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// <br /> GEOMATRIX <br /> borehole stability. Boreholes that are terminated above the water table and are not greater <br /> than 20 feet deep may be grouted by a continuous pour originating at the ground surface. <br /> If the well casing cannot be removed, grout may be tremied into the casing as described <br /> above. If the filter pack interconnects multiple distinct water-yielding zones, the casing <br /> must be cut opposite the aquifer to be sealed as well as through the intervening aquitard <br /> before grout is emplaced. This will allow the grout to seal the filter pack area, thereby <br /> prohibiting vertical movement of groundwater between the zones. Grout should be placed <br /> opposite the aquifer and for a vertical distance of at least ten feet above (and below the <br /> aquifer, if applicable). If the aquifer is confined and'the head pressure is great, the grout <br /> may need to be emplaced under pressure. <br /> Y P <br /> The volume of sealing material used will be calculated and compared to the casing or <br /> borehole volume to ensure bridging has not taken place during well destruction. If the well <br /> is in an urban area and if the casing remains in the borehole, a hole will be excavated <br /> around the well to a depth of five feet, and the casing will be removed to the bottom of the <br /> excavation. The sealing material will be allowed to spill over into the excavation to form a <br /> -cap. The remainder of the excavation will be backfilled with either native material,.grout, <br /> or concrete. <br /> INSTALLATION AND DESTRUCTION OF WELLS <br /> MSCIOEOMATMIRO REWMN DATE:NOVEMBM 1992 Page 8 of 8 <br />