Colorado crews planning mitigation of second underground coal mine fire near Marshall Fire's origin
State mining safety crews are moving forward with plans to unearth a second active underground fire later this year in the area where the most destructive wildfire in Colorado history was ignited.
The Marshall Fire destroyed more than 1,000 homes on Dec. 30, 2021. It was pushed by 100 mph winds across open space and into the communities of Superior and Louisville. Two residents there were killed.
Authorities, after an 18-month investigation, determined there were two ignition points - the first a smoldering wood pile on private property, the second below power lines. The latter is a point of contention, with Xcel Energy disagreeing with investigators' conclusions. The company is fighting litigation blaming its lines for at least partially causing the blaze.
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The investigation did not rule out the possibility that coal burning below ground for decades contributed to the fire. Winds as strong as those experienced during the Marshall Fire could conceivably draw heat from the underground coal fires to the surface.
One such site contains the Lewis Mines that were abandoned and buried in 1946. A surface vent emitting heat measured at 120 degrees was discovered in 2018.
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Crews from Colorado's Division of Reclamation, Mining and Safety started an overhaul of the Lewis Mine site in January. Excavators carefully extracted land adjacent to the Davidson Ditch, alternately digging and filling 10-foot "fingers" of steaming ground to keep the concrete irrigation channel from collapsing.
"We had some fracturing on the surface that was showing elevated temperatures following the Marshall Fire," said Tara Tafi, senior project manager with the inactive Mine Reclamation Program of the Colorado Division of Reclamation, Mining and Safety. "At Lewis we were pulling materials out that were, you know, four or five hundred degrees, blending them, and within 10 or 15 minutes, they would be below 100 degrees."
Where readings were greater than 90 degrees, crews mixed the heated soil with cool soil and rock until temperatures fell below that mark.
"We're just removing coal. All of the coal within the areas where we see elevated temperatures," said Tafi.
They try to mix five to 10 times as much soil and rock with the coal.
"The mining method at the Lewis Mine was room and pillar, and so they excavate out large rooms out of coal, and then they leave pillars in place to support the mine and that pillar. There was a remaining pillar adjacent to the Davison Ditch that was smoldering," said Tafi.
The project wrapped up in early April ahead of schedule.
Crews are now planning to turn ground 2,000 feet away above the Marshall Mines, a DRMS spokesman confirmed. The department is currently in the permitting process with Boulder County since the project, slated to start later this summer or fall, will affect access to county open space at the Marshall Mesa trailhead.
"The goal is to excavate down to the floor of the mine, or just below the floor of the mine," said Tafi.
They also expect to work in areas to the east along Marshall Road. There were several mines that were part of the Marshall Mine, spread out through the area.
It will be the second time mitigation efforts have occurred at the Marshall Mines. A vent from the mines there was blamed for starting a small brush fire in 2005. Three years later, 275 tons of rock was dumped on the site, raising its surface 18 inches.
The recent Lewis Mines mitigation cost $316,002, according to the department's spokesman, Chris Arend. The Marshall mitigation will be done now that additional federal money has been received by the department to address coal mine fires throughout the state.
In a 2018 DRMS study, there are 1,736 known abandoned coal mines in Colorado. A contractor hired by the state to examine them found 38 were actively burning or were dormant and extinguished after previously burning.
"I would say the lion's share of the underground fires in Colorado. We're not really sure how they started," Tafi explained. But she went on to indicate many may have simply ignited via spontaneous combustion. "The oxidation of that coal creates heat. And it kind of just becomes a runaway reaction that then causes the temperatures to get high enough that the coal will spontaneously combust." In addition there may be other causes for the fires. Some of the miners smoked. Sometimes they started fires for warmth. There was coal dust ignition in some of the mines that were operated under far looser safety rules than current mines and sometimes there might have been a lightning strike or wildfire. But origins are hard to pin down.
There are no additional coal mine fires along the Front Range. Most are on the Western Slope. The closest to the Boulder County fires are in Fremont County.