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outside the crawl spaces and samples will be collected via clean, dedicated 1/4-inch Nylaflow® tubing with compression fittings inserted into the crawlspace sufficient far enough away from exterior access points. 2.4 OUTDOOR AIR SAMPLES Outdoor air samples will be collected using 6-liter Summa® canisters with a flow controller set to collect a time-integrated sample(same duration as indoor air samples). The canisters would be placed 3 to 5 feet above ground surface and at representative locations to be selected in the field. Preferred sampling locations will: • Have unobstructed airflow, especially in the direction of the source area; • Be at least 3 feet from any structure; • Be on the windward side of the structure. • Not placed next to or under the canopy of a tree. 2.5 LABORATORY METHODS All vapor samples will be analyzed by a certified laboratory. Summa® canisters will be individually certified. The initial vacuum reading will be measured and recorded to ensure that the canister has not leaked during shipment to the Site. At the end of the sample period, the final vacuum (preferably 2 to 10 inches of mercury [in. Hg]) will be measured and recorded on both the field forms and the canister laboratory label. Following sample collection, the Summa® canisters will be shipped to the laboratory under chain-of-custody control at ambient temperature. Upon receipt of the canisters at the laboratory, the vacuum will be measured again to ensure that the canister did not leak during shipment. The field vacuum gauges are generally accurate within ±4 in. Hg, so any canister with initial vacuum reading less than 26 in. Hg will not be used. Any canister with a discrepancy of more than 4 in. Hg between the final field vacuum reading and the vacuum reading upon receipt by the laboratory will be identified as such during the data validation process. Summa® canisters will be analyzed by U.S. EPA Method TO-15 SIM. 3 2020