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Remedial Investigation QAPP Stockton Army Aviation Support Facility,California reallocated, as defined in Section 17.3. If concentrations at a potential release area are less than the soil SLs, the site characterization will be considered complete, and the potential release area will not have subsurface soil sampling performed. 17.2 Soil Boring Sampling Design and Rationale Collection of soil samples from soil borings will be completed to refine the nature and extent of PFAS in soil at each release area, to evaluate the results as part of the comprehensive HHRA and ERA, and to define more precise boundaries for potential response actions during the FS, if warranted. Representative exposure areas for all risk scenarios, human and ecological, were considered in determining the size of the sampling areas. During RI Mobilization 1, a total of 48 soil boring samples (not including QC samples) will be collected from 12 permanent groundwater monitoring well locations (described in Section 17.4). Soil borings will be advanced using direct push technology (DPT) or sonic drilling techniques at locations designated permanent monitoring well installation. A sonic dual-tube sampling system (or equivalent) or DPT will be used to collect continuous soil cores to the target depth; however,air knife/hand augers will be used to clear the top 5 feet of the boring in accordance with utility clearance protocols. A total of three soil samples will be collected from each boring location: one surface soil sample (0 to 1 ft bgs; collected during the hand clearance process), subsurface soil from 5 to 6 ft bgs (collected during the hand clearance process), one subsurface sample from 9 to 10 ft bgs, and soil from approximately 2 ft above the water table. If refusal is encountered or shallow groundwater is encountered at 6 ft bgs or shallower, only two samples will be collected per boring: one surface soil (0 to 1 feet bgs) and one sample approximately 1 foot above refusal. Additionally, geotechnical soil samples will be collected to support the evaluation of aquifer permeability from the screen intervals at the permanent monitoring well locations.Soil samples will be collected in accordance with the procedures presented in Worksheet#14 and further detailed in Parsons SOP PFAS ENV-05 Soil Borings and Monitoring Well Installation (Appendix D). The soil boring sampling design and rationale are provided in Table 17-2. Mobilization 1 sample locations are shown on Figure 17-2.Soil samples will be analyzed under standard TAT for the target list of 40 PFAS by USEPA Method 1633, as specified in Worksheet#15.Additionally, at the groundwater monitoring well locations, other geochemical and physical parameters will be analyzed in a subset of samples to support evaluation of PFAS fate and transport, in addition to the remedial alternatives analysis. One soil sample at each location (selected from various depth intervals to represent the range of Iithologies identified at the sampling locations)will be analyzed for TOC (USEPA Method 9060A) and pH (USEPA Method 9045D). Geotechnical soil samples will be collected from the well screen interval at permanent monitoring well locations to support the evaluation of aquifer permeability.Soil samples will be analyzed under standard TAT for grain size analysis with sieve and hydrometer (ASTM D-422). Depending on the results of surface and subsurface soil samplingfrom RI Mobilization 1,additional soil sampling may be performed in RI Mobilization 2 in order to further refine the nature and extent of PFAS in soil at each release area and obtain additional data required to complete the comprehensive HHRA and ERA. 17.3 Vertical Aquifer Profiling Sampling Design and Rationale During RI Mobilization 1, VAP groundwater samples will be collected to support identification of the lateral and vertical extents of groundwater impacts and to assist in the determination of permanent monitoring well placements during Mobilization 2. The rationale for the VAP locations and general proposed sample depths is provided in Table 17-3.A total of 8 proposed VAP sample locations are shown on Figure 17-2.The VAP sampling PARSONS Worksheet#17&18:Sampling Design and Rationale Page 114