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DRAFT Geosyntec consultants 5. SOIL VAPOR INVESTIGATION Geosyntec collected soil vapor samples at three locations in the vicinity of SS-817B-04A (Figure 3). The sampling locations were positioned outside in a paved area. These sample locations were chosen to provide data to assess potential soil vapor intrusion risks in the vicinity of SS-817B-04A. 5.1 Objectives, Scope of Work, and Methodology The primary objective of the soil vapor investigation was to determine if UST 817B met LTCP criteria for vapor intrusion to indoor air. As described in the Soil Vapor Work Plan, Geosyntec installed three temporary soil vapor probes at 5 feet bgs on June 13, 2019 and sampled the probes on June 17, 2019. The probes are identified as SVP-1 through SVP-3. The collected soil vapor samples were analyzed for TPHg, BTEX, and naphthalene. The locations of the soil vapor probes are shown in Figure 3. A summary of the soil vapor sample results is presented in Table 2 and in Figure 3. The soil vapor investigation was conducted in general accordance with DTSC guidance, including the Advisory—Active Soil Gas Investigations (Advisory; DTSC, 2015). A summary of the field sampling methodology is presented in the following sections. Field logs documenting soil vapor sampling activities are included in Appendix E. 5.1.1 Field Preparation Prior to the initiation of field work, Geosyntec conducted the following pre-field planning and permitting activities: • A Health and Safety Plan and site-specific Task Hazard Analyses were prepared and continually updated based on the scope of field activities and conditions encountered in the field; • The CVRWQCB was provided with a figure indicating the proposed soil vapor probe locations, which was approved by the CVRWCB on April 22, 2019; • Boring permits were obtained from the San Joaquin County Environmental Health Department(SJCEHD; Appendix C); and • Subtronic Corporation, a private utility locator, conducted utility clearance for the planned boring locations. Underground Service Alert was notified prior to the investigation regarding the planned boring activities. 5.1.2 Drilling and Soil Vapor Probe Construction Temporary soil vapor probes were installed to 5 feet bgs using a hand auger. Once the target depth was reached, a 6-inch long by'/2-inch diameter stainless-steel screened vapor probe was installed with dedicated t/4-inch Nylaflow®tubing attached. A 1-foot depth interval of the borehole surrounding the probe (i.e., approximately 3 inches above and below the vapor probe screen)was filled with clean# 3 sand. The remainder of the borehole was sealed using hydrated granular bentonite. Draft Soil and Soil Vapor Investigation 10 August 30,2019