The U.S. Supreme Court on Monday ruled 6-3 that a unit of Coeur d'Alene Mines Corp. (CDE) received a valid permit from the U.S. Army Corps of Engineers to deposit mining waste in an Alaska lake.

Justice Anthony Kennedy, writing for the majority, said the Army Corps. of Engineers has the authority to issue the permit over the Environmental Protection Agency.

"We conclude that the Corps was the appropriate agency to issue the permit and that the permit is lawful," Kennedy wrote.

The case came to the Supreme Court to clarify a division of power between the EPA and Army Corps of Engineers in making certain decisions regarding the Clean Water Act.

Central to the case was the question of whether the Army Corps properly issued a permit allowing a mining company to release waste by-products into an Alaskan lake. The Ninth Circuit Court of Appeals invalidated the permit in May 2007, citing sections of the Clean Water Act in which the Environmental Protection Agency broadly prohibits the release of newer pollutants.

Coeur Alaska, Inc. applied for a permit at Kensington Gold Mine, located about 45 miles north of Juneau, Alaska. The permit, issued by the Army Corps of Engineers in 2005, would allow the company to release around 4.5 million tons of mine tailings, a by-product of the gold ore milling process, into nearby Lower Slate Lake over a period of 10 to 15 years.

The Southeast Alaska Conservation Council, the Sierra Club and Lynn Canal Conservation sued the Corps and the Forest Service on the grounds that the permit violated sections of the Clean Water Act. Though one section of the act grants the Corps the authority to issue permits for the discharge of "fill material" - a substance that raises a body of water's elevation when added - another sets stricter guidelines, encouraging "where practicable, a standard permitting no discharge of pollutants."

In an associated case, the plaintiffs also sued the state of Alaska.

The cases are Coeur Alaska Inc. v. Southeast Alaska Conservation Council, 07-984, and Alaska v. Southeast Alaska Conservation Council, 07-990. Justices John Paul Stevens, David Souter and Ruth Bader Ginbsurg dissented.

-By Kristina Peterson and Mark Anderson, Dow Jones Newswires; 202 862-6619; mark.anderson@dowjones.com