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• -15- • <br />layer should be placed immediately beneath the slabs. The gravel <br />should have a maximum -200 sieve content of 10~, at least 50~ <br />retained on the No. 4 sieve and a maximum size of 2 inches. <br />SEDIF1EttTATION FOND <br />The proposed sedimentation pond will be constructed mainly by <br />cutting below the natural ground surface and Filling on the down- <br />hill side. Cut and fill slopes are proposed to be 2 horizontal <br />to 1 vertical. Percolation tests were performed in the proposed <br />sedimentation pond area and laboratory permeability tests were <br />performed to help assess seepage loss front the pond area. The <br />percolation rates obtained under relatively low head indicate <br />seepage loss could be substantial. The laboratory tests indicate <br />isolated clay layers could be relatively impervious. <br />Based on the test results, it appears that lining should be <br />provided to reduce the seepage loss. We expect that the on-site <br />clays can be used as a liner provided some seepage loss is <br />acceptable. A minimum two-foot thick clay liner should be <br />used. The clay material should have at least 60p passing the No. <br />200 sieve and a minimum liquid '_imit of 30. Bentonite may be <br />added to further reduce the liner permeability. The fill portion <br />of the pond embankment should consist of predominant clay like <br />the soil liner. Embankment and ]finer materials should be <br />compacted to at least 95~ of stan~!ar•d Proctor density (ASTM D698) <br />at a moisture content near optimum. <br />Chen & Associates <br />