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Geosyntec consultants 4.3.2 Monitoring Well Construction Monitoring wells MW-5C and MW-7C will be constructed in accordance with standards presented in the San Joaquin County Well Standards. Each well will be constructed in the same general configuration as the well it is intended to replace.A schematic diagram depicting the anticipated construction details for wells MW-5C and MW-7C is presented on Figure 3. Once the hollow stem auger reaches final depth at each boring, the monitoring wells will be constructed through the hollow stem auger casing. One foot of sand will be placed at the bottom of the borehole below the well screen. MW-5C and MW-7C will both be constructed using 4-inch diameter, flush-threaded Schedule 80 polyvinyl chloride (PVC) casing, bottom caps and well screen (0.020-inch factory-slotted). Both wells will be screened within the shallow groundwater zone;well MW-5C will be screened from approximately 10 ft bgs to 25 ft bgs,and well MW-7C will be screened from approximately 12 ft bgs to 27 ft bgs. However, Geosyntec will specify the exact screen elevations during the installation,and may adjust these intervals based on the observed depths of coarse-grained materials and the depths of the underlying fine-grained clayey material assumed to represent the bottom of the shallow zone. To reduce the potential for cracking or root incursions at well joints, 10-foot sections of PVC riser and screen will be used where feasible to reduce the total number of joints, and the exterior of the joints may be reinforced using stainless steel clamps. Graded silica sand pack(#2/16 or similar) will be tremie-filled into the annular space across the screened interval of each monitoring well, extending two feet above the top of the screen. After the filter pack is installed and prior to placement of the bentonite seal,each well will be pre-developed by surging to settle the filter pack. During and after pre-development, a weighted tape will be used to monitor sand settlement. If settlement of the filter pack is observed, then additional filter pack material will be added to extend the filter pack two feet above the top of the well screen. A minimum of two feet of bentonite pellets will then be placed on top of the sand pack and hydrated a minimum of one-half hour before introducing additional backfill (i.e., grout) to provide a seal above the filter pack. Above the bentonite seal, a bentonite and neat cement grout mixture will be added using tremie pipe to fill the remainder of the borehole annulus to ground surface in accordance with applicable SJCEHD requirements. The borehole grout seal will be inspected after a 24-hour period and additional grout added, if needed, until firm grout is present at the ground surface. Both wells will be completed in accordance with SJCEHD requirements, and Geosyntec will coordinate with SJCEHD for inspection of well construction and grouting activities. A waterproof locking cap will be installed over each monitoring well within an appropriately- sized, traffic-rated, well box set in concrete. Additionally, the elevation and location of the north side of each well box and top of the PVC well casing will be surveyed by Morrow OxyChem-Stockton MW Replacement Work Plan 7.18.25 5 2025.07.18