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Ground Water Contamination G - US EPA

C 1 round Water Contamination is nearlyalways the result of human activity. Inareas 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 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 on itsphysical, chemical,and biological prop-erties, a contaminantthat has been releasedinto the environmentmay move within anaquifer in the samemanner that groundwater moves.

Ground water and contaminants can move rapidly through fractures in rocks. Fractured rock pre-sents a unique problem in locating and controlling

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Transcription of Ground Water Contamination G - US EPA

1 C 1 round Water Contamination is nearlyalways the result of human activity. Inareas 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 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 on itsphysical, chemical,and biological prop-erties, a contaminantthat has been releasedinto the environmentmay move within anaquifer in the samemanner that groundwater moves.

2 (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 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 . Ground WaterContaminationGG Water TableDirection of Ground Water FlowFigure 1 CONTAMINANTPLUMEG round Water and contaminants can move rapidlythrough fractures in rocks.

3 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 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 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.

4 In several cases, this practice hasresulted in increased concentrations of nitrates,metals, microbes, or synthetic chemicals in 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 , 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 .

5 Evencontaminants 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 OFGROUNDWATERCONTAMINATIONG round 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 .

6 NNatural 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 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. C 2 Getting Up to Speed: Ground Water Contamination C 3 Approximately one-fourth of all homes in theUnited States rely on septic systems to dispose oftheir human wastes.

7 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 Up to Speed: Ground Water contaminationTYPICALSOURCES OFPOTENTIALGROUNDWATERCONTAMINATION BYLANDUSECATEGORYT able 1nImproper 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.

8 Many chemicals should notbe disposed of in household septic systems,including oils ( , 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 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 and Spills from StoredChemicals and Petroleum ProductsUnderground 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.

9 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 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 underground tanks pose anotherproblem because their location is often storage tanks can also pose a threatto Ground Water if a spill or leak occurs and ade-quate barriers are not in 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.

10 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 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.


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