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one, or having a geosynthetic component [under¶(a)(2)], shall have these aspects of their design specifically supported in the slope stability report required under §21750(0(5) (emphasis added). Because the design slopes of the final landfill configuration is less than three to one (Figure 6), it does not appear that stability analysis is required. The landfill is located in an area of low seismicity (Appendix F). Stability analysis has been performed for the overall refuse slope stability of Module "I" and 1, and the long-term partial cover of Module "I". The refuse fill, and cover soils were found to be stable under design conditions (Appendix F). 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 Investigation groundwater levels were measured in three domestic wells located within a 1-mile radius of the landfill. Groundwater elevations ranged from 64 to 110 feet MSL (Appendix D). 4.10.2 Site Hydrogeology 4.10.2.1 Hydraulic Conductivity During the 1985 Geologic Investigation, six borings were advanced to depths ranging from 70 to 100 feet in the central area of the site (Appendix D). Approximately two-thirds of the soils encountered in the six borings consisted of moderately cemented clay/claystone and cemented silt/siltstone with in- Foothill Sanitary Landfill Page 13 of 57 Public Works/Solid Waste Joint Technical Document County of San Joaquin—Revised 7/30/10