Ground Water Contamination
round water contamination is nearly ical or chemical properties, do not always follow GG always the result of human activity. In ground water flow.) It is possible to predict, to areas where population density is high and human some degree, the transport within an aquifer of use of the land is intensive, ground water is espe- those substances that move along with ground cially vulnerable. Virtually any activity whereby water flow. For example, both water and certain chemicals or wastes may be released to the envi- contaminants flow in the direction of the topogra- ronment, either intentionally or accidentally, has phy from recharge areas to discharge areas. Soils the potential to pollute ground water. When that are porous and permeable tend to transmit ground water becomes contaminated, it is difficult water and certain types of contaminants with rela- and expensive to clean up. tive ease to an aquifer below.
To begin to address pollution prevention or reme- Just as ground water generally moves slowly, so diation, we must understand how surface waters do contaminants in ground water. Because of this and ground waters interrelate. Ground water and slow movement, contaminants tend to remain surface water are interconnected and can be fully concentrated in the form of a plume (see Figure 1) understood and intelligently managed only when that flows along the same path as the ground that fact is acknowledged. If there is a water sup- water. The size and speed of the plume depend on ply well near a source of contamination, that well the amount and type of contaminant, its solubility runs the risk of becoming contaminated. If there is and density, and the velocity of the surrounding a nearby river or stream, that water body may ground water. also become polluted by the ground water. Figure 1 CONTAMINANT PLUME
HOW DOES GROUND WATER BECOME CONTAMINATED? Depending on its physical, chemical, and biological prop- erties, a contaminant
that has been released Water Table into the environment may move within an
aquifer in the same manner that ground Direction of Ground Water Flow water moves. (Some contaminants, because of their phys-
C•1• ➤ Getting Up to Speed: ground water contamination
Ground water and contaminants can move rapidly contaminants that reach ground water directly, through fractures in rocks. Fractured rock pre- without passing through the unsaturated zone, sents a unique problem in locating and controlling can become less concentrated by dilution (mixing) contaminants because the fractures are generally with the ground water. However, because ground randomly spaced and do not follow the contours water usually moves slowly, contaminants general- of the land surface or the hydraulic gradient. ly undergo less dilution than when in surface Contaminants can also move into the ground water. water system through macropores—root systems, animal burrows, abandoned wells, and other sys- SOURCES OF GROUND WATER tems of holes and cracks that supply pathways for CONTAMINATION contaminants. Ground water can become contaminated from In areas surrounding pumping wells, the potential natural sources or numerous types of human for contamination increases because water from activities. (See Tables 1 and 2 and Figure 1.) the zone of contribution, a land area larger than Residential, municipal, commercial, industrial, the original recharge area, is drawn into the well and agricultural activities can all affect ground and the surrounding aquifer. Some drinking water water quality. Contaminants may reach ground wells actually draw water from nearby streams, water from activities on the land surface, such as lakes, or rivers. Contaminants present in these releases or spills from stored industrial wastes; surface waters can contribute contamination to from sources below the land surface but above the the ground water system. Some wells rely on arti- water table, such as septic systems or leaking ficial recharge to increase the amount of water underground petroleum storage systems; from infiltrating an aquifer, often using water from structures beneath the water table, such as wells; storm runoff, irrigation, industrial processes, or or from contaminated recharge water. treated sewage. In several cases, this practice has resulted in increased concentrations of nitrates, ■ Natural Sources metals, microbes, or synthetic chemicals in the Some substances found naturally in rocks or soils, water. such as iron, manganese, arsenic, chlorides, fluo- rides, sulfates, or radionuclides, can become dis- Under certain conditions, pumping can also cause solved in ground water. Other naturally occurring the ground water (and associated contaminants) substances, such as decaying organic matter, can from another aquifer to enter the one being move in ground water as particles. Whether any pumped. This phenomenon is called interaquifer of these substances appears in ground water leakage. Thus, properly identifying and protecting depends on local conditions. Some substances may the areas affected by well pumping is important to pose a health threat if consumed in excessive maintain ground water quality. quantities; others may produce an undesirable odor, taste, or color. Ground water that contains Generally, the greater the distance between a unacceptable concentrations of these substances is source of contamination and a ground water not used for drinking water or other domestic source, the more likely that natural processes will water uses unless it is treated to remove these con- reduce the impacts of contamination. Processes taminants. such as oxidation, biological degradation (which sometimes renders contaminants less toxic), and ■ Septic Systems adsorption (binding of materials to soil particles) One of the main causes of ground water contami- may take place in the soil layers of the unsaturat- nation in the United States is the effluent (out- ed zone and reduce the concentration of a con- flow) from septic tanks, cesspools, and privies. taminant before it reaches ground water. Even C•2• ➤ Getting Up to Speed: ground water contamination
Table 1 TYPICAL SOURCES OF POTENTIAL GROUND WATER CONTAMINATION BY LAND USE CATEGORY
Approximately one-fourth of all homes in the thetic organic chemicals (such as 1,1,1- United States rely on septic systems to dispose of trichloroethane or methylene chloride). These their human wastes. Although each individual sys- cleaners can contaminate water supply wells and tem releases a relatively small amount of waste interfere with natural decomposition processes in into the ground, the large number and widespread septic systems. use of these systems makes them a serious conta- mination source. Septic systems that are improper- Most, if not all, state and local regulations require ly sited, designed, constructed, or maintained can specific separation distances between septic sys- contaminate ground water with bacteria, viruses, tems and drinking water wells. In addition, com- nitrates, detergents, oils, and chemicals. Along puter models have been developed to calculate with these contaminants are the commercially suitable distances and densities. available septic system cleaners containing syn-
C•3• ➤ Getting Up to Speed: ground water contamination
■ Improper Disposal of Hazardous Waste Improper chemical storage, sloppy materials han- Hazardous waste should always be disposed of dling, and poor-quality containers can be major properly, that is to say, by a licensed hazardous threats to ground water. Tanker trucks and train waste handler or through municipal hazardous cars pose another chemical storage hazard. Each waste collection days. Many chemicals should not year, approximately 16,000 chemical spills occur be disposed of in household septic systems, from trucks, trains, and storage tanks, often when including oils (e.g., cooking, motor), lawn and materials are being transferred. At the site of an garden chemicals, paints and paint thinners, disin- accidental spill, the chemicals are often diluted fectants, medicines, photographic chemicals, and with water and then washed into the soil, increas- swimming pool chemicals. Similarly, many sub- ing the possibility of ground water contamination. stances used in industrial processes should not be disposed of in drains at the workplace because ■ Landfills they could contaminate a drinking water source. Solid waste is disposed of in thousands of munici- Companies should train employees in the proper pal and industrial landfills throughout the coun- use and disposal of all chemicals used on site. The try. Chemicals that should be disposed of in haz- many different types and the large quantities of ardous waste landfills sometimes end up in munic- chemicals used at industrial locations make proper ipal landfills. In addition, the disposal of many disposal of wastes especially important for ground household wastes is not regulated. water protection. Once in the landfill, chemicals can leach into the ■ Releases and Spills from Stored ground water by means of precipitation and sur- Chemicals and Petroleum Products face runoff. New landfills are required to have Underground and aboveground storage tanks are clay or synthetic liners and leachate (liquid from a commonly used to store petroleum products and landfill containing contaminants) collection sys- other chemical substances. For example, many tems to protect ground water. Most older land- homes have underground heating oil tanks. Many fills, however, do not have these safeguards. Older businesses and municipal highway departments landfills were often sited over aquifers or close to also store gasoline, diesel fuel, fuel oil, or chemi- surface waters and in permeable soils with shal- cals in on-site tanks. Industries use storage tanks low water tables, enhancing the potential for to hold chemicals used in industrial processes or leachate to contaminate ground water. Closed to store hazardous wastes for pickup by a licensed landfills can continue to pose a ground water con- hauler. Approximately 4 million underground tamination threat if they are not capped with an storage tanks exist in the United States and, over impermeable material (such as clay) before closure the years, the contents of many of these tanks to prevent the leaching of contaminants by precip- have leaked and spilled into the environment. itation.
If an underground storage tank develops a leak, ■ Surface Impoundments which commonly occurs as the tank ages and cor- Surface impoundments are relatively shallow rodes, its contents can migrate through the soil ponds or lagoons used by industries and munici- and reach the ground water. Tanks that meet fed- palities to store, treat, and dispose of liquid eral/state standards for new and upgraded systems wastes. As many as 180,000 surface impound- are less likely to fail, but they are not foolproof. ments exist in the United States. Like landfills, Abandoned underground tanks pose another new surface impoundment facilities are required problem because their location is often unknown. to have liners, but even these liners sometimes Aboveground storage tanks can also pose a threat leak. to ground water if a spill or leak occurs and ade- quate barriers are not in place. C•4• ➤ Getting Up to Speed: ground water contamination
Table 2 POTENTIAL HARMFUL COMPONENTS OF COMMON HOUSEHOLD PRODUCTS
C•5• ➤ Getting Up to Speed: ground water contamination
■ Sewers and Other Pipelines levels higher than federal maximum contaminant Sewer pipes carrying wastes sometimes leak fluids levels or health advisory levels. Only 10 percent of into the surrounding soil and ground water. the wells classified as rural were actually located Sewage consists of organic matter, inorganic salts, on farms. There is a higher incidence of contami- heavy metals, bacteria, viruses, and nitrogen. nation by agricultural chemicals in farm wells Other pipelines carrying industrial chemicals and used for drinking water. oil brine have also been known to leak, especially when the materials transported through the pipes After further analysis, EPA estimated that for the are corrosive. wells that contain pesticides, a significant percent- age probably contain chemical concentrations that ■ Pesticide and Fertilizer Use exceed the federal health-based limits (e.g., maxi- Millions of tons of fertilizers and pesticides (e.g., mum contaminant levels or health advisory levels). herbicides, insecticides, rodenticides, fungicides, Approximately 14.6 percent of the wells tested avicides) are used annually in the United States for contained levels of one or more pesticides above crop production. In addition to farmers, home- the minimum reporting limit set in the survey. The owners, businesses (e.g., golf courses), utilities, most common pesticides found were atrazine and and municipalities use these chemicals. A number metabolites (breakdown products) of dimethyl of these pesticides and fertilizers (some highly tetrachloroterephthalate (DCPA, commonly known toxic) have entered and contaminated ground as Dacthal), which is used in many utility easement water following normal, registered use. Some pes- weed-control programs and for lawn care. ticides remain in soil and water for many months ■ to many years. Another potential source of Drainage Wells ground water contamination is animal wastes that Drainage wells are used in wet areas to help drain percolate into the ground from farm feedlots. water and transport it to deeper soils. These wells Feedlots should be properly sited and wastes may contain agricultural chemicals and bacteria. should be removed at regular intervals. ■ Injection Wells/Floor Drains Between 1985 and 1992, EPA’s Office of Injection wells are used to collect storm water Pesticides and Toxic Substances and Office of runoff, collect spilled liquids, dispose of waste- Water conducted a National Pesticide Survey to water, and dispose of industrial, commercial, and determine the number of drinking water wells utility wastes. These wells are regulated by the U.S. nationwide that contain pesticides and nitrates EPA’s Underground Injection Control Program. In and the concentration of these substances. The New England, these wells may not be used to inject survey also analyzed the factors associated with hazardous wastes from industrial, commercial, and contamination of drinking water wells by pesti- utility operations. The injection wells used in this cides and nitrates. The survey, which included region are typically shallow and include sumps and samples from more than 1,300 public community dry wells used to handle storm water. and rural domestic water supply wells, found that approximately 3.6 percent of the wells contained Floor drains were historically used by businesses concentrations of nitrates above the federal maxi- to handle spills. Today, if a business operates or mum contaminant level, and that over half of the handles waste fluids that drain to a septic system, wells contained nitrates above the survey’s mini- dry well, or floor drain, it is required to submit mum reporting limit for nitrate (0.15 mg/L). information regarding its operation to the U.S. EPA or its state environmental protection agency. The survey also reported that approximately 0.8 Disposal wells that pose threats to drinking water percent of the wells tested contained pesticides at supplies are prohibited and must be closed, con-
C•6• ➤ Getting Up to Speed: ground water contamination nected to a public sewage system, or connected to (known as spoils or tailings) into the ground a storage tank. water below. These wastes often contain metals, acid, minerals, and sulfides. Abandoned mines are ■ Improperly Constructed Wells often used as wells and waste pits, sometimes Problems associated with improperly constructed simultaneously. In addition, mines are sometimes wells can result in ground water contamination pumped to keep them dry; the pumping can cause when contaminated surface or ground water is an upward migration of contaminated ground introduced into the well. water, which may be intercepted by a well.
■ Improperly Abandoned Wells EFFECTS OF GROUND WATER These wells can act as a conduit through which CONTAMINATION contaminants can reach an aquifer if the well cas- Contamination of ground water can result in poor ing has been removed, as is often done, or if the drinking water quality, loss of water supply, casing is corroded. In addition, some people use degraded surface water systems, high cleanup abandoned wells to dispose of wastes such as used costs, high costs for alternative water supplies, motor oil. These wells may reach into an aquifer and/or potential health problems. that serves drinking supply wells. Abandoned exploratory wells (e.g., for gas, oil, or coal) or test The consequences of contaminated ground water hole wells are usually uncovered and are also a or degraded surface water are often serious. For potential conduit for contaminants. example, estuaries that have been impacted by high nitrogen from ground water sources have ■ Active Drinking Water Supply Wells lost critical shellfish habitats. In terms of water Poorly constructed wells can result in ground supply, in some instances, ground water contami- water contamination. Construction problems, nation is so severe that the water supply must be such as faulty casings, inadequate covers, or lack abandoned as a source of drinking water. In other of concrete pads, allow outside water and any cases, the ground water can be cleaned up and accompanying contaminants to flow into the well. used again, if the contamination is not too severe Sources of such contaminants can be surface and if the municipality is willing to spend a good runoff or wastes from farm animals or septic sys- deal of money. Follow-up water quality monitor- tems. Contaminated fill packed around a well can ing is often required for many years. also degrade well water quality. Well construction problems are more likely to occur in older wells Because ground water generally moves slowly, that were in place prior to the establishment of contamination often remains undetected for long well construction standards and in domestic and periods of time. This makes cleanup of a contami- livestock wells. nated water supply difficult, if not impossible. If a ■ cleanup is undertaken, it can cost thousands to Poorly Constructed Irrigation Wells millions of dollars. These wells can allow contaminants to enter ground water. Often pesticides and fertilizers are Once the contaminant source has been controlled applied in the immediate vicinity of wells on agri- or removed, the contaminated ground water can cultural land. be treated in one of several ways:
■ Mining Activities • Containing the contaminant to prevent migration. Active and abandoned mines can contribute to ground water contamination. Precipitation can • Pumping the water, treating it, and return- leach soluble minerals from the mine wastes ing it to the aquifer.
C•7• ➤ Getting Up to Speed: ground water contamination
• Leaving the ground water in place and gasoline, is a known human carcinogen. The seri- treating either the water or the contami- ous health effects of lead are well known—learn- nant. ing disabilities in children; nerve, kidney, and liver problems; and pregnancy risks. Concentrations in • Allowing the contaminant to attenuate drinking water of these and other substances are (reduce) naturally (with monitoring), fol- regulated by federal and state laws. Hundreds of lowing the implementation of an appropri- other chemicals, however, are not yet regulated, ate source control. and many of their health effects are unknown or not well understood. Preventing contaminants Selection of the appropriate remedial technology from reaching the ground water is the best way to is based on site-specific factors and often takes reduce the health risks associated with poor into account cleanup goals based on potential risk drinking water quality. that are protective of human health and the envi- ronment. The technology selected is one that will achieve those cleanup goals. Different technolo- REGULATIONS TO PROTECT gies are effective for different types of contami- GROUND WATER nants, and several technologies are often com- Several federal laws help protect ground water bined to achieve effective treatment. The effective- quality. The Safe Drinking Water Act (SDWA) ness of treatment depends in part on local hydro- established three drinking water source protection geological conditions, which must be evaluated programs: the Wellhead Protection Program, Sole prior to selecting a treatment option. Source Aquifer Program, and the Source Water Assessment Program. It also called for regulation Given the difficulty and high costs of cleaning up of the use of underground injection wells for a contaminated aquifer, some communities choose waste disposal and provided EPA and the states to abandon existing wells and use other water with the authority to ensure that drinking water sources, if available. Using alternative supplies is supplied by public water systems meets minimum probably more expensive than obtaining drinking health standards. The Clean Water Act regulates water from the original source. A temporary and ground water that is shown to have a connection expensive solution is to purchase bottled water, with surface water. It sets standards for allowable but it is not a realistic long-term solution for a pollutant discharges to surface water. The community’s drinking water supply problem. A Resource Conservation and Recovery Act (RCRA) community might decide to install new wells in a regulates treatment, storage, and disposal of haz- different area of the aquifer. In this case, appropri- ardous and nonhazardous wastes. The ate siting and monitoring of the new wells are Comprehensive Environmental Response, critical to ensure that contaminants do not move Compensation, and Liability Act (CERCLA, or into the new water supplies. Superfund) authorizes the government to clean up contamination or sources of potential contamina- Potential Health Problems tion from hazardous waste sites or chemical spills, A number of microorganisms and thousands of including those that threaten drinking water sup- synthetic chemicals have the potential to contami- plies. CERCLA includes a “community right-to- nate ground water. Drinking water containing know” provision. The Federal Insecticide, bacteria and viruses can result in illnesses such as Fungicide, and Rodenticide Act (FIFRA) regulates hepatitis, cholera, or giardiasis. Methemo- pesticide use. The Toxic Substances Control Act globinemia or “blue baby syndrome,” an illness (TSCA) regulates manufactured chemicals. affecting infants, can be caused by drinking water that is high in nitrates. Benzene, a component of
C•8• ➤ Getting Up to Speed: ground water contamination
• Clean Water Act • Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA, or Superfund) • Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) • Interaquifer Leakage • Plume • Resource Conservation and Recovery Act (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 for Small Communities. Chapter 3. EPA/625/R-93/002. C•9• ➤ Getting Up to Speed: ground water contamination Infiltration to Water Ground Urban Runoff Not Drawn to Scale Not Drawn Landfills Industrial Station Service Impoundments Gasoline Seepage ONTAMINATION C Road Salt Uncovered Uncovered ATER Surface Water Ground Water Water Ground and W Ground Water Water Ground Flow Acid Rain Recharge to Acid Rain Recharge River Containment Migration ROUND G Waste Dumpsites Hazardous U.S.E.P.A.Massachusetts Audubon Society and NEIWPCC. U.S.E.P.A.Massachusetts OURCES OF Cone of Depresstion S OTENTIAL Shale Confining Layer Shale Confining Layer P Municipal Water Municipal Water Supply OME S Manure Piles Manure Septic Sand and Gravel Aquifer Sand and Gravel Systems The Power to Protect:Three Stories about Ground Water. to Protect:Three Stories The Power about Ground Ground Water Water Ground Flow Airborn Sulfur & Nitrate Compounds Fertilizers Pesticides and Pesticides Water Table Water Figure 2 Figure Source: Paly. Melissa and Lee Steppacher.
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