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4.07 SEALING OF DRILLED HOLES AND UNDERGROUND OPENINGS <br /> 4.07.1 GENERAL REQUIREMENTS <br /> With the exception of drillholes completed as either water supply wells or <br /> monitoring wells, all exploration drillholes, boreholes, and exposed <br /> underground openings will be plugged and sealed in order to prevent acid or <br /> toxic drainage, minimize disturbance to the prevailing hydrologic <br /> balance and ensure the safety of animals, persons and equipment within the <br /> permit and adjacent areas. <br /> 4.07.2 TEMPORARY SEALING <br /> Drillholes completed as water supply or monitoring wells will be cased to <br /> just above the ground surface and capped. No other temporary sealing <br /> measures are proposed since capping of wells will adequately address any <br /> potential concerns and will facilitate access to the wells when needed. As <br /> part of the hydrologic monitoring program, the condition of well <br /> installations including surface casing and caps will be inspected on a <br /> regular basis. Any damage will be noted and repairs will be completed on a <br /> timely basis. <br /> 4.07.3 PERMANENT SEALING <br /> Any drillholes not completed as monitoring wells will be sealed and <br /> abandoned. Abandonment will involve digging a small slit trench alongside <br /> each cased hole/well with a backhoe to provide subsurface access to the <br /> casing. The casing will be cut off approximately 3 feet below ground level <br /> and a mixed, high yield bentonite slurry will be pumped down the open <br /> hole/well until the hole/casing is filled to within 10 feet of the top. (The <br /> bentonite slurry continues to yield and swell in the hole/well wherever water <br /> is contacted, whereas cement slurries have the potential to contract and <br /> crack over time). A cement slurry plug will be placed into the hole well <br /> annulus extending from the bottom of the slit trench filling the remainder of <br /> the hole/well. A non-slip plug (oc-to plug) will be installed in the casing at <br /> the top of the bentonite slurry to assure that the cement plug does not settle <br /> into the bentonite slurry. <br /> MR-63 4.07-1 Revised: 7-28-2014 <br />