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Aug. 14—The state plans to start mitigation work this fall on the underground coal mine fire at the Lewis site, located northeast of the intersection of Marshall and Cherryvale roads in Boulder County.
While monitoring the site, the Colorado Division of Reclamation, Mining and Safety recently observed increased activity from the smoldering coal seam fire, which has burned for more than 50 years, according to a news release.
"The Colorado Division of Reclamation, Mining and Safety Lewis Coal Mine Fire Mitigation Project is a proactive effort to reduce the potential for surface ignition as a result of the increased underground coal mine fire activity. Additionally, the work will help protect the water supply ditch on site," Jeff Graves, the director of the state's Inactive Mine Reclamation Program, wrote in the news release.
Increased activity that was observed includes more surface subsidence, surface fracturing and cracking; higher surface temperatures; increased venting and gas emissions; and stressed vegetation.
The state also observed conditions that are damaging to the Davidson Ditch, increasing the chance of flooding. The Lewis Mine site is partially located underneath the ditch, which is a large supplier of water in the area.
Another factor playing a role in prioritizing the site, Graves said, is that a couple of nearby residents who lost their homes in the Marshall Fire are rebuilding and will have structures in close proximity. He added that it's a relatively shallow mine, so fire activity can get to the surface quickly.
To complete the work before the ditch fills with water in the spring, mitigation must begin this fall. To allow that to happen, Boulder County is set to issue an emergency declaration Tuesday to acknowledge the potential dangers of the site.
"It's an important project," Boulder County Community Planning and Permitting Director Dale Case said. "We want to take care of it before it causes more damage. We can hopefully completely get it mitigated and help reduce the risk in that section of the county."
The county and the Reclamation, Mining & Safety division also are hosting an online information session from 5:30 to 6:30 p.m. Aug. 28 to answer resident questions. The online session will be hosted in English. A recording of the meeting, along with a Spanish transcript, will be available on YouTube.
To attend the online session, register at tinyurl.com/8kud2rrd.
The mitigation work, which is expected to start in mid-October, requires excavating an acre to an acre-and-a-half of land. The actual size of the area will depend on what's found once the digging starts, Graves said.
"It tends to be pretty dynamic," he said.
The plan is to excavate about 30 feet to just below the coal mine workings and remove any burning or smoldering coal, according to the news release. The coal then will be blended thoroughly with rock or soil.
The temperature of the blended material will be monitored until it's lower than 100 degrees. While the material is exposed, the state will monitor the piles and, if needed, take measures to keep the surrounding area safe. Those include dousing the piles with water and covering them with cold rock or soil, if needed, on high wind days.
"We recognize that having any hot material on top can create a potential problem," Graves said.
Finally, the extinguished material will be returned and graded to match adjacent natural contours and revegetated with native vegetation. The heavy equipment that's needed will be stored on site.
The Lewis Mine site is located in unincorporated Boulder County about one mile south of Boulder, underneath two private properties. The property owners are supportive of the state's mitigation project, according to the news release.
The project is expected to cost close to $1 million and will be paid for with federal money from an infrastructure bill approved in 2021, Graves said. More than $11 billion from the bill went into the federal government's Abandoned Mine Reclamation Fund, according to Colorado Public Radio, and is adding up to $10 million annually over the next 15 years for Colorado coal mine restoration.
Recent testing and ongoing monitoring indicated lesser fire activity at the nearby Marshall coal mine fire, which is located near and under Boulder open space, according to the news release. Following the devastating Marshall Fire in late 2021, the city of Boulder — which owns most of the property involved — asked the state to further examine the Marshall coal mine fire.
Mitigation work on the Marshall coal mine fire is tentatively scheduled for next year, while the state continues to monitor the site, according to the news release.
An investigation didn't find evidence that the Marshall coal seam was one the ignition sites in the Marshall Fire, but it could not be completely ruled out.
Graves said the Marshall and Lewis sites are the only two coal seam fires the state is monitoring in Boulder County.
