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GeoSyntec Consultants <br />cover for the low permeability layer, test results confirming the suitability of <br />such materials shall be included; <br />3.4.2.1 Final Cover Grading <br />The proposed WMU B grading plan for the final cover design is shown on <br />Figure 3-1. Twenty -foot wide benches will be placed for every fifty -feet of vertical <br />height. All future waste slopes will be placed at 3H:1 V. The existing north and east <br />side slopes of WMU B are at 2H:1 V, and the steepest section of the existing south slope <br />is at 1.75H:1 V. The existing south slope will be regraded by Forward to a slope of <br />2H:1 V for the final cover. The southeast comer has already been excavated back to the <br />desired flatter slope, while the remaining length will be flattened by placing additional <br />intermediate soil cover. Bench drainage ditches will be graded at 2%, and the top deck <br />will be graded at 5%, toward side slope down drain inlets. The final cover stability <br />analysis for the proposed grading plan is discussed in Section 3.4.2.4. <br />A geotechnical field investigation and laboratory testing program was performed to <br />estimate the level of foundation settlement beneath the landfill at final grading <br />[CH2M HILL, 1994]. Minor settlements are expected at the landfill perimeter and a <br />maximum of approximately two feet of settlement was calculated under the maximum <br />final elevation of the landfill (elevation of 210 -ft). The maximum differential <br />settlements were estimated to be approximately 0.36 percent. The foundation settlement <br />calculations are discussed in Appendix D. <br />Differential settlement of the waste and foundation could affect the drainage grades <br />and potentially damage the components of the WMU B final cover system. <br />Approximately half of the waste settlement in the WMU B area should occur during the <br />5 -year settlement period between the end of waste placement and the start of final cover <br />construction. A minimum 2 -ft thick intermediate soil cover and temporary drainage <br />control system will be in place during the 5 -year settlement period. A 1 to 2 -inch thick <br />hay/straw layer will be placed over the intermediate soil cover to minimize rainfall <br />induced erosion. Drainage grades will be maintained during the 5 -year settlement <br />period by placing fill or re -grading as necessary. <br />After completion of all closure activities, an initial aerial photographic survey will <br />be performed for the closed WMU B area per §21090(e), Final Cover Surveys. This <br />0 J:\AL.LIED\FORWARD\CLOSUREPLAN\REPORT 3-4 99.11.30 <br />