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3.2 Piezometric Conditions The piezometric head was modeled as average one foot above and parallel to the lined surface. This is consistent with the conditions used in Amendment Nos. 6, 7, 8, and 9 (CC&V 1993a, 1998, 2000, 2008). 3.3 Methodology For potential failure modes considered in this study, slope stability was evaluated according to the Spencer's Method of Analysis (Spencer's Method). Spencer's Method considers potential failure masses as rigid bodies divided into adjacent regions or "slices" separated by vertical boundary planes and is based on limit equilibrium; i.e., the method calculates the shear strengths that would be required to just maintain equilibrium, and then calculates a Factor of Safety (FS) by dividing the available shear strength by the required shear strength. Consequently, the FS calculated by Spencer's Method indicates the percentage by which the available shear strength exceeds, or falls short of, that required to maintain equilibrium. Therefore, a FS equal to or in excess of 1.0 indicates stability and that less than 1.0 indicates instability. The greater the mathematical difference between the FS and 1.0, the larger the "margin of safety" (for a FS in excess of 1.0), or the more extreme the likelihood of failure (for a FS less than 1.0). Stability analyses were conducted using SLIDE Version 8.0 (Rocscience, 2018), a commercially- available computer program, with the input parameters presented in this section. For both the wedge and the circular failure modes, the SLIDE critical surface search routine was initially used to determine the least stable failure surface. The program automatically iterates through a variety of potential failure surfaces, calculates the FS for static and pseudo-static conditions for each surface according to Spencer's Method, and selects the surface with the minimum FS, commonly referred to as the critical surface. Static analyses were conducted with no applied horizontal forces, while pseudostatic analyses modeled design seismic conditions by incorporating a constant horizontal force. For the pseudo- static analyses, a conservative design coefficient of 0.01 g (which is -2/3 of the currently approved peak ground acceleration [PGA]2 of 0.14g for the Cresson Project VLF)was used in the slope stability models, which is consistent with that used for Amendment Nos. 6, 7, 8, and 9 (CC&V 1993a, 1998, 2000, 2008). 3.4 Results Results of the stability analyses are summarized in Table 1. The output from the stability analyses are presented in Appendix B. Table 1. Stability Analyses Results Condition . FS (Critical Structure) Static Non-circular 1.6 1.3 Pseudostatic Non-circular 1.3 1.15 z Design earthquake has a recurrence interval of 2,475 years. Page 3