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Weldon Church Site Background Information Page 9 of 12 approximately 15 feet into the crawl space through the crawl space access area (Figure 2). On 25 May 2011 at 12:30 pm, the Summa canister valve for Crawl Space-1 was opened to begin air sample collection. On 26 May 2011 at 11:00 am, the Summa canister valve for Crawl Space-1 was closed.Crawl Space-1 was collected for approximately 22.5 hours.The initial vacuum was measured at 28.5 in/Hg and the final vacuum was measured at 8.0 in/Hg. For ambient air samples (Ambient-SW and Ambient-SE), Summa canisters were placed and secured on folding chairs in the backyard approximately 20 feet south of the residence, 12 feet away from the neighboring fence lines, and three feet above the ground surface. On 25 May 2011 at 10:10 am, Summa canister valves for Ambient-SW and Ambient-SE were opened to begin air sample collection. On 26 May 2011 at 10:00 am, the Summa canister valves for Ambient-SW and Ambient-SE were closed. Ambient-SW and Ambient-SE were collected for approximately 24 hours. The initial vacuum's of Ambient- SW and Ambient-SE were measured at 29.0 and 29.5 in/Hg, respectively; the final vacuum's were measured at 9.5 in/Hg and 6.0 in/Hg, respectively. A total of three air samples (Crawl Space-1, Ambient-SW and Ambient-SE)were collected and analyzed during the crawl space air investigation performed at the site on 25 and 26 May 2011. The following is a summary of findings: • TPH-g were detected in Crawl Space-1 at a concentration of 680 micrograms per cubic meter (pg/m3). • BTEX compounds were detected in Crawl Space-1 at concentrations of 0.53 pg/m3 benzene, 5.3 pg/m3 toluene, 1.2 pg/m3 ethylbenzene, and 2.53 pg/m3 total xylenes. • Toluene was detected in Ambient-SW and Ambient-SE at concentrations of 0.43 pg/m' and 0.44 pg/m3, respectively. • The TPH-g concentration detected in Crawl Space-1 (680 pg/m') was above the established San Francisco Bay Regional Water Quality Control Board's (SFBRWQCB) Residential Environmental Screening Level (ESL) of 10 pg/m' for indoor air (Table 1 and Appendix D). • The benzene concentration detected in Crawl Space-1 (0.53 pg/m')was above the established SFBRWQCB Residential ESL of 0.084 pg/m'for indoor air(Table 1 and Appendix D). • The ethylbenzene concentration detected in Crawl Space-1 (1.2 pg/m3) was just above the established SFBRWQCB Residential ESL of 0.98 pg/m3 for indoor air (Table 1 and Appendix D). • Toluene and xylene concentrations detected in Crawl Space-1 (5.3 and 2.53 pg/m3) were below the established SFBRWQCB Residential ESL's of 63 pg/m3 (toluene) and 21 pg/m3 (xylene) for indoor air (Table 1 and Appendix D). .Ad�•niiced GeoEmironmental,Inc.