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DRAFT Geosyntec consultants 4. DATA GAP INVESTIGATION According to the CVRWQCB's analysis presented in letters to the Port dated September 26, 2017, February 16, 2018, and September 20, 2018, UST 817B met the general and media- specific criteria for closure under the State Water Resources Control Board(SWRCB) Low- Threat Underground Storage Tank Case Closure Policy(LTCP), except for benzene, which exceeded the LTCP media-specific criteria(CVRWQCB, 2017, 2018a, and 2018b). To address the data gaps in the vicinity of UST 817B as requested by the CVRWQCB, Geosyntec prepared the Data Gap Work Plan, which was approved by the CVRWQCB on January 28, 2019 (CVRWQCB, 2019a). Three groundwater monitoring wells (917-03, 917-04, 917-10) are in the immediate vicinity of the 2019 soil locations. CVRWQCB staff recommended that the Port collect groundwater samples from these monitoring wells to simultaneously evaluate concentrations of TPH and benzene in groundwater(CVRWQCB, 2018b). However, these locations are monitored as part of the RRI groundwater monitoring program(Geosyntec, 2018b), so Geosyntec proposed in the Draft Addendum to Draft UST Data Gap Investigation Work Plan (Draft Addendum)to evaluate groundwater concentrations in 917-03, 917-04, 917-10 based on 2018 annual monitoring results (Geosyntec, 2018c). CVRWQCB staff concurred with this recommendation in their letter dated December 5, 2018 (CVRWQCB, 2018c). A summary of the findings of the data gap investigation and recent groundwater monitoring results are presented in the following sections. 4.1 Objectives The primary objective of the soil investigation was to assess subsurface conditions at UST 817B to evaluate if the former UST Site was eligible for closure in accordance with the LTCP. Five soil borings were advanced on January 28, 2019 adjacent to the previous highest area of benzene detection(historical soil borings 817-D2, 817-D3, 817-D4, 817-D5 and 817-D7; Figure 2). These borings are identified as SS-817B-01A through SS-817B-05A (Figure 2). The field sampling methodology used during this investigation is described in detail in the Draft Request for Closure of UST Sites;Low-Threat Underground Storage Tank Case Closure Policy report dated August 7, 2019 (Geosyntec, 2019c). This draft report was submitted to the CVRWQCB on August 7, 2019. The soil samples from 4 feet bgs at each of the five borings (SS-817B-01A through SS-817B- 05A) were analyzed for a select list of volatile organic compounds (VOCs) and TPHg by Method 8260B, and/or TPHd by USEPA Method 8015B as follows: • Two soil samples (SS-817B-01A-4 and SS-817B-02A-4)were analyzed for benzene, naphthalene, TPHd, and TPHg; and • Three soil samples (SS-817B-03A-4, SS-817B-04A-4, and SS-817B-05A-4) were analyzed for BTEX and TPHg. The results of the previous data and the data gap investigation are presented in Figure 2. Boring logs are provided in Appendix A and boring permits are included in Appendix C. Draft Soil and Soil Vapor Investigation 8 August 30,2019