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Ms. Gail Wiggett Project 20C42-001.026 <br /> May 15, 1997 <br /> Page 2 <br /> pressure grouted to ground surface using 9 sack sand-cement grout pumped to the base of <br /> the well bores through tremie pipe. <br /> Monitoring Well Decommissioning <br /> Twenty-four monitoring wells are proposed for decommissioning based on location, <br /> construction, and limited utility in groundwater monitoring and remediation (see Table 1). <br /> Wells will be decommissioned by a licensed drilling contractor consistent with state and <br /> county regulations. Eighteen of the wells proposed to be decommissioned were installed <br /> between 1987 and 1989 for monitoring and product recovery in the northwestern part of <br /> the site. These wells range in diameter from 2 to 12 inches, and completion depths are <br /> generally 10 feet or less. The majority of the wells were installed in test pits excavated <br /> using a backhoe and do not have surface seals. At present, free product is limited to an <br /> intermittent sheen, and further recovery efforts are not practical. Water level data would <br /> still be provided by wells not proposed to be decommissioned. <br /> Five of the wells proposed for decommissioning were installed for groundwater monitoring <br /> purposes between 1989 and 1992. Two of these wells (UP/MW-2 and UP/MW-3) are <br /> located in the southwest comer of the site and outside the A zone dissolved petroleum <br /> hydrocarbon plume. A zone well PS/MW-16 is located west of Stork Road in an area <br /> currently being developed for agricultural chemical storage. Well pair PS/MW-11 and <br /> PS/MW-12 installed by Woodward Clyde are located east of Stork Road. Nearby wells <br /> currently sampled in the quarterly monitoring program provide coverage of these areas for <br /> water level and water quality monitoring. <br /> Twelve of the monitoring wells will be decommissioned by drilling out the surface seal, <br /> filter pack, and well casing to the total depth of each well using 8- to 12-inch hollow stem <br /> augers. Auger diameter used will depend upon the well construction; 8-inch diameter <br /> augers will be used for 2-inch diameter wells, 10-inch augers will be used for 4-inch <br /> diameter wells, and 12-inch diameter augers will be used for 6-inch diameter wells. The <br /> borings will be grouted. <br /> Twelve of the monitoring wells are located in areas inaccessible to drilling rigs. EMCON <br /> proposes to decommission these wells using a backhoe to excavate the surface seal and pull <br /> the well casing. These wells are completed at depths between 7 and 10 feet below ground <br /> surface. The cavity remaining after removal of the well casing will be grouted to ground <br /> surface using a bentonite cement grout pumped through tremie pipe. <br /> SA(W:\PJODW,4Z\11C420012.6YS-97Ncib:3 Rev.0.5f!/97 <br />