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Draft Environmental Impact Report Page 13 Forward Landfill Expansion The potential seismic shaking impacts described have been evaluated in the Joint Technical Document (2007 update), Geo-Logic (2008a, 2008b)and Geosyntec (1999) reports. Site-specific geotechnical and seismic analyses studies were performed (Geo-Logic,2008x, 2008b) and presented to the CIWMB and # RWQCB. The stability analyses for the proposed landfill detailed in the JTD indicates a factor of safety of at least 1.0, on par with the expectation of the CIWMB, the reviewing regulator. These studies concluded that the design criteria used (maximum peak horizontal accelerations and durations) are conservatively based on the maximum seismic potential, given the location of active faults and their associated maximum credible earthquakes. Geosyntec concluded that the Mw 7.9 event on the San �. Andreas Fault system could be the most damaging earthquake for the Forward Landfill. The Geo-Logic reports (2008a, 2008b) used MCE of 6.7 on the Great Valley V fault approximately 20 miles form the site for their pseudo-static and failure analyses, which showed a factor of safety of 1.0. Slopes along the banks of Littlejohns Creek could potentially be susceptible to localized creek bank failure in the case of the largest peak accelerations and shaking durations;however, since there is a low likelihood of a major earthquake generating peak acceleration at the site over the lifetime of the project, this potential impact is negligible. The geotechnical data collected and modeled indicated that under the loading design of the maximum credible earthquake horizontal site acceleration,the material is too dense to liquefy. The calculated factor of safety against liquefaction ranged from 1.4 to 8.0 compared to the 1.1 to 1.3 required factor of safety (GeoLogic, 2008a,2008b). I The following procedures are proposed as part of the project: • The project sponsor has prepared a seismicity study for the site, with details in Appendix D of the Geotechnical Investigation Report(Geo-Logic, 2008a, 2008b).and the Geosyntec (1999) report. If the potential maximum peak ground acceleration in the seismicity study is greater than that assumed in the preliminary design, the final project design analysis will make modifications needed to meet the factor of safety (determinations may be subject to the approval of the CIWMB and/or RWQCB). Impacts to the new liner and drainage system installed over the Austin Road Landfill will be monitored as appropriate based on any stipulations of the CIWMB and/or RWQCB. Implementation of these procedures, along with appropriate slope maintenance that is also proposed as part of the project,would reduce this impact to a less-than-significant level. rc Mitigation Measure G.2: None required. Impact G.3: Slope instability caused by an earthquake could result in damage to existing and ' proposed relocated landfill administrative facilities,scale house, groundwater treatment system, and support facilities. 1 Steep slope faces are easily compromised by earthquake shaking and the location of some of the administrative building and facilities near the landfill slope faces could result in their being damaged. The following procedures are proposed as part of the project in the Joint Technical Document (2007): • Overall reduction—or, in some cases, elimination or improvement—of slope instability at the P*N. project site can be achieved through the implementation of the seismic design measures designed to meet CCA Title 27. .a. Implementation of these procedures would reduce this impact to a less-than-significant level. .: Mitigation Measure G.3: None required.