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Geosyntec consultants Following boring advancement to the target depth, soil vapor probes will be constructed in each borehole using a '/Z-inch-diameter, 6-inch long stainless-steel screen attached to '/4-inch diameter NylaflowTM tubing. A soil vapor probe will be installed at approximately 5 and 10 ft bgs, respectively, for the shallow and deep borehole at each location. The exact depth of probe installation will depend on field conditions, geology encountered, depth to groundwater, and potential refusal by the drill rig. The annular space of the borehole will be filled with filter pack sand from the bottom of the borehole to 3 inches above the top of the screen, then with granular bentonite,hydrated bentonite,and cement grout to ground surface. Soil vapor probes will be semi- permanent and have a concrete apron as the surface completion. The proposed probe construction details are shown in Figure 4. 4.3 Soil Physical Properties Sampling Undisturbed soil samples will be collected during installation of soil vapor probes to evaluate the physical properties of soil on-Site. The soil samples will be collected from approximately 4.5 to 5 ft bgs and 9.5 to 10 ft bgs at both locations using a slide hammer. The soil samples will be collected in stainless-steel liners and sealed on each end with Teflon® tape and slip-on end caps. The samples will be labeled with project identification, sample location, analytical method, and time and date of sampling. Samples will be transported under chain-of- custody procedures to Cooper Testing Laboratory (Cooper Testing) of Palo Alto, California, for analysis. 4.4 Soil Vapor Sampling Soil vapor samples will be collected at all four soil vapor probes. Soil vapor sampling techniques will include leak testing, shut-in testing, and purging in accordance with DTSC guidance, including the Advisory (DTSC, 2015), as described in the following sections. Soil vapor probes will be sampled a minimum of 48 hours following probe installation. 4.4.1 Sampling Equipment At each soil vapor probe location, the sample train will be set up with dedicated well fittings and new Nylaflow tubing. The Nylaflow tubing will be field screened with a PID for the presence of VOCs before use at each location.Field instruments(PID,multi-gas detector,and helium detector) will be calibrated prior to conducting sampling activities. 4.4.2 Shut-In Testing After the aboveground sampling equipment is assembled at each location, a shut-in test will be conducted to test for leaks in the sample apparatus. A vacuum of approximately 100 inches of water will be applied to the sampling train and the vacuum will be monitored for approximately one minute. If the vacuum dissipates during the shut-in test, the aboveground fittings will be tightened, and the test will be repeated until the vacuum is maintained for one minute, indicating a leak-free assembly.This protocol will be repeated after leak testing and before sampling to ensure the integrity of the sampling equipment seals has been preserved. Work Plan for Vapor Intrusion Investigation 7 July 30,2021