P?;;; iiiia •'•

i 2 1 2 . 0 96GR

GROUNDWATER:A THREATENED

ESOURCE

*P*?;;;

• ' • < • '

iiiiai.•i .;:

'^ :-'y ..-

United Nations Environment ProgrammeGroundwater: a threatened resourceNairobi, UNEP, 1996 . . • • • '(UNEP Environment Library No 15)

This publication is produced within the framework or meEarthwatch process of the United Nations system.

Copyright ©UNEP 1996United Nations Environment ProgrammePO Box 30552Nairobi, Kenya

Text: Robin Clarke, with Adrian Lawrence and StephenFoster of the British Geological Survey, Groundwater andGeotechnical Surveys Division.

Layout and artwork: Words and Publications,Oxford, United Kingdom

This publication is printed on Savanna Natural Art, a papermade from 75 percent sugar cane waste and 25 percentfibre from sustainably managed softwood forests. It isbleached without damage to the environment.

The views expressed in this publicationare not necessarily those of theUnited Nations Environment Programme

Also in this series:1. The Greenhouse Gases2. The Ozone Layer3. The African Elephant4. Urban Air Pollution5. Food Contamination6. Freshwater Pollution7. The Impact of Ozone Depletion8. The El Nino Phenomenon9. Glaciers and the Environment10. The Impacts of Climate Change11. Global Biodiversity12. The Pollution of Lakes and Reservoirs13. The Impacts of Climate on Fisheries14. Water Quality of World River Basins

UNEP Environment Library No 15

GROUNDWATER:A THREATENED

RESOURCELIBRARY IRC

PQ Box 93190, 2509 AD THE HAGUETel.: +31 70 30 689 80Fax: +31 70 35 899 64

BARCODE: V 3 * 9 2 4O :

The UNEP GEMS/Water Programme and the Environment Library

Since 1976, UNEP has participated in worldwide efforts to assess and improve freshwater quality bymanaging the Global Environment Monitoring System's Water Programme (GEMS/Water). GEMS/Waterwas launched by UNEP as a joint effort with three other United Nations agencies: the World HealthOrganization (WHO), the United Nations Educational, Scientific and Cultural Organization (UNESCO)and the World Meteorological Organization (WMO). GEMS/Water is a global programme dealing mainlywith water quality monitoring and assessment. Some 60 nations participate in its global network ofstations which monitor water quality in rivers, lakes, reservoirs and groundwater. UNEP is also workingon means of improving the use made of the data collected for water resource management.

The programme operates jointly with a number of Collaborating Centres including the Danish WaterQuality Institute, the British Geological Survey and the Robens Institute in the United Kingdom, and theNational Water Research Institute in Canada. These centres constitute the scientific backbone of themonitoring and assessment activities.

UNEP/GEMS started its Environment Library series in 1987 in order to disseminate environmentalinformation on major topics to a non-technical audience. This is the 15th volume in the series and the 4thvolume on water issues. The other three are Freshwater Pollution, The Pollution of Lakes and Reservoirs and

Water Quality of World River Basins.

Contents

Foreword

Overview

The scientificbackground

The importanceof groundwater

The deteriorationof groundwater

Implications for policy

Sources

The hydrogeological cycleWater in aquifersHow groundwater flows

Early uses of groundwaterWhere groundwater is usedThe advantages of groundwaterGroundwater quality

Inadequate controlThe pollution of groundwater

Protecting groundwater resourcesAssessing groundwater resources

3

4

679

10101214

1522

3033

36

Cover: 'Earth and Water'designed and produced byWords and Publications

Foreword

The world's water is one of our most precious resources. Lack of water is one of theprincipal causes of delayed development. Polluted water is one of the biggest killerswe know, responsible for up to 27 000 deaths a day in the world's poorest countries.

Of the limited volume of freshwater that is available to us, some 97 percent(excluding permanently frozen water) is stored underground. More than 1500million people rely on this groundwater for their drinking water. Farmers all overthe world use it to irrigate their crops. In arid areas, where rainfall is low orvirtually non-existent, groundwater may be the only source of water for thehuman population.

As populations grow and their need for water increases, the pressures on ourgroundwater resources also increases. In many areas of the world, groundwater isnow being over-abstracted, in some places massively so. The result is falling waterlevels and declining well yields, more expensive supplies, land subsidence, theintrusion of salt water into freshwater supplies and ecological damage such as thedrying out of wetlands.

Groundwater is also being polluted. Cities with poor sanitation systems areallowing foul water to seep into underground aquifers, whence it eventuallycontaminates the boreholes and wells that supply drinking water. Industriesaccidentally spill or release their effluents into the ground or into surface watercourses whence pollution is carried deep underground. Chemical fertilizers andpesticides are leached through the soil and down into the aquifers as a result of theintensification of agriculture.

The end result is a serious deterioration of groundwater quality. It is alwaysextremely difficult and very costly to clean up a polluted aquifer. Often it is simplyimpossible. Because water flows so slowly underground, it takes many years ordecades for pollution to show up. Many of the aquifers from which we arecurrently abstracting pure water may already be contaminated.

It is therefore urgent that we protect our groundwater supplies with diligence,and that everyone understands the importance of doing so. This publication isintended to explain to readers how important groundwater is, the extent of thethreat to it, and the actions that can be taken to protect it.

Elizabeth DowdeswellExecutive DirectorUnited Nations Environment Programme

Overview

More intensivemonitoring isrequired inalmost allcountries in orderthat a clearerpicture is paintedof the state ofthe world'saquifers andwhat must bedone to preservethem for futuregenerations.

Some 97 percent of all the freshwater that is found on the planetis stored underground (excluding water locked in the polar icecaps and glaciers). This vast water reserve, on which at least1500 million people depend for their drinking water supply, isstored in the pores that exist in materials such as sand andgravel, and in the fractures that are found in rocks such assandstone and limestone.

Groundwater supplies are recharged by rainwater thatinfiltrates down through the soil and the unsaturated layerbelow it. When rainwater reaches the water table and joins anaquifer, it begins a long and slow journey underground, movingat rates ranging from a few millimetres to a few metres a day.Eventually it finds an outlet, in a riverbed, a spring, a man-madewell or straight to the sea.

Groundwater can be extremely old, and some is derived inpart from rainwater that fell as long as 30 000 years ago. Manygroundwater sources have supplied water for humanconsumption for several thousand years since the first humansettlements were established around wells or springs.

Groundwater supplies are coming under increasing pressurefrom growing human populations that consume increasingamounts of water as development proceeds. One result is thatmany groundwater reserves, particularly in arid areas, are beingover-exploited, with water being abstracted from them atunsustainable rates.

Over-abstraction causes a number of serious problems. Oftenyields from boreholes and wells are reduced, which ultimatelyincreases the cost of pumping and thus the price of urban watersupplies. As water levels fall, so may the ground settle. Landsubsidence is now a major problem in many cities in developingcountries, causing expensive damage to urban structures. Over-abstraction is also leading in many coastal areas to the intrusionof salt water into groundwater reserves many kilometres inland.In some inland areas, saline water from deep underground isrising in response to over-pumping.

Groundwater is also becoming increasingly polluted. One ofthe major sources is foul water and sewage from cities indeveloping countries with inadequate sanitation systems. Inmany urban aquifers, levels of nitrate are high and potentiallydangerous micro-organisms are finding their way into wells andboreholes used for drinking water. Other chemicals are leachedby the rain from rubbish tips and landfills, eventually findingtheir way into aquifers. Industry is also polluting groundwater,

overview

allowing liquid wastes to be released intothe ground or into surface water coursesand spilling chemicals such as hydrocarbonfuels and chlorinated solvents from leakingstorage tanks. Mining, and disused mineswhere pumping has stopped, are furthersources of pollution.

Agriculture is another source ofgroundwater pollution. Some of thechemical fertilizer and pesticide used inagriculture never reaches the plants forwhich it was intended. Instead it is washedby the rain from the soil and down intounderground water reserves.

Groundwater pollution is insidious andexpensive: insidious because it takes manyyears to show up in abstracted water, bywhich time it may be too late to preventserious contamination; and expensivebecause the cost of providing alternativewater supplies, and remediating pollutedaquifers, is very high. Indeed, restoration todrinking water standards is often impossible.

For these reasons, there is a need to assessaquifer vulnerability and improve theprotection of groundwater resources.Abstraction must be better controlled andland-use zoning controls introduced toprotect the most vulnerable aquifers. Moreintensive monitoring is required in almostall countries in order that a clearer picture ispainted of the state of the world's aquifersand what must be done to preserve them forfuture generations.

While surface water sourcesare sometimes spectacular,they are tiny compared to thewater resources storedunderground.

The scientific background

Some of thewater in theChalk aquiferthat lies underLondon fell as rainas long ago asthe last Ice Age.

Diagram of thehydrogeological cycleshows groundwaterand surface waterrelationships, andgroundwaterpollution risks.

The hydrogeological cycle

Groundwater is water that accumulatesunderground. There is a lot of it. Of the 37million km3 of freshwater that is to befound on the planet, some 8 million km3—roughly 22 percent—is storedunderground in the form of groundwater.Excluding water locked in the polar icecaps, groundwater constitutes some 97percent of all the freshwater that ispotentially available for human use on orbeneath the Earth's surface. The remainderis stored in lakes, rivers and swamps.

Groundwater reserves are recharged forthe most part by rain that infiltratesthrough the soil into the underlying layers.These reserves are occasionally augmentedby streams and rivers that lose water to theunderground strata. Once underground,the water flows at rates ranging from morethan 10 metres a day to as little as 1 metre a

year, until it reaches an outlet. This maytake the form of a spring or of a system ofslow seepages at the ground surface. It isthese seepages that keep rivers flowingduring dry periods. In some places, a systemof natural springs provides sufficient waterto create a river. The River Touvre incentral France, for example, is created by justsuch a system of springs which vent to thesurface as much as 60 m3 of water a secondduring times of maximum flow.

The time scales of groundwater flow arelong. It may take years or even decades forwater to find its way down through thesoil to reach the water table, the level atwhich the ground is fully saturated. Oncethere, the water may remain undergroundfor tens or even thousands of years beforeit reappears at the surface. Some of thewater in the Chalk aquifer that lies underLondon fell as rain as long ago as the lastIce Age. According to one estimate, onaverage the water vapour in theatmosphere is renewed every 8 days,

transpiration

saturated zone

Impermeable layer

groundwater flowregional groundwater flow

the scientific background

stream water every 16 days, soil moistureonce a year, swamp water every 5 yearsand lake water every 1.7 years. The averagefor groundwater is 1400 years but therecycle time for some aquifers is muchlonger even than this.

Occasionally, geological events trapwater underground, cutting it off fromboth its source of supply and its outlets.Climatic change may also depriveunderground stores of any means ofrecharge, as has happened under a number

of regions which are now desert but whichwere formerly much wetter.

Groundwater reserves which are notrecharged are known as fossil water. Suchwater can be tapped and used throughwells or boreholes but once the water ispumped out it may never be replenished.Examples of fossil water are found underthe Saharan desert, for example, whereplans for its intensive use have arousedfierce controversy from the countries thatshare the aquifer (see box on page 8).

Water in aquifers

The water-bearing material in whichgroundwater is stored and through whichit flows is called an aquifer. Aquifers canconsist of unconsolidated materials such assand and gravel, or consolidated rock suchas sandstone. Unconsolidated materialscan store large volumes of water. Sands,for example, can store up to 30 percent oftheir volume as water. Consolidatedmaterials may also be very porous in thatthey can store large volumes of water buttheir pores are usually too small to allowthe water to flow easily through thematerial. In some rocks the pores act as aform of unextractable water storage,

i

s\

•)-?

• " - • ^

j

' • • /

\ L

i

_ / '•,

\ . v , . • /x*\

'! /'

;.: • ' '

¥"v ''iv

,,.;'

/ ' •

/

j ,

i

; '(,/ '

K\

'"-

J!

)

unable to release their water because of thecapillary attraction between the water andthe pore surface.

However, consolidated materials also storewater in tiny fractures in the rock. Althoughthese fractures rarely occupy more than 1percent of total volume, in rocks such aslimestone they can become enlarged as therock is dissolved away. These enlargedfractures enable the aquifer both to storelarge volumes of water and permit high ratesof water movement (see illustration below).

The major aquifers in the United Kingdomare made of limestone or sandstone. They areextensive, covering an area of several

Unconsolidated materialssuch as sand (below left)can store up to 30 percentof their total volume aswater. In consolidatedrocks (below centre) wateris stored only in fractures,and rarely exceeds 1percent of total volume,in soft rocks such aslimestone, however, thesefractures are enlarged bysolution and providesignificant water storage(below right).

Groundwater: a threatened resource

thousand square kilometres, and in placesare more than 100 metres deep. The greatlimestone aquifer that lies under large areasof southern and eastern England, called theChalk, is estimated to contain 2000 km3 ofwater (compared to the 0.8 km3 of water inthe major water reservoirs of England andWales). Though more water could beextracted from these aquifers, doing so couldsignificantly reduce river flow in the area.

The great aquifers of the world, such asthose that underlie the Ganges and Indusbasins in south Asia, are of course muchlarger than the Chalk, and the total volumeof water pumped from them is also muchlarger. The aquifer that lies under the350 000 km2 Huang-Hai-Hai Plain ofeastern China, for example, providesdrinking water for 160 million people andirrigates 20 million hectares of land.

Aquifers are usually bounded above byan unsaturated zone, containing both airand water, and below by an impermeablebed of clay or rock. The boundary betweenthe saturated and unsaturated areas isknown as the water table. In arid areas, thewater table may be as much as 100 metresbelow the surface while in more humidareas it can be close to the surface.

Some aquifers, however, are boundedentirely by impermeable layers and containwater under pressure. When wells aredrilled down to such pressurized aquifers,the water will rise to the surface under itsown pressure. In the Middle Ages a numberof these pressurized aquifers were tapped inthe ancient province of Artois (now the Pas-de-Calais) in France; these wells became sofamous that all flowing wells weresubsequently called artesian wells.

Fossil groundwater in the sub-Saharan aquifer

One of the world's most extensive aquifers lies under parts ofChad, Egypt, Libya and Sudan in the Sahara desert. Thisaquifer, of Nubian sandstone, has delivered water to many ofthe deserf s oases for millennia. Water in the aquifer is renewedvery slowly, and most of it has been in the aquifer for at least30 000 years. It is essentially fossil water dating from a timewhen rainfall over north Africa was much higher than it is now.

Libya has an ambitious programme of pumping water fromthe aquifer to supply the populated coastal regions of thecountry, where overpumping of groundwater has diminishedsupplies and caused saltwater intrusion. A giant pipeline to dothis, capable of carrying 730 million m3 of water a year, wasopened as the first phase of this programme in August 1991. Bythe end of the five-phase programme, estimated to costUS$25 000 million, the volume of water pumped from theaquifer every year will approach the flow rate of a large river—indeed, in Libya the project was named 'The Great Man-madeRiver Project'.

Part of the sub-Saharan fossil aquifer; arrows showthe direction of water movement.

the scientific background

How groundwater flows

humid regions

aquifer recharge area

unsaturated zone

minorperennialdischarge

area

majorperennial artesian

discharge dischargearea area

groundwater plezometrlc level(with maximum and minimumlevels in the non-confined aquifer

semi-arid regions

aquifer recharge area

minor perennialdischarge area

Groundwater moves through aquifers as aresult of differences in pressure orelevation of the water table within theaquifer and can be compared withmovement of water through a pipe. As inpipes, various obstructions may occur asthe water moves from the point ofrecharge to its exit from an aquifer. Somerock formations, such as shale, are soimpermeable to water that they effectivelystop groundwater flow completely; theseare called aquicludes. Other geologicalstrata, such as clay 'lenses' embedded withsand, may slow down the flow of water;these are called aquitards.

The rate at which water flows through anaquifer depends on the permeability andporosity of the rock, and on the pressuregradient. Limestone, for example, is highlypermeable and limestone aquifers, such asthose under southern England, Denmarkand northern France, respond rapidly tochanges in recharge and abstraction rates.Groundwater levels in such areas oftenfluctuate by as much as 10 metres a year,and can change by up to 50 metres a year.

Even so, groundwater flow rates are verysmall compared to those of surface water.

The water abstracted from many of thedeeper alluvial basins is likely to bethousands or even hundreds of thousandsof years old. The slow movement ofgroundwater contributes greatly to itspurity since contaminants become highlyattenuated during groundwater's normallylong journey from the surface, through theaquifer and into a borehole.

Salt water, as well as freshwater, can flowthrough rock. Near coastlines, saltwaterintrusion can occur where the water tableis lowered due to abstraction of freshwater, contaminating the aquifers fordistances of several kilometres inland.Climatic change, resulting in rising sealevels, is likely to accentuate this problem.

Basic elements ofgroundwater flow inhumid regions (left)and semi-arid regions(right).

The importance of groundwater

Lateral tapping ofgroundwater, the basisof the qanat system

Protected dugwell

Early uses of groundwater

Groundwater is used extensively by humanpopulations on all continents. While manyearly populations settled by sources ofwater such as rivers and lakes, many othersbased settlements on the existence of aspring or a well—hence the commonending '-well' for place names in Englandand '-ac' for place names in France.

The earliest wells were probably built in theNear East where, although they were rarelydeeper than 50 metres, they were often wideenough to accommodate a donkey path usedto collect the water. The ancient Chinesedeveloped slow drilling methods thatenabled wells to be dug down to 1500metres or so, using drilling techniques thatcontinued for years or even decades.

Some 2500 years ago, the use of qanatswas developed in Iran. These are longhorizontal galleries connecting aquifers atthe foot of mountains to fields and villages

several kilometres away. The use of qanatsspread as far afield as Egypt andAfghanistan, and many such systems arestill used today.

Flowing or pressurized wells were firstdeveloped in Europe in Flanders in about1100 A.D. where by that time a water wheelwas being powered by four lined wellsdriven more than 100 metres down into aconfined Chalk aquifer.

During the 20th century, both drillingand pumping technology developed so fastthat it became easy to sink deep boreholesquickly, and to extract large volumes ofwater from them. While thesedevelopments have increased supplies ofdrinking and irrigation water, they haveled to the rapid lowering of the water tableunder many cities and to the virtualexhaustion of some of the aquifers used tosupply irrigation water in arid climates.

Borehole or tubewell

Where groundwater is used

No authoritative estimates exist of thepercentage of world water use thatdepends on groundwater. About one-thirdof Asia's population, some 1000-1200million people, are thought to depend ongroundwater. Some 150 million LatinAmericans also depend on groundwater(see maps on page 11). Some individualcountries, such as Barbados, Denmark andthe Netherlands, depend almost entirelyon groundwater. More than one-third ofwater use in France and the UnitedKingdom is supplied from aquifers andthe United States is 50 percent dependenton groundwater.

Many of the world's most important cities,including Mexico City, Lima, Dhaka and

Jakarta, for example, depend largely ongroundwater. In Mexico City, thegroundwater supply is from some 1500boreholes supplying more than 3200 millionlitres a day. While groundwater suppliesare of obvious importance to cities in aridareas, they are also extensively used inhumid areas—largely because they providewater that requires little or no treatmentand which can be cheaply developed.

It is often thought that recharge beneathcities is reduced as a result of covering theland surface with impermeable roads,parking areas and buildings. In fact, this isnot so, particularly in cities that haveinadequate sewerage systems. Rechargerates have been found to be up to six times

10

the importance of groundwater

higher in urban areas than in rural ones asa result initially of water being importedfrom peri-urban areas and then leaking intothe ground from water mains, sewers andseptic tanks, and soakaway drainage fromhomes and roads. This is particularlystriking in one of the suburbs of Lima, acity situated in Peru's arid zone. There thenatural recharge rate under pre-urbanconditions would be zero. Today it is700 mm a year, due largely to leaking watermains and over-irrigation of amenity areas.

Groundwater now supplies more than 90percent of the rural population in suchcountries as Costa Rica, El Salvador andGuyana. Rural communities often dependon low-yielding boreholes, producingperhaps only 0.5 to 5.0 litres a second(high-yielding boreholes used for irrigationand urban water supply can produce 20times as much).

proportion of potable.'water supplyestimated to bederived fromgroundwater

cities known tc-be highlydependent ongroundwater(figures denoteground waterabstraction rate. Ml/a}

Surface water courses often receive domesticand industrial effluent which may infiltrate toshallow groundwater.

Groundwater usestatistics areincomplete inmost developingcountries. Themaps on the leftand below provideestimates of theextent to whichSouth andCentral Americanand Asianpopulationsdepend ongroundwater fordomestic supplies-

V

proportion ofpotablewater supplyestimated tobe derivedfromgroundwater

EH °~25%

[Hj 25-50%

50-100%

11


The advantages of groundwater

Whereas thedevelopmentof surfacereservoirs involvesthe constructionof large andcostly dams andreservoirs,groundwatercan bedeveloped asand whenneeded throughthe addition ofboreholes andwells.

Groundwater has numerous advantagesover surface water sources. First, itssupplies are not subject to abrupt changeas a result of abnormal weather. Whereasin some countries, an exceptionally hot anddry summer is sufficient to reduce surfacereservoirs to dangerously low levels,groundwater supplies will be little affectedby one dry summer. In Asia, theseadvantages are pronounced. In manyAsian countries the hot season lasts as longas nine months and dries up many surfacewater supplies. During the three-monthmonsoon, in contrast, rainfall is often soheavy that water courses are turned intoturbulent mixtures of mud and water.

Secondly, as has been mentioned,groundwater is cheap to develop. This ispartly because, if it is unpolluted, it

requires little or no treatment before useand partly because it can be developedstage by stage. Whereas the developmentof surface reservoirs involves theconstruction of large and costly dams andreservoirs, groundwater can be developedas and when needed through the additionof boreholes and wells.

Thirdly, groundwater can often betapped near to where it is needed whilesurface water must either be developed atthe sites of natural dams or reservoirs, orpiped considerable distances to where itwill eventually be used.

However, groundwater is not just analternative to the use of surface water. Inmany areas, it is groundwater that makes theuse of surface water sources possibleduring dry seasons. Groundwater provides

Groundwater in the United States: key facts

• Groundwater resources under the United States areestimated at 125 000 km3, roughly the equivalent ofthe flow of the Mississippi River for 200 years.

• Groundwater supplies more than half of US drinkingwater, and 96 percent of the drinking water consumedin rural areas.

• Some 30 percent of the groundwater used in theUnited States for irrigation comes from one aquifer—the Ogollala running from Dakota to Texas.

• Dams along canals in southern Florida are needed toprevent saltwater contaminating the Biscayne aquiferwhich supplies drinking water to 3.5 million Floridians.

• Groundwater abstractions have lowered the groundby up to 3 metres in the Houston-Galveston area,

giving rise to coastal and inland flooding. Land inCalifornia's San Joaquin Valley has sunk by as muchas 8 metres since the 1920s.

• Over-abstraction caused water levels in the NorthernMidwest aquifer system to fall by more than 300metres. Many Chicago suburbs switched to waterfrom Lake Michigan and the water table has nowrisen by 75 metres since 1985.

• Radioactive waste from a former nuclear productionfacility near Richland, Washington, has contaminatedparts of the aquifer below.

• Some three million people are supplied from a three-tiered aquifer below Long Island—but the top tier ofthe aquifer is now contaminated by oil and gasoline,septic tank effluents and pesticides.

12

High-yieldingboreholes are widelyused for irrigation andurban water supply.

the baseflow to many of the world's rivers,and this flow continues throughout theyear, regardless of weather conditions.Many of the world's rivers would dry up inhot and dry summers were they not fed bygroundwater. In this, groundwater resemblesglaciers which are also an important source ofriver flow near mountainous areas during hotsummers—the hotter the summer, in fact,the greater the flow provided by glaciers.

Finally, groundwater resources are alsostrategic resources in that they are oftenunaffected by catastrophic events such asearthquakes, volcanic eruption and war.While catastrophes of this kind can havelong-lasting and serious consequences forsurface water supplies, groundwater israrely affected—though the poisoning ofwells was an important part of medievalwarfare in Europe.

How aquifers respond to drought

Aquifers can store considerable volumes of groundwaterand, where the water table is deeper than 3 metres,evaporation losses from this stored water are negligible.For these reasons, groundwater is less affected bydrought than surface water.

However, not all aquifers are insensitive to drought;those with limited groundwater storage can besusceptible to extended dry periods, particularly insemi-arid and arid regions where a relatively smallchange in the rainfall pattern can cause adisproportionate reduction in infiltration. This isbecause a considerable volume of water may be neededto satisfy the moisture deficit in the soil before deepinfiltration to groundwater can occur.

In some areas of Africa and south Asia, a successionof years of below-average rainfall has caused severewater shortages. The effect of these extended dryperiods on groundwater levels may be worsened if

excessive groundwater abstraction depletes aquiferstorage further.

The Deccan basalts of central India are particularlysusceptible to drought. Less than 20 metres belowground surface, these aquifers store the equivalent ofonly 1-2 years of current abstraction. In the state ofMaharashtra, groundwater pumping has increasedmore than six-fold in recent years. As a result, thereappears to be a long-term decline in the water table, atleast in some areas, and this has resulted in water levelsapproaching the base of the aquifer at the end of the dryseason. Failure of the monsoon causes many of theirrigation wells in these areas to dry up completely andleads to serious crop losses. In some villages, even thecommunity drinking-water wells become dry andexpensive, emergency drilling programmes and water-tankering schemes have to be introduced.

13


Groundwater quality

Most groundwater originates from waterthat has permeated first the soil and thenthe rock below it. The soil removes manyimpurities and the rock through which thewater then flows, perhaps for thousands ofyears, filters and purifies the water evenfurther. It therefore usually reappears at theEarth's surface free of pathogenic micro-organisms—hence the strong and risingdemand for bottled 'source' water (see boxbelow). The fact that most groundwaterneeds no treatment before it is put tohuman use means also that groundwater is

Bottled water: a fashionable resource?Bottled water, obtained from springs and boreholes, often inmountain areas, has long been drunk in countries where thequality of rural or urban water supplies is suspect. As rivers andreservoirs have become increasingly polluted, and water treatmentneeds have increased, many households have turned to bottledwater to avoid the increasingly unattractive taste of tap water.

In the United Kingdom, for example, the consumption of bottledwater reached 500 million litres by the end of 1992. However, itwas still only one-tenth the consumption in Belgium, France andItaly where average consumption is 100 litres per person per year.Bottled water typically costs 500 to 1000 times more than tapwater, and—in restaurants, at least—is more expensive thanpetrol or even wine served by the carafe.

In the United States, as much as half of the bottled water that isdrunk is purified mains water, known as 'designer water'.

While many people drink bottled water because they believe it tobe healthier than mains water, tests have shown that many bottledwaters have a low mineral content. According to a report in the UKjournal Which, 'most stillwaters contain high levels ofbacteria'—although most, ifnot all, of these are likely tobe harmless.

Rise in sales of bottled water in

the United Kingdom, 1982-92.

sales of bottled water (million litres)600

600

400

300

200

1982 1984 1986 1988 1990 1992

a cheap source of water. While this isadvantageous, it also increases the risk thatgroundwater reserves become over-exploited. While groundwater is less easilypolluted than streams and rivers, it oftencontains high concentrations of dissolvedsolids from the rock through which it haspassed. As Pliny put it some 19 centuriesago, 'Water takes on the properties of therocks through which it has passed'.

When groundwater is polluted, manyprocesses occur during the water's longjourney from the surface to a borehole inthe aquifer which help attenuatecontamination. Not only do contaminantsbecome diluted but they can be absorbedby the rock itself and, in some cases,biochemically transformed into othercompounds that are often less harmfulthan the original contaminants.

However, should groundwater becomeseverely polluted—by industry, by landfillsor by agricultural discharges, for example—the damage can be severe and very longlasting. Once pollutants reach the water table,it may take a very long time to flush out theaquifer completely. Furthermore, pollutioncan take a very long time to show itself sincethe water within aquifers moves so slowly.

Worse still, some industrial pollutants arerelatively insoluble and heavier than water.They therefore sink to the bottom of anaquifer where they are slowly dissolved anddispersed into deep circulating groundwaterover a period of many years. Once polluted,aquifers are difficult—indeed, sometimesimpossible—to clean up. The process hasbeen likened to trying to squeeze out the lasttraces of soap from a sponge.

Groundwater pollution, which is nearlyalways persistent and often irreversible, isbecoming increasingly serious in manyareas of the world.

14

The deterioration of groundwater

In many areas of the world, groundwatersources are under threat from humanactivities. These threats takes two mainforms: the inadequate control ofgroundwater abstraction, resulting usuallyin some form of of over-exploitation; andthe pollution of groundwater resources,usually by cities, industry or agriculture.

Both threats can result in either reversibleor irreversible damage. In the first case,matters can be corrected and only thequestion of costs is involved. In the secondcase, costs are also involved but, inaddition, sustainability issues arise sincefuture generations are deprived of animportant resource.

Inadequate control

Many aquifers are being over-exploited inthe sense that water is being abstractedfrom them faster than the average rate ofrecharge. This leads to a reduction ingroundwater in permanent storage and issometimes called groundwater mining.Development of this kind isunsustainable and deprives future

generations of a resource which is beingused up by this generation.

In some countries, fossil groundwatersare being deliberately mined in attempts tospeed the rate of development or reducethe cost of food imports. The mining of thesub-Saharan aquifer by Libya is oneexample (see box on page 8). A similar

Over-abstraction: the case of the Gaza stripThe shallow, sandy coastal aquiferthat underlies the Gaza Strip isheavily over-pumped and becomingpolluted. The Strip currentlysupports 800 000 people and aserious pollution risk is posed by theindiscriminate disposal of liquid andsolid wastes. The aquifer isessentially the only source of water.The natural replenishment rate of theaquifer is estimated at 50-65 millionm3 a year. Abstraction rates areestimated at 80-130 million m3 ayear, of which most is used ininefficient forms of irrigation. Over-abstraction is causing salineintrusion, and irrigation with this

water is causing soil salinization.Most of the population is notconnected to mains sewerage anduses latrines draining to cesspits,many of which overflow into surfacedrains. Faecal contamination ofgroundwater is widespread andnitrate concentrations in some partsof the aquifer are reported to be 10times the WHO guideline. Pesticidelevels are also believed to be highand there is indiscriminate dumpingof solid wastes throughout the area.Groundwater is no longer potable insome central areas, and Israel istransporting 5 million m3 of drinkingwater into the Gaza area every year.

15


approach is being taken by Saudi Arabiawhich uses fossil groundwater to supplysome 75 percent of its needs. Groundwaterabstraction averages more than 5000million m3 a year, much of it used for theirrigation of wheat, in which the countrybecame self-sufficient in 1984.

However, in many cases groundwatermining is more difficult to define thanmight at first appear. The recharge rate ofgroundwater resources is not a constantand can vary substantially with the rainfallpattern. What may be over-exploitation inone year may be a perfectly acceptable rateof exploitation in another. To complicatematters, in some arid areas major rechargeoccurs only once a decade or even lessfrequently. Defining a sustainableabstraction rate in such a situation is

difficult. Nor are sustainable abstractionrates themselves constant. Climates areundergoing constant change, and thesechanges are reflected in the dynamicbalances of groundwater resources.Furthermore, if global warming becomes areality, the climatic changes that result willhave a major impact on groundwaterresources. Infiltration rates to theseresources are likely to be substantiallymodified in some area of the world.

Even when recharge to groundwaterexceeds levels of overall abstraction fromthe aquifer, groundwater development canhave a number of negative consequences.The uncontrolled drilling of boreholes, forexample, can lead to severe losses of yieldand uneconomic production in some places.The lowering of water levels by borehole

Social equity and groundwaterThe kinds of equity issue raised by shortages andpollution of groundwater are exemplified by thesituation in the state of Gujarat in northern India. Waterthere is in short supply, particularly in the north whereit rains on only a few days a year and where half theannual rainfall can occur over a period of two to threehours during the monsoon. Inevitably, groundwatersupplies most domestic water and more than three-quarters of irrigation water.

Over-abstraction has caused the water table to fall, insome places by as much as 40 metres. This has deprivedmany poor farmers of water since they can afford onlydug wells, which are often limited to depths of 10metres or so by wall instability. Only richer farmers canafford the US$13 000-14 000 required to sink boreholesdown to the 400-metre depths that may be required.Elsewhere over-abstraction has caused saline intrusionand richer farmers have responded by buying land

further inland, pumping uncontaminated water from itand piping the water to their fields.

Many management plans to deal with over-abstractionhave worsened equity problems. For example, attemptsto control over-abstraction have involved refusing creditand the supply of electric power for pumping for newwells and boreholes in areas where extraction ratesexceeds 65 percent of recharge. Some rich farmerscontinue to develop the groundwater resource, andavoid these restrictions by financing new developmentsthemselves and obtaining electric power illegally. Equityissues are accentuated by the fact that the poor have littlerepresentation in the government organizations thatdevelop groundwater policies. Attempts to managegroundwater resources sustainably may worsen equityissues: limiting access to groundwater under thesecircumstances may result in the allocation, by default,of the bulk of the resource to wealthy sections of society.

16

abstraction can reduce spring flow; thesesprings may be essential for water suppliesor for maintaining wetland habitats.

Problems of social equityGroundwater (like fish stocks) is a resourcewhose legal ownership is difficult todefine. It is often regarded as a commonproperty and, like many resources of thiskind, users can benefit from the resourcewhile not themselves suffering from theresults of their own actions. They can, forexample, continue to draw water whilediminishing or polluting the supply forothers. Conversely, they may be deprivedof the resource through the action ofothers. Furthermore, the cause and effectchain is difficult to establish for degradedaquifers, making it difficult to apply thewell established 'polluter-pays' principle.

The effects of falling water tablesOver-abstraction leads to physical as wellas social problems in some areas. Thewater table has fallen so low under parts of

Mexico City, for example, that there hasbeen widespread ground subsidence,involving costly rebuilding. Subsidence iscaused by water draining from the pores inunderground strata, causing the rock tocompact. Unconsolidated strata, especiallyclays which have a high water content, areparticularly susceptible.

Parts of the Las Vegas valley in theUnited States have fallen by more than 1.5metres as a result of over-abstraction in anarea where annual rainfall averages only100 mm. Arizona is marked by a series ofhundreds of fissures in the ground, causedby over-abstraction, which have disruptedroads, railways and housing.

Such problems are neither confined toarid countries nor to developed ones.Bangkok is suffering from acute waterproblems as a result of the over-exploitation of the water table beneath thecity. In Beijing recently, over-abstractioncaused the water table to drop by morethan four metres in a year. According tothe Chinese National Environment

Land subsidencecaused by a fallingwater table in aMexican city.

17


abstractionrates anddeclininggroundwaterevels in theNakhon Luangsands, Bangkok

abstraction rates(106rr

14

12

10

8 **

6

4

2

0

6 per day)

Kmgaol

NakhonNvLuang %,/Lsands 7fi

Jfpurtipage from

MetropolitanWaterworks

Authority weils

groundwaterlevels (m)

total

-50k

Bangkok -60

1955 1960 1965 1970 1975 1980 1985

plezometrlcdepression andland surfacesubsidence Inthe NakhonLuang alluvialaquifer, Bangkok

•\ depression ofI plezometric/ surface of' confinedv Naknon Luang

alluvial aquiferIn 1987 (m)

cumulative landsurface subsidenceto 1987:

[___~J 20-40 cm

• • f l 60-80 cm

Abstraction rates andland subsidence inBangkok, Thailand.

Protection Agency, as many as 45 Chinesecities are now experiencing some form ofland subsidence as a result of the over-abstraction of groundwater.

In the United States, according to oneestimate, 21 percent of irrigated land isnow fed from groundwater resources thatare being depleted faster than they arereplenished. The problem is the mostsevere in the arid south-west where citiesfrom Utah and Colorado to Nevada andNew Mexico are being forced to buyfarmland in order to acquire the rights touse the groundwater that lies under theland. In 1987, for example, Phoenix, inArizona, bought nearly six million hectaresof farmland for US$29 million to helpsatisfy its citizens' demand for water.

In many countries, competition forgroundwater is forcing cities to obtainadditional supplies from surface watersources some distance away. Inevitably,water costs then increase.

Saltwater intrusionUnder natural conditions, coastalaquifers discharge freshwater into thesea. Where substantial volumes ofgroundwater are abstracted, however,this process may become reversed, withsalt water moving inland and pollutingthe aquifer. Salt water intrusion hasoccurred in many places of the worldincluding India, China, Mexico and thePhilippines. The problem is particularlysevere tinder Metropolitan Manila, wheregroundwater abstraction has lowered thewater level by 50-80 metres. As a result,salt water has seeped into the Guadalupeaquifer that lies under the city, reachingas far as 5 km inland. The situation iseven worse north of Madras in Indiawhere salt water intrusion has moved asmuch as 10 km inland, causing manyirrigation wells to be abandoned.Chloride concentrations in parts of theaquifer that lies under Bangkok—where

18

the deterioration of groundwater

the water level has dropped by up to60 metres—have risen from 10 mg/litre tomore than 600 mg/litre. Here the saltcomes not from the sea but from salinefossil water trapped deep in the aquifer.Increasing salinity has caused manytubewells to be abandoned.

Salt water intrusion is a particularlyserious problem on small ocean islandssuch as the Maldives. On many of theseislands, the freshwater aquifer is only afew metres thick and is surrounded bysalt water. Furthermore, groundwater isthe only reliable source of freshwater. Forthese reasons, aquifer abstraction has tobe well managed.

The threat to wetlandsAs water tables fall, groundwaterdischarge reduces or ceases and the landdries out. This can have serious effects on

wetlands, one of the few remainingecosystems still to support large numbersof plant and animal species not foundelsewhere.

A number of the world's major wetlandareas are now under threat from the over-abstraction of groundwater. The threat isnot only to the habitat of many rare speciesof plants and animals. Wetlands also playimportant roles in purifying the watersupplies of inland lakes, and their removaloften leads to serious problems.

The Goto Dofiana National Park insouthern Spain occupies an area of 85 000hectares and is fed by the RiverGuadalquivir. It is one of the mostimportant wetlands in Western Europe forthe conservation of biological diversity.As demand for groundwater hasincreased from tourism development andfor horticulture—mainly to grow

Natural wetlands arehome to many plantand animal species,and act as naturalpurification systemsfor lakes downstream..Many are threatenedby over-abstraction ofgroundwaterresources.

19


strawberries in March for export to northEurope—the freshwater aquifer that feedsthe marshes has become seriouslydepleted, leading to a risk of salineincursion and a shortage of freshwater.

This is not an isolated case, and there isan urgent to protect other threatenedwetlands in the Mediterranean basin, inparticular in Algeria, Cyprus, Tunisia,Egypt and Turkey. In all these countries,

increasing salinity and changing waterlevels are leading to vegetation changes inimportant wetlands.

The effects of rising water tablesConversely, some forms of developmentresult in rising water tables. This occurscommonly on over-irrigated land andcan lead to substantial losses ofagricultural production. One result is

The fall and rise of the city water table

Urbanization, and the heavy demand for water thataccompanies it, has resulted in falling water tablesunder many of the world's cities, leading to reducedyields, the threat of saline encroachment and landsubsidence.

Abstraction by wells and boreholes from shallowaquifers under cities causes a 'cone of depression' inthe aquifer. Where this occurs in a coastal aquifer,seawater may move inland and contaminate theaquifer. Seawater intrusion has occurred over distancesof several kilometres beneath Manila and Cebu City inthe Philippines and Jakarta in Indonesia.

Excessive groundwater abstraction may also induceupward movement of saline water, trapped withinsediments at depth. This has happened in Bangkokwhere pumping has lowered the water level in the mostimportant confined aquifer by more than 60 metres.

These problems have led to decreasing dependenceon groundwater for some cities and the importation ofsurface water over long distances.

Similar declines in water tables have been found undercities in industrialized countries. Water levels underLondon, Liverpool and Birmingham in the UnitedKingdom, for example, declined by up to 30 metresduring the first half of the 20th century. Since then,however, the water table has begun to rise again asheavy industry has either closed down or has moved

groundwaterlevels underTrafalgarSquare,London(metresabove meansea level)

-0

-10

-20

-30 \\

-40 \

-50 \ /

60 V /-70 >y 1

-so N/fy-90

-1001820 1860 1900 1940 1980

away from city centres. Water levels are now risingtowards those prevailing at the beginning of the century,raising fears about future flooding of basements andtunnels, and damage to foundations. In Liverpool aBritish Rail tunnel has also flooded, and two largepumping stations on either side of the Mersey estuaryhave to be operated to keep railway tunnels fromflooding. In London the water level rise is currentlymore than two metres a year; since the Chalk underLondon is confined by a deep clay layer, there are fearsthat rising water pressure could lead to expensivedamage to the foundations of many London buildings.

20


waterlogging of agricultural land, whichmakes land impossible to till and thuseffectively puts it out of agriculturalproduction. Waterlogging is oftenassociated with salinization, which hastwo causes: a rising water table thatbrings saline water into contact withplant roots; and the evaporation ofirrigation water by the sun, leaving thesalts behind. In the mid-1970s, the UnitedNations Food and AgricultureOrganization estimated that 952 millionhectares of agricultural land were affectedby salt. The area of land being abandonedeach year as a result of salinization andwaterlogging is now roughly equal to theamount of land being reclaimed andirrigated (see box below).

Water tables are also rising under someof the world's major post-industrialcities. This results from the fact, already

mentioned, that urban recharge rates maybe higher than natural, pre-urban ones.While this was of little import when citieswere also industrial centres, consuminglarge quantities of water, in manydeveloped countries the city and heavyindustry have now been divorced, withindustry either closing down or beingmoved to less urban areas. In addition,groundwater abstraction rates withinurban areas have declined dramaticallybecause public water supplies are nowmostly obtained from outside the city (toavoid potential problems ofcontaminated groundwater). The rise inthe water table that then results canbecome an expensive embarrassment incities where, for example, largeunderground car parks exist, which thenhave to be regularly pumped dry—or putout of action.

The area of landbeingabandonedeach year as aresult ofsalinization andwaterlogging isnow roughlyequal to theamount of landbeing reclaimedand irrigated.

Salinity and irrigation

The UN Food and Agriculture Organization estimatesthat of the 237 million ha currently irrigated, about 30million ha are severely affected by salinity and anadditional 60-80 million ha are affected to some extent.UNEP recently reported that the rate of loss of irrigatedland from waterlogging and salinity is 1.5 million haper year. Millions of hectares of irrigated land, fromMorocco to Bangladesh and from northwestern Chinato central Asia, suffer from this condition. Salinity-affected areas as a percentage of total irrigated area isestimated to be 10 percent in Mexico, 11 percent inIndia, 21 percent in Pakistan, 23 percent in China and28 percent in the United States.

Salinity is caused by a combination of poor drainageand high evaporation rates which concentrate salts onirrigated land; it mainly occurs in arid and semi-arid

regions. All irrigation water contains some salt and canleave behind tonnes of salt per hectare each year.Unless this salt is washed down below the root level,soil salinity will result.

A related concern is the rapid rise in groundwaterlevels, leading to waterlogging and depressed cropyields. Waterlogging is not an inevitable result ofirrigation. It occurs when excessive water is used insystems with finite natural drainage.

At the end of the 1950s, Pakistan began to sink wellsto pump out salt-laden water. The initial capital costswere high and operating costs have been increasingconstantly. Today, Pakistan spends more money onreclaiming land than on irrigation.

Source: The State of Food and Agriculture, FAO, 1993, p. 289

21


Restoration of aseriouslycontaminatedaquifer todrinking waterstandards isalways costlyand oftenimpossible.

The pollution of groundwater

Once polluted, groundwater is extremelydifficult to purify on account of itsinaccessibility, its huge volume and itsslow flow rates. Unfortunately, the world'saquifers are becoming increasinglypolluted as a result of human action. Threeeffects will be examined in more detail inthe pages that follow: pollution resultingfrom urbanization, from industrial activityand from agriculture. All are serious.

Some of the contaminants found ingroundwater are listed in the table on theright, which also shows World HealthOrganization drinking water qualityguidelines. In parts of many aquifers, someof these values are exceeded, particularlythat for nitrate which is an increasinglywidespread pollutant resulting frominadequate sewerage treatment andintensive agricultural cultivation.Restoration of a seriously contaminated

WHO drinking waterquality guidelines (1984, mg/lltrG)

aluminium (Al) 0.2arsenic (As) 0-05chloride (CD 250chromium (Cr) 0.05cyanide (CN) 0.1fluoride (F) 1.5iron(Fe) 0.3lead(Pb) 0.05manganese (Mn) 0.1nitrate (N03-N) 10sodium (Na) 200sulphate (SO^ 400

2,4-D 0.1benzene 0.01carbon tetrachloride 0.003chloroform 0,03DDT 0.001tetrachloroethene 0.01

faecal conforms (/100 ml) nil

The impact of urbanization of groundwater in Merida, Mexico

Merida, a city of 535 000 inhabitants located on theYucatan Peninsula of Mexico, is underlain by a highlypermeable limestone from which it obtains all its watersupply of 240 million litres a day. Most of this isimported from wells outside the city limits.

There is no mains sewerage system nor pipedstormwater drainage, all wastewater being returned tothe ground via on-site sanitation units and all surfacedrainage via soakaways. Because of this, and the highwater consumption per capita (460 litres a day), urbanrecharge is very high (600 mm a year) and substantiallygreater than the pre-urban background infiltration togroundwater of 100 mm a year.

The water table is some 5-9 metres below the groundsurface and is of very low gradient (1 m in 35 km). Theshallow groundwater immediately beneath the city isseriously contaminated by faecal coliforms and nitrate is

kept partly in check only by the dilution provided by theincreased recharge and high throughflow. There isconcern that this polluted water could eventually migrateto the wellfields outside the city which supply Merida.

Groundwater recharge and flow In the Merida aquifer

(aquifer Is unconflned karstlc limestone; surface terrain Is flat kursticlimestone, no soil, no surface watercourses)

r.:.̂ > potable water

22


aquifer to these drinking water standardsis always costly and often impossible.

The effects of urbanizationUrbanization introduces many changes tothe aquifers that lie under cities. Naturalrecharge mechanisms are modified orreplaced and new ones introduced.Leakages and seepages from mains waterand sanitation systems become animportant part of the hydrological cycle inthe urban environment.

Many sub-city aquifers in the developingworld, where few of the urban populationare connected to mains sewerage, arepolluted with human wastes. Septic tanks,cesspits and latrines are common in allmajor cities in developing countries. Septictanks, when properly operated, produce aneffluent of acceptable quality in areas oflow population density. In practice,however, they are often overloaded andoperate inefficiently. Effluent is oftendischarged directly into inland waterways,whence pollutants find their way into theunderlying aquifer. In cities such as Jakartaand Metro Manila, which have 900 000 and600 000 septic tanks respectively, theensuing pollution is serious.

Other forms of excreta disposal can beeven more dangerous since they oftendrain directly into the ground, carryingwith them pathogens responsible for manyhuman diseases. Since in many citiesdrinking water is provided by shallowprivate boreholes, many of which areinadequately protected from pollutants,bacteriological quality can be poor. Astudy in Sri Lanka has shown that waterfrom a latrine soakaway in a suburb ofKandy entered a borehole 25 metres awaywithin two or three days—-insufficient timeto attenuate or eliminate any pathogens.

Pathogens in groundwaterFour types of pathogen are found in human excreta: helminths,protozoa, bacteria and viruses. Under favourable conditions,pathogens are large enough to be filtered out of water passingthrough the soil and the unsaturated layer but bacteria andviruses, and occasionally protozoa, can sometimes be transportedinto groundwater.

Most pathogens do not survive long in groundwater: at 20 °C, a90 percent reduction usually occurs within about 10 days.However, some species may survive for 200 days or more as aresult of the absence of ultraviolet light, lower temperature andless competition for nutrients.

Overall, however, filtration, die-off and aquifer dilutionnormally reduce numbers to acceptable levels well within 50days. For granular aquifers, where travel times to the water tableand water movement are slow, this is long enough to protect thewater in wells. However, the rapid transport that occurs infractured rocks can carry large number of pathogens into wells.

Surveys of groundwater quality in fourIndian cities (Madras, Hyderabad, Nagpurand Lucknow) which are largelyunsewered show that there is widespreadcontamination of shallow groundwater bynitrate, with nitrate concentrations wellabove the WHO drinking water guidelineof 10 mgN/litre. Nitrate concentrations inthe groundwater beneath Beijing exceedthe WHO guideline over an area of morethan 20 km2.

In Sri Lanka, the water supply for the cityof Jaffna comes entirely from groundwater.The urban population of 150 000 isvirtually unsewered and domesticeffluents are discharged to the ground viaseptic tanks and latrines. Partly as a resultof this, the aquifer is contaminated; nitrateconcentrations are double the WHOguideline in many places and in some theyreach values of five times the guideline.

23


In many cities in developing countries—particularly where the monsoon brings thewater table to the surface and disposal ofsanitation wastes to the ground is notpossible—human faeces and other wastesare discharged directly into streams, canalsand rivers. Heavy loads of untreatedeffluent exceed the natural purificationcapacity of these watercourses for manykilometres downstream. In many areas, on-site sanitation systems also lead toincreases in organic carbon concentrationsand reduced oxygen concentrations. This,in turn, can lead to the production of moresoluble iron compounds, resulting inunacceptably high levels of iron in the

groundwater. Sulphate, derived largelyfrom detergents, may also be high.

Wastewater discharge and reuseWhile sewage and wastewater from cities isnormally regarded as a major source ofpollution, it is really a large and importantresource. In some arid areas, it is used, withminimal, if any, treatment to irrigate crops,including some intended for direct humanconsumption. The water used also suppliescrops with essential elements such as nitrogenand phosphate which would otherwise haveto be added as artificial fertilizer.

There is debate about the safety of thisprocedure and some experts believe that a

Incipient contamination of deep groundwater under Santa CruzThe city of Santa Cruz, located on plains to the east ofthe Andes in Bolivia, obtains all its water from a deepsemi-unconfined aquifer system below the city. Thecity is largely unsewered and most of the wastewater isdischarged to the ground. Groundwater in the deeperaquifer below 100 metres is of high quality. However,at depths of less than 45 metres there are high nitrateand chloride concentrations, typically in the range10-40 mgN/litre and 40-120 mg/ litre respectively,beneath the more densely populated districts.Bicarbonate and manganese concentrations are alsoraised and dissolved oxygen levels reduced.

The nitrate and chloride is believed to come fromunsewered sanitation. Oxidation of organic wastes inthe shallower groundwaters consumes the availabledissolved oxygen and produces carbon dioxide, whichin turn reacts with carbonate minerals in the aquifermatrix to produce bicarbonate. Manganese, whichoccurs naturally in the aquifer matrix, is dissolved inthe reducing conditions thus produced. The highersulphate concentrations also found in the shallow

groundwater are thought to be partly derived fromdetergents and highway runoff.

Concentrations of these pollutants in water at depthsof 45-100 metres have begun to increase, though less sothan in the shallow aquifer. Downwards leakage fromthe shallow aquifer as a result of groundwaterabstraction from depth is thought to be the cause ofthis increase in concentration.

24


precipitation

evapotransplratlon

abstraction _ - - - ^ —

' H : ' . 1 ' " " ' : ! ' ' ' i ; . ! ' 1 " . ; " ; : : •••','"/' : ' ' : ' • . " • ; ; ' • • • ... • • '••• ; s a t u i c i t * i

evapotranspiration

runoff

F/oiy paths ofcontaminants from awaste disposal site.

better use for urban wastewater is probablyto recharge the aquifer from which it came.During the recharge process, the water isconsiderably purified. If it is required forirrigation, it can then be abstracted eitherfrom irrigation wells or from streams whoseflow has been increased by the recharge.

Letting sewage water stand in shallowsurface ponds and filter down through thesoil and the aquifer below can be an effectivemeans of treatment. The more slowly this isdone, and the more that the surface pondsare rested between treatments, the morecomplete will be the treatment. Allowing theponds to dry out regularly encourages thebreakdown of nitrates in the sewage, withthe release of harmless nitrogen gas. Withcareful control nitrogen concentrations inthe recharge water can be reduced tobelow 5 mg/litre. At the same time, mostbacteria and protozoa are eliminated, andlevels of organic compounds andphosphates are greatly reduced. Althoughthe technique is expensive in terms of landarea used because the surface pondsshould be allowed to dry out for periodsthat are twice as long as the period for which

they are used, infiltration treatment has theadded advantage of providing a cheapunderground storage system from whichwater can be pumped for non-potable uses.

Solid waste disposalLarge volumes of solid wastes areproduced and disposed of in all majorcities. In China alone, the domestic refusefrom 370 cities exceeds 60 million tonnes ayear. Disposing of these wastes can giverise to serious groundwater pollution. Theworst risks occur where uncontrolledtipping, as opposed to controlled sanitarylandfill, is practised, and where hazardousindustrial wastes, including drums ofliquid effluents, are disposed of atinappropriate sites which are selected onthe basis of their proximity to where thewaste is generated rather than theirsuitability as landfill sites.

Often no record is kept of the nature andquantity of wastes disposed of at a givensite and abandoned sites represent apotential hazard to groundwater fordecades. To make matters worse, disposal isoften on low ground where the water table

25


is high and direct contamination of shallowgroundwater likely. In a study made of sixsolid waste tips in Jaipur, India, it wasfound that water quality was clearlycorrelated with distance from the tips. Wellseven 450 metres away had high levels ofchloride, sulphate, bicarbonate andammonia, even though the tips had been inuse for only 12 years. In a study of selectedlandfill sites in the Bandung area of

Indonesia, all sites were found to generate aleachate containing high quantities ofchloride, sodium, calcium, bicarbonate,boron and various organic compounds. Atone site pollution from the landfill wasdetected in a well 120 metres away.

A further complication in developingcountries is that urban expansion mayeventually lead to the erection of marginalhousing on areas previously used for solid

Groundwater pollution from industrial solventsBefore their damaging effects on the ozone layer werefully appreciated, chlorinated solvents were widelyused as degreasers in the metal, paper, electronics andleather industries. These solvents are also insidiouspollutants of groundwater because they have lowsolubility in water, and are denser and less viscousthan water. This means that once they enter an aquiferthey penetrate to great depths extremely quickly. Theyare also very resistant to biodegradation. In Europethere are many places, especially beneath cities andlong-standing industrial sites, where chlorinatedsolvents are still present at concentrations many timesthe EC drinking water guideline value (less than 10Hg/ litre) even 20 years after they entered the aquifer.

Research after a spill at a leather processing factory inCambridgeshire showed that the pollutant hadtravelled down to a depth of some 50 metres andlaterally by about 1 kilometre. How much of thechemical—perchloroethylene—was originally spilled isnot known but sampling later suggested that 10-100tonnes of the material could be in the aquifer.

'Pump and treat' is the name given to the mostcommon means of restoring aquifers polluted in thisway. The process involves pumping contaminatedgroundwater from close to the pollution source, treatingthe water and then returning it to the aquifer upstreamfrom the site of pollution. This effectively contains the

spread of pollution although restoration of the aquifer toa state even approaching its original pristine conditioncan take many years and cost millions of dollars.Complete restoration is often impossible.

Typical distribution of chlorinated solvent in a fracturedporous aquifer after a major spill.

solvent enssotvosInto theHfoundwqter

26


waste disposal. These settlements are rarelysupplied with piped mains water and relyinstead on privately-constructed shallowwells. These supplies are unmonitored andpose a serious threat to human health.

Pollution from industryNearly all industries produce liquideffluent. In the developed countries, strictlegislation has ensured that much of thiseffluent is now properly treated before it isallowed to be discharged to a water course.This is not yet the case in many developingcountries, where industries are commonlysited on the unsewered outskirts of townsand cities. The worst polluters are usuallynot the largest industries (which cannormally afford some form of effluenttreatment) but small industries producingpaper and textiles, processing leather,metals and other materials, and repairingvehicles. These industries generateeffluents containing spent acids, oils, fuelsand solvents, many of which aredischarged directly into the ground ornearby water courses, particularly canals.Small service industries—such as metalworkshops, dry cleaners, photo processorsand printers—also use considerablequantities of potentially toxiccontaminants, and their disposal practicesare often poorly controlled.

Chlorinated solvents are particularlyinsidious pollutants because of theirpersistency, toxicity and the way theytravel in aquifers (see box opposite). Asurvey of 15 Japanese cities has shown that30 percent of all groundwater supplieswere contaminated by chlorinated solventsand in 3 percent of the samples takenconcentrations exceeded WHO drinkingwater guidelines (30^g/ litre). In some casessolvents were found in groundwater as far

as 10 km from the site of the spill. Acommon cause of solvent pollution isleaking storage tanks and at one sitegroundwater beneath such tanks has beenfound to contain 40 000 fig/litre of thechlorinated solvent trichloroethene. Solventcontamination has in fact been found inalmost all surveys of urban groundwater.Unfortunately, cleaning up a pollutedaquifer—usually by removingcontaminated soil and continuous pumpingof the aquifer—is extremely difficult, verycostly and takes a great deal of time. In1982, some 50 m3 of a chlorinated solventleaked from a tank on the island of PuertoRico. Five years later concentrations of thechemical in the aquifer below had beensomewhat reduced but the cost ofsupplying alternative water sources hadalready exceeded US$10 million.

Industrial effluents also often containhigh levels of metals such as iron, zinc,chromium and cadmium. Many are highlytoxic, even carcinogenic, and even lowconcentrations in groundwater pose aserious threat to health. A study of metalcontamination in Ludhiana, in the IndianPunjab, revealed high concentrations ofheavy metals several kilometres from anindustrial site where foundries andfactories associated with electroplating andbicycle manufacture were dischargingeffluents directly into unlined channelsand shallow soakaways. Highconcentrations of chromium and cyanidewere found in shallow groundwater andcopper and lead were also present.

Solvents and heavy metals are only two ofthe products of industrial activity. There aremany others. A survey of industrial activityin Sao Paulo State in Brazil has attempted tocategorize the groundwater pollutionpotential of 22 industries (see list right).

Groundwaterpollution potentialof industry types

Group 3:high riskmetal processingmechanicalengineeringpetrol and gasrefineriesplastic productsorganic chemicalsPharmaceuticalsleather tanning

pesticidemanufactureelectric andelectronicmanufacture

Group 2:medium riskiron and steelnon-ferrous metalsrubber productsinorganicchemicalspulp and papersoap anddetergentstextile millsfertilizerssugar and alcoholelectric powerproduction

Group 1:low risknon-metallicmineralswoodworkfood and ,beverages

27


A study in SriLanka has shownthat more than60 percent of theapplied nitrogenis lost.,.producinggroundwaterconcentrations of20-50 mgN/litre.

The graph below showsthat fertilizerconsumption in anumber of Asiancountries has nowovertaken Europeanand American levels.

fertilizerconsumption 250per hectareof cultivatedland forselectedAsiancountries(kg/ha)

200

150

100

50....

Mining and petroleum developmentMining and petroleum extraction posespecial risks to groundwater. Quarryingand open-cast mining, for example,remove the protective layer above anaquifer, leaving it more vulnerable topollution. Deep mines or oil fields mayproduce fluids that are disposed of at thesurface and may therefore contaminateshallow aquifers. And contaminants fromspoil heaps may leach into groundwater.

Several serious cases of groundwaterpollution are on record from these causes.In Zibo city in north-east China, petroleumwastes from a major petrochemical workshave seeped into the ground and pollutedgroundwater over an area of more than10 km2. Both Australia and Canada havedevoted considerable effort to trying toreduce leaching from spoil heaps, since thematerial that is leached away is often veryacid and contains high concentrations ofsulphate and toxic metals. In Thailand, anumber of drinking wells have becomecontaminated with arsenic following leachingfrom the spoil from small-scale mining.

• ' ' ' , ; ' • •;.'

.'/f-.'.'ii.Europs (112.6)

Asia (62.9)

America (45",B)

Rising water levels in abandoned minesproduce what is called acid minedrainage—the mobilization of oxidizedmetal ores which produce water rich insulphate, iron, manganese and othermetals. This can cause seriousgroundwater contamination.

Pollution from agricultureFertilizers and pesticidesAgriculture is responsible for the seriouspollution of many of the world's aquifers.The main problem arises from theintensive use of nitrogen-rich fertilizersand of pesticides, a problem that hasspread from the industrialized countriesto developing ones, particularly those inAsia where the use of new, high-yieldingcrop varieties depends on the intensiveapplication of fertilizer. In India, forexample, fertilizer use has quadrupledover the past 20 years or so. In someAsian countries, fertilizer use has nowovertaken that of Europe and the UnitedStates (see graph).

The high levels of nitrate and, in someareas, pesticides in groundwater havebeen identified as originating fromintensive agriculture in a number ofplaces. Pollution of groundwater isgenerally worse where the soil is verypermeable, allowing agriculturalchemicals to be quickly washed down tounderlying aquifers. However, not allnitrate in groundwater is due toagriculture—much of it, as we have seen,also comes from untreated sewage.Monitoring techniques cannot differentiatebetween agricultural and sewage nitrate.

The leaching of nitrate from fields notonly leads to pollution but is also aserious source of waste—nitrate thatpercolates down into aquifers has done

28


nothing to stimulate plant growth. Astudy in Sri Lanka has shown that morethan 60 percent of the applied nitrogen islost in this way, producing groundwaterconcentrations of 20-50 mgN/litre.Elsewhere in Sri Lanka, a survey of theJaffna Peninsula found that 79 percent ofwells had concentrations of more than11.3 mgN/litre and 48 percent greaterthan 22.6 mgN/litre. Other componentsof fertilizers, including potassium andchloride, also find their way from fieldsto aquifers.

More than 300 pesticides are currently inuse. By definition they are designed to betoxic and, sometimes, persistent. Permittedconcentrations in drinking water rangefrom 0.1 to 100 parts per billion, and thereis little doubt that pesticides do find theirway into groundwater. However, theextent of pollution is not accuratelyknown, even in Europe and the UnitedStates. Most observed concentrations havebeen in the range 0.1 to 100 ̂ g/litre. Onereason they are not higher is that theaverage half-life of a pesticide in the soil—normally less than 100 days—is relativelyshort compared to the rate at which theyare leached through the soil and carrieddown to underlying aquifers.

One encouraging aspect for the future isthat high levels of artificial fertilizer andpesticide application are not now seen asthe principle means of developingsustainable agriculture. Instead the UNFood and Agriculture Organization isencouraging the use of Integrated PlantNutrition (IPN) and Integrated PestManagement (IPM)—techniques that aimto promote plant growth through a varietyof different techniques which are oftencheaper and more effective than theapplication of chemicals alone.

SalinitySoil salinization and waterlogging havealready been described on pages 20-21.They are caused not by pollution but bypoor land management and the inadequatedrainage of irrigated areas. The solution tothese problems involves measures such asthe lining of irrigation canals, introducingsprinklers or drip irrigation techniques,improving the flow of irrigation water and,in extreme cases, physically lowering thewater table to 2-3 metres below the surfaceby pumping.

However, irrigation can also lead to thesalinization of groundwater if excessirrigation water leaches out salts present inthe soil and the unsaturated zone -particularly where rainfall is low and thesalts have accumulated over thousands ofyears. This is a less common problem thansoil salinization and its effects are notgenerally as serious. Careful control of thevolumes of irrigation water used and thesites chosen for irrigation can reducegroundwater salinization.

Irrigation withgroundwater. The highcapital and operatingcosts of such intensiveirrigation must bematched by heavyagrochemical inputs toensure highproductivity and goodeconomic returns.

29

Implications for policy

Althoughgroundwater isone of theworld's keynaturalresources, onwhich more than1500 millionpeople dependfor drinkingwater, it is stillundervalued,inefficientlyexploited andinadequatelyprotected.

Unprotected springsources are still widelyused for drinkingwater supplies and arehighly vulnerable tos w rface con tarn inatio n.They are responsiblefor the spread of manywater-borne diseases,particularly amongchildren.

Although groundwater is one of theworld's key natural resources, on whichmore than 1500 million people depend fordrinking water, it is still undervalued,inefficiently exploited and inadequatelyprotected. In many parts of the world,groundwater use is poorly controlled; inothers, groundwater is heavily polluted. It

may well be that much of this pollution hasyet to be detected, given the slow flow ratesof groundwater and the volume of storageinvolved. What we know of pollution levelsin aquifers may be only the tip of anunderground iceberg. There is, in any case,no doubt that this important resourceurgently needs to be better protected.

Protecting groundwater resources

There are two basic means of protectinggroundwater resources:

• controlling groundwater abstraction,particularly in areas subject toirreversible side-effects such as saltwaterintrusion and land subsidence; and

• controlling groundwater pollution with acombination of techniques that includeevaluating aquifer pollutionvulnerability, assessing potential

contaminant loads and implementingland-use plans specifically designed toprotect groundwater resources.

Controlling abstractionThe control of groundwater abstraction isthe first priority since, in many urbanareas, large numbers of boreholes havebeen drilled in shallow aquifers withoutregard to the overall yield, the rights ofother users or their effect on salt waterintrusion and land subsidence.

Controlling abstraction requires anumber of legal and administrative steps.National governments need first to declaregroundwater a 'natural resource available forpublic use in a controlled fashion'. Thisestablishes the legal precedent for control. Agovernment agency can then be appointed todevelop and implement a series of detailedregulations and codes covering groundwaterabstraction. This agency will issue permitsfor the development of groundwaterresources such as well digging, springcapture and borehole drilling. The permitnormally specifies the depth, diameter andallowed intake of the installation.

The next stage is to issue licences toabstract groundwater, where this isappropriate. This is not always the case

30

implications for policy

Source protection zonesBoreholes and springs may need individual protectionin addition to the protection provided for the aquifer.This can be provided by a 'source protection zone'around the borehole within which potentially pollutingactivities are restricted.

In Western Europe, these source protection zones canbe complex and relatively large, and may encompass allthe recharge capture area for the source. To eliminate allrisks of contamination, all potentially pollutingactivities would have to be prohibited or controlledwithin the protection zone. In practice, the capture zoneis divided into two or three sub-zones and the mostsevere restrictions are applied only close to the source.

An inner protection zone has been widelyrecommended to protect against the effects of humanactivity. The principal concern is the prevention ofpathogenic contamination and is based on acceptedbiological (principally bacteriological) decay criteria.The extent of the zone is often defined by thehorizontal saturated zone groundwater flow traveltime, and travel times of 50 to 100 days have beenadopted by several European countries. The inner zoneincludes the operational area immediately around thewellhead, where activities are restricted to thoserelated to water abstraction itself. The dimension andshape of this area are necessarily somewhat arbitraryas they depend in part on the geological and soil

formations present. A radius of 30-50 metres appearsreasonable from experience in the United Kingdom.

Few cases of pathogenic contamination have occurredwhere the horizontal distance between the borehole orspring and the proven source of pollution was equivalentto more than the distance travelled by groundwater in 20days, despite the fact that pathogens are capable ofsurviving in the sub-surface for up to 400 days.

In some African countries, similar but less complicatedprotection zone guidelines have been adopted. Ruralwater supplies in particular are rarely treated, soprotection of these sources is especially important. Ruralcommunity water supply wells or boreholes often havea sloping concrete apron around the source to preventspilled water leaking back into the wellhead. Animalsare prohibited from the area immediately around thesource and instead water is discharged into animal-watering troughs some distance from the well.

A circular protection zone 50-100 metres in radiuscan be introduced to reduce the risk of pathogeniccontamination. Within this zone pit latrines, septictanks and other potential sources of sub-surfacecontamination are not allowed. The extent of this zonemay need to be increased where recharge and flow tothe well is along fissures, because travel times are somuch faster. Karstic limestones and poorly vveatheredbasement are especially vulnerable in this respect.

and it is often neither profitable norpractical to insist on licences for smallusers, especially those using spring water.Regulatory agencies can charge forconstruction permits and for abstractionlicences. Charges can be based both on thevolume of water abstracted and the usethat is made of it. While abstractionlicences are a useful means of generatingincome to finance the regulatory function,issuing construction permits in the first

place is a better means of controllinggroundwater development.

Regulations of this kind can beunpopular, particularly in relation to aresource that has historically been regardedas a common good freely available toanyone who wants it. Regulatory agenciestherefore need sound public relationscampaigns to inform the public of whatthey are doing, and why. They should alsoprovide free advice to drilling contractors.

31


Aquifer vulnerability and pollution loadThe risk of groundwater pollution is determined by thevulnerability of the aquifer to pollution and the loading ofpotential pollutants to which it may be subjected. Vulnerabilitydepends partly on the extent to which pollutants are attenuatedbetween the land surface and the water table, and partly on therate with which water and its accompanying pollutants travelthrough the aquifer. Since pollutants travel much faster in theaquifer than in the soil and unsaturated layer above it, the natureof the material within the aquifer is of great importance inassessing vulnerability. The most vulnerable aquifers arecomposed of highly fractured rock such as limestone and haveshallow water tables. Pollutants reach the water in such aquifersin a just a few days with little or no attenuation. The leastvulnerable aquifers are those where pollutants take many yearsor decades to travel down to the saturated zone, as is the casewith many semi-confined aquifers.

vulnerability of land to groundwater pollution

porous j,uneonsolidc • : :.

porousconsolidate • i

non-poro- •consolidot- :

low vulnerability1 .\; •."•'•;| variable vulnerability high vulnerability

The risk of groundwater |contamination dependson two factors: thecontaminant load andthe vulnerability of the ^aquifer to pollution. r

Controlling groundwater pollutionThe first requirement in the control ofgroundwater pollution is to assess thevulnerability to pollution of the nation'saquifers. The basic principles ofvulnerability are well understood (see boxon left) and a map of aquifer vulnerabilitywill indicate the zones most in need ofprotection. The risk of contamination, ofcourse, depends on the nature of the threat.Some industries are much more likely thanothers to lead to groundwatercontamination (see list on page 27).

It is important to distinguish betweenpoint sources of pollution, such as landfillsand specific industrial discharges, and thediffuse sources of pollution produced bythe application of fertilizer and pesticidesin agriculture and, to a lesser extent, fromatmospheric deposition.

Efforts should be made to reduce pollutionfrom point sources by improving wastedisposal practices, paying particularattention to practices in areas where aquifersare highly vulnerable. In sensitive areas,land-use planning regulations should beintroduced to restrict the kinds of industrialactivity to be practised or developed.

Where there is widespread diffuse pollutionfrom agriculture, restrictions may have tobe made on the quantities of fertilizers andpesticides that can be applied, or on thecrops that can be grown. Where salinity andwaterlogging are being caused by irrigation, itmay be possible to persuade farmers to switchto dryland crops, such as figs and grapes.

Finally, when plans have been made andput into place for the control of bothabstraction and pollution, a monitoringand assessment programme will be neededto provide feedback on the success of theseplans and to provide early warning ofpossible future threats.

32


Assessing groundwater resources

The need to protect groundwater resourcesis pointing up the need for more reliabledata on both the quality and the quantity ofwater in aquifers, and on how they arechanging. Such data can only be providedby well constructed monitoring systems.Groundwater monitoring is largely anational responsibility but, becausegroundwater does not respect nationalboundaries, assessment of the results needsto be carried out at national, regional andinternational levels.

National monitoringImproved monitoring systems need to be setup in many countries to provide informationon the rates of depletion of aquifers and thedeterioration of groundwater quality.Monitoring can also provide managers withfeedback on the effects of their policies. It isimportant that water quality monitoring

includes assessment of levels of syntheticorganic compounds that are widely used inindustry and agriculture. In areas where largepopulations are still not connected to mainssewerage systems, it is also important tomonitor microbiological pollution indicators.

However, monitoring groundwaterquality and quantity provides no earlywarning of pollution. By the timepollutants show up in groundwater, themajor damage may already have beendone. Monitoring networks shouldtherefore be developed to includemonitoring of pollution loads, particularly invulnerable recharge areas. The key elementsof such an early warning monitoringstrategy are shown in the table below.

Groundwater quality monitoring has atleast four objectives, which need to becarefully distinguished in the design ofmonitoring systems:

Key elements in anearly warningmonitoring strategy.

() brackets Indicate less common or uncertainFC = fa&cal conforms

froctawd :: granular . . •• -

thin un$oturated zone deep unsaturated zone

travel time from surface tosaturated aquifer zone hours-weeks days-months years-decades decades +

bacteriaiofjlcal

high

high moderate

N$h for mobile and-pastetent compounds

tow

eafymming monltoflng required monitor alwater table

monitor utwator table

1. monitor unsaturafedzone

2. monitor at watertable

moderate for persistentcompounds only

very low

rnontror seml-corrflnlng layer and

aquifer

pollution

domesticwostewofer

a , NO3 , (NH4),SO4.FC

chlorinatedhydrocarbons,wide range ofother organiccompounds,

metals

a NO3, (NH4),SO4.FC

metals, range oforganic

compounds

Cl, NO3, (NH4),SO4.(FC)

persistent organics,(metals)

Cl, NO3, (NH4), SO4

persistent organics,(metals)

33


Four types ofgroundwater qualitymonitoring: evaluationmonitoring, drinkingwater surveillancemonitoring, andoffensive and defensivedetection monitoring.

Dependence ongroundwater fordrinking water inthe EuropeanCommunity (1976)

Denmark, 98%

Italy, 93%

German FederalRepublic, 71%

Belgium, 71%

Luxembourg, 70%

Netherlands, 64%

France, 50%

UnitedKingdom, 31%

Ireland, 15%

groundwaterflow g t

I c ;• boreholes used; for monitoring

O

evaluation monitoring (plan view)

offensive detection monitoring

• definition of the extent ofgroundwater pollution (evaluationmonitoring);

• quality control of groundwater used asdrinking water (drinking water supplysurveillance);

• early discovery of groundwaterpollution from a given activity(offensive detection monitoring); and

• provision of advance warning of thearrival of polluted water at importantsources of supply (defensive detectionmonitoring).

Information from national monitoringprogrammes of this type does not, ofcourse, provide an overall picture of thecondition of individual aquifers, some ofwhich extend across at least one nationalboundary. There is therefore a need tosynthesize national assessments on aregional or international basis.

water quality monitored atabstraction borehole

drinking water supply surveillance

defensive detection monitoring

Regional and international actionA number of important regionalassessments of groundwater resourceshave already been made.

Tn 1982, the Directorate-General for theEnvironment, Consumer Protection andNuclear Safety of the EuropeanCommunity produced a major assessmentof ground water resources within its (then)nine member states. Tt consisted of ageneral survey (Groundwater Resources ofthe European Community: synthetical report)and individual reports for each member state.These reports dealt with four major themes:• the aquifer inventory—location and type;• groundwater hydrology—flows within

these aquifers;• groundwater abstraction; and• groundwater availability by area.The study concluded that the Community

had enough groundwater to meet most of

34


its needs but that in most countriesabstraction rates were already high—Belgium was abstracting some 70 percentof its available groundwater resources,Denmark 40 percent, France 25-50 percent,Italy 50 percent, Luxembourg 37 percent,the Netherlands 62 percent and the UnitedKingdom at least 25 percent. Only Ireland,which was abstracting only 3 percent of itsgroundwater resources, had majoruntapped resources.

This assessment was concerned mainlywith groundwater quantity. Since it waspublished, attention has turned in Europe(and the United States) to quality, and notonly have groundwater quality monitoringprogrammes been greatly expanded butmany groundwater protection schemeshave been put into place.

Two other regional assessments (onwhich this publication is largely based)have been prepared for the LatinAmerican-Caribbean and the Asia-PacificRegions. The first of these is part of a

regional groundwater pollution controlprogramme being developed by the PanAmerican Center for Sanitary Engineeringand Environmental Sciences (CEPIS) whichhas its headquarters in Lima, Peru. Itconsists of seven reports covering thegeneral situation, the extent ofgroundwater pollution, risk assessment,monitoring, protection and the impact ofwastewater reuse. The studies were carriedout by members of the staff of CEPIS andthe British Geological Survey withfinancial support from the World HealthOrganization, the Pan American HealthOrganization and the UK OverseasDevelopment Administration.

The most recent GEMS/Waterassessment is for the Asia-Pacific Region,which has been carried out by the BritishGeological Survey. The report assesses theimpact of urbanization, industry andagriculture on groundwater quality, andmakes a number of recommendations ongroundwater protection and monitoring.

35

Sources

Chilton, P. J., Jegat, H. J., and Stuart, M. E.Groundwater and agriculture: theinterrelationship. Tn Proceedings of anInternational Seminar, Merida, Venezuela, 14-17October 1992. British Geological SurveyTechnical Report WD / 95 / 26,1994.

Commission of the European Communities.Groundwater Resources of the European

Community: synthetical report. ECSC, EEC and

EREC, Brussels and Luxembourg, 1982.

Foster, S. S. D. Unsustainable developmentand irrational exploitation of groundwaterresources in developing nations—anoverview. In 1AH Hydrogeology Selected Papers

3, 321-36,1992.

Foster, S. S. D., Gale, I. N., and Hespanhol, I.Impacts of Wastewater Use and Disposal on

Groundwater. British Geological Survey,Key worth, United Kingdom, 1994, TechnicalReport WD/94/55.

Foster, S. S. D., and Skinner, A. C.Groundwater protection: the science andpractice of land surface zoning. In IAHSPublication 225, 471-82,1995.

Food and Agriculture Organization. The Stateof Food and Agriculture 1993: water policies and

agriculture. FAO, Rome, 1993.

Klink, B. A., Crawford, M. C, and Noy, D. J.A Ground-water Hazard Assessment Scheme for

Solid Waste Disposal. British Geological

Survey, Key worth, United Kingdom, 1995,Technical Report WC / 95 / 7.

Morris, B. L., Lawrence, A. R., and Stuart, M.E. The Impact of Urbanization on Groundwater

Quality (Project Summary Report). British

Geological Survey, Keyworth, UnitedKingdom, 1994, Technical Report WC/94/56.

Pan American Center for SanitaryEngineering and Environmental Sciences(CEPIS), Lima, Peru.Groundwater: an undervalued resource in need of

protection, 1987.

Groundwater Pollution: an executive overview of

the Latin American-Caribbean situation in

relation to potable water supply, 1987.

An Evaluation of Groundwater Pollution by On-

site Sanitation, 1988.

Groundwater Pollution Risk Assessment: a

methodology using available data, 1988.

Groundwater Quality Monitoring: an appraisal of

practices and costs, 1989.

Groundwater Protection Strategies: a guide

towards implementation, 1993.

Price, Michael. Introducing Groundwater.

George Allen and Unwin, London, 1985.

UNEP/GEMS. Characterisation and Assessment

of Groundwater Quality in-Asia-Pacific Region:

the aquifers of the Asia-Pacific region—an

invaluable but fragile resource. British

Geological Survey, Wallingford, UnitedKingdom, 1995.

36

Documents

*P*?;;; iiiia •'•

P?;;; iiiia •'•