Colorado crews set to extinguish coal smoldering underground at Marshall Mesa Trailhead

The City of Boulder is taking action to extinguish smoldering underground coal that has been active under the Marshall Mesa trailhead for more than 100 years. They will be working with the Colorado Division of Reclamation Mining and Safety on the project, which will start next week.

The underground coal fires in the area -- the result of long-ago mining operations -- were considered as a possible cause of the destructive Marshall Fire in 2021, but it was later determined they were not the trigger. However, an investigation didn't rule out the possibility that they may have contributed to the wildfire's growth. This is the second recent coal fire mitigation project near the Marshall Fire's ignition point.

Next week the Marshall Mesa Trailhead will be closed and the beginning stages of the current project will get underway. After a few weeks, crews will begin to excavate all hot smoldering coal under the trailhead as well as any coal that could catch fire in the future. They will smother the smoldering coal and have a 30,000 gallon sistern of water on site for safety reasons.

The project is expected to take at least 4 months, and extensive precautions will be taken during windy days and wind events to make sure no fire spreads. On such days there's a possibility the wind could conceivably draw heat from the underground coal fires to the surface.

"Excavation of hot materials will not be allowed during windy conditions," the City of Boulder Open Space and Mountain Parks wrote in a news release. "All hot work operations will be halted in the event of a red flag warning being issued for the Marshall Mesa area. ... Additionally, if sustained on-site surface winds, or frequent gusts exceeding 15 mph are recorded on site, all hot work activities will be suspended. In the event that hot work activities are halted, any hot or smoldering coal will be immediately covered with a minimum of two feet of cold soil and rock."

While the trailhead will be closed during the project, trails in the area generally won't be blocked from usage by hikers, bikers and walkers.