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<br /> <br />Foothill Sanitary Landfill Page 11 of 52 San Joaquin County DPW - Solid Waste <br />Joint Technical Document Revised 12/04/2025 <br /> <br /> <br />Beyond formational contacts, the geology mapped in the near vicinity and at the landfill <br />does not indicate significant geologic structural features (i.e. folding, attitude of beds, faulting, <br />etc). A review of the Wagner, 1981 geologic map and boring logs from previous site <br />investigations (Kleinfelder, 1985-1990) suggested that the primary mechanisms for the <br />deposition of the soil and rock types found at the site were fluvial (stream deposits) and fluvial <br />deposits that were reworked by volcanic mudflows. Evidence of volcanic deposits included the <br />presence of devitrified glass, tuff, and fine black inclusions (andesite detrital grains) <br />characteristic of the Mehrten Formation was found in siltstone at the site. The attitude of <br />bedding planes was not observed. However, the thickness of the bedding ranged from massive <br />(>10 feet thick) to laminated (< 3/8 inch thick). Contacts between the various soil types ranged <br />from gradational to sharp. Many of the soil types were weakly to moderately cemented. At <br />depths greater than 150 feet bgs in MW-3, chert and quartz filled veins were encountered in <br />siltstones and sandstones (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. <br />These lithologic units are typically underlain by cemented sandy silt to approximately 30 feet <br />bgs. 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 site <br />(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 <br />referenced a 2002 EMCON/OWT study. Because of new data in the earthquake catalogue, <br />recent guidance documents, and new attenuation relationships, the 2002 EMCON/OWT <br />analysis has been updated in this JTD Addendum (2012). <br /> <br />Six nearby faults/fault zones (Central Valley Coast Range, Greenville, Concord-Green <br />Valley, Calaveras, Hayward, and San Andreas) were used in estimating ground motions at the <br />landfill. It should be noted that in this analysis one additional fault was characterized in addition <br />to those characterized in the 2002 EMCON/OWT report. The additional fault characterized in