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� ' <br /> OF'�EC <br /> � � 9C <br /> V 70 <br /> �:1:� <br /> '/[LINO\Y <br /> September 26, 2000 <br /> ENGINEERING & INFRASTRUCTURE MEMORANDUM <br /> NO. 2000 - 16 <br /> MEMORANDUM TO: Honorable Mayor and City Council <br /> FROM: Steve Garman, City Manager <br /> Stephen P. Swanson, P. E. <br /> Acting Director of Engine & Infrastructure <br /> SUBJECT: Silt Basin Retention Repairs - Phase II <br /> City Project 9834 <br /> A Special Use Permit was issued to the City by the Macon County Board in 1992 for the <br /> City to construct a silt retention basin in Oakley Township. This basin was used to store and <br /> dewater the silt dredged from Lake Decatur. The City ceased depositing silt in the facility in <br /> 1994. In 1995, the City breached the dike surrounding the retention area at three locations to <br /> drain water from the facility to further aid in drying the silt in the basin. <br /> The construction of the basin caused a number of field drain tiles to be cut. The cut drain <br /> tiles were either rerouted or plugged to prevent water from inside the basin entering the drain <br /> tiles. A major complaint about the City's management of the basin is a drain tile located outside <br /> of the eastern end of the basin. This tile was installed by the City's contractor as part of the <br /> sediment basin project to replace a cut drain tile that ran in a more north-south direction (refer to <br /> attached Exhibit A). The replaced drain tile was found to be poorly draining. The City, in 1996, <br /> replaced about 1,000 feet of this drain tile (refer to Exhibit B). This work was planned as the <br /> first phase to repair the drain tile to improve its draining capacity. After this work was done, the <br /> line would be inspected or observed to see what additional work, if any, was needed. <br /> In the process of making the repairs, it was found that the original drain tile was essentially <br /> collapsed for its entire length. The cause or causes for the failures may have been improper <br /> bedding, backfilling techniques, depth of cover over the pipe or a combination of these. Based <br /> on the condition of the original drain tile that was replaced and the subsequent minimal <br />