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Work Plan, PFAS Site Inspection Naval Computer and Telecommunications Station Stockton, California Background Information 2-6 DCN: TRBW-0202-5183-0010 at Site 3. During training operations, the open ASTs were filled with water, floating fuel was placed on top, lit on fire, and extinguished. In 2016, the United States Environmental Protection Agency (USEPA) issued drinking water lifetime health advisories (LHA) for perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). As a result of this new criteria and due to the historical use of Site 3 as a Firefighting Training Area, the DTSC requested that the Port of Stockton develop a sampling approach to assess fluorinated compounds associated with firefighting foams at Site 3 (DTSC 2016). A work plan proposing groundwater sampling at Site 3 was approved by the DTSC in 2018 (Geosyntec 2018a). Groundwater sampling activities were conducted in 2018 by Geosyntec following work plan approval. The sampling identified PFAS constituents in groundwater at concentrations greater than the USEPA LHA of 0.07 micrograms per liter (µg/L). Four existing groundwater monitoring wells (W-002, W-075, W-077, and W-097) were sampled during the 2018 event (Geosyntec 2018b). Monitoring well W-075, located downgradient of the Burn Pit and former ASTs, contained the highest concentration of PFOA at 24 µg/L. The remaining monitoring wells contained PFOA concentrations ranging from 0.0054 to 0.042 μg/L, less than the LHA. Other PFAS compounds that were detected in samples included perfluorobutane sulfonate, perfluorobutanoate, 4-3 perfluoroheptanesulfonic acid, perfluoroheptanoate, perfluorohexanoate, perfluorononanoate, and perfloropentanoate. To confirm groundwater analytical results, a second sampling event was conducted in 2018 at well W-075. Laboratory results from the second event detected PFOA at a concentration of 21 μg/L and 26 μg/L in the primary and duplicate samples, respectively, confirming the results of the initial sampling event (Geosyntec 2018c). Based on the findings of the 2018 sampling events, results of the site research, and interviews with persons knowledgeable of the site, the PA recommended additional groundwater and soil sampling for the presence of PFAS in areas where AFFF was potentially released at Site 3 including the former Burn Pit, fuel storage area, and equipment shed during the SI. Sediment investigation for the presence of PFAS in the drainage channels along the north and south perimeter of Site 3 was also recommended as contaminated groundwater may have infiltrated the drainage channels and impacted sediment in this location. 2.4.2.2 Site 45 - Soil Stockpile Area According to a review of previous reports, Site 45 is an undeveloped 5.5-acre parcel that is approximately 400 feet wide and 600 feet long and is located in the northern half of the west end of the Central Island Area (Figure 1-2). Seven groundwater monitoring wells are located near Site 45 including monitoring wells W‐24, W‐124, W‐125, and W‐126 located near the southern Site