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Work Plan,Decommissioning Monitoring Wells MW-3,MW-4,and MW-7 2130 West Washington Street Stockton,California Sierra-Pacific Project No.92-033.04 F.i 3.0 SCOPE OF PROPOSED WORK The well decommissions will be done by a State-licensed C-57 drilling contractor in conformance with State and San Joaquin County guidelines for well abandonment. Sierra-Pacific will oversee the decommissioning. 3.1 Field Preparations Field preparations will include one pre-construction meeting, telephone conversations, and correspondence with various parties, including Unocal, RWQCB, San Joaquin County, and the drilling contractor. Well decommissioning permits will be obtained from the San Joaquin County Department of Public Health Services,Environmental Health Division. (:3:.2::O:yerboring, Casing Removal and"Grouting l The pro ed--w casings, over-boring of the wells to total- depths, and sealing with bentonite-cement grout. A truck-mounted, 9-inch diameter, hollow-stem auger, fitted with a pilot shaft,will be used to drill-out the well casing and screen. The over-boring will be advanced slowly to allow complete destruction and removal of the PVC-casing fragments. Potable water for drilling and decontamination of equipment is available at the site. Each of the open well r borings will be sealed with cement/bentonite mixture. The water table lies within 10 feet of the surface, therefore the cement grout mixture will be placed down the hollow-stem auger as the auger is slowly removed from the well boring. 3.3 Site Cleanup Construction debris and soil cuttings will be contained and removed from the site. Waste materials will be placed in 55-gallon drums, sampled, characterized, and properly disposed. A high-pressure washer - will be used to clean the drilling equipment.tools and a ui ment. Decontamination rinsate will be placed in 55- gallon drums and disposed. Sierra-Pacific Groundwater Consultants,Inc. 3