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Foothill Sanitary Landfill Page 13 of 52 San Joaquin County DPW - Solid Waste Joint Technical Document Revised 12/04/2025 Shaw Environmental, Inc. performed an update of the slope stability analyses reported by EMCON/OWT in 2002 and has provided the results of the updated analysis in Appendix L of this report (2012). The updated slope stability analysis for Foothill Sanitary Landfill investigated both the global stability of the final landfill configuration, and the stability of two interim waste slopes that will be created between landfill modules 1 and 2 and modules 2 and 3 within the expansion area. The global and interim slopes were all analyzed for stability under static conditions, and the critical global slope was additionally assessed for stability under seismic loading. The static stability of slopes with respect to a calculated factor of safety is not formally addressed in Title 27 CCR; however, traditional geotechnical practice typically requires a calculated factor of safety of at least 1.5 for the stability of permanent slopes. A factor of safety of 1.25 is traditionally considered acceptable for interim slopes that will eventually be buttressed by waste filling in adjacent modules. Conversely, it is noted that Title 27 CCR section 21750(f)(5)(D), does address the stability of slopes with respect to a calculated factor of safety for slopes under dynamic conditions. Under dynamic loading the required calculated factor of safety is 1.5 or greater. The results of our investigation indicate that the critical global section has a factor of safety in excess of 1.5 for both the static and dynamic conditions (2.34 and 1.83 respectively), and the two interim slopes located between modules 1 and 2 and modules 2 and 3 have static factors of safety in excess of 1.25 (1.26 and 2.02 respectively). Therefore, it is our opinion that that the proposed final and typical interim slopes at the Foothill Sanitary Landfill meet the stability criteria specified in CCR Title 27 21750(F)(5) using material properties assumed for this analysis (reference Appendix L). 4.10. Hydrogeologic Setting 4.10.1. Regional Hydrogeology Most of groundwater used in the vicinity of eastern San Joaquin County is drawn from the Arroyo Seco, Laguna, and Mehrten Formations. These regional groundwater systems are continuously being recharged by percolation of surface waters. The groundwater gradient direction is generally to the southwest. Shallower groundwater bearing zones can produce significant yield in some areas. These areas are typically located adjacent to streams where Quaternary alluvial systems deposited thin sand and gravel beds. During the 1985 Geologic