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TECHNICAL MEMORANDUM Page 8 June 3, 1992 SAC31583.AC.ZZ typically ranged from approximately 4,000 psf to over 10,000 psf. Based on these CPT logs, a lower bound shear strength value of 2,000 psf was used in Insitu-Tech's stability evaluation for WMU E (Insitu-Tech, 1987). Groundwater Groundwater levels could not be observed at the time of drilling because the borings were drilled using drilling mud. In the Comprehensive Landfill Description report (CH2M HILL, 1992), the shallow groundwater in the vicinity of the site was reportedly encountered at 70 to 80 feet below ground surface. Groundwater measured during EMCON's subsurface exploration in 1972 indicated groundwater at depths of between 55 and 60 feet below the ground surface. In one of EMCON's boring, in the southwestern comer of the site, a one - foot thick lens of perched water was encountered at a depth of 21 feet. Based on a review of available groundwater data, there is, however, little potential for significant perched water across the site. A review of the Comprehensive Landfill Description report (CH2M HILL, 1992) also indicated that the groundwater levels in the area have declined over the past 30 years because of groundwater pumping for irrigation and domestic use and because of the current drought. This reported decline in the groundwater level in the area partly explains the higher groundwater levels measured by EMCON in 1972. Based on these groundwater table depths and available history of groundwater levels in the area, a groundwater table depth of 75 feet was assumed for purposes of the stability and settlement analyses. Results of Slope Stability Analyses Method of Analyses Slope stability analyses were performed using PCSTABL5M (J. Verduin, 1987), a computer program for analyzing general two-dimensional slope cross sections by limit equilibrium methods.: This computer program is a modified version of STABL (Siegel, 1975). This program was used to determine safety factors against slope failure for static (gravity) loading and to calculate yield accelerations for pseudostatic (earthquake) loading. Safety factors and yield accelerations were calculated using the modified Janbu procedure. Two cross sections were analyzed to estimate static safety factors. The location of these two 11