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4.3.1.4 Fault Identification and Proximity The Tracy -Stockton Fault is mapped approximately 6 miles south of the landfill (Jennings, 1994) as a buried/concealed reverse fault, thus it does not exhibit surface rupture and is not considered an active fault according the Alquist Priolo (AP) Earthquake Fault Zoning Act. The Act considers an active fault to have had surface rupture within Holocene time (within 11,000 years). Although it is not considered active, the fault may be considered potentially active. If an earthquake were to occur along the Tracy -Stockton fault, there would be a potential for the landfill structures to be affected by ground shaking. Although liquefaction is associated with ground shaking, groundwater is approximately 150 feet below the ground surface at the landfill and the soils are predominately siltstone and sandstone. Therefore, there is a low potential for liquefaction to occur at the site. Historically the ground shaking experienced in San Joaquin County in the vicinity of the landfill has not resulted in significant structural damage (City of Lodi, Draft EIR 2001). Furthermore, the site is not mapped in an area containing potentially damaging earthquakes that have produced magnitude 5 or greater from 1800 through 1999 (T. Toppozada and others, 2000). Based on historic data, it does not appear that the Tracy -Stockton Fault represents a significant hazard to the landfill. Fault proximity was assessed in three reports [Preliminary Closure/Postclosure Maintenance Plan, February 10, 2010 (Appendix B), Geologic and Hydrogeologic Report, January 1988 (Appendix C) and draft Seismic Hazard report, December 8, 1994 (Appendix D)]. These reports discuss fault proximity and activity. Plate 13 shows faults in the vicinity of the landfill. One fault (the Tracy -Stockton Fault) is not discussed in either the 1988 or 1994 reports. Additional information on this fault is provided in this Section. 4.4 HYDROGEOLOGY 4.4.1 Surface Water NCRC&SL is not within the 100 -year floodplain (FEMA digital Q3 flood maps for the landfill and areas surrounding the landfill, as provided on the FEMA and ESRI map server). Surface water from the landfill is directed to the seasonal wetlands on site. If these wetlands become full, surface water flows into a tributary of the South Paddy Creek, which flows into the San Joaquin AdamhL River. North County RC&SL Page 18 of 69 Public Works/Solid Waste Joint Technical Document County of San Joaquin — February 10, 2010