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i4.7.2 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 <br /> approximately 30 feet bgs. These units correlate with the mapped Mehrten and <br /> Laguna Formations described above. The assessment of site geology is based on <br /> boring logs at various locations on the facility (Appendix E). <br /> 4.8. Regional Faulting and Seismicity <br /> Five nearby faults (Central Valley Coast Range, Greenville, Calaveras, 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 /> 4.9. Engineering and Chemical Properties of Soil <br /> Soil samples were collected and analyzed by Kleinfelder in 1985 (Appendix D) and 1990 <br /> (Appendix E). Laboratory testing included moisture content, unit weight, sieve size/gradation <br /> analyses, moisture density, plasticity index, dry density, hydraulic conductivities, and Atterberg <br /> Limits. Soil properties are as follows: <br /> • Dry unit weights of soil samples varied between 73 to 82 pounds per cubic foot <br /> • Moisture contents ranged from 9 to 41% <br /> • Plasticity limits ranged from 8 to 29 (PI) <br /> • Liquid limit of soil ranged from 35 to 45 <br /> 4.9.1 Stability Analysis <br /> Requirements for seismic stability are found in Title 27 Chapter 3 Subchapter 5, <br /> addressing requirements for landfill closure. According to Section 21090 of that <br /> subchapter, "Designs having any slopes steeper than a horizontal to vertical ratio of three to <br /> i <br /> I <br /> Foothill Sanitary Landfill Page 12 of 57 Public Works/Solid Waste i <br /> Joint Technical Document County of San Joaquin—Revised 7/30/10 <br /> i <br />