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GeosyntecO consultants SUGGESTED OPERATING PROCEDURE SOIL GAS SAMPLING Geosyntec Consultants,Inc. Last revision: October 2020 1 INTRODUCTION This suggested operating procedure (SOP) describes the methods for sampling sub-slab and soil gas probes of sufficient quality to assess potential human health risks due to subsurface vapor intrusion to indoor air and subsequent inhalation exposures. 2 SUMMA CANISTER CHECK Prior to the start of soil gas sampling,connect a vacuum gauge to the summa canister to record the initial vacuum in the canister. Connect the vacuum gauge directly above valve V-3. Open V-3 and record the initial vacuum gauge reading. Close valve V-3 after the reading is recorded. The initial vacuum reading will be used to document that the canister did not leak during shipment from the laboratory.A summa canister should not be used for sample collection if the initial vacuum reading is less than 25 inches of mercury (in-Hg) compared to a standard laboratory provided vacuum of 30 in-Hg. 3 VACUUM SHUT-IN LEAK TEST The sampling equipment will be assembled as shown in Figure 1, and will be checked for leaks by conducting a "shut-in" test prior to purging. Valves V-1 and V-3 will be closed (valves V-2 and V-4 open) and then the lung box and Tedlar®bag will be used to exert a vacuum on the sampling train (80— 100 inches of water in-H20). Valve V-2 will then be closed and the vacuum observed for at least 60 seconds to ensure it does not dissipate. If the test indicates a leak, the connections should be disconnected and carefully reconnected one at a time until the leak is fixed. The leak test must be repeated until all leaks have been fixed. 4 PURGING,FIELD SCREENING,AND HELIUM LEAK TEST After the "shut—in"test, a Tedlar bag will be attached to the tubing inside the lung-box and the lid of the lung box will be secured. Valve V-3 will remain closed while the valves under the shroud (V-1 and V-2) will be opened and the shroud filled with helium (10 to 30%). The minimum and maximum concentrations of helium observed in the shroud during the collection of each Tedlar bag sample will be recorded. The lung box will be turned on and valve V-4 opened to begin purging. The Tedlar bag will fill at flow rate constrained by the flow controller, typically about 200 mL/min. The time to fill the Tedlar bag should be recorded. The Tedlar bag will visibly fill inside the lung box. As it approaches 3/4 full, valve V-4 will be closed and the lung box will be turned off. 1 October 2020