Principles Problems of Pollution Groundwater Resources Case...

Environmental Health PerspectivesVol. 83, pp. 39-68, 1989

Principles and Problems of EnvironmentalPollution of Groundwater Resources withCase Examples from Developing CountriesB. C. E. Egboka,* G. 1. Nwankwor,t 1. P. Orajaka,* andA. 0. Ejiofor*

The principles and problems of environmental pollution and contamination are outlined. Emphasis isgiven to case examples from developing countries of Africa, Asia, and Latin America with a comparativeanalysis to developed countries. The problems of pollution/contamination are widespread in developedcountries but are gradually spreading from the urban to rural areas in the developing countries. Greatefforts in research and control programs to check pollution-loading into the environment have been madein the industrialized countries, but only negligible actions have been taken in developing countries. Pol-lutants emanate from both point and distributed sources and have adversely affected both surface waterand groundwaters. The influences of the geologic and hydrologic cycles that exacerbate the incidences ofpollution/contamination have not been well understood by environmental planners and managers. Profes-sionals in the different areas of pollution control projects, particularly in developing countries, lack theintegrated multiobjective approaches and techniques in problem solving. Such countries as Nigeria, Kenya,Brazil, and India are now menaced by pollution hazards. Appropriate methods of control are herebysuggested.

IntroductionEnvironmental pollution and contamination are be-

coming a common occurrence in parts of the developingworld. It is difficult to distinguish precisely betweenpollution and contamination. In modern hydrogeologicliterature, pollution is regarded as occurring in suchhigh dosages or concentrations that it renders the pol-luted medium very hazardous or highly deleterious tobiota. Contamination may occur to a lesser magnitudewhen compared to pollution, but it also may render thecontaminated medium unusable or make it slightly haz-ardous to life. Many urban and rural areas of the de-veloped or industrialized world have been adversely af-fected by large-scale pollution and contamination,resulting in losses of human, material and financial re-sources. In many American, European, and Asiaticcountries, huge amounts of money are spent annually

*Water Resources and Environmental Pollution Unit, Departmentof Geological Sciences, Anambra State University of Technology,P.M.B. 5025, Awka Campus, Awka, Nigeria.

tSchool of Applied and Natural Sciences, Federal University ofTechnology, P.M.B. 1526, Owerri, Nigeria.tDepartment of Applied Microbiology, Anambra State University

of Technology, P.M.B. 5025, Awka Campus, Awka, Nigeria.Address reprint requests to B. C. E. Egboka, Water Resources

and Environmental Pollution Unit, Department of Geological Sci-ences, Anambra State University of Technology, P.M.B. 5025, AwkaCampus, Awka, Nigeria.

for research to combat and control widespread pollu-tants and contaminants. Volumes of these pollutants/contaminants are produced yearly through natural andanthropogenic activities such as industrial activities, ag-ricultural practices, waste disposal systems, etc. High-level, medium-level, and low-level wastes in solid, liq-uid, or gaseous forms are released into the environmentat discrete intervals or on a continuous basis. Thesepollutants may be physical, chemical, biochemical, bi-ological, or microbiological in nature. They may haveshort or long half-lives in the environment. They havecontinued to damage many environments of the indus-trialized countries, having defied many painstaking con-trol programs (1,2). Many urban centers of developingcountries are now also similarly threatened. Unfortu-nately, these poor countries lack the necessary exper-tise and funds to wage any meaningful war against pol-lution, which continues to spread unabated.

Parts of the environment currently being pollutedinclude the atmosphere, pedosphere, hydrosphere, lith-osphere, and biosphere. This paper shall focus on pol-lution/contamination of the hydrosphere, with particu-lar emphasis on the groundwater regime, and pollutionincidences in developing countries. The scope shall em-brace sources and types of pollution/contamination,processes generating them, implications of geology/hy-drogeology, and pollution dynamics and mechanisms.Potentials of groundwater pollution in developing coun-

EGBOKA ET AL.

tries vis-a-vis the developed ones shall be outlined, high-lighting their health hazards. Relevant suggestions forcombating pollution more effectively shall be made. Theprimary objective is to review the general incidences ofenvironmental pollution/contamination in relation to theeffects of pedology and geology in close association withthe dynamics of the hydrologic cycle. Proper under-standing of sources and types of pollutants/contami-nants and their genesis and hydrodynamics would helpdetermine the appropriate control measures to be con-sidered for the situation. The goal is to contribute tobetter control methods. It is believed that present con-trol methods in parts of the world lack the depth ofunderstanding required. In addition, many of these con-trol efforts seem to be uncoordinated. Developing na-tions still at the threshold of widespread pollution/con-tamination could learn from the costly mistakes of theindustrialized nations and hence take the necessary ac-tions to protect their environments.The natural processes and anthropogenic activities

that generate pollutants/contaminants are many andvaried, and so are their sources. The natural processesinclude products of soil and gully erosion, physicochem-ical weathering and mass wasting, sediment transport,floods, volcanic eruptions, seawater intrusions, etc. Themanmade ones include industrial, agricultural, sewagewastes and lagoons, garbage dumps and barnyards,mining wastes, etc.These pollutants/contaminants in one way or the

other via the hydrologic cycle reach the groundwatersystems to pollute/contaminate them. Through the cir-culation of water within the hydrologic cycle, pollutantson the ground surface are transferred through the soilzone into the aquifer horizons where they damage po-table water supplies. To reduce degradation of thesewater supplies, a comprehensive management strategyis required, as discussed later. The present control tech-niques with regard to pollution and contamination haz-ards, particularly in developing countries, need to begreatly improved. Priority and concern are not shownadequately by government authorities, and hence, ap-propriate planning and management strategies to checkpollution are generally absent. The expertise or req-uisite manpower may be lacking. Funds for basic re-search may not be provided. Environmental protectionlaws or edicts may be nonexistent and where availableare rarely enforced. These have exacerbated thespreading phenomenon of many pollutants/contami-nants in many developing countries. In this review, nec-essary suggestions for improvement of this situationshall be given.

Sources and Types of Pollutants/ContaminantsThe two main sources of pollutants/contaminants are

point sources (Table 1) and distributed sources (2) (Ta-ble 2). Pollutants/contaminants from the two sourcesmay be released continuously (3) or at discrete intervals

Type of pollutionSewage disposal systems

Surface waste disposal sites

Underground waste disposal sites

Spills, washings, and intrusions

Mining sources

Natural mineral/ore deposits

ExamplesSewage lagoonsSeptic systemsCesspoolsBarnyards/feed lotsLandfills/garbage dumpsSurface waste dumpsStorage tanks (low-, medium-,

high-level wastes)Pit latrines, tunnels, trenches,

cavesWaste subsurface injectionsOil/gas/waste spillsAuto workshop washingsResearch/laboratory washingsSeawater/saltwater intrusionsAcid mine drainagesGas explosions/seepagesMine dumps and gangue depositsTunnels/excavations outflowsSaline ponds/lakesHot springs/mineralized watersAnhydrite/pyrite deposits/

evaporites

Table 2. Distributed sources of pollution and contamination (1).

Source ExamplesAgriculture Cropland

Pasture and rangelandIrrigated landWood landFeed lots

Silviculture Growing stockLoggingRoad building

Construction Urban developmentHighway construction

Mining SurfaceUnderground

Terrestrial (many and scattered) LandfillsDumps

Utility maintenance Highways and streetsDeicing

Urban run-off Floods and snowmeltPrecipitation Rainfall, snowfall, etc.Background sources Native forests

Prairie land, etc.

(4). Point sources of pollution can be geometrically de-fined and the dimensions amenable to mathematicalanalysis in assessing pollution loads and rates of dis-charge determined. Point sources of pollution may as-sume any geometrical shape such as circular, triangular,spherical, etc. The areal sources of pollutants/contam-inants or leachates are comparatively smaller, easilymappable, and readily distinguishable. However, wherethe input/output load functions from point sources intothe hydrogeologic environment are continuous, the pol-luted/contaminated area may eventually become wide-spread. Distributed sources of pollutants/contaminantsare much more widespread and can rarely be geomet-rically defined as precisely as a point source. Hence, itis more difficult to subject the input/output source to

Table 1. Point sources of pollution and contamination.

40

GROUNDWATER POLLUTION IN DEVELOPING COUNTRIES

precise mathematical analysis. Rather, a measured andintelligent assumption of the affected area is made foruse in modeling and analysis. In heavily polluted/con-taminated areas, both point sources and distributedsources may be occurring together or may be indepen-dent of one another. Successful control methods ormathematical modeling of the affected/polluted areamust recognize this situation in order for the controlprogram to be effective.

Point Sources of Pollution/ContaminationIn the list of point sources given in Table 1, the pol-

lutants or contaminants come from zones or areas ofknown and definable boundaries that are easily ame-nable to mathematical analysis and modeling. The pol-lution loads can be controlled at the point of input beforethey can spread into the surrounding environment in atime-discrete or continuous manner. Point sources in-clude sewage lagoons (solid, gaseous, and liquid), in-dustrial wastes, landfills/garbage dumps/barnyards, liq-uid/gaseous spills (oil, chemicals, etc.), mining (pits,holes, excavations, wastes, and gangue minerals), salinelakes and deposits, evaporite sequences, etc. Throughthe complex interplay of various soil and geologic factorsand rain/water events of the hydrologic cycle, pollutant/contaminant substances reach the groundwater systemsto pollute them. For example, buried refuse or garbageundergoes biodegradational decay in the pedologic/soilzone. The resulting leachates are released into thegroundwater flow system where dissolved geochemicalconstituents are transported in various distances anddirections. Piled up animal wastes in barnyards or liquidwastes in lagoons are similarly leached out and trans-ported causing pollution of surface waters and ground-water areas. In many developing countries today, in-dustrial and domestic wastes are indiscriminatelydumped into rivers, lakes, streams, dry valleys, etc.This was the case in many developed countries, and suchpractices still persist in some of them today. Thesewastes damage surface waters and eventually destroyparts of the groundwater regime. Mining wastes andgangue products and other point sources of pollutants/contaminants produce similar havoc for the environ-ment (4-9).

Distributed Sources of Pollution/Contamination

Distributed sources of pollutants/contaminants givenin Table 2 are those in which the pollutants or contam-inants are spread through a large area of hydrogeologicenvironment and in which they extend over the entiresource area. A distributed source is very widespread,and the pollutants/contaminants may be introducedfrom various sources and directions. Spreading is en-hanced by wind, rain, and snowfall activities throughatmospheric circulation and precipitation. The areal ex-tent or boundary conditions for the pollutants are dif-ficult to define because of the regional nature of sources,

thereby posing problems for mathematical analysis. Thesources include acid-alkaline rain, floods, erosion, ag-ricultural fertilizer applications, and generated agricul-tural wastes, seasprays and intrusions, volcanoes, etc.Acid rain is a major distributed source of pollution indeveloped countries such as the United States, Canada,Germany, etc. Localized pollution of groundwater byacid rain in some developing countries such as Nigeriahas been reported (10). Surface waters and shallowgroundwater are polluted by atmospheric fallouts (3,11-13). In urban, suburban, and rural areas of many de-veloping countries, particularly in the tropics, soil andgully erosion produce heavy sediment loads carried byfloods that pollute surface water and groundwater sys-tems (14-19). Waste products in urban areas are trans-ported away by runoff. In mining areas, gangue ma-terials dumped about recklessly on ground surface,decay and liquid wastes are leached from them becomingcomponents of the hydrogeologic environment (20-22).In regions of intense geomorphic degradation and mass-wasting, physicochemical and biological weathering dis-integrate pedologic and geologic materials to producesediments that provide great quantities and varietiesof pollutants. Fallouts from volcanic activities or at-mospheric tests in one area may be spread into otherregions of the world; wind, wave action, seaspray, orsaltwater intrusion may drive contaminants inland androad salt application for de-icing during winter andwidespread fertilizer usage, particularly in developedcountries, are also major distributed sources of pollu-tion. Similar events are now becoming prevalent in de-veloping countries, particulary the industrializing ones.

Biological Pollutant/Contaminants inGroundwaters

Biological pollutants of groundwaters include dis-solved organic constituents and microorganisms thatseep or leach into groundwaters from polluted surfacewaters. Microorganisms may contribute to pollution inmany ways, namely they may themselves be patho-genic; aesthetically they may produce undesirable bio-mass, or they may generate toxic metabolites in thegroundwater. The microorganisms may be either patho-genic or nonpathogenic. In both cases, they produceundesirable effects in the groundwater itself and in thedistribution network (where water may be distributedfor domestic uses) and the populations using it.Pathogenic Microorganisms. Pathogenic microor-

ganisms are present in groundwaters, especially in thevicinity of facilities that are discharging sewage ef-fluents or contaminated surface waters, and new septictanks, agricultural wastes, and refuse tips. Microor-ganisms, however, must survive the tortuous task ofpassing through the soil cover, which constitutes anexcellent natural process for water filtration and treat-ment. Even with this barrier, it follows that the nearerthese sources of pollution are to groundwater sources,the greater the chance of successful seepage of these

41

EGBOKA ET AL.

microorganisms. Shallow wells and some deep boreholesare prone to contamination by these pathogens.The isolation of pathogenic microorganisms from

groundwaters is difficult but, when achieved, it servesas obvious proof of potential danger to the users, re-gardless ofthe number ofpathogens present. Generally,however, the majority of waterborne pathogenic mi-croorganisms enter water supplies as a result of fecalcontamination. Therefore, the ability to detect fecal con-tamination at low levels is the main safeguard in pre-serving the potability of water supplies (23). Pathogenicmicroorganisms normally associated with water sup-plies are shown in Table 3 (24). All of these have beenisolated from contaminated shallow wells and deep bore-holes in Kaduna, Kano, Niger, and Plateau States ofNigeria (25). In addition, Dracunculus medinesis (Gui-neaworm) was reported from wells in parts of Nigeriasuch as in Kwara State (25). These parasites are wide-spread in many parts of Nigeria, sometimes occurringin epidemic proportions.

Fecal contamination in water is usually demonstratedby the detection of specific bacteria that are present invery large numbers in the intestines. The test normallyemployed is the presumptive Coliform test, which in-volves the most probable number (MPN) counts usingliquid media. Coliform organisms include Escherichiacoli, Citrobacter, Klebsiella, and Enterobacter spp.,which are members of the family Enterobacteriaceae.They are gram-negative, oxidase-negative, nonspore-forming rods that can grow aerobically in a mediumcontaining bile salts. They are able to ferment lactosewithin 48 hr, producing acid and gas at 37°C. A pre-sumptive coliform test with a very high count is usually

followed by a confirmatory test which is specific for E.coli (26).Nonpathogenic Microorganisms. Many nonpatho-

genic bacteria are as important as the pathogenic onesin the pollution of surface water and groundwater sup-plies. These include the sulfur and iron bacteria. Amongthe sulfur bacteria are the sulfate reducers such as De-sulfovibrio, Desulfomonas, and Desulfotomaculatum,which produce elemental sulfur from sulfates. On theother hand, some ofthe sulfur bacteria oxidize elementalsulfur to sulfates, all ofwhich involve complex oxidation-reduction reactions. These include the ubiquitous chem-olithotrophic Thiobacillus and the filamentous glidingbacteria Beggiatoa and Achromatium. The sulfur-oxi-dizing bacteria normally associated with groundwatershave been described by Trudinger (27), LeGall and Post-gate (28), and Ehrlich (29) (Table 4).

Iron bacteria are frequently present in groundwatersand in particular those subject to a degree of organicpollution. They obtain energy for their metabolism bythe oxidation of ferrous and/or manganous ions. Theseinclude the gliding bacteria Toxothrix; the sheathed bac-teria, Spaethilus, Leptothrix, Crenothrix, and Clono-thrix; the budding and/or appendage bacteria, Pedom-icrobium, Gallionella, Metallogenium, and Kusnezoviaand the gram-negative chemolithotrophic bacteria,Thiobacillus (T. ferrooxidans), Siderocapsa, Nauman-iella, Ochrobium, and Siderococcus (30). Pathogenic andnonpathogenic microorganisms (bacteria, fungi, vi-ruses) are thus hazardous environmental pollutants tothe hydrogeologic environment. They enter this envi-ronment from waste disposal and treatment areas, sew-age lagoons, barnyards, landfills, and mine areas (31).

Table 3. Pathogens associated with water supplies.

PathogensBacterialSalmonella typhisSalmonella paratyphi A and BSalmonella typhimuriumShigella sonneiShigella dysenteriaeShigella flexneriHycobacterium tuberculosisVibrio choleraeFrancisella tularensisEnteropathogenic Esherichia coliLeptospira icterohaemorrhagia

ViralHepatitis A virusEnteroviruses (polio, Coxsackie A and B and echo)AdenovirusesParvovirusesReoviruses

Protozoan and metazoanEnteamoeba histolyticaAcanthamoeba spp.Naegleria spp.Giardia lambliaAscaris lumbricoidesThichuris trichuraTaenia spp.

Diseases caused

Typhoid feverParatyphoid feverSalmonellosis

Bacillary dysentery

TuberculosisCholeraTularaemiaEnteritisLeptospirosis

Viral hepatitis Type ARespiratory tract infection, nonbacterial

enteritis

Amoebic dysenteryAmoebic meningoencephalitisAmoebic meningoencephalitisGiardiasisHelminthiasis

42


Table 4. Sulfur oxidizing bacteria in groundwaters.

Genus or group HabitatChemotrophs

Sulfobacillus Mine tipsThiobacillus Water, soil, marineSulfolobus Geothermal springsThiobacferium WaterMacromonas WaterThiovulum WaterThiospira WaterBeggiatoa Water, soil, marineThioploca Water, soilThiothrix Water, soil, marineAchromatium WaterThiodendron Water, soil

PhototrophsChromatiaceae (purple S bacteria) Water, marineChlorobiaceae (green S bacteria) Water, marineChloroflexaceae Geothermal springsOscillatoria (Blue-green algae) Water

They occur in varying degrees in both oxidizing andreducing environments. In the process of complex redoxactivities that break down organic and inorganic ma-terials to release energy for metabolic activities, poi-sonous substances are generated that may be fatal tothe hosts that ingest them. These redox microbial ac-tivities may also degrade their habitats, rendering themunusable. Such degraded states may remain so for along time.

Organic Pollutants in GroundwaterOrganic pollutants that may be found in groundwater

through shallow wells and deep boreholes include dis-solved organic carbon (DOC) and particulate organiccarbon (POC). They, in association with microorgan-isms, cause destructive pollution or contamination inhydrogeologic environments. They may serve as nu-

trient/energy sources for microorganisms. Where theyare heavily loaded into groundwaters, DOC and POCenhance microbial multiplication and growth, therebyrendering the habitat anoxic. In such environments,denitrification, desulfurization, etc., are rampant, en-gendering an abundant growth of bacteria, fungi, andviruses that may be highly pathogenic. Hence, seriousorganic pollution signals a potential heavy microbial pol-lution of a groundwater system.

Thermal Pollution/ContaminationThermal pollution/contamination may result from two

main sources, namely, industrial and geothermal pol-lution. In industrialized countries and some developingones, heat generated by industries is dischargedthrough wastewater into the environment. High tem-perature waters eventually reach shallow aquifers andadversely affect groundwater. Hot waters dischargedinto lakes that are influent may form high temperaturehaloes that extend into the aquifers underlying the lake.Unchecked thermal pollution not only negatively affects

the life in the lake but also that of the groundwatersystem associated with the lake. Other problems thatcan arise are the changing of physical, chemical, andbiological characteristics of the hydrogeologic system,thereby rendering the surface water and groundwaterunusable.

In many parts of the world, the locations of geo-thermal pollution hazards are known. Geothermal pol-lution is much more common in tectonically unstableenvironments where high temperature effluents andgases emanate from deep horizons or the core withinthe earth. They move up to the shallow hydrogeologiczones through fractures (joints, faults, shear zones) andheat up surrounding groundwaters to generate hot andwarm springs. In addition to the hotness of such waters,they are also highly mineralized because the high tem-peratures enhance the dissolution of soil and geologicmaterials.

Geologic and Hydrologic- CyclesPedologic, geologic, and hydrologic cycles have sev-

eral components and characteristics that enhance or ag-gravate the incidences of pollutant/contaminant origin,transport, and spread through hydrodynamic dispersion(diffusion, advection and dispersion) into the hydrogeo-logic environments that embrace the atmosphere, pe-dosphere, lithosphere, hydrosphere, and biosphere.

Geologic CycleGeologic rock units may be fractured, faulted, and

jointed during tectonic movements or may be layeredduring the deposition and consolidation of sediments.Weathering disaggregates rocks into soils and sedi-ments that are transported away by wind, water, and/or man. During these processes of the geologic cycle,pollutants and contaminants may be formed or released.Figure 1 shows significant parts of the complex geologiccycle that are relevant to groundwater pollution. Soiland geologic characteristics vary in horizontal, lateral,and vertical directions. Soil characteristics include grainsize, porosity, permeability, stress-strength properties,cohesiveness, and other physical and chemical proper-ties. The soil components of unconsolidated geologicunits that form aquifers have similar physicochemicalcharacteristics. Additionally, layering or stratificationproperties of both consolidated and unconsolidated geo-logic units are factors that affect pollutant/contaminantinputs, transport and dispersion. Stratigraphic prop-erties of directional lithologic changes, facies changes,stratification and stratal thicknesses, degrees of sedi-mentation, cementation, and diagenetic changes affectthe life of pollutants/contaminants in groundwater(Fig. 2) (14). The structural characteristics of fractures,faults, joints, and folds (Fig. 3) of igneous and meta-morphic rocks and consolidated sedimentary rocks arealso significant in groundwater pollution and contami-nation.

43

EGBOKA ET AL.

AnticlineAnticline

(a) FOLD Syncline

Sand ----40

Shale -

Gravelly ________________Sand

(b) JOINTS

Sandstone e

Limestone. o*.

GravellySandstone -O.

Fault Line/Face/Zone

(C) FAULT

Sandstone -FIGURE 1. Geologic cycle.

(a) Horizontal Stratification and Facies Changes

-i - * DIRECTION OF MOVEMENT

Shale -.

Gravelly - A.Sandstone >Upthrown Side

Fault Lines

SandstoneAquifer

(b) Layering and Vertlcal StatificationGround Surface

DIRECTION OF INPUT Water Table

i I I

noIkMMSoil Zone* * .W r

Sand .a blePermeable Aquifer

Impermeable --. Aqutard

* ,' ' * , e * Sand *.* & s * * Confined Aquifer

Permeable * . . -. *

Rock AquicludeImpermeable

FIGURE 2. Lithologic changes.

Subsequent discussions of the geologic and hydro-geologic settings shall explain further the obvious im-plications of these properties in the genesis, transport,and dispersion of pollutants/contaminants in ground-water flow systems. It will then be clear that any suc-cessful stoppage or control of groundwater pollutantsand contaminants must take into serious considerationthe implications of geologic and hydrogeologic charac-teristics of the particular polluted or threatened envi-ronment. Currently, pollution/contamination plannersand managers do not seriously consider geologic prop-

FIGURE 3. (a) Folds, (b) joints, (c) fault, (d) graben.

erties and characteristics in design and control pro-grams, thereby creating situations that frequently pro-duce failures in engineered structures.

Hydrologic CycleThe several processes as briefly outlined below that

occur within the hydrologic cycle (Fig. 4) are the drivingforces and agents of groundwater pollution. The at-mosphere serves as the gaseous envelope surroundingthe earth. Precipitation through condensation of rainclouds falls down to earth as rain, snow, hail, etc. At-mospheric pollutants and contaminants may be washedout of the atmosphere as fallout. Runoff carries pollu-tants into surface waters for possible evaporation backinto the atmosphere or storage in rivers, streams, lakes,and oceans, seas, etc. Some of the fallout or rainout mayinfiltrate into the soil zone to be evapotranspired to theatmosphere or percolate into the groundwater zone.Here moisture joins a complex hydrodynamic flow sys-

Joints

Igneous RocAquiclude

10 A a 1 4-'a.' .4,6"PS - 'A:--c4-7'

Downthrown

'I V

44

,:\_,_...


Surface WaterDivide

Groundwater /Divide

GroundwateRecharge /

FIGURE 4. The hydrologic cycle.

\* * 9 1 * w

\ DISCHARGE Watertable

* .. *-Groundwater Flow~~.~~~~~~ Bedrock '.~~

i5E-~~(Aquiclude)',

tem possibly to be transported to the oceans or othersurface waters where evaporation may return the waterback to the atmosphere. In all these processes, pollu-tants and contaminants may be produced and cyclicallydispersed from one point of the hydrologic cycle to an-other. This is graphically shown in the cyclic pollution/contamination of the hydrogeologic system otherwisecalled the hydrogeopollution cycle (Fig. 5). Pollutantsand contaminants may be generated through natural oranthropogenic processes and circulated in the environ-ment (atmosphere, pedosphere, lithosphere, biosphere,

FIGURE 5. The hydrogeopollution cycle.

and hydrosphere) through the activities of air, water,chemical, physical, and microbiological processes. Thesecomplex and cyclic processes may be continuous withrespect to distance and time and may be localized orregional in areal spread. Thus, pollution at one sourceor an area may threaten nearby or distant places unlessits spread is checked or controlled.The implications of the geologic and hydrologic cycles

are much more pronounced when one relates them tothe long half-lives and transport of high-level radioac-tive wastes from industries. These materials are beingstockpiled in different parts of the industrialized nationsand some developing countries waiting to be safely dis-posed of in secure geologic rock units. It is now knownthat even deep-seated geologic hard rock formationshave cracks, joints, and even faults through which mov-ing groundwaters can transport pollutants/contami-nants in many directions. It is also possible that thegrain size and lattice structure of such rock units maypermit widescale diffusion/dispersion of gaseous/liquidpollutants that may eventually threaten the biosphericenvironment with time. Hence, structural and strati-graphic characteristics of geologic units and the hydro-dynamics of percolating or flowing groundwaters mustprominently occupy the minds of planners, designers,and managers of waste disposal and management sys-tems. Unfortunately, at present, this has not been thecase, particularly in developing countries where pollu-tion/contamination is becoming more commonplace.Even though those in developed countries now considergeologic and hydrogeologic effects, it has been late incoming, and pollution has ravaged many areas, precip-itating devastating losses in financial, water, land, andhuman resources. Even with graphic examples that il-lustrate the consequences of poor planning, many plan-

U.

45

EGBOKA ET AL.

ners and managers are still skeptical about the role ofgeology in environmental pollution. At the same time,the lack of consideration of geologic, pedologic, and hy-drologic/hydrogeopollution cycles has not been fully ap-preciated in developing countries. There does not seemto be enough consciousness given to understanding theimplications of these cycles. Because of this, no priorityis given to examining the impact of pollution incidencesand the consequences of spread in the hydrogeologicenvironments.

Processes and Activities GeneratingPollutants/ContaminantsVarious processes, some of which may be manmade

or anthropogenic, generate pollutants and contaminantsthat enter groundwater flow systems. These processesinclude physicochemical weathering, mass wasting, ero-sion, sediment transport, and deposition; agriculturalactivities; mining, mine-waste disposal, and acid minedrainage problems; oil exploration, exploitation, and gasflaring; other industrial activities such as manufactur-ing, distribution of manufactured products, arms, andarmaments, etc.; sewage treatment, disposal, and man-agement; runoff, floods, and snowmelt; biological pol-lution of wetlands and impounded reservoirs; salinelakes, ponds, and evaporite deposits; geothermalsprings and mineralized waters; atmospheric fallout andrainout; burial grounds, garbage dumps, landfills, etc.Some pollution sources in rural environments that areusually ignored, even though they may be hazardous,include pit latrines, open-space communal toilets,widescale and indiscriminate uses of the bush for def-ecation, personal hygienic uses of water for washings,etc., microbiological activities (bacteria, virus, fungi,worms, etc.), radioactive material, and thermal prod-ucts, heavy metals, trace elements, ions, etc.

Chemical Pollutants/Contaminants ofGroundwaterMany developing countries are witnessing a stage of

development where groundwaters from shallow wellsand boreholes are gradually supplementing the originalsource of drinking water (surface water). The prefer-ence for groundwater to surface water is borne out ofthe belief that when surface water has been distributedas tap water it must always be subjected to some pu-rification prior to distribution. Although surface watersare easily accessible where they exist in lakes, rivers,streams, and springs, many people believe that waterwells produce water of excellent quality. Thus, ground-water is not treated before use and is believed to befree from pollution.One place where one can find groundwater about as

pure as rainwater is under a bare dune made of purequartz sand (32). The water under quartz sandstone isclean and pure because quartz is so insoluble in waterthat for practical purposes, it is inert and neither soil

nor vegetation contributes dissolved substances to thegroundwater it contains. Areas ofpure quartz sand duneare few. Most surface soils and water-bearing forma-tions are not pure quartz sandstone. A sandstone ismade up of soil particles of different mineralogy. Theseparticles are bound together by cementing materials,which are generally calcite, hematite, or silica. In con-trast to quartz sand, surface materials of soils, lime-stone, shale, and other lithologic types react with per-colating and infiltrating water to produce dissolvedmaterials that pollute groundwater (Figs. 4 and 5).Any groundwater system may be naturally polluted

or contaminated to a certain degree at all times. Theconcern of many water resource planners and managersis whether the amount ofmeasured pollutants are withinthe acceptable limits of water quality. The number ofchemical pollutants and the degree of chemical pollution/contamination of groundwater depend on the geology,pedology, and the mineral composition of the soil androck through which the water flows before reaching theaquifers. Groundwaters may have pollutants that notonly depend on the pedology, geology, and mineralogyof the formations it flows through but also on the con-stituent pollutants/contaminants in the water that re-charges the groundwater.Recharge water, on the other hand, may be contam-

inated by atmospheric fallout, industrial and domesticwastes, etc. The type of physical, economic, agricul-tural, and social activities of the people living in agroundwater recharge area (Fig. 6) may affect its waterquality. Thus, urban planners and managers must bewary of human activities that occur in recharge areasof aquifers in urban and rural areas. This is one of themain avenues by which pollutants or contaminants enterthe groundwater. Hydrogeologic maps of the areas arelacking or have not been produced, so the rechargeareas are not identified. This problem affects both de-veloped and developing countries. Massive pollution ofgroundwater systems is a common occurrence becausewastes are recklessly deposited on top of rechargeareas.Groundwater pollution is an ever present risk in de-

veloping countries, particularly in areas of mining andextensive industrial activities. This must constantly bein the minds of those responsible for water supplies inthese areas. Borehole waters must, as a rule, be ana-lyzed for chemical contaminants before the water is dis-tributed and supplied to households. Unsatisfactorycolor and taste are easily detected and are good indi-cators for groundwaters of poor quality. Some ground-waters taste of iron, others may have a disagreeableodor. Such groundwaters should be avoided and notused for domestic purposes. Water containing only sev-eral parts per million of sodium and chloride ions tastesslightly salty. Lead and sulfur are distasteful when pres-ent in appreciable quantities in water. Conversely, how-ever, some toxic elements have no taste, but when pres-ent in very small quantities may be dangerous to health.Very small concentrations of poisonous trace elementssuch as lead, arsenic, mercury, cyanide, and boron must

46


Pflollutant Source

(a) Recharge Zone

Zone of Groundwater

Contamination

Surface Water

* . : e. . Aquifer

(b) Discharge Zone

*\. \ \ ~~Pollutant SourceZone of Contamination

Sce Water

Aquifer

FIGURE 6. Schematic illustration of the extent of groundwater con-tamination for pollutants entering (a) recharge and (b) dischargezones.

be carefully documented. Water sampling and monitor-ing may reveal their presence.The three components of water quality are bacterio-

logical quality, physical quality, and chemical quality.Filtration and sedimentation processes take care of thephysical quality. In practice, groundwaters are filteredby natural processes as they pass through columns ofsoils, sands, strata, or sedimentary layers of rocks.Groundwaters are usually clear of solid materials asthey come from the aquifer, particulary ifthey are deep-seated ones. The intricate pore spaces or water pas-sageways of the aquifer materials act as a fine filter andremove small particles of clay or any other fines. Or-ganic materials decay or are destroyed in transit. Thus,the dirtiest and most polluted sewage water may be-come clear of suspended/particulate solid materials onceit has gone through a thick bed of sand or geologic andpedologic units. As a result of this natural self-cleansingof polluted water by deep-seated aquifers, physical andsome biological aspects of pollution may not pose seriousproblems in groundwaters.

Bacteriological quality of groundwater is taken careof by treatment with various chemicals that kill bac-teria. Dissolved geochemical constituents, on the otherhand, are difficult to remove entirely. They may be

removed through filtration in charcoal, through cationexchange, precipitation, dissolution, degassing, etc.The treatments may be expensive and may result in thecreation of new pollutants and contaminants and theirintroduction into the treated waters. In developed coun-tries, waters supplied for public use are routinely ana-lyzed to certify that the content of toxic elements orcontaminants are below mandatory limits. In many de-veloping countries, groundwaters and even surfacewaters are often distributed to various communities un-treated. In general, it is wrongly believed that exploitedgroundwaters are free of pollution. Emphasis is usuallyplaced on water supply and quantity, and minimal prior-ity is given to water quality and treatment. This is themain cause of outbreaks of epidemics of waterbornediseases in many developing countries because un-treated surface water and groundwater are consumedby the people, particularly in rural areas, without watertreatment. Since there are no monitoring programs, itis not possible to detect incidences of pollution.The most undesirable trace elements-pollutants in

groundwater are mercury (Hg), lead (Pb), cadmium(Cd), arsenic (As), barium (Ba), boron (B), cyanide (CN)selenium (Se), chromium (Cr), uranium (U), sulfur (S),and nitrogen (N). The United States Food and DrugAdministration has specified the lower mandatory limitsof these elements in domestic water. In addition, thereare internationally accepted water quality guidelines forconcentrations of these elements in water for varioususes. Most groundwaters may also contain many majorinorganic elements, compounds, and ions in excess ofacceptable standards, such as iron oxide (Fe2O3), man-ganese (Mn), calcium (Ca), magnesium (Mg), chloride(Cl), aluminum (Al) and silica (SiO2). Anions and cationscan be found in their dissolved states. Temperature,where high, affects the properties of groundwater, es-pecially the solubility of minerals. Deep groundwaterscontain more chemical elements dissolved in them thando shallow ones. Very deep, hot groundwaters may beobjectionable because they contain very high concen-trations of these mineralized elements dissolved out ofrocks by the high temperatures. This is characteristicof hydrogeothermal regions.Groundwaters in limestone or Karstic terrains may

contain dissolved calcium and magnesium salts. Thesesalts make water hard. Hardness in excess affects tasteand soap consumption in laundry. Temporary hardnessis caused by carbonates and bicarbonates of calcium andmagnesium; permanent hardness is caused by sulfates,chlorides, nitrates, and silicates of calcium and mag-nesium. The combination of both of these groups of sub-stances gives total hardness. Hard water may also havea slight taste that is caused by other ions in solution.A few groundwaters naturally become softened as

they pass through and react with geologic formationscontaining zeolite minerals, which remove calcium andother ions. Zeolites and hydrous silicates chemically ex-change certain ions from water for other ions bound inthe solids. If, for example, water carrying calcium ionstravels through a zeolite formation that exchanges Na+

47

EGBOKA ET AL.

for Ca2", the water comes out with sodium instead ofcalcium and the zeolite becomes richer in Ca and poorerin Na.

Iron in water gives a bitter taste and makes waterreddish or brownish in color. It is found in the form ofbicarbonates and sulfates. Iron in groundwater is dueto the presence of hematite below the ground surface.Iron is soluble in water containing carbonic acid. Watercontaining high iron is unsuitable for laundries, papermills, film industries, etc.Manganese acts in a manner similar to iron. It pro-

duces an undesirable taste, and white clothes washedin water containing manganese or iron turn yellow orbrown. In small concentrations, Mn affects odor. Ironand Mn in water precipitate and produce undesirableturbid yellow-brown water that stains laundry. Theseelements support growth of microorganisms in distri-bution systems. These growths can accumulate and re-duce the carrying capacity of pipes and clog valves.Small concentrations of Fe and Mn impart a metallictaste to water. Groundwater supplies contain more Mnand Fe than surface waters.Excess carbon dioxide in water makes water corro-

sive to metals. It can be present in the form of carbonicacid, bicarbonate, carbonate or as free carbon dioxide(CO2). Groundwaters drawn from great depths are de-ficient in dissolved oxygen (DO). Shallow groundwatersare usually saturated with dissolved oxygen. Hydrogensulfide (H2S) makes water unpalatable because of badodor and taste. It is found in groundwaters where sul-fide minerals such as galena, pyrite, sphalerite, etc.,are present. Other dissolved gases in addition to CO2,DO, and H2S that may cause pollution problems ingroundwater include nitrogen dioxide (4,33), methane(31), and sulfur dioxide. They cause degrees of hazardin hydrogeologic systems that are functions of concen-tration but are hazards that can be removed duringwater treatment processes.

Geologic and HydrogeologicSettingsGeologic Settings

Natural geological processes are primary contribu-tors to groundwater pollution. In this regard, the rocksof the earth's crust are the major contributors ofgroundwater pollutants (Figs. 1 and 5). These contam-inants are mostly minerals, gases, and the toxic ele-ments they contain. A good understanding ofthe origin,occurrence, and distribution of these undesirable ele-ments is essential for people concerned with the devel-opment of surface water and groundwater resources.Contaminants enter groundwaters from the rechargeareas of aquifers. It is therefore very necessary to knowthe geology and mineral distribution in recharge areasof aquifers. Groundwater that is recharged from miningareas, fertilized agricultural farmlands, and industrialareas may not be safe for human consumption unlessthe recharge area is protected. Rain and surface water

can leach pollutants from mine dumps, ore deposits, citydumps, and fertilizer applied to farm lands into the re-charge areas for groundwater supplies (Fig. 6).Groundwaters recharged from polluted areas must

either be avoided or pollution sources checked and mon-itored very carefully. The geology of recharge areas ofaquifers influences the quality of groundwater. Thenumber of pollutants and the degree of pollution ingroundwaters depend on the geology and the minera-logical compositions of the rocks through which thewater flows. Groundwaters may also acquire pollutantsand contaminants as they flow across difference geolog-ical and mineralogic zones or units of formations. Chem-ical reactions between the water and rock fragments inthe soil and numerous chemical and physicochemical re-actions between water and rock in the groundwaterenvironment alter the composition of the groundwater.Surface waters recharged by surface water drainingthrough limestone areas may be hard and need consid-erable softening treatment before being supplied fordomestic and industrial use. Rainwater absorbs carbondioxide in the air, forming carbonic acids, which reactwith limestone, liberating bicarbonates and carbonateswhich, when added to percolating groundwaters, makethem hard. Surface materials of soils and shale reactwith rain to produce dissolved materials that contributeto the taste and color of groundwaters. The taste andcolor of such waters depend on the composition of therocks through which the water passes. Surface watersdraining metamorphic areas containing talc dissolvemagnesium salts that contribute to the hardness ofgroundwater.

Surface water draining areas of sulfide mineralizationintroduce sulfur and many other metallic ions intogroundwaters. The chemical characteristics of ground-water vary greatly as a result of the diversity of rockmaterials through which the water passes. Sedimentaryrocks provide the largest aquifers and water passingthrough such rocks acquire considerable concentrationsofchemical components ofthese rocks. Carbonate rocks,such as limestone and dolomite dissolve easily in acidwater with the result that water in contact with theserocks are high in calcium and magnesium bicarbonates.In igneous and metamorphic terrains, groundwater oc-curs in weathered parts of the basement rocks or faults,joints, and fissures. Rainwater percolating throughthese fissures dissolve many soluble elements. Thegroundwater in basement areas may be contaminatedby ions dissolved from the basement rocks (Fig. 3).Weathering and oxidation of basement rocks create

a favorable acid environment for mobilization of manymetals. Weathering and fracturing of basement rocksalso create porosity necessary for storing water. Con-sider a granite containing about 5 ppm of uranium insolution. During weathering uranium will be oxidizedto the soluble uranyl oxide in the near surface weath-ering environment. The oxidized uranium is then mo-bilized and dissolved in shallow groundwater in thebasement area. Data from Trenthan and Orajaka (34)and Orajaka (35) show that significant amounts of ura-

48


nium are leached and mobilized from felsic igneous rockby carbonic acid water. A significant quantity of ura-nium is leached from the albite-riebeckite-granite inKaffo Valley, Northern Nigeria, during weathering ofthe roof of the granite mass (36). This example illus-trates how abnormally high uranium and other major,minor, and trace elements are leached and introducedinto shallow groundwaters in the veins, fissures, andporous parts of basement rocks.

It is thus important to test all shallow groundwatersin basement or hard rock areas for metal contaminationbefore supplying such water to homes and industries.In many developing countries, rural dwellers obtaintheir water from shallow, hand-dug wells (37). In mostcases where the water is tested, they are usually con-taminated, particularly for shallow wells in urban cen-ters situated in basement rock areas. Toxic metals, no-tably Pb from weathering products of ores inmineralized veins of faults and fissures, can enter nat-ural water systems. The metal concentrations are ab-normally high for water descending through fissuresexposed during mining operations. These contaminatedwaters find their way into groundwaters, thereby pol-luting them. Surface water and floods in the Pb-Zn min-eral belt of southeastern Nigeria contain high concen-trations of Pb-Zn. These metal ions are also present inshallow groundwaters in the area. The high Pb contentof the shallow groundwater have posed some serioushealth problems. Their implications and extent of haz-ards are yet to be fully investigated.

Structural Features and SedimentaryCharacteristicsThe structural and sedimentary properties of rocks

that affect groundwater quality include layering, frac-tures, joints, faults, and shear zones (Figs. 2 and 3).These structural features act as hosts for mineraliza-tions and also serve as channel ways that conduct sur-face waters to aquifers. Faults, shear zones, and jointsare often mineralized. The most common veins and fis-sure-filling minerals are sulfides. Oxygen-laden surfacewaters and carbonic acid waters entering these fissuresoxidize and dissolve cations and anions from the sulfideminerals and introduce them into shallow groundwa-ters. The toxic metallic elements introduced into thegroundwater by this method include As, Cs, Hg, Pb,Ni, etc. Thus, in the surface or subsurface disposal ofwastes, the structural, stratigraphic, and sedimento-logical natures of the area must be mapped, described,and known in order to produce a waste managementdesign that would contain the wastes safely and keepthese toxic elements from migrating into surroundingsurface waters and groundwaters.

Hydrogeologic SettingsBecause contaminants are transported in large part

by the bulk motion of groundwater, the parameters ofgroundwater flow are of major importance in the un-

derstanding of contaminant processes. The various as-pects ofthe groundwater environments, as well as strat-igraphic factors that control or could influencegroundwater motion, are also of major consideration.The hydrogeological environment is shown schemati-cally in Figures 2 and 4. It consists mainly of the sat-urated and unsaturated zones. The unsaturated zoneoccurs above the capillary fringe where the soil poresare partially saturated with water. This zone is impor-tant in waste management because in most cases, it isthe burial zones for wastes. Consequently, a thick un-saturated zone may sometimes be preferred for wastedisposal since it would take a much longer time for con-taminants to reach the water table. In the saturatedzone, the pores are saturated with water. When thiszone is capable of transmitting significant quantities ofwater for economic use it is referred to as an aquifer.In most field situations, two or more aquifers occur,separated by impermeable strata or aquitards. In thesituation illustrated in Figure 2, the upper or unconfinedaquifer is much more prone to pollution than the lowerconfined aquifer.

Fluid motion in saturated geological materials is de-pendent on the hydraulic gradient, porosity, and hy-draulic conductivity. Average groundwater velocity -vis obtained from the relation (38),

Ki . dhv =

- KI =

n ' dl (1)

where i(dh/dl) is the hydraulic gradient, n is the poros-ity, K is the hydraulic conductivity, and dh/dl is thechange in hydraulic head (h) with respect to the changein distance (1). Porosity and hydraulic conductivity, inparticular, are properties that are dependent on thegeologic conditions of the waste disposal site. Differ-ences in hydraulic conductivity values across a strati-graphic section could appreciably determine whetherflow is upward, downward, or horizontal, as demon-strated by Freeze and Witherspoon (39). Thus, the ul-timate fate of contaminants emanating from waste dis-posal sites can be strongly dependent on whethergroundwater flow is upward or downward. Therefore,the direction of flow of groundwater is an importantfactor in the evaluation of sites for waste disposal. Theactual magnitude of groundwater velocity is also an im-portant factor. In low permeability geological materials,groundwater velocity can be as low as a few centimetersper year. For such conditions, contaminants would betransported over very short distances over a very longtime span and hence may not pose hazards to the en-vironment.

In contrast to the low velocity of groundwater thatoccurs in low permeability materials such as shales, thevelocity in permeable deposits or fractured media canbe quite large. High groundwater velocity zones providea pathway through which water supply sources becomequickly polluted. The search for and the evaluation ofsuch high-velocity pathways is therefore an importanttask in the groundwater pollution studies. The ease and

49

EGBOKA ET AL.

extent to which contaminants can pollute an aquifer arealso dependent on whether the contaminants are intro-duced into the groundwater system at the recharge ordischarge areas. Figure 6 shows that a major portionof an aquifer may become contaminated if the contam-inant is introduced into the subsurface from an uplandrecharge site. Hence in designing or planning a wastedisposal site, the entire hydrogeological properties ofthe area must be well established to ensure a safe andlong-lasting disposal network.

Contaminant Pathways andProcesses in Groundwater SystemsPathways of entry of contaminants into groundwater

systems depend largely on patterns of waste disposaland human interferences with the environment. An un-derstanding of the general methodologies of waste dis-posal is thus a prerequisite to any discussion of contam-inant pathways into the subsurface environment. Thevarious waste disposal options currently in use includesanitary landfills, open dumps, septic tanks and cess-pools, and deep well injection systems.

Table 5. Representative ranges for various inorganicconstituents in leachate from sanitary landfills (36).

ParameterK+Na+Ca2+Mg2+Cl-sO-2AlkalinityFe (total)MnCuNiZnPbHgNO3NH4+

po4Organic NTotal dissolved organic carbonChemical oxygen demandTotal dissolved solidspH

Representativeconcentration range, mg/L

200-1000200-1200100-3000100-1500300-300010-1000500-10,0001-10000.01-100< 100.01-10.1-100< 5< 0.20.1-1010-10001-10010-1000200-30,0001000-20,0005000-40,0004-8

Sanitary Landfills and Garbage DumpsMuch of the solid waste that is now disposed of on

land is placed in sanitary landfills. In humid areas, inparticular, buried waste in sanitary landfills and dumpsis subject to leaching by percolating rainwater. Theleaching process is accompanied by chemical reactionsthat tend to consume all available oxygen, while re-leasing carbon dioxide, methane, ammonium, bicarbon-ate, chloride, sulfate, and heavy metals. The liquid mixofthese constituents is referred to as leachate. The totalnumber and chemical concentrations of these constitu-ents can be variable depending on the initial compositionof the waste climatic conditions. Table 5 shows thatleachates contain large numbers of inorganic contami-nants and also have high total dissolved solids. Leach-ates also contain many organic contaminants. Robertsonet al. (40), for example, identified over 40 organic com-pounds in leachate samples (contaminated groundwaterin a sandy aquifer in Oklahoma). Leachates emanatingfrom landfills contain contaminants and toxic constitu-ents derived from solid wastes, as well as from liquid,industrial wastes placed in the landfill (41).

Rain water percolation through refuse in the landfillcauses water table mounding, i.e., a rise in water tableelevation within or below the landfill. The moundingprocess, according to Freeze and Cherry (38) causesleachate to flow downward and outward from the land-fill, as illustrated in Figure 7. Thus, for shallow aquifers,in particular, water table mounding provides a pathwayfor the entry of contaminants into the groundwater sys-tem as a result of the buildup in hydraulic gradient andpressure head.

Septic Tanks and CesspoolsSeptic tanks are designed to remove settleable solids,

reduce biochemical oxygen demand, eliminate micro-

PRECIPITATION

Leachate Spring

Groundwater Zone Contaminated by Leachate

FIGURE 7. Water table mound beneath a landfill, causing migrationof contaminants deeper into the groundwater zone (38).

organisms before (the treated) sewage is releasedthrough a drainfield into the ground. A generalized dia-gram illustrating the layout of a septic tank waste-dis-posal system is shown in Figure 8. The figure demon-strates that septic tank system effluents can quite easilyreach and contaminate the groundwater system. Ac-cording to the United States Environmental ProtectionAgency (42), septic tanks and cesspools are the largestcontributors of wastewater to the ground and are themost frequently reported sources of groundwater con-tamination in the United States.Apart from the effluent that is directly released into

the ground, there are large volumes of solid residualmaterials known as sewage sludge. In many parts ofthe world, this sludge, which contains a large numberof potential contaminants, is applied on agriculturallands to enhance crop nutrients such as nitrogen, phos-phorous, and heavy metals that are needed for plantgrowth. Although this practice actually improves soilfertility, it has been observed that one of the potential

50


_ PRODUCTION PRETREATMENT DISPOSAL

i ~~~Vdose Zone BDDgcIEVAPOANSITRATION

DitibtonB x A ie/il

FIGURE 8. Contamination from a septic field (57).

negative impacts of this type of sewage disposal is deg-radation of groundwater quality (38). Contaminants inthe sewage sludge/effluent reach and contaminategroundwater through infiltrating water from rain orsnow.

Radioactive Waste DisposalRadioactive wastes are generated at various stages

in the nuclear industry. Mining and milling of radioac-tive ores result in the production of large volumes ofwaste rock and tailings. Nuclear plant operation gen-erates radioactive fission products, reactor coolingwaters, irradiated fuel rods, and other by-products.

Figure 9 illustrates several types of waste burial al-ternatives. In all cases, the wastes are stored in strong,engineered concrete containers. In the option illus-trated by Figure 9a, the containers are placed on thesurface of the ground and then covered with earth ma-

terials. Figures 9b and 9c illustrate the options in whichthe containers are placed a few meters below the surfaceof the ground either below or above the water table.The difference between these two options is that in thelatter (Fig. 9c) the fill in the excavation is designed toprovide enhanced containment capability for the sys-tem. A large number of burial options for radioactivewastes in Canada and the United States are in the cat-egory represented by Figure 9b (38). In Figures 9d and9e, the containers are buried in large holes about 10 to20 m deeper than in the previous examples.Because of the highly lethal nature of radioactive

wastes, particularly for those with long half-lives, it isnecessary that these wastes are disposed of in systemsthat have high containment capability. Failure of theburial sites could result in the leakage of radioactivematerials into the groundwater environment or into thebiosphere. To avoid problems of subsurface radionuclidemigration, numerous reported investigations includingCherry et al. (43) have suggested that burial sites shouldhave the following characteristics: geomorphic and

structural stability, isolation from fractured bedrock,absence of subsurface flowlines that lead directly to thebiosphere or to subsurface zones of potable water, lowmeasured or predicted radionuclide velocities, andwater table conditions that are deep enough to permitwaste burial to remain entirely in the unsaturated zone.

Deep-Well DisposalDisposal of liquid wastes of industrial origin by in-

jection into the deep underground is a widely acceptedpractice. The growing acceptance of this waste disposaloption is mainly due to the numerous problems of pol-lution in near surface hydrologic environments (44). Thegrowing acceptance of this option is suggested by theresults of a survey conducted by Warner and Orcutt(45), which showed that waste injection wells increasedfrom 30 in 1964 to at least 280 in 1973 in the UnitedStates. There are now more than 100,000 of these wellsin North America. Although deep-well injection of liquidwastes is meant to minimize the problem of pollution inthe near surface hydrologic environment as suggestedby Piper (44), the potential for pollution of deep-seatedaquifers is still obvious. If the pollution of deep-lyingaquifers is to be avoided, the disposal option requiresthe isolation of formations receiving waste injectionsfrom permeable contact with other elements of the hy-drologic environment.

Human Activities and Pollution/ContaminationContaminants can be introduced into the groundwa-

ter system as a result of myriads of human activities.This category of contamination of groundwater systemsdiffers from the ones described earlier in that such hu-man activities do not ab initio introduce wastes into thesubsurface. The major human activities that eventuallyend up polluting groundwater systems include agricul-tural activities, storage of gasoline tanks in the sub-surface, pipe lines, road deicing, mining and pumpageof aquifers, etc.

Nitrate loading of shallow groundwater systems aris-ing from fertilizer application occurs mainly throughleaching. Where there is significant downward flow,deep-seated aquifers can become affected. According toFreeze and Cherry (38), widespread nitrate contami-nation of aquifers through fertilizer application is rare.Numerous investigators including Grisak (46) and Cus-ter (47) have shown from case studies in various partsof the United States and Canada that nitrate derivedby oxidation and leaching of natural organic nitrogen inthe soil is more often responsible for extensive nitratecontamination of shallow groundwaters. The pathwaydown to the water table of those contaminants gener-ated through mining activities and road salt applicationis similar to that for nitrates, i.e., they reach the watertable through leaching and flushing through the unsat-urated zone by infiltration of percolating water fromrain and snowmelt.

51

EGBOKA ET AL.

(a) - -

Specially Designed Earth Material

AL

_ *_(c)

Zone of _Water TableI

Fluctuation

Backfill

M._

ProtectGeolog

(e)FIGURE 9. Schematic diagrams illustrating methods of disposal of radioactive wastes (38).

Petroleum leakage from underground storage tanksand oil pipe lines, as well as spills from oil-producingwells, constitute an increasing threat to groundwaterquality (Fig. 10). Petroleum contaminant pathways into

Leaky Storage Tankor Oil Spill

/

the groundwater system are illustrated in Figure 10. Asimple hydrogeologic condition is assumed. Accordingto Freeze and Cherry (38), in the initial migration stage(seepage stage), the oil moves primarily in a downward

* Vadose 2* X **D > @@OilPhase

*Vapor Zone

GROUND WATER FLOW DIRECTION . . . * . .; :.

I Hundreds of Th4

Zone

*.i~.

.

Capillary Fringe

_. Watertable

Dissolved ContaminantsI

I

ousands of Meters

FIGURE 10. Contamination from a leaky storage tank or oil spill (57).

... ... ....

tive)ic Materials

k - - 14

52


direction under the influence of gravitational forces. Onreaching the water table, the oil zone spreads laterally,first under the influence ofgravity-related gradients andsubsequently in response to capillary forces. Capillaryspreading becomes very slow, and eventually a rela-tively stable condition is attained. Figure 11 summa-rizes the movement of mining wastes and pollutantswithin the total environment. At each state and posi-tion, metal-rich mine materials may get into the air,surface water, soils, and groundwater to possibly pol-lute them.

Figures 12a and 12b illustrate pathways by whichcontaminants in polluted surface waters and salinewater can enter groundwater zones. In Figure 12a, con-taminated surface water reaches the groundwater zoneas induced by water recharge under the influence of thegradients set up by the well. Instances of polluted sur-face waters are common, particularly in industrial areaswhere effluents are discharged untreated or partiallytreated into streams and lagoons. Figure 12b shows apossible effect of overpumping that is often observed incoastal areas. Overpumping can cause contaminantsfrom sea water to enter a freshwater aquifer.

Contaminant Transport:Hydrogeochemical ProcessesThe migration of contaminants in groundwater flow

systems is due mainly to groundwater motion. Trans-port rates, however, are moderated by a variety of geo-chemical and biochemical processes that include com-plexation, acid-base reactions, oxidation-reductionprocesses, precipitation-desorption reactions, and mi-

FIGURE 11. Movements of mining pollutants within the total envi-ronment. Modified from Press and Siever (32).

Pumping Well

OriginalWater Table-t.,

Contaminated / .<..Pumping..Surface Water water Level

*: S.:.IQnduced Rec ag

(a)

Pumping Well

Fresh-Water Aquifer '..

''Saline-Water Aquier*

(b)

FIGURE 12. Contaminant pathways into an aquifer (a) through in-duced infiltration from contaminated surface water and (b) throughover pumping near saline water aquifers (89).

crobial reactions. According to Jackson and Inch (48),precipitation-dissolution, adsorption-desorption, andmicrobial reactions can lead to the removal of contam-inants from solution, whereas the other processes affectthe availability of the contaminant for adsorption orprecipitation. Appropriate instrumentation, sampling,and monitoring would make these hydrogeochemicalspecies veritable environmental tracers.

Complex-Ion FormationComplex-ion formation is important in the study of

groundwater pollution because the concentration andmobility of most contaminants are governed by the con-centration and nature of the complexes they form. Forexample, hydroxide and carbonate complexes appreci-ably affect the mobility of uranium and the heavy metalsin groundwater flow systems. It has also been observedby Jackson and Inch (48) that when heavy metals (e.g.,Pb2+, Cd2+) are complexed by inorganic or organic li-gands (e.g., Cl-, EDTA), the contaminants may not beimmediately available for adsorption or precipitation,and consequently the mobility of heavy metal contam-inants may be increased in the groundwater flow sys-tem. On the other hand, contaminants may become as-sociated with adsorbed complexing ligands such as

53

EGBOKA ET AL.

humic acids. In that case, their mobility will be reduced.It is thus concluded that adsorbing and nonadsorbingligands may compete for contaminant ions and thus de-termine, on the basis of the relevant formation con-stants, the distribution of complexed contaminants be-tween adsorbed and solution states.

Acid-Base ReactionsAcid-base reactions are those chemical reactions in-

volving the transfer of protons. Proton activity, H+,expressed as -log H+, is referred to as pH. The nu-merical value of pH gives an indication of the acidity ofnatural waters. The pH of natural waters is controlledby calcite (CaCO3) dissolution and the CO2 in the soilzone according to the following equations:

CO2 + H20 = H2C03

H2C03 + CaCO3 = Ca+2 + 2HC03

(2)

(3)According to Stumm and Morgan (49), CaCO3 is an

efficient pH buffer only in the neutral and acid pH range.In the pH range of 9 and above, the incongruent dis-solution of aluminosilicate minerals provides a greaterbuffer capacity. In pollution studies, it is important toknow the pH of the groundwater and its bufferingagents since the solubility ofmany minerals as potentialcontaminant sources and sinks are dependent on pH.Acid-base reactions become prominent in environmentalpollution and degradation where situations create ex-tremes of acidity or alkalinity. Thus, in acid mine drain-age areas, acid rain, alkalinity, or alkaline rain situa-tions, the hydrogeological processes such as oxidation-reduction, cation exchange, adsorption-desorption, etc.,may result in the ultimate release of pollutant and con-taminants into these systems to damage them.

Oxidation-Reduction ProcessesOxidation-reduction (or redox) processes are of a ma-

jor importance in governing the geochemical behaviorof those elements that may gain or lose electrons ingroundwaters. By definition, oxidation is the loss ofelectrons and reduction is the gain in electrons, asshown in the following illustrated examples for the ox-idation of iron:

02 + 4H+ + 4e- = 2H20 (reduction)

4Fe+2 = 4Fe+3 + 4e- (oxidation)

(4)

(5)In reality, a reduction reaction is coupled to the cor-

responding oxidation reaction, so that the overall redoxreaction for the oxidation of iron, for example, is of theform:

02 + 4Fe+2 + 4H+ = 4Fe+3 + 2H20 (6)The redox state of groundwater is described by theredox potential pE (or Eh). Water infiltrating into shal-low groundwaters has high redox potential due to its

high dissolved oxygen content. Along the flow system,the tendency is toward oxygen depletion. The first stagein the oxygen depletion process is the oxidation of or-ganic matter (CH20):

02+ CH20 = C02 +H20 (7)

Reaction 7 is catalyzed by bacteria or isolated enzymes.They derive energy by facilitating the process of elec-tron transfer. Organic matter oxidation of the type il-lustrated in Eq. (7) is a major redox reaction occurringin landfills and other similar waste disposal sites. Thus,leachates emanating from landfills have much lower re-dox potential. The leachates also have elevated concen-trations of NH, H2S, Fe2+, Mn2+, and FeS.As the leachate enters the groundwater system, the

following sequence of redox processes would occur (38):(i) Oxidation of Sulfide to Sulfate,

-2 (8)202+HS-=S04 +H+

(ii) Oxidation of Ferrous Iron,

02 + 4Fe+2 + 4H+ = 4Fe+3 + 2H20and the precipitation of Fe+3 as Fe(OH)3

(9)

(iii) Nitrification

(10)202 + NH4 = N03 + 2H+ + H20

(iv) Manganese Oxidation

(11)02 + 2Mn+2 + 2H20 = 2MnO2 + 4H+

When all the dissolved oxygen in the groundwater isconsumed, oxidation of organic matter can still occur asindicated in the following reaction equations (38):

(i) Denitrification

5CH20 + 4N03 = 2N2 + 5HC03 + H+ + 2H20

(ii) Manganese (iv) Reduction

CH20 + 2MnO2 + 4H+ = 2Mn+2 + 3H20 + CO2

(12)

(13)

(iii) Iron (iii) Reduction(14)

CH20 + 4Fe(OH)3 + 8H+ = 4Fe+2 + 11H20 + C02

(iv) Sulfate Reduction

-22CH20 + S04 = HS- + 2CH03 + H+

(v) Methane Fermentation

(15)

(16)

2CH20 + H20 = 'I4 + H+ + HCO3

54

- - I


It is clear from these reaction sequences that ade-quate knowledge of the redox environment is neededfor the purpose of predicting the mobility of those ele-ments that have variable valences and which form lowwater-solubility oxides. For example, oxidized forms ofiron [Fe(OH)3] and manganese (MnO2) are highly in-soluble; the reduced forms (Fe2+; Mn2"), however, aresoluble in water and thus move with the groundwater.Uranium, selenium, arsenic, and molybdenum are in-soluble under reducing conditions and soluble under ox-idizing conditions. Thus, depending on the physical,chemical, and biological conditions within the hydro-geochemical environment, contaminants may exist inpolluted groundwater systems in various concentrationsand forms. Detailed instrumentation and closely spacedmonitoring programs easily delineate the geochemicalzones (4,7,33,41).

Precipitation-Dissolution ReactionsPrecipitation-dissolution reactions are a set of reac-

tions by which contaminants may be removed from so-lution either by direct precipitation or by isomorphoussubstitution with an ion of similar atomic radius in acrystal that is forming or that has formed (48). Theformation of metal carbonates, e.g., Sr(C03)2,Cd(CO3)2, provide good examples of removal of contam-inants from solution in groundwater by precipitationreactions. Saturation index calculations may be em-ployed to determine whether a mineral species is likelyto dissolve or precipitate in a groundwater flow system(38).

Adsorption-Desorption ReactionsAdsorption occurs when a dissolved ion becomes at-

tached to the surface of a preexisting solid substrate(50). In porous media, contaminants can become ad-sorbed onto colloidal-size particles. The adsorption ca-pacity of colloids is thought to be due to their ability togenerate a charged solid-solution interface. The pres-ence of a solid surface charge arises from imperfectionsor ionic substitutions within the crystal lattice of thecolloids. The charge imbalance arising from the accu-mulation of charge on the colloid surface, however, iscompensated for by a surface accumulation of ions ofopposite charge known as counterions. Ion exchangeoccurs when the ions in the counterion layer becomeexchanged for other ions. Cation exchange capacity hasbeen defined by Jackson and Inch (48) as the excess ofcounterions which can be exchanged for other cationsin the bulk of the solution. It is usually expressed asthe number of milliequivalents of cations that can beexchanged in a sample with a dry mass of 100 g. Cationexchange reactions are important in the predictiveanalysis of the mobility of contaminants in geologicalmedia. A measure of the mobility of contaminants thatis used in predictive analysis is the distribution coeffi-cient (Kd). It is defined as "the number of milliequiva-lents of an ion adsorbed per gram of exchanger divided

by the number of milliequivalents of that ion per mil-liliter remaining in solution at equilibrium" (48). Themagnitude of the distribution coefficient is a measureof the extent of partitioning of a contaminant speciesbetween the solid and liquid phases along a groundwaterflow system.

Microbial ReactionsMost of the geochemical reactions leading to the

breakdown and transformation of complex molecules ingroundwater systems are microbially mediated. Thesemicroorganisms derive energy and constituents neededfor survival from these reactions. For bacteria to func-tion and proliferate, it is also important for suitabletemperatures and pH conditions to prevail in the me-dium (48). In the investigations carried out by Jacksonand Inch (48), it was also observed that bacterially me-diated chemical processes may have either beneficial ordetrimental effects on particular pollutants. The bene-ficial effects include purification of contaminated wateras organic pollutants are broken down into substancessuch as CO2, H20, NO , and SO2P-. Elements such asN, S, C, and P are used in the synthesis of microbialprotoplasm and are thereby removed from the ground-water system. Among the detrimental effects is thedepletion of dissolved oxygen.Two phases are involved in the infiltration of unpol-

luted groundwaters by polluted surface waters. Theseare associated with the oxygen-rich unsaturated zoneand the oxygen-deficient zone which is usually satu-rated. Organic pollutants are usually removed by fl-tration in the unsaturated zone where an effective bi-ological filter can be formed. By these processes somesoils constitute an efficient filter for water treatment.Most microorganisms are not adapted to this tortuousand highly competitive environment, which limits theirmovement to no more than 3 m in depth (51). For thisreason, any well or borehole not properly lined for itsentire length stands a chance of being polluted by mi-croorganisms from surface waters.

Adsorption is the main mechanism by which micro-organisms are removed from the oxygen-depleted sat-urated zone. Under this condition, microorganisms maybe carried passively in groundwaters up to a distanceof 30 m horizontally (51). In view of this, a minimumprotection zone of 30 m is essential in siting boreholesand wells if contamination from polluted surface waterfrom septic tanks, agricultural wastes, and refuse tipsis to be avoided. Fissured rock strata constitute an ad-ditional problem. Where they exist, the extent of pas-sive travel by microorganisms is unlimited, as naturalpurification through soil is almost nonexistent (52).During hydrogeomicrobiological processes, the activ-

ities of nonpathogenic bacteria in groundwaters couldbe beneficial because they are involved in the degra-dation of detergents, herbicides, pesticides, and generalmineralization, including cycling of essential elements,nitrogen, phosphorus, and sulfur. When pollution is inexcess, these beneficial processes could lead to problems

55

EGBOKA ET AL.

for groundwaters, such as depletion of dissolved oxy-gen, reduction of nitrate to nitrite or ammonia, reduc-tion of sulfate to sulfide with attendant offensive odorsand growth of filamentous bacteria, reaction of sulfidewith iron to form an insoluble precipitate that can re-strict groundwater flow, and mobilization of iron fromsoil under conditions of reduced oxygen tension only tobe oxidized and precipitated in other regions of the aqui-fer either by chemical or microbiological means (24).Under anoxic conditions, gram-negative chemolitho-trophic bacteria utilize nitrates, sulfates, and iron/man-ganese oxides as terminal hydrogen acceptors in res-piration and other physiological processes.

Contaminant Transport: PhysicalProcessesAn accurate description of the spatial and temporal

distribution of contaminants in groundwater systems isof major importance in groundwater pollution studies.The model widely applied in the evaluation of contam-inant migration is based on the advection-dispersionequation. It is derived from considerations of mass fluxinto and out of a fixed elemental volume within the flowdomain. The physical processes that control these fluxesare advection (i.e., contaminant transport due to bulkmovement of groundwater) and hydrodynamic disper-sion that accounts for the mechanical mixing and mo-lecular diffusion within the flow system. Loss or gainof contaminant mass in the elemental volume resultsfrom chemical or biochemical reactions, radioactive de-cay, or combinations of these. The exact form of theadvection-dispersion equation depends on whether thecontaminants under consideration are nonreactive orreactive.For nonreactive constituents, the one-dimensional

form of the advection-dispersion equation in saturated,homogeneous, isotropic materials under steady-stateuniform flow is (38):

ac a2C aC (17)a t ax ax

where x is a curvilinear coordinate direction taken alongthe flowline, v is the average linear groundwater ve-locity, D, is the coefficient of hydrodynamic dispersionalong the x direction, C is the contaminant concentra-tion, and t is time. The coefficient of hydrodynamic dis-persion is of the form:

Dx= axl vl+DD (18)

where txx is the dispersivity, a characteristic propertyof the porous medium, and D* is the coefficient of mo-lecular diffusion. The term axj IVI expresses the me-chanical mixing component of the dispersion process,which is the result of velocity variations within the po-rous medium.The advection-dispersion equation is solved under

prescribed boundary conditions. For the followingboundary conditions:

C(x,O) = 0;

C(O,t) = co;

C(oo,t) = 0;

x >O

t > 0

t > 0

(19)

(20)

(21)

the solution to Eq. (18) for a saturated homogeneousporous medium is given by Ogata (53) as

Co =0.5 )fCIO 42

+ exp (Dx)(22)

erfc tJ]

where erfc represents the complementary error func-tion and all other terms are as previously defined.

Figure 13 illustrates the concentration profiles ob-tained with Eq. (22) and what is normally referred toas a breakthrough curve for contaminants migratingthrough a porous medium. The figure demonstrates theeffect of mechanical dispersion and molecular diffusion,namely that of causing some of the contaminants tomove faster and others to move slower than the averagelinear groundwater velocity. This causes a spreadingout of the concentration proffle along the direction offlow and to some extent in directions transverse to it.In the absence of dispersion and diffusion, the contam-inant front will move as plug flow, and its position alonga flow system will be entirely determined by the averagelinear groundwater velocity.

In the case of reactive contaminants, a sorption termis added to Eq. (22) to account for the transfer to orfrom the solids in the elemental volume. The advection-dispersion equation then takes the form (38):

ac Pbas a2c acat n+a-t =D2 a x (23)

where Pb is the bulk density of the porous medium, nis the porosity, and s is the mass of the chemical con-stituent adsorbed on the solid part ofthe porous mediumper unit mass of solids; as/at represents the rate at which

Contaminant Frontif Diffusion Only

a 1

o 05.0

U A0

Position ofGroundwater

Distance X

FIGURE 13. Schematic diagram showing the contribution of molec-ular diffusion and mechanical dispersion in causing spreading dur-ing contaminant migration (38).

56


the contaminant is adsorbed, and the term (pbjn) (as/at)represents the changes in concentration in the fluidphase caused by adsorption or desorption. If biochem-ical processes are ignored, the sorption term then de-pends only on ion exchange, precipitation and coprecip-itation.When a contaminant is adsorbed by a solid, it mi-

grates at a rate slower than if there was no adsorption.Assuming a fast and reversible adsorption-desorption(cation-exchange) process, and if the concentration ofthe adsorbed contaminant is small compared with thetotal concentration of cations in solution, the rate ofadvance of the contaminant front is given by (50):

v vPbKd (24)n

where Vc is the velocity of the adsorbed contaminantand Kd is the distribution coefficient. The terms in thedenominator are referred to as the retardation factor,which can be used to estimate how rapidly a contami-nant would migrate through the flow system. The effectof retardation on contaminant migration is schemati-cally shown in Figure 14. The contaminant front in thecase of the adsorbed species, A', moves at a muchslower rate than that of the nonadsorbed species, B+.An important implication of this condition is that com-pared with a nonadsorbed species, it will take a muchlonger time for the adsorbed contaminant species toreach and pollute a groundwater supply source, andhence is less of a threat or hazard to the environment.

UCs0

Time t1

Distance X(a)

Time t2 >tl

A \0

Distance X(b)

FIGURE 14. Schematic diagram showing the effect of retardation.The migration of an adsorbed species (A+); the position of non-adsorbed species (B + ) (50).

Field Application of Advection-DispersionEquationAn example of the application of the advection-dis-

persion equation in the solution of problems in contam-inant migration is provided by a field study carried outby Egboka et al. (41). In the study, an analytical solutionto the one-dimensional form of the advection-dispersionequation was used to simulate the distribution of tritium(a nonreactive species) produced during atmospherictesting and use of nuclear weapons along a contaminantplume under a landfill site in Borden, Ontario, Canada.Field values of radioactive bomb tritium were correctlysimulated by using longitudinal dispersivity values ofbetween 30 and 60 m and groundwater velocity valuesof about 10 m/year (Fig. 15). These aquifer parameterswere used to predict the movement, spread, and dis-persion of contaminants in the polluted groundwatersuch as sulfate (Fig. 16), chloride, etc. While Egbokaet al. (41) investigated dispersion of contaminants in-troduced into the hydrogeologic system under naturalconditions, Sudicky et al. (54) introduced artificialtracers into the same area and arrived at similar resultsusable for the planning and management of landfills andgarbage dumps.

28011_ 24

20

gj 16

(. 12E a

i 4

Velocity=12.5m yr-'00 <><\ | ~~~~~19533H Plug Flow Front

30 -

40 Detection Limit

0040 80120160200240280320 36400440480520560004

Distance Along Pollutant Plume Path (Meters)

FIGURE 15. Simulated bomb 3H versus distance in a landfill aquiferusing varied velocities and longitudinal dispersivities (41).

1-E.E

StE

57

EGBOKA ET AL.

Pollution Situation in Developedand Developing CountriesAs a result of the ever-increasing industrial estab-

lishments and man's general activities, physical, chem-ical, and biological substances are being fed into thegroundwater environment on a daily basis. This sectionsummarizes the pollution situation in both developedand developing countries. Emphasis is focused on thedeveloping countries.

Developed CountriesGroundwater literature is filled with incidences of

groundwater pollution in many parts of the developedcountries including the United States, Canada, USSR,and various parts of Europe. Table 6 presents a sum-mary of groundwater contamination incidents in partsof the United States as reported by Lindorff (55). Thenumber and percentage of incidents affecting or threat-ening groundwater supplies is shown in the second col-umn. The third column shows the number and per-centage of the cases that threatened or produced firesor explosions.

Table 6. Summary of groundwater contamination incidents (46).

ContaminantIndustrial wastesLandfill leachatePetroleum productsOrganic wastesChloridesRadioactive wastesPesticidesFertilizerMine drainage

No. ofincidents50462721167433173

Watersupplies, %31 (62)7 (15)

18 (57)15 (71)13 (81)2 (29)2 (50)3 (100)1 (33)

92 (53)

Fire orexplosion, %2 (4)010 (37)00000012 (7)

The ever-increasing use of organic pesticides and her-bicides has constituted another source of groundwatercontamination. Various investigators in the southwest-ern United States have observed that pollution by pes-ticides must be listed as an important potential hazard.Croll (56) arrived at a similar conclusion on the basis ofa literature review and field studies in Kent, England.

In Canada, numerous cases of groundwater pollutionhave been reported. A comprehensive coverage of thesecases has been presented by Cherry (57). Shallowgroundwaters that have been contaminated by leach-ates from landfills include those that occur below threelarge landfills in the outskirts of the city of North Bayand near Alliston and Kitchenor-Waterloo in Ontario.Severe groundwater contamination from chlorophenolshas been reported from Pentritton, British Columbia(57). Mine tailings are another major source of ground-water contamination in the mining districts of Canada.Extensive nitrate contamination of shallow aquifershave been observed in the Canadian prairies. This hasbeen attributed to the use of agricultural fertilizers.Similar widespread occurrence of nitrate has been re-ported in a large regional carbonate-rock aquifer in Eng-land and the United States.Leakages in nuclear power plants constitute another

source of groundwater contamination. This is becausethe radiation would eventually be returned to thegroundwater environment. Recent nuclear leakages in-clude the Chernobyl incident in the Soviet Union. Theimpact of these leakages on the groundwater environ-ment has, however, not been fully investigated. Nodoubt, a large number of cases of groundwater contam-ination have been reported. However, disposal sitesthat are known contamination sources probably accountfor only a small fraction of the total number of siteswhere groundwater contamination now occurs (57). Itshould, in addition, be expected that more severe cases

-I

aIcC..I

Unpolluted GroundwaterTritiated and Non-Tritiated (Low Sulfate)Groundwater Boundary -250- Conc. SO4-2 (mgl-')

100 50 0 lOOmVert. Exag = 10

FIGURE 16. Sulfate pollution of ground with tritiated tritium boundary (41).

58


of pollution could arise in the future as technology bringsnew and more hazardous chemical compounds into pro-duction and use. At the moment, great amounts of fi-nancial and material resources have been spent on thecontrol of pollution. Health and environmental hazardsposed by pollutants and contaminants are immense asmany pollution-related diseases continue to emerge.Great losses in human and animal life and property havecontinued. As the developed countries are engrossed inthese problems, it is unfortunate that the developingcountries are becoming equally affected because no ar-ticulated control programs exist to any extent.

Developing CountriesInformation on environmental pollution situations of

developed countries such as the United States, Canada,and parts of Europe abound in the hydrogeologic lit-erature (20,58-65). Acid rain has obliterated many an-cient forests, acidified both surface water and shallowgroundwaters, and defaced many buildings and monu-ments. Industrial wastes dumped as solids or dis-charged as liquids into surface waters have destroyedthe fauna and flora of these waters. Many landfills andsewage lagoons dotted all over these industrialized na-tions have damaged the hydrogeologic environments.Many medium-level and high-level wastes from nuclearindustries are stockpiled, waiting for safe disposal sitesyet to be located in any part of the world. These pol-lutant/contaminant materials and their attendant prob-lems have devoured huge funds for research and controlactivities. -Despite the available manpower and exper-tise and the adequate financial resources in these coun-tries, minimal successes in combating pollution havebeen achieved, so pollution threats so far seem to havedefied man's efforts.The fate of developed countries magnifies the help-

lessness of some developing countries that have nowexposed parts of their hydrogeologic environments topollution. Many of these countries in their race to be-come industrialized have accumulated waste productsthat now pollute the environment. Many of these coun-tries have copied the developed countries in their sci-ence and technology, packaged and acquired the re-sulting technological outputs, and transplanted theminto their countries without the necessary checks andbalances such as an appropriate adaptation to the needsof their environments. These countries produce hugevolumes of pollutants and contaminants from industriesand urban centers and dispose of them into surfacewaters or dump them at the outskirts of their cities.They do not have enough pollution management expertsand the necessary finances to control the spread of pol-lutants. Outbreaks of diseases that are pollution basedoccur from time to time. It is strongly believed thatunless these developing countries do something to stopthe present pollution trends that are fast growing, manyof their environments shall be worse off than those nowprevalent in parts ofthe developed world. Already somecountries are closely approaching this stage.

The specter of widescale pollution of environments ofdeveloping countries is becoming more threatening formany other reasons. More and more urban, suburban,and rural communities are being polluted or exposed topollution. Few of these countries have plans or man-agement programs to combat pollution. Pollution prob-lems are thus tolerated and given no priority. There islittle or no public or government awareness because thedangers seem to be ignored or overlooked. There areno Environmental Protection Laws and where avail-able, they are rarely enforced. When these poor coun-tries soon reach the level of pollutant/contaminant gen-eration as the rich industrialized countries, they shallbe much worse off. Already various health hazards andpolluted waters with waterborne diseases and epidem-ics ravage these countries from time to time. Eventhough it is known that many of these pollutants areproduced through industrialization and urbanization ac-tivities, governments, groups, and individuals have notbeen doing anything to control their emission or pro-duction. Even in rural environments where agricul-tural, mining, and urbanizing programs continue to gen-erate pollutants and contaminants, no one seems toshow much concern.Some developed countries, as a result of their stiff

Environmental Protection Laws, indirectly encouragethe export of waste products. This practice is eithercarried out directly because these materials cannot bedisposed of economically or safely in their home coun-tries or indirectly through establishment of industriesin developing countries. These industries produce haz-ardous wastes that are carelessly dumped or dis-charged. Such exported industries lack adequate safetydevices and efficient monitoring systems. Finally, in thedrinking water supply program, emphasis is placed onlyon water quantity and little or none on quality. Becauseof this emphasis water potability is questionable mostof the time. Typical pollution case examples from somedeveloping countries shall be given below to providemore credence to these unfortunate observations.

Environmental/Health Hazards andImplicationsVarious environmental problems can arise as a result

of groundwater pollution. A major consequence ofgroundwater pollution includes the potential contami-nation of surface waters. This can happen if the rivers,streams, or lakes in the area are recharged by a pollutedaquifer. The converse becomes the case if contaminatedsurface waters recharge an aquifer. These cases areillustrated in Figures 17a and 17b, respectively. Waterpollution can result in a reduction in economic and ag-ricultural activities. For example, when surface watersare contaminated, they can result in higher fish mor-tality. In third world countries, in particular, wherefishing on a subsistence level provides a means of live-lihood, a significant drop in fish productivity due to pol-lution can have unpleasant consequences on the eco-

59

EGBOKA ET AL.

Water Table

Aquifer

Confining Layer

FIGURE 17. A schematic diagram showing the potential for contam-ination of (a) surface waters when an aquifer is polluted and (b)contamination of groundwaters when surface waters are polluted.

nomic life of the community. Polluted irrigation waterposes health risks. It can also result in reduced cropproductivity. Thus, water pollution can have seriousnegative effects on the agricultural sector too.Other environmental hazards arising from water pol-

lution include the presence of odor and color in the af-fected water. Pollution of surface waters (lakes, dams,rivers) may affect groundwater adversely. Water sup-plies are contaminated resulting in health risks and in-creased load on water treatment plants; increased costson water treatment plants; fish kills or decline in pro-ductivity, quality and quantity; polluted irrigationwater, posing health risks or inhibiting crop productiv-ity; degradation of recreational and aesthetic charac-teristics of waters; etc. (1). Sometimes poisonous ions,dissolved gases, trace elements, heavy metals, and ra-

dioactive materials in water endanger the biosphericparts of the environments. Hence waterborne diseasesare of epidemic occurrence in many developing countrieswhere they form debilitating scourges to humans. Alsomajor physiological ailments such as cancer, that maysometimes be caused by water or food have becomerampant in both developed and developing countries.Many surface water and groundwater bodies are deadand remain anoxic as a result of heavy inputs of pollu-tants and contaminants. Many pollutants from one

source can move for long distances through ground-water flow systems to polluted faraway areas, precip-itating large-scale environmental destruction. Somehigh-level wastes have pollutants and contaminants

with long half-lives. Because of this property, they re-main hazardous for long times within the hydrogeologicenvironment and are very difficult to remove.

In the hydrogeomicrobiologic literature, cases of mi-crobial pollution and hazards abound that are a threatto both surface water and groundwater systems. Undercertain circumstances, the pathogenic microorganismslisted in Table 3 escape the purification processes ac-companying percolation of polluted surface waters intogroundwaters where they constitute a dangerous healthhazard. Salmonellosis, bacillary dysentery, schistoso-miasis, helminthiasis, and viral infections are known tohave been transmitted through drinking groundwaterspolluted by surface waters and sewage in this way (66).Public interest in nitrogen oxides arises from the toxiceffects of nitrite when nitrite ions enter the bloodstream and react with hemoglobin, leading to an im-pairment of oxygen transport, particularly in infants.The disease is almost always attributable to high levelsof nitrates in drinking water supplies including pollutedgroundwaters (23,31,35). Under certain conditions ni-trate may be reduced to ammonia by some of the nitratereducers. The ammonia can react with chlorine to pro-duce chloramines, which can lead to undesirable tastesand odors. The presence of sulfides produced by sulfatesreducers in groundwaters also impart unacceptabletastes and odors. Iron bacteria have caused problemsin water supplies since the dawn of civilization, andthere are many references in history to "red" water,undrinkable water covered with slime, and pluggedwells (67).

In wells and boreholes, the major problems are a)growths that plug the screens; b) coatings on pipingsystems, impellers and motors, that reduce flow rates;c) reduced potability of water; and d) total plugging ofthe well. The iron and manganese bacteria that causethese problems are thought to be introduced into thewells and boreholes from their soil habitat during initialboring operations or by seepage into the aquifer feedingthe well (68).Groundwaters drawn from wells and boreholes con-

stitute a major source of water supply in many Africancountries including Nigeria. In these circumstances, thewater is usually untreated. The inadequate practices ofwaste disposal in these countries lend themselves asbeing a large source of pollution for groundwaters.

In Nigeria, feces are disposed of by one or more ofthe following ways, depending on the locality: disposalon ordinary dry ground, bucket latrines, the pit-latrineor pit-privy, and septic tank latrine (aqua privy). Do-mestic and industrial wastes are disposed of either bycomposting, sewage, or open drainage systems (66). Thecontent of these waste products are usually organic andinorganic matter as well as microorganisms, some ofwhich are pathogenic. Some of the wastes in refuse tipsare washed into surface waters leading to eutrophica-tion. In most circumstances in Nigeria, parts of Lagos,Ibadan, Benin, Enugu, Onitsha, Kaduna, Kano, Jos,Abakaliki, etc., adequate hydrological data are notsought on soil strata and the direction and rate of flow

60


of groundwaters before wells are sunk (37). The resultis that sometimes wells are sunk less than 5 m awayfrom obvious sources of pollution like pit latrines (69,70).Worse still, the wells are usually not lined at all, withthe result that the groundwaters easily get contami-nated by seepage from pollute surface waters.

Cases of guinea worm infestation in parts of Ilorinand Abakaliki have continually been linked to the drink-ing of groundwaters contaminated by heavily pollutedsurface waters. The outbreak of cholera in Ohaozaraarea of Nigeria in 1981-1984 was also linked to poorlysited wells in the area (25). It is obvious that, if sys-tematically investigated, most outbreaks of waterbornediseases could be linked to pollution of groundwatersfrom surface waters, septic tanks, pit latrines, and com-post heaps. It is in recognition of this danger that theFederal and State governments of Nigeria as well asmany international organizations like the WHO andUNICEF are currently tackling health problems in Ni-geria by the provision of properly sited boreholes in allthe rural communities.

In 1977 the Food and Drug Administration Unit ofthe Federal Ministry of Health in Kaduna Nigeria (25)reported a widespread occurrence of iron bacteria in upto 60% of the boreholes in the Funtua, Bida, Malum-fashi, Dutsi-ma, Daura, Katsina, and Kano areas (23).Except in the Kano areas, the genera of iron bacteriaencountered were Siderocapse and Siderococcus. Thesemicrobial pollutants have caused many groundwatersupplies problems, resulting in loss of well yields, watercontamination, and increased costs of water supplies.These problems are worsened by the absence of contin-uous monitoring programs.

In the Kano area, the filamentous iron bacteria Lep-tothrix and Crenothrix were found abundantly in nearlyall the boreholes in the Bompai area, on the outskirtsof Kano municipality. The pollution was traced to themyriad of refuse tips made up of the waste productsfrom the sugar, sweets, and biscuit factories in Kano.The global distribution of iron bacterial problems ingroundwater was reported by Cullimore and McCann(67). Among the developing countries included in thedraft are El Salvador, Guyana, India, Malaya, Nigeria,Singapore, and Sri Lanka. Crenothrix was found to beplugging water supply systems in Sri Lanka; Clonothrixreduced flow rates and potability of water in the Cal-cutta area of India. In all others, the offensive ironbacteria were not specified, but the damage they causedwas observed.The industrialized world has accumulated great

amounts of pollutants and contaminants within theirenvironments. Many of these pollutants have spreadwidely and in such a complex manner that their controlwill be a most difficult and costly venture. Many wastesare now piled up in storage tanks above and below theground surface, while painstaking research efforts arebeing made to scout out possible safe geologic environ-ments for their disposal. Unfortunately, so far, as aresult of the structural, stratigraphic, sedimentological,and geotechnical properties of the pedologic and geo-

logic units, no safe disposal environments have yet beenfound for waste products that have long half-lives. Itseems that until a safe and more reliable disposalmethod is found, both the developed and developingcountries, have no option but to reduce the volume ofwastes both societies are now generating and abandon-ing or storing within hydrogeologic environments.

Pollution Case Examples fromSome Developing Countries

Parts of urban and rural environments of many de-veloping countries such as India, Kenya, Nigeria, Su-dan, Egypt, Iraq, and Brazil are being polluted with awide variety of hazardous substances. Such countriesare struggling to become industrialized without ade-quate plans to contain the spread and hazards of pol-lution. There are many sources of pollution in devel-oping countries. Some of those related to mining,mineralization, agricultural, domestic, municipal, hu-man, and animal wastes shall be discussed. Typical caseexamples shall also be briefly described, and these shallbe generally related and at some instances specific tosome developing countries that are now industrializingat a rapid rate.

Mining PollutionContamination of groundwater due to mining activity

is a major problem in many developing countries. Pre-vious or present mining activities result in contamina-tion from waste dumps, mine workings, fragments, anddust from ore and rock piles and smelter operations.Sulfides (usually pyrite, galena, and sphalerite) in minedumps are especially susceptible to oxidation and pro-duce acid mine waters that can be leached out in varyingvolumes and amounts. The ore minerals are not com-pletely recovered during the beneficiation processes.The acid mine waters that also contain trace metalsmake their way into groundwater flow systems.

Acid mine waters from an abandoned mine in theCharcas District, San Luis Potosi, resulted in high metalvalues in drainage systems and groundwaters (71). Theacid mine drainage problems in Enugu coal mines ofNigeria and their effects on groundwater pollution werehighlighted by Egboka and Uma (21). Many coal bedsmay contain up to 10% sulfur, chiefly in the form ofpyrite and marcasite. As the coal deposit is worked, airand water gain access to the seams that contain sulfurminerals, oxidizing the sulfide minerals. This results inthe formation of enormous amounts of sulfuric acid.Groundwater recharged by water from the mine needsconsiderable treatment with lime before it can be usedto supply domestic homes and industries. In the acidmine drainage problems in the Enugu coal mines ofNigeria, about 18.1 million liters of acid water with highiron content is pumped out daily into nearby rivers.Some of this acid water eventually enters groundwaterflow systems. The acid waters also attack and corrodemining equipment causing great financial losses. Some

61

EGBOKA ET AL.

mine waters are colored brown by tannins from bark oftrees. They have an objectionable taste and they renderthe water unfit for drinking. Sometimes the waters ac-tually are sterile enough for use even though they arecolored and may have a bad taste. Phenols are abundantin waters in coal swamps. Phenols are poisonous tomany bacteria and are capable of making mine waterssterile if they are present in large quantities.

In most developing countries there is no legislationguiding the safe disposal ofmine wastes and mine dumpsor their proper management. Most of the mining com-panies involved are mostly foreign firms. The companiesdo not show much interest in tackling environmentalpollution problems associated with the mining wastesthey produce annually. Little or no money is spent onwastes research and management in many parts of Ni-geria and other countries. The uneducated rural peopleoften use polluted waters discharged from mines. Manypeople from Abakaliki Mining district of AnambraState, Nigeria, suffer from lead poisoning resultingfrom the contamination of their water sources by lead.The area is also ravaged by guinea worm and otherwaterborne diseases.

Domestic, Municipal, Human, and AnimalWaste ContaminationDomestic wastes contribute a large number of ele-

ments to groundwater systems, all with unpleasantramifications. The most common contaminants fromhousehold products include phosphates and boron inlaundry detergents, copper and other elements as or-ganometallic compounds in garbage; metals in urine andexcreta; copper, lead, zinc, and asbestos from pipes;nickel from stainless-steel pipes and well casings. Mu-nicipalities that treat sewage and garbage reduce metalconcentration in drinking waters, but the recent ten-dency to dispose of the treated material on land even-tually yields metals to the drainage basin. Such metalsmay eventually reach the surface water and ground-water flow systems and pollute them. Similarly, metalsare introduced into the hydrogeologic environment fromthe resultant ashes when garbage or solid wastes arecomposted as is commonly done in developing countries.The tremendous increase in the use of septic tanks

for home sewage disposal has contributed a great dealof dissolved polluting materials to groundwater (Fig. 8).The septic tank waters seep into the soil and where

water supply aquifers are shallow, will contaminategroundwater with phosphate and boron from detergentsand a variety of other substances such as nitrates thatare undesirable or harmful to health. In many ruralcommunities in developing countries shallow pit latrinesare used for disposal of human exereta. Other undesir-able materials like expired drugs and unwanted chem-icals are also dumped into pit latrines or shallow water-ways. Human exereta collected in bucket toilets are alsoemptied into the pit latrines. Water infiltration into theground through the pit latrines introduces a number of

undesirable compounds into groundwaters (18,69,70,72).

In many cities all kinds of waste materials are strewnabout on the outskirts of towns or are thrown intostreams, lakes, and rivers as most of those cities orig-inated and developed close to major rivers. Aerosolcans, drug containers, hospitals, and research labora-tories, washings or wastewaters that may contain heavymetals such as mercury, lead, zinc, etc., may eventuallydecay or spread and become transported into ground-water flow domains. Underground and surface storagetanks, septic systems/fields, etc., washings from motormechanic sheds and garages produce contaminatingleachates (Fig. 7). These types ofpollutants have threat-ened hydrogeologic systems in parts of Nigeria(69,70,72). In some urban areas of developing countriessuch as India in temperate climates, large quantities ofroad salt (NaCl and CaCI) are used for deicing the roadin winter. Leachates from these activities will eventu-ally contaminate aquifers. Egboka (15) briefly describedthe traditional habit ofusing the bush for toilet purposesin many rural areas and suburban centers. It is believedthat defecation of this type contributes to widespreadand prevalent waterborne diseases in such areas. It alsoaccelerates large-scale incidences of eutrophication inlakes. Unfortunately, it is yet to be estimated the de-gree and extent of environmental pollution through def-ecation in the rural areas.

Agricultural ContaminationThe use of pesticides, herbicides, fertilizers, and

other materials to increase agricultural yields has somegreat negative effects on groundwater quality. Pesti-cides and herbicides applied to fields or orchards mayfind their way into groundwater when rain or irrigationwater leaches the dissolved constituents downward intothe soil. Nitrate from its fertilizer, one of the mostwidely used agricultural fertilizers, is harmful in drink-ing waters even in relatively small quantities. The ni-trate is very soluble and although some may be used byplants, much of the dissolved nitrate escapes unusedinto deeper parts of the soil and into groundwater. Sew-age and fertilizer can increase nitrate levels in someaquifers (4). Nitrate is toxic to humans even in amountsas small as 10 to 15 ppm.Uranium and fluorine in phosphate fertilizers and

probably rubidium in potash fertilizer are soluble undermost conditions and will eventually find their way intothe groundwater regimes. The use of lime for the pro-duction of fertilizer may result in lead and zinc contam-ination, if the lime is produced from metal-containinglimestones. Mississippi-type lead-zinc deposits are com-mon in limestones. Some limestone deposit used for pro-duction of lime may contain appreciable quantities oflead-zinc minerals.

In developing countries, the people and governmentsplace their priorities on food production in enough quan-tities to stem the tide of hunger and mass deprivationand little or no consideration is given to the pollution

62


implications. The poor farmers, most of whom practicesubsistence agriculture, are highly encouraged to applyfertilizer and use insecticides/herbicides for maximumcrop yields. The prices for these chemicals are very lowand affordable as the governments have subsidized thecosts. Thus, the chemicals may be used indiscrimi-nately. A large amount is released to the environmentto pollute surface water and shallow groundwaters. Thispractice is common in many developing countries.

Radioactive Contamination ofGroundwaterAnother source of groundwater contamination is ra-

dioactive wastes from power plants and mine dumps.One of the serious long-range problems associated withthe use of nuclear power plants is the disposal of highlyradioactive nuclear wastes. These highly toxic wastesare by-products of nuclear power plants and the man-ufacture of nuclear weapons. These radioactive wastesare temporarily stored as liquids in tanks. Despite thefact that the waste must be isolated from humans andother organisms for many centuries before it is safe, ithas not been possible to store the wastes for even a fewdecades without mishap. Several thousand gallons ofwaste do seep into groundwater from storage tanks be-fore anyone realizes there is a leak. Radioactive ma-terials in water even in very small amounts are harmfulto all forms of life. Some developing countries are be-lieved to have nuclear power.The problem of disposal of radioactive wastes is es-

pecially common in industrialized countries, but the dis-posal of radioactive wastes in uranium mines is a prob-lem that occurs more in developing countries. Somedeveloping countries are producers of uranium andother raw materials needed for nuclear power plants.In most of these countries, there are no regulationsgoverning the disposal of mine wastes. They aredumped around and abandoned by the operators in themine environment.Uranium is usually present in the tetravalent state

(U4+). In this valence state, uranium is not soluble, andis immobile. When exposed during mining and dumpedin mine waste, uranium is oxidized to the hexavalent(U6+) state occurring as uranyl ion (UO"+). Uraniumthen moves from an oxygen-rich surface environment,in which uranium is in the hexavalent state or com-plexed with carbonate into the subsurface groundwaterenvironment. The problem of contamination of ground-water in uranium mining areas by uranium and itsdaughter products in active and abandoned mines is asserious as those associated with nuclear wastes. In nu-clear power plants, adequate precautionary measuresare always taken in handling the radioactive wastes. Inuranium mining areas no such precautions are takenand the danger of contamination of groundwater by ra-dioactive materials leached from mine dumps is great.The problem is most serious in those developing coun-tries where the inhabitants of mining areas are notaware of the problems. When it is realized that some

developing countries have nuclear capabilities andhence are generating high-level radioactive wastes, itbecomes a matter of great concern to conjecture howthese wastes are being isolated from the biospheric en-vironment. So far, it is a top secret matter and thosefew developing countries that have nuclear capabilityhardly provide any information to the public.

Pollution/Contamination from NaturalSources

Pollution and contamination may come from naturalsources such as during physicochemical weathering andmass wasting, soil and gully erosion, flooding, snowfall,wind activities, and seawater intrusion through waveaction, volcanic or gas eruptions, geochemical evolutionthrough groundwater infiltration, and percolation. Alarge quantity of pollutants and contaminants are re-leased from these sources but it is very difficult to quan-tify and control release by natural processes. Duringweathering, geologic units are corroded, weathered,disintegrated, and disaggregated, thereby releasingdissolved geochemical constituents into the hydrogeo-logic systems. During sediment transport and deposi-tion, geochemical reactions (38,49) may result in therelease of more ions and dissolved gases that may be-come concentrated enough to be hazardous. In addition,soil and gully erosion (16,17) may remove volumes ofsediments with potential pollutants and contaminantsthat may threaten the environment. In some situationsdeep gullying that intersects the watertable and shaleyterrains may result in hydrogeomicrobiological reac-tions that may release deleterious pollutants intogroundwater (17).Snowmelt and rainfall and anthropogenic activities

such as farming, excavation, and mining accelerate thetransport of sediments and enhance their pollution po-tentials. Thus, in parts ofthe humid tropics, floodwatersare densely brownish in color, reflecting high sedimentloads. Wind activities in areas at the fringes of desertsalso transport sediments that pollute the environment.Nigeria, Chad, Sudan, Niger, and other countries thatare close to the Sahara Desert suffer from these prob-lems. These types of pollutants are very serious, par-ticularly in developing countries because there does notexist any plan to combat them. Some of these countriesmay not even recognize their existence or just ignorethem. Meanwhile the pollutants continue to ravage theirenvironments.

Case Examples: Review of Pollution/Contamination in Some DevelopingCountries

India has emerged as an industrial nation and a majorproducer of manufactured and agricultural productswithin the last 20 years. Because the population is largeand industrial activities are intense, large volumes ofgaseous, liquid, and solid wastes are continuously re-

63

EGBOKA ET AL.

leased into the environment. Surface waters and shal-low and deep groundwaters have been polluted in urbanand rural areas (73-75). Neighboring countries of Pak-istan and Bangladesh are equally polluted or threat-ened. The excessive withdrawal of groundwater in theSaurashtra area of India has resulted in sea-water in-trusion. Parts of the groundwater in Gujarat State aremineralized and polluted by high temperature waters.The groundwaters from the Khetri copper mines in Ra-jasthan, Mahakali coal field area of Maharashtra, andthe Panandhro lignite field pose geotechnical and pol-lution problems. Currently, as a result of tourist activ-ities, many ancient forest lands, hills, valleys, and evenmountains are being strewn with garbage thrown awayby tourists thereby polluting the environments.Kenya is a typical industrializing East African coun-

try producing varying degrees of pollution. Other neigh-boring countries of Uganda, Zimbabwe, Tanzania, Ma-lawi, and Botswana are not spared. In a water resourcesquality survey by Nair et al. (76) from 1286 boreholesfrom parts of Kenya, the majority of the samples(61.4%) have fluoride values above 1.0 ppm while 19.5%had above 5.0 ppm and sometimes in even greateramounts (76). Table 7 lists the summary of maximumfluoride levels taken from each province and in differentlocations in Kenya. The high fluoride areas coincidedwith volcanic rock areas. The high fluoride water causedextensive public health hazards such as deformity inchildren. In Malawi, localized pollution of groundwateraffects the quality adversely. Waters of up to 4000 to7000 ,umhos/cm of electrical conductivity occur. Highsulfate iron and magnesium concentrations are common(77). Foster et al. (78) reported serious nitrate and fecalpollution of shallow groundwaters in parts of Botswanathrough pit latrines.Many hydrogeologic environments in Nigeria are pol-

luted (10,15,18,19,22,69,70). Saline lakes and hotsprings occur (79,80). Coastal towns such as Lagos andPort Harcourt suffer from saltwater intrusions from theAtlantic ocean. Inland waters such as rivers (Kaduna,Niger, Anambra) and lakes (Chad, Agulu) have receivedpollutants in varying degrees. Industrial wastes are in-discriminately disposed of on land or into surfacewaters. Sewage is similarly disposed of. Mineralizedwaters attack and destroy borehole networks in theMaiduguri areas of northern Nigeria. The rural com-

Table 7. Maximum fluoride concentrations in Kenyan watersamples taken from each province (76).

Flouride concentration,Province District ppmNairobi 30.2Central Nurang'a 22.0Coast Taita Taveta 15.0Eastern Machakos 19.3Northeastern Wajir 38.2Nyanza Kisumu 10.4Rift Valley Nakuru 57.0Western Bungoma 7.1Nationally 57.0

munities are equally not spared as present attempts todevelop rural areas have introduced many pollutantsand contaminants into the environment. Soil and gullyerosion and flooding have become rampant and pollutesurface waters and groundwater. Outbreaks of water-borne disease such as cholera, yellow fever, dysentery,diarrhea, and Guineaworm occur periodically, resultingin fatalities. Mining companies in Jos, Abakaliki, En-ugu, Nkalagu, and the Port Harcourt areas pollute theenvironments without restraint. Flaring of gases andoil spills have contaminated surface waters and ground-waters (10). There is yet no effective legislation to checkthese problems.

In a geochemical study of the Otamiri and Aba riverwatershed in southeastern Nigeria by Nwankwor andOkpala (81), nitrate concentrations in the order of 100mg/L were found in the groundwater and surface watersystems of the Otamiri watershed. Nitrate loading ofthe waters in the Otamiri watershed were attributed tointensive use of fertilizer by various government-spon-sored agricultural establishments in the basin. Resultsfrom the Aba River, which drains the largely industrialcity of Aba, showed abnormally high concentrations ofCo + and gave values for pH that varied between 4.0and 6.5 (81).Egypt and the neighboring countries of Sudan and

Libya have polluted surface waters and groundwaters.Primary sources of pollution are industrial/sewagewastes, agricultural/irrigation activities, and saliniza-tion processes. Volumes of waste products are drainedinto the River Nile and eventually into the sea througha complex network of canals. Some of the irrigationwaters react with soil water/groundwater and with soilmaterials dissolving the soluble salts, salinizing the soil,and increasing the salt concentration in irrigation canalsand groundwaters (82).

Alexandria, with a population of about 3 million peo-ple, is the main industrial center and is burdened withpollutants and contaminants from many sources. Partsof Meryut Lake have been destroyed by sewage,thereby contaminating fish. According to Preul (82),groundwater levels in lower Egypt rose considerablywith the building of the Aswan dam in 1965. The re-gional rise in water levels of shallow aquifers com-pounded the problems of pollution spread through sub-surface disposal of wastewaters and irrigation water.Villages "are experiencing considerable difficulties withwastewater disposal due to subsurface saturation, highgroundwater, emerging surface pools of septic waters,gross groundwater pollution, deterioration of buildingsand structures due to moisture absorption, and otherrelated problems. A further complication in certainareas is the existence of a large irrigation canal whichusually carries a level of flow above the general eleva-tion of the village and therefore creates a hydraulicgradient of seepage through the dykes towards the vil-lage" (82).Even though the government of Egypt has environ-

mental protection laws, their enforcement, particularlyin the rural areas, needs to be encouraged. These rural

64


communities continue to be exposed to increasing soil,surface water and groundwater pollution.

Al-Jabari and Al-Ansari (83) described the dissolutionof geological outcrops and soils in Iraq. These are richwith calcium carbonate and gypsiferous deposits. Waterinputs from flood plains and valleys with organic mattercontents reaching up to 20%, high suspended sediments,inputs from springs (Table 8), and human activities pol-lute the environment. Their pollution potentials are en-hanced by erosion. Tremendous amounts of dust gen-erate fallouts from sediments in central Iraq at the rateof 2.1 cm/yr (83-85). The sediments contain pollutantsand contaminants in the form of carbonates (calcite,dolomite grains) quartz, feldspars, gypsum, chert, mus-covite, heavy minerals (pyroxenes, zircon, biotite, horn-blende, epidote, rutile, garnet, chlorite, staurolite andKyanite), and pyrites (83-85). The heavy minerals as-semblage in the outfalls have been correlated with theheavy mineral content of the Tigris and Euphrates Riv-ers flood plains and older dune deposits (Table 8). Sal-man et al. (84), in their investigation of bacterial densityin Tigris River within Bagdad, measured a high densityof coliform bacteria and Escherchia coli, suggestive offecal pollution from sewage disposal. The bacterial den-sity correlated well with high suspended sedimentloads, which are believed to transport the bacteria inwater. The high sediment concentration is acceleratedby anthropogenic activities such as dredging, swim-ming, and solid/liquid disposal on land and water.

Pollution of surface water and groundwater in thedeveloping countries of South America have also beenreported. Argentina, Brazil, Chile, Cuba, Nicaragua,etc., have been equally exposed. Brinkman (86) dis-cussed the hydrogeochemistry of groundwater re-sources in the central Amazonian area of Brazil. Ducloux(87) also treated the central zone of La Pampa Provinceof Argentina. Other countries in Africa such as Ghana,Zaire, Sudan, Mauritania, Ivory Coast, etc., have beenunduly exposed to the destructive hazards of environ-mental pollution (88,89).

Summary and SuggestionsAccording to Fano et al. (1), "it may be expected that

over the next decade the management of water quality

Table 8. Water discharge and solute concentration of springs onRiver Euphrates (83).

Average discharge, Average TDS,Spring no. L/sec ppm1 31102 24 32723 33784 3700 39275 4 30026 100 38807 26 279108 360 3662910 100 344511 366212 4 269013 29 3080

problems will be one of the outstanding issues relatingto the protection and conservation of the national stockof water in each country ... The rapid aggregation ofpopulation in major urban centers, the polarization ofindustries, and the heavy dependence of chemical prod-ucts, particularly in the agricultural sector, are leadingto a serious deterioration of water quality in developingcountries." Already parts of the environments of manyindustrialized nations are highly polluted. The problemsare being tackled with available manpower, expertise,and financial resources in these countries. Encouragingsuccesses are yet to be achieved, as the pollutants con-tinue to diffuse and disperse into the hydrogeologic en-vironment, and several tons of high-level wastes arepiling up in storage tanks while desperate efforts arebeing made to locate geologic formations for safe wastedisposal.

Unfortunately, in an obvious attempt by many de-veloping countries to industrialize and compete with thedeveloped nations, waste products are being generatedin large quantities. These countries have neither themanpower, expertise, nor the financial resources to con-trol or safely dispose of these deleterious wastes. As aresult, their environments are becoming heavily pol-luted at an alarming rate. The leadership of these coun-tries seem to lack the will or the serious understandingto recognize and mount a control program. Because ofthis, pollution continues to spread unabated with itsattendant hazards and problems. In the next 10 years,unless something is done quickly, pollution levels inmany developing countries' hydrogeologic environ-ments would have reached such destructive levels thatthey may become uncontrollable. Destruction of plants,animals, and humans through pollution-caused epidem-ics/diseases would have become commonplace as req-uisite funds and materials for their control may not beavailable.

Developing countries must now learn from the mis-takes of the developed nations vis-a-vis pollutants andcontaminants, to save their environments from pollutiondamages for future generations. Some of the followingpollution-control programs being pursued or imple-mented in many industrialized countries should be ofworldwide application. The present consciousness aboutthe hazards of pollutants and contaminants in developednations must be highly encouraged. Every effort mustbe made to reduce pollutant/contaminant loads into theenvironment through improvements in manufacturingtechniques that could recycle waste products. More ef-ficient techniques for the destruction of high-level pol-lutants and contaminants before they can reach the hy-drospheric zones should be found through moreresearch. Through more intense investigations, safe pe-dologic, and geologic formations for disposal of wastescan be located. The present careless dumping of wastesinto surface waters or the poorly engineered subsurfaceburial of wastes must be stopped. These practices havedamaged many hydrogeologic environments as thesematerials spread locally and regionally. The effects ofgeologic and pedologic structures and characteristics on

65

66 EGBOKA ET AL.

the dispersion of pollution must be recognized in orderto be able to apply the correct engineered control meth-ods.At the moment, there is a loose/poorly coordinated,

nonintegrated approach in the control of pollutants andcontaminants by various professionals involved in pol-lution research and control. Hydrogeologists, chemicalengineers, civil engineers, soil scientists, etc., do notseem to work together. The multidisciplinary and mul-tiobjective techniques are not appreciated by pollutioncontrol planners and managers, particularly in devel-oping countries. This unfortunate behavioral tendencymay result from poor training or professional pride andhence must be discarded. Professionals working in pol-lution control must appreciate the contributions of oth-ers to maximize their successes. This could be achievedby proper training through improved curricula in highereducation that exposes all trainees to the origin, life,spread, and hazards of pollution in the environment andthe need to develop appropriate coordinated integratedcontrol methods. Seminars, workshops, symposia, andshort courses should be organized to educate all profes-sionals, planners, and managers of pollution problems.Countries and international aid agencies should givethese the desired priority.The developed countries should assist developing

ones in controlling pollution. Manpower, expertise, andsome financial resources should be made available tothese poor countries to aid them in planning and man-agement of waste disposal programs. Industrial con-cerns in developing countries must now discard theirpolluting tendencies in many developing countries andcooperate in pollution control. Most of their industrialactivities exacerbate incidences of pollution. Environ-mental Pollution Control laws must be enacted by de-veloping countries to protect their environments. Suchlaws, when made, must also be effectively enforced.Egypt has established such laws and has been fairlysuccessful in enforcing them and achieving beneficialresults (1). Strong emphasis should be placed on publichealth and education programs and enlightenment.Even though pollution is becoming widespread in de-veloping countries, there is still a paucity of data andrecords, poor documentation and information ex-changes. Research centers and institutes devoted pri-marily to teaching and research on pollutants and con-taminants are still not given any priority. Suchinstitutions should be established urgently to work onthe various aspects of pollution with particular emphasison its genesis, spread, hazards, and control in relationto the geologic, hydrologic and hydrogeopollution cycles(Figs. 1, 4, and 5) (91).

Coordinated sampling and monitoring programs arerequired by zones, nations, and regions to check wide-spread/regional pollution. Hence, local, international,and regional pollution events should be traced and mon-itored on a continuous basis and warning signals againsthazards issued to areas affected. Information exchangesshould be encouraged between nations, among experts/professionals, governments, and aid-giving agencies.

Research programs in both developed and developingcountries must give attention to sources and types ofpollution, modes of occurrence and spread, dynamics oftransport and dispersion, pollutants-life-expectancy,and means of disposal of wastes. Development of effec-tive control technology should be continuously and ade-quately funded.

The authors are grateful to The Anambra State University of Tech-nology, Nigeria and Federal University of Technology, Owerri, fortheir moral and financial support; Dr. K. 0. Uma, Dr. I. C. I. Okafor,and G. Onwuemesi for their various contributions; C. Nwokolo, Emer-itus Professor of Internal Medicine, University of Nigeria TeachingHospital, Enugu, Nigeria, for his fatherly and academic encourage-ments; and Bessie Nri for typing the manuscript.

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