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3-6 10 Mw 7.9 event on the San Andreas fault system should be considered for evaluation of both MPE and MCE design ground motions at Forward Landfill, along with the appropriate Mw event on the Great Valley blind thrust system. A target acceleration response spectral envelope was developed by Geosyntec for each of the MCE/MPE candidate events using the median and 84th percentile acceleration response spectra evaluated using the Abrahamson and Silva [1997] attenuation model. Based upon the target significant duration of strong ground shaking and acceleration response spectral envelope for each candidate event, the following four time histories were selected to represent potential ground motions at a hypothetical bedrock outcrop at the site: ♦ the 270 -degree component of the Saratoga -Aloha Avenue record from the Mw 6.9 Loma Prieta earthquake, scaled to either 0.19 g to represent the MCE or to 0.13 g to represent the MPE; ♦ the 315 -degree component of the Santa Teresa Hills record from the Mw 6.9 Loma Prieta earthquake, scaled to either 0.19 g to represent the MCE or to 0.13 g to represent the MPE; ♦ the 360 -degree component of the Corralitos-Eureka Canyon Road record from the Mw 6.9 Loma Prieta earthquake, scaled to either 0.19 g to represent the MCE or to 0.13 g to represent the MPE; and ♦ the Magnitude 8+ synthetic accelerogram generated by Seed and Idriss [1969] to simulate distant large -magnitude event on the San Andreas fault, scaled to 0.10 g to represent both the MCE and MPE. 3.5 Soils 3.5.1 Surface Soils The surface soils near the site are mainly comprised of two soil types typical of Victor Formation sediments. The two soils, as mapped by the U.S. Soil Conservation Service, are known as Clear Lake clay (CL) and Jacktone clay (ST). These soils are similar in composition, being formed from alluvium. The Jacktone and Clear Lake clays are equally pervasive at the site with the Clear Lake clay more prevalent in the northern and southern portions of the site and the Jacktone Clay more prevalent through the middle portion. These soils are subject to rare flooding in years of abnormally high rainfall over short durations. The Jacktone clay (ST) covers the nearly flat terrain 100 to 200 feet from the North Fork and South Fork of Littlejohn's Creek. Typically, this soil type is found on 0 to 2 percent slopes forming a moderately deep hardpan of somewhat poorly drained soil made up of generally dark gray clay about 2 inches thick, underlain by light gray clay loam, followed by hardpan of Forward Landfill SWT Engineering Joint Technical Document - April 2014 z:\projects\allied waste\forward\five year permit rvw 2013\1td-5 yr pr 2013\text\sec 3_final.doc