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Foothill Sanitary Landfill Preliminary Closure Plan <br /> Revision #1 May 6, 1994 <br /> As the attached flood insurance map (Drawing 6) indicates , the <br /> Foothill Sanitary Landfill site is not in the 100 year flood <br /> plain. <br /> SLOPE PROTECTION AND EROSION CONTROL <br /> Slope protection and erosion control will be mainly by vegetating <br /> and keeping slopes at or below a maximum of 3 : 1. The 3 : 1 slopes <br /> will be along the perimeter of the landfilled area. The other <br /> final cover slopes will be 3-6% to prevent drainage slope <br /> reversal from landfill settlement. The 3-6% slopes will also <br /> keep sheet flow on the landfill surface at minimal eroding <br /> velocities. <br /> The entire final site face will be vegetated with drought <br /> resistant grass to provide a low maintenance form of erosion <br /> control. The grass will be fertilized as needed and it will not <br /> require irrigation. <br /> Silt fencing may be constructed along the steeper toe slopes <br /> parallel to the drainage ditches to prevent soil from being <br /> washed into the drainage ditches. The design details for the <br /> sediment and erosion control features will be shown in the <br /> landfill construction drawings. <br /> A run-off analysis is included in this report as Appendix D to <br /> determine the potential sediment load that might run-off the <br /> site. An empirical method using the Universal soil loss equation <br /> was used to calculate the soil loss. The allowable sediment <br /> loss load was established to be 2 ton/Acre/year per the EPA <br /> Guideline Manual For Landfill Design Liner Systems and Final <br /> Cover document dated July 1982 . The Sediment Load computed in <br /> Appendix D for the site is 0 . 95 ton/acre/year. Since the <br /> sediment load is within the allowable loads, sediment load run- <br /> off is not considered a run-off problem. Additionally, the <br /> County will construct silting basins along the landfill's <br /> perimeter in order to capture this sediment load. These basins <br /> are shown on Drawing 2 of this Preliminary Closure Plan. It is <br /> anticipated that the 447 , or so, cubic yards of sediment <br /> deposited in the site drainage system would be removed as a <br /> normal course of annual maintenance of drainage ditch grading. <br /> LEACHATE CONTROL <br /> A leachate collection and removal system will be installed as <br /> each module is excavated. A High Density Polyethylene (HDPE) <br /> liner, leachate collection system, and a geonet will be installed <br /> over the 2 ' clay liner to provide a barrier with a permeability <br /> of 1 . 0 x 10"' cm/sec or less. The geonet will act as a drainage <br /> 15 <br />