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DATA GAP ASSESSMENT WORK PLAN AND PATH TO CLOSURE REVIEW Chase Chevrolet, 424 N. Van Buren Street Proposed Scope of Work January 2, 2018 4.8 SOIL VAPOR SAMPLE COLLECTION AND ANALYSIS Soil vapor samples will be collected from the soil vapor probe following a minimum vapor equilibration time period of 48 hours. Prior to the collection of soil vapor samples from probes SV- 1, SV-2, and SV-3, Stantec will verify that a significant precipitation event has not occurred within 5 days prior to the scheduled sampling event. The soil vapor samples will be collected using 1-liter(L) or less Summallm canisters, which will be obtained from a California DHS-certified laboratory with the proper vacuum of approximately 30 inches of mercury (in Hg). Teflon® tubing will be used to connect the probes to SummaTM canisters fitted with flow regulators restricting flow to less than 200 millimeters per minute (mL/min) and in-line particulate filters. Additionally, a Swagelok® type valve will be installed on the down-hole side of the flow regulator/particulate filter assembly to allow for the performance of a 10-minute leak check. Prior to sample collection, soil vapor well purging will be performed using a 6-L SummaTm canister installed in-line with the sample canister using a sampling tee. Schematics of the soil vapor sampling apparatus are included as Figure 3. Field procedures for the collection of vapor samples are outlined in Appendix E. A vacuum of approximately 5 in Hg or less will be left in the sample canisters at the completion of sampling. Sample collection and helium tracer gas monitoring data for each sampling location will be recorded on the soil vapor sample collection data log provided in Appendix F. Soil vapor samples will be sent to a California DHS-certified laboratory under chain-of-custody documentation and analyzed for the presence of TPHg, BTEX, MTBE, and naphthalene using US- EPA Method TO-15 Modified in full scan mode, and for the presence of atmospheric gases oxygen (02), carbon dioxide (CO2), methane (CH4), and helium using American Standard Testing Materials (ASTM) Method D-1946 Modified. Since helium is routinely used by laboratories as a carrier gas, helium as a target compound will be specifically requested on the chain-of- custody. 4.9 SENSITIVE RECEPTOR SURVEY Stantec proposes to perform a sensitive receptor survey 1,000 feet from the boundaries of the site. The following tasks will be performed during the sensitive receptor survey. 4.9.1 Agency Survey Stantec will submit a Well Drillers Report Inspection Request and Agreement form signed by the CVRWQCB to the Department of Water Resources (DWR) to access well completion records. Once approved, Stantec will review well completion records at the DWR office and identify water wells within 1,000 feet from the boundaries of the plume. Stantec will also contact the MUD to identify the potential presence of wells within the proposed search area. Stantec bm \ \us1312- f02 \ workgroup \ 1857 \ active \ 185703766 \ 05_report_deliv \ deliverable \work_plan\185703766_20180102_424_van_buren_work_plan_final.docx 4.4