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• <br />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 )TD). 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 )TD. <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,potenti,al,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 />Forward Landfill PCPCMP 3-6 <br />L:\Allied\2000.193\Reports\FinaIPCPCMP:FL-sec3: 8/20/01 BRYAN A. STIRRAT 6 ASSOCIATES <br />