Water samples were collected from 175 wells in 12 Midcontinental States (Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, Wisconsin) from 1992 through 1994 to determine the spatial distribution of nutrients, pesticides, and volatile organic compounds in ground water, and to document the potential effects of the historic flooding that occurred during 1993 on ground- water quality. Concentrations of nitrate greater than the 0.05 mg/L reporting limit were found in 69.1 percent of the water samples, and nitrate concentrations exceeded the U.S. Environmental Protection Agency maximum contaminant limit of 10 mg/L in 9.6 percent of the 249 samples analyzed for nitrate. Pesticides or pesticide metabolites were detected in 72.4 percent of the 210 pesticide analyses, and 28 different compounds were found. Concentrations of multiple pesticide compounds above analytical reporting limits were found in water from about 60 percent of the wells sampled. Although pesticides were frequently detected, only one sample had a pesticide concentration that exceeded a maximum contaminant level for drinking water. The most frequently detected compounds, however, were pesticide metabolites for which maximum contaminant levels have not yet been established. Volatile organic compounds were detected in 13.5 percent of the 155 samples analyzed for these compounds. Only one sample had concentrations of volatile organic compounds that exceeded a maximum contaminant level for drinking water.
