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San Joaquin County Environmental Checklist <br /> capacity of the basin is unknown;however,Hotchkiss and Balding(197 1) <br /> estimated the groundwater storage capacity for the Tracy Subbasin at <br /> 1,300,000 acre-feet. <br /> Groundwater Quality <br /> In general,the northern part of the subbasin is characterized by a sodium water <br /> type,and the southern part of the subbasin is characterized by a calcium-sodium <br /> water type. Dissolved solid concentrations in well water sampled within the <br /> subbasin ranged from 50 to 3,520 mg/L,with a mean of 463 mg/L and a medium <br /> of 269 mg/L(Department of Water Resources 2004). Areas of poor water <br /> quality exist throughout the subbasin. Elevated levels of chloride occur along the <br /> western side of the subbasin. Elevated levels of nitrate occur in the northwestern <br /> part of the subbasin and in the vicinity of the city of Tracy. <br /> Flooding <br /> According to the FEMA Flood Insurance Rate Maps,the landfill facility is <br /> located in flood Zone C. Zone C is the flood insurance rate zone that <br /> corresponds to areas of minimal flooding, located outside of the 100-year <br /> floodplain. <br /> Impact Discussion <br /> a,e,f. Operation of the landfill at an increased elevation will involve additional surface- <br /> disturbing activities. The proposed project and future operations would continue <br /> to involve the use of mechanized equipment with potential for release of <br /> construction-related hazardous materials. Both of these factors could adversely <br /> affect surface water bodies if associated materials are allowed to enter them. <br /> Existing and post-project expansion facilities include several facilities to control <br /> runon,runoff,and erosion; some of these are listed below. <br /> ■ Perimeter ditch surrounding landfill. <br /> ■ Vegetation and drainage berms to direct stormwater. <br /> ® Sedimentation basin on site for all stormwater runoff. <br /> The previous EIR for the NCRC&SL identified areas that should not be disturbed <br /> in order to protect groundwater. These areas will continue to be protected, <br /> because no additional surface would be disturbed in the context of the proposed <br /> project. In addition,the landfill operator is required to comply with the CWA, <br /> including the requirements of the NCRC&SL's existing NPDES permit,and <br /> must continue to do so under future operations. The NCRC&SL's stormwater <br /> sampling plan conforms to the requirements of its NPDES permit, and the <br /> Notice of Preparation for the June 2006 <br /> North County Recycling Center and Sanitary Landfill 2-53 <br /> Permit Revision gas 0630T06 <br />