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I I <br /> Geosyntec Oakland, <br /> Broadway, Floor <br /> Oakland,Californias 94607 <br /> PH 510.285.2700 <br /> consultants www.geosyntec.com <br /> Memorandum <br /> Date: June 5, 2026 <br /> To: Frank Girardi, Lead Senior REHS, RDI, San Joaquin County <br /> Environmental Health Department <br /> Copies to: Eric Suchomel, PhD, PE; Zizheng Qu, EIT <br /> From: Jessica Ramirez, PE <br /> Subject: Justification for Well Destruction by Pressure Grouting <br /> Former Olin Chlor Alkali Facility, Tracy, California <br /> Geosyntec Project Number: WR331313/04 <br /> This memorandum has been prepared in response to a request for additional information about the <br /> proposed method of well destruction in permit applications to the San Joaquin County <br /> Environmental Health Department (SJCEHD) for the destruction of eight monitoring wells <br /> associated with the subject site. <br /> In September 2025, Olin submitted a no further action (NFA) request for site groundwater to the <br /> Central Valley Regional Water Quality Control Board(CVWB).1 At the time of Olin's request for <br /> an NFA determination for groundwater,the site conditions in groundwater included the following: <br /> • Onsite sources have been remediated to the extent feasible and there are no onsite <br /> sources contributing to groundwater detections downgradient of the Site. <br /> • The extent of contaminants of concern(COCs)in groundwater has been delineated and <br /> is limited. On-site concentrations of Site COCs are below maximum contaminant levels <br /> (MCLs). Off-site COC detections above MCLs are low and limited to carbon <br /> tetrachloride in one well and one grab sample. <br /> • Natural attenuation of COCs in groundwater is occurring. COCs are not migrating <br /> beyond historical boundaries, which indicates that the CVWB-approved monitored <br /> natural attenuation(MNA)remedy is protective of human health and the environment. <br /> Where detected, COC concentrations exhibit stable or decreasing trends. Where COCs <br /> are present above MCLs, concentrations are projected to decrease to below the MCLs <br /> within approximately 10 years, which the CVWB considers a reasonable period of <br /> time. <br /> ' Geosyntec, 2025. Revised Request for No Further Action—Groundwater, Former Olin Chlor Alkali Facility. <br /> September 19. <br /> engineers I scientists I innovators <br />