Occurrence of nitrate in ground water in the White River Basin, Indiana, 1994–95

Nitrogen-based fertilizers are used extensively in the White River Basin. Water samples were collected for nitrate analysis from 103 monitoring wells in four networks in the basin. Ninety-four "shallow" wells were screened near the top of the uppermost aquifer encountered; the remaining 9 wells were paired with shallow wells but screened 18 to 45 feet deeper. Samples from 6.4 percent of the shallow wells exceeded the U.S. Environmental Protection Agency's Maximum Contaminant Level of 10 mg/L (milligrams per liter). Elevated nitrate concentrations (higher than 3 mg/L) were common in unconfined, permeable deposits underlying agricultural areas; nitrate concentrations decreased with depth in these deposits. Low nitrate concentrations (less than 0.05 mg/L) were found in aquifers confined by clay-rich tills that retard downward movement of nitrate and oxygen into the ground water.