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Desanding Operation <br /> Desander equipment consisted of one 1,800 pound submersible pump, tank reservoir, screened <br /> shaker, and diesel generator mounted on a reinforced steel sled. This equipment was mobilized for <br /> use due to concerns regarding the settlement of sands from the slurry to the bottom of the trench. The <br /> equipment used was specifically manufactured for use in cleaning sand from the trench bottom and <br /> suspended in the slurry during the slurry wall excavation. The desander began operation at Station <br /> 7+00. From Station 7+00 to the end of the project at Station 48+45, the desanding equipment was <br /> felt to be efficient and effective in reducing the deposition of sand in the trench bottom. <br /> Local lignite coal seams were encountered during construction at Stations 02+50 to 5+00 and locally <br /> through Stations 43+00 to 48+00 near the bedrock contact. Where narrow coal seams were <br /> encountered as the trench was deepened. <br /> Slope Stability <br /> To prevent highwall sloughs and slurry wall damage, the reservoir slope should be reclaimed to at <br /> least 3:1 (horizontal to vertical) slope along the highwall as soon as possible after mining is completed. <br /> Reservoir side slope material, compacted to 95 percent of Maximum Standard Proctor Density, should <br /> prevent major slope failures that may damage the slurry wall. <br /> ' CONCLUSION AND RECOMMENDATIONS <br /> Construction of the Koenig Pit Slurry Wall was performed in conformance with the specified quality <br /> control standards. Corrective field actions were quickly implemented when specified by on-site <br /> testing. Backfill that appeared to not meet allowable specifications was not used. As a final quality <br /> control measure, periodic inspections of the pit wall are recommended to check for any localized seep <br /> zones. The final constructed slurry wall length of 4,846 feet encompassed approximately 36 acres. <br /> Reservoir capacity is to date undetermined. Final reservoir capacity will depend on future mining and <br /> reclamation operations. <br /> -5- <br />