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Publication Abstract

Water-level Trends and Pumpage in the Cambrian and Ordovician Aquifers in the Chicago Region, 1980 - 1985 Sasman, Robert T., R. Scott Ludwigs, Curtis R. Benson, and James R. Kirk, 1986  Illinois State Water Survey, Champaign, IL,  ISWS C-166    Full Text Available

This report considers pumpage and water-level changes from 1980 through 1985 in deep sandstone wells penetrating the Cambrian and Ordovician aquifer system in northeastern Illinois, the most highly developed aquifer system for large ground-water supplies in Illinois. The term "Cambrian and Ordovician aquifer system" is an unofficial designation for the "Cambrian-Ordovician Aquifer" in northeastern Illinois that has been described in previous reports. Its usage in this report is for convenience only, since formal names of hydro-stratigraphic units in Illinois are in the process of change to reduce confusion with rock stratigraphic terminology (Visocky et al., 1985). The Cambrian and Ordovician aquifer system is encountered at depths ranging from less than 300 feet in areas of central northern Illinois to an average of about 500 feet below land surface at Chicago. The aquifer system has an average thickness of 1000 feet and is composed chiefly of sandstones and dolomites: most of the water is obtained from the sandstones. In this report, emphasis has been given to eight counties of the Chicago metropolitan area.

Pumpage from deep wells for public and self-supplied industrial supplies in the Chicago region increased from 200,000 gallons per day (gpd) in 1864 to 175.9 million gallons per day (mgd) in 1980 and by 1985 declined to 157.7 mgd. Peak pumpage of 182.9 mgd occurred in 1979. As a result of the pumpage, artesian pressure in the Cambrian and Ordovician aquifer system declined more than 850 feet in Chicago. Pumpage from deep wells in the Chicago region is concentrated in northwestern and western Cook County, eastern Du Page and eastern Kane Counties, and around Joliet in northwestern Will County. Heavy pumpage from deep wells outside the Chicago region occurs at Rockford in southeastern Winnebago County, Belvidere in south central Boone County, De Kalb-Sycamore in central De Kalb County, Rochelle in southeastern Ogle County, and Ottawa-Peru in central and west central La Salle County. Numerous other municipalities and self-supplied industries throughout northeastern Illinois pump small to large quantities of water from deep wells.

During the period from October 1980 through December 1985, pumpage from deep wells in the Chicago region decreased from 175.9 mgd to 157.7 mgd, a decrease of 18.2 mgd or 10.3 percent. This is the first time that there has been an extended period of decreased pumpage from deep wells in the area since the post-depression pre-World War II period. Changes in pumpage primarily reflect the transition from use of deep wells to water from Lake Michigan for public and industrial supplies, decreasing use of deep wells by self-supplied industries, and use of Fox River water to supplement the public water supply at Elgin in northeastern Kane County.

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