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Ms.Lori Duncan February 28,2012 RE:2911 E.Fremont St,Stockton,CA Page 2 of 6 area(former clarifier). The results are summarized below. TPHg: Indoor air samples collected on February 8,2012 contained TPHg at 22 micrograms per cubic meter (µg/ru )to 42 µg/m3,which are similar to the results from the previous indoor air samples(30-34 µg/m3). All of the indoor air samples collected at the site contained TPHg at concentrations exceeding the Environmental Screening Level (ESL) of 14 µg/m3 for indoor air in commercial/industrial settings. No California Human Health Screening Level(CHHSL)has been established for TPHg. It should be noted that the ESL for TPHg is basedu on conservative noncancerous exposure(hazard quotient of 0.2)rather than the hazard quotientf :0,41ti by Cal/EPA to establish CSHHLs for other noncancerous exposure. ij Benzene: Concentrations of benzene in indoor air samples collected February 8, 2012 were 1.4 and 1.6 µg/m3, similar to earlier samples (1.3 to 1.6 µg/rn). All of the indoor air samples contained benzene at concentrations exceeding the CHHSL of 0.14 µg/m3. Toluene: Concentrations of toluene in indoor air samples were 5.9 and 6.3 µg/m3, as compared to previous results of 6.8 and 7.1 gg/m3,all of which are well below the CHHSL(non-carcinogenic)of 438 gg/m3- Ethylbenzene: Concentrations of ethylbenzene in indoor air samples were 0.75 and 1.8 gg/m3, as compared to previous results of 1.0 and 1.1 pg/m3.Only one of the four samples contained ethylbenze at a level marginally above the CHHSL (carcinogenic)of 1.6 gg/m3. Xylenes: Concentrations of xylenes in indoor air samples were all well below the CHHSL (non- carcinogenic) of 1,020 gg/m3. Naphthalene: Naphthalene was detected at an elevated concentration of 55 µg/m3 in sample 759-IAI, located in the center of the warehouse, near excavated area and the replaced floor drain. The only other sample containing naphthalene was sample 602-IA2 (October 12, 2011), which contained 0.47 gg/m3 naphthalene. The elevated result of 55 µg/m3 is flagged in the report, noting "an estimated value for tentatively identified compounds in mass spectrometry where a 1:1 response is assumed." When questioned further the laboratory chemist responded that they used the qualifying flag "because naphthalene does not perform well from canisters and the%RSD [relative standard deviation] is>40. It is a semi-vol[atile] compound and not [a] very good responder. The Relative Response Factor for naphthalene is 0.07, which means any small change in area is a huge change in the %RSD." With the exception of the uncertainty of the naphthalene detections,the analytical results of the indoor air samples collected February 8,2012 were very similar to the those collected October 12,2012,with relative percent differences of the ratios of detected constituents ranging from 0.47%to 6.58%(comparing average ratios of October 2011 samples to the average ratios of February 2012 samples). Table 1 summarizes the results of the indoor air samples,and also includes the results of indoor air and ambient air samples collected previously. Attachment 1 contains a copy of the laboratory report for the most recent indoor air samples. 10759-Vapor Sampling