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North County RC&SL Page 16 of 64 Public Works/Solid Waste <br />Joint Technical Document County of San Joaquin – Revised July 14, 2025 <br />4.3.1 Geology <br />4.3.1.1 Regional Geology (Soils) <br />The NCRC&SL is located east of Lodi, California near the northwestern edge of the San Joaquin <br />Valley. Alluvial sediments deposited by river and streams characterize the geology of the eastern <br />portion of the San Joaquin Valley (Appendix C). <br /> <br />4.3.1.2 Site Geology <br />The 1988 report presented a site-specific topographic map and cross-sections (Appendix C <br />Figures 1 and 2) of soils encountered in borings. Geologic maps of the site (Wagner, D.L., et. al, <br />1981 and Jennings, C.W. 1977) show that the geology consists of semi-consolidated Quaternary <br />sediments of the Modesto and/or Riverbank formations. <br /> <br />4.3.1.3 Seismicity <br />An assessment of seismicity at NCRC&SL has been prepared by Dr. Norman Abrahamson in <br />2007 as part of the Preliminary Closure/Postclosure Maintenance Plan, Appendix B. The <br />average horizontal ground acceleration for the site was estimated to be 0.098g resulting from the <br />design earthquake (i.e. Maximum Probable Earthquake (MPE)) (Appendix C in Appendix B). <br /> <br />4.3.1.4 Fault Identification and Proximity <br />The Tracy-Stockton Fault is mapped approximately six miles south of the NCRC&SL (Jennings, <br />1994). This fault is characterized as a buried/concealed reverse type, thus it does not exhibit <br />surface rupture and is not considered an active fault according the Alquist Priolo (AP) Earthquake <br />Fault Zoning Act. The Act considers an “active fault” to have had surface rupture within Holocene <br />time (within 11,000 years). Although it is not considered active, the fault may be considered <br />potentially active. If an earthquake were to occur along the Tracy-Stockton fault, there would be <br />a potential for the landfill structures to be affected by ground shaking. Although liquefaction is <br />associated with ground shaking when groundwater is near the surface, groundwater at the site is <br />approximately 150 feet below the ground surface and the soils are predominately siltstone and <br />sandstone, therefore, there is a low potential for liquefaction to occur at the site. Historically the <br />ground shaking experienced in San Joaquin County in the vicinity of the landfill has not resulted <br />in significant structural damage (City of Lodi, Draft EIR 2001). Furthermore, the site is not