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MPE is defined by the California Division of Mines and Geology (1975) as "the earthquake that is likely to occur in 100 years, but it is not to be smaller than the largest historical earthquake." Title 27 CCR Section 21750(f)(5)(D) requires that a dynamic factor of safety of 1.5 or greater must be achieved for the critical slope, unless a more rigorous method of analysis is used that provides a quantified estimate of the magnitude of slope movement. If a rigorous method is used, it should also be demonstrated that the predicted slope movement could be accommodated without jeopardizing the integrity of ' the landfill. A permanent displacement of 12 inches along the cover liner is considered as allowable, based on the RCRA Subtitle D (258) Seismic Design Guidance for Municipal Solid Waste Landfill Ricilifies(U.S. Environmental Protection Agency [EPA], ' 1995). Seismic data for the site developed by Shaw has been used for this analysis. 2.2 Method of Static Slope Stability Analysis The soil cover for the landfill cap extension was analyzed based on equations for the factor of safety discussed by Giroud et al. (1995). In the analysis presented by the authors they discuss a soil veneer as a two part system consisting of an active wedge residing upslope from a passive wedge at the toe of the slope. The active wedge partly relies on the strength of the interface between the geosynthetic and the overlying soil. The passive wedge relies on strength developed within the soil at the toe of the slope. The equations developed by Giroud et al. take into account all parameters necessary to perform a limit equilibrium analysis of a soil veneer over a geomembrane. It is our opinion that the method of stability analysis is sufficiently conservative because the height of the slope being analyzed compared to the thickness of the landfill final cover is much less than a factor of 30 (-8 ft/2 ft = 4). According to Thiel (2008) the toe buttressing effect of a double wedge analysis only becomes ineffective when the ratio of slope height compared to cover thickness approaches 30, which is significantly higher than the ratio for this project. 2.3 Method of Seismic Slope Stability Analysis As noted previously, the seismic slope stability analysis presented herein was performed to satisfy Paragraph(f)(5)(D)of Section 21750 of Title 27 CCR. The analyses performed include: ® A site-specific seismicity evaluation that estimated the MPE for faults that may impact this site and the corresponding magnitudes of peak ground acceleration(PGA) • Static slope stability analyses using the double wedge equations to calculate the static factors of safety t • 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 Slope Stability Anaiysi Corral Hollow Landfill 4/512012 3