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12. Sub-slab samples will be collected in one-liter Summa canisters. 13. Following sample collection Summa canisters will be closed and secured. 14. Measure the canister vacuum before and after sample collection and record both measurements on the sampling form and chain of custody form. 15. Samples will be shipped to the analytical laboratory under chain-of-custody procedures and analyzed for VOCs by EPA Method TO-15-SIM. 16. Sample number, collection time, location, sample depth,volume purged, purge time and flow rate, type of probe, and other pertinent site-specific observations will be recorded on field forms. To monitor for potential introduction of ambient air or short-circuiting during soil gas sampling a helium leak check test will be used,which consists of the following: 1. Place a shroud over the boring and all aboveground sampling equipment for purging. 2. Fill the shroud with approximately 10 to 30 percent helium using a handheld field helium detector. 3. In final 200 mL of purging, collect a soil gas sample in a Tedlar° bag using a lung box. 4. Measure helium concentration in the Tedlar° bag with the field helium detector. 5. If the concentration of helium is greater than 0.5 percent (or greater than 5 percent of the minimum concentration in the shroud), resample after checking seals and fittings. 6. Proceed with sub-slab gas sample collection upon confirmation that helium leak detection within acceptable range. 7. Record field measurements and other observations on field sampling forms. Sub-slab samples will be analyzed by EPA Method TO-15-SIM (Summa cannisters) per Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air-Second Edition (EPA 1999). The sub-slab samples will also be analyzed for leak check compound helium using ASTM D-1946. Air sampling(both indoor and outdoor)will include deployment of approximately three Summa canisters within the Site building and one canister outside the building to collect outdoor air (all four Summa canisters will be set for an 8-hour exposure). Indoor air sample locations will be co-located with the three sub-slab Vapor Pin locations.The outdoor air sample location will be based on the Beacon sampler results, utility investigation, and Site considerations (e.g., vehicular and foot traffic). Indoor air and outdoor air sampling procedures are as follows: 1. Obtain Individually certified clean Summa canisters and flow controllers from the laboratory and record the pre-test vacuum pressure (must be 27-30 inches of mercury [Hg] vacuum), canister and flow controller serial numbers. FINAL RIPON PCE INVESTIGATION WORK PLAN.DOCX 4-9 PROJECT NO.631021512