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<br /> <br />Foothill Sanitary Landfill Page 11 of 53 San Joaquin County DPW - Solid Waste <br />Joint Technical Document Revised 6/09/2020 <br /> <br />and rock types found at the site were fluvial (stream deposits) and fluvial deposits that were <br />reworked by volcanic mudflows. Evidence of volcanic deposits included the presence of <br />devitrified glass, tuff, and fine black inclusions (andesite detrital grains) characteristic of the <br />Mehrten Formation was found in siltstone at the site. The attitude of bedding planes were not <br />observed; however, the thickness of the bedding ranged from massive (>10 feet thick) to <br />laminated (< 3/8 inch thick). Contacts between the various soil types ranged from gradational to <br />sharp. Many of the soil types were weakly to moderately cemented. At depths greater than 150 <br />feet bgs in MW-3, chert and quartz filled veins were encountered in siltstones and sandstones <br />(Emcon, 2002). <br /> <br />4.7.2. Local Geology <br />Site soil consists of silty sand, clayey silt, and silty clay to approximately 10 feet bgs. These <br />lithologic units are typically underlain by cemented sandy silt to approximately 30 feet bgs. <br />These units correlate with the mapped Mehrten and Laguna Formations described above. The <br />assessment of site geology is based on boring logs at various locations on the site(Appendix E). <br /> <br />4.8. Regional Faulting and Seismicity <br />The seismicity characterization provided in the 2002 JTD referred to in the 2010 JTD referenced <br />a 2002 EMCON/OWT study. Because of new data in the earthquake catalogue, recent guidance <br />documents, and new attenuation relationships, the 2002 EMCON/OWT analysis has been <br />updated in this JTD Addendum (2012). <br /> <br />Six nearby faults/fault zones (Central Valley Coast Range, Greenville, Concord-Green Valley, <br />Calaveras, Hayward, and San Andreas) were used in estimating ground motions at the landfill. <br />It should be noted that in this analysis one additional fault was characterized in addition to those <br />characterized in the 2002 EMCON/OWT report. The additional fault characterized in preparation <br />for this report was the Concord-Green Valley Fault Zone. The maximum probable earthquake <br />(MPE) magnitudes for the six faults ranged from 6.8 (Green Valley-Concord and Calaveras) to <br />8.1 (San Andreas). Peak ground acceleration at the site, based on the six nearby faults, ranged <br />from 0.03 g to 0.05 g (Appendix L) Updated Slope Stability Analysis for Foothill Sanitary Landfill, <br />San Joaquin, California dated January of 2012. Please note that estimated values of peak