SPOKANE, Wash. (AP) – The massive cleanup of a century's worth of mining pollution in Idaho's Silver Valley would cost $635 million and take up to 30 years under a final plan approved by the federal government on Tuesday.

The U.S. Environmental Protection Agency released the interim Record of Decision Amendment, which details its proposal to clean up arsenic, lead and other heavy metals pollutants in the valley, which is located 50 miles east of Spokane.

“This will bring real human health and environmental protections in the basin,” said Dan Opalski, director of EPA's Superfund office in Seattle. “This is an important milestone.”

The EPA has already received written concurrence from the state of Idaho and the Coeur d'Alene Tribe, the other main players in efforts to clean up the Upper Basin of the Coeur d'Alene River.

The agreement follows disputes over the scope of the cleanup work, which in a 2010 proposal called for spending $1.3 billion over a time frame of some 50 years.

Earlier this year, the EPA proposed sharp cuts in the costs and time of the work. The changes were partially the result of a huge outcry from Silver Valley residents and Idaho politicians. Opponents contend that much of the cleanup work is unnecessary, and federal restrictions and the stigma of a Superfund designation have stymied economic growth in the depressed region.

Most of the nearly 7,000 public comments received by EPA about the original cleanup plan, one of the largest in the nation, called for doing less work and getting the job done faster, the EPA has said.

The Coeur d'Alene River Basin is one of the nation's largest Superfund sites, with heavy metals poisoning land, streams, wildlife and humans. The wastes washed into waterways and moved downstream, some extending into the state of Washington.

A lawsuit calling for the cleanup was originally brought in 1991 by the Coeur d'Alene Indian Tribe against several mining companies. Agreements have since been reached with several mining companies that had historic operations in the valley, creating a trust fund of about $800 million to pay for the work.

Much cleanup work has already occurred around Kellogg, Idaho, where the pollution was making people sick. Before that work, the Silver Valley was so saturated with pollution that it stripped the hillsides of vegetation and poisoned the blood of children, causing physical and emotional problems that continue.

Opalski has said the original plan called for cleanup at 342 mine sites, but the revised plan would clean up some 200 sites. He cautioned that the cutbacks mean that when the work is done, the area might not qualify to have the Superfund designation removed.

Among the changes from the original plan, the EPA dropped a $300 million project to install a plastic liner along portions of the South Fork of the Coeur d'Alene River; active mine sites would be removed from the cleanup; numerous remote mine and mill sites that were found to contain little pollution or did not pose much public risk will be removed from cleanup.

The new cleanup plan has received letters of support from the state Of Washington, The Spokane Tribe, Bureau of Land Management, U.S. Fish & Wildlife Service and the U.S. Forest Service.