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• Pt'Clrminary Environmental Assessment Report Pittman Elementary School,Stockton,CA December 10,2003 Page 25 allows a back-calculation of the concentration of lead in soil that would result in a threshold blood level of lead in each receptor at two certainty levels: 950' percentile and 99th percentile. Inputs chosen for the Pittman Elementary School analysis were 0.028 pt for lead in air (DTSC example default), 4,600 µg/g lead in soil (maximum value of site samples), 15 pg/L lead in water (DTSC example default), 0% homegrown produce (DTSC example default), and 1.5 pg/m3 respirable dust(DTSC example default). Given these default assumptions, Condor is 99 percent certain that the lead levels detected at the site would result in blood levels of lead in a child of 102.2 micrograms per deciliter (µg/dL), above the 10 µg/dL health threshold identified by DTSC. Results of the Leadspread 7 Model are included in Appendix C. Thus we conclude that the concentrations of lead detected in the soil samples collected at the proposed school site do pose a significant risk to human health. 9.0 SUMMARY Condor conducted a PEA for the proposed Pittman Elementary School located in central San Joaquin County in Stockton, California in general accordance with the Preliminary Environmental Assessment Work Plan, prepared by Condor, dated April 21, 2003 and revised July 2, 2003. As indicated in Section 2.0, the site was used as a state hospital and developmental center in the past. Lawn Area All metals and pesticides identified as COPC underwent HHRA. Hexavalent chromium, cobalt, and dieldrin were the primary contributors to elevated cancer risk (greater than one chance-in-a-million over a lifetime). The chromium and cobalt samples that contributed significantly to the overall risk (L3, L7, • and L9) were located in the northern portion of the site (Figures 9 and 10, Appendix A). The samples of dieldrin that contributed significantly to the overall risk (L9 and 1,15/1,16) were located near structures (Figure 8, Appendix A), a fact consistent with the use of these chemicals in pest control and gardening applications. Sticture Dri In ine.c Lead was detected in all of the surface soil samples (Figure 11, Appendix A). Concentrations of lead in soil did not exceed the DTSC PRG of 255 mg/kg around the warehouse, sewage lifting station, Delta Center, Houses I through 6, and Garages 2 through 4. Lead concentrations did exceed the DTSC PRG in soil samples collected from around the Grant House, Grant House garage, the Rehabilitation Center, the Delta Center garage, Garage 1, and House 7. Concentrations of lead generally decreased with depth. The subsurface lead results were above the DTSC PRG in two samples (3638F-P9-D and 3638F-P58-D). The highest detected lead concentration was 4,600 mg/kg collected from the southern dripline of House 7. According to the DTSC Leadspread 7 Model, this concentration would result in blood lead levels of 102.2 µg/dL in a child, well above the allowed 10 µg/d1,. One of the three paint chip samples collected from the warehouse building had a concentration of lead that qualifies it as lead-based paint. Natural CTas Field Concentrations of methane were detected in all soil gas samples but never exceeded 0.0009%by volume, far below the lower explosive limit of 5%. The low concentrations of methane measured in soil gas at the site pose no physical hazard. Hydrogen sulfide was not detected in any of the soil gas samples. Fa.stem Former Iindergrnnnd Storage Tanks Site Seventeen VOCs were detected in the soil gas samples and were identified as COPC. These chemicals • were evaluated for risk and hazard using the Johnson and Ettinger Vapor Intrusion Model and were ZJ CONDOR