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Publication Abstract

Water-level Trends and Pumpage in the Deep Bedrock Aquifers in the Chicago Region, 1985 - 1991 Visocky, Adrian P., 1993  Illinois State Water Survey, Champaign, IL,  ISWS C-177    Full Text Available

The deep bedrock aquifer system in northeastern Illinois is encountered at depths ranging from about 200 feet below land surface in areas of north-central Illinois to an average of about 1,000 feet at Chicago. The aquifers have a collective thickness of 300 to 1,300 feet in the Chicago region, with an average of 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 use in the Chicago region increased from 200,000 gallons per day in 1864 to a peak withdrawal of 182.9 million gallons per day (mgd) in 1979. Between 1985 and 1991, pumpage decreased from 157.7 mgd to 112.7 mgd, mostly due to a shift to Lake Michigan water. As a result, water levels in many deep wells rose between 1985 and 1991, particularly in northwestern Cook and southern Lake Counties. Average annual water- level changes during the six-year period varied from a rise of 12 feet in Cook County to a decline of 8 feet in Will County, for an overall average rise of about 3 feet. This marked the first time that the average change was upward since detailed record-keeping began in the 1950s.

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