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positive drainage would have to be maintained. <br /> Assuming the presence of a large (3 ft. x 3 ft. x 6 ft.) void beneath a 5% landfill <br /> slope, Beck's calculations indicate that ponding conditions could exist if the void <br /> is within 10 feet of the final cover. The calculations also indicate that the <br /> geomembrane could be endangered if the void exists within 3 feet of the final <br /> cover. In order to minimize this potential, load checks and waste disposal <br /> inspections will be employed to verify that large, void-promoting decomposable <br /> materials are not disposed within 10 feet of final landfill grades. <br /> 5.3.4.4 SETTLEMENT OF EXISTING REFUSE <br /> R.W. Beck (1995) calculated that the refuse within the existing Austin Road <br /> Landfill could settle as much as 2 to 4 feet under the anticipated new refuse <br /> loads. However, since the planned"'landfill expansion grades will mimic the <br /> existing grades, the differential settlement of existing refuse was calculated to be <br /> minimal, resulting in a differential final cover grade that ranges from 4.9% to <br /> 5.6%. Since this existing and need Aconfiguration.lexists at the existing <br /> Forward Landfill, this conclusion is also considered applicable at that location. <br /> Based on this evaluation;the 6vera1l strain on"the fiiner system associated with <br /> differential settlement of the underlying existing refuse, is anticipated to be <br /> negligible. <br /> 5.3.4.5 VOID SETTLEMENT AND POTENTIAL LINER DISTRESS <br /> As shown in Appendix F, R W. Beck (1995) also evaluated the magnitude of <br /> refuse settlement that could endanger the integrity of the new landfill liner <br /> system. Beck assumed that a 60-mil HDPE geomembrane would be irtsta <br /> over existing wastes and native soils, with an initial minimum slope gradient of <br /> 5%. The interim final cover system (as discussed in Section 5.2.2.3) is proposed <br /> at a 3 to 5 percent minimum gradient, has no geomembrane component and is <br /> only intended to serve as an infiltration mitigation measure during placement of <br /> the Class III waste above the existing Austin Road refuse. The new Class III <br /> waste will be placed with a 5:1 slope ratio on the south facing slope. The 5:1 <br /> slope (20 percent gradient) will be overlaid by the proposed intermediate liner <br /> system. <br /> Forward Landfill jTD 5-19 <br /> L:\AII ied\2000.193\Reports\finaljtd:Sec-5.0:08/22/01 <br /> BRYAN A.STIRRAT&.ASSOCIATES <br />