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The pseudo -static analyses that were completed for the project to evaluate earthquake loading conditions indicate yield accelerations from about 0.10g to 0.11 g for the range of interface shear strength parameters shown in Figure 3. The yield acceleration is the seismic coefficient (k,) that yields a static factor of safety of 1.0. As shown in the attached calculations, using these yield accelerations and Bray & Rathje's method, an insignificant amount of seismic -induced permanent displacement of the landfill liner system is calculated for the two design earthquake events (i.e., Great Valley and San Andreas fault MCE's). 4.0 FINAL COVER STABILITY ANALYSES 4.1 Anticipated Final Cover Geometry The final cover for the proposed development is a multi -layer system that, from top to bottom, will consist of the following: 1 -foot thick vegetative soil layer; drainage layer; 60 -mil thick HDPE geomembrane, textured.on.both sides;...l_-foot.thick compacted.clay layer with maximum permeability of 10-6 cm/sec and; 2- foot thick compacted foundation layer. The proposed final cover,wi11,,have a -s1< ,,gradient of 3:1,�,[+V) between benches that will be installed on 40 -foot vertical intervals. Recognizing that a drainage layer will preclude developm.ent.of,pore-water,pressu.res, the -interface between the vegetative soil layer and the underlying textured HDPE is considered the critical potential failure surface. 4.2 Analytical Methods Because the length of cover between benches._(about 126_.feet),is,.significantly.greater than the thickness of the cover system (4 feet), the semi -infinite slope analysis procedure was considered appropriate to evaluate the stability of the ..final cover slope. Slope stability was evaluated for both static and seismic loading conditions. Since ..aaboratory tests have not been performed to obtain shear.strength parameters.for.the textured HDPE/vegetative soil interface, the analyses were directed to "back -calculate" .the strength properties that will be required to provide a static factor -of safety_of l._5. This information will then be used to establish minimum criteria for later construction of the final cover. 4.3 Final Cover Stability Results As shown in the attached calculations, the results of the semi -infinite slope analyses indicate that a static factor of safety of 1.5 can be obtained for the proposed final cover configuration providing that the interface between textured HDPE and the vegetative layer above it or clay below it develops an angle of friction of 27 degrees with no cohesion (i.e. � = 27° and c= 0). Review of the native soil data generated in the area by CH2MHill (1992) suggests that the required interface strength parameters can be achieved. L:Allied\2000.193\Reports\finaljtd:Appendix E GLA:08/16/01