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<br />The La Poudre Pit is an alive sand and gravel mine operated by Hall-Irwin Construction. Current <br />mining operations include stripping and stockpiling of clay and silt overburden, and extraction of sand <br />and gravel with front~nd loaders and excavators loading off road haulers. The extracted sand and <br />gravel is processed for use as construction aggregate at a screening plant and concrete batch plant in <br />the northwest corner of the site. <br />The slurry wall as-built dimensions are as follows: an average total width of 3.5 feet, total trench depth <br />from 16 to 25.5 feet with an average value of 19.6 feet, and overall slurry wall length of 9,480 feet. <br />The total area surrounded by the slurry wall is approximately 93 acres. Preliminary reservoir capacity <br />is estimated to be 1,100 acre-feet. This value is an estimate of the water storage volume available if <br />sand and gravel, overburden, and wash plant fines are fully removed within the slurry wall perimeter. <br />Some reduction in storage is included to account for reclaimed reservoir side slopes and soils left as a <br />setback between the slurry wall and top of bank of the reservoir. An allowance was also made for <br />soils left in-place along a 100-foot wide gas line easement which transects the property. A topographic <br />survey of the property should be made after the completion of mining and site reclamation to <br />determine the actual storage volume. <br />CONSTRUCTION SUMMARY <br />The typical slurry wall construction crew consisted of five to six men managed by one superintendent <br />who oversaw and coordinated construction activities. Major equipment used included a trackhoe <br />excavator, Komatsu PC 650 LC, which excavated the trench through the bentonite slurry; a smaller <br />trackhoe, Dresser 6220, which provided initial mixing of the soil-bentonite backfill, unloaded bagged <br />bentonite, and constructed slurry mixing ponds; and a John Deere dozer, which provided final soil- <br />bentonite backfill mixing, trench backfilling, and slurry mixing pond construction. In addition to <br />equipment operators, two laborers maintained the slurry mixing ponds, slurry pump, and slurry <br />delivery system. The equipment used can be seen in the construction photographs provided on <br />Figures 2, 3, and 4. <br />Two slurry mixing/holding ponds were constructed. A consistent slurry was produced by combining <br />and mixing bulk bentonite, delivered in pneumatic trucks, with local ground or surface water using a <br />conical static mixer. Aker mixing, the slurry was discharged into one of the two slurry ponds. Once in <br />the pond, the slurry was continuously mixed and circulated until thoroughly hydrated. The finished <br />1 slurry product was pumped through four-inch diameter high density polyethylene piping to the trench <br />section under construcrtion. <br />-2- <br />