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Additional Site Assessment Report and Human Health Risk Screening Evaluation www.arcadis.com 6 minutes. If any loss within the sample train was observed after 2 minutes, the fittings were adjusted and the test was repeated until the vacuum in the sample train did not dissipate. A helium leak detection test was conducted during purging to verify the integrity of the sample train and probe installation. The soil vapor probe and entire sample train (valves, tubing, gauges, manifold, and sample canister) were placed under a plastic shroud. A tracer compound (high-purity helium) was permitted into the enclosure. During the test, a helium concentration of approximately 20 percent by volume was maintained within the enclosure and monitored using an MGD-2002 portable helium detector. Soil vapor was purged from the soil vapor probe into a Tedlar bag at a flow rate of 200 mL per minute using a GilAir Plus pump attached to the purge valve. The purged soil vapor was then screened for helium concentrations less than a corrected 5 percent cutoff to verify that samples were representative of subsurface conditions. During purging, the soil vapor was monitored for moisture or water and excessive purge-induced vacuum. During purging, soil vapor was also screened for volatile organic compounds (VOCs) with a PID and for methane, carbon dioxide, oxygen, hydrogen sulfide, and carbon monoxide with a LANDTEC GEMTM 5000 landfill gas meter. Soil vapor field measurements are presented on the soil vapor sample collection logs provided in Appendix D. The soil vapor samples were packaged and delivered to Eurofins Air Toxics, LLC. under proper chain of custody procedures. The Work Plan (Arcadis 2019a) called for analysis of a full suite of VOCs, naphthalene, and fixed gases. Due to a laboratory error, the 2020 soil vapor samples were analyzed instead for the following: • TPH-g by Modified USEPA Air Method TO-15 • BTEX by Modified USEPA Air Method TO-15 • Fixed gases, including helium, oxygen, methane, nitrogen, and carbon dioxide, by ASTM International (ASTM) Method ASTM D-1946. The 2022 soil vapor samples were analyzed for the constituents listed below, in accordance with the Work Plan (Arcadis 2019a): • A full suite of VOCs, including naphthalene, by Modified USEPA Air Method TO-15 • Fixed gases by Method ASTM D-1946. 3.2.4 Equipment Decontamination Procedures All downhole equipment, including sampling devices, and any other reusable equipment, was decontaminated between use or replaced with clean equipment. Decontamination of sampling equipment was completed using a Liquinox® solution and deionized water rinse to prevent cross-contamination between each sample. 3.2.5 Investigation-Derived Waste The IDW generated during field activities was contained in United States Department of Transportation approved 55-gallon steel drums. These drums were appropriately labeled and temporarily stored at the associated residential properties pending analytical results and waste profiling. The IDW was classified as nonhazardous. The waste drums were removed by Clean Harbor Environmental Services and transported to a CEMC-approved