"This is great news for Utah and the millions of people who rely on the Colorado River for their water supply," Gov. Jon Huntsman Jr. said.

Energy Secretary Samuel Bodman said in April that the department would ship the waste from the former Atlas mill site just outside Arches National Park by rail to Crescent Junction, about 30 miles north of Moab.

"This decision demonstrates our commitment to fulfilling our Cold War cleanup obligations as well as preserving the long-term environmental health of the river and the many communities it serves," said Jim Rispoli, assistant energy secretary, whose signature made formal the previously announced decision.

Contaminants from the tailings pile have seeped into the river, threatening endangered fish and alarming downstream water users. An estimated 25 million residents in Nevada, Arizona and California rely on the Colorado for water.

The Atlas pile spans about 130 acres on the 439-acre site. The thick sludge in the pile contains remnants of Cold War uranium production. Cleanup of the pile stalled when Atlas Minerals Corp., which bought the mill in 1962, filed for bankruptcy in 1998, leaving the pile with an interim cap and an inadequate cleanup fund.