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Publication Abstract

A Summary of Pumpage from the Cambrian-Ordovician Aquifers of Northeastern Illinois, 2000-2004. Burch, Stephen L., H. Allen Wehrmann., 2007  Illinois State Water Survey, Champaign, IL,  ISWS DCS 2007-03    Full Text Available

Cambrian-Ordovician aquifers underlying the Chicago region at depths of 500 to 1,600 feet have been prolific sources of groundwater for more than 100 years. The Chicago region includes Cook, Kendall, DuPage, Lake, Grundy, McHenry, Kane, and Will Counties. Groundwater pumpage from the Cambrian-Ordovician aquifers (the St. Peter and Ironton- Galesville sandstones) has increased from about 200,000 gallons per day (gpd) in 1864 to a peak of 182.88 million gallons per day (mgd) in 1979. Pumpage from the Cambrian-Ordovician aquifers decreased rapidly to 63.3 mgd in 1993 as a result of expanded use of Lake Michigan water by Chicago collar communities. Deep aquifer withdrawals increased to 67.3 mgd by 1995 and to 71.9 mgd in 1999.

This report documents that deep aquifer withdrawals continue to increase steadily. The Illinois Water Inventory Program (IWIP) compiles responses to annual letters of inquiry sent to community, commercial, and industrial water-using facilities. The IWIP database was queried for pumpage from wells using the Cambrian-Ordovician aquifers during the study period of 2000-2004. A tally of the pumpages for the Chicago region determined that withdrawals had increased from 72.47 mgd in 2000 to 84.40 mgd in 2004. The largest community water supplies using the Cambrian-Ordovician aquifers continue to be Joliet and Aurora.

The last pumpage summary concluded with data through 1999. Since then, 38 new community supply wells were constructed, with the greatest number (11 wells) located in Kane County. Well development for community supplies is favoring use of the deeper Ironton- Galesville aquifer likely because of concerns over the long-term dependability of the shallower St. Peter sandstone. Thirty other large-diameter, high-capacity wells have been drilled for irrigation and industrial purposes. Ten of those wells were drilled in Lake County and accounted for more than half of the 19 irrigation wells constructed during the study period.

Increasing use of the Cambrian-Ordovician aquifers by domestic wells is apparent. Based on well records maintained by the Illinois State Water Survey, more than 1,000 domestic wells were drilled into these aquifers from 2000 to 2004, mostly in Kane and Kendall Counties. The total amount of water pumped by these wells is small in comparison to high-capacity and community uses tallied by the IWIP; however, the trend suggests an increasing use of the Cambrian-Ordovician aquifers for individual households.

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