The water-table configuration of the Calumet aquifer in the vicinity of the Grand Calumet River/Indiana Harbor Canal in Lake County, northwestern Indiana, reflects the complexity of the shallow ground-water-flow system. Large depressions in the water table in sewered areas interrupt broad ground-water divides between rivers. The aquifer/stream interactions along the Grand Calumet River/ Indiana Harbor Canal are directly related to Lake Michigan water levels because of a direct connection of the Grand Calumet River/Indiana Harbor Canal to the lake. Fluctuations in lake levels and evapotranspiration result in reversals in ground-water flow near the river and canal that last from several hours to several months.

Most of the water from the Calumet aquifer discharges into sewers, the Grand Calumet River/Indiana Harbor Canal, Lake Michigan, and Silurian carbonate bedrock. Model simulations of ground-water flow for the study area indicate that the Calumet aquifer discharges about 15 ft³/s (cubic feet per second) of ground water to sewers, about 10 ft³/s to the Grand Calumet River/Indiana Harbor Canal, and about 4 ft³/s to Lake Michigan along a 25-mile section of shoreline. Estimates of groundwater flow from the Calumet aquifer to the bedrock range from 0 to 10 ft³/s. Results of analyses of water samples collected from wells in five land-use types steel industry, petrochemical industry, commercial and light industry, residential, and parks were compared. The highest median concentrations of inorganic ions and the most detections of organic compounds generally occurred in water samples from wells on the steel and petrochemical land-use areas. Water samples collected from wells on the commercial and light industrial land-use areas generally had lower median chemical concentrations than the samples from the steel and petrochemical land-use areas and greater median concentrations than the samples from the residential and park land-use areas. Seven of 52 acid-extractable and base/neutralextractable organic compounds and 17 of 36 volatile organic compounds analyzed were detected in a total of 35 wells. Only 4 of the 88 organic analytes phenols, bis(2-ethylhexyl)phthalate, benzene, and toluene were detected in more than 5 of the 35 wells.

A comparison of primarily inorganic-constituent data from the five land-use groups to inorganic-constituent data from sites known to be contaminated shows that constituent concentrations in ground waters from wells in the land-use areas generally are lower than those in ground water from contaminated areas. Abstract 1 Likewise, a comparison of inorganic-constituent data from the land-use groups to inorganic-constituent data from areas relatively unaffected by human presence shows that constituent concentrations in ground water from wells in the land-use areas generally are greater than those in ground water from the unaffected areas. Some documented but unaccounted for chemical loads in the Grand Calumet River are from ground water. Ground water probably contributes more than 10 percent of the total chemical load of ammonia, chromium, and cyanide to the Grand Calumet River. In comparison, about 1 to 3 percent of the total streamflow in the Grand Calumet River is from ground water. Of the four major groundwater sinks in the aquifer, the east branch of the Grand Calumet River and the Indiana Harbor Canal generally receive the greatest chemical loads from ground water, whereas Lake Michigan generally receives the smallest loads.