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Revised Workplan-Additional Site Investigation for PFAS BSK Project E20-016-01F Stockton Metropolitan Airport(SCK) March 1, 2023 Stockton, California Page 24 Materials used inside the sampler to collect groundwater and seal the sampler from the formation will be constructed of a material that is considered acceptable (i.e., high-density polyethylene, vinyl, acetate, etc.,) according to the California State Water Quality Control Board, Division of Water Quality document titled "Per- and Polyfluoroalkyl Substances (PFAS) Sampling Guidelines for Non-Drinking Water" dated September 2020. According to Mr. Miles Koehler, Field Operations Manager for the SimulProbe manufacturer (BESST Inc.) "When a client is using the tool for a PFAS investigation, we change out the Teflon water conduit tubes for PVC tubes. We leave the other consumables the same. We have not performed testing to verify that the tool is PFAS free - but it has been used on PFAS sampling projects based on the material content...." Additionally, the "balloon" (probe cover) is made normally made of latex, which is not desirable for PFAS investigations. According to BESST, the supplier of the balloon says one made of Polyisoprene can be substituted which is PFAS-free. BSK will obtain a "materials blank" sample evaluating the SimulProbe and associated materials as a part of this investigation. If necessary, alternate sampling methods such as nested or multiple temporary wells will be considered. Groundwater samples will attempt to be obtained once first groundwater is encountered and in 10 ft intervals thereafter, for 40 ft beyond first encountered groundwater (i.e., groundwater encountered at 40 ft bgs, sampled to 90 ft bgs). A total of(6)groundwater samples will be collected per boring including one (1) duplicate groundwater sample per boring. Additionally, a field blank would be collected at each boring location and/or each day of groundwater sampling. For additional Quality Assurance/Quality Control (QA/QC) procedures please refer to the SAP included in this workplan as Appendix A. Groundwater and QA/QC samples would be labeled and placed into a chilled cooler immediately following collection. Samples would be transported under chain of custody protocol to an ELAP approved laboratory for analysis. 6.3.2.3 Monitoring Well Construction Wells installed during the Second Phase of investigation, would have similar construction using similar materials to the monitoring wells installed during the First Phase of investigation (see Section 6.2.3). The exact specifications for these wells will not be known until the results from vertical groundwater sampling have been received and reviewed by BSK's Project Manager. Prior to finalizing well specifications, BSK's Project Manager would request a meeting with CVRWQCB staff to review results from vertical groundwater sampling and discuss placement and construction details of groundwater wells for the Second Phase of investigation. Note, one (1) of the monitoring wells installed during the second phase of investigation will be installed within approximately 50 ft of former boring TW-2.As previously mentioned, the exact location of the monitoring well will depend on the potential impact to Airport activities.