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SUPPLEMENTAL SITE INVESTIGATION WORK PLAN <br /> South Pointe Property <br /> Stockton, California <br /> Site Background <br /> Results of the passive soil vapor survey were used to select subsequent 'active' soil vapor <br /> sampling locations. The five dual-depth soil vapor probe locations are illustrated on Figure 5 in <br /> Appendix B. Several VOCs (benzene, ethylbenzene, tetrachloroethene [PCE], and toluene) were <br /> detected at concentrations exceeding unrestricted site use screening criteria. Overall, <br /> concentrations were low, and Stantec concluded that soil vapor data did not suggest the <br /> presence of significant onsite source(s) of VOCs in soil vapor; rather, soil vapor concentrations <br /> likely represent ambient conditions attributable to multiple documented and undocumented <br /> sources of petroleum hydrocarbon impacts to groundwater and the cumulative effects of over <br /> 100 years of industrial use at the site and surrounding areas. Concentrations of benzene, <br /> ethylbenzene, and toluene (VOCs typically associated with petroleum fuel releases) in soil vapor <br /> exceed risk-based screening criteria for unrestricted site use.These conditions can likely be <br /> managed effectively during future redevelopment through the targeted use of vapor barriers <br /> and/or placement of occupied buildings away from areas with documented soil vapor impacts. <br /> It is also likely that earthwork associated with redevelopment (such as removal of OCP- and <br /> lead-impacted soils, or removal and/or re-compaction of fill materials for geotechnical <br /> purposes) would result in improvement of soil vapor conditions, a condition which can be further <br /> assessed following completion of pre-development earthwork activities. <br /> 2.7 <br />