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Weldon Church Site Background Information Page 10 of 12 • Toluene concentrations detected in Ambient-SW and Ambient-SE (0.43 and 0.44 pg/m3)were below the established SFBRWQCB Residential ESL of 63 pg/m3 for indoor air (Table 1 and Appendix D). • MTBE were not detected above laboratory reporting limits in the air samples collected. Laboratory reporting limits were below the established SFBRWQCB Residential ESL of 9.4 pg/m3 for MTBE in indoor air. • DIPE, ETBE, TAME, and TBA were not detected above laboratory reporting limits in the air sample s collected. SEPTEMBER 2011 Two passive integrated air samples were collected from the crawl space (Crawl Space-2 and Crawl Space-3) beneath the residence at 104 West Beverly Place, Tracy, CA. Additionally, one passive integrated ambient air sample was collected from the east side of the residence in the backyard (Ambient-East) and one passive integrated ambient air sample was collected from the west side of the residence in the backyard (Ambient-West). Crawl Space-3 was collected as a duplicate sample to Crawl Space-2.All air samples were collected using six-liter Summa canisters. The sampling inlet on each canister was connected to a mass flow controller containing a particulate filter; the flow controllers were calibrated to a flow rate of 3.5 milliliters/minute (ml/min) in order to collect air samples over a 24-hour period. Each canister's initial vacuum was measured and recorded to ensure the initial vacuum was greater than 25 inches of mercury (in/Hg); Initial vacuum's were measured between 29 and 30 in/Hg prior to air sample collection. For Crawl Space-2 and Crawl Space-3, polyethylene tubing (PET) was connected to the mass flow controller inlet and inserted horizontally through 0.5-inch diameter polyvinyl chloride (PVC)conduit approximately 15 feet into the crawl space through the crawl space access area (Figure 2). On 26 September 2011 at 11:26 am, the Summa canister valves for Crawl Space-2 and Crawl Space-3 were opened to begin air sample collection. On 27 September 2011 at 11:30 am, the Summa canister valves for Crawl Space-2 and Crawl Space-3 were closed. Crawl Space-2 and Crawl Space-3 were collected for approximately 24 hours. The initial vacuum of Crawl Space-2 was measured at 30 in/Hg and the final vacuum was measured at 8 in/Hg; the initial vacuum of Crawl Space-3 was measured at 29 in/Hg and the final vacuum was measured at 6 in/Hg. For ambient air samples(Ambient-East and Ambient-West), Summa canisters were placed and secured on folding chairs (several feet above the ground surface) in the backyard on the east and west sides of the residence; ambient air sampling locations are depicted in Figure 2. On 26 September 2011 at 11 :15 am, Summa canister valves for Ambient-East and Ambient-West were opened to begin air sample collection. On 27 September 2011 at Advanced GeoEncironoiental,Inc.