Work underway to douse potential fires from former Colorado coal mines in Marshall south of Boulder
Heavy equipment is now at work at the Marshall Mesa Trailhead in Boulder County, digging and tossing and mixing and replacing. That is how a coal fire is doused.
"Certainly based on its location, proximity all the infrastructure. It's been a priority for us," said Jeff Graves, program director for Colorado's Inactive Mine Reclamation Program with the Division of Mining Reclamation and Safety.
Attention has been focused on the potential for underground fires in the area after the Marshall Fire gained its start nearby. An investigation determined that wildfire that claimed two lives and over 1,000 homes on the flare-up of a fire started on the property of the 12 Tribes religious sect six days before to burn tree branches. About an hour later, a second fire started south of the Marshall Mesa Trailhead, ignited by hot particles discharged from an Xcel Energy power line.
A Division of Mining Reclamation and Safety study in 2018 identified 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. Among them are the former mines in Marshall, near the area where the Marshall fire began.
Coal mines allow oxygen to be exposed to coal underground. That oxidizes the coal, leading to heat. Over time the heat builds. But the temperature of burning coal is well over 400 degrees.
Investigators found no reason to believe the smoldering coal beneath the surface in the old Marshall Mines caused the fire.
"That's certainly what our investigations have shown so far," said Graves. "I mean, things are very dynamic in a coal fire situation where collapses can occur in the mine workings, and suddenly you can get oxygen that might come into an area that was poorly combusting, and it could combust more. But, generally speaking, we did not identify any temperatures that would suggest combustion currently."
Multiple borings at the site have shown temperatures below 200 degrees.
Nonetheless, there remains potential. The state along with Boulder Open Space are working to smother and disperse the hot coal.
"It's definitely a big job. I mean, we're going to be excavating over 180,000 cubic yards of material, which is a pretty significant effort with respect to excavation and covering over 5 acres," said Graves.
The work is right in the area of the Marshall Mesa Trailhead, which has been re-routed. Most of the mining done in the area when it was called Langford was rather shallow.
"The coal is buried about 30 feet deep through those areas. Mining went down to that elevation, and so we've got to dig all the way down to that coal, coal seam, excavate it, cool it, and then put it back in the ground," said Graves.
There will be no work allowed during windy conditions. Winds over 15 miles an hour will lead to the suspension of work with hot materials.
The seam of coal runs northeast through the area, with some tunnels likely beneath areas to the east of the work in the open space. But over time shallow coal mining tunnels are known to collapse, says Graves.
"It does get a little bit deeper to the east. But we didn't note any areas of higher temperatures towards the east. So we're only excavating where we identified higher temperatures and where it's relatively shallow."
The coal runs all the way through Superior, Erie and up to Firestone. Graves says there is no indication of high heat in those areas.
"We don't think so. The coal does get deeper as you move out to the east, and you also encounter the water table, which prevents pretty much any of that coal from combusting. And so you've got a lot of flooded workings as you move farther to the east."
The state believes the work will take until January, weather permitting. Federal tax money set aside to treat inactive mines is helping defray the cost. After work is complete, Boulder Open Space & Mountain Parks will redevelop the central portion of the site in a new trailhead facility.
