Illinois State Library

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Title

• Dewatering well assessment for the highway drainage system at four sites in the East St. Louis area, Illinois (FY00-phase 17)

Description

• In the East St. Louis vicinity, the Illinois Department of Transportation Division of Highways (IDOT) owns 56 high-capacity wells that are used to maintain the elevation of the groundwater table below the highway surface in areas in which the highways were constructed 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 about 70 to 100 feet of medium to coarse sand. 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 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 scheduled for FY 00 (Phase 17) included conducting 18 condition-assessment and posttreatment step tests, monitoring of the chemical treatment of 11 wells, and observing and documenting the construction of 2 new (replacement) dewatering wells. Of the 18 step tests conducted, 11 were post-chemical-treatment step tests, 5 were routine condition assessment step tests on existing wells, and 2 were condition assessments on newly constructed wells. The results of the five condition assessment step tests indicated specific capacities ranging from 25.1 to 65.2 gallons per minute per foot (gpm/ft), corresponding to very poor to fair well conditions, respectively. It was recommended that all five wells be chemically treated in FY01. Posttreatment step tests were used to help document the rehabilitation of 11 dewatering wells during FY 00 (Phase 17): I-70 Wells 2A and 8A; 25th Street Wells 2, 3, 4, 5, 7, 8, and 9; and Missouri Avenue Wells 2 and 3. Chemical treatments used to restore the capacity of these seven wells were moderately successful. There was a wide range of improvement in specific capacity per well, ranging from 2 percent to 503 percent improvement, and averaging 124 percent based on specific-capacity data from pre- and posttreatment step tests. A sand pumpage investigation, which was conducted during 15 of the 18 step tests during FY 00, revealed that 25th Street Wells 2, 3, and 4 were pumping sand. These conditions may pose a threat to the long-term operation of these wells, especially 25th Street Well 4. Smaller amounts of sand were found following the step test for 25th Street Wells 2 and 3.

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1. Dewatering well assessment for the highway drainage system at four sites in the East St. Louis area, Illinois (FY00-phase 17) (20061003184100_ISWSCR2003-08.pdf).
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