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TECHNICAL MEMORANDUM Page 9 �. June 3, 1992 SAC31583.AC.ZZ sections, CS -A and CS -B, are shown in Figure 1. Profile views of these two sections are shown in Appendix III. Cross sections taken through the maximum refuse height (approximately 200 feet) and through the North Sedimentation Basin located between the proposed toe of landfill and the South Fork. This first section was selected because it is at the expected location of greatest refuse fill height and it crosses the North Sedimentation Basin, the deepest proposed permanent excavation near the toe of the proposed landfill extension (21 -foot deep excavation). Section CS -B, the second section analyzed, was selected because it crosses an existing ash disposal pit, which is lined with a compacted clay liner founded at approximate elevation 15 feet, and also crosses the South Fork at the expected location of greatest refuse fill height. No section was analyzed for the portion of the proposed landfill extension south of the South Fork because soil conditions in that area are similar to subsurface conditions near Sections CS -A and CS -B, and because the proposed maximum refuse height in that area is considerably less (approximately 120 feet). For the two cross sections described above, various potential shear surfaces were analyzed to determine the "most critical' surface having the lowest safety factor under static loading conditions. The shapes of potential shear surfaces analyzed included circular arcs and surfaces formed by sliding blocks. Potential shear surfaces analyzed included surfaces entirely within the refuse fill, surfaces passing wholly or partially along interfaces within the proposed lining system underlying the refuse fill (both smooth and textured FML liner was considered), and surfaces passing wholly or partially through the underlying foundation materials. PCSTABLSM cross section plots showing the "most critical" potential shear surfaces analyzed are included in Appendix III. Material Properties Material properties that were used in the stability analyses include shear strengths, friction angles, and unit weights. These properties are based on laboratory test results, SPT blow - counts, and pocket penetrometer test results performed for this exploration. Shear strength test results are summarized in Table II -1, Appendix II, and the SPT blow -counts and pocket penetrometer shear strength test results are shown in the borings logs in Appendix I. Shear strength properties used for refuse fill is based on a review of refuse properties by S. Singh of the Santa Clara University (S. Singh, 1989). Because the proposed landfill extension will accept mainly commercial and industrial waste, less frequent cover material will be required and the density of refuse will therefore be less than the typical unit weight of refuse for municipal solid waste landfill (typically 70 to 80 pounds per cubic foot). For