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18 August 2023 AdvancedGeo Project No. 17-4073 An Employee-Owned Company Page 4 of 7 � Laboratory Accreditation Program (ELAP)-certified laboratory for the following constituents: • VOCs, including chlorinated volatile organic compounds (CVOCs) in accordance with EPA Method 8260B. Laboratory reports for all analyses, testing methods, laboratory quality assurance/quality control (QA/QC) reports, and sample chain-of-custody documentation will be presented in a report with the findings and recommendations. Electronic deliverable format (EDF) files of the laboratory analytical results will be submitted to the State of California GeoTracker database. 2.3. SOIL VAPOR POINT INSTALLATION AND SAMPLING AGI proposes to advance four (4) soil borings at the site to install and sample four (4) temporary soil vapor points to total depths of 6.5 feet bsg to delineate VOC impact to soil vapor. Soil vapor points will be located in the south-central portion of the property and in the northwestern, northeastern, and southeastern corners of the subject property (Figures 2 and 3). Four pilot soil borings will be advanced to total depths of 6.5 feet bsg for installation of soil vapor points. Pilot borings will be advanced using the Geoprobe, a 2.0-inch diameter hand auger, or 0.5-inch diameter hand tooling with a rotary hammer. Upon reaching total depth, approximately 6-inches of#2/12 sand will be placed at the bottom of the borehole for the vapor implant to be placed on. The vapor implant will be installed by lowering a 1/4-inch diameter, 1-inch-long polyethylene soil-vapor implant and approximately 8 feet of '/4 inch Teflon tubing into the boring; 2-feet of tubing will remain outside the borehole for sample collection. Once the initial 6 inches of sand, vapor implant, and tubing are in place, an additional 6-inches of sand will be added to the boring to cover the implant to 5.5 feet bsg. Following the placement of the filter pack, approximately 1 foot of dry granulated bentonite will be placed on the filter pack to 4.5 feet bsg. The remaining space in each boring will be filled with hydrated bentonite chips to surface grade. A minimum of 2-hours of equilibrium time will be allowed at each soil-vapor well prior to purging and sample collection. After the equalization time, a peristaltic pump, calibrated at 200 milliliters per minute (ml/min) will be used to purge the vapor wells of a minimum of three calculated volumes of air. Once purging is complete, one-liter Summa canisters, with attached flow restrictors calibrated to 150 to 200 ml/min, will be connected to the above ground tubing and the canister will be opened. Thereafter, each soil-vapor sampling well will be isolated from ambient air by enclosing the well, tubing, and canister assembly in a plastic shroud. Helium gas will be infused into the shroud and measured using a helium meter to verify that a 15 to 20% concentration of helium is introduced and maintained in the shroud. The initial pressure and time will be recorded. Installation of the helium shroud will be completed in accordance with the laboratory standard operating procedure included as Appendix B.