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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 JTD. <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 loss analysis, the landfill was divided into regions <br /> based upon the average slopes of the final grades and surface drainage (Drawing <br /> 11 of the JTD). 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 0.15 inches. The 30-year soil loss <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 EROSION 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.doc:5/21/02 BRYAN A.STIRRAT&ASSOCIATES <br />