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4a @�4f GAVIN NEWSOM <br /> � E/ GOVERNOR <br /> x <br /> JAREu <br /> C 0.LIFQRNIA NFELO <br /> SECRETARRY FOR <br /> Water Boards ENVIRONMENTAL PROTECTION <br /> CENTRAL VALLEY REGIONAL WATER QUALITY CONTROL BOARD <br /> 30 July 2021 <br /> Tom Patti, Chair of the Board <br /> San Joaquin County Board of Supervisors <br /> 44 North San Joaquin Street <br /> Sixth Floor, Suite 627 <br /> Stockton, CA 95202 <br /> rdebord@sjgov.org <br /> To All Interested Parties, <br /> This is a Proposition 65 notification being made as a result of environmental <br /> investigations associated with the Stockton Metropolitan Airport (SCK) located at 5000 <br /> S. Airport Way, Stockton, CA (GeoTracker Case File T10000012778; the Site). The <br /> purpose of the investigations was to assess for perfluorooctanoic acid (PFOA) and <br /> perfluorooctane sulfonate (PFOS) in soil and groundwater in the vicinity of the Site. The <br /> Stockton Metropolitan Airport performed a Preliminary Site Investigation for per- and <br /> polyfluoroalkyl substances (PFAS) in response to the State Water Resources Control <br /> Board (SWRCB) California Water Code (CWC) Section 13267 Order WQ 2019-0005- <br /> DWQ (Order) for the determination of the presence of PFAS impacts at 27 California <br /> airports, including the Stockton Metropolitan Airport (BSK Associates, 2020). Elevated <br /> concentrations of PFOS and PFOA were found in several soil borings and temporary <br /> groundwater wells at the Stockton Metropolitan Airport. <br /> One area of concern is the Former Runway (Potential Release Area "PRA 2") where the <br /> interior of the former runway has been used for planting row crops since the 1990s. The <br /> lateral and vertical extent of PFAS in soil and groundwater is not defined but PFAS was <br /> detected in soil from which the row crops are cultivated and in groundwater that is <br /> considered a source of drinking water per the Central Valley Regional Water Quality <br /> Control Board's (Central Valley Water Board's) Basin Plan. <br /> In order to determine potential risk at "PR 2", Central Valley Regional Water Quality <br /> Control Board staff assumed the row crops where PFAS was detected in soil are grown <br /> for human consumption and groundwater is a potential drinking water source. <br /> Therefore, Central Valley Water Board staff compared PFOA and PFOS concentrations <br /> to the conservative San Francisco Bay Regional Water Quality Control Board <br /> (SFBRWQCB) Environmental Screening Levels (ESL). Screening levels for agricultural <br /> use have not been established; therefore, comparable screening levels were evaluated. <br /> For groundwater, Central Valley Water Board staff determined "Direct Exposure Human <br /> KARL E. LONGLEY SCE}, P.E., CHAIR I PATRICK PULLIPA, ESQ., EXECUTIVE OFFICER <br /> 11020 Sun Center Drive#200, Rancho Cordova, CA 95670 1 www.waterboards.ca.gov/centralvalley <br />