The extent and costs of groundwater contamination by agriculture

MORE than 97 percent of all rural, domestic drinking water in the United States comes from underground sources, along with 55 percent of all livestock water and 40 percent of all irrigation water ( 17 ). According to U.S. Census data, more than 30 million people obtain their drinking water from private wells. Heavy reliance on groundwater is not limited to rural America. In 1980 ground-water served 40 percent of the population using public water supplies—nearly 74 million people ( 17 ). Moreover, groundwater withdrawals increased 158 percent from 1950 to 1980 compared to a 107 percent increase in surface water withdrawals ( 17 ). Little is known about the extent of most groundwater contamination from human activities (4). The question, however, is critical. There are documented and suspected risks to human health from exposure to contaminated groundwater (12). Because of the slow movement of groundwater in many areas, as well as the slow degradation of many chemicals, contamination can persist for years, even centuries. Cleanup costs can be prohibitive. Moreover, the interaction between surface water and groundwater can mean that in some areas aquifer contamination may ultimately lead to pollution of streams, lakes, and estuaries. Although groundwater contamination has many sources, evidence …