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11. Project Description <br /> The final cover or cap of the proposed landfill expansion would be constructed in compliance <br /> with State guidelines in effect at the time of closure of the landfill. The preliminary design of <br /> the cap consists of a 24-inch foundation layer, 12-inch compacted material layer with a <br /> permeability of I x 10-6 cm/sec,and 12-inch vegetative/top soil layer,as shown in Figure IIA. <br /> The final cover is designed to route as much rainfall as possible off the site to minimize leachate <br /> generation and reduce the potential for odors and gas emissions. <br /> The final vegetative cover must provide maximum coverage and tolerate site conditions with <br /> minimum maintenance. According to California regulations,the roots must not penetrate the <br /> barrier layer of a soil cover,limiting the root depth of the vegetation for soil covers.The <br /> expansion areas would use a geomembrane cover which is not nearly as susceptible to <br /> degradation by roots. An additional advantage of the geomembrane cover is protection of the <br /> vegetative cover from landfill gas. Establishment and maintenance of the vegetative cover is <br /> particularly critical in the first year of closure. <br /> The minimum slope on the closed landfill would be five percent and the maximum slope would <br /> be 25 percent(4 horizontal:I vertical)on the sides of the landfill. The proposed final grading of <br /> the site is shown in Ft 11.6. Perimeter drainage ditches,benching,and revegetation would be <br /> h <br /> used to minimize erosion of the cover. <br /> The estimated final cover annual soil erosion for the landfill is approximately 27 tons per year. <br /> It is estimated that this would result in approximately 20 cubic yards per year deposited in the <br /> surface water detention pond. <br /> It should be noted that a final cover similar to the one describe above will be placed on top of the <br /> existing landfill within a few years. <br /> The excavated areas to the north of the existing landfill would be reclaimed with 3:1 slopes and <br /> revegetated with similar materials to those used in landfill closure operations. <br /> Most of the landfill structures would be removed during closure. The scale would be removed <br /> and the scale house would be utilized for storing records. The PEn facility would be responsible <br /> for dismantling and removing its equipment when the plant is no longer economically viable. <br /> 11.35 <br />