This Idaho gold mine just had air permit withheld by environmental review board. Here’s why

A state environmental board on Thursday withheld an air quality permit issued for a proposed gold and antimony mine near McCall.

The Idaho Board of Environmental Quality, a seven-member advisory body at the Department of Environmental Quality, issued a decision that the agency had not followed the law when it analyzed the health effects that arsenic pollution related to the mine could have on people nearby.

Perpetua Resources, an Idaho company, has proposed to mine for gold and antimony, a critical mineral used in batteries, at a mountainous location in west-central Idaho, which the company says is the largest known deposit of antimony in the U.S.

Gold mining began in the area at the tail end of the 19th century and degraded the nearby environment, but the company said it would clean that up as part of its operations.

Complaints about the large-scale mining operation’s air quality permit were brought by the Nez Perce Tribe, as well as the Idaho Conservation League and Save the South Fork Salmon, two environmental groups. After DEQ issued an initial permit in 2022, the opponents filed an administrative appeal, which made its way to the Board of Environmental Quality.

Though the board upheld DEQ’s decision on four matters related to the permit, members unanimously had doubts over the agency’s calculations about increased arsenic levels from the mine’s operations. The board remanded the permit back to an administrative hearing officer at DEQ to be addressed, according to the order.

“It’s validating to know that others agree with us on our concerns,” Will Tiedemann, a regulatory conservation associate at the Idaho Conservation League, told the Idaho Statesman by phone.

Arsenic, which is carcinogenic, is a regulated pollutant that DEQ analyzed as part of its review of the Stibnite project’s environmental impact. Mine operations such as ore blasting and heavy use of dirt roads can stir the heavy metal into the air, which could injure hikers, hunters and other people who are nearby.

DEQ conducted modeling of the amount of arsenic that would potentially be released by the mine, which is evaluated using a complex formula that examines the daily added risk of cancer over a person’s lifetime, or roughly 70 years. The agency calculated that even with mitigation measures in place, the mine was likely to exceed the allowable cancer risk.

DEQ then calculated that because the mine is expected to operate for 16 years, the cancer risks could be diminished to acceptable levels because the impacts would not continue for a 70-year period.

The agency’s advisory board disagreed.

“Nowhere in the air rules does it provide that a project that will operate more than 5 years but less than 70 years may be adjusted in proportion to the amount of time it will operate,” the board wrote.

The board added that it “cannot find sufficient evidence in the record to support the proposition that a higher exposure to arsenic for a shorter period of time is equally or more protective than a lower annual lifetime average exposure.”

The board’s chairman, Mark Bowen, told the Statesman by phone that DEQ had not provided sufficient evidence to back up its approach, which led the board to remand the permit. He said he expects the agency will need to provide more justification for its decision or turn to a different approach to reduce the risks from arsenic.

Bowen said the permit will need to be approved before any construction can begin.

At a public meeting earlier this month, the board’s vice chair, Randy MacMillan, said DEQ’s calculations would have created “a new, higher level of cancer risk for 16 years,” according to Boise State Public Radio.

“By applying the, what I would call short-sighted, project-specific adjustment factor to the Stibnite Gold project … DEQ created a misleading risk analysis that greatly underestimates the actual cancer risk,” he said.

A spokesperson for the agency could not immediately be reached for comment Friday.

Tiedemann said he expects the proceedings over the permit could take several months.

Perpetua Resources is awaiting several other permits related to its mine, which it aims to begin construction of next year.

“We hope this sets an important precedent to the way those permits will be examined,” Tiedemann said.

A spokesperson for Perpetua, Marty Boughton, said in an email that the dust control issue has been “thoroughly studied.”

The permit “underwent three years of rigorous review, three extended public comment periods, numerous proposal improvements, and thousands of pages of technical review,” Boughton said. “IDEQ’s permit imposes incredibly robust air quality compliance controls on the Stibnite Gold Project.”

“Creating a project that is protective of human health and the environment has always been at the heart of Perpetua’s mission and vision for the Stibnite Gold Project, and we’ll continue working with IDEQ to respond to this narrow additional review,” she added.

The same two environmental groups involved in the air quality permit appeal also recently sued the U.S. Forest Service over its approval of an exploratory project near the mine site they believe would cause ecological damage to the area.

Boughton said that endeavor is a “soil sampling project” that is expected to take less than six weeks and would “temporarily disturb less than one acre of land, after which all investigation sites areas will be restored.”

She said the project was appropriately approved and is of “minimal size and scope.”

A spokesperson for the Forest Service could not immediately be reached for comment.

Reporter Kevin Fixler contributed.