(KPAX) The new tribal owner of Montana’s largest coal mine, the Spring Creek Mine, shut down the mine Thursday, saying it hasn’t reached agreement with the state over the terms of mine regulation.

Navajo Transitional Energy Co. (NTEC), which is controlled by the Navajo Indian Nation, said Montana regulators are demanding the company and tribe agree to a “full and complete waiver” of sovereign immunity from state laws.

“We simply cannot consent to a full waiver of the rights preserved in our treaties,” said Tim McLaughlin, the chairman of NTEC. “To do so would put the foundations of Indian Country at great risk.”

But state environmental officials said Thursday they’ve been trying to negotiate the language of a waiver, so that Montana can be assured it can enforce its environmental and mining laws.

“Unfortunately, it wasn’t until just this week, just days before (NTEC) closed on Cloud Peak’s holding that we started in earnest to talk about negotiating the language of the waiver,” said Rebecca Harbage, public policy director for the Department of Environmental Quality. “Our hope is that we can move forward as quickly as possible to ensure that operations can continue with the mine.”

Harbage said NTEC and DEQ officials, including the agency’s director, have been conducting talks this week in Helena.

NTEC completed its acquisition of Cloud Peak Energy on Wednesday, buying out the bankrupt company’s coal mines in Wyoming and Montana.

The Spring Creek Mine, which is just east of the Crow Indian Reservation in southeast Montana, is the largest coal mine in the state, producing nearly 13 million tons of coal in 2017 – about 35 percent of all coal mined in Montana that year.

NTEC announced Thursday via press release that it had shut down the mine Thursday, because it couldn’t reach an agreement with Montana over sovereign immunity for a tribal entity.

Harbage said NTEC notified the state just two weeks ago that it would be taking over the mine.

State regulators believe that without some sort of partial or limited waiver of that immunity, DEQ cannot enforce state mining and environmental laws for Spring Creek, she said.

The state followed up last week, but talks didn’t really begin until this week, just days before the acquisition closed on Wednesday, she said.

“We’re negotiating with NTEC this week to try to determine exactly what the language of some sort of partial waiver would look like, in order to ensure that continued operation of the mine could happen and could happen in a way that meet our environmental laws,” Harbage said.

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