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Ms.Lori Duncan <br /> November 15,2011 <br /> RE:2911 E.Fremont St,Stockton,CA <br /> Page 9 of 14 <br /> at the time of sampling, a 3york truCk WAS parked ins' housc. According to site employees,the <br /> work truck had been parked there the previous day pending repairs. Figure 7 shows the locations of the air <br /> samples. Attachment 5 contains photographs of the sample locations. <br /> The air samples were transported to ALS Laboratory Group for analysis of the following constituents using <br /> the EPA TO-15 SIM analytical method,based upon previous results and the availability of California Human <br /> Health Screening Levels(CHHSLs)for a given constituent: <br /> • Total Petroleum Hydrocarbons as gasoline(TPHg); <br /> • Benzene; <br /> • Toluene; <br /> • Ethylbenzene; <br /> • Xylenes <br /> • Methyl tert-butyl ether; <br /> • Naphthalene; <br /> • Tetrachloroethene; <br /> • 1,1,2,2-Tetrachloroethane; <br /> • 1,1,2-Trichloroethane. <br /> Laboratory results indicate that TPHg,benzene,toluene,ethylbenzene,and xylenes were detected in all four <br /> air samples collected at the site,regardless of whether the samples were indoor air or ambient air samples. hi <br /> addition,naphthalene was detected in the indoor air sample collected at the rear of the warehouse. Table 3 <br /> summarizes the results of indoor and ambient air samples collected at the site. Attachment 6 contains a copy <br /> of the laboratory report. <br /> Data Comparison <br /> In order to determine if the residual contamination beneath the building is entering the indoor <br /> environment, L&P evaluated separate lines of evidence: <br /> 1. Ambient Measurements: Although low level gasoline constituents were found in ambient air and <br /> indoor air samples,indoor air concentrations(samples 1A and IA2)were generally greater than <br /> ambient air concentrations. <br /> 2. Constituent Ratios: L&P evaluated the ratio between concentrations of different chemicals in <br /> ambient air samples compared to indoor air samples.If the ratios of constituents in the indoor air <br /> sample are similar to the ratios observed in ambient air samples, one may conclude that the two <br /> have the same source for detected constituents. A comparison of the ratios indicates that the ratios <br /> of indoor air samples are similar to one another and the ratios of the ambient air samples are <br /> similar to one another,but there are sufficient differences in the ratios of indoor air to ambient air <br /> samples to suggest that they have differing sources. Table 4 shows the constituent ratios for <br /> indoor air and ambient air samples. <br /> 10759-EXC SUMMARY LTR <br />