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Site Inspection UFP-QAPP Addendum <br />Stockton AASF, Stockton, California <br />QAPP Worksheet #10: Conceptual Site Model <br />The information presented in this section was gathered during the PA at Stockton AASF. The PA <br />process included the following tasks: <br />• Reviewed available administrative record documents and Environmental Data Resources, <br />LLC (EDR)Tm report packages to obtain information relevant to potential PFAS releases, <br />such as: drinking water well locations, historical aerial photographs, Sanborn maps, and <br />environmental compliance actions in the area surrounding the facility; <br />• Conducted a 1 -day site visit on 6 March 2019; <br />• Interviewed current Stockton AASF personnel, including the California ARNG (CAARNG) <br />Maintenance Officer, Environmental Compliance Officer, and Safety Officer; and, a <br />Montezuma Fire District representative; <br />• Completed visual site inspections (VSI) at known or suspected PFAS release locations and <br />documented with photographs; <br />• Developed CSM(s) to outline the potential release and pathway of PFAS for the Area(s) of <br />Interest (AOIs) and the ARNG facility. <br />The findings of the PA are summarized in this worksheet. Additional details about Stockton AASF <br />can be found in the PA Report (AECOM, 2020). <br />Facility Location and Description <br />Stockton AASF is located at 2000 Stimson Road, Stockton, CA 95206 and borders the Stockton <br />Metropolitan Airport to the south. The Stockton Metropolitan Airport has a history of military use <br />as a training installation and has been formerly referred to as Stockton Field and Sharpe Army <br />Depot Field Annex. In 1973 the US Army vacated the airport; however, the CAARNG presence <br />remains. The AASF is situated in the Sacramento -San Joaquin Valley within the Central Valley, <br />approximately equidistant from the Pacific Ocean and Sierra Nevada Mountains (Figure 10-1). <br />The latitude, longitude, and surface elevation at the main gate of the AASF are 37053'13.0" N; <br />121014'37.2" W, and 21 feet (ft) above mean sea level (amsl), respectively. <br />Stockton AASF is a CAARNG aviation maintenance facility for helicopters. Impervious surfaces <br />make up 82% of the 22 -acre facility and include roadways, parking lots, helipads, and taxi lanes. <br />Physical structures include a hangar, maintenance shop, fuel tank farm, wash rack, and <br />equipment storage areas. Stockton AASF has been leased from the San Joaquin County since <br />1972. <br />Four state-owned divisional areas comprise the entire CAARNG facility, including the AASF, Field <br />Maintenance Shop (FMS) #24, Armory, and Combined Support Maintenance Shop (CSMS). <br />However, only the AASF was specifically evaluated in this addendum. FMS #24 is a one-story <br />maintenance building and the site of two former underground storage tanks (USTs). FMS #24 lies <br />adjacent to the southwest of the AASF and has been extensively investigated as a source of <br />petroleum hydrocarbons and related compounds in soil and groundwater (Adanta-ECM Joint <br />Venture, 2018). <br />Facility Environmental Setting <br />The areas surrounding Stockton AASF comprise light and heavy industrial areas directly <br />north/northwest and farmlands to the east, south, and west. Few residents reside in the rural <br />AECOM QAPP Worksheet #10 <br />Page 1 of 10 <br />