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GAVIN NEWSOM <br /> 06 0 GOVERNOR <br /> C 0.L I F0 R N I AJAIREo BLuMENIFELD <br /> RECRETARRy FOR <br /> Water Boards ENVIRONMENTAL PROTECTION <br /> Central Valley Regional Water Quality Control Board <br /> 23 August 2022 <br /> Steve Azevedo <br /> West Clay Properties/Knife River Corporation <br /> P.O. Box 6099 <br /> Stockton, CA 95206 <br /> RESPONSE TO GROUNDWATER MONITORING REPORT— <br /> SECOND QUARTER 2021, WEST CLAY PROPERTY(T0607700323), <br /> 639 WEST CLAY STREET, STOCKTON, SAN JOAQUIN COUNTY <br /> Central Valley Water Quality Control Board (Central Valley Water Board) staff (Staff) <br /> has reviewed the 26 August 2021 Groundwater Monitoring Report— Second Quarter <br /> 2021 (2Q21 GMR) submitted on your behalf by AdvancedGeo Inc. (AGI). AGI submitted <br /> the 2Q21 GMR for the underground storage tank (UST) release case located at 639 <br /> West Clay Street in Stockton (Site). In the 2Q21 GMR, AGI recommended preparation <br /> of a site conceptual model and low threat closure evaluation report. AGI suggested <br /> groundwater monitoring at the Site be suspended until the evaluation is prepared. <br /> Staff has evaluated the case against the State Water Resources Control Board's (State <br /> Water Board's) Low-Threat UST Case Closure Policy (Low-Threat Closure Policy) and <br /> does not concur with AGI's recommendation to prepare a closure evaluation report. <br /> Additional offsite investigation is needed to fully delineate dissolved hydrocarbon <br /> plumes to water quality objectives east and northeast of the Site. Staff's Low-Threat <br /> Closure Policy evaluation follows: <br /> • General Criteria: The Site meets seven of the eight criteria. The Site does not <br /> meet general criteria "e."; a conceptual site model that assesses the nature, <br /> extent, and mobility of the release has not been developed. The offsite extents of <br /> dissolved plumes are not laterally defined to the east and northeast. <br /> • Media-Specific Criteria: The Site meets the Petroleum Vapor Intrusion to Indoor <br /> Air and the Direct Contact and Outdoor Air Exposure criteria. The Site does not <br /> meet the Groundwater criteria. Offsite petroleum hydrocarbon groundwater <br /> plume boundaries that exceed water quality objectives have not been defined <br /> north and east of CPT-1 and south and east of borings B16 and B18. <br /> In the 23 January 2020 Additional Site Assessment Report (Assessment Report), AGI <br /> presented the results of offsite cone penetration testing (CPT) soil borings and <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 />