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Foothill Sanitary Landfill Preliminary Closure Plan <br /> Revision #1 May 6, 1994 <br /> FINAL COVER <br /> EXISTING 80 ACRES <br /> Final cover for the existing 80 acres will consist of a 2 foot <br /> foundation layer followed by a 1 foot clay layer and a 1 foot <br /> vegetative layer. By the time of closure, one foot of the <br /> foundation layer will have already have been placed. Therefore, <br /> only one foot of additional soil will be needed to complete the <br /> foundation layer. Soils from the site will be utilized for the <br /> foundation layer, vegetative layer, and part of the clay layer. <br /> Clay from an off-site source will be mixed with on-site material <br /> to achieve the desired permeability for the low-permeability <br /> layer. Total soil needs for the landfill are shown in the cost <br /> estimate section. The final cover will be applied by on-site <br /> landfill equipment. <br /> The foundation layer will consist of the materials that will be <br /> excavated on-site borrow material. The next one foot layer will <br /> consist of on-site material mixed with clay from an off-site <br /> borrow source. The mixture will be compacted to 95% of maximum <br /> density to obtain a permeability of 1. 0 x low cm/sec or less. <br /> The vegetative layer soil will also come from the site. It will <br /> be taken directly from top soil of the adjacent modules to be <br /> opened. The vegetative layer will be seeded with grass upon <br /> completion of each module. <br /> 20 ACRE LINED MODULE <br /> Final cover for the 20 acre lined module will consist of a two <br /> foot foundation layer, ,a two foot clay barrier layer with a <br /> permeability of 1 x 10-' cm/sec or less, a layer of geosynthetic <br /> liner material, and a one foot vegetative layer. By the time of <br /> closure, one foot of the foundation layer will have already have <br /> been placed. Therefore, only one foot of additional soil will be <br /> needed to complete the foundation layer. <br /> FINAL GRADING <br /> The final landfill slopes will be constructed to a minimum of <br /> three percent grades to provide adequate drainage and prevent <br /> ponding after settlement of wastes underlying the upper landfill <br /> slopes. Drainage swales will be constructed in some areas of the <br /> landfill slopes to reduce the overland flow velocity and direct <br /> overland drainage to the swales thereby reducing erosion <br /> problems. The drainage swales will be constructed at a minimum <br /> 0 . 5 percent slope. The maximum final landfill slope will be 6 <br /> percent along the perimeter to prevent drainage slope reversal <br /> from landfill settlement (Drawing 3) . <br /> 13 <br />