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partially to fully cemented mudflow in many areas. The Mehrten Formation soils <br />are believed to be reworked volcanic mudflow deposits such that they contain <br />stream deposited silt, sand, and minor gravel. Surface soils can contain <br />expansive clay soil. <br />Beyond formational contacts, the geology mapped in the near vicinity and at the <br />landfill does not indicate significant geologic structural features (i.e. folding, <br />attitude of beds, faulting, etc). A review of the Wagner, 1981 geologic map and <br />boring logs from previous site investigations (Kleinfelder, 1985-1990) suggested <br />that the primary mechanisms for the deposition of the soil and rock types found <br />at the site were fluvial (stream deposits) and fluvial deposits that were reworked <br />by volcanic mudflows. Evidence of volcanic deposits included the presence of <br />devitrified glass, tuff, and fine black inclusions (andesite detrital grains) <br />characteristic of the Mehrten Formation was found in siltstone at the site. The <br />attitude of bedding planes were not observed; however, the thickness of the <br />bedding ranged from massive (>10 feet thick) to laminated (< 3/8 inch thick). <br />Contacts between the various soil types ranged from gradational to sharp. Many <br />of the soil types were weakly to moderately cemented. At depths greater than <br />150 feet bgs in MW -3, chert and quartz filled veins were encountered in <br />siltstones and sandstones (Emcon, 2002). <br />4-8.34.7.2 Local Geology <br />Site soil consists of silty sand, clayey silt, and silty clay to approximately 10 feet bgs. <br />These lithologic units are typically underlain by cemented sandy silt to approximately 30 <br />feet bgs. These units correlate with the mapped Mehrten and Laguna Formations <br />described above. The assessment of site geology is based on boring logs at various <br />locations on the facility (Plate -9 -and Appendix E). <br />44.8. Regional Faulting and Seismicity <br />Five nearby faults (Central Valley Coast Range, Greenville, Calavaras, Hayward, and San <br />Andreas) were used in estimating ground motions at the landfill. The maximum probable <br />earthquake MPE magnitudes for the five faults ranged from 6.3 (Greenville) to 8.0 (San <br />Foothill Sanitary Landfill Paae 32 Public Works/Solid waste <br />Joint Technical Document County of San Joaquin — Revised 7/30/10 <br />