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Site Inspection UFP-QAPP Addendum Stockton AASF, Stockton, California QAPP Worksheet #17: Sampling Design and Rationale Worksheet #17a -e describes the sampling design, basis for its selection, and field investigation details. Field activities will be completed per the Standard Operating Procedures (SOPs) in Appendix B. The objective of the SI is to identify whether there has been a release to soil and groundwater (if present) at each AOI and determine the presence or absence of PFOA, PFOS, and PFBS at or above SLs, as well as the presence or absence of 15 additional PFAS at the facility. As discussed in Worksheet #10, three AOIs were identified at Stockton AASF. Regional groundwater at Stockton AASF generally flows to the east/northeast. AOI 1 is the Airfield. Potential PFAS releases to soil occurred at AOI 1 as early as 1992 during fire extinguisher familiarization. The training occurred on a once -annual basis until approximately 2010 and occurred less frequently after 2010. During the training, personnel would discharge the Tri-MaxTM fire extinguishers in the northeast direction towards the center of the airfield. The quantity and percentage of AFFF released at AOI 1 are unknown. AOI 1 also includes a former Wash Rack; however PFAS releases to the former Wash Rack are not known. AOI 2 is the Wash Rack. Potential PFAS releases to soil occurred at AOI 2 as early as 1992 during fire extinguisher familiarization. The training occurred on a once -annual basis until approximately 2010 and occurred less frequently after 2010. A HAZMAT locker was observed at AOI 2 for AFFF storage. The quantify and percentage of AFFF released at AOI 2 are unknown. AOI 3 is the Butler Building Parking FTA. Potential PFAS releases to the paved surface at Butler Building parking lot occurred as early as 1992 during fire training activities. AOI 3 was used for fire training activities that involved extinguishing live fire from jet propellant fuel that was poured and then ignited in tray pans. The precise location, amount, and type of AFFF released to the pavement and the condition of the pavement are not known. The soil beneath the parking lot was disturbed during construction and was used to fill in a depression on the west side of the road. Exact locations of soil refill could not be confirmed. Environmental media samples will be collected from the AOI in accordance with the applicable CSM, as summarized in Table 17-1. Temporary monitoring wells will be installed where PFAS were potentially released and downgradient of the potential source areas. In instances where deviations from this sampling design and rationale are made due to unforeseen Site conditions, a Field Change Request Form will be generated to document the change and request feedback from the AECOM Task and Project Managers, USACE, and ARNG. iamplinq Tasks The field program will include tasks as detailed in the following Worksheet elements: • Worksheet #17a - Mobilization • Worksheet #17b - Direct Push Boring Installation and Soil Sampling • Worksheet #17c - Temporary Groundwater Monitoring Well Installation and Grab Groundwater Samples • Worksheet #17d - Synoptic Water Level Measurements AECOM QAPP Worksheet #17 Page 1 of 10