Groundwater can be defined as any body of water that is contained in underground waterways known as aquifers. Because groundwater flows through compressed gravel and soil deposits, it flows very slowly. John Cary Stewart, in Drinking Water Hazards, estimates that groundwater typically flows from a few inches per year to a few feet per day.
There are two ways in which groundwater is replenished. The first is from water percolating through the soil from rain or snowmelt, and the second is through recharge zones where the aquifer contacts the surface. During its replenishment groundwater is vulnerable to contaminants that may be in the surface water or the soil. The aquifer may be protected from surface contamination by the presence of underground deposits of impervious materials such as clay or bedrock. For example, a sanitary landfill constructed in sand and gravel deposits is more likely to lead to groundwater contamination than a landfill constructed in clay deposits.
Microorganisms, inorganic chemicals, and organic chemicals from many sources may contaminate groundwater. Joseph Salvato, in Environmental Sanitation and Engineering, lists sources of groundwater contaminants that fall into the following four categories:
- Waste Category I. These are systems designed to discharge wastewater onto the surface of the land or to the groundwater. This category includes land application of wastewater, septic systems, waste disposal wells, and brine injection wells.
- Waste Category II. These are systems that may discharge wastewater to the land or groundwater but are not designed to do so. This category includes surface impoundments such as lagoons, landfills, and other excavations; animal feedlots; leaky sanitary sewer lines; and acid mine drainage.
- Nonwaste Category III. These are nonwaste systems that may discharge contamination to the land or the groundwater. This category includes buried storage tanks or pipelines, stockpiles of such things as highway de-icing materials, agricultural activities, and accidental spills.
- Nonwaste Category IV. These are nonwaste and nondischarge sources of contamination. This category includes saltwater intrusion, river infiltration, improperly constructed or abandoned wells, and farming practices.
Groundwater contamination presents very complex issues. Because groundwater moves so slowly it may take many years for contaminants to travel to the drinking water of a community from their original source. Once an aquifer is contaminated, merely removing the source of contamination will not clean it up. Control of groundwater contamination is dependent on four interrelated systems: regulation, design, monitoring, and remediation.
Regulations intended to control groundwater contamination are very difficult to enforce. Numerous federal acts such as the Resource Conservation and Recovery Act, the Superfund Act, and the Safe Drinking Water Act are all designed to protect groundwater. Building control and monitoring measures into new facilities is the most promising method for long-term regulation of groundwater contamination. The use of liners, leachate collection systems, monitoring wells, and the impervious strata of natural geology must be incorporated into new facilities that may pose a future threat of contamination to groundwater. Finally, remediation or cleanup of a contaminated aquifer through air stripping, a process by which water is removed from an aquifer, treated to remove contaminants, then returned to the aquifer, may be performed in limited situations.
William J. Franks
(see also: Environmental Determinants of Health; Groundwater; Land Use; Waterborne Diseases )
Nielson, D. M. (1991). Practical Handbook of Groundwater Monitoring. Chelsea, MI: Lewis.
Salvato, J. A. (1982). Environmental Engineering and Sanitation, 3rd edition. New York: John Wiley and Sons.
Stewart, J. C. (1990). Drinking Water Hazards. Hiram, OH: Envirographics.
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