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Remedial Investigation QAPP <br /> Stockton Army Aviation Support Facility,California <br /> 1.0 INTRODUCTION <br /> 1.0.1 Project Authorization <br /> This Remedial Investigation (RI) Uniform Federal Policy-Quality Assurance Project Plan (UFP-QAPP)addresses RI <br /> activities to be completed at the Stockton Army Aviation Support Facility (AASF) in Stockton, California. The <br /> Stockton AASF is also referred to as the "Facility"throughout this UFP-QAPP. <br /> The California Army National Guard (CAARNG) controls and operates the Facility and partners with the National <br /> Guard Bureau (NGB)and the Army National Guard (ARNG),who functions as the technical and financial support <br /> lead in this effort.Army National Guard (ARNG)G-9 is the lead agency performing Remedial Investigations(RI)/ <br /> Feasibility Studies (FS), Decision Documents (DDs), and Time and Non-Time Critical Removal Actions <br /> (TCRA/NTCRA)for Per-and Polyfluoroalkyl Substances(PFAS)Impacted Sites at ARNG Installations,Nationwide. <br /> This work is supported by the United States (US) Army Corps of Engineers (USACE) Baltimore District and their <br /> contractor Parsons Government Services, Inc. (Parsons) under Contract Number W912DY-21-D-0062, Task <br /> Order (TO)W912DR22F0316, issued 30 September 2022, and Performance Work Statement(PWS) dated 08 <br /> September 2022. <br /> Programmatically, the ARNG is assessing the potential environmental impacts primarily from aqueous film <br /> forming foam (AFFF)and similar chemical releases suspected at their properties related to processes that used <br /> PFAS (e.g., fire training, firefighting, and metal plating). A Preliminary Assessment (PA) and Site Inspection (SI) <br /> were performed under a separate contract vehicle on behalf of the ARNG. The PA determined whether there <br /> were potential sources and releases to the environment related to processes that used PFAS. Based on the <br /> findings of the PA,Stockton AASF moved forward to the SI phase for further evaluation.The SI concluded further <br /> evaluation of the Areas of Interest(AOIs)identified in the PA is warranted based on concentrations of PFAS above <br /> screening levels (SLs) established in a memorandum from the Office of the Secretary of Defense (OSD) dated <br /> 06 July 2022(Assistant Secretary of Defense,2022).Since the SI,a subsequent memorandum from OSD dated <br /> 24 August 2023 was released stating that United States Environmental Protection Agency (USEPA) Regional <br /> Screening Levels(RSLs)for PFAS will be adopted (Assistant Secretary of Defense, 2023c). <br /> The RI project elements will be performed by Parsons in accordance with the Comprehensive Environmental <br /> Response, Compensation, and Liability Act (CERCLA; US Environmental Protection Agency [USEPA], 1980), as <br /> amended, the National Oil and Hazardous Substances Pollution Contingency Plan (also referred to as the <br /> "National Oil and Hazardous Substances Pollution Contingency Plan [NCP]"; 40 Code of Federal Regulations <br /> [CFR] Part 300; USEPA, 1994)and the Superfund Amendments and Reauthorization Act,and in compliance with <br /> US Department of the Army (DA) requirements and guidance for field investigations, including specific <br /> requirements for sampling the group of compounds known in the industry as PFAS.The term PFAS will be used <br /> throughout this plan to encompass all PFAS being evaluated. This RI QAPP focuses on the eight compounds <br /> presented on the Department of Defense (DoD) PFAS 101 Regional Screening Levels Used in DoD Cleanups <br /> website regarding investigating PFAS within the DoD Cleanup Program (OUSD A&S,2024).The eight compounds <br /> include perfluorooctanesulfonic acid(PFOS),perfluorooctanoic acid(PFOA),perfluorobutanesulfonic acid(PFBS), <br /> perfluorononanoic acid (PFNA), perfluorohexanesulfonic acid (PFHxS), hexafluoropropylene oxide dimer acid <br /> (HFPO-DA;also known as GenX), perfluorobutanoic acid(PFBA),and perfluorohexanoic acid(PFHxA).These eight <br /> compounds are collectively referred to as "relevant compounds" throughout the document, and the applicable <br /> SLs are provided in Table 10-2. Two additional compounds, bis(trifluoromethylsulfonyl)amine (TFSI) and <br /> perfluoropropanoic acid (PFPrA), have been added to the DoD PFAS investigations scope (OUSD A&S, 2024); <br /> however,as there are currently no USEPA-approved analytical methods for measuring TFSI and PFPrA,the list of <br /> PARSONS 1.0 Introduction <br /> Page xii <br />