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3.3.4 Assessment of the Potential for Permanent Deformation As the pseudo-static factor of safety for slopes analyzed was less than 1.5, permanent seismic displacement is expected to occur(Bray et al., 1998). Using the yield accelerations from the current analyses, seismic displacement was calculated using the Makdisi-Seed method using the lower-bound curve for a Magnitude 6.9 earthquake and peak ground acceleration of 0.56g. The results of the deformation ' analysis are presented in Section 4.1. 4. CONCLUSIONS AND RECOMMENDATIONS This section presents conclusions and recommendations based on the results of the static and seismic slope stability analyses performed for the Corral Hollow Landfill cap extension 4.9 Slope Stability The static factor of safety for the slope analyzed is I.S. The pseudo-static factor of safety for the section is 0.62, which is less than 1.5 and therefore required a rigorous method of analysis be used to estimate the magnitude of possible displacements. The calculatedield acceleration value is 0.154 . Using the yield acceleration of 0.154 Y g g Y g, seismic displacement was calculated using the Makdisi-Seed method using an interpolation between the lower- and middle-bound curves for Magnitude 6.5 and 7.5 earthquakes, respectively, and a peak ground acceleration in rock of 0.568. The maximum displacement is approximately 10.1 inches. A permanent displacement of 6 to 12 inches is considered as the maximum allowable limit, based on the RCRA Subtitle D (258) Seismic Design Guidance for- AluniciRal Solid Waste Landfill Facilities (U.S. Environmental Protection Agency [EPA], 1995). Additionally, the design guidance document goes even further in specific reference to cover systems, and suggests that "...larger permanent deformations may be considered acceptable," due to the ease of ' accessibility for repair post-earthquake. Therefore, the results of this analysis indicate the landfill design results in stable slopes per California Code of Regulations Title 27 requirements. 4.2 Liner System Shear Strength and Testing Requirements Shaw will require that material-specific interface direct shear testing be performed prior to the start of construction. The cover liner system for the landfill cap extension should provide a minimum shear strength represented by a friction angle of 21.0 degrees(96 psf) ' for normal stresses of 250 psf. We believe this shear strength is achievable with proper selection and testing of the textured LLDPE geomembrane, GDN, geotextile, and soil components of the liner systems. However, it is important that the weakest interface shear strength be verified using direct shear testing for each of the possible interfaces in the liner system. This will consist of testing the soil to geocomposite drainage net, geocomposite drainage net to Slope Stability Analysis Corral Hollow landfill 91512612 6