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Rantec April 24, 2009 Ms. Kristi Shelton ABANDONMENT OF DOMESTIC PRODUCTION WELL AND GROUNDWATER MONITORING WELLS Stantec proposes abandoning the on-site domestic well and three groundwater monitoring wells prior to beginning excavation activities. The domestic well consists of a 6-inch-diameter steel casing installed to approximately 110 bgs, and the pump is installed at 87 feet bgs. The screened interval of the well is unknown. The domestic well is not currently in use, and is within the boundary of the proposed excavation (see Figure 3). Similarly, groundwater monitoring well MW-1 is in the center of the proposed excavation. For the sake of economy, Stantec proposes abandoning wells MW-2 and MW-3 during the same mobilization. Well Abandonment The four wells will be abandoned pressure grouting, under permit from San Joaquin County Environmental Health Department. The work will be performed by Woodward Drilling of Rio Vista, California under supervision of a Stantec geologist. The pump and drop pipe will be removed from the domestic well and the casing backfilled to 100 feet bgs using pea gravel, in accordance with county requirements. The remaining casing will be backfilled with neat cement grout to 5 feet bgs, and the upper five feet of casing removed and a mushroom cap installed. Each of the three groundwater monitoring wells will be pressure-grouted, and the upper 5 feet of casing removed and a mushroom cap installed. Waste Management and Reporting Water displaced during the grouting process will be collected in 55-gallon steel drums, which will be labeled as to contents and stored on-site pending profiling and disposal of the waste.Associated waste debris such as well casings, well boxes, and pump equipment will be either left on-site or disposed of as general waste by Woodward Drilling. Following completion of well abandonment activities, Stantec will complete and file well destruction forms as required by the State Water Resources Control Board. PRE-EXCAVATION INVESTIGATION In order to more precisely determine the extent of excavation required to achieve cleanup goals, Stantec proposes advancing up to six direct-push soil borings to approximately 20 feet bgs. Field observations and soil chemical data will be used to refine the proposed area of excavation, and analytical results will be used to pre-profile the soils for disposal. One soil boring will be advanced along each side of the 15-foot-by-15-foot square centered on MW-1, as illustrated on Figure 3. Based on observations made during examination of recovered soils, up to two additional soil borings may be advanced at appropriate'step-out' locations. Chemical data and field observations will be used to confirm the extent of impacted soils previously observed in the vicinity of MWA. Permitting and Preliminary Activities Stantec will obtain a soil boring permit from the San Joaquin County Department of Environmental Health, and update the existing site-specific health and safety plan to incorporate the proposed activities. Stantec will mark the drilling locations with white paint, notify Underground Service Alert, and subcontract with a private utility locator to confirm the locations of detectable underground utilities identified during previous investigations.