The U.S. Geological Survey, in cooperation with the Indiana Department of Environmental Management, computerized the available government agency data on the occurrence of pesticides and pesticide metabolites in Indiana ground water. Results of analyses of 725 samples were summarized for the period December 1985 through April 1991. The data had been collected during 6 statewide surveys and 15 localized studies by the Indiana Department of Environmental Management, the Indiana Department of Natural Resources, the U.S. Environmental Protection Agency, and the U.S. Geological Survey. Ground-water samples were collected from 521 sites in 81 of 92 Indiana counties, including 179 public-supply wells, 304 domestic-supply wells, 36 observation wells, and 2 springs; 41 percent of all sites were sampled more than once. Thirty wells were sampled in response to alleged groundwater contamination with pesticides.

Of 87 pesticides and 10 metabolites analyzed, 18 pesticides and 5 metabolites were detected in 51 samples of ground water from 22 domestic wells, 8 community-system wells, 5 observation wells, 4 non-community-system wells, and 2 springs. Detections associated with complaints of ground-water contamination from pesticide storage, handling, or application occurred at five domestic wells. Three-fourths of all the pesticide detections were in water from wells completed in unconsolidated materials to a depth of less than 100 feet, but well depths ranged from 12 to 260 feet.

The highest frequency of occurrence was observed for the most commonly used herbicides alachlor, atrazine and two atrazine metabolites (de-ethylatrazine and de-isopropylatrazine); dicamba; 2,4-D; and metolachlor. Also reported in Indiana ground water were eight insecticides whose registration had been cancelled by the U.S. Environmental Protection Agency prior to their detection in Indiana EDB, DBCP, aldrin, endrin, dieldrin, lindane, heptachlor, and DOT.

More than 1 pesticide was present in 16 of the 51 samples that had detections, for a total of 90 individual pesticide detections. Concentrations of the detected pesticides ranged from 0.04 to 49 micrograms per liter, and two-thirds of the detected concentrations were less than 1 microgram per liter. In about 29 percent of all detections, the concentration of 9 pesticides alachlor, aldrin, atrazine, dieldrin, EDB, heptachlor, heptachlor epoxide, simazine, and terbufos exceeded either the U.S. Environmental Protection Agency's Maximum Contaminant Level or adult lifetime Health Advisory.