Ground Water Contamination: Magnificient Ground Water Connection

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round water contamination is nearlyalways the result of human activity. In

areas where population density is high and humanuse of the land is intensive, ground water is espe-cially vulnerable. Virtually any activity wherebychemicals or wastes may be released to the envi-ronment, either intentionally or accidentally, hasthe potential to pollute ground water. Whenground water becomes contaminated, it is difficultand expensive to clean up.

To begin to address pollution prevention or reme-diation, we must understand how surface watersand ground waters interrelate. Ground water andsurface water are interconnected and can be fullyunderstood and intelligently managed only whenthat fact is acknowledged. If there is a water sup-ply well near a source of contamination, that wellruns the risk of becoming contaminated. If there isa nearby river or stream, that water body mayalso become pollutedby the ground water.

HOW DOESGROUND WATERBECOMECONTAMINATED?Depending on itsphysical, chemical,and biological prop-erties, a contaminantthat has been releasedinto the environmentmay move within anaquifer in the samemanner that groundwater moves. (Somecontaminants,because of their phys-

ical or chemical properties, do not always followground water flow.) It is possible to predict, tosome degree, the transport within an aquifer ofthose substances that move along with groundwater flow. For example, both water and certaincontaminants flow in the direction of the topogra-phy from recharge areas to discharge areas. Soilsthat are porous and permeable tend to transmitwater and certain types of contaminants with rela-tive ease to an aquifer below.

Just as ground water generally moves slowly, sodo contaminants in ground water. Because of thisslow movement, contaminants tend to remainconcentrated in the form of a plume (see Figure 1)that flows along the same path as the groundwater. The size and speed of the plume depend onthe amount and type of contaminant, its solubilityand density, and the velocity of the surroundingground water.

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Direction of Ground Water Flow

Figure 1 CONTAMINANT PLUME

Ground water and contaminants can move rapidlythrough fractures in rocks. Fractured rock pre-sents a unique problem in locating and controllingcontaminants because the fractures are generallyrandomly spaced and do not follow the contoursof the land surface or the hydraulic gradient.Contaminants can also move into the groundwater system through macropores—root systems,animal burrows, abandoned wells, and other sys-tems of holes and cracks that supply pathways forcontaminants.

In areas surrounding pumping wells, the potentialfor contamination increases because water fromthe zone of contribution, a land area larger thanthe original recharge area, is drawn into the welland the surrounding aquifer. Some drinking waterwells actually draw water from nearby streams,lakes, or rivers. Contaminants present in thesesurface waters can contribute contamination tothe ground water system. Some wells rely on arti-ficial recharge to increase the amount of waterinfiltrating an aquifer, often using water fromstorm runoff, irrigation, industrial processes, ortreated sewage. In several cases, this practice hasresulted in increased concentrations of nitrates,metals, microbes, or synthetic chemicals in thewater.

Under certain conditions, pumping can also causethe ground water (and associated contaminants)from another aquifer to enter the one beingpumped. This phenomenon is called interaquiferleakage. Thus, properly identifying and protectingthe areas affected by well pumping is important tomaintain ground water quality.

Generally, the greater the distance between asource of contamination and a ground watersource, the more likely that natural processes willreduce the impacts of contamination. Processessuch as oxidation, biological degradation (whichsometimes renders contaminants less toxic), andadsorption (binding of materials to soil particles)may take place in the soil layers of the unsaturat-ed zone and reduce the concentration of a con-taminant before it reaches ground water. Even

contaminants that reach ground water directly,without passing through the unsaturated zone,can become less concentrated by dilution (mixing)with the ground water. However, because groundwater usually moves slowly, contaminants general-ly undergo less dilution than when in surfacewater.

SOURCES OF GROUND WATERCONTAMINATION

Ground water can become contaminated fromnatural sources or numerous types of humanactivities. (See Tables 1 and 2 and Figure 1.)Residential, municipal, commercial, industrial,and agricultural activities can all affect groundwater quality. Contaminants may reach groundwater from activities on the land surface, such asreleases or spills from stored industrial wastes;from sources below the land surface but above thewater table, such as septic systems or leakingunderground petroleum storage systems; fromstructures beneath the water table, such as wells;or from contaminated recharge water.

■ Natural SourcesSome substances found naturally in rocks or soils,such as iron, manganese, arsenic, chlorides, fluo-rides, sulfates, or radionuclides, can become dis-solved in ground water. Other naturally occurringsubstances, such as decaying organic matter, canmove in ground water as particles. Whether anyof these substances appears in ground waterdepends on local conditions. Some substances maypose a health threat if consumed in excessivequantities; others may produce an undesirableodor, taste, or color. Ground water that containsunacceptable concentrations of these substances isnot used for drinking water or other domesticwater uses unless it is treated to remove these con-taminants.

■ Septic SystemsOne of the main causes of ground water contami-nation in the United States is the effluent (out-flow) from septic tanks, cesspools, and privies.

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Getting Up to Speed: ground water contamination

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Approximately one-fourth of all homes in theUnited States rely on septic systems to dispose oftheir human wastes. Although each individual sys-tem releases a relatively small amount of wasteinto the ground, the large number and widespreaduse of these systems makes them a serious conta-mination source. Septic systems that are improper-ly sited, designed, constructed, or maintained cancontaminate ground water with bacteria, viruses,nitrates, detergents, oils, and chemicals. Alongwith these contaminants are the commerciallyavailable septic system cleaners containing syn-

thetic organic chemicals (such as 1,1,1-trichloroethane or methylene chloride). Thesecleaners can contaminate water supply wells andinterfere with natural decomposition processes inseptic systems.

Most, if not all, state and local regulations requirespecific separation distances between septic sys-tems and drinking water wells. In addition, com-puter models have been developed to calculatesuitable distances and densities.


TYPICAL SOURCES OF POTENTIAL GROUND WATER CONTAMINATION BY LAND USE CATEGORYTable 1

■ Improper Disposal of Hazardous WasteHazardous waste should always be disposed ofproperly, that is to say, by a licensed hazardouswaste handler or through municipal hazardouswaste collection days. Many chemicals should notbe disposed of in household septic systems,including oils (e.g., cooking, motor), lawn andgarden chemicals, paints and paint thinners, disin-fectants, medicines, photographic chemicals, andswimming pool chemicals. Similarly, many sub-stances used in industrial processes should not bedisposed of in drains at the workplace becausethey could contaminate a drinking water source.Companies should train employees in the properuse and disposal of all chemicals used on site. Themany different types and the large quantities ofchemicals used at industrial locations make properdisposal of wastes especially important for groundwater protection.

■ Releases and Spills from StoredChemicals and Petroleum Products

Underground and aboveground storage tanks arecommonly used to store petroleum products andother chemical substances. For example, manyhomes have underground heating oil tanks. Manybusinesses and municipal highway departmentsalso store gasoline, diesel fuel, fuel oil, or chemi-cals in on-site tanks. Industries use storage tanksto hold chemicals used in industrial processes orto store hazardous wastes for pickup by a licensedhauler. Approximately 4 million undergroundstorage tanks exist in the United States and, overthe years, the contents of many of these tankshave leaked and spilled into the environment.

If an underground storage tank develops a leak,which commonly occurs as the tank ages and cor-rodes, its contents can migrate through the soiland reach the ground water. Tanks that meet fed-eral/state standards for new and upgraded systemsare less likely to fail, but they are not foolproof.Abandoned underground tanks pose anotherproblem because their location is often unknown.Aboveground storage tanks can also pose a threatto ground water if a spill or leak occurs and ade-quate barriers are not in place.

Improper chemical storage, sloppy materials han-dling, and poor-quality containers can be majorthreats to ground water. Tanker trucks and traincars pose another chemical storage hazard. Eachyear, approximately 16,000 chemical spills occurfrom trucks, trains, and storage tanks, often whenmaterials are being transferred. At the site of anaccidental spill, the chemicals are often dilutedwith water and then washed into the soil, increas-ing the possibility of ground water contamination.

■ LandfillsSolid waste is disposed of in thousands of munici-pal and industrial landfills throughout the coun-try. Chemicals that should be disposed of in haz-ardous waste landfills sometimes end up in munic-ipal landfills. In addition, the disposal of manyhousehold wastes is not regulated.

Once in the landfill, chemicals can leach into theground water by means of precipitation and sur-face runoff. New landfills are required to haveclay or synthetic liners and leachate (liquid from alandfill containing contaminants) collection sys-tems to protect ground water. Most older land-fills, however, do not have these safeguards. Olderlandfills were often sited over aquifers or close tosurface waters and in permeable soils with shal-low water tables, enhancing the potential forleachate to contaminate ground water. Closedlandfills can continue to pose a ground water con-tamination threat if they are not capped with animpermeable material (such as clay) before closureto prevent the leaching of contaminants by precip-itation.

■ Surface ImpoundmentsSurface impoundments are relatively shallowponds or lagoons used by industries and munici-palities to store, treat, and dispose of liquidwastes. As many as 180,000 surface impound-ments exist in the United States. Like landfills,new surface impoundment facilities are requiredto have liners, but even these liners sometimesleak.

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POTENTIAL HARMFUL COMPONENTS OF COMMON HOUSEHOLD PRODUCTSTable 2

■ Sewers and Other PipelinesSewer pipes carrying wastes sometimes leak fluidsinto the surrounding soil and ground water.Sewage consists of organic matter, inorganic salts,heavy metals, bacteria, viruses, and nitrogen.Other pipelines carrying industrial chemicals andoil brine have also been known to leak, especiallywhen the materials transported through the pipesare corrosive.

■ Pesticide and Fertilizer UseMillions of tons of fertilizers and pesticides (e.g.,herbicides, insecticides, rodenticides, fungicides,avicides) are used annually in the United States forcrop production. In addition to farmers, home-owners, businesses (e.g., golf courses), utilities,and municipalities use these chemicals. A numberof these pesticides and fertilizers (some highlytoxic) have entered and contaminated groundwater following normal, registered use. Some pes-ticides remain in soil and water for many monthsto many years. Another potential source ofground water contamination is animal wastes thatpercolate into the ground from farm feedlots.Feedlots should be properly sited and wastesshould be removed at regular intervals.

Between 1985 and 1992, EPA’s Office ofPesticides and Toxic Substances and Office ofWater conducted a National Pesticide Survey todetermine the number of drinking water wellsnationwide that contain pesticides and nitratesand the concentration of these substances. Thesurvey also analyzed the factors associated withcontamination of drinking water wells by pesti-cides and nitrates. The survey, which includedsamples from more than 1,300 public communityand rural domestic water supply wells, found thatapproximately 3.6 percent of the wells containedconcentrations of nitrates above the federal maxi-mum contaminant level, and that over half of thewells contained nitrates above the survey’s mini-mum reporting limit for nitrate (0.15 mg/L).

The survey also reported that approximately 0.8percent of the wells tested contained pesticides at

levels higher than federal maximum contaminantlevels or health advisory levels. Only 10 percent ofthe wells classified as rural were actually locatedon farms. There is a higher incidence of contami-nation by agricultural chemicals in farm wellsused for drinking water.

After further analysis, EPA estimated that for thewells that contain pesticides, a significant percent-age probably contain chemical concentrations thatexceed the federal health-based limits (e.g., maxi-mum contaminant levels or health advisory levels).Approximately 14.6 percent of the wells testedcontained levels of one or more pesticides abovethe minimum reporting limit set in the survey. Themost common pesticides found were atrazine andmetabolites (breakdown products) of dimethyltetrachloroterephthalate (DCPA, commonly knownas Dacthal), which is used in many utility easementweed-control programs and for lawn care.

■ Drainage WellsDrainage wells are used in wet areas to help drainwater and transport it to deeper soils. These wellsmay contain agricultural chemicals and bacteria.

■ Injection Wells/Floor DrainsInjection wells are used to collect storm waterrunoff, collect spilled liquids, dispose of waste-water, and dispose of industrial, commercial, andutility wastes. These wells are regulated by the U.S.EPA’s Underground Injection Control Program. InNew England, these wells may not be used to injecthazardous wastes from industrial, commercial, andutility operations. The injection wells used in thisregion are typically shallow and include sumps anddry wells used to handle storm water.

Floor drains were historically used by businessesto handle spills. Today, if a business operates orhandles waste fluids that drain to a septic system,dry well, or floor drain, it is required to submitinformation regarding its operation to the U.S.EPA or its state environmental protection agency.Disposal wells that pose threats to drinking watersupplies are prohibited and must be closed, con-

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nected to a public sewage system, or connected toa storage tank.

■ Improperly Constructed WellsProblems associated with improperly constructedwells can result in ground water contaminationwhen contaminated surface or ground water isintroduced into the well.

■ Improperly Abandoned WellsThese wells can act as a conduit through whichcontaminants can reach an aquifer if the well cas-ing has been removed, as is often done, or if thecasing is corroded. In addition, some people useabandoned wells to dispose of wastes such as usedmotor oil. These wells may reach into an aquiferthat serves drinking supply wells. Abandonedexploratory wells (e.g., for gas, oil, or coal) or testhole wells are usually uncovered and are also apotential conduit for contaminants.

■ Active Drinking Water Supply WellsPoorly constructed wells can result in groundwater contamination. Construction problems,such as faulty casings, inadequate covers, or lackof concrete pads, allow outside water and anyaccompanying contaminants to flow into the well.Sources of such contaminants can be surfacerunoff or wastes from farm animals or septic sys-tems. Contaminated fill packed around a well canalso degrade well water quality. Well constructionproblems are more likely to occur in older wellsthat were in place prior to the establishment ofwell construction standards and in domestic andlivestock wells.

■ Poorly Constructed Irrigation WellsThese wells can allow contaminants to enterground water. Often pesticides and fertilizers areapplied in the immediate vicinity of wells on agri-cultural land.

■ Mining ActivitiesActive and abandoned mines can contribute toground water contamination. Precipitation canleach soluble minerals from the mine wastes

(known as spoils or tailings) into the groundwater below. These wastes often contain metals,acid, minerals, and sulfides. Abandoned mines areoften used as wells and waste pits, sometimessimultaneously. In addition, mines are sometimespumped to keep them dry; the pumping can causean upward migration of contaminated groundwater, which may be intercepted by a well.

EFFECTS OF GROUND WATERCONTAMINATION

Contamination of ground water can result in poordrinking water quality, loss of water supply,degraded surface water systems, high cleanupcosts, high costs for alternative water supplies,and/or potential health problems.

The consequences of contaminated ground wateror degraded surface water are often serious. Forexample, estuaries that have been impacted byhigh nitrogen from ground water sources havelost critical shellfish habitats. In terms of watersupply, in some instances, ground water contami-nation is so severe that the water supply must beabandoned as a source of drinking water. In othercases, the ground water can be cleaned up andused again, if the contamination is not too severeand if the municipality is willing to spend a gooddeal of money. Follow-up water quality monitor-ing is often required for many years.

Because ground water generally moves slowly,contamination often remains undetected for longperiods of time. This makes cleanup of a contami-nated water supply difficult, if not impossible. If acleanup is undertaken, it can cost thousands tomillions of dollars.

Once the contaminant source has been controlledor removed, the contaminated ground water canbe treated in one of several ways:

• Containing the contaminant to preventmigration.

• Pumping the water, treating it, and return-ing it to the aquifer.


• Leaving the ground water in place andtreating either the water or the contami-nant.

• Allowing the contaminant to attenuate(reduce) naturally (with monitoring), fol-lowing the implementation of an appropri-ate source control.

Selection of the appropriate remedial technologyis based on site-specific factors and often takesinto account cleanup goals based on potential riskthat are protective of human health and the envi-ronment. The technology selected is one that willachieve those cleanup goals. Different technolo-gies are effective for different types of contami-nants, and several technologies are often com-bined to achieve effective treatment. The effective-ness of treatment depends in part on local hydro-geological conditions, which must be evaluatedprior to selecting a treatment option.

Given the difficulty and high costs of cleaning upa contaminated aquifer, some communities chooseto abandon existing wells and use other watersources, if available. Using alternative supplies isprobably more expensive than obtaining drinkingwater from the original source. A temporary andexpensive solution is to purchase bottled water,but it is not a realistic long-term solution for acommunity’s drinking water supply problem. Acommunity might decide to install new wells in adifferent area of the aquifer. In this case, appropri-ate siting and monitoring of the new wells arecritical to ensure that contaminants do not moveinto the new water supplies.

Potential Health ProblemsA number of microorganisms and thousands ofsynthetic chemicals have the potential to contami-nate ground water. Drinking water containingbacteria and viruses can result in illnesses such ashepatitis, cholera, or giardiasis. Methemo-globinemia or “blue baby syndrome,” an illnessaffecting infants, can be caused by drinking waterthat is high in nitrates. Benzene, a component of

gasoline, is a known human carcinogen. The seri-ous health effects of lead are well known—learn-ing disabilities in children; nerve, kidney, and liverproblems; and pregnancy risks. Concentrations indrinking water of these and other substances areregulated by federal and state laws. Hundreds ofother chemicals, however, are not yet regulated,and many of their health effects are unknown ornot well understood. Preventing contaminantsfrom reaching the ground water is the best way toreduce the health risks associated with poordrinking water quality.

REGULATIONS TO PROTECTGROUND WATER

Several federal laws help protect ground waterquality. The Safe Drinking Water Act (SDWA)established three drinking water source protectionprograms: the Wellhead Protection Program, SoleSource Aquifer Program, and the Source WaterAssessment Program. It also called for regulationof the use of underground injection wells forwaste disposal and provided EPA and the stateswith the authority to ensure that drinking watersupplied by public water systems meets minimumhealth standards. The Clean Water Act regulatesground water that is shown to have a connectionwith surface water. It sets standards for allowablepollutant discharges to surface water. TheResource Conservation and Recovery Act (RCRA)regulates treatment, storage, and disposal of haz-ardous and nonhazardous wastes. TheComprehensive Environmental Response,Compensation, and Liability Act (CERCLA, orSuperfund) authorizes the government to clean upcontamination or sources of potential contamina-tion from hazardous waste sites or chemical spills,including those that threaten drinking water sup-plies. CERCLA includes a “community right-to-know” provision. The Federal Insecticide,Fungicide, and Rodenticide Act (FIFRA) regulatespesticide use. The Toxic Substances Control Act(TSCA) regulates manufactured chemicals.

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KEY TERMS

• Clean Water Act

• Comprehensive EnvironmentalResponse, Compensation, and LiabilityAct (CERCLA, or Superfund)

• Federal Insecticide, Fungicide, andRodenticide Act (FIFRA)

• Interaquifer Leakage

• Plume

• Resource Conservation and RecoveryAct (RCRA)

• Safe Drinking Water Act

• Toxic Substances Control Act (TSCA)

• Zone of Contribution

“Getting Up to Speed” for section C,“Ground Water Contamination” is adapted from US EPA Seminar Publication. Wellhead Protection: A Guide forSmall Communities. Chapter 3. EPA/625/R-93/002.

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Ground Water Contamination: Magnificient Ground Water Connection