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taken in front of the leading edge of the backfill indicated that athree-foot key way depth was <br />maintained in all of the areas where the sand content was found to be above 20 percent. <br />Slump cone, gradation, and moisture content test results on the S-B backfill material were used to <br />control the backfill material properties. Test results in each of these areas were consistently within the <br />acceptable range, except as noted in the Backfill Quality section. In a few instances, the slump test <br />and/or visual inspection resulted in construction directives, which specified corrective actions that were <br />carried out immediately. Corrective actions included addition/reduction ofslurry added to backfill <br />material and adjustments to the mixing operations. <br />Visual inspection of excavated soils and bedrock were extensively conducted during trenching to detect <br />when bedrock was encountered and when the trench depth was at least three feet deep into the <br />unweathered bedrock. The majority of the bedrock that was encountered was a hard, dry, bluish <br />claystone. In some areas, hard to very hard, well cemented, fine-grained sandstone was encountered <br />beneath the claystone bedrock. These areas were generally on the eastern two-thirds of the site: <br />As a quality control measure, the depth of the trench was periodically checked to determine if the <br />bedrock key trench depth was maintained and not filling with sediment or other material. These results <br />indicated that a bedrock key was maintain with a minimal amount of sand settling at the bottom of the <br />trench. A desanding unit was used to clean sediments from the trench slung and trench bottom to <br />maintain an effective key. <br />A comparison of quality control requirements, field testing, and observations indicate that the <br />construction requirements were adequately met. Adjustments were made when required as indicated by <br />test results and visual observations. <br />General <br />Slurry wall construction began in early January 2004 and was completed in late June 2004. <br />Construction was delayed temporarily on occasion due to equipment maintenance, logistics, and <br />inclement weather. During January, February, and March the contractor kept the backfill from freezing <br />by using a "Thaws All" system of heated liquid circulating through tubing covered with concrete <br />blankets. This allowed constmction to continue through all but the coldest parts of the winter season. <br />Field adjustments to the slurry wall alignment were made byHall-Irwin as the work progressed. The <br />slurry wall as-built alignment is shown on Figure 2. <br />Desandinp Operations <br />The desanding equipment consisted of a submersible pump, tank reservoir, and screened shaker <br />mounted to a reinforced steel sled with a diesel generator attached. The equipment used was <br />specifically manufactured for use in cleaning sand from the trench bottom and reducing the volume of <br />- 4 - November 2004 <br />F:~D6)6 IeTCOnniunion ReponWissrn Final Cmuwction Reportdoc <br />