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Site Inspection UFP-QAPP Addendum Stockton AASF, Stockton, California AOls were identified based on preliminary data and assumed groundwater flow directions. These AOIs are described below and presented on Figure 10-4. In general, the potential routes of exposure to PFAS are ingestion and inhalation. Human exposure via the dermal contact pathway may occur, and current risk practice suggests it is an insignificant pathway compared to ingestion; however, exposure data for dermal pathways are sparse and continue to be the subject of toxicological study. The facility lies within the San Joaquin Valley Groundwater Basin, and all surface water is eventually drained by tributaries to the San Joaquin River. PFAS are water soluble and can migrate readily from soil to groundwater or surface water via leaching and run-off. If PFAS releases to surface and subsurface soil occurred, it is possible that PFAS migrated from surface soil to groundwater and waters in the San Joaquin River. In addition, precipitation infiltrating into the grassy areas surrounding the AOls may cause the migration of PFAS from surface and subsurface soil to groundwater and surface water. Ground -disturbing activities to soil could result in construction worker exposure to potential PFAS contamination via inhalation of dust or ingestion of surface and subsurface soil. Inhalation of dust or ingestion of surface soil may also occur during the routine activities of site workers. Therefore, the inhalation and ingestion pathways for these receptors are considered potentially complete. Site workers, construction workers, and trespassers at the facility may be exposed to PFAS via ingestion of surface water and sediment in the San Joaquin River and its tributaries. Similarly, recreational users may be exposed to PFAS in surface water and sediment off -facility. Due to the presence of public water system wells within a 4 -mile radius of the facility, the pathway for PFAS exposure to off -facility residents via ingestion of groundwater is potentially complete. Further the location of Stockton Municipal Utilities Water Service groundwater wells that may serve the AASF are unknown, therefore pathway for PFAS exposure to site workers via ingestion of deep groundwater is also potentially complete. AOI 1 Airfield and Former Wash Rack AOI 1 is the airfield where controlled AFFF releases through familiarization training have occurred annually potentially as early as 1992 and then less frequently after 2010. The footprint of AOI 1 also includes a former Wash Rack shown on historical figures as previously located south of the southwest corner of the airfield. There are no known PFAS releases at this former Wash Rack. AOI 2 Wash Rack AOI 2 is the wash rack area and includes the HAZMAT locker with AFFF storage, located at the southwest corner of the wash rack. Controlled AFFF releases to the wash rack through activities related to fire training and familiarization training have occurred annually, potentially as early as 1992, and then less frequently after 2010. Potential AFFF releases from incidental spills in the wash rack area may have also occurred. The wash rack drains lead to an oil water separator that connects to the Stockton sanitary sewer system. Therefore, discharges of AFFF in the wash rack would release directly into the sanitary sewer system. However, the HAZMAT locker is located near unpaved, grassy areas. Potential PFAS releases nearby the HAZMAT locker drains via overland surface flow to the adjacent ditch canal (Rydberg Creek), which is a tributary to the San Joaquin River. AECOM QAPP Worksheet #10 Page 4 of 10