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The perimeter side slopes will be excavated at 3:1 (horizontal to ver- <br />tical) down to an average excavation depth of 30 feet. Based on the <br />hydrogeologic investigations (see Appendix A), these base grades will <br />be from 96 to more than 118 feet above existing ground -water eleva- <br />tions. The base of excavation will be sloped towards the perimeter at <br />2 percent minimum with a cross -slope of 2 percent into the center of <br />each module. A temporary runoff containment sump outside the limits <br />of the active module will be excavated to collect runoff from within <br />the active fill and excavation modules. <br />Based on the proposed excavation grades, the total of approximately <br />9,000,000 cubic yards of soil far exceeds the estimated soil needs for <br />landfill operation and final soil cover. However, the additional ex- <br />cavation will provide greater volume for refuse filling, thus extend- <br />ing the service life of the site. Excess excavated soils will be dis- <br />posed of off site, at areas designated by the County, or sold to pro- <br />spective buyers. <br />4.3.2 Earthfill <br />Earthfill will be required at the landfill for various design features <br />such as perimeter berms, foundations for access roads, and drainage <br />facilities over refuse fill. Areas to receive earthfill will be <br />stripped of vegetation and topsoil, scarified, and compacted before <br />placing the initial layer of earthfill. Earthfill will then be placed <br />by spreading the specified soil in uniform layers not over 8 inches <br />thick. Each soil layer will be watered or dried as needed to bring <br />the soil to the specified moisture content and compacted with suitable <br />equipment to at least 90 percent relative compaction (ASTM Test Desig- <br />nation D1557-78). <br />Selective stockpiling of excavated soils will be necessary for later <br />use as cover material. A screening berm north of the landfill limits <br />PJ9 9390209A.00D 14 <br />