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Tom Till, Associated Press
Undated photo shows tailings, lower right, next to the Colorado River near Moab, that officials want moved instead of capped.

WASHINGTON — A giant pile of radioactive waste sitting near the banks of the Colorado River poses unacceptable risks and needs to be moved, California and Utah officials told a congressional briefing Tuesday.

The 12 million tons of tailings sit several miles northwest of Moab and 750 feet from the river that provides drinking water to 25 million people, most of them in California. The tailings are residue from a uranium mill that stopped operating in 1984 and was taken over by the Department of Energy in 2000.

"You can't consider our water supply safe if those are in our headwaters," said Dennis Underwood, vice president for Colorado River resources at the Metropolitan Water District of Southern California. "It's public health that's endangered here."

The Energy Department recently finished collecting comments on a draft environmental impact statement and will issue a recommendation this summer on whether to move the pile or try to contain it on-site.

Uranium, ammonia, sulfate and other contaminants have been found in groundwater around the site and are leaching gradually into the river. So far, drinking water from the river remains safe, but Western state officials fear that would change if a big flood washed huge quantities of the waste into the Colorado. They are convinced that the only acceptable solution is to move the pile.

"It's not a question of if there's going to be a catastrophic flood, it's a question of when it's going to happen," said Joette Langianese, a council member from Grand County, where the tailings site is located.

Underwood, Langianese and other officials spoke at a briefing convened by Rep. Jim Matheson, D-Utah.

They expressed concern that because the government estimates it would be cheaper to leave the pile in place — $160 million compared to $400 million to move it — the Department of Energy will recommend treating it on-site. On-site treatment would be ineffective if there were a big flood, they said.

"Cost may be trumping what's the right thing to do," Matheson said.

Western state officials were concerned when the Energy Department didn't select a preferred solution in its draft environmental impact statement. Instead, the department outlined several options, including capping the pile on-site or moving it to one of two sites to the north, Klondike Flats or Crescent Junction, both of which are on Bureau of Land Management land.

Energy Department spokesman Joe Davis said the department received thousands of comments on the draft environmental impact statement and would review those before issuing the final statement.