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4 07 SEALING OF DRILLED HOLES AND UNDERGROUND OPENINGS <br />4.07.1 GENERAL REQUIREMENTS <br />All exploration drillholes, boreholes, monitoring wells, water wells. and exposed underground <br />openings will be plugged and sealed in order to prevent acid or toxic drainage, minimize disturbance to <br />the prevailing hydrologic 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 just above the ground surface <br />and capped. No other temporary sealing measures are proposed since capping of wells will adequately <br />address any potential concerns and will facilitate access to the wells when needed. <br />4.07.3 PERMANENT SEALING <br />EFCI will seal all open drill holes, boreholes, wells, and monitoring wells which will not be utilized in <br />conjunction with post -mining land uses or that have been approved for transfer of ownership and <br />permanent retention. Sealing of any drillholes is discussed in detail in permit Section 2.05.4. <br />Abandonment will involve digging a small slit trench alongside each cased hole/well with a backhoe to <br />provide subsurface access to the casing. The casing will be cut off approximately 3 feet below ground <br />level and a mixed, high yield bentonite slurry will be placed down the open hole/well until the <br />hole/casing is filled to within approximately 10 feet of the top of the hole. (The bentonite slurry <br />continues to yield and swell in the hole/well wherever water is contacted, whereas cement slurries have <br />the potential to contract and crack over time). A cement slurry plug will be placed into the hole/casing <br />extending from the bottom of the slit trench filling the remainder of the hole/well. Before placing the <br />cement slurry, a non -slip plug or equivalent will be installed in the hole/casing at the top of the <br />bentonite slurry to assure that the cement plug does not settle into the bentonite slurry. The slit trench <br />will then be backfilled, graded and seeded with the approved seed mix. A 3/4 inch diameter steel pipe <br />marker will then be installed in the hole to mark the site. <br />4.07-1 Revised 10/28/15 <br />MR -69 <br />