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eoLogic Associates <br /> E"°" p <br /> ';'� Geologists,Hydrogeologists and Engineers <br /> June 5,2005 <br /> Project No. 2005-082 <br /> Mr. Richard Genzel <br /> Bryan Stirrat Associates <br /> 1360 Valley Vista Dr. <br /> Diamond Bar, California 91765 <br /> COVER SLOPE STABILITY EVALUATION <br /> PHASE 1 PARTIAL FINAL CLOSURE <br /> FORWARD LANDFILL <br /> SAN JOAQUIN COUNTY, CALIFORNIA <br /> INTRODUCTION <br /> GeoLogic Associates(GLA)is pleased to present the results of engineering analyses conducted <br /> to evaluate the cover stability of the proposed Phase 1 Partial Final Closure of the Forward <br /> Landfill in San Joaquin County, California. GLA has reviewed the construction plans prepared <br /> by BAS. In support of this effort, GLA reviewed the documents listed in the attachment,which <br /> provide site-specific geologic,seismic,engineering information, and regulatory guidance for the <br /> design and construction of solid waste facilities. <br /> The final grading plan for the landfill (BAS,2005)indicates a cover inclination from 3.2:1 to 5:1 <br /> (horizontal:vertical)over the northern and northwestern portion of the landfill. The slope height <br /> (between benches)ranges from 25 to 36 feet. The benches are designed at 15 feet width with a <br /> 2:1 (horizontal to vertical)base slope inclination. The maximum deck elevation is <br /> approximately 93 feet above mean sea level(msl). <br /> ANALYSIS <br /> The cover slopes must have a factor of safety of at least 1.5 under both static conditions and <br /> seismic loads associated with the anticipated Maximum Probable Earthquake(return period <br /> approximately 100 years)horizontal acceleration(MHA)or a more rigorous form of analysis per <br /> CCR Title 27 Section 21750. For the purpose of this analysis,we used the more conservative <br /> Maximum Credible Earthquake(which has a much greater return period). <br /> GLA conducted a seismic risk assessment to determine an appropriate MHA for the landfill. <br /> Using the attenuation relationship from Cambell and Borzongia(1989) for an alluvial soil <br /> condition and the program EQFAULT(Blake,2004), yields an earthquake of Magnitude 6.7 on <br /> the Great Valley Fault at a distance of approximately 20 miles(Appendix A). This event yields a <br /> horizontal ground acceleration of 0.13g. A horizontal acceleration of 0.158 was used in the <br /> analysis for calculation of dynamic displacement. _ <br /> GLA analyzed the proposed final grading plans developed by BAS to determine if the proposed <br /> cover geometries were stable under static conditions and foreseeable seismic loads. <br /> 16885 W. Bernardo Dr., Suite 305, San Diego, CA 92127 Phone:(858)451-1136 Fax: (858)451-1087 <br />