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• Seismic screening, or pseudo-static, slope stability analysis using veneer slope stability equations to calculate the factors of safety with respect to 0.75 x PGA (Bray et al. 1998). To assess the stability of the landfill cap extension, the equations established by Koerner and Soong (1998) were used. The method developed by Koerner and Soong is similar to that used in the static slope stability in that it too employs a stability analysis that considers the slope in two parts. The two parts are again an active wedge resting above a passive wedge that is at the toe of the slope. The equations developed by Koerner and Soong take into account all necessary ' parameters to perform a pseudo-static stability analysis. • Yield acceleration was determined for the cover section if the pseudo-static FS < 1.5 ' • An assessment of the potential for permanent displacement during the design earthquake based on a comparison of the PGA and yield acceleration for cross sections ' with pseudo-static factors of safety < 1.5 using the method from Makdisi and Seed (1978) ' 3. MATERIAL PARAMETERS 3.1 Orientation and Strength of Landfill Cap Components The cap extension for the Landfill has been designed utilizing the following items listed in ascending order: • 1.0 foot of prepared subgrade • 60-mil double-sided textured LLDPE • 200-mil geocomposite drainage net(GDN) (HDPE core with non-woven polyester or polypropylene geotextile on either side) • 1.0 foot of earthfill • 1.0 foot of vegetative cover soil The soils on site that are anticipated to be used to construct the earthfill, vegetative cover ' and prepared subgrade have been assumed to be poorly graded sands to silty sands having no cohesion and an internal angle of friction of 32 degrees. To establish a lower limit strength requirement for the landfill cap, the minimum interface friction angle was solved for using the previously noted stability equations. 3.2 Slope Stability Analysis for Static Conditions ' The slope analyzed for stability is referenced in Section 1.1 above and is shown in Figure 1. As can be seen in the stability analysis presented in Calculation 1,to obtain a minimum ' factor of safety of 1.5, an interface friction angle of 21.0 degrees is required. The minimum interface friction angle applies to any of the components within the landfill cap system, although it is anticipated that the weakest interface will be the textured ' LLDPE/soil interface at the bottom of the liner section. It is worth noting that the 'stability of the soil veneer was not analyzed in a saturated condition because an adequate drainage layer has been designed to be incorporated into Slope Stability Analysis Corral Hollow Landfill—Rev 2 512012012 4