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GeolagicalTecknirslHr Page 9 Sinclair&Thompson Property Soil Gas Survey Report +� January 29,2007 &W 4.1 Environmental Screening Levels The Shallow Soil Gas Screening Levels for Residential Land Use in Summary Table E of the Le CRWQCB-SFs: Screening for Environmental Concerns at Sites with Contaminated Soil and Groundwater, dated February 2005 was used for this evaluation. For the constituents of concern detected during the soil gas investigation, the following thresholds are listed in the LW 2005 ESL table: Benzene (85 [Ag/m3) • Ethylbenzene (420,000 [kg/m') r•• • Toluene (63,000 µg/m3) • Xylenes (150,000 [tg/m3) Benzene was found in the SG-1 and SG-I Duplicate soil gas samples and is the only constituent detected above the ESL thresholds. The highest detected levels in SG-4 will be considered in the following summary of results: • Benzene was detected in only the SG-1 and SG-1 Duplicate soil gas samples, at concentrations of 410 µg/m3 and 430 4g/m3, respectively. These levels are approximately 5 times the ESLs. i" • Ethylbenzene was detected in three samples (SG-1, SG-I Duplicate, and SG-4). The concentrations ranged from 110 (SG-1 Duplicate and SG-4) and 120 µg/rn3 (SG-1). These levels are more than 3 orders of magnitude below the ESLs. • Toluene was detected in all the soil gas samples. The concentrations ranged from 220 . (SG-6) and 430 µg/m3 (SG-4). These levels are more than 2 orders of magnitude below the ESLs. a Total xylenes were detected in all the soil gas samples. The concentrations ranged from 390 (SG-6) and 670 �tg/m3(SG-2). These levels are approximately 3 orders of magnitude below the ESLs. 4.2 Discussion of SG-1 Results L. The results from SG-I and SG-1 Duplicate are elevated compared to the remaining soil gas survey soil borings. During the February 2005 excavation activities, GTI and SJCEHD personnel noted that soil contamination was present near the southwestern edge of the excavation. Photos of the r„ excavation and residual contaminated soil next to the shop were included in GTI's Remedial Action Report dated August 11, 2005. The contaminated soil in this location was left in place due to restraints imposed on the volume of soil allowed to be excavated. This location was the furthest from the residence and excavation priority was directed to removing contaminated soil found closer to the dwelling. It appears that the SG-1 boring was advanced into some contaminated soil, which explains the elevated benzene and TPH levels. All other analyzed constituents were still below the ESLs. L.