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Partner received the SUMMA canisters evacuated to approximately minus 30 inches of mercury. The <br /> SUMMA canisters were fitted with stainless-steel flow controllers, which SunStar calibrated to maintain <br /> constant flow (approximately 0.1 liter per minute) for approximately 5 to 10 minutes of sampling time. <br /> Each probe was allowed to equilibrate for a minimum of two hours after installation prior to sampling.After <br /> equilibration, the sample tubing and sampler screen were purged of ambient air using a purge pump. A <br /> tracer gas [1,1-diflouroethane (1,1-DFA)] was placed around each probe at the ground surface while <br /> sampling to detect ambient air intrusion. The tracer gas was detected in one of the soil gas samples (131- <br /> SG15); however, the tracer gas was not detected in any of the remaining samples, indicating that the <br /> integrity of the bentonite seals were maintained. Once the sampling tubing was purged of ambient air, the <br /> sampling end of the tubing was fitted to the sampling canister and the port valve was opened, causing air <br /> to enter the sample container due to the pressure differential. Partner closed the valves after the canister <br /> was evacuated to approximately minus 1 to 2 inches of mercury, with pertinent data (e.g., time, canister <br /> vacuum) recorded at the start and end of sampling. <br /> The SUMMA canisters were labeled for identification and stored away from direct sunlight prior to analysis. <br /> Soil gas samples were collected from borings 131 and B2 at 5 and 15 feet bgs.The sub-slab soil gas samples <br /> (SS-5 through SS-6) were collected from each sub-slab probe at approximately 6 inches bgs. <br /> 3.8 Post-Sampling Activities <br /> Temporary well points and probes were removed from the subsurface and the boreholes were backfilled <br /> with neat cement grout following sampling activities. Boreholes advanced in improved areas were capped <br /> with concrete patch to match existing ground cover after being backfilled. <br /> No significant amounts of derived wastes were generated during this investigation. <br /> Additional Subsurface Investigation Report PARTNER <br /> Project No.23-400162.14 <br /> July 31,2023 <br /> Page 8 <br />