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Soo Stantec Revised Well Destruction Work Plan Chevron and ARCO Commingled Plume No. CP0034 December 5, 2012 Permitting Prior to beginning field work, all necessary permits and access agreements will be obtained. Underground Utility Location and Clearance. Well locations will be marked or cleared of underground facilities prior to well destruction activities. As required by the California Government Code 4216, Underground Service Alert (USA) North and 811 will be notified at least two working days before drilling activities. Well locations will be marked with white paint to indicate the area of drilling. This will allow USA North members, including local utility companies, to identify and mark the horizontal path of their underground facilities located within the area of drilling. The area will be cleared if no underground facilities are found. In conjunction with USA North and 811, a private utility locator will be utilized for clearing proposed well boring locations for underground utilities. Well Destruction Activities A C-57-licensed drilling company will complete the well destruction activities following all relevant sections in the California Well Standards, Bulletin 74-90. Four wells (Chevron offsite monitoring well MW-10 and ARCO offsite monitoring wells PR-1, PR-2, and BHD-2) will be destroyed by pressure-grouting. Prior to pressure-grouting activities, the well casing will be inspected for obstructions; if obstructions are found, they will be removed. Each well will be pressure-grouted with neat cement using a tremie pipe system forming a mushroom grout cap/surface seal. If groundwater is expelled during the grouting process, it will be properly contained, characterized, and disposed of. After completing the grouting activities, the well borehole around each well will be air-knifed to approximately five feet bgs and each well casing will be cut at approximately five feet bgs. The borehole locations will be backfilled and resurfaced with appropriate materials to match the existing grade. The remaining wells (eight Chevron groundwater monitoring wells, 13 ARCO groundwater monitoring wells, and 20 ARCO remediation wells) will be destroyed by over-drilling. Each well borehole will be air-knifed to approximately eight feet one inch bgs to investigate that no underground facilities exist within the area of drilling. Prior to over-drilling activities, the well casing will be inspected for obstructions; if obstructions are found, they will be removed. Each well will be over-drilled using a drill rig equipped with a hollow stem auger (auger to be eight or ten inch diameter depending on the borehole diameter) to remove material within the original borehole including the well casing, filter pack, and annular seal. The borehole will then be grouted with neat cement using a tremie pipe system forming a grout cap/surface seal from the bottom of the borehole to one foot bgs. If groundwater is expelled during the grouting process, it will be properly contained, characterized, and disposed. The borehole locations will be backfilled and resurfaced with appropriate materials to match the existing grade. Waste Management All investigation derived waste, including soil and groundwater(if present)from the well and soil vapor probe destruction activities will be stored on-site in Department of Transportation- approved 55-gallon drums pending proper disposal. All waste will be transported and disposed of at an appropriate State-certified disposal facility. Revised Well Destruction Work Plan 2012.docx 2