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Groundwater Monitoring Well Constructlon Workplan January 2024 Monitoring Well Design Justification Four-level nested monitoring wells will be constructed at this drill site. The levels (depths) of the screen intervals were selected to provide groundwater levels above and below the Corcoran Clay, groundwater use in the area, potential differences in water quality, and to assess whether the groundwater pumping is raising the base of fresh water.These monitoring wells (four-levels) will also better characterize groundwater conditions by establishing groundwater outflow gradients from or to the Northern Delta-Mendonta Subbasin into the TSb. The lithologic information will also help to confirm/support Airborne Elecromagnetic(commonly know as AEM) survey findings. Figure 8 shows the preliminary monitoring well designs. All well screens, filter packs and annular seals(bentonite clay pellets or chip)intervals may change based on the geophysical logging which will provide site specific details to support the final monitoring well design. The monitoring wells screen locations were developed based on the depth and thickness of the Corcoran Clay, the base of fresh water, and information obtained from MW-203. MW-203 is about 30 feet lower than at MW-204 site. Therefore, the depths of the screen locations and the Corcoran Clay at MW-204 site will be about 30 feet deeper than encountered at MW-203. The monitoring well screens at MW-204 will be positioned to monitor similar aquifers as present at MW-203. Corcoran Clay is present beneath the drill site. Figure 3 shows the extent and structure of the Corcoran Clay based on geologic profiles and geophysical logs as well as USGS datasets in the Subbasin (Page 1968). The top of the clay is about 310 feet bgs and is about 80 feet thick at the proposed monitoring well location, based on MW-203 exploration. The base of fresh water is at elevation -1,600 feet amsl or about 1,800 feet bgs (refer to Figure 4). MW-203 geophysical survey suggests the base of fresh water is greater than 1,350 feet bgs in the area. MW-204's total proposed borehole depth is 1,100 feet bgs, staying well above the base of fresh water. The shallowest monitoring well (named MW-204A)will be constructed in the Upper Aquifer, above the Corcoran Clay.Aquifers above the Corcoran Clay are used by domestic wells that are constructed to depths of 30 to 150 feet bgs. Some irrigation wells also use this aquifer. This monitoring well will be used to monitor groundwater levels in the Upper Aquifer to track changes and inform the GSAs if lowering of groundwaters could affect these domestic well owners. Three monitoring wells(named MW-204B, C, D)will be screened below the Corcoran Clay. The screens for MW-204B will be positioned just below the Corcoran Clay, 500 to 510 feet bgs where low salinity groundwater may be present, based on other occurrences in the Subbasin. MW-204C screens will be positioned about half-way between the bottom of the Corcoran Clay and the base of fresh water, about 740 to 750 feet bgs. Both MW-204B and MW-204C will be GEI Consultants, Inc. 16