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09 November 2021 Project No. 21-6640 Page 4 of 5 3.1.2. Soil-Vapor Sampling & Analysis At the proposed soil-vapor sampling locations, the borings will be advanced to 5 feet bsg using hand tooling. Once the total depth is reached, semi-permanent soil-vapor sampling wells will be installed within the boring. The temporary sampling points will consist of 7 feet of ¼-inch Teflon tubing and a sampling tip (generally inert ceramic stone). Prior to installing the tubing and sampling stone, #2/12 sand will be poured in the annuals of the boring for the sample tip to rest on. The tubing and sampling tip will then be lowered to a depth of five feet bsg and one foot of #2/12 sand will be poured around the tip to create a filter pack. Above the sand, one foot of dry granular bentonite will be placed to a depth of 4 feet bsg. Thereafter, hydrated bentonite will be placed from 3 feet bsg to near surface grade to seal each location and prevent ambient air intrusion during sampling. A soil-vapor sample will be collected after allowing a minimum of two hours equalization time following installation of the soil-vapor wells. Prior to soil-vapor sample collection, three calculated volumes of air will be purged utilizing a 6-liter purge canister or pump, calibrated to 200 milliliters per minute (ml/min). One-liter Summa® sampling canisters will be used to collect soil-vapor samples for VOC/TO-15 analysis. The sampling inlet manifold consists of a vapor-tight valve; a particulate filter; a flow restrictor calibrated to 200 milliliters per minute (ml/min). The manifold assembly will be attached to the ¼-inch Teflon® tubing from the soil-vapor well. The canister’s initial vacuum will be measured and recorded between -26 and -30 inches of mercury (in hg). Shut-in tests will be performed on each assembly by attaching and securing the sample and purge canisters to the manifold and opening the valves on the purge canister and the manifold. The shut-in test is performed for approximately 10 minutes on each assembly. The soil-vapor point will be isolated from ambient air by enclosing the borehole, tubing and manifold/canister assembly in a 100-liter shroud. Helium will be emitted into the shroud surrounding the well borehole, tubing and manifold/canister assembly and acts as a tracer gas to evaluate if leaks in the sampling apparatus have allowed infiltration of ambient air. Upon achieving a successful leak test, the purge canister valve will be opened for a period to allow the three calculated volumes of air to be purged. The purge vacuum gauge will be monitored to ensure a proper decrease of vacuum purged. Upon achieving the targeted purge volume, the sample canister valve opened. The initial pressure and time are recorded. Upon reaching at least -5 in Hg or less, the sample canister valve will be closed, and final pressure and time recorded. The sampling port on the sampling canister will be capped with a brass end-cap.