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Geosyntec Q consultants SUGGESTED OPERATING PROCEDURE SOIL GAS SAMPLING Geosyntec Consultants,Inc. Last revision: January 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 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. 3 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. V-2 will remain closed while the valve under the shroud (V-1 and V-4) 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 V-2 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-2 will be closed and the lung box will be turned off. The lid of the lung box will be opened, the valve on the Tedlar bag closed, and the Tedlar bag removed from the lung box. The Tedlar bag will be connected to the helium meter,photoionization (PID), and landfill gas meter (oxygen, carbon dioxide and methane) in sequence, by opening the Tedlar bag valve, and recording the stabilized readings. If the concentration of helium in the Tedlar bag is greater than 5% of the concentration in the shroud, the probe seal and fittings should be checked to determine the location of the leak. Once the leak has been fixed, resume purging and field screening. The purging and field screening procedure will be repeated for a minimum of three sets of readings. I January 2020