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Geosyntec consultants 2.2 Well Redevelopment Activities Three monitoring wells(W-091,W-093, and W-095)were attempted to be redeveloped during the 2024 monitoring event; however, obstructions were noted that prevented well redevelopment with the equipment available during the field effort, as documented in the 2024 GMR. These wells will be redeveloped as part of the 2025 well maintenance activities (Table 1). Well redevelopment will be performed in accordance with the well development standard operating procedure (SOP) included in Appendix A. The contractor will come prepared with equipment to facilitate removal of obstructions, if feasible, and alternative pumps (such as peri-pump) that can be utilized in high sediment water. 2.3 Well Replacement Two monitoring wells (W-101 and W-342) are proposed to be replaced due to noted damages to the well casing at depth during well redevelopment efforts performed in 2024. The monitoring wells are presumed to have damages to the well casing that has allowed for sediments to block the entire screened section of the wells. W-101 monitors the down and cross-gradient extent of the chlorinated VOC plume at Site 3 and W-342 monitors the cross gradient extent of the chlorinated VOC plume at Site 4. Both wells are considered to be critical for continued monitoring of the extent of the chlorinated VOC plumes, and are therefore proposed to be replaced to ensure representative groundwater data can be collected. The locations of the replacement wells are shown on Figure 3 and the proposed well construction details are described in Table 3. 2.3.1 Well Destruction Activities Well destruction permits for W-101 and W-342 will be obtained from San Joaquin County Environmental Health Department(SJCEHD). The well destructions will be conducted by a C-57 licensed drilling contractor working under the supervision of a California-licensed professional geologist. Each well that is destroyed will be overdrilled using the hollow stem auger(HSA)drilling method to the total well depth using an auger diameter greater than the original well borehole and the well materials removed from the subsurface. Once the well materials have been removed, the borehole will be tremie-grouted with Portland cement grout under inspection by SJCEHD from the bottom of the borehole to 5 feet bgs. In accordance with the California Well Standards, the top 5 feet bgs will be backfilled with native soil(Department of Water Resources 1991). Materials removed will be managed according to Section 4. 2.3.2 Well Installations Monitoring well installation activities will be conducted in accordance with the SOP in Appendix B and monitoring well development in accordance with the SOP in Appendix A. The well construction details included in the SOP and in Table 3 are based on the original well screen 4 DTSC and CVRWQCB will be notified if an alternative drilling method will be used. RRI 2025 Groundwater Monitoring Work Plan 11 May 2025