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Site Inspection UFP-QAPP Addendum Stockton AASF, Stockton, California farmlands within a one -mile radius of the AASF, although the community of French Camp, CA is located approximately 1.5 miles to the west. The site sits at an elevation of 26 ft amsl with a slight general topographic gradient to the west. There are no significant natural topographic features surrounding the facility. Stockton AASF lies in the border of the Sacramento Valley and San Joaquin Valley. Deposits found within this region are composed of unconsolidated Quaternary sediments made up of alluvial and lake deposits. The Sierra Nevada Mountains to the east and the Sacramento Valley Coast Ranges to the west are both contributing sources of deposits that originate from a variety of metamorphic and sedimentary rocks (Adanta-ECM Joint Venture, 2018). The uppermost geologic unit comprises marine and nonmarine (continental) sedimentary rocks (Figure 10-2). The Stockton Fault (trending northeast -southwest) is located within Stockton city limits; the Midland Fault Zone (trending north) is located approximately 25 miles northwest of Stockton AASF (Oneida Total Integrated Enterprises [OTIE], 2010). The Stockton fault forms the divide between the Sacramento and the San Joaquin Valleys. Two major soil components were found at the Stockton AASF property (EDRTM, 2019). The Jacktone and Stockton soil units are both somewhat poorly drained, partially hydric clays. The deposits underlying the site are characterized by interbedded silty clays, clayey silts, sands, and silty to clayey sands (Oneida Total Integrated Enterprises [OTIE], 2010; 2013). Boring logs from previous subsurface investigations at FMS #24 encountered fine silts and clays to depths of approximately 20 to 30 ft below ground surface (bgs) overlying coarser, relatively continuous sands and silts (OTIE, 2010). Hydrogeology Stockton AASF is located within the San Joaquin Groundwater Basin, which contains several water -bearing zones within the upper 700 to 800 ft of unconsolidated fill. Shallow groundwater primarily occurs in unconfined conditions, although it may occur in semi -confined condition due to the distribution of clay lenses in the sediments. Based on historical investigations performed in the vicinity of the AASF, coarser sediments are generally discontinuous in the lateral and vertical direction above the groundwater table and more laterally continuous below the groundwater table (Versar, Inc., 2004; URS Corporation, 2007; OTIE, 2010, 2012, 2013; Environmental Cost Management, Inc., 2015). According to the California Water Board Groundwater Ambient Monitoring and Assessment Program database, multiple public water system wells are located within a 4 -mile radius. A public water system well is defined as serving "15 or more connections or more than 25 people per day" (California Water Board, 2019). Drinking water wells from the City of Lathrop public water system were identified in the Unregulated Contaminant Monitoring Rule 3 (UCMR3) data to exceed USEPA Health Advisory values for PFAS. These wells lie within a 5- to 10 -mile radius from the Stockton AASF. Stockton AASF receives potable water from the Stockton Municipal Utilities Water Service, which derives approximately 25% of its water supply from groundwater wells, while the remaining water supply is from treated surface water supplied by the Stockton East Water District. The locations of Stockton Municipal Utilities Water Service wells are unknown. The Stockton East Water District also supplies surface water for agricultural irrigation in the area. The Stockton East Water District sources surface water from the New Melones Reservoir and the New Hogan Reservoir, located approximately 30 and 38 miles northeast of the AASF, respectively (City of Stockton, 2019; Stockton East Water District, 2019). AECOM QAPP Worksheet #10 Page 2 of 10