This report examines groundwater levels of deep wells (800-1700 ft) in a 14-county area of Illinois that extends from Lake Michigan to north-central Illinois and from the Wisconsin border south to Kankakee County. Particular emphasis has been given to the eight counties of the Chicago region because of the significant shift in water usage during the late twentieth century from groundwater supplies of the deep bedrock aquifers to Lake Michigan and other sources. This report details fall 2007 water-level measurements of wells reaching to the St. Peter and Ironton-Galesville sandstones (deep sandstone aquifers), provides a map illustrating the surface and slope of groundwater levels, and compares fall 2007 levels to fall 2000 observations. The rapid decrease in groundwater pumpage from the deep bedrock aquifers during the 1980s initially resulted in a rapid recovery of groundwater levels. However, the rate of water-level change flattened and has resumed a slow decline since 2000. The greatest recovery during the past seven years occurred in Winnebago County. In locations where the deep sandstone aquifers of Cambrian-Ordovician age continue to be used, declines in groundwater levels were observed. Most notable declines were in Kane County, Kendall County, southwestern Lake County, and southeastern McHenry County. Outside the Chicago region, water-level declines were observed in deep wells at Rockford and Loves Park in Winnebago County and in the vicinity of DeKalb and Sycamore in DeKalb County. Comparison of the 2000 and 2007 potentiometric surface maps indicates groundwater declines in the eight-county Chicago region have resumed. Large portions of the study area again have water-level decreases of 25 to 50 feet. This contrasts with the 2000 measurement that observed generally small changes. The largest drawdown of groundwater levels occurred in southeastern Kendall County. New wells, built since 2003 by Joliet, have caused the potentiometric surface to decline by up to 350-400 feet. Declines also continued at the Aurora pumping center and at the developing pumping center in northern Kendall County. The water allocation program that substituted Lake Michigan water lessened groundwater withdrawals from deep sandstone aquifers for 10 to 15 years. Today, however, the trend has reversed because of growing usage of groundwater from the deep sandstones, causing a return to declining groundwater levels throughout many inland counties of northeastern Illinois.
|Original language||English (US)|
|State||Published - 2008|
|Name||ISWS Data Case Study 2008-04|