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Forward Landfill Summary of Slope Stability Analyses for WMU D-01 4 The purpose of the evaluation was to verify that the minimum static factor of safety for a typical East-West refuse fill slope was approximately equal to or greater than 1.5 and that the seismic deformations for the design earthquake were acceptable. The slip surfaces evaluated involved the liner system. After determining the various static factors of safety for various liner strengths, the yield accelerations were also estimated. The yield accelerations were used to estimate deformations for the design earthquake for the site. Material Properties Four materials were modeled: subgrade, base liner system, side slope liner system, and refuse fill. For subgrade, the properties assumed were a unit weight of 125 pcf, an internal friction angle of 20 degrees, and a cohesion of 400 psf. Because only slip surfaces involving the liner system and the refuse were evaluated, the properties assumed for the subgrade do not affect the results of the analyses. Furthermore, previous slope stability evaluations for the site evaluated slip surfaces into the foundation materials. . These evaluations concluded that slip surfaces involving the foundation had higher factors of safety than movements through the lining system. For refuse fill, the unit weight assumed was 75 pcf. The internal strength was a friction angle of 33 degrees and no cohesion (Kavazanjian et al., 1995). The minimum strength for the base liner system was assumed to be the interface between the HDPE geomembrane and the compacted clay liner. The minimum strength for the liner system along the side slopes was assumed to involve either the interface between the smooth side of the HDPE geomembrane and the geocomposite drain, or the .interface between the HDPE and the GCL. To arrive at a strength envelope, strength values from direct shear tests completed in general accordance with ASTM D5321 for previous cells were plotted and generalized strength envelopes were developed for the Base Lining System and the Side Slope Lining System. The Base and Side Slope Lining System strength envelopes are shown of Figures 1 and 2, respectively. A summary of the previous test results is provided in Table 1. Section Details The proposed liner system for WMU D-01 is shown as Section A on Sheet 4 of the Construction Drawings for VVW D-01 (attached). The final grading plan. in the area of WMU D-01 is attached in Figure 3 and the refuse fill plan for WMU D-01 prior to the construction of future adjacent cells is shown on Figure 4. The excavation plan in the area of WMU D-01 is attached in Figure 5. The cross section evaluated is shown in Figure 6.