National Water Quality Assessment Program: Eastern Iowa Basins

Land Use And Shallow Ground-water Quality In Eastern Iowa And Southern Minnesota, 1997

Mark E. Savoca

Program abstract of the 43rd Annual Midwest Ground Water Conference, October 12-14, 1998, Lawrence, Kansas


The relation between land use and shallow ground-water quality in alluvial aquifers was investigated in the Eastern Iowa Basins study area as part of the U.S. Geological Survey's National Water Quality Assessment Program. The program is designed to assess the status and trends in the quality of the Nation's water resources, and to better understand the natural and human factors affecting water quality. The study area includes the Wapsipinicon, Cedar, Iowa, and Skunk River basins, and extends over an area of 19,500 square miles in eastern Iowa and southern Minnesota. Alluvial aquifers cover about 22 percent of the study area. About 85 percent of the area covered by alluvial aquifers is used for agricultural activities and about 3 percent is used for urban activities. Ground-water samples were collected from shallow monitoring wells completed in saturated alluvial deposits during the summer of 1997. Thirty-one wells were located within agricultural land-use areas, 30 wells were located in urban areas. Well depths ranged from 10 to 32.5 feet.

Nitrate (NO2- + NO3-), major ion, and volatile organic compound (VOC) concentrations in shallow ground-water reflect differences in land use. Nitrate concentrations were greater in agricultural land-use areas, while sodium, chloride, and sulfate concentrations were found to be greater in urban areas. Four VOC compounds were detected in samples from agricultural areas, but 34 compunds were detected in samples from urban areas.

Median nitrate concentrations were significantly greater in samples from agricultural areas (5.13 milligrams per liter or mg/L) than in urban areas (1.83 mg/L ). Nitrate concentrations exceeded the U.S. Environmental Protection Agency's Maximum Contaminant Level for drinking water of 10 mg/L in 39 percent of samples from agricultural areas and in none of the urban samples. Median sodium, chloride, and sulfate concentrations were significantly greater in samples from urban areas (23 mg/L, 41.5 mg/L, and 45 mg/L) than in agricultural areas (5.6 mg/L, 12 mg/L, and 22 mg/L). VOCs were detected in 19 percent of agricutural and 37 percent of urban land-use wells. Toluene was the most commonly detected (16 percent) VOC in samples from agricultural areas and methyl tert-butyl ether (MTBE), a fuel oxygenate, was the most commonly detected (23 percent) VOC in urban areas.


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