Trapper Mine featured in national industry publication

Tri-State’s Craig Station in northwest Colorado relies on two sources of coal to fuel its three units:  Trapper Mine, which is adjacent to and was developed for the plant, and ColoWyo Mine, which provides the balance of the coal by way of railcar from a mine located in member co-op White River Electric’s service territory.

Trapper and its historic 2006 landslide, which was a catalyst for new equipment, processes and production at the mine, was the subject of a recent feature article in the industry publication “Coal Age.”  Following is an abridged version of the lengthy feature story.

Trapper Mine doubles production with a new fleet of equipment

Not long ago, Trapper Mine was almost entirely dependent on its three identical draglines for all of its overburden removal needs.  Following a massive landslide in October 2006, Trapper redeveloped its mining plans and is now producing more coal with a mixture of new mobile surface equipment and draglines than ever before in its long history. Tri-State is a part owner of the Trapper Mine, and 100 percent of its coal is shipped to the adjacent Craig Station.  Trapper is contractually committed to mining more than 2.3 million tons per year through 2020, which is why the mine has purchased and deployed a more flexible mobile surface mining fleet.  Craig Station stacks Trapper’s coal and blends it on site.  “We work closely with Tri-State and communicate what we’re doing as we learn what they need on a daily basis,” said Stephen Hinkemeyer, Trapper Mine’s production and engineering manager.

100 year slide

On the morning of October 8, 2006, following unprecedented amounts of rain, Trapper experienced what the Colorado Geologic Survey classified as the third largest landslide in Colorado history.  In seconds, roughly 225 to 250 acres of the mountain — more than 35 million cubic yards — suddenly slid about 400 feet, covering haul roads and exposing coal blocks and everything else in its path to an average depth of 100 feet.  Trapper had a couple of dozers, drills and a Cat 5130 in the pit.  As the ground stabilized, Trapper employees found one generator that had been tossed around, tipped over and was raised 80 feet into the air.  Miraculously, nobody was hurt.

Fear of future landslides led Trapper to partner with a geotechnical firm and redouble its surveying efforts to figure out why that specific area had failed.

Prior to the slide, Trapper’s remaining reserve base was approximately 14 million tons.  However, the slide covered 10 million tons of those reserves.  Under contract to make deliveries to the Craig Station, Trapper had little choice but to actually mine in the slide area.

Slide hastens truck-shovel move

With stripping ratios growing prior to the landslide, Trapper had already begun evaluating the transition to a mobile stripping fleet and had begun using truck-shovel pre-stripping operations ahead of the draglines.  To fund the purchase of the trucks, loaders and necessary equipment, Trapper developed a workable mine plan and negotiated an agreement with Tri-State and the mine’s other owners that significantly increased production under long term contracts.

The purchase of new surface mining equipment, including a Le Tourneau L-2350 front-end loader with a 53-cubic yard bucket and four Komatsu 830E haul trucks, allowed Trapper to get back 10 million tons of reserve covered in the slide area and more than double overall reserves, since there are areas with coal that’s too deep for draglines to access.

Today, Trapper mines down to the L seam with the mobile equipment.  The draglines follow behind, picking up the M, Q and R seams.  Shovel cuts dig down the hill at a 7,100-foot elevation in 30-foot drops.  Trapper takes the slide material first with mobile equipment, then moves the dragline down the hill behind after it removes the material.

Once on the main block of the landslide, Trapper’s geo-technical analysts determined that, because of the thickness of the seams, the mine should be able to recover more than 50 percent of the affected coal.  In practice, however, Trapper is actually recovering about 75 to 80 percent of that coal because as it slid, it moved almost in unison.

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