This paper summarizes the information available concerning nitrate in Wisconsin’s groundwater. Previous papers have summarized the sources and concerns related to nitrate in groundwater (Bundy et al, 1994); the occurrence of nitrogen in groundwater and best management practices to reduce nitrate pollution (DATCP, 1989); and nitrogen application rates (Bundy et al, 1994). This paper provides additional information on the extent of nitrate pollution, the costs resulting from nitrate pollution and nitrate pollution sources and trends. Nitrate is the most widespread groundwater contaminant in Wisconsin. It has a federal Maximum Contaminant Level (MCL) and Wisconsin groundwater enforcement standard (ES) of 10 parts per million as nitrate-nitrogen. The standards are based on the risk of methemoglobenemia in infants. About 10 % of Wisconsin’s 800,000 private wells have nitrate-nitrogen concentrations exceeding the ES. Exceedences are not uniform across the state, however. Nitrate is rarely detected in areas with few pollution sources, such as much of northern Wisconsin. It is more frequently detected in wells located in agricultural parts of the state. A DATCP study showed exceedence rates between 17-26 % in some agricultural districts. Data collected by researchers at the University of Wisconsin at Stevens Point showed exceedence rates greater than 60 % in localized agricultura
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