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A=COM surrounding surface is gravel.The foam drums at the East Annex are located on the finished concrete surface. Both conditions at the East Annex prevent direct release of foam to ground surface. c. All available records of past AFFF storage or release were submitted as part of the preliminary work plan submission in 2021. d. The safety data sheet for the AR-AFFF used at the site is attached. Comment 2: Section 2.2 of the Work Plan documents the reported foam use at the truck rack area in the West Terminal in 2005. The Work Plan does not explain why the foam was discharged(e.g., due to a fire accident, annual testing, or system malfunction, among others). Please clarify the cause(s) for the foam discharge in 2005. Response: Terminal staff verbally explained that the foam discharge, which occurred in 2005, was the result of a valve misalignment. As described in the work plan, the foam that was released was contained and cleaned up. Comment 3: Section 3.1 of the Work Plan does not include adequate spatial coverage, in both horizontal and vertical directions, of the groundwater downgradient from the potential source zone in the West Terminal. In the horizontal direction, no monitoring well was proposed for the area northeast of the potential source zone. In the vertical direction, all the proposed monitoring wells are screened in the A-Zone and do not cover the B-Zone. Considering the likely downward and northeast groundwater flows on Site, please add monitoring wells TS/M-5, SP/WC-1M, and SP/WC-1S to the proposed PFAS groundwater sampling network for the West Terminal. Response: The requested wells TS/M-5, SP/WC-1 M, and SP/WC-1 S will be included in the proposed PFAS groundwater sampling network for the West Terminal. As discussed on the review call on November 18, 2022, well TS/M-5 may periodically be considered a downgradient well as A-Zone water levels vary at the Site and, as such, this well will be added for PFAS groundwater sampling (Figure 3). In addition, it should be reiterated that SP/WC-1 M (B-zone) and SP/WC-1 S (A-zone) are off-site wells and may be representative of upgradient conditions including but not limited to the West Terminal (Figure 3). The original groundwater sampling locations proposed in the 2021 work plan are not changed. Comment 4: Section 3.1 of the Work Plan proposes no groundwater samples from the East Annex due to the lack of existing monitoring wells near the foam storage areas. Considering the shallow groundwater table on Site and the storage and use history of AR-AFFF at the East Annex, the Central Valley Water Board staff considers it essential to collect groundwater samples from the East Annex. Please propose groundwater sampling locations near the possible PFAS source areas, including but not limited to the foam storage and fire monitor areas and the railcar offloading rack in the East Annex. Groundwater samples may be collected from existing monitoring wells, new wells, temporary wells, or using other methods (e.g., direct-push grab samples) compatible with PFAS sampling. Additionally, please collect groundwater samples from both A-Zone and B-Zone. Response: Existing groundwater monitoring wells AR/MW-21A and PS/WC-18, both A-Zone wells, located on the East Annex will be sampled (Figure 4). Well AR/MW-21A is considered the upgradient well for the two AFFF storage locations at the East Annex. Well PS/WC-18 serves as the proximal groundwater sampling location to the AFFF storage locations at the site. A grab groundwater sample from the A-Zone will be collected from a hand auger borehole location as approximately shown in Figure 4. It is anticipated that the borehole will be excavated to approximately 2 to 3 feet into groundwater prior to collecting the grab groundwater sample using a clean stainless- steel bailer. Comment 5: Section 3.1 of the Work Plan proposes no stormwater samples from the East Annex or the West Terminal. Considering the storage and use history of AR-AFFF at both properties, the Central Valley Water Board staff considers it essential to evaluate whether PFAS chemicals are transported off-site through stormwater runoff. Please propose stormwater sampling for the foam aecom.com 2/5