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Section 21750(f)(5)(D) of Title 27 CCR 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. As discussed subsequently in this report, a rigorous seismic slope stability analysis has been performed to determine the potential for permanent displacement of the landfill slopes during the MPE. Landfill regulations contained in Title 27 do not specify an acceptable value for permanent displacement. The generally accepted permanent displacement used by the solid waste industry is 6 to 12 inches (U.S. Environmental Protection Agency [EPA], 1995, and Seed and Bonaparte, 1992), with 12 inches being used most often. 2.3 Method of Static Slope Stability Analysis The static slope stability analysis was performed using the computer program SLOPE/W, which is part of the GeoStudio 2007 software package developed by GEO-SLOPE International, Ltd (2007). SLOPE/W performs two-dimensional limit equilibrium analysis using the method of slices to compute factors of safety against slope instability based on any of the following analysis procedures: • The ordinary method of slices • The Bishop simplified method (this method satisfies only moment equilibrium) • The Janbu simplified method (this method satisfies only force equilibrium) • The Spencer method (this method satisfies both force and moment equilibrium) • The Morgenstern -Price method (this method also satisfies both force and moment equilibrium) Because they satisfy both force and moment equilibrium, the factors of safety computed from the Spencer and the Morgenstern -Price methods are more accurate than those obtained from the other two methods. However, the factors of safety computed from the modified Bishop method for circular failure surfaces are typically very close to those computed from Spencer or Morgenstern -Price methods. The simplified Janbu method yields conservative factors of safety in most cases. The Morgenstern -Price method, with the half -sine inter -slice force function, has been used in this study. Rigorous seismic slope stability analyses have been performed to satisfy Paragraph (f)(5)(D) of Section 21750 of Title 27 CCR. The analyses performed include: Geotechnical Analyses for NCRCSL Department of Public Works/Solid Waste Shaw Environmental, Inc. County of San Joaquin, December 12, 2007 2-2