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Publication Abstract

Water-level Trends, Pumpage, and Chemical Quality in the Cambrian-Ordovician Aquifer in Illinois, 1971 - 1980 Sasman, Robert T., Curtis R. Benson, R. Scott Ludwigs, and Tamara L. Williams, 1982  Illinois State Water Survey, Champaign, IL,  ISWS C-154    Full Text Available

This report considers pumpage and water-level changes from 1971 through 1980, and 1980-1981 water quality, in deep sandstone wells penetrating the Cambrian-Ordovician aquifer, the most highly developed aquifer for large groundwater supplies in Illinois. Data from 43 counties, covering 27,000 square miles or 48 percent of the state, are discussed, with emphasis on the 8-county Chicago region in northeastern Illinois.

The Cambrian-Ordovician aquifer is encountered at depths ranging from less than 100 feet in areas of northwestern Illinois to an average of about 500 feet below land surface at Chicago, and as deep as 900 to 1100 feet below land surface in the extreme south of the area under consideration. It has an average thickness of 1000 feet and is composed chiefly of sandstones and dolomites. In the southwestern part of the region, the Cambrian-Ordovician aquifer is more than 2000 feet thick.

Production from deep wells in 20 northern counties of Illinois increased from 200,000 gallons per day (gpd) in 1864 to 239.0 million gallons per day (mgd) in 1971; approximately 63 percent of the 1971 pumpage was from wells in the Chicago area. As a result, piezometric levels in the Cambrian-Ordovician aquifer in Chicago have declined more than 850 feet since 1864. Production from deep wells in the Chicago region is concentrated in northwestern and western Cook County, eastern DuPage and eastern Kane Counties, and around Joliet in Will County. Large withdrawals from deep wells outside the Chicago region occur at Rockford, Belvidere, Freeport, DeKalb-Sycamore, Rochelle, Dixon, and Ottawa-Peru. Numerous other municipalities and self-supplied industries throughout northern Illinois pump small to large quantities of water from deep wells. Groundwater withdrawals in the southern portion of the study area are generally limited.

During the period from 1971 through 1980, production from deep wells in northern Illinois increased approximately 12 percent (28.4 mgd) to 267.5 mgd. In the Chicago region pumpage increased 22 percent to...

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