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Sealing and Managing Mine Openings <br />• Sealing of the openings which access the underground coal mining operations at the New <br />Elk Mine will be completed upon the final closure of the operation. Sealing will consist <br />of installation of bulkheads near the surface of the openings to prevent entry and collapse <br />of the surface. Bulkheads will consist of a minimum of 8 inches of reinforced concrete <br />installed below the ground surface. A typical mine opening seal is shown on Figure 15 - <br />Typical Mine Opening Seal. Particular care will be taken to ensure that excessive <br />pressures do not collect on the inside of the seal and cause seepage or erosion around the <br />seal. In addition, the seal will be sufficiently strong to support the surface material <br />placed over the opening. <br />Airshafts that have been constructed at the New Elk Mine are cement lined to maintain <br />the integrity of the shaft and prevent contamination of intercepted aquifers. Upon final <br />abandonment, these shafts will be sealed with a steel reinforced cement cap. The steel <br />form will be constructed adjacent to the shaft and set into place using a crane or other <br />mobile equipment. The cement cap will then be poured in the form to complete the seal. <br />Figure 16 Airshaft Seal, shows a typical airshaft seal which will be utilized by NECC. <br />All boreholes, wells, and exploration holes will be plugged or otherwise sealed to prevent <br />contamination of groundwater intersected by the hole itself. Surface plugs and <br />backfilling of the holes will be completed to minimize safety hazards to man and wildlife <br />in these areas. Figure 16A - Typical Borehole Seal, shows a typical borehole seal <br />• which will be utilized by NECC. <br />A probable roof failure in the West Portal Mains approximately 500 feet inby the sealed <br />Manway opening has resulted in a sink hole migrating to the surface. Repeated attempts <br />to backfill this area have failed due to piping of surface waters into the mine void. <br />Picketwire Processing will permanently seal this potential mine opening by excavating <br />down to competent strata surrounding the failure zone (approximated at 3-5 foot in <br />diameter). The zone of failure will be backfilled as necessary to the approximate level of <br />the competent strata. A wire-mesh reinforced concrete plug at leased twice the diameter <br />of the failure zone will be poured in place across the area. The concrete will be allowed to <br />cure followed by placing a six inch layer of bentonite over the cement cap. This layer <br />will extend across the width of the excavated area. The bentonite will provide a <br />hydrologic seal at the contact between the cement plug and the surrounding strata. The <br />excavation will then be backfilled to the natural surface. <br />2.05.5 Post-Mining Land Use <br />Similar to the pre-mining land use as determined by the Las Animas County Board and <br />updated to CMLRD definitions, the post-mining land <br /> <br />RN-05 2.05-54 (Revised 1/14/09)