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Ms.Lori Duncan February 28,2012 RE:2911 E.Fremont St,Stockton,CA Page 4 of 6 Toluene: Concentrations of toluene in soil vapor samples were 8.5 and 27 µg/m3,which are well below the CHHSL (non-carcinogenic)of 380,000 µg/m3. Ethylbenzene: Concentrations of ethylbenzene in soil vapor samples were ND(Q.9)and 4.0µg/m3,well below the CHHSL(carcinogenic)of 1,400 µg/m3. Xylenes: Concentrations of xylenes in soil vapor samples were all well below the CHHSL (non- carcinogenic) of 880,000 µg/m3. Naphthalene: No naphthalene was detected in either of the soil vapor samples collected at the site. Tetrachloroethene(PCE): PCE was detected at concentrations of 96 and 12µg/m3,which are well below the CHHSL of 600 µg/m3. Table 2 summarizes the analytical results of soil vapor samples. Attachment 2 contains a copy of the field notes related to the temporary soil vapor probes as well as pertinent portions of the sampling methodology recommended by Air Toxics,and Attachment 3 contains a copy of the laboratory report from Air Toxics. Summary Analytical results of indoor air samples collected February 8,2012 were essentially equivalent to those of samples collected October 12, 2011, and each sample contained TPHg and benzene at concentrations marginally above the CHHSL established by the California Environmental Protection Agency,Office of Environmental Health Hazard Assessment(OEHHA). However,the ambient air samples collected at the site (October 12, 2011) also contained TPHg, benzene, toluene, ethylbenzene, and xylenes in air. Notably, benzene in all samples was present at levels exceeding the conservative screening level (CHHSL). Naphthalene was also detected in 2 of the 4 indoor air samples collected at the site but,based upon their semi-volatile nature and poor response in Summa canister samples, are considered questionable. Soil vapor samples collected at a depth of approximately 5 feet bgs,both within(SV 1-5)and outside of(SV2- 5)the excavated/backfill area contained detectable concentrations of gasoline constituents as well as PCE. However,all ofthe detected constituents were present at levels well below their respective CHHSLs(ESL in the case of TPHg). No naphthalene was detected in either soil vapor sample collected at the site. Conclusions and Recommendations Based upon the analytical results of soil vapor samples collected at a depth of approximately 5 feet btgs in Warehouse#2,the residual contaminants remaining beneath the concrete flow do not pose an undue risk of vapor intrusion into the building. Although gasoline constituents were detected in indoor air samples collected at the site of the previous excavation,it is unclear if the residual contamination remaining beneath 10759-Vapor Sampling