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Geocon Project No. S2170-07-12 - 4 - June 6, 2022 Soil Vapor Sample Collection We will wait a minimum of 2 hours following installation of the soil vapor wells to allow subsurface conditions to equilibrate prior to connection of sampling equipment and purging the soil vapor wells. For sample collection at each well we will connect a soil vapor manifold to the well tubing consisting of a particulate filter, flow restrictor, manifold valve, and two pressure gauges connected to a batch-certified 1-liter Summa canister (for sample collection) and a 6-liter Summa canister (for purging), all enclosed within a plastic shroud (Figure 4). Purging and sampling procedures will include the following: • Attach the soil vapor manifold to the well tubing using a Swagelok fitting with the well valve in the closed position. • Conduct a “shut-in test” by exerting a vacuum inside the “purge train” by opening the purge valve of the 6-liter Summa canister with the well valve in the closed position. If the vacuum is not maintained for 5 minutes, we will adjust the fittings on the purge train until a successful shut-in test is achieved. We will then enclose the soil vapor manifold, the Summa canisters, and the well within the plastic shroud. • Fill the shroud with helium and maintain a minimum helium concentration of 20% throughout purging and sampling. We will position a helium detector inside the shroud to monitor the helium concentrations. • Open the well valve and purge three volumes of soil vapor (one well volume equals the total volume of the tubing, sand filter pack and dry bentonite used to construct the well) using the 6- liter Summa canister at a flow rate of 167 ml per minute (ml/min) and a vacuum of less than 7 inches of mercury (in-Hg). • Once the appropriate volume of soil vapor has been purged, we will close the purge valve and manifold valve, leaving the “sample train” open to the well. Then we will open the sample valve and draw soil vapor into the 1-liter Summa canister at a flow rate of 167 ml/min and a vacuum of less than 7 in-Hg. Once the 1-liter Summa canister has approximately 5 in-Hg of vacuum remaining, we will stop sampling by closing the Summa canisters and well valves. • Disconnect the manifold from the well and label the 1-liter Summa canister in preparation for submittal of the sample to Air Toxics under standard chain-of-custody protocol. One duplicate will be collected, representing approximately 10 percent of the samples. Per SJCEHD guidance, we will abandoned the temporary soil vapor wells after sampling is complete by removing the tubing and over-drilling the well to full depth using a 2.25-inch-diameter direct-push rod to remove the bentonite and sand from each well. We will then backfill each location with cement grout to the surface. Task 3 – Laboratory Analysis Air Toxics will analyze the soil vapor samples for VOCs by EPA Method TO-15 and for helium and oxygen following modified ASTM D-1946. Air Toxics will conduct the laboratory analyses on an expedited 5-business-day turnaround time.