6MN Ventilation Shaft, Mine Water Storage Reservoir, and Passive Treatment System (TR05-48, TR07-61,
<br /> TR07-62, TR16-84, MR06-208, MR06-210, MR06-212, MR07-224, MR08-227, MR09-234, MR15-290) --When
<br /> the 6-Main North Ventilation Shaft and supporting equipment and boreholes are no longer required to support
<br /> ongoing or future mining operations the associated surface facilities will be removed the shaft will be plugged and
<br /> sealed, and surface disturbance areas will be reclaimed. The supporting equipment and any structural steel, tanks, or
<br /> building framing and siding will be removed and reused, salvaged, or disposed of off-site. Buried utilities will be
<br /> stubbed-off below grade and abandoned. Concrete pads will be broken up, and foundations and piers will be demolished
<br /> to at least 2 feet below grade, and the resulting concrete debris will be disposed of in the shaft opening. The shaft collar
<br /> concrete will also be broken up and disposed of into the shaft opening, leaving an open space for the concrete slab and
<br /> backfill material/shaft cuttings to be placed in the shaft void. A cement plug will be placed in the bottom 15 feet of the
<br /> shaft and the remainder of the shaft will be filled with inert material including the shaft cuttings and collar excavation
<br /> materials. A cement plug will be poured from ten feet below grade to within approximately 3 feet of the surface. The
<br /> remaining 3 feet will be filled with soil and graded to blend with the surrounding terrain.
<br /> As noted in the discussion of construction for the 6-Main North Ventilation Shaft, any required pressure—grout
<br /> boreholes will be sealed at the time of construction. Cement grout will be pumped through the boreholes to seal any
<br /> wet zones encountered and the boreholes will be filled with grout and allowed to set-up on completion of grouting
<br /> operations. Any surface casing extending above ground surface would be cut-off flush with or below natural ground
<br /> level. At such time as the 6MN Shaft Heaters are no longer needed to address winter ventilation issues, the shaft
<br /> heaters will be disconnected from the propane tank and electrical connections, the vent tubing will be disconnected,
<br /> and all system components (ie: heater units, vent tubing, and propane tank) will be removed from the site. Utility
<br /> boreholes will be plugged, filled to within 10 feet of the ground surface with inert material, and a cement plug will
<br /> be poured from the top of the fill to within approximately 3 feet of the surface. Any surface casing will be cut-off
<br /> below grade, and the remaining hole will be filled with soil material and graded to blend with the surrounding
<br /> terrain.
<br /> The site geotechnical auger-holes and test pits were backfilled and leveled, and piezometers were either removed, or
<br /> plugged, cut-off below the ground surface, and capped with a clay or cement cap immediately following completion of
<br /> field investigations. The associated disturbed areas were seeded with the pastureland seed mixture within 6-months of
<br /> completion of the geotechnical investigations. Following removal of structures and equipment,and plugging and sealing
<br /> of the shaft and boreholes, any cuttings remaining in the temporary mine waste disposal pit will be covered with
<br /> excavated shaft collar material; road culverts will be removed and disposed of off-site; road-base and surfacing materials
<br /> will be removed and placed on the shaft pad; and the shaft pad and access road disturbance areas will be regraded to
<br /> reestablish effective drainage and blend with the surrounding terrain. Cover over any cuttings remaining in the cuttings
<br /> pit will be a minimum of 2 feet of suitable material, and the postmining configuration will approximate the pre-mining
<br /> contours. As-built certification will be provided to the CDRMS following final closure, backfilling, and grading of
<br /> the cuttings pit. Any excess road-base and surfacing materials not required to reestablish approximate original contour
<br /> will be hauled off-site and disposed of Stockpiled and windrowed topsoil will then be replaced on those disturbed areas
<br /> where it was previously removed and seeded with a pastureland seed mixture.
<br /> The surface disturbance resulting from construction of the mine water pipeline running from the 6MN Million-Gallon
<br /> Tank to the 10-Right Dewatering Pipeline was reclaimed concurrently with pipeline installation. After placement of the
<br /> pipeline in the excavated trench, the excavated material was backfilled into the trench and compacted around and over
<br /> the pipeline, topsoil which had been windrowed to the side of the trench excavation was re-spread over the disturbed
<br /> area, and disturbed areas were reseeded with the standard rangeland seed mixture. When use of the pipeline is no longer
<br /> necessary to support ongoing or future mining operations, the pipeline will be plugged and stubbed-off below grade at
<br /> both ends,and abandoned in-place.
<br /> With the planned construction and operation of the Passive Treatment System, the Treatment System and the existing
<br /> 6MN Storage Reservoir will function as an integrated water treatment and control system. Once discharge ceases, the
<br /> passive treatment cells will be allowed to dry-out, the 6MN Storage Reservoir will be drained, man-made discharge
<br /> structures will be removed, the embankments for each treatment cell and the 6MN Reservoir will be pushed into the
<br /> cell/pond basins, the ends of the transfer and discharge pipelines will be cut-off and plugged and the pipelines will be
<br /> abandoned in-place,road culverts will be removed and disposed of off-site; road-base and surfacing materials will be
<br /> TR16-84 2.05— 106 08/20/18
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