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• 3.4). The final cover described in Section 3.2 will then be placed over the refuse <br /> prism areas. The final slopes of the Forward Landfill are designed at maximum <br /> grades of 3:1 (horizontal to vertical) (Drawing 4 of the JTD). The final grading <br /> configuration was designed by a registered civil engineer in accordance with 27 <br /> CCR, Section 21090 (b)(1)(C). <br /> 3.4 LANDFILL SETTLEMENT <br /> 3.4.1 SETTLEMENT ANALYSIS <br /> Settlement analyses were completed to evaluate how the planned waste <br /> containment system will respond through time as refuse decomposes and is <br /> mechanically compressed. These analyses considered the consolidation <br /> potential of native subgrade soils as well as the settlement potential of both <br /> existing and future refuse materials. These analyses are included in Appendix F <br /> of the JTD. <br /> The results of the settlement analyses indicate that the subgrade soils could <br /> • consolidate up to 2 feet in response to maximum refuse loads, but that the <br /> differential settlement of subgrade soils across the planned refuse footprint <br /> would be relatively minor (0.36%). While the potential for existing refuse to <br /> settle continues to exist, since the existing landfill configuration mimics the <br /> geometry of the proposed expanded landfill, the differential settlement of <br /> existing wastes is expected to be negligible. The settlement analyses of new <br /> wastes indicate that significant settlement can occur. However, assuming a <br /> uniform settlement potential for refuse of 25%, the minimum landfill final cover <br /> slope gradient is calculated to drop from 5% to 3.75%. If randomly differential <br /> settlement of 22% to 28% occurs, the calculations indicate that the final cover <br /> gradient could range from 1% to 6% in areas where a 5% cover gradient is <br /> constructed. <br /> The settlement calculations also indicate a potential to promote ponding or to <br /> damage geomembrane cover layers if voids develop in refuse within 10 or 3 feet <br /> of the cover, respectively. In order to avoid this condition, additional load <br /> checks and waste disposal inspections will be performed to exclude large, <br /> potentially void-susceptible materials from the waste fill. <br /> • <br /> Forward Landfill PCPCMP 3-6 <br /> L:\Allied\2000.193\Reports\Fina[PCPCMP:FL•sec3.doc:5/21/02 BRYAN A.STIRRAT S ASSOCIATES <br />