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Page 3 December 20,2023 Brusca File No. 260-004 Groundwater Monitoring Wells Workplan GROUNDWATER MONITORING WELL INSTALLATION General/Planed Locations Three groundwater monitoring wells (identified as MW I, MW2, and MW3) are proposed at the site; the selected groundwater monitoring well locations are shown on Plate 4. As shown, groundwater monitoring well MW 1 is planned at the former UST location, and MW2 is planned to the south-southwest near the location where the highest concentrations of diesel were previously detected in groundwater (near Boring TH9). Groundwater monitoring well MW3 is planned to the west of the former UST location. One of the objectives of monitoring well MW3 is to evaluate/define the westerly extent of the diesel groundwater plume as required by the CVRWQCB. In the event that groundwater data from MW3 is not sufficient to define westerly extent of the plume (e.g., if groundwater from MW3 exhibits an elevated concentration of diesel), a step out boring to the west of MW3 will be planned for additional groundwater sampling. Permitting and Utility Clearance Prior to installation of the groundwater monitoring wells, the necessary well permits will be obtained from the San Joaquin County Environmental Health Department (SJCEHD). Prior to drilling for well installation, the well locations will be marked, and Underground Service Alert will be contacted to clear the locations of underground utilities. Well Installation The three planned groundwater monitoring wells will be constructed within minimum eight-inch diameter borings drilled with a truck-mounted drill rig using hollow-stem augers. The drilling and well installation will be performed by a C57-licensed contractor. The borings for the groundwater monitoring wells will extend to a total depth of 80 feet (about ten feet below the shallow groundwater level). Monitoring wells MW 1 and MW2 are planned to be installed very near former borings TH5 and TH9, respectively. As such, the lithology/logs from those previously drilled borings will be considered representative of the conditions at the monitoring well conditions, and soil sampling in the borings for MW 1 and MW2 will only be performed below the depths of available lithology information from the previous borings (i.e. soil sampling will be performed at depths of 75 and 80 feet. For groundwater monitoring well MW3, soil samples will be collected at five-foot depth intervals to the total depth of 80 feet for lithologic characterization. Drilling and well installation will be performed under the direct supervision of a Professional Geologist from our office who will log and classify the materials encountered. Two-inch diameter Schedule 40 PVC casing will be used for the wells. The lower 20 feet of the casing (about ten feet below the water level and ten feet above) will be screened. The screened portion of the well will be factory slotted (0.020-inch slots). The annular space surrounding the screened portion of the well and extending two feet above will be backfilled with washed graded silica sand. A one- to two-foot-thick bentonite plug will be installed and hydrated within the annular space directly above the sand filter, and the remaining annular space above will be backfilled with neat cement grout.