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Weldon Church Site Background Information Page 11 of 12 11:15 am, the Summa canister valves for Ambient-East and Ambient-West were closed. Ambient-East and Ambient-West were collected for approximately 24 hours. The initial vacuum of Ambient-East was measured at 29.5 in/Hg and the final vacuum was measured at 5 in/Hg; the initial vacuum of Ambient-West was measured at 29.25 in/Hg and the final vacuum was measured at 5 in/Hg. Air sampling locations are depicted in Figure 2. A total of five air samples (Crawl Space-2, Crawl Space-3, Ambient-East, Ambient-West, and Field Blank) were collected and analyzed during the crawl space air investigation performed at the site in September 2011. The following is a summary of findings: • TPH-g were detected in Crawl Space-2 and Crawl Space-3 at a concentration of 120,000 micrograms per cubic meter (pg/m3) and in Ambient-East at a concentration of 250 pg/m3. • BTEX compounds were detected in Crawl Space-2 at concentrations of 930 pg/m3 benzene, 8,400 tag/m3 toluene, 1,300 pg/m3 ethylbenzene, and 6,900 pg/m3 total xylenes. BTEX compounds were detected in Crawl Space-3 at similar concentrations of 830 pg/m3 benzene, 8,600 pg/m3 toluene, 1,400 pg/m3 ethylbenzene, and 7,500 pg/m3 total xylenes. • BTEX compounds were detected in Ambient-East and Ambient-West at maximum concentrations of 0.47 tag/m3 benzene, 1.4 pg/m3 toluene, 0.26 pg/m3 ethylbenzene, and 1.31 pg/m3 total xylenes. • The TPH-g concentrations detected in Crawl Space-2 and Crawl Space-3 (120,000 pg/m3) were significantly above the established San Francisco Bay Regional Water Quality Control Board's (SFBRWQCB) Residential Environmental Screening Level (ESL) of 10 pg/m3 for indoor air (Table 1 and Appendix D). • BTEX concentrations detected in Crawl Space-2 and Crawl Space-3 were significantly above the established SFBRWQCB Residential ESLs of 0.084 pg/m3 (benzene), 63 fag/m3(toluene), 0.98 fag/m3(ethylbenzene)and 21 pg/m3(xylene)for indoor air (Table 1 and Appendix D). • The TPH-g concentration detected in Ambient-East (250 fag/m3) was above the established SFBRWQCB Residential ESL of 10 fag/m3 for indoor air (Table 1 and Appendix D). • Benzene concentrations detected in Ambient-East and Ambient-West (0.47 and 0.44 pg/m3) were above the established SFBRWQCB Residential ESL of 0.084 fag/m3 for indoor air (Table 1 and Appendix D). • Toluene, ethylbenzene, and xylene concentrations detected in Ambient-East and Ambient-West were below the established SFBRWQCB Residential ESLs of 63 tag/m3 (toluene), 0.98 tag/m3 (ethylbenzene) and 21 pg/m3 (xylene) for indoor air (Table 1 and Appendix D). Advanced GeoEnvironmental,Inc.