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.

The U.S. Environmental Protection Agency on Tuesday 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.

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.