Illinois State Library

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Title

• Dewatering well assessment for the highway drainage system at five sites in the east St. Louis area, Illinois (FY95-Phase12)

Description

• In the East St. Louis vicinity, the Illinois Department of Transportation, Division of Highways (IDOT) owns 55 high-capacity wells that are used to maintain the elevation of the ground-water table below the highway surface in areas where the highway is depressed below the original land surface. The dewatering systems are located at five sites in the alluvial valley of the Mississippi River in an area known as the American Bottoms. The alluvial deposits at the dewatering sites are about 90 to 115 feet thick and consist of fine sand, silt, and clay in the upper 10 to 30 feet, underlain by medium to coarse sand about 70 to 100 feet thick. The condition and efficiency of a number of the dewatering wells became suspect in 1982 on the basis of data collected and reviewed by IDOT staff. Since 1983, IDOT and the Illinois State Water Survey (ISWS) have conducted a cooperative investigation to more adequately assess the operation and condition of the wells, to attempt to understand the probable causes of well deterioration, and to evaluate rehabilitation procedures used on the wells. Work conducted during FY 95 (Phase 12) included monitoring the rehabilitation of four wells, step-testing the rehabilitated wells and checking the discharge from two wells for sand pumpage, checking the quality of the water discharged during the step tests, and monitoring the ground-water levels at the dewatering system sites. Posttreatment step tests were used to help document the rehabilitation of four dewatering wells, Interstate-70 (I-70) Wells 3A, 5, 11A, and 15, during FY 95 (Phase 12). Chemical treatments used to restore the capacity of these four wells were moderately successful. The improvement in specific capacity per well averaged about 103 percent based on data from pre- and posttreatment step tests. The specific capacity of I-70 Well 15 was restored to about 109 percent of the average observed specific capacity of wells in good condition at the I-70 site and the other three wells were restored to about 72 to 87 percent of the average observed specific capacity for wells in good condition. The sand pumpage investigation conducted during the posttreatment step tests on I-70 Wells 3A and 11A showed little or insignificant amounts of sand in the portable settling tank after the step tests. The tank was required to divert the discharged water into the stormwater drainage system during the other two step tests, precluding a check for sand pumpage.

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1. Dewatering well assessment for the highway drainage system at five sites in the east St. Louis area, Illinois (FY95-Phase12) (20060930183920_ISWSCR2000-10.pdf).
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