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Memorandum 1607 EAST MAIN STREET, ST. CHARLES, ILLINOIS 60174 y 630-762-1400 y FAX 630-762-1402 y CB&I To: From: Cc: Date: Re: J.C. Isham, PG - CB&I Pam Thomas - CB&I Len Yamamoto, PE - CB&I January 20, 201 Foothill Sanitary Landfill - Seismic Displacement Analysis The seismic screening or pseudo-static analysis that was originally performed (refer to Shaw 2012 Updated Slope Stability Report) applied a constant horizontal acceleration of 0.75 x PGA (Bray et al., 1998) or 0.75 x 0.05g = 0.038g — deemed as a conservative approach for simplified seismic slope stability. With the assumed horizontal acceleration value of 0.038g, the results of the pseudo-static analysis yielded factors of safety greater than 1.5. In accordance with Title 27 California Code of Regulations (CCR) Section 21750, if the pseudo-static factor of safety is < 1.5, a rigorous analysis must be performed to estimate the potential for permanent seismic displacement along the critical slope stability cross section analyzed. The “Simplified Seismic Design Procedure” developed by Bray et al. (1998) is an accepted procedure for analyzing seismic displacement. To satisfy concerns that the Water Board has regarding the PGA used in the pseudo-static analysis, a seismic displacement analysis was performed based on the very conservative assumption that the PGA is equal to 0.200g — taken from the USGS 2014 National Seismic Hazard Map of the U.S. (see attached pages). A summary of the seismic displacement analysis performed is provided below with detailed calculations and supporting documentation provided in the attached pages. Seismic Displacement Analysis The seismic displacement analysis was performed for the final landform or final waste slopes using the Simplified Seismic Design Procedure developed by Bray et al. (1998). According to Bray (1998), the procedure is comprehensive because it takes into account the characterization of the design bedrock motions in terms of intensity, frequency content, and duration along with estimations of the seismic loading at the base of the landfill. Additionally, for input into the Bray (1998) method, estimates of a representative waste shear wave velocity of the sliding mass based on the thickness of the waste fill were developed according to procedures described by Kavazanjian (1995). Based on Kavazanjian (1995), the shear wave velocity was estimated as being approximately 385 meters per second (m/s) for the final landform using an average height of 180 ft (55 m). The displacement analysis utilizes yield acceleration to calculate the permanent displacements. The yield acceleration (ky) was determined to be 0.1399g for the final landform using the SLIDE slope stability software program (see attached pages). "55"$).&/5"