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EnergySolutions has asked the state to put its approval process on hold after regulators raised concerns about the firm's plan to permanently dispose of the nation's stockpile of depleted uranium at its Clive landfill.

On Monday, the Department of Environmental Quality (DEQ) released a safety evaluation, citing eight conditions that the nuclear-waste processor must meet before Utah will allow hundreds of thousands of drums of radioactive material to be shipped to and buried at the Tooele County site 80 miles west of Salt Lake City.

"Although we are confident we can address these unresolved questions, we believe the public comment period should only proceed once the questions are resolved," EnergySolutions executives said in a prepared statement. "The company's position has been and continues to be that science should determine whether DU [depleted uranium] can be safely disposed of at Clive. The company will not proceed until these questions are answered to the satisfaction of the appropriate regulatory bodies."

State scientists propose requiring the company to store the stuff underground and turn the site over to the federal government to manage and maintain it, among other restrictions.

Some of the conditions may be difficult if not impossible for EnergySolutions to meet, according to the proposal's chief critic, HEAL Utah.

"It's pretty clear when you read the review that EnergySolutions is stonewalling the state — and the public," said Matt Pacenza, HEAL's executive director. "We're confident it'll be an easy decision for Gov. Herbert to reject waste that grows increasingly hazardous for hundreds of thousands of years, given all these uncertainties."

Depleted uranium is a byproduct of the enrichment process required to produce fissionable material for nuclear bombs and fuel. The dense substance emits low-level radiation now, but it becomes hotter over time, peaking after 2 million years.

Right now, 750,000 tons of the waste are stockpiled in three locations in Kentucky, Ohio and South Carolina. The company proposes shipping up to half the waste to its Clive landfill over the next 30 years and covering the 1-ton barrels with concrete, clay and rocks.

EnergySolutions accepted 5,400 barrels of the waste from Savannah River, S.C., in 2006 before the state prohibited further shipments. Those 55-gallon drums are stored in a metal warehouse on site. The company also has buried 49,000 tons from past disposal contracts.

Thousands of years from now, the uranium will pose a far greater hazard, and DEQ officials want assurances that the federal Nuclear Regulatory Commission will not reclassify depleted uranium as Class B or C waste.

HEAL highlighted a section of the DEQ evaluation's executive summary: "The EnergySolutions [depleted uranium permit application] has not satisfied all of the department's concerns, and the topics are not resolved at this time."

Utah state law bars the disposal of any radioactive waste that is classified as anything more hazardous than low-level Class A waste.

State scientists also insist that EnergySolutions bury the depleted uranium below grade. The site once was under prehistoric Lake Bonneville, which geologists expect to return and recede over the next 100,000 years.

EnergySolutions' plan envisions digging an 80-acre cell 10 feet deep.

Barrels of the uranium and other wastes would be piled in the pit and capped in mounds towering 38 feet above grade.

Burying all the barrels below ground could be difficult because a shallow aquifer is just 20 to 25 feet under the cell.

A former chairman of the Radiation Control Board argued depleted uranium poses an "unacceptable" level of risk for Utah.

"Storing [depleted uranium] at Clive puts it in the path of a rising Great Salt Lake-Lake Bonneville system," said Steve Nelson, a geology professor and HEAL board member. "The lake rising to the proposed embankment elevation is not a matter of if but when. The piles will be obliterated by strong wave action, for which there is copious past evidence."

The public has until May 29 to submit comments to the Utah Division of Radiation Control.

Public hearings have been scheduled for May 6 in Tooele and May 7 in Salt Lake City.