The Trapper Mine is located in the Yampa coal field that is composed of coal-bearing rocks that are Upper Cretaceous in age. The coal-bearing rocks mainly outcrop south of the Yampa River in northwest Colorado. The Yampa coal field extends east to west about 50 miles (80.5 km) and is about 40 miles (64.4 km) north to south.

The surface bedrock in the Trapper Mine Project Area is mainly the Upper Cretaceous Williams Fork Formation, which is part of the Mesaverde Group, a regional unit that contains a large coal resource in northwest Colorado (Brownfield and Johnson 2008). The Williams Fork Formation consists of interbedded sandstones, siltstones, shale, and coals and crops out along a six-mile-wide (9.7-km) belt that extends along the entire length of the Williams Fork Mountains (Tweto 1976). The Williams Fork Formation is underlain by the Illes Formation, also part of the Mesaverde Group. The Illes Formation is lithologically similar to the Williams Fork Formation consisting of sandstones, mudstones, carbonaceous shale, and coal (Brownfield and Johnson 2008). The Lewis Shale, which is stratigraphically higher than the Mesaverde Group, outcrops in the northern extremity of the SMCRA permit area. The Lewis Shale also is Upper Cretaceous in age and is composed of uniform dark-gray marine shale, but also contains thin sandstones (Johnson 1987; Tweto 1976). Surficial deposits consist of alluvium, residuum derived from the Williams Fork Formation and the Lewis Shale, and landslide deposits (Madole 1989). Quaternary alluvial deposits composed of sand, silt, clay, and gravel are present in the stream drainages in the permit area and surrounding areas, but alluvium is thickest in the Yampa River and Williams Fork River valleys (CDRMS 2013). Residuum is composed of sand, silt, clay, gravel, and boulders derived from the underlying bedrock.

The landslide deposits that are part of the surficial deposits are either rotational slides or earthflows and involve the Williams Fork Formation (Madole 1989). A major landslide occurred at the mine in October 2006 (CDRMS 2013). Prior to the slide, there was heavy precipitation that facilitated the movement of an estimated 35 million cubic yards of material with original in-place dimensions of 250 acres and 100 feet (30.5 meters) deep (Buchsbaum 2011). The material was largely contained in an active pit, but the slide made it necessary for the mine to alter its mine plan.

Structurally, the mine is bounded on the west, north, and northeast by three major folds. From west to east, the Williams Fork Anticline, Big Bottom Syncline, and Breeze Mountain or Buck Peak Anticline (Brownfield and Johnson 2008). At the mine, the beds of the Williams Fork Formation dip generally to the north at an altitude of 14 to 16 degrees. The Project Area lies on the south flank of the Sand Wash Basin, a structural basin which is the southeast extension of the Greater Green River Basin (Horn and Richardson 1959; TMI 1981 et seq.).

A large unnamed down-to-the-north normal fault lies about two miles (3.2 km) south of the SMCRA permit area in T9N, R90W (Brownfield and Johnson 2008; Tweto 1976). The fault as mapped by Tweto (1976) is about four miles (6.4 km) long and is not classified as active. No active faults have been identified in the area (USGS and Colorado Geological Survey 2006). There is a low probability of strong ground motion if a maximum credible earthquake were to occur in the vicinity. Horizontal ground motions are expected to be 18 to 20 percent of the acceleration gravity with a 2 percent probability of exceedance in 50 years (Petersen et al. 2015).

The upper Williams Fork member contains the coals that are mined at the Trapper Mine and are designated (from lowest to highest): R, Q, M, L, K, I, and H. The coal seams that are mined at the Trapper Mine have consisted of a mixture of subbituminous A, B, and C, and high-volatile bituminous C coals. Average, as-received, values of ash yield are 7.05 percent and sulfur content is 0.40 percent, with a heat value of 9,931 British thermal units per pound (Johnson et al. 2000).

Coal mined at the Trapper Mine is delivered by truck to the Craig Station at an average rate of approximately 2.3 mtpy (with a maximum rate of 2.6 mtpy). The coal is mined from seven coal seams of the Upper Williams Fork Formation: the “H,” “I,” “K,” “L,” “M,” “Q,” and “R” seams. Within the Project Area, the “R” seam is too deep for surface mining. Draglines were the primary earthmoving equipment used until October 8, 2006, when a 250-acre landslide occurred within the Project Area. Following the landslide, mining has been accomplished by a combination of dragline, dozer, and truck and loader operations, depending on the depth and material being mined.

The overburden, or rock that lies above the coal seams to be mined, is drilled and blasted to break up the rock to allow it to be moved using the mining equipment. Blasting is performed using an ammonium nitrate and fuel oil (ANFO) mixture. After overburden blasting is completed, the overburden removal begins. For the Project Area, overburden removal would occur primarily using trucks and loaders. The maximum coal depth for the Project Area would involve the initial use of trucks and loaders because the draglines cannot economically remove materials deeper than 200 feet. The overburden ranges in depth from 100 to 150 feet.

Following removal of overburden by the trucks and loaders, dozers scrape the remaining thin layer of overburden material to expose the uppermost coal seam. Coal is either ripped with a dozer or drilled and blasted for removal using similar blasting material (ANFO) as is used for overburden. Depending on the depth of the uppermost coal seam within the pit, the uppermost coal seam is mined using draglines or front-end loaders. The coal is loaded into haul trucks for transfer to the Craig Station.

After the uppermost coal seam is removed, interburden, or the non-coal rock material located between multiple coal seams to be mined, is removed using trucks, loaders and dozers, or using draglines and dozers, depending on the depth. Dozers prepare the lower coal seams for mining by clearing the thin layer of interburden above the lower coal seams. The coal is then loaded into haul trucks by loaders and dozers or the draglines and dozers. The draglines typically work one pass down and one pass up each cut removing the deeper interburden and coal. At the Craig Station, coal is end dumped into the primary crushing system or is stockpiled in the immediate vicinity of the crusher. Coal that is stockpiled is placed in the crusher at a later date using front end loaders operated by TMI employees. Once the coal is dumped into the crushing system, it transfers ownership to the Craig Station. Coal Combustion Residuals (CCRs) are utility wastes generated during the burning of coal and include fly ash, bottom ash, and scrubber sludge. CCRs not recycled for use in cement products, wallboard, and road base are hauled back to the Trapper Mine for placement as pit backfill in permitted areas. Approximately 55 percent of the total CCRs produced at Craig Station, an estimated 501,000 tons annually, are placed at the Trapper Mine. CCRs are placed in areas located within the SMCRA permit boundary but outside of the Project Area.

Overburden and interburden, collectively known as spoil, removed to access the coal seams in an active mine pit are used as backfill in the adjacent mine pit to begin the reclamation process. The dragline casts the spoil into the adjacent cut to backfill the pit. Dozers also are used to backfill spoil into the adjacent cut, while loaders and haul trucks are used to move material into backfill areas farther behind the active mining operation.

Backfilling is completed contemporaneously at the Trapper Mine with backfilling beginning in the pit as soon as safely possible after the mining equipment has completed coal removal and moved to an adjacent pit. After the pit has been backfilled and mining has progressed away from the mined-out pit, the backfill material is rough graded, using dozers, graders, or draglines, in preparation for reclamation.

In most cases rough grading of the backfill begins within 30 days of placement, with a maximum of one pile of overburden and interburden material (referred to as a spoil pile) behind the active working area of the pit. The power to the dragline is typically supplied to the machine from the spoil pile side of the pit with power cables positioned on the ground behind the draglines. The rough grading of the piles is completed quickly to allow for ease of movement of the power cables supplying the dragline. Rough grading also reduces the potential for ponding of surface water on the steeply dipping slopes and promotes runoff to avoid the potential for water to promote landslides or inhibit operations.

The Coal would continue to be mined in the L Pit within the Project Area from July 1,2015, to approximately the year 2025 and in the portion of the N Pit located partially within the Project Area beginning in approximately the year 2023 (Figure 2-2).

The L Pit is where current mining operations are occurring. Coal is currently and would continue to be removed using a combination of loaders and trucks. Highwall mining also could be used in the endwalls or highwalls of the L Pit if further geologic and geotechnical studies demonstrate feasibility, and the timing of the stripping operations allows access (TMI 1981 et seq.).

TMI also proposes to mine the N Pit located partially within the Project Area over the life of the mine. Mining in the N Pit within the Project Area would not begin until near the end of the life-of-mine plan estimated to be in 2023, although mining of private coal within the N Pit outside of the Project Area could begin earlier. Mining previously has occurred in the N Pit area and some of that previous disturbance has been reclaimed. However, mining only recovered the coal seams closer to the surface; the “H” and “I” seams. The Proposed Action would initiate re-mining in this area to recover the coal from the deeper coal seams in the N Pit, specifically the “L,” “M,” and “Q” seams.

The N Pit area has steep grades, weak formations, wet ground, historical spoils, and a high stripping ratio. Due to these conditions it is possible that highwall mining could be the preferred mining method in some areas. However, all or portions of the N Pit also would be mined using the standard combination of dragline, dozer, and truck and loader equipment.