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Sampling and Analysis Plan for Phase II Environmental Site Assessment South Pointe Property: 701, 705, 833, 855 West Weber Avenue Stockton, California Field Methods and Procedures May 17, 2021 6.4 PASSIVE SOIL VAPOR SAMPLING Passive soil vapor sampling modules will be installed at 40 locations across the site as illustrated on Figure 3. Installation and retrieval procedures will adhere to the SOP presented in Appendix C. Sample modules will remain in place prior to retrieval and shipment to the analytical laboratory. Sample handling procedures are presented in Section 7. 6.5 ACTIVE SOIL VAPOR SAMPLING Active soil vapor sampling will be completed at an estimated ten locations based on results of the passive soil vapor survey(that is, active soil vapor sampling will be conducted in areas of the site with the highest reported mass accumulations of VOCs in subsurface soil vapor, and/or at locations where elevated mass is measured for VOCs of particular concern relative to potential vapor intrusion—such as trichloroethene, tetrachloroethene, and benzene). At each location, a direct-push drilling rig will be used to extend a borehole to approximately 12.5 feet below grade. A soil vapor collection probe consisting of a stainless steel or Teflon TM inlet fitting connected to '/-inch Teflon tubing will be installed at approximate depths of 12 and 5 feet below grade. The inlet fittings will be installed at the mid-point of 12 inches of bedding sand, followed by at least a foot of unhydrated granular bentonite. The probes will be 'nested', that is, both probes installed within a single borehole. The annular space between the deep and the shallow probe will be sealed with hydrated bentonite installed in six-inch lifts, as will the annular space in the upper 3 feet of the borehole (between the shallow probe and the ground surface). The two lengths of tubing will be labeled relative to their'shallow' or'deep' positions using zip ties and metal tags, sealed using a plastic plug, and coiled inside an 8-inch-diameter flush mount vault box installed in quick-set concrete. After allowing the soil vapor probes to equilibrate for at least 48 hours, soil vapor sampling will be conducted in accordance with California DTSC sampling guidance (Advisory, Active Soil Gas Investigations, July 2015). Soil vapor sampling procedures are described in the SOP included in Appendix C. Sample handling procedures are presented in Section 7. 6.6 DECONTAMINATION PROCEDURES Non-dedicated, reusable equipment will be decontaminated before use and between locations in accordance with the SOP included in Appendix C. Equipment will be decontaminated in a pre-designated area on pallets or plastic sheeting, and clean bulky equipment will be stored on plastic sheeting in uncontaminated areas. Cleaned small equipment will be stored in plastic bags. Materials to be stored more than a few hours will also be covered. B Project No.: 185704833.5.3&5.4 6.3