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Publication Abstract

A Reassessment of Aquifer Conditions West of Normal, Illinois Richards, Susan S., and Adrian P. Visocky, 1982  Illinois State Water Survey, Champaign, IL,  ISWS C-153    Full Text Available

In 1980 the town of Normal pumped an average of 1.66 mgd (million gallons per day) of water from 3 production wells, tapping 3 deeply buried sand and gravel aquifers (upper, intermediate, and lower) in the Danvers Buried Valley located west of Normal. The wells were developed in 1974 after a period of extensive exploration and testing. Since the wells went into service in February 1976, pumpage has increased from 1.16 mgd to present levels. Large water level declines (20 to 30 feet) have occurred in a number of wells in the vicinity of Normal's west well field, resulting in some nearby farm wells going dry. These large declines were not predicted, because, as has now been determined, aquifer properties calculated from tests of the production wells (T = 442,000 gpd/ft; S = 0.11) were not representative of regional values. The model originally used in predicting the impact of pumping could not reproduce observed declines. Therefore, a new model, based on combined thicknesses of the intermediate and lower aquifer and representative regional aquifer properties (T = 165,000 gpd/ft; S = 0.001), was used to successfully predict observed declines in nearby observation wells. This new model predicts that pumping an average of 3.88 mgdódepending upon the spacing of the production wellsówill cause additional declines of about 30-45 feet in nearby wells tapping the 3 deeply buried aquifers. Such an increased pumpage in Normal's well field will probably have negligible effects on other area pumping centers.

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