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Geosyntec O consultants an environmental insurance policy. The insurance policy sunsets on July 1, 2030. Consequently, the Trust is implementing remediation at the Site in a proactive manner with the goal of completing active remediation by 2028 to support Site closure by the policy sunset date. The well destruction activities described in this Work Plan are proposed to meet this timeline by implementing decommissioning efforts, as reasonable, in a stepwise manner leading up to the policy sunset date. Groundwater monitoring at the Site is conducted under two existing programs that complement each other: 1) the Sitewide Groundwater Monitoring Plan (GWMP, ERM, 2015) and 2) the CVRWQCB Waste Discharge Requirements (WDR) for In-Situ Groundwater Remediation and Discharge of Treated Groundwater to Land Order No. R5 2016 0012 013 Monitoring and Reporting Program (MRP), revised August 22, 2016 (CVRWQCB, 2016); December 22, 2020 (CVRWQCB, 2020); and May 30, 2022 (CVRWQCB, 2022). The GWMP is used to monitor changes in groundwater elevation and contaminant concentrations and the WDR monitoring program is intended to evaluate performance and the effectiveness of the current remedy and verify that no adverse groundwater impacts occur due to in situ chemical oxidation (ISCO) treatment, in accordance with the WDR permit. 3. RATIONALE AND APPROACH There are over 100 piezometers, groundwater monitoring, extraction, and injection, and other types of wells that have historically been used to support implementation of various phases of soil and groundwater remedial action and performance assessment at the Site. In alignment with advancing the Site towards completion of the current groundwater remedy and eventual decommissioning of remedial infrastructure, the Trust is proposing to iteratively decommission wells present at the Site that no longer provide benefit in performing or assessing the remedy (Table 1 and Figure 1). To inform the selection of wells for destruction, a Well Destruction Decision Tree (Decision Tree; Figure 2) was developed based on the monitoring reduction criteria presented in the 2020 Request(Appendix A). The Decision Tree is intended to provide a framework for destruction of all types of Site wells in the future,as the remedy progresses and meets the remedial objectives described in the Site Response Plan. Well Destruction Work Plan 2 June 27,2023