BOULDER COUNTY, Colo. — A large project is underway at the Marshall Mesa Trailhead in Boulder County, where crews are working to extinguish an underground coal mine fire that has been burning for more than 100 years.
The Colorado Division of Reclamation, Mining, and Safety (DRMS) is leading the charge on the Marshall Mine Fire Mitigation Project.
The Marshall Mine Fire, as well as the nearby Lewis Mine Fire, both garnered attention after the December 2021 Marshall Fire in Boulder County, which killed two people and destroyed 1,000 homes and businesses.
In the wake of the blaze, investigators looked at the Marshall Mine Fire as a possible starting point of the Marshall Fire. As of 2019, it was one of 38 coal mine fires in Colorado that were inspected in 2017 and 2018, and had a history of igniting at least one brush fire, which happened in December 2005 and was quickly contained and underwent a fire abatement project, according to a DRMS 2018 report.
However, officials determined that the two underground mine fires did not appear to be connected with the Marshall Fire origin. The Boulder County Sheriff's Office instead said in June 2023 that the massive blaze was likely caused by a downed Xcel Energy power line and embers from an earlier fire on private property, and was not related to any underground mines. Xcel Energy has denied these claims.
Still, worry grew in the wake of the Marshall Fire about the risk of future ground fires and so plans were put in place to mitigate both the Lewis Mine Fire and Marshall Mine Fire.
An inspection found that the Lewis Mine Fire site had an increase in surface fracturing and cracking, and increased venting, which led to a concern for future fire risk above ground. The Marshall Mine Fire on the other hand did not show signs of this, so the Lewis site was given priority.
State crews began a mitigation project at the Lewis Mine Fire, located on the northeast corner of the Marshall Road and Cherryvale Road intersection, in January 2024. It had been a small production mine that operated from 1914 until 1946. Crews finished this project ahead of schedule in April.
Learn more about the Lewis Mine Fire in our February 2024 report below.
After the completion of the Lewis Mine Fire project, DRMS announced in June that it was looking to tackle the Marshall Mine Fire Mitigation Project next. Equipment mobilization started about two weeks ago, said Jeff Graves, program director for DRMS' Inactive Mine Reclamation Program.
"We're in full-scale construction mode at this point," he said Wednesday.
The Marshall Mine Fire, which has burned for at least 100 years, is located on the southeast corner of the Highway 93 and Marshall Road intersection, not far from the Lewis Mine Fire site. DRMS has monitored it since the start of the Inactive Mine Reclamation Program around 1980, Graves said.
Currently, a coal seam under the Marshall Mesa Trailhead has areas of hot, smoldering coal that crews will work to excavate to about 30 feet under the surface, Boulder County's website describes. It has reached temperatures as high as 325 degrees.
Graves said this is a relatively shallow coal fire, which is part of why DRMS decided to mitigate it now. Its easy access — meaning DRMS can potentially completely extinguish the fire — paired with its proximity to important infrastructure put it high on the priority list.
The mitigation project, which spans about 12 acres near the trailhead, is expected to last four months and is already a few weeks in. Over the next few months, crews will blend the hot coal with cold soil and rock to cool it below 80 degrees, and then they will place it back in the ground. In addition, any unburned coal will be excavated and blended to reduce the potential for future ignition, according to Boulder County.
"The goal is to keep everything below that 80-degree temperature for the long term," Graves said.
Hear more details on this project from Jeff Graves in our extended interview clip below.
Excavation work will pause on windy days. And all operations will stop on Red Flag Warning days, when weather conditions lead to an increased risk for fire dangers. As a precaution, the project contractor will keep a minimum of 30,000 gallons of water on site — strictly for fire suppression — during any work involving the hot coal.
Graves said an influx of funding through the Infrastructure Investment and Jobs Act allowed DRMS to prioritize projects at many of Colorado's coal fires.
"And not just take a Band-Aid approach of monitoring and maintenance, but do full-scale mitigation and extinguishment. So that's really what raised this project to the surface — it's why we're starting on this project now," he said, adding that DRMS also listened to concerns from the community after the Marshall Fire and took that into account. "So, we're really trying to be proactive in our approach to address these fires where we have lots of infrastructure and community concern."
As a result of this work, the Marshall Mesa Trailhead is closed.
Once it is complete, crews will work to make the area resemble the natural topography, complete with native plants, and Boulder Open Space and Mountain Parks will then develop part of the site as a new trailhead. This secondary part of the project is expected to take about eight months, but will include better vehicle and shuttle access, improved parking, an accessible trail, restroom replacement, new signage, and more.
"The goal is to make it look like it did before, if not better," Graves said.
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Did DRMS do any mitigation work at the Marshall Mine Fire before this?
Graves explained that a few different projects were already completed at this site.
DRMS worked with Boulder Open Space and Mountain Parks to clear vegetation from existing vents, reducing the potential for it to catch fire. They have also plugged some vents, which sometimes simply entailed shoveling dirt into the holes.
How many mine fires are in Colorado, and should we be concerned about them?
Colorado has about 40 mine fires, Graves said on Wednesday, having just learned about two on the western slope. They are in various levels of burning, he explained. For example, the Marshall Mines Fire was smoldering and was not actively burning.
"We have a pretty full portfolio of fires that we monitor throughout the state and are developing mitigation plans for as we expend this (Infrastructure Investment and Jobs Act) money and try to extinguish as many of these fires as possible," he said. "It's certainly a pretty big concern for us. I know in those local communities where those fires are burning, it's also an additional concern. So there's always that potential for wildfire ignition associated with a lot of these sites, so it's definitely a priority for us to work on them."
DRMS will likely start another project in the fall of 2025 at the Wise Hill underground coal mine fire near Craig. That one will require excavating down to 100 feet or so, which is likely the deepest DRMS can go.
Only a few of these mines fires are accessible via excavation, so DRMS is investigating other mitigation strategies.
"Moving forward, since we've got increased funding for another 10 to 12 years, that gives us a pretty good window to attack many of our higher-priority sites and at least come up with a mitigation strategy and try to implement it within that time frame," Graves said.
Will the Marshall Mine Fire Mitigation Project impact local trails?
Boulder County said most trails around this area will stay open. Boulder Mountainbike Alliance volunteers helped to build an interim trail so visitors can still access the trail system. However, this trail is closed Nov. 19-22 while Xcel Energy completes work in the area.
Below is a map of this interim trail.
The Marshall Mesa Trailhead will remain closed for one year.
Visitors can still access the full Dirty Bismark loop.
