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Regional geologic mapping (Colton, 1978) indicates near surface bedrock at the site is most likely <br /> claystones, sandstones, and coal of the Laramie Formation. Bedrock at the site is overlain by <br /> unconsolidated alluvial deposits regionally mapped as Piney Creek Alluvium. <br /> Current mining operations at the Koenig Pit include stripping and stockpiling of clay and silt <br /> overburden, and extraction of sand and gravel with front-end loaders and excavators loading off road <br /> haulers. <br /> The slurry wall as-built dimensions are as follows: an average total width of 3.5 feet, total trench depth <br /> from 22.5 to 47.0 feet with an average value of 34.8 feet, and overall slurry wall length of 4,846 feet. <br /> The total area surrounded by the slurry wall is approximately 36 acres. Preliminary reservoir capacity <br /> is currently undetermined due to the uncertainty of future mining plans. A topographic survey of the <br /> property should be made after the completion of mining and site reclamation to determine the actual <br /> storage volume. <br /> CONSTRUCTION SUMMARY <br /> The typical slur wall construction crew consisted sted of five to six men managed by one superintendent <br /> who oversaw and coordinated construction activities. Motorized equipment used included a trackhoe <br /> excavator, Hitachi 750 xl, which excavated the trench through a bentonite slurry; a smaller trackhoe, <br /> Dresser 6220 that provided initial soil bentonite mixing, unloaded bagged bentonite, and constructed <br /> slurry mixing ponds; one John Deere dozer that provided final soil-bentonite backfill mixing, trench <br /> backfilling, and slurry mixing pond construction; and a stand-alone pneumatic trailer for on-site storage <br /> of bulk bentonite. In addition to equipment operators, two to three laborers maintained slurry mixing <br /> ponds, slurry pumping equipment, and slurry delivery to the trench. Construction are <br /> photographs <br /> shown on Figures 2, 3, and 4. <br /> One slurry mixing/holding pond was constructed along the slurry wall alignment. A consistent slurry <br /> was produced by combining and mixing bulk bentonite with local ground or surface water using a <br /> conical static mixer. After mixing, the slurry was discharged into the slurry pond. Once in the pond <br /> the slurry was continuously circulated until thoroughly hydrated. The finished slurry product was <br /> pumped through four inch high density polyethylene piping to the open trench section under <br /> construction. Pond recirculation and slurry delivery was accomplished using an eight inch diameter <br /> pump. <br /> The soil-bentonite (S-B) backfill was composed of four components: 1) soil excavated from the trench, <br /> 2) high clay content soil material borrowed on-site, 3) slurry removed from the trench heading during <br /> -2- <br />