The Iowa ground-water-quality monitoring program has been conducted cooperatively since 1982 by the Iowa Department of Natural Resources, Geological Survey Bureau; the University of Iowa Hygienic Laboratory, and the U.S. Geological Survey. The original objectives of the program were to provide baseline ground-waterquality data throughout the State for the major aquifers and to address any new areas of water-quality concern. Since the program began, the emphasis and objectives of the program have changed several times. For water years 1992 through 1996, more emphasis has been placed on determining trends in ground-water quality and correlating water quality with possible contributing factors such as location, land use, aquifer, aquifer depth, and precipitation.

From 1982 through 1996, a total of 2,529 water samples has been collected from 1,158 municipal wells throughout Iowa. The samples consisted of 1,048 alluvial aquifer samples (387 wells), 530 Pleistocene aquifer samples (224 wells), 139 Cretaceous aquifer samples (86 wells), 187 Carboniferous aquifer samples (104 wells), 447 Silurian-Devonian aquifer samples (222 wells), 177 Cambrian-Ordovician aquifer samples (134 wells), and 1 Precambrian aquifer sample (1 well).

Some samples had concentrations greater than or equal to drinking-water regulations established by the U.S Environmental Protection Agency. Of 1,901 samples analyzed for dissolved sulfate, 137 samples had concentrations greater than or equal to the Maximum Contaminant Level for sulfate. Of 2,510 samples analyzed for dissolved nitrite plus nitrate as nitrogen, 198 samples had concentrations greater than or equal to the Maximum Contaminant Level for nitrite plus nitrate. Of 1,945 samples analyzed for dissolved iron, 1,022 samples had concentrations greater than or equal to the Secondary Maximum Contaminant Level for iron. Of 1,946 samples analyzed for dissolved manganese, 1,082 samples had concentrations greater than or equal to the Secondary Maximum Contaminant Level for manganese. Of 1,659 samples analyzed for alachlor, atrazine, and cyanazine, 401 samples had concentrations greater than or equal to the respective minimum reporting levels. One sample had concentrations of alachlor, atrazine, and cyanazine greater than the respective drinking-water regulations.

Maps show the general location of wells that have been sampled in the various aquifers. Other maps show the location of wells where sulfate and nitrite plus nitrate concentrations exceed the respective Maximum Contaminant Levels and wells where concentrations of the pesticides alachlor, atrazine, or cyanazine exceeded the respective minimum reporting levels. The compact disc included with this report has information about water-quality properties and concentrations of dissolved solids, major ions, nutrients, trace elements, radionuclides, total organic carbon, pesticides, and synthetic organic compounds for water years 1982 through 1996.