The proposed development area is located in the Powder River Basin (PRB), a part of the Northern Great Plains that includes most of northeastern Wyoming and a smaller portion of southeastern Montana. The Absaloka Mine and the South Extension are located near the northwestern edge of the PRB, in an area consisting primarily of dissected rolling hills, plateaus, and ridges of moderate to low relief that formed in the near-flat lying sedimentary strata. Resistant sandstone and clinker beds cap most of the upland areas and form steep cliff escarpments and isolated knobs. Elevations range from about 3,500 to 3,790 feet above sea level, slopes range from nearly flat on the valley bottoms and ridge tops to around 40 and 50 percent on the flanks of the surrounding ridges and hilltops, and approximately 61 percent of the surface has a slope of 10 percent or less.

The three lowermost coal seams of the Tongue River Member of the Fort Union Formation are the Rosebud, McKay, and the Robinson. In the Absaloka Mine area, all younger, stratigraphically higher coal seams have been removed by erosion. In parts of the current mine area, the Rosebud and McKay seams are joined into a single seam referred to as the Rosebud-McKay, which averages 32 feet in thickness. Mining within the proposed development area would be limited to the Rosebud and McKay coal seams. Where not affected by erosion or oxidation, the Rosebud and McKay seams are relatively consistent in thickness throughout the proposed development area. The Rosebud coal seam thickness ranges up to 22.3 feet and averages 17.9 feet. The McKay coal seam thickness ranges up to 16.6 feet and averages 12.5 feet. All or parts of the Rosebud and McKay coal seams have been removed by erosion in the Middle Fork Sarpy Creek drainage bottom (Figure ES-3). Recent alluvial and/or colluvial deposits have replaced the coal in these areas. This feature effectively separates the proposed development area into western and eastern coal reserve blocks. A claystone parting, ranging from less than 1 foot to more than 30 feet and averaging 11.7 feet thick, separates the Rosebud and McKay seams throughout the proposed development area. Mining would remove an average of approximately 70 feet of overburden under the Proposed Action. The Robinson seam, which averages just over 20 feet in thickness, would not be mined in the proposed development area. The Robinson seam lies below and is separated from the McKay seam by approximately 80 to 100 feet of interburden. The Robinson seam was mined in the early years of the mine’s operation, but is no longer mined primarily due to customer concerns regarding poor combustion characteristics.

The Absaloka Mine is a 10,427 acre permitted, single-pit surface mine complex located near Hardin, Montana and the Crow Indian Reservation. The coal reserves are leased from the Crow Tribe of Indians. The Absaloka Mine was expressly developed to supply Powder River Basin coal to a group of Midwestern utilities, including Xcel Energy’s Sherburne County Station near Minneapolis, Minnesota. Over the years, it has also sold coal to several other upper Midwest utilities. Coal is shipped via a 38-mile rail spur to the main line of the Burlington Northern Santa Fe Railroad near Hysham, Montana.

The Absaloka Mine has the present capacity to produce up to 7.5 million tons of coal annually.

The first step of the mining process is soil salvage using rubber-tired scrapers. Soil is salvaged in two lifts: the first lift being the “A” horizon topsoil, and the second lift being the “B” horizon subsoil. During initial box cut development, soil is placed in temporary stockpiles for later use in final pit closure and reclamation. Once the pit has advanced far enough to establish room for regrading of dragline spoils, soil is hauled directly from salvage areas and redistributed on regraded areas.

After soil salvage operations are complete, blast holes are drilled down through the overburden to the top of the Rosebud coal seam. The drill holes are then loaded with explosives (ANFO) and detonated to fragment the overburden to facilitate dragline excavation.

Overburden removal is accomplished using a Bucyrus-Erie 2570W dragline with a 115-cubic yard bucket. High-overburden areas generally require prestripping to assist the dragline, using front-end loaders and off-highway haul trucks or scrapers. Exposed coal seams are cleaned with a dozer, drilled and blasted to facilitate efficient excavation, and then loaded using front-end loaders into off-highway haul trucks for transport to the coal crushing and storage facilities. As overburden is removed, it is directly placed into the previous empty pit where coal has been removed.

Replaced (backfilled) overburden is graded to approximate the original land surface contour, as required by MDEQ and OSM rules. Elevations consistent with the approved post-mining topography (PMT) plan are established as quickly as possible to construct a stable landscape and restore drainage. Backfilled and recontoured overburden is sampled and analyzed to verify suitability as subsoil. To date, acidic, toxic forming, or other unsuitable backfill materials have not been encountered at Absaloka Mine. Should unsuitable backfill materials be encountered, mitigation by additional soil depth, excavation and burial, or other special handling to remove them from the root zone would occur. Prior to soil redistribution, regraded backfill is scarified to relieve compaction. WRI’s monitoring and testing criteria currently used and that would continue to be used to determine suitability/unsuitability for backfill materials are discussed in detail in Chapter 3, Section 3.8 of this document.

Soil is typically redistributed on recontoured backfill using rubber-tired scrapers. Soil is replaced in two lifts with the “B” subsoil over the spoil and the “A” horizon topsoil at the surface. The surface is then tilled to establish a seedbed prior to seeding. Reclaimed areas are revegetated using native grasses, forbs, and shrubs that are consistent with the post-mining land use. As before mining, grazing land is the primary post-mining land use, with pastureland and some areas of cropland being replaced.

Mine facilities, including the railroad loop, coal handling/processing plant, coal storage areas, warehouse and shops, miscellaneous storage buildings, boiler plant, fresh water supply well and water treatment plant, and sedimentation pond (Dry Coulee Dam) are located in the northwest portion of the existing permit area in Section 26, T.1N., R.37E.

The facility operates a centralized coal processing and handling system including a truck dump, crushing, conveying, storage barn, and a train load out. An in-pit truck dump and crusher and an overland conveyor system are operated, as well as the necessary auxiliary equipment, including dragline, trucks, shovels, scrapers, drills, dozers, etc., as applicable.