For many years, our society has enjoyed the benefits of using pesticides to control weed, insect, fungus, parasitic, and rodent pests. An assumption behind much of this use has been that pesticides will either degrade quickly or bind to soil particles until they eventually break down into harmless substances.
Only within the last decades have scientists learned that pesticides on the land can leach through the soil and enter the ground water below. For this reason, the impact of agricultural chemicals, especially pesticides, on the quality of surface and ground water has become an issue of national importance.
The United States Environmental Protection Agency (EPA) has responsibility under a variety of statutes to protect the quality of the nation's ground water as well as direct responsibility for regulating the availability and use of pesticide products. Since the early 1970's, the EPA's Office of Pesticide Programs has been evaluating the leaching potential of new and existing pesticides.
While 50% of the nation depends upon ground water for drinking water, about 95% of all households in rural areas nationwide use ground water as their primary source of drinking water.
Beginning in the early 1980's, ground water contamination incidents by pesticides from field application began to appear.
Shortly after the EPA's Ground Water Protection Strategy was issued in August, 1984, the Agency initiated an intensive review of existing information and scientific knowledge about the extent of pesticide contamination, its causes, its potential health impacts, and statutory authorities and programs available to help address the problem.
The Agency also initiated a National Survey of Pesticides in Well Water to better characterize the problem. During this same period, many states began efforts to understand and address pesticide contamination of ground water.
These efforts have been stimulated, in part, by the development of state ground water protection strategies. EPA has supported state strategy development through grants under Section 106 of the Clean Water Act as a means for strengthening the capacity of state governments to protect ground water quality.
Other regulations and programs such as the Safe Drinking Water Act and its amendments, a new Wellhead Protection Program, Clean Water Act, the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), and the new Non-point Source Management Program have all been initiated in an attempt to protect the nation's ground water from contamination by all types of pollutants including pesticides.
The likelihood of pesticide contamination of ground water and water wells depends partly on the geologic and hydrologic characteristics that vary from location to location as well as on pesticide characteristics.
Contamination of drinking water wells by pesticides is usually the result of one or a combination of the following:
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