Marshall Mesa trailhead closing as crews begin excavation to cool smoldering coal seam
The highly trafficked trailhead, next to one of the Marshall fire's ignition points, could close as soon as Monday for up to a year as crews with the state Division of Reclamation, Mining and Safety perform mitigation work and the city makes trail improvements, officials announced Wednesday.
The coal seam below the Marshall Mesa trailhead, which contains many areas of smoldering coal, was once suspected of igniting Colorado's most destructive fire that ignited Dec. 30, 2021, and quickly spread, killing two people and burning more than 1,000 homes and businesses.
Investigators later pinned blame for the Marshall fire on a rekindled slash burn on private property, along with sparks from a nearby downed Xcel power line fanned by 100 mph winds. The power company disputes the finding and still points to the nearby coal fire as a possible cause.
Mitigation work will involve excavating the coal seam about 30 feet below the ground and blending cold soil and rock with any hot material, the state said. Materials must be cooled to below 80 degrees before being placed back into the ground and any unburned coal found in the area will also be blended with other materials to prevent future ignition "to the extent possible."
Excavation crews won't be allowed to work during windy conditions, and all handling of hot materials will be paused if National Weather Service forecasters issue a red flag warning, alerting for dangerous fire spread potential, the state said.
If the area sees sustained winds, or gusts exceed 15 mph, crews will suspend any work with hot coals and the coals will be covered with a minimum of 2 feet of cold soil and rock, the state said. At least 30,000 gallons of water will be required to be on-site while crews work, in the case of a fire.
After the mitigation below the ground is complete, the northern and southern parts of the site area will be graded to resemble the nearby natural topography and native plants, officials said. Then, a separate project with the city of Boulder will redevelop the central area into a new trailhead facility.
As mitigation work is underway, most trails in the area will remain open, city officials said. An interim trail will be installed for visitors traveling by bike and from the Colorado Department of Transportation parking lot at the intersection of Colorado 93 and Marshall Road.
Money for the project came from federal infrastructure funds, which also funded similar work at another long-burning coal seam nearby, Chris Arend, a spokesman for the state's Division of Natural Resources said. State crews dug a $1 million pit to snuff out the Lewis Coal Mine fire , northeast of Marshall and Cherryvale roads, a mile south of the city of Boulder.
