Laserfiche WebLink
Beyond formational contacts, the geology mapped in the near vicinity and at the landfill does not <br /> indicate significant geologic structural features (i.e. folding, attitude of beds, faulting, etc.). A <br /> review of the Wagner, 1981 geologic map and boring logs from previous site investigations <br /> (Kleinfelder, 1985-1990) suggested that the primary mechanisms for the deposition of the soil <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 /> 5.3.1.2. Site 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. <br /> The assessment of site geology is based on boring logs at various locations on the facility <br /> (Plate 9 and Appendix E). <br /> 5.3.1.3. 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 /> Andreas). Peak ground acceleration based on the five nearby faults ranged from 0.027 g to <br /> 0.054 g (Appendix F). <br /> it <br /> Foothill Sanitary Landfill Page 23 of 62 Public Works/Solid Waste <br /> JTD County of San Joaquin—Revised 10/6/05 <br />