Environmental groups sued the U.S. Department of the Interior this week to prevent Arch Coal from expanding its mine in western Colorado, saying the government failed to consider added methane emissions and climate change consequences.

The planned expansion would allow nearly 18 million more tons of coal to be removed from the mine.

The lawsuit, filed by WildEarth Guardians, the Center for Biological Diversity and three other groups, accuses the federal government of violating the National Environmental Policy Act when it approved the West Elk Coal Mine expansion in March.

The environmentalists say the mine is already Colorado’s biggest industrial source of methane. It covers more than 20 square miles of the Gunnison National Forest east of the town of Paonia.

“The West Elk mine is one of Colorado’s worst climate disasters,” said Matt Reed, public lands director at High Country Conservation Advocates in Gunnison County. “Given the climate crisis, it’s imperative to confront this destructive, dirty mine and the wasteful practice of venting methane.”

The underground mine would be expanded by 1,700 acres, mostly on federal land. The project calls for eight miles of new roads and 43 methane drainage wells.

Arch Coal’s website says the West Elk Coal Mine produced 4.9 million tons of sales for the company in 2017.

The Interior Department previously has tried to limit industrial expansion in the same area.

“Arch is now poised to expand its coal mining operations into the Sunset roadless area, building miles of roads and dozens of drainage well pads across this relatively undisturbed landscape at significant environmental cost,” says the lawsuit filed in U.S. District Court in Denver.

It asks for an injunction to block Arch Coal from beginning construction, which is scheduled to start within days.

Methane is one of the most potent greenhouse gases for its tendency to trap heat from the sun. Climatologists report that its level in the atmosphere has been rising to dangerous levels in recent years.

Methane drainage wells, which release the pressure and fire hazard created by methane produced during coal mining, can contribute to emissions of the gas into the atmosphere, according to environmentalists. They recommend wider use of flaring, which refers to controlled burning of gas.

However, some critics of flaring say it creates other health and environmental hazards.

WildEarth Guardians acknowledges Interior Department agencies reviewed the environmental impact of the West Elk Coal Mine expansion but overlooked important drawbacks.

The government failed to consider how much expanded West Elk coal mining would add to a Trump administration policy of “energy dominance,” the group says. The policy calls for the United States to free itself from dependence on foreign energy sources, despite concerns from critics that more U.S. oil, gas and coal production could create environmental problems. 

The West Elk Coal Mine expansion would produce 17.8 million tons of carbon dioxide, or about one-third of Colorado’s output of the greenhouse gas, according to the lawsuit.

The added emissions add to overall pollution increases under the energy dominance policy, which is supposed to be forbidden by the National Environmental Policy Act, the plaintiffs argue. 

Their lawsuit says, “The federal government has either proposed or authorized a number of similar federal coal leasing and mining projects that cumulatively impact the environment, particularly in terms of climate.”

Other environmental impacts overlooked by the government include construction of new roads in an area that was supposed to be preserved as wildland, the plaintiffs say. Each methane drainage well requires bulldozing an acre of land, the lawsuit says.

“With this latest lawsuit and motion for a restraining order, we’re taking a stand for our public lands and climate, as well as defending Colorado’s clean energy future,” WildEarth Guardians said in a statement.

Neither Arch Coal or the Interior Department has commented publicly on the lawsuit.

The planned West Elk Coal Mine expansion comes only weeks after Arch Coal announced another big business move. The company plans to combine its mining operations in Colorado and Wyoming with St. Louis-based Peabody Energy, one of the world’s largest coal producers.

The lawsuit is WildEarth Guardians et al. v. Bernhardt et al., case number 1:19-cv-01920, in the U.S. District Court for the District of Colorado.