Water samples were collected from 128 wells in a large industrial and urban area in northwestern Indiana and northeastern Illinois during June 1993. Samples were collected from wells completed inone of four geohydrologic units: surficial sand aquifer (Calumet aquifer), clay confining unit, confined sand aquifers, and a carbonate-bedrock aquifer (Silurian-Devonian aquifer). Samples wereanalyzed by U.S. Environmental Protection Agency contract laboratories for selected water-quality properties, common ions, trace elements, volatile and semivolatile organic compounds, pesticides, andpolychlorinated biphenyls. Water from wells in the Silurian-Devonian aquifer is predominantly a sodium bicarbonate type. Water types in confined sand aquifers and the confining unit are varied. Water types from wells in the Calumet aquifer also are varied, although approximately 42 percent of the wells in thisgeohydrologic unit produced water in which calcium and bicarbonate were the dominant cation-anion pair. Samples from several shallow wells in theconfining unit and the Calumet aquifer, and one well in a confined sand aquifer, were classified as sodium chloride-type water. The largest concentrations of trace elements and organic compounds were detected in samples from wells located in or near industrial areas or areas of waste disposal. A total of 14 volatile organic compounds and 23 semivolatile organic compounds on the U.S. Environmental Protection Agency's target compound list was detected in 20 and 56 samples. A total of 18 pesticide compounds was detected in 29 samples. Compounds containing polychlorinated biphenyls were detected in three samples.
Additional publication details
USGS Numbered Series
Ground-water quality in the Calumet Region of northwestern Indiana and northeastern Illinois, June 1993
Water-Resources Investigations Report
U.S. Geological Survey ;
U.S. Geological Survey, Branch of Information Services [distributor],
vii, 179 p.,  folded p. of plates :ill., maps ;28 cm.