Water level decline and pumpage during 1959 in deep wells in the Chicago region, Illinois

Abstract

The water-level decline during 1959 in deep wells pene-trating the Cambrian-Ordovician Aquifer, the most highly developed aquifer for large ground-water supplies in the Chicago region, is considered in this reporto The Cambrian-Ordovician Aquifer is en-countered at an average depth of about 500 feet below the land surface at Chicago; it has an average thickness of 1000 feet and is composed chiefly of sandstones and dolomites. Pumpage from deep wells has increased from 200,000 gallons per day (gpd) in 1864 to 78.3 million gallons per day (mgd) in 1958 (as reevaluated in 1960). As a result, artesian pressure in the Cambrian-Ordovician Aquifer at Chicago has declined 660 feet. Pumpage from deep wells is concentrated in six centers: Chicago area, Joliet area, Elmhurst area, Des Plaines area, Aurora area, and Elgin area. In 1959, pumpage from deep wells was 88.0 mgd or 9.7 mgd more than in 1958. This annual increase in pumpage is record high and has resulted in excessive declines in water levels in deep wells. Water-level declines during 1959 ranged from 9 feet in the Joliet area to 41 feet in the Elmhurst area and averaged about 20 feet. The 1959 average decline is much greater than the average annual rate of decline (10 feet) for the period 1945-1958. 3 4 Withdrawals In 1959 exceed the practical sustained yield of the Cambrian-Ordovician Aquifer, with the result that ground-water users in the Chicago Region have started to mine water and to borrow water from future generations. If the distribution of pumpage re-mains the same as in 1959 and pumpage from the Cambrian-Ordovician Aquifer continues to increase in the future, the lowest and most permeable unit of the aquifer will be partially dewatered in many areas much sooner than previously anticipatedo Pumping levels ex-ceeding 1000 feet below the surface will be common within 20 years.