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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 7 in the subsurface with respect to PFAS compounds, and a tentative project schedule and reporting following additional site investigation. Figures showing Potential Release Areas PRA 1, PRA 2, and PRA 3 location within the SCK property and boring locations are presented in Figures 3, 4, and S, respectively. Although PRA 3 does not require further investigation, a figure will be included to show its relative proximity to PRA 1, PRA 2 and other relevant data points at SCK. A Sampling and Analysis Plan (SAP) is included as Appendix A. 3 ENVIRONMENTAL SETTING 3.1 Topography and Drainage Site topography is generally flat with an approximate elevation of 2S ft msl. The topography slopes gently to the northwest toward the French Camp Slough. The French Camp Slough is located approximately 1,000 ft south of the southwest corner of the airport property and runs in a northwestern direction to the west of the airport. 3.2 Soils The Site is underlain by Hollenbeck,Jacktone,and Stockton series soils(SSURGO,2019). Hollenbeck series silty clay foams, which are encountered in the northern extent of PRA 2, typically consists of silty clay and clay horizons to a depth of 42 inches bgs and are underlain by duripan. Jacktone series soils underlay PRA 1 and much of PRA 2 and consists of several thin horizons of clay, indurated clay, stratified sandy loam, and duripan. Stockton soils underly the southeastern extent of PRA 2 and typically consist of clay horizons overlying duripan. 3.3 Geology and Hydrogeologic Setting The Site is located within the San Joaquin Valley, a broad structural trough bound by the Sierra Nevada Range to the east and Coast Ranges to the west sloping toward the trough's greatest depth near the western margin of the Valley. The San Joaquin Valley has been filled with several thousand feet of sedimentary deposits. Sediments in the Valley, derived from the erosion of the Sierra Nevada, have deposited sands with lesser silts, minor clays, and gravel by major to minor west-flowing drainages and their tributaries. The sedimentary deposits in the region form extensive coalescing alluvial fans with gradual slopes. The Site lies within the San Joaquin Valley—Eastern San Joaquin Valley Department of Water Resources (DWR) Groundwater Sub-basin. The underlying aquifer is used for drinking water supply and has designated Groundwater Beneficial Uses of"MUN"(Municipal and Domestic Supply), "AGR" (Agricultural Supply), "IND" (Industrial Water Supply), and "PRO" (Industrial Process Supply).