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call. Participants for the future TPP3 meeting will include the addition of other local stakeholders to be determined once the SI reporting phase has begun. Stockton AASF PA Findings (Slides 9-14): The PA findings for the Stockton AASF were presented. Information reported in the PA was collected through in-person interviews and a visual site inspection. Three areas of interest (AOIs) were identified where annual fire training with aqueous film forming foam (AFFF) was conducted as early as 1992 and less frequently since 2010: o AOI 1- Airfield Fire Training Area (FTA). Tri -Max TM fire extinguishers discharged and stationed at airfield. o AOI 2- Wash Rack FTA. Tri-MaxTM fire extinguishers used in live fire training and re -filled at wash rack. o AOI 3- Butler Building Parking Area FTA. Tri-MaxTM fire extinguishers used in live fire training. Underlying soil has been disturbed in area due to Butler Building construction. Potential adjacent sources were discussed including the Montezuma Fire Station, French Camp Fire Station, Stockton Metropolitan Airport, and Aramark Uniform and Career Apparel. Mr. Marcus Pierce (CA Water Board) pointed out a former wash rack located between the current wash rack and airfield and near a former petroleum site. The former wash rack may be a potential PFAS release area needing further investigation. Recent investigations at Stockton AASF are captured in the CA Water Board's GeoTracker site. Brian Pierskalla, CAARNG, noted a case associated with a petroleum -release at the AASF has been closed and associated monitoring wells abandoned. However monitoring wells associated with the CAARNG's Field Maintenance Shop (FMS) #24 (adjacent to the west of the AASF) are potentially available to be gauged during the SI for the purpose of assessing groundwater gradient. Stockton AASF SI Overview (Slides 15-18): • Data quality objectives (DQOs) were presented for the SI. The primary DQOs were to confirm the presence or absence of a PFAS release at a potential source area and to gather data to refine the conceptual site model (CSM). Secondary goals are to determine the presence/absence at the ARNG facility boundary. • The preliminary CSM presented the surrounding surface water flow direction. A ditch (labeled Rydberg Creek) is located along the southern and western boundary of facility and flows northwest before connecting to the French Camp Slough. The oil water separator at the wash rack is connected to the City of Stockton's sanitary sewer. • The preliminary CSM presented an inferred groundwater flow direction to the north/northeast which is generally consistent with groundwater gradients measured at Stockton AASF during previous investigations. Based on available data, groundwater is expected to be encountered at depths of 25 to 30 feet below ground surface. • The current understanding of the CSM is that there are potentially complete pathways between the potential source areas and human receptors (mainly site and construction workers) via inhalation of dust, ingestion of surface soil, ingestion of surface water/sediment, and ingestion of subsurface soil. A potentially complete pathway also exists for construction workers and off -facility residents via ingestion of shallow groundwater (for groundwater shallower than 15 feet). Additionally, potentially complete pathways exist for recreational users and trespassers via inhalation of dust, ingestion of surface soil, and ingestion of surface water/sediment. Stockton AASF SI Approach (Slides 19-23): • The scope of work for the SI was presented. Soil borings will be installed at locations within release areas as well as downgradient of the potential source areas at the facility boundary. Ten DPT borings are proposed and will be converted to temporary monitoring wells. Groundwater samples will be collected from each temporary well. Soil samples are proposed at the ground surface, mid -point, and above the water table at each boring location. Six hand auger surface soil samples are also proposed adjacent to the release areas. • As presented below, surveying the temporary monitoring wells was discussed. ARNG PA/SI, Stockton AASF CA 2 24 February 2021