Nitrate in Ground Waters of the United States--Assessing the Risk

Using data compiled by the National Water Quality Assessment Program (NAWQA), the USGS has evaluated the potential for nitrate contamination of ground waters in the United States. Soil-drainage characteristics and the amount of nitrogen contributed by fertilizer, manure, and atmospheric sources were found to markedly influence the concentration of nitrate in ground water. These two characteristics were compiled in a national map that shows patterns of risk for nitrate contamination of ground water. Areas with well-drained soils and high nitrogen input have the highest risk. Ground-water nitrate data generally verified the risk patterns shown on the national map. The verification analysis is based on over 10,000 samples collected through 1992.