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The soil loss analysis performed is based on a "closed landfill' condition as <br />required by CCR Title 27, and for a post final closure construction condition to <br />estimate sediment amounts as a basis for sizing the sedimentation basins. At <br />closure, the potential soil loss is minimal because the landfill will have a <br />compacted final cover, an erosion control surface of vegetation and a storm <br />drain system installed which all contribute to controlling soil erosion. The landfill <br />soil loss analysis data is presented in Appendix I of the )TD. <br />The following USLE constants were utilized for the "closed landfill" condition: <br />R = 11.6 Average annual rainfall value <br />K = 0.25 Soil erodibility <br />0.3 < LS < 9.0 Dependent upon length gradient <br />C = 0.05 Based on vegetative material <br />P = 1.0 Practice factor <br />For the purpose of the soil lose analysis, the landf ll was divided into regions <br />based upon the average slopes of the final grades and surface drainage (Drawing <br />11 of the )TD). The "closed landfill' average soil loss for the Forward Landfill is <br />1.0 ton/acre/year which is below the two tons/acre/year allowed by the <br />CIWMB. Over the 30 -year post -closure maintenance period, the average soil <br />loss over the entire site will be -approximately 0.45 inches. Tie 30-ye*ar soil joss <br />represents 1.5 percent of the total final cover thickness. This analysis assumes a <br />seventy to eighty percent ground cover of the specified vegetation will exist over <br />the post -closure period. <br />3.6.3 1ROSI,ON CONTROL <br />The landfill closure design has three primary erosion control features that will <br />reduce the potential for soil erosion due to water and wind. These features <br />include landfill grading, vegetation, and a slope bench system. <br />The decks will be graded for sheet flow run-off with a minimum slope of <br />approximately three percent. Any large erosion gullies formed during storm <br />events on the deck and slopes will be filled and the area track walked by a <br />crawler tractor to replace and recompact the soil. <br />The slope benches will be constructed at approximately 40 to 50 -foot vertical <br />intervals along the landfill slope. The final slope bench system and a series of <br />Forward Landfill PCPCMP 3-10 <br />L:\Allied\2000.193\Reports\FinaiPCPCMP:FL-sec3: 8/20/01 BRYAN A. STIRRAT s ASSOCIATES <br />