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Millions of tons of fertilizers and pesticides (including herbicides, insecticides, rodenticides, fungicides and avicides) are used annually in the United States for crop production. In addition to farmers, some home owners, businesses (such as golf courses), utilities and municipalities also use these chemicals. A number of pesticides (some highly toxic) and fertilizers have entered and contaminated surface and groundwater following normal, registered use. Some pesticides remain in soil and water for many months to many years. Routine monitoring of several public water system wells scattered around the state has resulted in some pesticide detections.
Agricultural runoff is considered one of the leading sources of nonpoint source pollution in Pennsylvania. Nutrients and other contaminants from animal wastes can percolate into the ground or runoff into streams. Feedlots should be properly sited, and wastes should be removed at regular intervals.
EPA's Office of Pesticides and Toxic Substances and Office of Water conducted a National Pesticide Survey (NPS) between 1985 and 1992. The purpose of the survey was to determine the number of drinking water wells nationwide that contained pesticides and nitrates and the concentration of these substances. It also analyzed the factors associated with contamination of drinking water wells by pesticides and nitrates. The survey included samples from more than 1,300 public community and rural domestic water supply wells. The NPS found that approximately 3.6 percent of the wells contained concentrations of nitrates above the federal maximum contaminant level and that over half of the wells contained nitrates above the survey's minimum reporting limit for nitrate (0.15 milligrams per liter). The NPS also reported that approximately 0.8 percent of the wells tested contained pesticides at levels higher than federal maximum contaminant levels (MCLs) or health advisory levels (HALs). Only 10 percent of the wells classified as rural were actually located on farms. The incidence of contamination by agricultural chemicals in farm wells used for drinking water is greater.
After further analysis, EPA concluded that a significant percentage of wells contained pesticides at concentrations exceeding MCLs or HALs. Approximately 15 percent of the wells tested contained one or more pesticides above the minimum reporting limit set in the survey. EPA established specific minimum reporting limits for each pesticide tested for in the NPS, ranging from 0.10 micrograms per liter for di-bromochloropropane to 4.5 micrograms per liter for ethylene-thiourea. The most common pesticides found were atrazine and metabolites (breakdown products) of di-methyl tetra-chloro-tere-phthalate (DCPA- commonly known as Dacthal), used in many utility easement weed control programs and for lawn care.