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Publication Abstract

Water-level Trends and Pumpage in the Deep Bedrock Aquifers in the Chicago Region, 1991 - 1995 Visocky, Adrian P., 1997  Illinois State Water Survey, Champaign, IL,  ISWS C-182    Full Text Available
The deep bedrock aquifer system in northeastern Illinois is encountered at depths ranging from about 200 feet in areas of central northern Illinois to an average of about 1,000 feet below land surface at Chicago. The aquifers have a collective thickness of 300 to 1,300 feet in the Chicago region, averaging 700 feet. They are composed chiefly of sandstones and dolomites, although most of the water is derived from the sandstone units. Pumpage from deep bedrock wells for public and self-supplied industrial supplies in the Chicago region increased from 200,000 gallons per day (gpd) in 1864 to a peak withdrawal of 182.9 million gallons per day (mgd) in 1979. Between 1991 and 1994, pumpage decreased from 112.7 mgd to 67.1 mgd, mostly due to a shift to Lake Michigan water, particularly in DuPage County. As a result, water levels in deep wells rose between 1991 and 1995, particularly in southern Lake, eastern DuPage, and western Cook Counties. Average annual water-level rises during the four-year period varied from one foot in Kendall County to 38 feet in DuPage County and averaged about 14 feet. This marked the first time that average water-level changes were upward in all eight counties of the Chicago area since detailed record-keeping began in the 1950s.

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