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Iowa River Alluvial Study The Iowa Department of Natural Resources, Geological Survey Bureau investigated the quality of groundwater within the Iowa River alluvial aquifer in northern Iowa County and southwest Benton County, between the towns of Marengo and Belle Plaine. Fourteen wells (depths ranging from 8 to 71 feet) and the Iowa River were monitored from June 1988 throught October 1991 for nitrate, pesticides, and water levels. Sampling occurred during the two driest consecutive years in Iowa history (1988 and 1989) followed by two wetter than normal years (1990 and 1991) during which extensive flooding occurred in the area. Water-level fluctuations greater than 12 feet occurred at some wells. The well nests showed little vertical gradient of water levels during 1988 and 1989 but a more pronounced gradient during 1990 and 1991. Nitrate concentrations were generally higher in the shallower wells at each nest, and varied from <1 to 81 mg/L of nitrate. For more information contact Lynette Seigley (Lynette.Seigley@dnr.iowa.gov) at (319)335-1575. For information on publications by the USGS on the Iowa River alluvial aquifer, click here.