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Justification for Well Destruction by Pressure Grouting June 5, 2026 Page 2 • There are no current or reasonably anticipated future receptors of COC-impacted groundwater. ■ In February 2026, CVWB staff collected a sample from a domestic drinking water well at a property approximately 1,400 feet east of the Site.No VOCs were detected above their laboratory reporting limits. ■ SJCEHD requires a 200-foot grout seal for any proposed water well at or in the vicinity of the site and Defense Logistics Agency, Tracy Site (DLA-Tracy), which means that potential future drinking water wells would be screened within or below the Corcoran Clay aquitard. The CVWB made a conditional NFA determination for the site in April 2026.2 As part of the conditional NFA, the remaining site monitoring wells must be destroyed for a final NFA determination to be granted.Based on the conditions documented above, a work plan was prepared and submitted to the CVWB for the destruction of the remaining monitoring wells with pressure grouting proposed as the method of destruction. In addition, the use of pressure grouting for destruction is not expected to negatively impact groundwater quality. All site monitoring wells were originally constructed with grout seals to prevent vertical migration of Site COCs to deeper groundwater zones and ensure groundwater quality is protected. The use of pressure grouting for destruction of the monitoring wells will: • Continue to prevent mixing of groundwater between the groundwater zones. • Mitigate potential future leaks by forcing grout through the screen into the filter pack and surrounding formation. • Because pressure grouting is completed with surface sealing, prevent surface runoff from entering the borehole and impacting groundwater. 2 Central Valley Regional Water Quality Control Board (CVWB), 2026. Conditional No Further Action Determination, Olin Chlor Alkali Facility. April 20. engineers I scientists I innovators