The U.S. Department of the Interior on Monday announced it intends to cancel a controversial oil and gas drilling lease in the Badger-Two Medicine area east of Glacier National Park.

In a legal filing, the department stated that the Bureau of Land Management, which issued the lease to Louisiana-based oil company Solenex in 1982, had illegally failed to conduct a complete study of the environmental impacts of the proposed drilling as required by the National Environmental Policy Act.

The filing applies only to the 6,200-acre lease held by Solenex, not to the other 17 leases that remain. The agency originally issued 47 leases in the area but most have been retired or withdrawn.

However, the announcement represents a major win for the Blackfeet Tribe, which has for decades fought against the leases.

The more than 165,000-acre Badger-Two Medicine Area is central to the Blackfeet religion and is the site of the creation story of the four Blackfoot tribes in the United States and Canada.

“We’ve had 33 years of sitting on the edge,” said John Murray, a historic preservation officer for the Blackfeet Tribe. “I think there’s going to be some celebration right now.”

But he noted that the announcement does not represent a complete victory. Solenex has 10 days to respond and then a federal judge will rule on the issue.

An official cancellation of the lease could come as early as Dec. 11.

The Department of the Interior officially suspended drilling activities on the land in 1993, and that suspension was continued indefinitely in 1998.

Solenex owner Sidney Longwell filed suit against the department in 2013, alleging that its decision had been unreasonably delayed and that the federal government had failed to live up to the terms of its contact.

On Oct. 6, a federal judge ordered the department to accelerate its review of the lease and criticized it for the delay.

In its response to that order, the Interior Department found that the Bureau of Land Management and the U.S. Forest Service approved the lease in violation of the Environmental Policy Act, which requires environmental review for actions that produce a substantial impact to the environment.

“Rather than undertaking a full environmental analysis before issuing the leases, the agencies attempted to defer their analysis of impacts until after the leases had been issued and an irretrievable and irreversible commitment of resources had taken place,” the filing reads.

Monday’s announcement came just weeks after Department of Agriculture Secretary Tom Vilsack wrote to department secretary Sally Jewell, urging her to cancel the lease.

The department also contends that the agencies issued the lease in violation of the National Historic Preservation Act.

The Bureau of Land Management neglected to “fully consider the effects of oil and gas development on cultural resources, including religious values and activities, within the Badger-Two Medicine area prior to lease issuance,” reads the response.

The federal Advisory Council on Historic Preservation in September concluded that no amount of mitigation for the proposed oil and gas drilling could offset the potential damage to the cultural and historic values to the tribe.

Bureau of Land Management spokesman Al Nash said in an emailed statement that “after a careful review of the record and completion of consultation with the U.S. Forest Service, Advisory Council on Historic Preservation, Blackfeet Tribe, leaseholder and others, the Bureau of Land Management has concluded that cancellation is warranted.”

While Murray acknowledged that the tribe’s fight is still far from over, he was optimistic that the decision could ultimately lead to the cancellation of the other remaining drilling leases in the Badger-Two Medicine.

“All the leases are illegal,” he said. “They were all issued identically.”

Reporter Sam Wilson can be reached at 758-4407 or by email at swilson@dailyinterlake.com.