m, and one downstream, 245 m, from pumping wells TW-1 and TW-2, respec-

pjw

stk|

4020

64|1

4354

3263

6

Case Studies 307

tively. These flumes were used to measure surface water discharge in the creek during planning and performance of the aquifer test in this area. Stilling wells were installed at each flume location to measure the water levels. Water level recorders were installed in each stilling well to continuously record data during the investigation. The location of stratigraphic borings, piezometers, Parshall flumes, and the pumping wells are shown on Figure 10.68.

A rain gage and Belfort microbarograph were installed at suitable locations to record the rain-fall, if any, and the changes in atmospheric pressure. Barometric pressure and water level data collected during the premonitoring period were used to compute the barometric efficiency for each area. Barometric efficiency is the ratio of the fluctuation of water level in the well to the change in atmospheric pressure causing the fluctuation. This data was used to adjust the collected water level data for external stresses prior to analyzing the aquifer test data.

Each of the piezometers and stilling wells at the upstream and downstream flumes were equipped with water level recorders to collect data continuously. The pumping wells at each location were monitored using in situ data loggers to collect water level data continuously during premonitoring, testing, and recovery. The water levels in each of the pumping wells were also frequently measured manually during the secondary test period and immediately after the termination of each test. The piezometers were also frequently monitored manually to ensure that the recorders were functioning properly. Flows at the upstream and downstream flumes were monitored continuously by recording the head at each flume location. Springs and seeps were frequently monitored before, during pump-ing, and after the termination of the test.

Water samples were collected from each of the pumping wells during the test to determine field parameters such as temperature, Eh, turbidity, pH, specific conductance, salinity, and dissolved oxygen. Field titrations were performed to determine chloride concentration (mg/L) in samples collected frequently from the creeks and pumping wells during test periods. Additional samples were collected from the pumping and monitoring wells, and shipped to a laboratory for chemical analysis for 22 parameters including chloride to provide data for the design of treatment and injec-tion systems.

An aquifer (pumping) test was performed in Upper Area XIII for a period of 7 d after the ter-mination of each test; water level recovery data were collected for a period of 4 d. Brine emissions (springs and seeps) were monitored regularly during these periods. Other activities were performed during the aquifer test:

Discharge rates from pumping wells were closely monitored (on a 1–2 h basis).•Emission (springs/seeps) were monitored.•Flow rates at both upstream and downstream flumes were monitored.•Areas were visually inspected to monitor any evidence of subsidence.•Wind direction and velocity were monitored as they affected the flow rate in Jonah Creek.•

table 10.12Pumping well specifications, upper area XIII, Jonah creek

Pz/bholewell

number

drilledtd

(ft bls)

constructedtd

(ft bls)

Screened interval(ft bls)

Sand pack(ft bls)

bentonite seal

(ft bls)

cement(ft bls)

casing(in/type)

TW-1 55.8 55.80 35.8–55.8 5.0–55.8 0.0–5.0 — 12.0/PVC

TW-2 54.0 54.00 34.0–54.0 5.0–54.0 0.0–5.0 — 12.0/PVC

Note: bls = Below land surface; in/type = diameter and type of casing; TD = total depth.


aquifer (Pumping) tests

Monitoring NetworkThe monitoring network for the pumping test was designed to monitor (1) water level in both the overburden/alluvial aquifer and the underlying bedrock aquifer system, (2) the impact of pumping on the flow of surface water in Jonah Creek, and (3) brine emissions during the 7 d pumping and 4 d recovery period of the test.

PremonitoringPremonitoring was performed for 3 d prior to the initiation of the aquifer (pumping) test to estab-lish ground- and surface water trends, and effects of barometric pressure changes on groundwater levels. Review of lithologic information and analyses of collected water level data, together with changes in barometric pressure during the premonitoring period, indicated that the bedrock aqui-fer system was under artesian condition, and water level fluctuations were caused by changes in barometric pressure. Barometric efficiency was 48%. Wind velocity and direction had a signifi-cant effect on the flow rates of surface water in Jonah Creek. When wind blew from the north, the flow recorded at both the upstream and downstream flumes in Jonah Creek increased propor-tionately with the wind velocity. Similarly, when wind blew from the south, the flow recorded in the flumes decreased.

Specific Capacity TestsSpecific capacity tests were performed on each of the pumping wells to determine an index of well productivity. Each of the pumping wells in Upper Area XIII were separately pumped at a series of specified rates; each rate was held constant until the water level stabilized. Drawdowns were mea-sured continuously in each of the pumping wells during the tests. The discharge rates and drawdown data collected were used to compute the productivity index of each of the pumping wells. These indices were used to determine the appropriate pump size for each pumping well and the discharge rate at which to pump each of the wells during the test.

Results of each of the specific capacity tests performed on each of the wells generally indicated that their productivity improved with increasing discharge rates. During pumping at a higher rate, clay-filled fractures, joints, and fissures were partially cleaned out, and the porosity and permeabil-ity of the bedrock aquifer in the vicinity of each of the wells were enhanced. Inhomogeneities in the formation causes changes in the specific yield, with increasing drawdown. Results of the tests are given in Table 10.13.

table 10.13results of specific capacity tests

area XIII (Jonah creek)

Welldischarge rate

q gpmdrawdown

S(ft)Specific capacity (q/s) gpm/ft.dd

TW-1 500 8.69 57.51

750 16.49 45.48

1060 14.87 71.31

1245 16.07 77.46

TW-2 750 2.80 267.85

825 4.66 177.21

1020 6.10 167.10

Note: gpm = gallons per minute; gpm/ft.dd = gallons per minute per foot of drawdown.

Case Studies 309

Potentiometric Surface in Upper Area XIIIUpper Area XIII (Jonah Creek)

Water level data collected in Upper Area XIII from the seven piezometers (P1 through P7), wells PW-95, TW-1, and TW-2 on April 9, 1996, prior to initiation of the test, were plotted to prepare a potentiometric surface map of the bedrock aquifer system (Figure 10.71). The map indicates that groundwater moves toward Jonah Creek; the gradient is generally shallow, but it becomes steep (up to 40 ft/mi) at the emission area. The gradient is influenced by the proximity to discharge locations. A depression in the potentiometric surface is shown near piezometer P6, which coincides with a low in the bedrock surface.

Two piezometers (P1S and P4S) were completed in the overburden/alluvium to monitor the water level in the overburden/alluvial aquifer. The water level elevations at P1S and P1D (piezom-eter completed in bedrock) were 1,706.85 and 1,707.35 ft, respectively. The head difference was 0.5 ft. Water level elevation in the alluvial aquifer was 0.5 ft lower than that in the bedrock aquifer, indicating a vertical gradient upward from the bedrock to the overburden/alluvium. In general, there is a vertical upward gradient in the Upper Area XIII. This upward movement of brine under relatively low head exists in the bedrock aquifer system, causing the emission of brine from seeps and springs.

Pumping TestThe surface collection of brine is a viable method to control emissions of brine into Jonah Creek. Therefore, the impact of the pumping of groundwater from designated wells in the aquifer test was evaluated from the changes in water levels in the bedrock aquifer system, the overlying overburden/alluvial aquifer, and surface water.

B3

B1

B2

P7

TW2TW1

P3

P4SP6

1700

POTENTIOMETRICSURFACE ELEVATION INFEET AT MONITORINGPOINTPOTENTIOMETRICCONTOUR IN FEETNGVD

400 200 0 400 800

SCALE IN FEET

1696.10

1694.32

1696.10

1703.

1705.84

1706

1704

1702

1700

1694

1696

1698

1698

1700

P1S707.33

1705.371705.93

1705.23

1705.31

P4D

P5

PW95

P1D

B4 B5

fIgure 10.71 Pre-pumping surface bedrock aquifer, April 9–10, 1996, Upper Area XIII.


The purpose of performing a test in Upper Area XIII was to determine

(a) The effect of lowering the water level in the bedrock aquifer system on the discharge of springs and seeps to control brine emissions and consequently the flow of surface water in Jonah Creek.

(b) The hydraulic characteristics of the water-bearing zones in the bedrock aquifer (c) The degree of isotophy and the vertical and lateral extent of the interconnection of the

fracture system (d) The existence of any geologic and hydrogeologic boundaries

Based on field investigations and understanding of stratigraphy, lithology, geologic structure, hydro-geologic settings, and location of brine emissions, two sites were carefully selected for performing aquifer tests to determine the impact of lowering water level and controlling brine discharges from springs and seeps. It was recognized that the aquifer test would also provide data to compute appro-priate abstraction rates to control brine emissions and design treatment and disposal facilities for pumped water. Two sites were located in Upper Area XIII. The locations of test wells are shown on Figure 10.68.

Analyses of Pumping TestsWater levels from pumping tests were adjusted for atmospheric pressure fluctuations using the baro-metric efficiency of 48%. Adjusted water level data were tabulated as time-drawdown and time-recovery, and plotted separately on double logarithmic graphic paper at the same scale as that of the type curve or curves, with time on the abscissa and drawdown or recovery on the ordinate. The log-log graphs of time-drawdown and time-recovery were separately superimposed, keeping the coordinate axis of the two graphs parallel and matched to the nonleaky and/or leaky artesian type curves. During the first few minutes of the test, some deviation of field data from the type curve is expected due to fluctuations in the pumping rates. An arbitrary point, designated the match point, was selected, representing the matched portion of the field data curve and the theoretical type curve. Match point coordinates W(u), W(u, r/B) 1/u, s, and t, were determined and are shown on the time-drawdown and time-recovery plots. The match point coordinates were submitted into Equations (10.1) and (10.2) to determine the transmissivity and the coefficient of storage of the aquifer.

T QW us

=114 6. ( )

(10.1)

or

T QW u r Bs

=114 6. ( , / )

(10.2)

where T = coefficient of transmissivity (gpd/ft) Q = discharge (gpm) W(u) = well function for nonleaky artesian aquifer W(u,r/B) = well function for leaky artesian aquifer s = drawdown (ft) s′ = recovery (ft) S = coefficient of storage (dimensionless) t = time in days after pumping started t′ = time in days after pumping terminated. r = distance in feet from pumped well to observation point (piezometer)

Case Studies 311

Aquifer Test (Pumping and Recovery) Upper Area XIIIThe 7 d pumping test was started at 11 a.m. on April 9, 1996 (locations, see Figure 10.68). Well TW-1 was pumped at a rate of 1,000 gpm. The pumping of well TW-2 was started at 7 p.m. on April 10, 1996, at a rate of 850 gpm. The combined discharge rate from both wells was 1,850 gpm. Pumping was terminated on April 16, 1996. A total of 17,424,000 gal of brine was pumped from the two wells (TW-1 and TW-2) during the pumping period of 7 d. No precipitation occurred during the test. The maximum drawdown in wells TW-1 and TW-2 was 15.05 and 8.39 ft, respectively. The minimum flow at both upstream and downstream flumes, 357 gpm (0.8 cfs) and 31 gpm (0.07 cfs), occurred on April 16 at 12:32 and 12:30, respectively. Vortexes were observed in Jonah Creek (Upper Area XIII) at the spring locations, indicating induced infiltration caused by the reversal of hydraulic gradient at these locations. The recovery test began at 1 p.m. on April 16, 1996, when pumping from both wells (TW-1 and TW-2) was terminated. Recovery data were collected for 4 d. In 4 d, groundwater had recovered to its prepumping level. Recovery data were also used to compute aquifer characteristics (transmissivity and coefficient of storage).

The water level data collected during the pumping and recovery periods were tabulated, adjusted, and plotted as time-drawdown and time-recovery curves. Graphical plots of log time versus log drawdown and log time versus log recovery were matched to type curves for nonleaky and leaky confined aquifers, presented in Lohman (1979). The arbitrary match points, representing the match portions of the field data curves, were noted on field data graphs and substituted in Equations (10.1) and (10.2) to compute transmissivity and the coefficient of storage. The value of transmissivity of the bedrock aquifer ranges from 12,000 to 471,000 gpd/ft. The transmissivity calculated from data collected at wells TW-1 and TW-2 ranges from 14,700 to 342,000 gpd/ft. The average transmissivity of the bedrock aquifer system is 170,000 gpd/ft. The higher values of transmissivity are indicative of the karst nature of the bedrock aquifer and its ability to transmit brine to the surface. The coefficient of storage ranges from 9.1 × 10−6 to 1.0 × 10−1, with an average of 2.0 × 10−2 (dimensionless).

The transmissivity of the overburden/alluvial aquifer ranges from 4,000 to 424,000, with an average of 166,000 gpd/ft. The coefficient of storage ranges from 1.1 × 10−1 to 5.2 × 10−3, with an average of 4.7 × 10-2.

The water levels monitored during the pumping test in piezometers P1-S and P4-S completed in the overburden/alluvial aquifer showed significant drawdown that varied from those observed in the bedrock aquifer, indicating vertical leakage from the alluvial aquifer into the underlying bedrock aquifer system. This demonstrates that the bedrock is a semiconfined aquifer system.

The pumping test results are summarized in Table 10.14. Time-drawdown and time-recovery plots for well TW-2 and piezometer P2 are provided in Figures 10.72–10.75.

10.5.5 inducEd inFiltration

Induced infiltration of creek water as a source of recharge occurs when a well is pumped near a creek that is in hydraulic connection with the aquifer. During pumping, water is first withdrawn from the storage within the aquifer in proximity to the well. The cone of influence then extends, and water levels in the aquifer are sufficiently lowered to fall below water levels in the creek. This results in a reversal of the hydraulic gradient and eventually causes induced infiltration of surface water into the underlying aquifer.

Because of the proximity of the pumping wells in Upper Area XIII to Jonah Creek, a certain amount of induced infiltration from each creek to the pumping wells is expected. Based on Darcy’s Law, the infiltration from the creek is directly proportional to the vertical permeability of the creek bed, and to the difference between the water level in the aquifer immediately below the creek bed and that in the creek. Induced infiltration from the creek is also dependent on the permeability and transmissivity of the alluvium/overburden and bedrock aquifer system; heterogeneity of the aquifer system; size, shape, density, and spatial distribution and connectivity of fractures and joints; the distance from the pumping well to the creek; lateral and vertical extent of the cone of influence;


table 10.14Summary of pumping test results, Jonah creek, upper area XIII

Welldrawdown/

recoverytransmissivity (t)

gpd/ftStorativity (S)

TW-1 Drawdown T2 138,072 —

T3 114,600 —

T4 88,153 —

Average 113,608

TW-1 Recovery T1 14,692 —

T2 81,857 —

T3 60,315 —

T4 127,333 —

T5 114,600 —

Average 79,759

TW-2 Drawdown T2 278,314 —

T3 124,884 —

T4 57,300 —

T5 110,693 —

T6 84,704 —

Average 131,179

TW-2 Recovery T3 341,789 —

T4 135,291 —

T5 34,178 —

T6 97,410 —

T7 108,233 —

Average 143,380

PW-95 Drawdown T3 212,010 9.1 × 10-6

Average 212,010 9.1 × 10-6

PW-95 Recovery T1 136,780 4.1 × 10-5

T2 232,978 1.8 × 10-6

Average 184,879 2.1 × 10-5

P1S Drawdown T3 4,077 5.2 × 10-3

T4 78,522 1.8 × 10-2

T5 212,010 7.7 × 10-3

Average 98,203 1.0 × 10-2

P1S Recovery T1 132,506 5.2 × 10-3

Average 132,506 5.2 × 10-3

P1D Drawdown T3 11,778 9.6 × 10-3

T4 92,178 1.4 × 10-2

T5 223,168 4.7 × 10-3

Average 109,041 9.4 × 10-3

P1D Recovery T1 176,675 3.0 × 10-3

—continued

Case Studies 313

table 10.14 (continued)Summary of pumping test results, Jonah creek, upper area XIII

Welldrawdown/

recoverytransmissivity (t)

gpd/ftStorativity (S)

T2 353,353 8.4 × 10-4

Average 265,012 1.9 × 10-3

P2 Drawdown T1 81,857 8.5 × 10-4

T2 114,600 2.1 × 10-3

Average 98,228 1.5 × 10-3

P2 Recovery T1 136,780 3.5 × 10-4

T2 22,316 1.5 × 10-5

Average 79,548 1.8 × 10-4

P3 Drawdown T3 184,356 1.3 × 10-2

Average 184,356 1.3 × 10-2

P3 Recovery T1 246,523 3.8 × 10-3

Average 246,523 3.8 × 10-3

P4S Drawdown T3 146,213 1.1 × 10-1

Average 146,213 1.1 × 10-1

P4S Recovery T2 424,020 6.3 × 10-2

Average 424,020 6.3 × 10-2

P4D Drawdown T2 23,688 3.2 × 10-4

Average 23,688 3.2 × 10-4

P4D Recovery T1 302,871 6.4 × 10-4

Average 302,871 6.4 × 10-4

P5 Drawdown T4 92,178 1.0 × 10-1

Average 92,178 1.0 × 10-1

P5 Recovery T1 471,133 1.4 × 10-2

T3 302,871 1.7 × 10-4

Average 387,002 7.1 × 10-3

P6 Drawdown T3 261,740 6.8 × 10-2

Average 261,740 6.8 × 10-2

P6 Recovery T2 757,178 4.1 × 10-2

Average 757,178 4.1 × 10-2

P7 Drawdown T3 13,006 3.1 × 10-2

T4 78,522 6.3 × 10-2

Average 45,764 4.7 × 10-2

P7 Recovery T2 252,392 2.8 × 10-2

Average 252,392 2.8 × 10-2

Note: gpd/ft = gallons per day per foot.


LEGEND

TYPE CURVEFIELD DATAMATCH POINT

W(u)

MP-1

ut

s

WELL FUNCTION

TIME (MINS)

DRAWDOWN(FEET)

r2S/4Tt

TIME-DRAWDOWN

MP-2

MP-4

MP-1

t = 2.35 MINSs = 18FTW(u) = 10

1/u = 1t = 0.295 MINSs = 9.1 FT

W(u) = 101/u = 1t = 0.1 MINSs = 4.55 FT

MP-5MP-3

W(u) = 0.11/u = 1t = 1.85 MINSs = 0.11 FT

TIME (MINUTES)

101 102 103 104 10510010–110–210–3

10–2

10–1

DRA

WD

OW

N (F

EET) 100

101

102

W(u) = 0.11/u = 1t = 0.6 MINSs = 0.11 FT

W(u) = 101/u = 1

fIgure 10.72 Upper Area XIII, TW-2 manual drawdown.

W(u) = 11/u = 1000t´ = 0.68 MINSs´ = 0.25 FT

LEGEND

TYPE CURVEFIELD DATAMATCH POINT

W(u)

MP-1

u´t´

s´

WELL FUNCTION

TIME (MINS)RECOVERY(FEET)

r2S/4Tt

TIME-RECOVERY

MP-2

MP-4W(u) = 11/u = 1t = 1.55 MINSs = 1.35 FT

MP-5

MP-3

MP-1

W(u) = 11/u = 1t´ = 0.165 MINSs´ = 0.63 FT

TIME (MINUTES)101 102 103 104 10510010–110–2

10–3

10–2

10–1

RECO

VER

Y (F

EET) 100

101

102

W(u) = 0.11/u = 10t´ = 4.2 MINSs´ = 0.128 FT

W(u) = 11/u = 1000t´ = 0.11 MINSs´ = 0.21 FT

fIgure 10.73 Upper Area XIII, TW-2 manual recovery.

Case Studies 315

102

101

100

10–1

DRA

WD

OW

N (F

EET)

10–2

10–3

10–2 10–1 100 101 102

TIME (MINUTES)103 104 105

MP-2

TIME-DRAWDOWNLEGENDTYPE CURVEFIELD DATA

MATCH POINTWELL FUNCTION

TIME (MINS)DRAWDOWN(FEET)

stu

W(u)

MP-1

r2/S/4Tt

MP-1W(u) = 11/u = 1t = 2.2 MINSs = 1.4 FT

W(u) = 101/u = 1t = 3.9 MINSs = 10 FT

fIgure 10.74 Upper Area XIII, piezometer P2.

102TIME-RECOVERY

101

100

Reco

very

(Fee

t)

10–1

10–2

10–3

10–2 10–1 100 101

TIME (MINUTES)102 103 104 105

MP-2w(u) =11/u = 1t´ = 0.68 MINSs´ = 9.5 FT

MP-1

w(u) =11/u = 1t´ = 2.5 MINSs´ = 1.55 FT

TYPE CURVEFIELD DATAMATCH POINTMP-1

W(u)

ut´

s´

WELL FUNCTION

TIME (MINS)

RECOVERY(FEET)

r2S/4Tt

LEGEND

fIgure 10.75 Upper Area XIII, piezometer P2.

pjw

stk|

4020

64|1

4354

3262

3


the time period for which the wells have been pumped; and climatological conditions and sea-son of the year.

The percentage and volume of induced infil-tration is calculated using the following equa-tions and the graph shown in Figure 10.76.

f a S

Tt=

1 87 2. (10.3)

Q Qpr

r=100

(10.4)

where T = transmissivity (gpd/ft) S = coefficient of storage (dimensionless) t = time since pumping started (d) a = distance from the pumping well to the recharge boundary Qr = amount of induced infiltration (gpm) Pr = percentage of surface water being diverted from the creek

The amount of actual induced infiltration is sig-nificantly less than the computed values because of a number of factors, including,

Heterogeneity of the bedrock aquifer •system

Low permeability of the creek bed•Presence of confining layers between the residuum/alluvium and the bedrock aquifer systems•Potential reduction in the hydraulic connectivity because of partial clogging of the frac-•tures, and fissures by deposition of fine sediments over timeMaintenance of the optimal head difference between groundwater and surface water to •control brine emissions and thereby reduce infiltration

Existing drainage channels and springs, which are potential avenues for infiltration, once dry, would not provide recharge to the underlying bedrock aquifer system. Diversion ditches and dikes could also reduce infiltration by rerouting surface water away from areas where the potential for infiltra-tion is highest.

upper area XIII (Jonah creek)

Vortexes were observed in Jonah Creek at spring locations near well TW-1, indicating induced infil-tration caused by a reversal of the hydraulic gradient at these locations. Pumping at a rate of 1,850 gpm (4.12 cfs) from both wells (TW-1 and TW-2) eliminated emissions of brine, reduced base flow, and caused surface water to infiltrate into dewatered overburden/alluvium and, through fractures and spring openings, into bedrock. The infiltrated water traveled laterally through bedrock to the pumping well. Drawdown in the pumping well continued to increase, though at a relatively slow rate, demonstrating that the rate of infiltration was lower than the rate of discharge. Infiltration is restricted because the lithologic composition of the creek bed consists mainly of silty sand, clayey

100

90

80

70

60

Pr, P

erce

nt o

f Pum

ped

Wat

er B

eing

Div

erte

d fro

m S

trea

m

50

40

30

20

10

00

0.2 0.3Values of f

For Upper Curve

0.4 0.5

1 2 3 4 51.87a2S

T†f =

0.1

fIgure 10.76 Relation between Pr and f.

Case Studies 317

sand, silty clay, sandy clay, and clay. The effective porosity and permeability of this material is low; therefore, infiltration from the creek through the overburden to the underlying bedrock is restricted and limited in quantity. Fissures and/or fractures, which act as conduits and are avenues for brine discharges, will eventually become clogged, resulting in temporal and spatial decline in the rate of infiltration into the bedrock aquifer system.

The percentage and volume of induced infiltration is estimated by substituting transmissivi-ties of 135, 000 gpd/ft and 100,000 gpd/ft (average volume for pumping wells TW-1 and TW-2), pumping test discharge rates of 1,000 gpm (2.23 cfs, or 63 L/s) and 850 gpm (1.9 cfs, or 53.63 L/s) into Equations 10.3 and 10.4, and using graph Figure 10.76. The estimated induced infiltration is provided in Table 10.15.

The induced filtration was also estimated for long-range discharge rates of 433 gpm (0.96 cfs) from two proposed collection wells (CW-1 and CW-3) and 316 gpm (0.7 cfs) from two wells (CW-2 and CW-4). The results are provided in Table 10.16.

10.5.6 draWdoWn in bEdrock aquiFEr systEm and ovErburdEn/alluvial aquiFEr

upper area XIII (Jonah creek)

Maximum drawdowns of 15.05 and 8.39 ft occurred in wells TW-1 and TW-2, respectively, prior to termination of pumping. The cone of influence extended in a northern direction during the first 1 h of pumping well TW-1 (Figure 10.77). After the initiation of pumping from well TW-2, a cone of influence developed around well TW-2. There were two cones of influence extending in a north and northwest direction after 24 h of pumping (Figure 10.78). The configuration of the cones indicates that there is a boundary between wells TW-1 and TW-2. The shape of the cone suggests induced infiltration from Jonah Creek. In other words, Jonah Creek was acting as a recharge boundary. The combined cone of influence extended primarily to the north, northwest, and northeast. (Fig-ure 10.79). The combined cone of influence caused by the pumping of both wells (TW-1 and TW-2) extended beyond the locations of both upstream and downstream flumes (Figure 10.80). The length of Jonah Creek encompassed by the cone of influence at the end of pumping was approximately 2,200 ft.

table 10.15estimated induced infiltration from Jonah creek during the pumping test in upper area XIII

Well time (t)transmissivity

(t) q r Pr qr

TW-1 1 d 100001000010000

100010001000

100012001500

291911

290190110

7 d 100001000010000

100010001000

100012001500

716658

710660580

TW-2 1 d 135000135000135000

850850850

100012001500

363018

306251136

7 d 135000135000135000

850850850

100012001500

756963

637586535

Note: Pr = percentage of pumped water diverted from the creek. Qr = amount of induced infiltration (gpm). T = transmis-sivity (gpd/ft). Q = proposed pumping rate (gpm). r = distance from the pumping well to the recharge boundary. t = time since pumping started.


Figures 10.77–10.80 illustrate the progression of the cones of influence caused by the pumping of wells TW-1 and TW-2 from April 9 through April 15, 1996.

Piezometers P1S and P4S, completed in the overburden/alluvial aquifer (Figures 10.79 and 10.80), were affected by pumping from bedrock wells TW-1 and TW-2. The maximum drawdowns observed in piezometers P1S and P4S were 3.59 ft and 1.76 ft, respectively. This indicates that the underlying bedrock is a semiconfined aquifer, and considerable variation exists in the amount of vertical leakage that occur from the overburden/alluvial aquifer to the underlying bedrock aquifer system. The areal extent of the confining layers is limited in comparison to the extent of the cone of influence.

10.5.7 EFFEcts oF pumping on Jonah crEEk

The flow in Jonah Creek (Upper Area XIII) was monitored by a pair of Parshall flumes located upstream and downstream from pumping wells TW-1, TW-2 in the Upper Area XIII, as shown in Figure 10.68, to measure the flow prior to, during, and after termination of pumping in the wells. The flows at upstream and downstream flumes in Jonah Creek is plotted as hydrographs (Figure 10.81).

Hydrographs for Jonah Creek (Figure 10.81) indicate that the flow downstream at 10:15 on April 9, 1996 (prior to initial pumping), was 1.82 cfs (816 gpm), whereas the flow upstream was 1.48 cfs

table 10.16estimated induced infiltration from Jonah creek, upper area XIII, using long-term minimum pumping rates

collection well time (t)transmissivity

(t) q r Pr qr

CW-1 1 d 100000100000100000

433433433

100012001500

291911

1268248

7 d 100000100000100000

433433433

100012001500

716658

307286251

CW-2 1 d 135000135000135000

316316316

100012001500

363016

1149351

7 d 135000135000135000

316316316

100012001500

756963

237218199

CW-3 1 d 120000120000120000

433433433

100012001500

787366

338316286

7 d 120000120000120000

433433433

100012001500

746962

320299268

CW-4 1 d 120000120000120000

316316316

100012001500

787366

246231209

7 d 120000120000120000

316316316

100012001500

746962

234228196

Note: Pr = percentage of pumped water diverted from the creek. Qr = amount of induced infiltration (gpm). T = transmis-sivity (gpd/ft). Q = proposed pumping rate (gpm). r = Distance from the pumping well to the recharge boundary. t = Time since pumping started.

Case Studies 319

B3

P3

P4SP4D

P6

B5

P50.00P2

PW953.277.64

TW1TW20.07

1 2 4 6 8

B1

P1SP1D

P70.00

B2

0.21

0.03

B4

0.03DRAWDOWN IN FEETAT MONITORING POINT

DRAWDOWN CONTOURIN FEET

4

400 200 0 400

SCALE IN FEET

800

10.24

fIgure 10.77 Cone of influence after 1 h of pumping, April 9, 1996, Upper Area XIII.

P1S0.42

B1

P4S

P31.58

B3 B4 B5

P4D

2

124

4

6

2.97

P25.68

P50.73

PW95TW2

P70.05

21 2.93 TW10.24

12.92B2

P1D

P60.18

0.18

400 200 0

SCALE IN FEET

DRAWDOWN IN FEETAT MONITORING POINTDRAWDOWN CONTOURIN FEET

400 800

fIgure 10.78 Cone of influence after 24 h of pumping on April 10, 1996, Upper Area XIII.


B3 B4

P3

P4S2

1

P5

P60.61

B5

1.00

P4D68

10R2

PW95TW114.3511.76B2

P1DP1S3.25 P1S

B1

TW27.8164

P71.93

21

0.61

1

400 200 0

SCALE IN FEET

400 800

DRAWDOWN IN FEETAT MONITORING POINTDRAWDOWN CONTOUR

fIgure 10.79 Cone of influence on April 14, 1996 (after 96 h pumping), Upper Area XIII.

P1S

P1D3.53L

B1

TW28.19

14.3511.76PW957.18P2

4

2P6

0.85

P51.16

6

P4D

P4S

P3

B3 B4 B5 DRAWDOWN IN FEETAT MONITORING POINT

0.85

4DRAWDOWN CONTOUR

400 200 0 400

SCALE IN FEET

800

3.19

4.48

810

B2 TW11 2

46

2.61P7

fIgure 10.80 Cone of influence on April 15, 1996 (144 hours), Upper Area XIII.

Case Studies 321

(666 gpm). After starting the pumping test, the flow downstream the flume in Jonah Creek continu-ously declined. It was 1.33 cfs (599 gpm) at 18:53 on April 9, 1996, which was lower than the flow of 1.42 cfs (637 gpm) at the upstream flume, indicating that brine emissions reduced or stopped after pumping the wells for 8 h. Visual observations throughout this period confirmed that spring and seep discharges gradually declined and eventually ceased. Flow at the downstream flume after ter-mination of pumping gradually increased to 1.46 cfs (655 gpm) at 15:02 on April 21, 1996. The flow at the Jonah Creek upstream flume was 1.48 cfs (666 gpm) prior to initiation of pumping; gradually it declined during pumping and was 0.83 cfs (371 gpm) immediately after the termination of pump-ing at wells TW-1 and TW-2 in the Upper Area XIII, at 13:32, on April 16, 1996.

The flow upstream in Jonah Creek declined because of reduction in the base flow, as the cone of influence caused by pumping extended beyond the upper flume. There was also some decline in the flow upstream of the upper flume in Jonah Creek due to natural conditions (dry period and evaporation losses).

10.5.8 EFFEcts oF pumping on brinE Emissions

In Upper Area XIII, springs and seeps were observed at three locations: (a) the main springs (brine emissions) at the top of the hill in the vicinity and north of well TW-1; (b) emissions of brine, 240 m west of the main spring, at the toe of the hill and north of well TW-2; and (c) the emission area, 150 m northeast of well TW-1. These emission areas are marked by spring symbols in Figure 10.68.

The total discharge of brine, prior to initiation of pumping, between the upstream and down-stream flumes was 0.34 cfs (153 gpm). Flow from the brine springs was also monitored by introduc-ing food color dye into the throat of the spring and watching the dye dissipate away from the spring due to discharge. Immediately after the start of pumping at well TW-1, flow at the main spring gradually and continuously declined, and at 11:25—after 25 min of pumping—it stopped flowing. After pumping well TW-1 at a rate of 1,000 gpm (2.23 cfs) for a period of 4 h, the water level in the bedrock aquifer declined, reversing the hydraulic gradient and causing flow at the main spring

1000

Wind Effects

End Pumping

800

600

400

Flow

Rat

e (G

PM)

200

0April 7 April 9 April 11 April 13 April 15 April 17

Upstream FlumeDownstream

Flume

April 19Time (Days)

Begin Pumping TW1 Begin Pumping TW2

fIgure 10.81 Flow rates at upstream and downstream flumes, Jonah Creek, Upper Area XIII, April 7–19, 1996.


to reverse. Flow from small springs and seeps ceased, and eventually the small pool areas of these springs and seeps were completely dry.

Springs in the vicinity of well TW-2 stopped flowing after pumping the well at a rate of 850 gpm (1.89 cfs) for a period of 25 min. The small pool areas of these springs dried up within 1–2 h of pumping. The entire length of the drainage feature that conveyed flow from these springs to the main creek in the vicinity of well TW-1 was dry within 60 h of pumping well TW-2.

The flow from springs located northeast of well TW-1 gradually declined, and the pool areas were completely dry within 60 h of pumping of both wells TW-1 and TW-2. Elimination of flow in the drainage channels occurred because of (a) cessation of spring discharge, (b) reduced base flow, and (c) infiltration of surface water into the underlying dewatered overburden/alluvium. The springs and seeps in the Upper XIII Area were affected by pumping, and emission of brine was completely stopped during the period of pumping.

10.5.9 chloridE load

Water samples were collected from Jonah Creek at the upstream and downstream flumes during the pumping test and were analyzed for chloride in a field laboratory. The concentration of chloride ranged 30,490–35,489 mg/L at the upstream flume and 28,991–39,487 mg/L at the downstream flume (Table 10.17 and Figure 10.82).

The chloride load was calculated using the flow rates of Jonah Creek and the concentration of chloride (mg/L) in creek water. Table 10.17 provides the chloride load in the creek at the upstream and downstream flumes. Figures 10.82 and 10.83 illustrate chloride concentration (mg/L) profiles and chloride load (tons/d) profiles measured during the pumping test at the upstream and down-

table 10.17chloride load at the upstream and downstream flumes during the pumping test at Jonah creek, upper area XIII

date remarks

upstream flume downstream flume difference in q (gpm) between

upstream and downstream

flumesq gpmchloride

mg/tchloride tons/day q gpm

chloride mg/t

chloride tons/day

4/9/96 Start pumping TW-1 at 11:00

666 32,990 132 781 30,990 145 +115

4/10/96 Start pumping TW-2 at 19:00

536 34,489 111 262 30,990 49 −274

4/11/96 — 603 34,989 127 260 35,988 56 −343

4/12/96 — 567 34,989 119 200 39,487 47 −367

4/13/96 — 492 30,490 90 160 34,989 34 −332

4/14/96 — 521 33,490 105 186 28,991 32 −335

4/15/96 — 365 35,489 78 74 35,988 16 –291

4/16/96 Terminate pumping at

TW-1 and TW-2 at 13:00

381 31,990 73 35 31,490 7 −346

4/17/96 — 439 33,989 90 290 32,489 57 −149

4/18/96 — 496 33,989 101 462 34,989 97 −34

Note: Q (gpm) = Flow through the flumes (gpm) measured at the same time as the chloride concentration mg/L.

mg/L = Milligrams per liter.

Case Studies 323

stream flumes. The graph (Figure 10.83) indicates that the chloride load (tons/d) gradually declined as the test progressed because of control of the brine emissions by pumping. After the termination of pumping, the chloride load increased and brine springs started flowing, contributing chloride to the creek. As shown in Table 10.17, the chloride load passing through the downstream flume ranged from 145 tons/d to 7 tons/d during the 7 d pumping period. The chloride load passing through the upstream flume ranged from 73 tons/d to 132 tons/d, indicating a source of chloride above the upstream flume location.

45000

Upstream FlumeDownstream Flume

40000

35000

Chlo

ride (

mg/

l)

30000

25000April 7 April 9 April 11 April 13

Time (Days)April 15 April 17 April 19

Begin Pumping TW2 End PumpingBegin Pumping TW1

fIgure 10.82 Chloride concentrations in surface water at upstream and downstream flumes, Jonah Creek, Upper Area XIII, April 7–19, 1996.

200END Pumping

180

160

140

120

100

80

60

40

20

0

Chlo

ride (

Tons

/Day

)

April 7 April 9 April 11 April 13Time (Days)

April 15 April 17 April 19

Upstream FlumeDownstream Flume

Begin Pumping TW1 Begin Pumping TW2

fIgure 10.83 Chloride load in surface water (tons/day) at upstream and downstream flumes, Jonah Creek, Upper Area XIII, April 7–19, 1996.


Salt flats in the vicinity of Jonah Creek indicate that a higher concentration of chloride exists in the alluvial aquifer than in the bedrock aquifer. Concentration of chloride in overburden/alluvium is due to capillary action and evaporation of brine. The highest chloride concentrations occur in the silty and/or clayey soil, whereas the concentration of chloride is lower in the sandy soil of the over-burden/alluvium. This ability of the alluvium to concentrate and store salts contributes to the large salt loads (“flush out”) of the creek during the initial stages of flooding.

Water samples were collected from two pumping wells during the pumping tests performed in Upper Area XIII during different time periods. These samples were sent to a certified laboratory for analysis to determine chloride and other parameters. Concentration of chloride in groundwater samples collected from each of the pumping wells (TW-1 and TW-2) in Upper XIII Area averaged 40,000 mg/L (Table 10.18).

10.5.10 collEction and disposal oF chloridE contaminatEd groundWatEr

Structural chloride control methods

Ten major chloride sources were identified in the Red River tributaries in the western portion of the basin. Of these, eight were deemed suitable for structural controls (see Figure 10.66). Structural controls include ring dikes to enclose brine springs, low-flow dams to capture and divert high-chloride stream flows to evaporation lakes, and the pumping of shallow wells to lower groundwater levels to prevent surface discharge of brine into the Red River tributaries.

The structural control method selected for Jonah Creek (emissions from Upper Area XIII) was the shallow-well collection and deep-well disposal of the brines.

The result of the pumping test, together with evaluation of site geology and hydrology, provided information to determine the optimum number and placement of the collection wells and deep injection wells.

The goal of the pumping effort will be to lower the groundwater level in the Upper Area XIII just far enough to stop spring and seep flow, and capillary salt deposition in the flood plain. Four col-lection wells will be required in the emissions areas in Upper Area XIII being investigated to con-trol brine discharge. Two of these wells will be continuously pumping and two will be on standby. The standby wells are necessary to help maintain the depressed groundwater level in the event of pump failure and well maintenance, and during periods of heavy rainfall, when local groundwater recharge occurs at higher rates.

The major design criteria for the project are the project life (100 years), and a requirement that operating supervision and maintenance be minimized. The system operation will be fully auto-mated and computer-controlled. A major design consideration was water quality and its effect on material and processes. The high chloride (4000 mg/L) and hardness (5000 mg/L), as CaCO3, of brine water have both scale-forming and corrosive effect on equipment.

table 10.18chloride load at wells tW-1 and tW-2 during the pumping test at Jonah creek, upper area XIII

q(gpm)

chloridemg/l

chloride(tons/day)

qgpm

chloridemg/l

chloride(tons/day)

tW-1 tW-2

1000a 40,000 240 850 40,000 204

Note: Q(gpm) = Discharge rate of well (gpm); mg/L = milligram per liter.a Values determined from laboratory analysis offsite.

Case Studies 325

collection Wells

It was determined that two collection and two standby wells will be required in Upper Area XIII—two collection wells (CW-1 and CW-2) for controlling brine emissions, and two standby wells (CW-3 and CW-7) for emergency purposes. The construction details are provided in Figure 10.84. The loca-tion and number of collection wells are decided based on the following factors:

Analysis and interpretation of the pumping test data•Understanding the geology and hydrology•Review of the areal extent of the composite cone of influence resulting from pumping of •two wells (TW-1 and TW-2) in the Upper Area XIII during each 7 d pumping test

LAND SURFACE

CONCRETE

GROUT

12"–INCH DIAMETER CASINGSCH 40 PVCO.D. – 12.750"I.D. – 11.888

BENTONITE

GRAVEL PACK (8–10)

18–INCH BOREHOLE

VERTICAL TURBINE PUMP

70 SLOT SCREENSCH 40 PVC

VARIES

3'

3'(MIN)

3'(MIN)

APP

ROX

IMAT

E D

EPTH

IN F

EET

BELO

W L

AN

D S

URF

ACE

6"

BOTTOM PLUG52' TO 112'

20'

fIgure 10.84 Collection well.


Impact of pumping on brine emissions•Cessation of flow of springs/seeps due to the reversal of hydraulic gradient caused by pumping•Review of water quality data, particularly chloride load, in Jonah Creek•Measurement of the creek flow at upstream and downstream flumes in Jonah Creek prior •to, during, and after each of the 7-d pumping tests in the Upper Area XIII

To control emissions, the total pumping rate in Upper Area XIII, based on the long-term pumping rate analysis, will be 1500 gpm.

Existing wells TW-1 and TW-2 can be used as collection wells (CW-1 and CW-2) for the Upper Area XIII; two standby wells can be drilled and completed as collection wells (CW-3 and CW-4). The locations of these wells are shown in Figure 10.85.

It is important to establish a network to monitor the impact of the pumping of the collection wells and the resulting ground water levels in both alluvial and bed rock aqufiers (hydraulic rela-tionship between these aquifers). Existing piezometers in Upper Area XIII would be used for moni-toring the water levels during the collection operation.

In order to control brine emissions and maintain a reversal of the hydraulic gradient (i.e., to maintain the water level in the bedrock aquifer at a significantly lower level than that in the alluvial aquifer), the pumping of collection wells must be continuous, with no or minimal interruptions. To avoid any cessation of pumping caused by maintenance, mechanical failure of pumps, and/or system malfunction, two standby wells (CW-5 and CW-6) should be constructed and be available online in the Upper XIII Area. These standby wells will maintain the reversal of hydraulic gradient in case maintenance/repair work is being performed on the existing wells or pumps. Locations of the proposed standby wells are shown in Figure 10.85.

Pumping of each collection well will be computer-controlled and remotely monitored from the regional project office. Monitored parameters will include the pumping level, flow rate and pressure, water temperature, and discharge value position. In addition, water levels in associated monitoring wells will be measured with electrical devices. Water level data will be used to control the number of wells operating and their pumping rates. The objective is to maintain an established groundwater level.

B3

P3

B1

P1SP1D

TW2

P7

B2 TW1PW95

P5P2

P6

B5

PROPOSED MONITORING WEEL(3)

EXISTING MONITORING WEEL(10)EXISTING TEST WELL (2)(PROPOSED COLLECTION WELL)PROPOSED COLLECTION WELL (2)PROPOSED STANDBYCOLLECTION WELL(2)BOREHOLEPARSHALL FLUME

SPRING

400 200 0 400

SCALE IN FEET

800

B4

P4DP4S

fIgure 10.85 Location of proposed collection wells and associated monitoring network Upper Area XIII.

Case Studies 327

long-term Pumping rates

The life expectancy of the collection, treatment, and disposal facilities of Upper Area XIII is expected to be 100 years. In order to minimize costs and maximize efficiency, the minimum long-term pumping rates required to meet the projected goals have been calculated using the Cooper–Jacob Equation (10.5).

Q Tsw

Ttr S

=4

2 3 102 25

2

Π

. log ( ).

(10.5)

During the pumping test in Upper Area XIII, the springs in the vicinity of well TW-1 stopped flow-ing after 25 min of pumping. The drawdown “sw” in the well at that time was 9.17 ft. The minimum pumping rates required to stop emissions in this area were computed as a function of time, using a transmissivity of 135,000 gpd/ft and a coefficient of storage of 3.18 × 10−2. A minimum pumping rate of 433 gpm for well TW-1 is required to control brine emissions in this area. Pumping rates versus time are graphically illustrated in Figure 10.86.

Emission of brine stopped near well TW-2 after 25 min of pumping. The drawdown in well TW-2 at that time was 3.11 ft. By substituting a value for transmissivity of 300,000 gpd/ft and a coefficient of storage of 3.8 × 10−2 into Equation (10.5), a minimum pumping rate of 316 gpm for well TW-2 was calculated to control emissions in this area. The pumping rates versus time are graphically illustrated by Figure 10.87.

The design discharge rate for each collection well in Area XIII should lie on the flattened portion of the respective curves (Figures 10.86 and 10.87). Selection of a pumping rate from the steeper por-tion of the curve would result in overdesign of the collection, treatment, and disposal systems. The pumping rates for 5 years (t = 5), as shown in Figures 10.86 and 10.87, are considered reasonable for achieving the project goals, because the rate of decline of the pumping rate thereafter is insignificant.

The estimated combined pumping rate of 750 gpm from the two wells (the existing test wells, at 434 gpm and at 316 gpm, respectively, Figures 10.86 and 10.87), is expected to control brine emis-sions into Jonah Creek within the upper emission area.

550

500

Pum

ping

Rat

e (G

PM)

450

4000 500 1000

449 gpm

1500 2000Time (Days)

2500 3000 3500 4000

2 Years

433 gpm

5 Years 10 Years

fIgure 10.86 Pumping rate required to control brine emissions in the vicinity of test well TW-1, Jonah Creek, Upper Area XIII.


The location of each of the wells in Upper Area XIII was identified for drilling and construction of the collection wells after consideration of the following features:

Topography, geology, and hydrogeology of the emission area•Review of pumping test data•Minimization of induced infiltration•Spatial distribution of brine discharges•

The pumping test is performed during a low-flow period; therefore, the minimum long-term pump-ing rates for Upper Area XIII is estimated to be 750 gpm. After initiation of pumping, brine emis-sions into Jonah Creek will gradually decline, and after 5 years of continuous pumping, significant control will have been achieved due to the decline of the potentiometric surface of the bedrock aqui-fer. Continuous pumping would also result in the reversal of the hydraulic gradient and dewatering of the overburden/alluvial aquifer, which would reduce the formation of salt crusts on landsurface, and the eventual elimination of the salt flats.

Pipeline and treatment facility

Polyethylene pipelines will transport brine from the collection wells to the treatment facility. Injec-tion pipelines will transport filtered and stabilized brine from the treatment facility to the injection pumps at the injection wells. The injection pipelines will be of the same material as the collection pipelines—polyethylene-lined carbon steel for buried sections and epoxy-lined stainless steel for aboveground sections, both at the treatment facility and at the injection wells.

Typically, groundwater is free of large particles. However, in this case, Jonah Creek will be recharging the shallow aquifer by flow reversal through the springs. The introduction of solids in this manner will be particularly significant during high stream turbidity events. To protect the deep receptor zones from particulate matter and the formation of scale that could plug the receiving (deep brine disposal) formation, a 4500 m3/d pressurized water treatment facility will be constructed. The first step of the process will be to boost the pressure of the incoming brine to 10 bars. Next, the brine passes through a cyclone separator to remove solids down to 75 µm. Brine from the cyclones

400

350

Pum

ping

Rat

e (G

PM)

300

2500 500 1000

328 gpm

1500 2000Time (Days)

2500 3000 3500 4000

2 Years

316 gpm

5 Years 10 Years

fIgure 10.87 Pumping rate required to control brine emissions in the vicinity of test well TW-2, Jonah Creek, Upper Area XIII.

Case Studies 329

will pass through back-washable fiber filters for final particle removal down to 8 µm. Following filtration, the brine will receive a scale inhibitor before passing into the distribution pipelines for the deep injection wells. For corrosion protection, all wetting parts will be constructed of stainless steel, PVC, fiberglass, or some other corrosion-resistant material.

deep Injection Wells and monitoring

Disposal of brine by deep-well injection is a technique that has been used by the petroleum industry for some time. Some geologic formations in the region at depths more than about 1525 m below the surface have sufficient porosity and permeability to serve as receptor zones for the injection of brine collected from upper formations. These receptor zones (Ellenburg Formation of the Ordo-vician Period) are confined by geologic formations that would prevent the upward migration of injected brine. Chloride concentrations of brines (over 100,000 mg/L) in the Ellenburger far exceed the concentrations of the water to be disposed. Other receptor zones will be evaluated during the drilling and logging of the test holes for each of the injection wells. Utilization of other porous and permeable zones would decrease injection pressures, thus extending the life of the injection well and reducing injection costs (U.S. Army Corps of Engineers, 1975).

For continuous disposal of brine that will be abstracted from Upper Area XIII, two deep injec-tion wells will be required. These wells will be located 760 m apart in a line about 2 km long. One additional well will be for standby operations. The number and spacing of injection wells was determined by the anticipated pressure buildup in the injection zone over its projected 100-year life. Increases in formation pressure from injection of fluids is an important factor to be considered because of the potential for hydraulic fracturing of overlying confining formation rocks, or induced rock displacement and subsequent seismic activity that could have an impact on the area. Fracture initiation pressure is conservatively estimated to be 300 bars based on the weight of the overlying rock and soil. With two wells injecting a total of 50–100 L/s continuously for 100 years, formation pressure should not exceed 150–200 bars.

Injection wells will be computer-controlled and remotely monitored from the regional project office. The monitored parameters include brine pressure and temperature at the wellhead and flow-rate. A flow valve will maintain brine flow at a uniform rate. Annulus pressure of the injection wells will be monitored to detect any leak in the well casing, injection tubing, or packer. The monitoring program for the deep-injection brine disposal system includes monitoring of the subsurface receptor and confining zones, and seismic monitoring of the region.

In addition to monitoring pressure changes in the receptor zone, monitoring wells will be required to make certain the integrity of the confining zones is maintained and upward migration of brine does not occur. Also, far-field pressure changes and progression of the brine through the recep-tor zone will be regularly checked. The depths of these wells will range from 1500 to 2000 m.

Due to the potential for hydraulic fracturing or other rock displacement caused by the injection of brine and increases in formation pressures, a microseismic monitoring network will be installed. This will provide information on seismic activity for the area before, during, and after injection of brine.

10.5.11 conclusions

Natural springs and seeps discharge brine in the upper Red River basin and contaminate surface waters with chlorides making the river unfit for municipal, industrial, and agricultural use most of the time.

Results of the pumping test performed in Upper Area XIII (Jonah Creek) demonstrate that close hydraulic relationships exist between groundwater from the bedrock aquifer system and surface brine emissions, and between overburden/alluvium and bedrock. They also provide information related to the efficiency of shallow groundwater well systems as a means to control the chloride load in the Upper Area XIII (Jonah Creek). The test provided information regarding the hydrau-


lic characteristics of the bedrock aquifer system (transmissivity and coefficient of storage), effects on streams flow, induced infiltration, and the prediction of long-term minimum discharge rates to control brine emissions and reduce the chloride load in the creek. Results of the test were used to identify the locations of four collection wells, two standby wells, the associated monitoring network in Upper Area XIII, and to estimate the life expectancy of the collection wells.

The Theis method was used to analyze pumping test data, and the Cooper–Jacob method was used to predict the pumping rates required to control brine emissions in Upper Area XIII. Conclu-sions included the following:

The results of the pumping test indicate that the bedrock aquifer is the primary source •of brine at Jonah Creek. Emission of brine occurs as springs and seeps, depending on the elevation of the potentiometric surface of groundwater in the bedrock aquifer system. The aquifer is semiconfined (leaky) and provides vertical leakage to the overlying alluvial aquifer. Under pumping conditions, the hydraulic gradient reverses, resulting in vertical leakage from the overburden/alluvial aquifer to the underlying bedrock aquifer.Data show that Jonah Creek acts as an individual recharge boundary when the potentio-•metric head of the underlying aquifer is lower than the water level in the creek.During the test, flow from brine springs was reversed, and a vortex at the main spring in •Upper Area XIII was induced. This indicates that induced infiltration from Jonah Creek to the underlying bedrock aquifer occurred through openings at the springs.The configuration and shape of the cones of influence indicate a boundary between pump-•ing wells TW-1 and TW-2 in Upper Area XIII.The average values of transmissivity and the coefficient of storage of the bedrock aquifer •in Upper Area XIII are 262,000 gpd/ft and 1.5 × 10−2, respectively.The average values of transmissivity and the coefficient of storage of the overburden/allu-•vial aquifer system are 166,000 gpd/ft and 4.7 × 10−2, respectively.Brine emissions at the main springs in the Upper Area XIII were controlled within 25 min •of pumping.Chloride concentration in Jonah Creek ranged 30,490–35,490 mg/L. The chloride load at •the downstream flume ranged from 7 tons/d to 145 tons/d.The chloride load passing through the upstream flume ranged from 73 tons/d to 132 tons/d, •indicating a source of chloride above the upstream flume location.Locations of collection wells, standby wells, and the associated monitoring network for •Upper Area XIII are provided in Figure 10.85.Life expectancy of each of the collection wells is estimated to be 30–40 years.•Four wells operating simultaneously and continuously are required in Upper Area XIII for •its projected 100-year life.The emission control methods selected for the eight areas in Jonah Creek (Upper Area •XIII) will reduce chloride contamination in the Red River by an estimated 145–150 t/d.The method to control emissions in Jonah Creek is to lower the groundwater level by •pumping shallow wells and the subsequent disposal of the collected brine into a deep receptor zone through injection wells.Two shallow collection wells (20 m deep) continuously pumping a total of about 750 gpm, •or 50–100 L/s, will depress the groundwater level to eliminate seep and spring flow into Jonah Creek.The collected brine will be filtered to remove particulate matter and chemically treated to •protect the deep receptor zone from plugging.Brine disposal will be through two deep injection wells (1500–2000 m deep), continuously •pumping at 50–100 L/s per well.

pjw

stk|

4020

64|1

4354

3262

9

Case Studies 331

bIblIograPHy

1. Cooper, H. H., Jr. and Jacob, C. E., 1946—A Generalized Graphic Method for Evaluating Formation Constants and Summarizing Well-Field History. Transection, American Geophysical University, Vol. 27, No. 4, pp. 526–534.

2. Driscoll, F. A., 1986—Groundwater and Wells, (2nd ed.), Johnson Division, St. Paul, MN, p. 1089. 3. Eifler, G. K. et al. (1968); Geologic Atlas of Texas, Plainview sheet, scale 1:250,000; Texas Bureau of

Economic Geology; Austin, TX. 4. Gustavson, T. C. et al., 1981—Geology and Geohydrology of the Palo Duro Basin, Texas Panhandle; A

Report on the Progress of Nuclear Waste Isolation Feasibility Studies (1980), Geological Circular 81-3, Bureau of Economic Geology, The University of Texas at Austin.

5. Johnson, S. K., 1974—Preliminary Geologic Map of Jonah Creek—Salt Creek Area (Areas XIII and XIV Childress Co., Texas) Showing Outcrops of Principal Dolomite Beds in the Blaine Formation and Associated Strata (Plate 7).

6. Johnson, S. K., 1981—Dissolution of Salt on the East Flank of the Permian Basin in the Southwestern U.S.A., Journal of Hydrology, 54 (75–93).

7. Johnson, S. K., 1989—Salt Dissolution, Interstratal Karst, and Ground Subsidence in the Northern Part of the Texas Panhandle, Engineering and Environmental Impacts of Sinkholes and Karst, pp. 115–121.

8. Johnson, S. K., 1990–1—Hydrogeology and Karst of the Blaine Gypsum-Dolomite Aquifer, South-western Oklahoma, SP 90–5, Field Trip #15 Guidebook, Geological Society of America 1990 Annual Meeting, Dallas, Texas.

9. Johnson, S. K., 1990–2—Standard Outcrop Section of the Blaine Formation and Associated Strata in Southwestern Oklahoma; Notes, Oklahoma Geology, Vol. 50, No. 5.

10. Johnson, S. K., 1992—Evaporite Karst in the Permian Blaine Formation and Associated Strata in West-ern Oklahoma, USA; Hydrogeology of Selected Karst Regions, IAH, Vol. 13.

11. Lohman, S. W., 1979—Ground-Water Hydraulics, Geological Survey Professional Paper, pp. 708. 12. Maher, C. J., 1964—The Composite Interpretive Method of Logging Drill Cuttings (2nd ed.), Oklahoma

Geological Survey, Guide Book XIV. 13. Pendery, C. E., 1963—Stratigraphy of Blaine Formation (Permian), North-Central Texas; Bulletin of

the American Association of Petroleum Geologists, Vol. 47, No. 10 (October 1963), pp. 1828–1839. 14. U.S. Army Corps of Engineers, Tulsa District; Chloride Control—Red River Basin, Texas; Areas IX,

XIII, and XIV—Design Memorandum No. 27 General Design—Phase II, 1982. 15. Walton, W. C., 1970—Groundwater Resources Evaluation, McGraw-Hill Book Company, New York. 16. Walton, W. C., 1963—Efficiency of Wells, Mimeographed Report of the Illinois State Water Survey

Division, Urbana Illinois, and personal communications, January 1963.


10.6 groundWater recHarge and ItS enVIronmental ImPact WItH caSe StudIeS

10.6.1 introduction

Groundwater recharge may be obtained by artificial or natural means. Artificial groundwater recharge is a planned operation of transferring water from ground surface into aquifers. Natural groundwater recharge is a phenomenon of water reaching aquifers, without manmade activities, from surface sources such as streams, natural lakes, or ponds.

The factors affecting natural groundwater recharge are the thickness and properties of soil formation and stratification, surface topography, vegetative cover, land use, soil moisture content, depth to water table, duration, intensity and seasonal distribution of rainfall, air temperature and other meteorological factors (humidity, wind, etc.), and influent and effluent streams.

Groundwater recharge may occur by infiltration, injection, or indication. The infiltration pro-cess is the entry of water into the saturated zone at the water table surface (Figure 10.88). The injec-tion method is the entry of water into confined or unconfined aquifers through the injecting wells (Figure 10.89). Recharge by induction is the entry of water into aquifers from surface water bodies caused by the extraction of groundwater (Figure 10.90).

Various investigators considered the problem of artificial recharge as a mean for ground-water management.

Gillette1 offered model legislation for artificial recharge. His work is divided into four parts: (1) technological considerations, (2) legal considerations, (3) present legislation, and (4) proposed legis-lation. Part 1 evaluated the technological complexities involved and set the foundation on which the proposed legislation was outlined. Part 2 elaborated on the legal problems involved and the stresses, and added to the foundation of the proposed legislation. Parts 3 and 4 reviewed current legislation and presented the proposed one.

fIgure 10.88

Case Studies 333

fIgure 10.89

fIgure 10.90


Scott and Johnson2 studied artificial recharge management in the urban environment. They indicated that artificial recharge is an essential component in management programs for aquifer replenishment. It also minimizes land subsidence and prevents impairment of water quality. Design of artificial recharge ponds should accommodate both good infiltration and also other environmen-tal purposes. If alternate sources of water with various solid contents are available for recharge, the water with the lowest solid content is most suitable and gives higher infiltration and longer cycles of maintenance.

Khordikaynen3 reviewed the principles of the application of artificial recharge for aquifer replenishment (availability of surface water, infrastructure, etc.). He discussed its application in Arizona, California, Germany, and England. He concluded that the availability of surface water and the existence of infrastructure in California is better than in Arizona.

Acrerkemann4 investigated several possibilities for increasing the water supply before the year 2020 for six northeastern Illinois counties. Many towns in his study area were expecting water deficits by the year 1990 unless additional water could be secured from Lake Michigan. In the same study, a second detailed analysis considered the economic aspects of groundwater development in the area. The unit cost of treated water was estimated between 22–53 cents per 1000 gal. The final conclusion indicated that additional water could come from artificial recharge of groundwater.

Bassett and Wood5 studied the reduction in infiltration rates after prolonged periods of sub-mergence. They attributed this reduction to the large number of anaerobic bacteria in the material underlying the floor of the basin. Spreading basin experiment results at Lubbock, Texas, showed that (1) bacteria reduced the sulfate concentration of the recharge water at this location by 80 mg/L, (2) the bicarbonate concentration was increased by more than 150 mg/L, and (3) the pH decreased one unit during the same time period. The anaerobic conditions appear to start at a certain depth and work toward the surface.

Foster and Sherwood6 conducted a study to evaluate the potential of water reclamation as a solution to water pollution and water storage problems. Physiochemical and biological studies of recharged water at the Flushing Meadows infiltration basins in Phoenix, Arizona, were carried out. Part of the reclaimed wastewater was stored in small artificial ponds. One desert pond was moni-tored for irradiance and chlorophyll concentrations, as well as net and gross photosynthesis. Results obtained from the monitoring indicated that these ponds had excellent photosynthetic capacity.

Wilson and Ramsey7 studied the effect of recharging more than 31,000 acre – feet of secondary treated sewage water in the Santa Cruz aquifer on groundwater. Analysis of the collected ground-water showed that quality deterioration decreased with the increase of the sample depth. They found an adverse proportion between water quality deterioration and aquifer depth.

Wood and Signor8 studied the type and magnitude of chemical control at a recharge site located on the southern high plains of Texas and New Mexico. They classified the chemical considerations in two categories: (1) changes in geometry of the interstitial pore space, and (2) prediction of the quality of water with time. Porous ceramic cups were used to collect water samples at depths of 0.6, 2, 8, 16, 23, and 33 m, first daily, then weekly. They concluded that chloride concentration increases with depth, but cation exchange dominated.

Ambroggi9 reviewed the advantages of the groundwater reservoir that facilitates artificial recharge, such as, (1) its relative large size or amount of water it holds, (2) assures water quality unless there are contamination sources, (3) no surface areas have to be flooded to create such res-ervoirs, and (4) groundwater investment always has low initial construction cost and low operation and maintenance cost.

Idelovitch et al.10 presented one of the most comprehensive, long-term monitoring programs for an extensive area influenced by recharge in Montaballo Forebay at Los Angeles. They described three categories of groundwater quality samples: indicative, basic, and comprehensive. Indicative samples are collected at 1–4 month intervals and used to ascertain the presence of injected effluent in water quality and purification provided by soil–aquifer systems. Comprehensive samples are taken at intervals of 6 months to 1 year to determine water quality with respect to specific standards.

Case Studies 335

Karlinger and Hansen11 presented an engineering economic analysis for two types of irrigation systems, a surface water irrigation system and a groundwater recharge system. They concluded that artificial recharge irrigation systems would be economically viable alternatives to surface-distribution irrigation in a conjunctive irrigation plan if electric power rates remain sufficiently low. As electric rates increase, this viability generally decreases.

Supalla and Comer12 discussed the economic value of groundwater recharge for irrigation use. They separated the recharge benefits into two components: saving on pumping cost, and aquifer extension benefits. Lincoln, Nebraska, was taken as a case study. Benefits are related to the treat-ment of the recharged water being allocated for irrigation.

Jansons et al.13 presented the movement of viruses after artificial recharge through soils and groundwater. The penetration of indigenous viruses through the recharged soils from treatment plant effluent was found to be much greater than that of seeded vaccine poliovirus. It was concluded that data on enteric virus survival in groundwater were required if safe abstraction distances were to be determined.

Subbaiah14 developed a decision model based on a linear programming technique and applied it to a typical alkali area under reclamation in the western Yamuna canal in Haryana, India. He concluded that storage of rainwater in aquifers through induced recharge is preferable to storage aboveground in farm ponds.

Bouwer15 presented the importance of artificial recharge for meeting the growing population demand. The pretreatment process as a role of artificial recharge for treatment and storage of sew-age effluent was discussed. He further discussed how artificial recharge enhances the aesthetics and the public acceptance of sewage water reuse, as the reclaimed water has had “soil–aquifer treat-ment” and comes out of wells rather than out of sewage treatment plants. In addition, he explained how the infiltration basins could contribute in saving the environment.

Peters16 answered the question, “Are there any blueprints for artificial recharge?” He presented the artificial recharge concept (design, research, modeling, and monitoring). The Netherlands artifi-cial recharge projects were taken as examples. He concluded that even in small countries, similari-ties in systems are small, contrasts are big, and every problem is unique.

10.6.2 purposE

One of the major challenges facing arid regions is the need for better management of limited fresh-water resources to meet increasing demands. This cannot be achieved unless integrated water resources management dictates the consideration of all possible water resources, including river water, groundwater, agricultural and domestic drainage water, and rainfall. In this context, the arti-ficial recharge of groundwater represents a good means for the replenishment of depleted aquifers.

Groundwater recharge focuses on experience gained as to the role of artificial recharge in aqui-fer protection. As a case study, two locations have been selected for the application of two different methods of artificial recharge. Figure 10.91 shows the selected locations, which are17,18

1. The Bustan extension area (using the infiltration method) 2. The Bahig area in a coastal region (using the injection method)

Recently, interest has been focused on the reuse of municipal wastewater. Land application prac-tices involve irrigation, spreading, overland flow, and recharge wells. Soil and subsurface condi-tions, climate, availability of land, and intended reuse of the wastewater govern the selection of a given system. A brief discussion on each method is given:

1. Irrigation method: Sprinklers or surface irrigation techniques to irrigate cropland can apply effluent. Application rates are low, ranging 0.5–0.2 m/week. Only the portion not consumed by plants percolates downward to the water table. In humid regions, low

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evapotranspiration rates and dilution with rainwater contributes good-quality water to the groundwater. In arid regions, brackish water that degrades groundwater can result.

2. Spreading methods: The application rates in this method are high, ranging from 0.1 to 1 m/d depending on local conditions. Thus, with a continuous recharge rate of 0.3 m/d, for example, a basin area of 1.4 ha would suffice for 100,000 people. Wastewater can be applied with surface irrigation or spray techniques, but spreading basins are often employed. A high-rate system requires deep permeable soils (sandy loams to loamy sands), and the water table does not rise to ground surface. Flooding is conducted intermittently, for example, 2 to 14 d wet alternating with 5 to 20 d dry. Movement of the effluent through the soil removes bacteria and viruses. Almost all biochemical oxygen demand and sus-pended solids, up to 50% of nitrogen, and 60 to 95% of phosphorus, can be removed. Because municipal use adds 300 mg/L of dissolved solids to water, this cannot be removed by recharging. Wastewater can deteriorate the quality of groundwater unless adequate sub-surface dilution is available.

3. Overland flow method: Where soil have low infiltration rates, such as clay and clay loam, wastewater is applied by irrigation or spray techniques to the upper end of sloping, veg-etated plots and allowed to flow in a shallow sheet to runoff collection ditches. Only a minor fraction of the applied water infiltrates; hence, this method contributes little to groundwater recharge.

4. Recharge well method: High-quality, tertiary-treated effluent can be pumped through recharge wells.

10.6.3 positivE impacts oF artiFicial groundWatEr rEchargE

The seawater intrusion in the Nile Delta aquifer in Egypt reached very dangerous limits. The salin-ity degradation at Kafer El-Sheikh (see Figure 10.91) has total dissolved solids (TDS) of about

fIgure 10.91

Case Studies 337

30,000 mg/L, whereas it is about 1,000 mg/L at El-Bagour in the middle of the Delta. This fact gives the recharge of the Delta aquifer by the injection of freshwater through wells located along the coastal areas a special importance.

10.6.4 EnvironmEntal impacts oF an artiFicial rEchargE

The main environmental impact that affects the artificial recharge of groundwater is clogging. It is one of the most troublesome phenomena concerning artificial recharge systems, irrespective of specific conditions such as water quality, aquifer properties, or type of recharge system.

Clogging is characterized by a reduction in the pore space of the aquifer, which can reduce the aquifer’s capacity to store and transmit water. In some circumstances, this may limit the viability of the artificial recharge operation. Therefore, any study of artificial recharge must at least consider the potential for clogging. Rates of clogging are viable and depend on suspended solid concentrations, temperature, injection rate, and the duration of injection.

There are three main types of clogging:

1. Physical clogging, caused by accumulation of particulate matter in the injecting flux 2. Biological clogging, caused by bacterial slime production 3. Chemical clogging, caused by precipitation reaction in the aquifer

Different approaches exist in dealing with clogging, such as the measurement of specific parameters and determination of correlation, as well as empirical models. More sophisticated models have been suggested to overcome the limitations of more simple methods. However, because clogging is affected by several mechanisms, a comprehensive model is still not available. But several trials have been made to develop a new clogging model to identify the main clogging processes.

Best results are obtained with an effluent of the following chemical specifications:

1. BOD ≥ 5 mg/L 2. Suspended solids < 1 mg/L 3. Phosphate < 1 mg/L 4. Iron < 0–5 mg/L 5. Turbidity < 0.3 turbidity units

The high cost of recharging effluent of this quality into wells can only be economically justified where there are some special purposes, such as:

1. Control of land subsidence. 2. Control of sea water intrusion. 3. Development of a costly alternative water supply source is to be delayed.

To ensure that potable water results from recharged effluents, the criteria governing the design of a recharge project should specify the following:

1. The degree of treatment required for the wastewater before recharging. 2. The minimum vertical distance of percolation through the unsaturated soil zone above the

water table. 3. The maximum quantity of wastewater to be recharged and diluted by native groundwater. 4. The minimum residence time of the reclaimed water underground before withdrawal for use. 5. The program of water quality monitoring for the groundwater influenced by recharging,

together with the limiting criteria for specified biological and chemical constituents.


10.6.5 advErsE rEchargE in arid rEgions oF Egypt

1. In the sandy and phreatic aquifer, considerable amounts of percolated excess water caused a rapid rise of groundwater levels, resulting locally in water logging and salinization.

2. Using poor-quality water for recharge may cause contamination to the aquifer, which may need long-term remediation. Chemical constituents of the recharge water may differ suf-ficiently from normal groundwater to cause undesired chemical reactions. Also, using wastewater for recharge may deteriorate the quality of the groundwater. So, the quality of injected water must follow the mandatory limits.

3. Recharge water may carry large amounts of dissolved air, tending to reduce the hydraulic conductivity of the aquifer by air binding. It may contain bacteria that can grow on the well screen and surrounding formations, thereby reducing the effective flow area.

10.6.6 artiFicial rEchargE in arid rEgions oF Egypt

One of the major challenges facing an arid region is the need for better management of its limited freshwater resources to meet its increasing demands. This cannot be achieved unless an integrated water resources management plan is applied. Egypt is taken in this respect as an example, where the overall water resources management dictates the consideration of all possible water resources, including the Nile water, groundwater, agricultural and domestic drainage water, and rainfall. In this context, artificial recharge of groundwater represents a good means for the replenishment of depleted aquifers. Large-scale uncontrolled artificial recharge has occurred since the sixties in Egypt as a result of an agricultural expansion policy in combination with a water policy giving mainly attention to surface water resources.

The application of controlled artificial recharge in Egypt has been triggered by the drought period in upper Nile catchment areas at the end of the eighties. This renewed discussions on the need for storage mechanisms additionally to the high Aswan dam. In 1993, Egypt’s Ministry of Water Resources and Irrigation launched the artificial recharge program. This program is a part of the Environmental Management of Groundwater Resources Project. The project lasted from 1993 to 1998. From 1994, experimental studies were conducted in two sites at the Bustan and Bahig areas, a description of which are given in the following text.

a-el-bustan extension area

The Bustan area is completely occupied by sedimentary rocks belonging to the quaternary, with a maximum thickness of about 200 m, essentially developed into deltaic sands and gravel. These are underlain by tertiary clay (Pliocene) and overlain by shifting sands and calcareous loam. Water in this aquifer exists under semiconfined or phreatic conditions. The total transmissivity ranges from 500 sqm/d in the southwest to 5000 sqm/d in the east and northeast. The depth to the groundwater table increases from <2 m in the north along Nubariya Canal to >40 m south of the Bustan Extension Area. The average depth to groundwater level approaches 17 m. Continued rise of the groundwater level is observed due to the extension of the land reclamation project by using Nile water. The salin-ity of the groundwater is 1000 ppm and increases in the northwest direction.

Site SelectionIntensive fieldwork at the Bustan Extension Area (Figure 10.92) shows the complexity and het-erogeneity of the underground. New interpretation of the previous studies, additional drilling, and geophysical investigation result in selection of the chosen area, located south of Bustan canal. The selection of the final location of the basin was chosen using the following criteria: shallow thickness of the hydraulic conducting layers in the unsaturated zone, availability of land, and the preferred gravity flow from the canal to the basin.

Case Studies 339

Design, Construction of the Basin, and the Monitoring NetworkThe surface dimension size of the basin is 185 × 170 m with side slope 1:8 and 1:6, respectively. The average basin depth is 2.5 m. The dimension of the bottom of the basin is 155 × 135 m. Figure 10.92 presents a general layout of the recharge experiment area, with the monitoring network. Three deep observation wells were drilled at the basin center for monitoring purpose.

b-bahig area

The experimental site lies 50 km west of Alexandria and 8 km from the Mediterranean Sea, and is situated in an area that was reclaimed by surface water irrigation. The climate is typically Medi-terranean and subject to arid conditions. The mean annual rainfall is 150 mm and average daily temperature ranges from 12°C in winter to 26°C in summer. The main land use is agriculture. Nile water is transported to this area for irrigation.

The local aquifer system (Figure 10.93) is overlain by a layer of quaternary limestone and loam, with a thickness of 23 m, where the phreatic water table is located. The main aquifer itself consists of Pliocene clastic and can be subdivided into two parts—the upper highly permeable and occupied freshwater (TDS 900–1,000 ppm), with a thickness of about 17 m, and the lower clayey layer, with a thickness of 60 m, containing saline water (TDS > 30,000 ppm). Miocene clay underlies the aquifer system. The transmissivity of the main aquifer is 1,100 sqm/d, which, for the greater part, is reached by the high hydraulic conductivity (50 m/d) and is located from 20 to 40 m below ground level.

fIgure 10.92


Recharge Facilities in Bahig AreaThe Nile water from the irrigation system is treated with settling and gravel bed passage, and is recharged to the aquifer under gravity flow through injection wells. Recovery of the water and back flushing of the wells are performed by submersible pumps.

In both the saline and freshwater parts of the aquifer, a dual purpose well, for both injection and recovery of water, has been constructed. Injection well 1 (IW-1) has a screen length of 21.5 m (18–39.5 m below ground level). Injection well (IW-2) has a total screen length of 16 m, starting at 54 m below ground level. The well bore holes are 66 cm in diameter. Into both wells, three PVC injection pipes have been constructed, enabling the control of injection rates and prevention of air bubbles entrapment. Based on step-drawdown tests, the recommended maximum discharges for the wells were 30 cum/h for IW-1 and 15 cum/h for IW-2.

The hydrogeological situation of the El Bustan Extension Area allows for reasonable infiltra-tion rates when using Nile water. The infiltration rates are comparable to the values in the operating schemes in other countries (e.g., The Netherlands). Regular cleaning of the infiltration basin will be needed to prevent clogging, especially after dust storms. The environmental effects of artifi-cial recharge in areas with groundwater depletion are positive. The adverse effect of soil leaching occurred only during the starting phase.

A direct conclusion that can be drawn is that, at the present recharge facilities, aquifer stor-•age and recovery by wells is technically feasible at short injection periods (< 1 week).The storage performance of the shallow system increased with successive cycles, as a rela-•tively fresh environment is created in the aquifer, acting as a buffer against local ground-

fIgure 10.93

Case Studies 341

water, with a higher TDS. During the short period of experiments, fair to good recovery efficiencies of more than 70% are obtained. It is expected that the efficiency will improve with further similar cycles. The relatively good quality of the native groundwater in the aquifer partly accounts for this result, for the occurrence of mixing does not lead to a rapid deterioration of water quality. The presence of saltwater within meters under the well affects negatively the recovery efficiency. For the reduction of the upcoming effect, recovery discharges must therefore be kept low.Very poor recovery efficiencies are obtained from deep saline aquifers. This is due to the •small volumes of injected water and the highly saline native groundwater in the target part of the aquifer system. Further, injections in this aquifer endanger the upper shallow aqui-fer, which includes freshwater, by pushing saline groundwater upward.Relatively simple treatment of injection water has resulted in permissible clogging rates. •At the highest applied discharge, a clogging rate was found to be 0.86 cm/h. Back flushing has been applied successfully to reduce the clogging, and all clogging seems to be removed over a period of recovery. The main cause of clogging is due to suspended solids in the injection water accumulating on the borehole walls. No indication of clogging caused by air entrapment or bacterial growth has been observed.Exact conclusions cannot yet be drawn of the risk of clogging that could have occurred in •the test program, as it was typically caused by particles in the injection water; this type of clogging usually does not pose a threat in the short term, but does so long term. Also, clogging by growth of bacteria may unexpectedly start to play a role when recharging for a longer time.More experimental work is needed to obtain the recovery percentage. Also, different •designs of the infiltration scheme to minimize clogging can be tested. Future experimental work should also include comparison between basin infiltration and deep-well injection.Following technical feasibility studies, an economic evaluation is required to define the role •of artificial recharge in Egypt’s water resources management. When using treated sewage water as a source for artificial recharge experiments, appropriate treatment requirements or techniques should be evaluated.

10.6.7 FuturE rolE oF artiFicial rEchargE in Egypt’s WatEr managEmEnt

The most promising applications of future artificial recharge schemes are:

1. Strategy of recycling Nile aquifer water: The controlled use of the Nile aquifer system is required for better groundwater management. Review of the existing infiltration rates from canals, excess irrigation, etc., is required to decide on the need for new infiltration schemes. In the integrated approach of the surface- and groundwater systems, lining of the main irrigation water carriers caused by infiltration losses should be compared with the benefits of infiltration for the recharge groundwater system.

2. Strategy of recycling wastewater after treatment: The reuse of treated sewage water is expected to increase from 0.5 billion cubic meters (BCM)/year in 2000 to 2.5 BCM/year by 2010. Groundwater reservoirs can be used for storage and treatment. The order of mag-nitudes of individual schemes may increase to hundreds of million cubic meters (MCM)/year.

3. Strategy of utilization of rainwater:Diversion channels and small dams are required in coastal areas aiming to decrease •direct water losses to the sea. The order of magnitude of the harvested surface water is approximately tens of MCM/year.Overland spreading of Nile water originating from rainfall (Nile Delta fringes) is •expected to be between tens to hundreds of MCM/year approximately.


4. Strategy of improvement of water quality: Infiltration or injections of freshwater in the coastal area is suffering from seawater intrusion (northeast delta). The order of magnitudes is expected to be tens to hundreds of MCM/year, originating from Nile flow, treated sew-age, or drainage water to improve the groundwater quality in the area.

Surface infiltration or deep-well injection of Nile water is for public water consumption objectives. As the allowable costs for water are relatively high for public and industrial water supply, the high-est economic return from artificial recharge schemes is expected from these schemes. The order or magnitudes of individual schemes is expected to be a maximum of tens of MCM/year.

referenceS

1. Gillette, F. L., Proposed Legislation for Artificial Groundwater Recharge, National technical informa-tion service, Springfield, VA 22161 AS PB-230 089, 1972.

2. Scott, H. and Johnston, W. E., Artificial recharge in the urban environment-some questions and answers, Hydraulic engineering and the environment, Proceedings of the 21st Annual Hydraulic Division Spe-cialty Conference, Montana State University, 1973.

3. Khordikaynen, M. A., Artificial Replenishment of Groundwater Storage, Vodnyye Resursy, No. 2 pp. 170–179, 1974.

4. Ackermann, W. C., The future of water resources in Northeastern Illinois, Journal of American Water Works Association, Vol. 67, No. 12, pp. 691–693, 1975.

5. Bassett, R. L. and Wood, W. W., Water quality changes related to the development of anaerobic condi-tions during artificial recharge, Water Resources, Vol. No. 4, pp. 553–558, 1975.

6. Foster, J. M. and Sherwood, B. I., Light and assimilation number in small desert, recharged groundwater pond, Oecolgia, Vol. 18, No., pp. 155–194, 1975.

7. Willson, L. H. and Ramsey, C., Transformation in quality of recharging effluent in Cruz River, Pro-ceedings of the 1975 Meetings of the Arizona Section, American Water Resources Association and the Hydrology Section, Arizona Academy of Science, 1975.

8. Wood, W. W. and Singor, D. C., Geochemical factors affecting artificial groundwater recharge in the unsaturated zone, Transactions of the ASAE, Vol. 18, No. 4, pp. 677–683, 1975.

9. Ambroggi, R. P., Underground reservoir to control the water cycle, Scientific American 236(5): 21–27, 1977.

10. Idelovitch, E., Terkeltoub R., and Michail, M., the Role of Groundwater Recharge in Wastewater Reuse: The Dan Region Project, Israel, in: Asano, T. and Roberts, P. V. (Eds.). Wastewater Reuse for Ground-water Recharge, Symposium Proceedings, Promoa CA, pp. 146–178. California State Water Resources Control Board, Sacramento, 1980.

11. Karlinger, R. G. and Hansen, A., Engineering economic analysis of artificial recharge, Water Resources Bulletin, Vol. 19, pp. 967–975, 1983.

12. Supalla, R. and Comer, D., The economic value of groundwater recharge for irrigation use, Water Resources Bulletin, Vol. 18, pp. 679–686, 1984.

13. Jansons, J., Edmonds, L. W., and Speight, B., Movement of viruses after artificial recharge, Water Research, Vol. 23, pp. 293–299, 1989.

14. Subbaiah, R., Decision support for managing water, Indian Journal of Agricultural Engineering, 1:1, 59–65, 1991.

15. Bouwer, H., New development in groundwater recharge and water reuse, Proceedings of Third Inter-national Symposium, Finland, 1996.

16. Peters, J., Are there any blueprints for artificial recharge at Groot Berkheide, Proceedings of Second International Artificial Recharge Symposium, Florida, U.S.A., 1994.

17. Mostafa, M. and Abdel Futuh, A., A Ragal and Smith, Impact of Artificial Recharge on Groundwater Potential—A Case Study from Egypt. ICID 16th Congress on Irrigation and Drainage, Cairo, Egypt, 1996.

18. Attia, F. l., Mostafa, M., Olsthoorn, T. N., and Shmidt, E.-H, The role of artificial recharge in integrated water management in Eygpt, Proceedings of Third International Symposium on Artificial Recharge of Groundwater, Amsterdam, September, 1998.

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Appendix A: GlossaryThe terms included in this glossary originated from the following references:Glossary of Geology and Related Sciences, American Geological Institute, Washington, DC, 1996.Hydrology and Water Resources for Sustainable Development in a Changing Environment, UNESCO, New

York, 1990.

Acid precipitation Any atmospheric precipitation that has an acid reaction through the absorp-tion of acid-producing substances such as sulfur dioxide.

Aggradation The general building up of the land by deposition processes.Air instability This state exists in a body of air that is marked by a strong vertical temperature

decrease and high moisture content. Unstable air tends to rise.Albedo The amount of light reflected by a given surface compared to the amount received.Alluvium Material deposited by running water (gravel, sand, silt, clay).Anaerobic condition Characterized by absence of air or free oxygen.Andesitic basalt A fine-grained extrusive igneous rock composed of plagioclase feldspars and

ferromegnesian silicates.Anticline A fold in which the rocks are bent convex upward.Aquiclude A body of relatively impermeable rock that is capable of absorbing water slowly but

functions as an upper or lower boundary of an aquifer and does not transmit groundwater rapidly enough to supply a well or spring.

Aquifer A porous, permeable, water-bearing geologic body of rock. Generally restricted to materials capable of yielding an appreciable amount of water.

Aquifuge A rock that contains no interconnected openings or interstices and therefore neither absorbs nor transmits water.

Aquitard A confining bed that retards but does not prevent the flow of water to or from an adja-cent aquifer; a leaky confining bed. It does not readily yield water to wells or springs, but may serve as a storage unit for groundwater.

Artesian An adjective referring to groundwater confined under sufficient hydrostatic pressure to rise above the upper surface of the aquifer.

Artesian aquifer Confined aquifer.Artesian head The level to which water from a well will rise when confined in a standing

pipe.Artesian well A well in which water from a confined aquifer rises above the top of the aquifer.

Some wells may flow without the aid of pumping.Auger mining A method of extracting ore by boring horizontally into a seam, much like a drill

bores a hole into wood.Avalanche A large mass of either snow, rock debris, soil, or ice that detaches and slides down

a mountain slope.Barometer An instrument that measures atmospheric pressure. The first liquid barometer was

designed by Torricelli in 1644.Basalt A fine-grained, dark-colored igneous rock composed of ferromagnesian minerals.Bedding plane A plane that separates or delineates layers of sedimentary rock.Biosphere That part of the earth system that supports life.BOD (biochemical oxygen demand) The oxygen used in meeting the metabolic needs

of aquatic aerobic microorganisms. A high BOD correlates with accelerated eutrophication.

Brackish water Water with a salinity intermediate between that of freshwater and seawater.


Brine Concentrated salt solution remaining after removal of distilled product; also, concen-trated brackish saline or seawater containing more than 100,000 mg/L of total dissolved solids.

Canopy fire A forest fire that involves the crowns of trees. It is also called a crown fire.Carbon dioxide (CO2) A gaseous product of combustion about 1.5 times as heavy as air. A rise

in CO2 in the atmosphere increases the greenhouse effect.Carbon monoxide (CO) A product of incomplete combustion. CO is colorless and has no odor,

and it combines with hemoglobin in the blood leading to suffocation caused by oxygen deficiency.

Cement Chemically precipitated mineral material that occurs in the spaces among the indi-vidual grains of a consolidated sedimentary rock, thereby binding the grains together as a rigid coherent mass; it may be derived from the sediment or its entrapped waters, or it may be brought in by solution from outside sources. The most common cements are silica (quartz, opal, chalcedony), carbonates (calcite, dolomite, siderite), and various iron oxides; others include barite, gypsum, anhydrite, and pyrite. Clay minerals and other fine clastic particles should not be considered as cements.

Centipoise A unit of viscosity based on the standard of water at 20°C (which has a viscosity of 1.005 centipoises).

Chain reaction A self-sustaining nuclear reaction that, once started, passes from one atom to another (see also fission).

Chemical treatment Any process involving the addition of chemicals to obtain a desired result.

Clay minerals One of a complex and loosely defined group of finely crystalline, metacolloidal, or amorphous hydrous silicates essentially of aluminum with a monoclinic crystal lat-tice of the two or three layer type in which silicon and aluminum ions have tetrahedral coordination in respect to oxygen. Clay minerals are formed chiefly by chemical altera-tion or weathering of primary silicate minerals such as feldspars, pyroxenes, and amphi-boles, and are found in clay deposits, soils, shales, and mixed with sand grains in many sandstones. They are characterized by small particle size, ability to adsorb substantial amounts of water, and ions on the surfaces of the particles. The most common clay min-erals belong to the kaolin, montmorrilionite, and illite groups.

Climate The statistical sum total of meteorological conditions (averages and extremes) for a given point or area over a long period of time.

Cloud seeding The artificial introduction of condensation nuclei (dry ice or silver iodide) into clouds to force precipitation.

Cold front The boundary on the earth’s surface, or aloft, along which warm air is displaced by cold air.

Colloidal dispersion The process of extremely small particles (colloids) being dispersed and suspended in a medium of liquids or gases.

Colluvium An accumulation of soil and rock fragments at the foot of a cliff or slope under the direct influence of gravity.

Compressibility The reciprocal of bulk modules of elasticity. Its symbol is β. Syn: modulus of compression.

Concentration (a) The amount of a given substance dissolved in a unit volume of solution. (b) The process of increasing the dissolved solids per unit volume of solution, usually by evaporation of the liquid.

Concentration tank A settling tank of relatively short detention period in which sludge is con-centrated by sedimentation of floatation before treatment, dewatering, or disposal.

Cone volcano A steep-sided and cone-shaped volcano that is composed of both lava flows and layers of pyroclastic materials. This type is also called a stratovolcano.

Appendix A: Glossary 345

Confined aquifer An aquifer bounded above and below by impermeable beds or beds of dis-tinctly lower permeability than that of the aquifer itself; an aquifer containing confined groundwater.

Confined groundwater A body of groundwater overlain by material sufficiently impervious to sever free hydraulic connection with overlying groundwater except at the intake. Confined water moves in conduits under the pressure caused by the difference in head between intake and discharge areas of the confined water body.

Confining bed A body of impermeable or distinctly less permeable material stratigraphically adjacent to one or more aquifers. Cf: aquitard; aquifuge; aquiclude.

Convection Mass motion within gases and liquids caused by differences in density brought about by cooling or heating.

Core barrel (a) A hollow tube or cylinder above the bit of a core drill, used to receive and pre-serve a continuous section or core of the material penetrated during drilling. The core is recovered from the core barrel. (b) The tubular section of a corer, in which ocean-bottom sediments are collected either directly in the tube or in a plastic liner placed inside the tube.

Core drill (a) A drill (usually a rotary drill, rarely a cable-tool drill) that cuts, removes, and brings to the surface a cylindrical rock sample (core) from the drill hole. It is equipped with a core bit and a core barrel. (b) A lightweight, usually mobile drill that uses drill tubing instead of drill pipe and that can (but need not) core down from grass roots.

Corrasion Wearing away of the earth’s surface forming sinkholes and caves and their widening due to running water.

Corrosion The gradual deterioration or destruction of a substance or material by chemical action, frequently induced by electrochemical processes. The action proceeds inward from the surface.

Creep A slow movement of unconsolidated surface materials (soil, rock fragments) under the influence of water, strong wind, or gravity.

Crustal plates In the theory of plate tectonics, it is stated that the earth’s crust is not continuous but is composed of many large and small plate units that are in relative motion to one another.

Cuttings Rock chips or fragments produced by drilling and brought to the surface. The term does not include the core recovered from core drilling. Also: well cuttings; sludge; drill-ings. Syn: drill cuttings.

Darcy A standard unit of permeability, equivalent to the passage of one cubic centimeter of fluid of one centipoise viscosity flowing in one second under a pressure differential of one atmosphere through a porous medium having an area of cross section of one square cen-timeter and a length of one centimeter. A millidarcy is one one-thousandth of a darcy.

Darcy’s law A derived formula for the flow of fluids on the assumption that the flow is laminar and that inertia can be neglected. The numerical formulation of this law is used generally in studies of gas, oil, and water production from underground formations.

DDT (dichloro diphenyl trichloroethane) An insecticide, one of several chlorinated hydrocarbons.

Debris slide A sudden downslope movement of unconsolidated earth materials or mine waste particularly once it becomes water saturated.

Deep-well injection A technique for disposal of liquid waste materials by pressurized infusion into porous bedrock formations or cavities.

Degradation The general lowering of the land by erosional processes.Desalination Any process capable of converting saline water to potable water.Desertification The creation of desert-like conditions, or the expansion of deserts as a

result of humans’ actions that include overgrazing, excessive extraction of water, and deforestation.


Desertization A relatively new term that denotes the natural growth of deserts in response to climatic change.

Deserts Permanently arid regions of the world where annual evaporation by far exceeds annual precipitation. They cover about 16% of the earth.

Detrital Relates to deposits formed of minerals and rock fragments transported to the place of deposition.

Diamond dust This phenomenon occurs in arctic haze and produces bright, shimmering lights intermixed with rainbow colors that result in confusing images and reduced visibility.

Dip slope Topographic slope conforming with the dip of the underlying bedrock.Discharge The volume of water passing a given point within a given period of time.Doppler radar This instrument emits a radar frequency that appears to be changing as the wave is

bounced back from a moving object. The frequency lengthens when the distance between transmitter and object increases, and it shortens as the distance decreases.

Downdrafts Downward and sometimes violent cold air currents frequently associated with cumulonimbus clouds and thunderstorms.

Downwind effect Severe turbulence can develop on the downwind [leeward] side of large build-ings and mountains. This turbulence could be called the “snow fence” effect; it can be dangerous to aircraft.

Drainage basin The area that is drained by a river and its tributaries.Drilling fluid A heavy suspension, usually in water but sometimes in oil, used in rotary drill-

ing, consisting of various substances in a finely divided state (commonly bentonitic clays and chemical additives such as barite), introduced continuously down the drill pipe under hydrostatic pressure, out through openings in the drill bit, and back up in the annular space between the pipe and the borehole walls and to a surface pit where cuttings are removed. The fluid is then reintroduced into the pipe. It is used to lubricate and cool the bit, to carry the cuttings up from the bottom, and to prevent sloughing and cave-ins by plastering and consolidating the walls with a clay lining, thereby making casing unneces-sary during drilling, and also offsetting pressures of fluid and gas that may exist in the subsurface. Syn: drilling mud.

Drill-stem test A procedure for determining productivity of an oil or gas well by measuring res-ervoir pressures and flow capacities while the drill pipe is in the hole and the well is full of drilling mud. A drill stem test may be done in a cased or uncased hole.

Drought An extended period of below-normal precipitation especially in regions of sparse pre-cipitation. Prolonged droughts can lead to crop failures, famines, and sharply declining water resources.

Dust storm A severe weather system, usually in dry area, which is characterized by high winds and dust-laden air. Major dust storms were observed during the 1930s in the Dust Bowl region of the United States.

Earthquake A sudden movement and tremors within the earth’s crust caused by fault slippage or subsurface volcanic activity.

Ecosystem A functional system based on the interaction between all living organisms and the physical components of a given area.

Effective porosity The measure of the total volume of interconnected void space of a rock, soil, or other substance. Effective porosity is usually expressed as a percentage of the bulk volume of material occupied by the interconnected void space.

Effective stress The average normal force per unit area transmitted directly from particle to particle of a soil or rock mass. It is the stress that is effective in mobilizing internal fric-tion. In a saturated soil, in equilibrium, the effective stress is the difference between the total stress and the neutral stress of the water in the voids; it attains a maximum value at complete consolidation of the soil.

Ejecta Solid material thrown out of a volcano. It includes volcanic ash, lapilli, and bombs.


Elastic rebound This concept implies that rocks, after breaking in response to prolonged strain, rebound back to their previous position or one similar to it. This sudden breaking and rebound may cause earthquakes.

Entomologist A scientist who studies insects.Environmentalism This concept, also called environmental determinism, proposes that the

total environment is the most influential control factor in the development of individuals or cultures.

Epicenter The point on the earth’s surface that is located directly above the focus on an earthquake.

Evapotranspiration The sum of evapotranspiration from wetted surfaces and of transpiration by vegetation.

Extension fault A branch rupture extending from a major fault line.Eye (of a hurricane) The mostly cloudless, calm center area of a hurricane. This center is sur-

rounded by near-vertical cloud walls.Facies A term used to refer to a distinguished part or parts of a single geologic entity, differing

from other parts in some general aspect; e.g., any two or more significantly different parts of a recognized body of rock or stratigraphic composition. The term implies physical closeness and genetic relation or connection between the parts.

Facies change A lateral or vertical variation in the lithologic or paleontologic characteristics of contemporaneous sedimentary deposits. It is caused by, or reflects, a change in the depositional environment. Cf: facies evolution.

Facies map A broad term for a stratigraphic map showing the gross areal variation or distri-bution (in total or relative content) of observable attributes or aspects of different rock types occurring within a designated stratigraphic unit, without regard to the position or thickness of individual beds in the vertical succession; specifically a lithofacies map. Conventional facies maps are prepared by drawing lines of equal magnitude through a field of numbers representing the observed values of the measured rock attributes. Cf: vertical-variability map.

Fault A surface or zone of rock fracture along which there has been displacement, from a few centimeters to a few kilometers.

Filtrate The liquid that has passed through a filter.Filtration The process of passing a liquid through a filtering medium (which may consist of

granular material, such as sand, magnetite, or diatomaceous earth, or may be finely woven cloth, unglazed porcelain, or specially prepared paper) for the removal of sus-pended or colloidal matter.

Firestorm A violent and nearly stationary mass fire that develops its own inblowing wind sys-tem. It develops mostly in the absence of preexisting ground wind.

Fishery The commercial extraction of fish in a given region.Fission The splitting of an atom into nuclei of lighter atoms through bombardment with neu-

trons. Enormous amounts of energy are released in this process, which is used in the development of nuclear power and weapons.

Fissure eruption A type of volcanic eruption that takes place along a ground fracture instead of through a crater.

Flank eruption A type of volcanic eruption that takes place on the side of a volcano instead of from the crater. This typically occurs when the crater is blocked by previous lava eruptions.

Flash flood A local, very sudden flood that typically occurs in usually dry river beds and nar-row canyons as a result of heavy precipitation generated by mountain thunderstorms.

Floc Small masses, commonly gelatinous, formed in a liquid by the reaction of a coagulant through biochemical processes or by agglomeration.


Flood crest The peak of a flood event, also called a flood wave, which moves downstream and shows as a curve crest on a hydrograph.

Floodplain A stretch of relatively level land bordering a stream. This plain is composed of river sediments and is subject to flooding.

Flood stage The stage at which overflow of the natural banks of a stream begins to cause dam-age in the reach in which the elevation is measured.

Flow rate The volume per time given to the flow of water or other liquid substance, which emerges from an orifice, pump, or turbine, or passes along a conduit or channel, usually expressed as cubic feet per second (cfs), gallons per minute (gpm) or million gallons per day (mgd).

Focus The point of earthquake origin in the earth’s crust from where earthquake waves travel in all directions.

Foliation A textural term referring to the planar arrangement of mineral grains in metamorphic rock.

Formation A body of rock characterized by a degree of lithologic homogeneity; it is prevail-ingly, but not necessarily, tabular and is mappable on the earth’s surface or traceable in the subsurface.

Formation water Water present in a water-bearing formation under natural conditions as opposed to introduced fluids, such as drilling mud.

Fossil fuel Fuels such as natural gas, petroleum, and coal that developed from ancient deposits of organic deposition and subsequent decomposition.

Fuel load The total mass of combustible materials available to a fire.Geophysical logs The records of a variety of logging tools that measure the geophysical prop-

erties of geologic formations penetrated and their contained fluids. These properties include electrical conductivity and resistivity, the ability to transmit and reflect sonic energy, natural radioactivity, hydrogen ion content, temperature, and gravity. These geo-physical properties are then interpreted in terms of lithology, porosity, fluid content, and chemistry.

Geothermal gradient The rate of increase of temperature in the earth with depth. The gradient near the surface of the earth varies from place to place depending upon the heat flow in the region and the thermal conductivity of the rocks. The approximate geothermal gradi-ent in the earth’s crust is about 25°C/km.

Glacial drift A general term applied to sedimentary material transported and deposited by glacial ice.

Glacis A protective earthen bank that slopes away from the outer walls of a fortification.Graben A down-faulted block; may be bounded by upthrown blocks (horsts).Gradation The leveling of the land through erosion, transportation, and deposition.Granite A light-colored, or reddish, coarse-grained intrusive igneous rock that forms the typi-

cal base rock of continental shields.Greenhouse effect The trapping and reradiation of the earth’s infrared radiation by atmospheric

water vapor, carbon dioxide, and ozone. The atmosphere acts like the glass cover of a greenhouse.

Ground avalanche An avalanche type that involves the entire thickness of the snowpack and usually includes soil and rock fragments.

Ground fire A type of fire that occurs beneath the surface and burns rootwork and peaty materials.

Group (general) An association of any kind based upon some feature of similarity or relation-ship (stratigraphy). Lithostratigraphic unit consisting of two or more formations; more or less informally recognized succession of strata too thick or inclusive to be considered a formation; subdivisions of a series.


Grout A cementitious component of high water content, fluid enough to be poured or injected into spaces such as fissures surrounding a well bore and thereby filling or sealing them. Specifically, a pumpable slurry of portland cement, sand, and water forced under pressure into a borehole during well drilling to seal crevices and prevent the mixing of groundwa-ter from different aquifers.

Horst An up-faulted block; may be bounded by downthrown blocks (grabens).Hot spot (geol.) Excessively hot magma centers in the asthenosphere that usually lead to the

formation of volcanoes.Humus The partially or fully decomposed organic matter in soils. It is generally dark in color

and partly of colloidal size.Hurricane A tropical low-pressure storm (also called baguio, tropical cyclone, typhoon, willy

willy). Hurricanes may have a diameter of up to 400 mi (640 km) and a calm center (the eye), and must have wind velocities higher than 75 mph (120 km/h). Some storms have attained wind velocities of 200 mph (320 km/h).

Hydrate Refers to those compounds containing chemically combined water.Hydraulic [eng.] Conveyed, operated, effected, or moved by means of water or other fluids,

such as a “hydraulic dredge,” using a centrifugal pump to draw sediments from a river channel.

Hydraulic [hydraul.] Pertaining to a fluid in motion, or to movement or action caused by water.

Hydraulic action The mechanical loosening and removal of weakly resistant material solely by the pressure and hydraulic force of flowing water, as by a stream surging into rock cracks or impinging against the bank on the outside of a bend, or by ocean waves and currents pounding the base of a cliff.

Hydraulic conductivity Ratio of flow velocity to driving force for viscous flow under saturated conditions of a specified liquid in a porous medium.

Hydraulic gradient In an aquifer, the rate of change of total head per unit of distance of flow at a given point and in a given direction.

Hydraulic head (a) The height of the free surface of a body of water above a given subsurface point. (b) The water level at a point upstream from a given point downstream. (c) The elevation of the hydraulic grade line at a given point above a given point of a pressure pipe.

Hydraulics The aspect of engineering that deals with the flow of water or other liquids; the practical application of hydromechanics.

Hydrocarbon Organic compounds containing only carbon and hydrogen. Commonly found in petroleum, natural gas, and coal.

Hydrodynamics The aspect of hydromechanics that deals with forces that produce motion.Hydrogeology The science that deals with subsurface waters and with related geologic aspects

of surface waters. Also used in the more restricted sense of groundwater geology only. The term was defined by Mead (1919) as the study of the laws of the occurrence and movement of subterranean waters. More recently, it has been used interchangeably with geohydrology.

Hydrograph A graph that shows the rate of river discharge over a given time period.Hydrography (a) The science that deals with the physical aspects of all waters on the Earth’s

surface, especially the compilation of navigational charts of bodies of water. (b) The body of facts encompassed by hydrography.

Hydrologic cycle The constant circulation of water from the sea, through the atmosphere, to the land, and its eventual return to the atmosphere by way of transpiration and evaporation from the sea and land surfaces.

Hydrologic system A complex of related parts—physical, conceptual, or both—forming an orderly working body of hydrologic units and their human-related aspects such as the


use, treatment, reuse, and disposal of water and the costs and benefits thereof, and the interaction of hydrologic factors with those of sociology, economics, and ecology.

Hydrology (a) The science that deals with global water (both liquid and solid), its properties, circulation, and distribution, on and under the Earth’s surface and in the atmosphere, from the moment of its precipitation until it is returned to the atmosphere through evapo-transpiration or is discharged into the ocean. In recent years the scope of hydrology has been expanded to include environmental and economic aspects. At one time there was a tendency in the U.S. (as well as in Germany) to restrict the term hydrology to the study of subsurface waters (DeWeist, 1965). (b) The sum of the factors studied in hydrology; the hydrology of an area or district.

Hydrosphere The waters of the Earth, as distinguished from the rocks (lithosphere), living things (biosphere), and the air (atmosphere). Includes the waters of the oceans, rivers, lakes, and other bodies of surface water in liquid form on the continents; snow, ice, and glaciers; and liquid water, ice, and water vapor in both the unsaturated and saturated zones below the land surface. Included by some, but excluded by others, is water in the atmosphere, which includes water vapor, clouds, and all forms of precipitation while still in the atmosphere.

Hydrothermal Of or pertaining to hot water, to the action of hot water, or to the products of this action, such as a mineral deposit precipitated from a hot aqueous solution, with or without demonstrable association with igneous processes, also said of the solution itself. Hydrothermal is generally used for any hot water but has been restricted by some to water of magmatic origin.

Hydrothermal processes Those processes associated with igneous activity that involve heated or superheated water, especially alteration, space filling, and replacement.

Hygroscopic particles Condensation nuclei in the atmosphere that attract water molecules (car-bon, sulfur, salt, dust, ice particles).

Impermeable Impervious to the natural movement of fluids.Induction The creation of an electric charge in a body by a neighboring body without having

physical contact.Injection well (a) A recharge well. (b) A well into which water or a gas is pumped for the pur-

pose of increasing the yield of other wells in the area. (c) A well used to dispose of fluids in the subsurface environment by allowing them to enter by gravity flow or injection under pressure.

Intensity (earthquake) A measurement of the effects of an earthquake on the environment expressed by the Mercalli scale in stages from I to XII.

Ion An electrically charged molecule or atom that lost or gained electrons and therefore has a smaller or greater number of electrons than the originally neutral molecule or atom.

Ionization The process of creating ions.Iron Age The period that followed the Bronze Age when mankind began the use of iron for

making implements and weapons around 800 bc. The earliest use of iron may go back to 2500 bc.

Ironstone A term sometimes used to describe a hardened plinthite layer in tropical soils. It is primarily composed of iron oxides bonded to kaolinitic clays.

Isopach A line drawn on a map through points of equal thickness of a designated stratigraphic unit or group of stratigraphic units.

Isopach map A map that shows the thickness of a bed, formation, or other tabular body through-out a geographic area; a map that shows the varying true thickness of a designated strati-graphic unit or group of stratigraphic units by means of isopachs plotted normal to the bedding or other bounding surface at regular intervals.

Isotopes Atoms of a given element having the same atomic number but differ in atomic weight because of variations in the number of neutrons.


Jet stream A high-velocity, high-altitude (25,000 to 40,000 ft or 7,700 to 12,200 m) wind that moves within a relatively narrow oscillating band within the upper westerly winds.

Joint (geol.) A natural fissure in a rock formation along which no movement has taken place.Karst A type of topography characterized by closed depressions (sinkholes), caves, and subsur-

face streams.Landslide A general term that denotes a rapid downslope movement of soil or rock masses.Land-subsidence A gradual or sudden lowering of the land surface caused by natural or human-

induced factors such as solution (see karst) or the extraction of water or oil.Lapse rate Expresses the rate of change (temperature or pressure) of atmospheric values with

a change in elevation.Latent energy The heat energy that produces changes of state in a substance without increasing

the temperature of such substance. An example would be the melting of ice into liquid water and the subsequent evaporation to vapor. Latent energy is released when the pro-cesses are reversed.

Leachate The solution obtained by the leaching action of water as it percolates through soil or other materials such as wastes containing soluble substances.

Lithification The conversion of unconsolidated material into rock.Lithology (a) The description of rocks on the basis of such characteristics as color, structures, min-

eralogic composition, and grain size. (b) The physical character of a rock.Lithosphere The outer solid layer of the earth that rests on the nonsolid asthenosphere. The

lithosphere averages about 60 mi (100 km) in thickness.Loess Fine silt-like soil particles that have been transported and deposited by wind action. Some

loess deposits may be hundreds of feet thick.Magma Naturally occurring molten rock that may also contain variable amounts of volcanic

gases. It issues at the earth’s surface as lava.Magma chambers Underground reservoirs of molten rock (magma) that are usually found

beneath volcanic areas.Mantle (geol.) The intermediate zone of the earth found beneath the crust and resting on the

core. The mantle is believed to be about 1,800 mi (2900 km) thick.Member A division of a formation, generally of distinct lithologic character or of only local

extent. A specially developed part of a varied formation is called a member if it has con-siderable geographic extent. Members are commonly, though not necessarily, named.

Mercalli scale Used to describe the effects of an earthquake’s intensity on a scale of I to XII rang-ing from “imperceptible” to “major catastrophe.” It is not a quantified scale.

Metamorphism The process that induces physical or compositional changes in rocks caused by heat, pressure, or chemically active fluids.

Meteorology The scientific study of weather and atmospheric physics.Millidarcy The customary unit of fluid permeability, equivalent to 0.001 darcy. Abbrev: md.Moho discontinuity A zone between the earth’s crust and mantle that shows a marked change

in the travel velocity of seismic waves caused by density changes between these layers. Named after the seismologist Mohorovicic who discovered this discontinuity in 1909.

Mudflow A downslope movement of water-saturated earth materials such as soil, rock frag-ments, or volcanic ash.

Mud logs The record of continuous analysis of a drilling mud or fluid for oil and gas content.Neutralization Reaction of acid or alkali with the opposite reagent until the concentrations of

hydrogen and hydroxyl ions in the solution are approximately equal.Nonrenewable resources Resources (coal, oil, ores, etc.) that cannot be renewed once they have

been used up. In contrast, wood, air, and water are renewable resources.Overburden (spoil) Barren bedrock or surficial material that must be removed before the under-

lying mineral deposit can be mined.


Oxidation The addition of oxygen to a compound. More generally, any reaction that involves the loss of electrons from an atom.

pH The negative logarithm of the hydrogen-ion concentration. The concentration is the weight of hydrogen ions in grams per liter or solution. Neutral water, for example, has a pH value of 7, a hydrogen ion concentration of 10.

Packer In well drilling, a device lowered in the lining tubes that swells automatically or can be expanded by manipulation from the surface at the correct time to produce a watertight joint against the sides of the borehole or the casing, thus entirely excluding water from different horizons.

Percentage map A facies map that depicts the relative amount (thickness) of a single rock type in a given stratigraphic unit.

Perched aquifer A water body that is not hydraulically connected to the main zone of saturation.

Permafrost Permanently frozen ground.Permeability The property of capacity of a porous rock, sediment, or soil for transmitting a

fluid without impairment of the structure of the medium; it is a measure of the relative ease of fluid flow under unequal pressure. The customary unit of measurement is the millidarcy.

Pesticide Any chemical used for killing noxious organisms.Plugging The act or process of stopping the flow of water, oil, or gas in strata penetrated by a

borehole or well so that fluid from one stratum will not escape into another or to the sur-face; especially the sealing up of a well that is tube abandoned. It is usually accomplished by inserting a plug into the hole, by sealing off cracks and openings in the sidewalls of the hole, or by cementing a block inside the casing. Capping the hole with a metal plate should never be considered as an adequate method of plugging a well.

Porosity The property of a rock, soil, or other material of containing interstices. It is commonly expressed as a percentage of the bulk volume of material occupied by interstices, whether isolated or connected.

Potentiometric surface An imaginary surface representing the static head of groundwater and defined by the level to which water will rise in a well. The water table is a particular potentiometric surface.

Pressure (a) The total load or force acting on a surface. (b) In hydraulics, without qualifica-tions, usually the pressure per unit area, or intensity of pressure above local atmospheric pressure, expressed, for example, in pounds per square inch, kilograms per square centimeter.

Primary porosity The porosity that develops during the final stages of sedimentation or that was present within sedimentary particles at the time of deposition. It includes all deposi-tional porosity of the sediments or the rock.

Resistivity Refers to the resistance of material to electrical current. The reciprocal of conductivity.

Refusal During drilling, the maximum depth beyond which augers (drill bits) cannot be advanced, usually the top of bedrock.

Resource A concentration of naturally occurring solid, liquid, or gaseous materials in or on the earth’s crust in such a form that economic extraction of a commodity is currently or potentially feasible.

Rotary drilling A common method of drilling, being a hydraulic process consisting of a rotat-ing drill pipe, at the bottom of which is attached a hard-toothed drill bit. The rotary motion is transmitted through the pipe from a rotary table at the surface, that is, as the pipe turns, the bit loosens or grinds a hole in the bottom material. During drilling, a stream of drilling mud is in constant circulation down the pipe and out through the bit, from where it and the cuttings from the bit are forced back up the hole outside the pipe

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and into pits where the cuttings are removed and the mud is picked up by pumps and forced back down the pipe.

Runoff That part of precipitation that flows over the surface of the land as sheet wash and streamflow.

Salinization The excessive build-up of soluble salts in soils or in water. This often is a serious problem in the crop irrigation system.

Saltation A form of wind erosion where small particles are picked up by wind and fall back to the surface in a “leap and bound” fashion. The impact of the particles loosens other soil particles, rendering them prone to further erosion.

Sanitary landfill A land site where solid waste is dumped, compacted, and covered with soil to minimize environmental degradation.

Sea level An imaginary average level of the ocean as it exists over a long period of time. It is also used to establish a common reference for standard atmospheric pressure at this level.

Secondary porosity The porosity developed in a rock formation subsequent to its deposition or emplacement, either through natural processes of dissolution or stress distortion, or artifi-cially through acidization or the mechanical injection of coarse sand.

Secondary wave (S) A body earthquake that travels more slowly than a primary wave (P). The wave energy moves earth materials at a right angle to the direction of wave travel. This type of shear wave cannot pass through liquids.

Sedimentation The process of removal of solids from water by gravitational settling.Seismic activity Earth vibrations or disturbances produced by earthquakes.Seismic survey The gathering of seismic data from an area; the initial phase of seismic

prospecting.Seismograph A device that measures and records the magnitude of earthquakes and other

shock waves such as underground nuclear explosions.Seismology The science that is concerned with earthquake phenomena.Seismometer An instrument, often portable, designed to detect earthquakes and other types of

shock waves.Semiarid regions Transition zones with very unreliable precipitation that are located between

true deserts and subhumid climates. The vegetation consists usually of scattered short grasses and drought-resistant shrubs.

Septic-tank system An onsite disposal system consisting of an underground tank and a soil absorption field. Untreated sewage enters the tank, where solids undergo decomposition. Liquid effluent moves from the tank to the absorption field via perforated pipe.

Shear The movement of one part of a mass relative to another, leading to lateral deformation without resulting in a change in volume.

Shear strength The internal resistance of a mass to lateral deformation (see shear). Shear strength is mostly determined by internal friction and the cohesive forces between particles.

Sinkhole A topographic depression developed by the solution of limestone, rock salt, or gyp-sum bedrock.

Sludge (a) Mud obtained from a drill hole in boring; mud from drill cuttings. The term has also been used for the cuttings produced by drilling. (b) A semifluid, slushy, and murky mass or sediment of solid matter resulting from treatment of water, sewage, or industrial and mining wastes, and often appearing as local bottom deposits in polluted bodies of water.

Slurry A very wet, highly mobile, semiviscous mixture or suspension of finely divided, insol-uble matter.

Soil failure Slippage or shearing within a soil mass because of some stress force that exceeds the shear strength of the soil.


Soil liquefaction The liquefying of clayey soils that lose their cohesion when they become satu-rated with water and are subjected to stress or vibrations.

Soil salinization The process of accumulation of soluble salts (mostly chlorides and sulfates) in soils caused by the rise of mineralized groundwater or the lack of adequate drainage when irrigation is practiced.

Soil structure The arrangement of soil particles into aggregates that can be classified according to their shapes and sizes.

Soil texture The relative proportions of various particle sizes (clay, silt, sand) in soils.Solution A process of chemical weathering by which rock material passes into calcium carbon-

ate in limestone or chalk by carbonic acid derived from rainwater containing carbon dioxide acquired during its passage through the atmosphere.

Sorting A dynamic gradational process that segregates sedimentary particles by size or shape. Well-sorted material has a limited size range whereas poorly sorted material has a large size range.

Specific conductance The electrical conductivity of a water sample at 25°C (77°F), expressed in micro-ohms per centimeter.

Specific gravity The ratio of the mass of a body to the mass of an equal volume of water.Spontaneous combustion Type of fire started by the accumulation of the heat of oxidation until

the kindling temperature of the material is reached.Stage Refers to the height of a water surface above an established datum plane.Standing wave An oscillating type of wave on the surface of an enclosed body of water. The

wave acts similarly to water sloshing back and forth in an open dish.Stock An irregularly shaped discordant pluton that is less than 100 km2 in surface exposure.Storage coefficient In an aquifer, the volume of water released from storage in a vertical col-

umn of 1 ft2 when the water table or other potentiometric surface declines 1 ft. In an unconfined aquifer, it is approximately equal to the specific yield.

Stratification The structure produced by a series of sedimentary layers or beds (strata).Stratigraphy The study of rock strata, including their age relations, geographic distribution,

composition, and history.Stratosphere The part of the upper atmosphere that shows little change in temperature with

altitude. Its base begins at about 7 mi (11 km) and its upper limits reach to about 22 mi (35 km).

Stream terraces Elevated remainders of previous floodplains; they generally parallel the stream channel.

Stress Compressional, tensional, or torsional forces that act to change the geometry of a body.Structure-contour map A map that portrays subsurface configuration by means of structure

contour lines; contour map; tectonic map. Syn: structural map, structure map.Summit aridity Dry conditions that may develop on convex hills as a result of excessive drain-

age and thin soil layers.Surface casing The first string of a well casing to be installed in the well. The length will vary

according to the surface conditions and the type of well.Surficial deposit Unconsolidated transported or residual materials such as soil, alluvial, or gla-

cial deposits.Surge A momentary increase in flow in an open conduit or pressure in a closed conduit that

passes longitudinally along the conduit, usually due to sudden changes in velocity.Swab A piston-like device equipped with an upward-opening check valve and provided with

flexible rubber suction caps, lowered into a borehole or casing by means of a wire line for the purpose of cleaning out drilling mud or lifting oil.

Talus debris Unconsolidated rock fragments that form a slope at the base of a steep surface.Tectonic Said of or pertaining to the forces involved in, or the resulting structures or features

of, tectonics. Syn: geotectonic.


Till Unstratified and unsorted sediments deposited by glacial ice.Topsoil The surface layer of a soil that is rich in organic materials.Tornado A highly destructive and violently rotating vortex storm that frequently forms from

cumulonimbus clouds. It is also referred to as a twister.Total porosity The measure of all void space of a rock, soil, or other substance. Total porosity

is usually expressed as a percentage of the bulk volume of material occupied by the void space.

Toxin A colloidal, proteinaceous, poisonous substance that is a specific product of the metabolic activities of a living organism and is usually very unstable, notably toxic when introduced into the tissues, and typically capable of inducing antibody formation.

Transmissivity In an aquifer, the rate at which water of the prevailing kinematic viscosity is transmitted through a unit width under a unit hydraulic gradient. Though spoken of as a property of the aquifer, it embodies also the saturated thickness and the properties of the contained liquid.

Transpiration The process by which water absorbed by plants is evaporated into the atmo-sphere from the plant surface.

Triangulation A survey technique used to determine the location of the third point of a triangle by measuring the angles from the known end points of a base line to the third point.

Tsunami A Japanese term that refers to a seismic sea wave that can be generated by severe submarine fault slippages or volcanic eruptions. The tsunami reaches great heights when it enters shallow waters, but it is unnoticeable on the high seas.

Turbulence (meteorol.) Any irregular or disturbed wind motion in the air.Twister An American term used for a tornado.Unconfined aquifer A groundwater body that is under water table conditions.Unconsolidated material A sediment that is loosely arranged, or whose particles are not

cemented together, occurring either at the surface or at depth.Urbanization The transformation of rural areas into urban areas. Also referred to as urban

sprawl.Vapor pressure That part of the total atmospheric pressure that is contributed by water vapor.

It is usually expressed in inches of mercury or in millibars.Vesicular A textural term indicating the presence of many small cavities in a rock.Viscosity The property of a substance to offer internal resistance to flow; its internal friction.

The ratio of the rate of shear stress to the rate of shear strain is known as the coefficient of viscosity.

Vorticity (meteorol.) Any rotary flow of air such as in tornadoes, mid-latitude cyclones, and hurricanes.

Wastewater Spent water. According to the source, it may be a combination of the liquid and water-carried wastes from residence, commercial buildings, industrial plants, and institu-tions, together with any groundwater, surface water, and storm water that may be present. In recent years, the term wastewater has taken precedence over the term sewage.

Water quality The chemical, physical, and biological characteristics of water with respect to its suitability for a particular purpose.

Water table The surface marking the boundary between the zone of saturation and the zone of aeration. It approximates the surface topography.

Weather The physical state of the atmosphere (wind, precipitation, temperature, pressure, cloudiness, etc.) at a given time and location.

Well log A log obtained from a well, showing such information as resistivity, radioactivity, spontaneous potential, and acoustic velocity as a function of depth; especially a lithologic record of the rocks penetrated.

Well monitoring The measurement, by on-site instruments or laboratory methods, of the water quality of a water well. Monitoring may be periodic or continuous.


Well plug A watertight and gas-tight seal installed in a borehole or well to prevent movement of fluids. The plug can be a block cemented inside the casing.

Well record A concise statement of the available data regarding a well, such as a scout ticket; a full history or day-by-day account of a well, from the day the well was surveyed to the day production ceased.

Well stimulation Term used to describe several processes used to clean the well bore, enlarge channels, and increase pore space in the interval to be injected, thus making it possible for wastewater to move more readily into the formation. Well stimulation techniques include surging, jetting, blasting, acidizing, and hydraulic fracturing.

Windbreak Natural or planted groups or rows of trees that slow down the wind velocity and protect against soil erosion.

Zone of aeration The zone in which the pore spaces in permeable materials are not filled (except temporarily) with water. Also referred to as unsaturated zone or vadose zone.

Zone of saturation The zone in which pore spaces are filled with water. Also referred to as phreatic zone.

357

Appendix B: Conversion Tablesen

glis

h-SI

con

vers

ion

tabl

e

Len

gth

1 in

ch=

2.5

4 cm

Mas

s1

oz=

28.

35 g

1 ft

= 0

.304

8 m

1 lb

m=

0.4

536

kg

1 m

i=

1.6

09 k

m1

s. to

n=

907

kg

1 l.

ton

= 1

016

kg

Are

a1

inch

2=

6.4

516

cm2

1 lb

m/f

t3=

16.

02 k

g/m

3

1 ft

2=

0.0

929

m2

1 ac

re=

0.4

047

haF

orce

1 lb

f=

4.4

48 N

= 0

.404

7 · 1

04 c

m2

Tem

pera

ture

× °

F=

(9/

5) ×

°C

+ 3

2

1 m

i2=

2.5

90 k

m2

Stre

ss a

nd p

ress

ure

1 lb

f/fo

ot2

= 4

7.88

Pa

Vol

ume

1 U

S ft

oz

= 2

9.54

cm

31

psi

= 6

.895

· 10

3 Pa

1 ft

3=

2.8

32 ·

10–2

m3

1 at

m=

1.0

13 ·

105

Pa

= 2

8.32

lite

r1

bar

= 1

05 P

a

1 U

S ga

l=

3.7

85 ·

10–3

m3

= 0

.1 M

Pa

= 3

.785

lite

r

1 U

K g

al=

4.5

46 ·

10–3

m3

Wor

k or

ene

rgy

1 ft

lbf

= 1

.356

J

= 4

.546

lite

r1

calo

rie

= 4

.185

J

1 U

S bu

shel

= 3

.524

· 10

–2 m

31

BT

U=

1.0

55 ·

103

J

= 3

5.24

lite

r

1 oi

l bar

rel

= 0

.156

m3

Hyd

raul

ic c

ondu

ctiv

ity

1 ft

/s=

0.3

048

m/s

= 1

56 li

ter

1 U

S ga

l/day

ft2

= 4

.720

· 10

–7 m

/s

Flu

id fl

ux1

cubi

c ft

/s=

2.8

32 ·

10–2

m3/

sT

rans

mis

sivi

ty1

ft2/

s=

9.2

90 ·

10–2

m2/

s

= 2

8.32

lite

r/s

1 U

S ga

l/day

ft

= 1

.438

· 10

–7 m

2/s

1 U

S ga

l/min

= 6

.309

· 10

–5 m

3/s

= 6

.309

· 10

–2 li

ter/

sIn

trin

sic

perm

eabi

lity

1 ft

2=

9.2

90 ·

10–2

m2

1 U

K g

al/m

in=

7.5

76 ·

10–5

m3/

s=

9.4

12 ·

1010

dar

cy

= 7

.576

· 10

–2 li

ter/

s1

darc

y=

0.9

87 ·

10–1

2 m

2

pjw

stk|

4020

64|1

4354

3264

0


Prefixes for multiplying and dividing of SI units

10–1 tenth deci d 101 ten deca da

10–2 hundredth centi c (%) 102 hundred hecto h

10–3 thousandth milli m (‰) 103 thousand kilo k

10–6 millionth micro μ (ppm) 106 million mega M

10–9 billionth nano n 109 billion giga G

10–12 trillionth pico p (ppb) 1012 trillion tera T

Note: ppm (parts per million)—particles per million particles; ppb (parts per billion)—particles per billion particles.

chemical Symbols

Mass Number Ion charge Examples

SYMBOL612 2+

2C,Ca ,ONumber of protons Number of atoms

pjw

stk|

4020

64|1

4354

3264

2

359

Appendix C: Math Modeling and Useful ProgramsGroundwater governing 2-D equation:

δδ

δδ

δδ

2

2

2

2

hx

hy

ST

hr

+ = (9.1)

a. Finite difference method (backward-difference simulation), see Figure 9.1

h i J n h i J n h i J n h i J n( , ), ( , ), ( , ), ( , ),− + + + − + +1 1 1 1 −−

=− −

4

1

2

h i j na

ST

h i J n h i J nt

( , ),

( , ), ( , ), ( )∆

(9.2)

where

a x y= =∆ ∆

b. Finite element method Equation 9.1 may take the following form, including recharging (+) or discharging (–) well Q,

fIgure c.1 Finite difference notation.


∇⋅ ∇ ± =[ ]( , ) ( , , ) ( , )T h Q S htx y x y t x y

δδ

(9.3)

Using variational methods, Equation 9.3 may take the following form:

U T hx

T hy

S ht

Q hx y= + +

1 2

2 2

/ δδ

δδ

δδ∓

∫∫ dxdy (9.3a)

Minimizing Equation 9.3,

δδ

δδ

δδ

δδ

δδ

δδ

Uh

e T hx h

hx

T hyi

s

xi

y=

+∫ hhhy

s ht

Q hh

ds

i

i

δδ

δδ

δδ

+

±

(9.4)

Considering δδht for simplicity to be

hn h nt

− −( )1∆ as given in the finite difference notation,

and differentiating Equation 9.3 with respect to hJ,hk, also, noting that (see Figure 9.2)

hp = a1 + a2x + a3y (9.5)

where

fIgure c.2 Finite element (for a triangular element).

Appendix C: Math Modeling and Useful Programs 361

aaa

abc

a

bc

abc

i

i

i

j

J

J

k

k

k

1

2

3

12

=

∆

h

h

h

pi

pJ

pk (9.6)

ai,J,k, bi,J,k, and ci,J,k can be given by substitution in Equation 9.5 in terms of xi,J,k and yi,J,k 2∆ = 2 area of the triangle = determinate of the triangle.

Equation 9.5 then becomes

hp a b x c y h a b x c y h

a

i i i pi J J J pJ

k

= + + + + + +

+

12∆

[( ) ( )

( bb x c y hk k pk+ ) ] (9.7)

having Ni = (ai + bix + ciy)/2∆ NJ = (aJ + bJx + cJy)/2∆ NK = (aK + bKx + chy)/2∆ Equation 9.7 then becomes

hp N N N h

h

h

N hi J k pi

pJ

pk

=

=[ ] [ ]( )

(9.8)

After assembling the whole set of minimizing equations for the whole region,

[N][H] + [F] = 0 (9.9)

Equation 9.9 describes the steady-state condition, and for the unsteady state conditions, ∆t can be set for reasonable time length, and the finite difference approximation for hn – hn–1/∆t can be included in Equation 9.9.

For the solute transport equation:

δδ

δδ

δδ

δδ

δδ

δδ

ct+u c

x+w c

y-x

D cx

+y

DL

TT

cy

+kc =0δδ

′ (9.10)

Equation 9.4 is identical with Equation 7.7 and can be simulated the same way as the groundwater Equation 9.3 when the finite element method is used. The difference between the two equations is that Equation 9.9 contains symmetrical matrices, whereas solute trans-port finite element equations do not have this symmetry. For this reason, for any numerical model of a solute transport problem, a memory of at least 1 MB in the computer is required for more than 500 elements model.

363

Appendix D: Software Manual of Drawdown Around Multiple WellsThis program can be used to calculate the drawdown of the water table around multiple well systems for dewatering purposes or for any other environmental problem. The modified Theis equation is used to develop the drawdown contours around the well system for both confined and unconfined aquifers. The aquifers are considered isotropic for simplicity, having uniform saturated thickness. In this respect, the two-dimensional solution is adopted. The three-dimensional solution is tried for solute transport problems that will be demonstrated in another book by the author.

The executable files are written in TPASCAL designed by Dr. A. A. Hassan and modified by the author to suit some environmental problems. The name of this file is MULTIP4.EXE. The data file name can be any name the user can select. For the example given here, the data file name is MUL-TIP4.DAT. This file should include all the boundary conditions, aquifer characteristics, well posi-tions, complete network of the area, etc. The following steps can be followed to create your data file.

Step 1: Assign the name of your data file and write the data needed for each of the following step on a separate line.

Step 2 (line 1): Specify the kind of aquifer: 0 for confined, and 1 for unconfined. This should be stated on the first line of your data file.

Step 3 (line 2): Assign the maximum and minimum coordinates of the problem boundaries with their scales as given in the following line:

xm1 xm2 ym1 ym2 delta(x) delta(y)

Step 4 (line 3): Try to adjust the groundwater flow direction parallel to one of the axes and then type the values of transmissivity, T, storativity, S, water-table slope, gi, and saturated thickness, M, as

T S gi M

Step 5 (line 4): Write the number of the pumping wells, n.Step 6: Type the x, y coordinates of the pumping well and discharge (Q) of each well. For

example, if we have three wells, those values should be arranged as

(line 5) X1 Y1 Q1 (line 6) X2 Y2 Q2 (line 7) X3 Y3 Q3

Step 7 (line 8): On the next line, type the number of times (NT) selected: NTStep 8 (line 9): Type the value of the selected times (it) for the drawdown values to be calcu-

lated. Note: keep in mind the time units to be the same in the problem; this means that if T is m2/d, the time unit is a day. Thus, line 9 contains

t1 t2 ............ tr


Step 9 (line 10): Type the number of points in the domain (np), the number of rows (nrows), and the number of vertical lines (nl) as follows:

np nrows nl

Step 10 (line 11): For irregular boundary problem, assign an integer 0, or integer 1 for regular boundary (regular boundaries are either square or rectangular in shape).

0 or 1

Step 11 (line 12): On line 12, type the number of points on x-axis (nx) and the number of points on y-axis (ny) as:

nx ny

Step 12 (line 13): For drawing the drawdown contours, assign the element dimensions delta x1 and delta y1 as

delta x1 delta y1

Step 13 (line 14): Write the number of the corners: ncStep 14 (line 15): Write the corner numbers nc(i) of the boundary problem as

i ii iii iv (supposing we have 4 corners)

Step 15 (line 16): Write the number of contours (nhl) you want to draw as

nhl

Step 16 (line 17): Write the contour values, hl(i) (note that you must have the exact number of contour values as specified in step 15):

hl(1) hl(2) ............ hl(i)

Step 17 (line 18): In the last line of the data file, write the contour information, considering a = contour interval, b = the lowest value of the contours, and c = the highest contour needed for demonstration; then line 18 should include

contour intervals = a (from b to c)

Step 18: After preparing the data file, you can start the program using MULTIP4.EXE. Write the data file name upon request, then press (enter ←). The first figure appears on the screen showing the well locations. Press (enter ←) to give the drawdown contours as specified after the first period. Press (enter ←) again to show the drawdown contours for the second period, and so on until you execute the number of time periods required in the problem.

As an example, the following problem is given:For an unconfined aquifer with a saturated thickness of 50 m, three wells were drilled to dis-

charge 100 m3/h/well. Find the drawdown contours around the well group after three successive time periods 0.5, 1, and 1.5 d, respectively, if you are given the following data:

Appendix D: Software Manual of Drawdown Around Multiple Wells 365

T = 750 m2/d, S = 0.01, ig = 0.0001

if the aquifer occupies an area of 20 × 10 km, and the well coordinates are (3500,4500), (3250,4250), and (3750, 4000) m, respectively.

Notice that the data file for this problem is given in MULTIP4.DAT, which follows Steps 1 to 17.