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P Former Discovery ChevroTt February-15, 1999 <br /> Tracy,California Well Destruction Letter Report <br /> I- Overdrilline On February 11 and 12, 1999, Horizon and an SJC PHS/EHD inspector were onsite to <br /> witness Spectrum conducting well abandonment activities on wells MW-2 through MW-5. <br /> Well MW-1 had been previously destroyed during previous site excavation activities <br /> (Horizon, September 16, 1998).-Spectrum.removed"the steel traffic boxes and overdrilled h <br /> wells MW-2, MW-4, and NIW-5 with 8-inch diameter hollow-stem-flight augers. Well. <br /> MW-3 was overdrilled with 10-inch diameter augers. A special auger bit equipped with a <br /> 12-inch long, 1%-inch diameter, steel guide point and well casing cutters -was-utilized to <br /> shred the 2-inch-inside diameter (ID) polyvinyl chloride (PVC) casing of each-well. As the <br /> augers were advanced to the total.depth of-each boring, the well casing, well seal grout, <br /> bentonite seal, and filter sand were"removed in one continuous operation. <br /> Grouting <br /> At the completion of the_overdrilling of each well, Spectrum prepared a neat cement grout at <br /> a ratio of seven gallons of water per 96 pound-sack of Portland cement. Each boring was <br /> backfilled by placing the grout through the augers from the bottom of each boring to the-top <br /> in one continuous operation. The top of each:boring_was bachfilled to surrounding grade. <br /> The 8-inch diameter borings for wells MW-2;MW-4, and MW-5 were each backfilled with - - <br /> approximately 55 to 60 gallons of grout. .The 10-inch:diameter boring for well MW-3 was <br /> backfilled with approximately 100 gallons :of-grout. The calculated and actual grout <br /> volumes placed for each boringare-shown on Table,1. <br /> This work completes regulatory closure requirements as related to the'underground storage <br /> tanks (USTs) at this site. <br /> l <br /> i <br /> 3001-21.wdr 2 HORIZON ENVIRONMENTAL INC. <br />