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~. ra..::.· ... --·~· <br />CB! <br />Taj M. Bahadori, P.E. <br />San Joaquin Department ofPublic Works <br />Solid Waste Division <br />1810 E. Hazelton A venue <br />Stockton, CA 95205 <br />Re: Review of the Stability Analysis at the Foothill Sanitary Landfill <br />Dear Mr. Bahadori: <br />CB&I <br />180 Promenade Circle, Suite 320 <br />Sacramento, CA 95834 <br />Teleohone: 916-565-4316 <br />January 20,2015 <br />Project 149259 <br />This letter is CB&I's response to the Central Valley Regional Water Quality Control Board (CVRWQCB) staff <br />request for the review of the stability analysis at the Foothill Sanitary Landfill (FSL). This is the second letter <br />addressing seismic stability at FSL; a previous letter was submitted to CVRWQCB dated January 13, 2015. <br />The seismic analysis that was performed by Shaw in 2012 applied a constant horizontal acceleration of0.75 x peak <br />ground acceleration (PGA) (0.75 x 0.05g = 0.038g). With the horizontal acceleration value of 0.038g, the results of <br />the analysis yielded factors of safety greater than 1.5. To respond to the concerns the CVRWQCB has regarding <br />the PGA used in the 2012 analysis, a seismic displacement analysis was performed based on the very conservative <br />assumption that the PGA is equal to 0.20g taken from the USGS 2014 National Seismic Hazard Map of the U.S. <br />(see Attachment A). <br />The seismic displacement analysis was performed for the Central Valley Coast Range (CVCR) fault and the San <br />Andreas Fault. The results of the seismic displacement analyses yielded median displacement values of0.022 inch <br />for the CVCR Fault and 0.33 inch for the San Andreas Fault; and 16% probability of exceedance values of 0.65 <br />inch for the CVCR Fault and 3.7 inches for the San Andreas Fault. All values are deemed negligible and are less <br />than the limit of 12 inches recommended by the U.S. Environmental Protection Agency in their 1995 Seismic <br />Design Guidance for Municipal Solid Waste Landfills. Title 27 California Code of Regulations does not specifY an <br />acceptable value for permanent displacement under seismic loading. Based on our experience in performing <br />landfill stability analyses in California, these displacement values are acceptable and verifY that the Foothill <br />Sanitary Landfill meets Title 27 slope stability requirements. <br />Please call if you have any questions. <br />Sincerely, <br />CB&I Environmental and Infrastructure, Inc. <br />Julian C. Isham, PG, CEG, CHG <br />Geology Manager <br />Attachment A-Seismic Displacement Analysis <br />2015-01-20 FSL Seismic Ana lysis .docx <br />Leonard 0. Yamamoto, PE <br />Senior Civil Engineer <br />(Attached).