The U.S. Environmental Protection Agency has made a veiled threat to take Canada to the International Joint Commission in a dispute over plans to expand coal production in the Elk River Valley of southeastern B.C., near the Montana border.

The threat was made in a letter that outlines concerns about the potential for pollution running down B.C.’s Elk and Fording rivers into two bodies of water shared by B.C. and Montana — Lake Koocanusa and the Kootenay (Kootenai) River.

The letter was sent to Canadian Environment Minister Peter Kent in December by EPA Administrator Lisa Jackson.

She told Kent she hopes the federal and B.C. governments will support a study of the cumulative effects of existing and planned coal mine expansion in the area, mostly by Teck Resources Ltd.

“A cooperative bilateral approach on potential mine development in the Elk River Valley could obviate the need for a joint reference to the International Joint Commission,” wrote Jackson, who resigned last month.

The U.S. government is under pressure from Montana’s senators, who wrote to the U.S. Secretary of State in September complaining about the threat to the “treasured” Kootenai-Koocanusa watersheds.

Senators Max Baucus and Jon Tester argued mine expansion may be a violation of the 1909 Boundary Waters Treaty.

The treaty established the International Joint Commission to settle cross-border disputes involving pollution of rivers and lakes. It is made up of three Americans appointed by the president and three by Canada’s federal cabinet.

The letters from the EPA and the senators complained Canadian authorities are examining coal projects on a piecemeal basis and are not considering overall impacts, including the “significant and continuing” increase in selenium leaching from waste rock into rivers and lakes.

Selenium is a “naturally occurring substance that is toxic at high concentrations,” according to the EPA.

“B.C. is evaluating each coal mine expansion individually, with no legal requirement to conduct a programmatic environmental review to delineate the cumulative water quality and aquatic life impacts from contaminant loading from all of the mines,” the senators wrote.

“Drainage from the Elk Valley mines present serious risks to the Kootenai Basin water quality and valued trout fisheries. It is imperative that international scrutiny be applied to the mines’ downstream impacts.”

A spokesman for Environment Minister Peter Kent said there hasn’t been a formal referral to the International Joint Commission.

“The government of Canada is committed to working with the Province of British Columbia on addressing issues of concern to the U.S. in the Elk Valley,” the spokesman, Rob Taylor, said in a statement.

He said environmental officials from the EPA and the state of Montana are participating in the B.C. government’s review of Teck’s Line Creek mine expansion proposal.

There will also be American participation in a planned federal review of Centermount Coal Ltd.’s proposal to construct the Bingay mine about 21 kilometres north of Elkford.

The EPA has raised concerns about both the Bingay and Line Creek mines.

The EPA said in a statement that it is pleased a federal review has been ordered for the Bingay proposal.

Teck spokesman Chris Stannell said his company has submitted regulatory applications for two mines, Line Creek and Fording River, in order to “extend the life of the existing mines and maintain jobs at those operations.”

He said the applications do, in fact, consider the cumulative impact of all the Teck mines on the health of the watershed, and the company is proposing “significant investments” in water treatment facilities and water diversions.

“We are confident our existing and future development can be conducted in a way that balances environmental priorities, while also supporting jobs and economic growth in B.C.”

The expansion of coal production in the area has drawn interest from environmental groups who say the mines threaten water quality and aquatic life in an important international watershed.

The coal is exported to Asian steelmakers.

“We’re especially concerned about the proposed Bingay coal mine that would be located next to the Elk River, smack in the middle of a globally significant wildlife corridor that connects the Flathead River Valley to Banff National Park,” said Sarah Cox, acting executive director of Sierra Club B.C. “Three years ago, the World Heritage Committee recommended a moratorium on new mining in that corridor.”

She said there are several coal exploration projects underway in the area.

The EPA wrote to the B.C. Environmental Assessment Office in December expressing concerns about B.C.’s assessment of the Line Creek expansion, stating “we do not agree” with B.C.’s conclusion that the impact of selenium on water quality would be “negligible.” It also expressed concern about the affect of selenium on bull trout, a threatened species in the U.S.

B.C. Environment Minister Terry Lake was not available for an interview, but said in an emailed statement that the B.C. government understands the need to consider the issue of selenium “very seriously.” It said an update of B.C.’s guidelines for selenium in water has been proposed and is out for “external review.” And it said Teck is developing a valley-wide selenium management plan.

But the EPA letter complained Teck considered but dismissed additional mitigation measures - such as speeding up construction of a water treatment plant - due to “costs, operational complexities and … limited environmental benefits.”

“These additional mitigation measures have potential to further reduce the extent of water quality impairment and adverse aquatic life effects, and reduce selenium loads to Lake Koocanusa,” wrote the EPA’s Montana director, Julie DalSoglio, noting high selenium concentrations found in waters not only near the mine but in Montana’s Lake Koocanusa.

“Consequently, we are concerned about the dismissal by Teck of these measures.”