Underground or aboveground disposal practices of domestic, municipal, or industrial liquid waste can cause groundwater contamination. Among all disposal practices of domestic liquid waste, septic tanks and cesspools contribute the most wastewater to the ground and are the most frequently reported sources of groundwater contamination (U.S. EPA 1977). Septic tanks and cesspools contribute filtered sewage effluent directly to the ground which can introduce high concentrations of BOD, COD, nitrate, organic chemicals, and possibly bacteria and viruses into groundwater (Mallmann and Mack 1961; Miller 1980). Also, chlorination of the wastewater effluent and the use of chemicals to clean septic systems can produce additional potential pollutants (Council on Environmental Quality 1980).
With regard to municipal liquid waste, land application of sewage effluent and sludge is perhaps the largest contributor to groundwater contamination. Treated waste-water and sludge have been applied to land for many years to recharge groundwater and provide nutrients that fertilize the land and stimulate plant growth (Bauer 1974; U.S. EPA 1983). However, land application of sewage effluent can introduce bacteria, viruses, and organic and inorganic chemicals into groundwater (U.S. EPA 1974).
Another major municipal source of groundwater contamination is urban runoff from roadway deicing. In many urban areas, large quantities of salts and deicing additives are applied to roads during the winter months. These salts and additives facilitate the melting of ice and snow; however, they can percolate with the water into the ground and cause groundwater contamination of shallow aquifers (Field et al. 1973). In addition, the high solubility of these salts in water and the relatively high mobility of the resulting contaminants such as chloride ions in groundwa-ter can cause the zone of contamination to expand (Terry 1974).
With regard to industrial liquid waste, surface impoundments and injection wells are probably the largest contributors to groundwater contamination. As legislation to protect surface water resources has become more stringent, the use of surface impoundments and injection wells has become an attractive wastewater effluent disposal option for many industries. However, leakage of contaminants through the bottom of a surface impoundment or migration of fluids from an injection well into a hydro-logically connected usable aquifer can cause groundwater contamination (Council on Environmental Quality 1981). The extent and severity of groundwater contamination from these sources is further complicated by the fact that, in addition to being hazardous, many of the organic and
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