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2.5.1 Final Cover <br />The County proposes placement of a geosynthetic clay liner barrier as an engineered alternative <br />to the prescriptive 1 -foot -thick low -permeability soil layer, as allowed under Section 21090. <br />Design of the final cover, including testing of the suitability of material and demonstration that it <br />meets requirements of Title 27, will be submitted within the Final Closure Plan. <br />2.5.2 Final Grading and Drainage Plan <br />The Final Grading and Drainage Plan incorporates the following constraints and objectives <br />(Drawing 1): <br />1. Maximum fill elevation to 320 feet msl. <br />2. The minimum 100 -foot setback of waste from the west, south, and east property <br />boundaries. The setback includes the perimeter soil berm and outboard drainage <br />ditch (Drawing 3, Detail 1). <br />3. Minimum surface slopes of 5 percent for top deck areas <br />4. Maximum perimeter slopes of 3 horizontal to 1 vertical. <br />5. 20 -foot -wide drainage benches at 50 -foot maximum elevation intervals, with <br />2 percent grades and overside drains for drainage and erosion control. The design of <br />the drainage system is based on protection from the 100 -year storm event, as required <br />by Title 27 CCR (Appendix B). <br />6. Stormwater management facilities are comprised of the following: <br />Diversion berms to intercept flows from the top deck areas <br />• 20 -foot -wide drainage benches at maximum 50 -foot vertical intervals with V <br />ditches to intercept flows from the 3:1 perimeter slopes <br />• Pipe inlets and overside drains to receive and carry runoff downslope to ditches <br />along the perimeter of the landfill (Drawing 1) <br />7. Stormwater management facilities also include stormwater basins that are excavated <br />to temporarily retain runoff from the active landfill module(s). This runoff is pumped <br />to an interim large sedimentation pond developed within the footprint of future <br />Module 10 (Drawing 2). Runoff from Modules 10 and 11 will be pumped to the <br />perimeter ditch and retained as needed for sediment control before discharge off-site. <br />PCMP for NCRCSL 2-4 <br />O.ISan Joaquin CountyWCRCSL11180401PCPMffinal ReportlPCPMP Ret_Jan_2010.Doc <br />Department of Public Works olid Waste <br />County of San Joaquin —January 7, 2010 <br />