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® GAYIN NEWSOM <br /> G CiVFRNOR <br /> Water Boards YE"EGME FOR <br /> ENVIRONMENTAL PROTECTION <br /> Central Valley Regional Water Quality Control Board <br /> 3 April 2023 <br /> Helene Nussbaumer CM, Interim Airport Director <br /> Stockton Municipal Airport <br /> 5000 S. Airport Way, Suite 202 <br /> Stockton, CA 95206 <br /> CONCURRENCE WITH REVISED ADDITIONAL PFAS INVESTIGATION WORK <br /> PLAN AND RESPONSE TO COMMENTS STOCKTON MUNICIPAL AIRPORT, <br /> 5000 S. AIROPORT WAY, STOCKTON, CALIFORNIA (T10000012778) <br /> Central Valley Regional Water Quality Control Board (Central Valley Water Board) staff <br /> reviewed the Revised Work Plan Additional Site Investigation Per- and Polyfluoroalkyl <br /> Substances (PFAS) in Soil and Groundwater Stockton Municipal Airport dated <br /> 1 March 2023 (Revised Work Plan) and the Response to Comments Additional PFAS <br /> Site Investigation Workplan Stockton Metropolitan Airport dated 1 March 2023 (RTC). In <br /> response to the Central Valley Water Board comment letter dated 13 January 2023, <br /> BSK Associates (BSK) submitted the Revised Work Plan and RTC on behalf of the <br /> Stockton Metropolitan Airport (Airport). The Revised Work Plan and RTC describe the <br /> investigative activities to delineate the PFAS plumes in soil and groundwater at the <br /> Airport. The RTC also acknowledges the potential need for additional off-site <br /> investigations should elevated concentrations of PFAS are observed at the Airport <br /> boundary. <br /> In the Revised Work Plan, BSK proposes a phased approach (Phases I and II) to study <br /> the PFAS contamination at the Airport. At a minimum, BSK will conduct the following <br /> activities: <br /> Phase I: <br /> 1) Install six and eight borings, with the boring depths ranging between 10 and 40 <br /> feet below ground surface (bgs), in PFAS source zones of PRA-1 and PRA-2, <br /> respectively. <br /> 2) Install four groundwater monitoring wells in the vicinity of the PFAS source zones <br /> and collect groundwater samples for PFAS analysis. <br /> 3) Collect soil samples at 1, 5, and 10 feet bgs, respectively, in all borings and <br /> monitoring wells; additionally, for borings greater than 10 feet deep, also collect <br /> soil samples at a five-foot interval beyond 10 feet bgs till the total depth of the <br /> MARK BRADFORD, CHAIR I PATRICK PULUPA, ESQ., EXECUTIVE OFFICER <br /> 11020 Sun Center Drive#200, Rancho Cordova, CA 95670 1 www.waterboards.ca.gov/centralvalley <br />