SITE INFORMATION AND CORRESPONDENCE

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Ms.Lori Duncan November 15,2011 RE:2911 E.Fremont St,Stockton,CA Page 11 of 14 Toluene: Concentrations of toluene in ambient air and indoor air samples were all well below the CHHSL (non-carcinogenic) of 438 µg/m3. Ethylbenzene: Concentrations of ethylbenzene in ambient air and indoor air samples were all below the CHHSL(carcinogenic) of 1.6 gg/m3. Xylenes: Concentrations of xylenes in ambient air and indoor air samples were all well below the CHHSL (non-carcinogenic) of 1,020 µg/m3. Na lit ne: Naphthalene was detected in only one sample,indoor air sample IA2,ata concentration of 0.47µg/m3,which exceeds the CHHSL(carcinogenic)of 0.12µg/m3. It should be noted that although the other three air samples collected from the site were non-detect for naphthalene,the detection limit of 0.26 µg/m3 is also greater than the C4SL. N MTBE, PCE, 1,1,2,2-tetrachloroethane, 1,1,2-trichloroethane, 1,1,1-trichloroethane, and 1,2- dibromoethane were not detected in either ambient air or indoor air samples, although the attainable detection limits for several of these chemicals were above the ESL for target cancer risk. None of the detection limits exceeded the ESL for non-carcinogenic health effects. Tier 2 Risk Evaluation Since several chemicals of concern exceeded their respective CISLs and/or ESLs in air samples collected at the site, L&P conducted additional evaluation of risk. The Tier 2 evaluation focused on calculating the specific excess cancer risk and hazard quotients at the site, based upon the specific concentrations detected. As indicated in Cal/EPA's Vapor Intrusion Guidance document, the default exposure scenario when evaluating vapor intrusion is the residential home dweller. The resident is assumed to remain at home 24 hours per day and live in the same home for 30 years. The CH4SLs and ESLs were developed using this conservative assumption. The indoor worker is the most common alternative site-specific exposure scenario, as is the case with this site. In this case, it is assumed that the work day is eight hours and the worker remains at the same job location or facility for 25 years. Further,office buildings and other indoor work spaces are generally assumed to have higher air exchange rates than residential buildings. The relevant default exposure parameter values(modified for the indoor worker) are: ET = exposure time, 8 hours per day EF = exposure frequency, 250 days per year ED = exposure duration, 25 years ATS = averaging time for carcinogens, 70 years AT„C = averaging time for noncarcinogens, 25 years (equal to ED) 10759-EXC SUMMARY LTR