The U.S. Forest Service has consented to two federal coal lease expansions that would let Arch Coal mine beneath about 1,700 acres in the Sunset Roadless Area in the upper North Fork Valley.

The decision, released Monday, opens the door for the Bureau of Land Management to decide whether to modify the leases. The BLM also is evaluating whether to permit exploration on the leases if they are issued. The exploration would involve drilling into underground coal reserves to determine if mineable quantities exist.

Long-term, the lease authorizations could mean Arch Coal would build roads and drill wells to vent potentially explosive methane it would encounter in the underground expansion of its West Elk Mine near Somerset.

Scott Armentrout, supervisor of the Grand Mesa, Uncompahgre and Gunnison national forests, signed the record of decision on the leases.

The expansion has support from entities including Delta County because of the importance of coal jobs to the North Fork economy. But some conservation groups object to it for reasons including opposition to coal as a source of power production, impacts on roadless forest, and concern about the amount of methane vented during the mining. Methane is a potent greenhouse gas and West Elk is the largest single industrial source of methane emissions in Colorado.

"It's just disappointing to see the continual push forward of something that we know we really need to keep in the ground," said Allison Melton, an attorney with the Center for Biological Diversity. "I feel like the evidence is pretty clear on the record if we want our forests to be protected and we want our communities to move to future economies, that time is right now. I would really hope to see that kind of leadership from the Forest Service and from our government and it's just disappointing to not see it time and time again."

Asked about a possible court challenge of the decision, Melton said that normally the BLM review would allow for an administrative appeal process, but it's her understanding that agencies "are looking to steamroll this through as quickly as possible" and such a process may not be available. She said her group is hearing Arch Coal could move in bulldozers as soon as Friday if it gets BLM approval, so her group might end up seeking a court injunction to try to keep that work from going forward.

BLM spokesman Steven Hall said Monday his agency hasn't yet made a decision on the lease modifications, and he didn't know when that decision would be made.

"It could be in the next few hours, it could be in the next few weeks," he said.

As for the possibility of bulldozing occurring within days if the modifications are approved, he said he thinks that is up to the Forest Service. Kim Phillips, a spokesperson for the Grand Mesa, Uncompahgre and Gunnison forests, said the Forest Service isn't aware of any such plans.

Arch Coal spokesperson Logan Bonacorsi said in an email that the company appreciates the Forest Service's "diligent efforts in providing its consent" and looks forward to receiving BLM's approval for the lease modifications in a timely manner.

"Appropriate consents from the BLM are necessary to ultimately develop these underground reserves in a way that sustains jobs in the North Fork Valley, optimizes the value of an important public resource, and protects the safety of our employees as well as the natural environment," she said.

She didn't specifically respond to questions about how soon work in the lease areas could start if BLM approval is obtained.

Arch Coal's efforts to obtain the leases have ended up in court before. In 2014 a federal judge vacated the lease authorizations and the underlying North Fork Valley coal mining exemption to Colorado's national forest roadless rule because they lacked adequate environmental analysis. The Forest Service since has conducted additional analysis and reinstated the Colorado rule, and the agency has done more analysis on the leases based on the court order. Armentrout wrote in his decision that he has considered the order and resulting further analysis "with particular attention to greenhouse gas emissions, social cost of carbon (emissions), socioeconomics, and recreation. The additional analysis and clarifications did not compel me to make a decision dissimilar to my predecessor."

He also said that considering the 100-year history "and importance to custom and culture of coal mining in the North Fork area," the scope and scale of the Forest Service decision are quite small and within precedent.

Melton believes the Forest Service has failed to adequately address flaring as a viable means of addressing methane's climate impacts. Burning methane by flaring sharply reduces those impacts. A study conducted by Raven Ridge Resources of Grand Junction concluded it would be safe and economically feasible to flare gas from West Elk's methane venting wells and sell the carbon capture credits.

Armentrout wrote in his decision that it doesn't preclude the future inclusion of methane mitigation measures including flaring.