2023-08-25_PERMIT FILE - C1982056A (2)

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MR22-321 2.05-45.8 07/29/22 resource survey of potential disturbance areas, soil and foundation characterization as the basis for shaft pad and access road design, and completion of a wetland/AVF survey for the shaft pad and access road. The cultural resource survey was conducted by Metcalf Archaeological Consultants, the engineering soils characterization by Northwest Colorado Consultants, and the soils/wetland/AVF survey by Habitat Management, as described in Section 2.04. Development, construction, and installation of the intake ventilation shaft (Exhibit 49A, Figures EX49A-F1 through F4 and Maps EX49A-M1 through M3, and Exhibits 49E and 49N) involve the following sequential activities: • Completion of environmental and engineering investigations • Placement of disturbed area markers • Marking of wetland buffer zone • Temporary drainage and sediment control measures • Recovery and stockpiling of available topsoil • Installation of drainage and sediment control structures • Construction of an access road and site preparation for shaft pad • Drilling and casing of seven (7) boreholes for: • 3 power boreholes • 1 water borehole • 1 air compressor borehole • 1 rockdust borehole • 2 bulk-material drop borehole (will also be used as the nitrogen injection borehole), 2nd drilled in 2022 • Construction of shaft collar structure and temporary drilling equipment pad • Conventional blind sink excavation and casing operations • Driving of additional entries to the south of the existing 6-North Main entries • Installation of electrical sub-station and extension of power distribution line • Fabrication of Million-Gallon Tank for mine water storage • Construction of the 6MN Mine Water Storage Reservoir and connections to the mine water system • Installation of Rock-Dust Tank and Compressor • Installation of a modular nitrogen injection system • Final clean-up and dressing of roads and site pads These activities are briefly described in the following sections: Site-specific investigations required for design and permitting of the new ventilation shaft included a cultural resource survey of potential disturbance areas, soil and foundation characterization as the basis for shaft pad and access road design, and completion of a wetland/AVF survey for the shaft pad and access road. The cultural resource survey was conducted by Metcalf Archaeological Consultants, the engineering soils characterization by Northwest Colorado Consultants, and the soils/wetland/AVF survey by Habitat Management, as described in Section 2.04. The perimeter of all areas affected by surface facilities was clearly marked before initiating surface disturbance activities. The shaft pad surface area is approximately 11.1 acres in size with minimal cut and fills. The associated access road corridor is approximately 2,930 feet long, with a finished top width of 24 feet (road corridor 35 feet wide, 2.4 acres). See Exhibit 25U, 6-North Mains Ventilation Shaft - Geotechnical Pavement Design, for details on the road, and Map EX49A-M1, a new road profile and cross-section. Given an average topsoil depth of approximately 6 inches and a total road disturbance area of approximately 2.4 acres, approximately 1,940 cubic yards of topsoil were salvaged from the road corridor, and 8,954 cubic yards from the 11.1 acre pad area. Prior to initiating topsoil removal activities, stream and wetland buffer zones were marked with identifying signs to limit surface disturbance within these areas to the planned and approved activities. Topsoil from the road corridor was recovered and placed in a stockpile at the north end of the road corridor beyond the edge of the 35-foot road disturbance area. Topsoil from the pad area was placed in a stockpile within the shaft pad on the southwest edge of the pad and along the west edge of the access road, just south of the pad, for future reclamation use. Topsoil salvage volumes are indicated on Table 49A. Natural vegetative materials (mulch) incorporated into the topsoil, and seeding with the topsoil stockpile stabilization seed mixture identified on page 2.05-121 will stabilize the stockpiled topsoil.