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Revised Workplan-Additional Site Investigation for PFAS BSK Project E20-016-01F Stockton Metropolitan Airport(SCK) March 1, 2023 Stockton, California Page 8 Drilling and soil sampling conducted by Ramage Environmental, Inc. in the area of the former fuel farm during the former Fuel Farm UST investigation indicated that shallow sediments in that area consist of clay and silts with thin, discontinuous sand intervals with thicknesses of up to 5 ft to the explored depth of 104 ft bgs. Soils observed using the CPT drilling rig to the total drilling depth of 105 ft reportedly consisted of massive clay and silt soils, interrupted by relatively thin and discontinuous sand intervals up to five ft thick. Based on Ramage's CPT log interpretation, the most significant sandy intervals were reported to occur between approximately 56 and 60 ft bgs and 99 and 104 ft bgs (Ramage, 2007). Both of these intervals are likely saturated. The 2014 Ramage Environmental, Inc. report also indicated that groundwater in the area of the former tank farm was encountered during drilling in 2003 at approximate depths of 56 to 57 ft bgs and that the static water level were observed at depths of 46 to 47 ft bgs. Groundwater depths measured in monitoring wells during 2014 ranged from 33.91 to 37.32 ft bgs. The groundwater flow direction was determined to be to the northeast with a calculated groundwater gradient of 0.0012 ft/ft. There are no monitoring wells in the vicinity of the PRAs and the depth to groundwater at the PRAs is unknown. There are no groundwater depth or elevation contour data for the Site area currently available on the California Department of Water Resources (DWR) Groundwater Information Center Interactive Map Application web page (GICIMA) (DWR, 2019). During BSK's Preliminary Site Investigation for PFAS, groundwater was noted at depths of 38-41 feet bgs in PRA-1 (Temporary Wells TW-4, TW-5, and TW-6) in June 2020. During the same investigation groundwater was noted at depths of 44-48 feet bgs in PRA-2(Temporary Wells TW-1,TW-2, and TW-3) in June 2020. 3.4 Sensitive Receptors BSK performed a sensitive receptor analysis for potential PFAS discharge areas from the SCK. The objective of this analysis was to identify municipal water supply wells, domestic wells, and surface water bodies located within one mile of a PRA on the SCK. Municipal supply well locations were provided by the City of Stockton. BSK identified six (6) municipal water supply wells operated by the City of Stockton that are located within one mile of PRA at SCK. None of the identified wells are within half a mile of a PRA. Table 1 shows the distance from the identified wells to the nearest PRA.