SANDPOINT - The Montana Supreme Court is yanking a permit the proposed Rock Creek Mine needs in order to discharge treated wastewater into the Clark Fork River.

The state's high court has concluded that the Montana Department of Environmental Quality did not conduct an independent examination of the pollution discharge. The court also held that the department acted arbitrarily and capriciously when it issued a discharge permit without scrutinizing all the consequences of boring a mining tunnel that cannot be plugged once the copper- and silver-extraction project is played out.

The court's conclusions were contained in a 25-page ruling issued on Thursday. The Supreme Court is remanding the case back to the lower court so Montana DEQ can address the issues.

How the department intends to proceed was not clear on Friday.

"We're still trying to figure out what the impact is going to be on us," said Montana DEQ spokeswoman Lisa Peterson.

Revett Minerals proposes driving a horizontal mining shaft, or adit, three miles beneath the Cabinet Mountains Wilderness in northwestern Montana in order to extract ore. Water from the mine would be treated before being pumped into the Clark Fork, which flows into Idaho's Lake Pend Oreille.

The discharged water is expected to contain arsenic, ammonia, nitrates and heavy metals. The discharge could be permanent, although Montana DEQ asserts that the pollution would be insignificant due to the treatment, according to court documents.

The life of the mine is projected to be 37 years. Once the mine closes, the adit would either be plugged or wastewater coming from the mine would have to be treated until it stops coming out of the mountain or meets water quality standards.

But the Supreme Court found that Montana DEQ failed to take a hard look at what will be required to protect water quality in the Clark Fork if the discharge is lasting or even permanent.

"A simple statement that a perpetual discharge of polluted water will always be treated is insufficient to justify a determination that an irreversible discharge is nonsignificant," Justice John Warren wrote in the opinion.

The prospect of a permanent discharge has raised concerns that taxpayers will be paying for the treatment after Revett closes the mine.

Five environmental groups, including the Sandpoint-based Rock Creek Alliance, sued in 2002 to overturn the discharge permit. The coalition argued Montana DEQ issued the permit based upon the assumption that the discharge would not be permanent, court records indicate.

The groups called on DEQ to conduct a non-degradation review to examine the duration of the discharge. But DEQ said such a review was not warranted because the treated effluent would meet water quality standards prior to reaching the river.

Jim Costello of the Rock Creek Alliance believes the court is essentially advising DEQ to undertake the non-degradation review.

"I don't think the court is leaving them with very many other options besides doing a 'non-deg' review," Costello said.

Such a review would require an examination of the social and economic impacts of the discharge, which is expected to reach 3 million gallons a day. The contamination of Lake Pend Oreille would also factor into the analysis, Costello said.

"That would be a can of worms that I don't think Revett Minerals or Montana DEQ wants to open," he said.

Carson Rife, Revett's vice president of operations, was out of the office Friday and could not be reached on his cell phone.