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Geosynte& consultants Site monitoring wells are installed in the Upper Horizon, within site-specific upper, middle, and lower groundwater zones.As presented in the Revised Monitoring and Reporting Program(MRP), adopted in 2022, the site-specific groundwater zones in relation to the horizons within the Tulare formation are summarized below (CVRWQCB 2022b). Tulare Upper Tulare Site-Specific Site-Specific Approximate Well Screen Formation Formation Formation Groundwater Intervals Member Horizons Horizon Zones (feet bgs) Above Upper Upper 10-27 Tulare Upper Upper Middle 42-58 and Upper Lower 68-89 Abbreviation: bgs=below ground surface Regionally, groundwater flows in a northeast direction and drains to the San Joaquin River and its tributaries (Amec Foster Wheeler 2017). The Corcoran Clay separates the Upper and Lower Tulare members and confines the Lower Tulare groundwater. Local to the Site, large-scale agricultural, municipal, and industrial groundwater extraction is from below the Corcoran Clay. Some small domestic wells may be screened above Corcoran Clay; however, groundwater above Corcoran Clay is often of poor quality based on elevated chloride, nitrate, and boron (California Department of Water Resources 2006). Construction details of Site monitoring wells are presented in Table 1. To date, all monitoring wells owned by Olin have been destroyed, except for MW-5, MW-9, MW-10, MW-11, MW-12, MW-13, MW-14, and MW-15. Additionally, Olin destroyed three on-site industrial production wells, Banta-1 through Banta-3, in January 2026 (Geosyntec 2026). One additional well, Olin-1, is present on-site and was historically used by the Site operators for potable water. Olin-1 is installed below the Corcoran Clay (screened between 490 and 530 feet bgs), and therefore, does not pose a risk to potential receptors (CVRWQCB 2026b). Well Destruction Work Plan 3 May 2026