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Draft Supplemental Environmental Impact Report Page III-25 Forward Inc.Landfill 2014 Expansion Project Closure and Postclosure A Preliminary Closure and Postclosure Maintenance Plan has been prepared for the currently permitted Forward Landfill. The anticipated closure date for the existing Forward Landfill is in t+. 2021. The current postclosure land use for the landfill is non-irrigated open space. Environmental Control and Monitoring Program a. Surface Water and Erosion Control The surface water control plan for the existing Forward Landfill consists of an integrated system of bench ditches,perimeter channels, and storm water retention basins. The final landfill is designed so that surface water would run off via sheet flow until it is intercepted by a bench ditch. Bench ditches subsequently drain toward downdrains,which discharge to perimeter channels. Finally, r, the perimeter channels drain to the sedimentation/detention basin. As required by the site's Waste Discharge Requirements(WDRs)issued by the Central Valley Regional Water Quality Control Board,permanent storm water runoff and drainage control facilities for the existing Forward Landfill have been designed to convey peak discharge resulting from 1,000-year,24-hour storm event runoff volumes. The storm water and drainage facilities of the proposed landfill expansion would be designed for the 1,000-year storm event. The drainage network for the completed landfill is designed to carry storm water at velocities that would minimize ditch erosion. Currently,all landfill surface water is routed to one of three sedimentation/detention basins. Two sedimentation basins are located in the southwest corner of the site,on either side of the South Branch. The basin located north of the South Branch collects runoff from the landfill area in the southern portion of the site,and the basin located south of the South Branch collects runoff from the FRRF area. A third sedimentation/detention basin, located on the northwest side of the existing landfill,directly west of WMU FU-03,collects runoff from the northern portion of the ' landfill. w. For purposes of the 2014 Expansion Project, the sedimentation basins currently located in the southern portion of the site would be relocated. Closure and relocation of the sedimentation basin would be conducted in accordance with applicable regulations and as approved by the regulatory agencies. An additional sedimentation pond and leachate collection pond may be added in the area of the existing administrative offices,if necessary. The erosion control measures incorporated in the site design include the following: • Collection and control of runoff,diverting it away from highly erodible areas • Construction of intermediate and final landfill slopes with drainage benches at intervals designed to control slope runoff velocities and volumes • Hydroseeding with fast germinating drought-tolerant grass seed on intermediate surfaces that would be exposed for more than 180 days and all surfaces once they reach tw final grade. Seeded surfaces would be watered until growth is well established. Soil erosion from the proposed landfill slopes was calculated to be less than the maximum allowed by the EPA for landfill final covers. The vegetative layer of the final soil cover would be seeded Iry with native grasses to protect the upper layer of soil,and to minimize erosion.