BOULDER COUNTY, Colo. — Colorado will soon begin mitigation work on a coal mine fire burning underground near Superior.
The Lewis Cole Mine fire has been burning for more than 50 years, the county said. It's underneath two private properties northeast of the intersection of Marshall Road and Cherryvale Road, about a mile south of Boulder.
Boulder County said the Colorado Division of Reclamation, Mining & Safety has been monitoring the site and recently observed increased activity from the fire.
The county said the division has observed increased surface subsidence, surface fracturing and cracking, higher surface temperatures, increased venting and gas emissions, and stressed vegetation. They've also observed conditions that are damaging to an adjacent water supply ditch, which could increase the chance of flooding.
The county said the mitigation will involve digging about 30 feet below ground to just below the coal mine workings and removing any burning or smoldering coal. The coal will then be blended thoroughly with rock or soil. The temperature of the blended material will then be monitored until it's less than 100 degrees Fahrenheit.
The extinguished material will then be put back, graded to match the land's natural contours and replanted with native vegetation, the county said. The state will begin the project soon and hopes to have it completed by spring, the county said.
“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, director of the division's Inactive Mine Reclamation Program, said in a news release.
The county said they will issue an emergency declaration Tuesday to acknowledge the potential dangers of the site and enable the project to be completed this fall and winter.
The county said testing and monitoring show less fire activity at the nearby Marshall coal mine fire, which is located under City of Boulder open space. They said mitigation work there is tentatively scheduled for next year.
RELATED: State investigates extent of the Marshall Mesa Coal Fire smoldering underground in Boulder County
The fires are burning in the area where the Marshall Fire, Colorado's most destructive wildfire, started on Dec. 30, 2021.
The Marshall Fire started with a dormant blaze burning on a religious group’s property and was fed by a second fire believed to have been sparked by Xcel Energy equipment, according to a report released in June by the Boulder County Sheriff's Office and District Attorney's Office.
The investigation into the Marshall Fire's cause did not find that the underground fire played a significant role in its eruption. However, Boulder County Sheriff Curtis Johnson said the coal fire's involvement cannot be completely ruled out as a source of the second fire, which started near the Marshall Mesa Trailhead.
RELATED: Marshall Fire cause: Fire on religious group's land, Xcel power line both to blame, officials say
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