If the Moab uranium tailings pile stays where it is, eventually a big flood will wash it into the Colorado River.
"Not could. It will happen. It's just a matter of when," says one of the authors of a report on the subject, D. Kip Solomon, a University of Utah professor of geology and geophysics.
Even if no giant flood hits in the near future, radioactive and chemical contamination apparently has leached from it and migrated under the river. On the other side of the Colorado are a nature preserve and the city of Moab.
About 11.9 million tons of uranium tailings and contaminated soil were left near the Colorado River, three miles northwest of Moab, when Atlas Minerals Corp. stopped production in 1984. According to the U.S. Department of Energy, the wastes cover 130 acres and were placed in an unlined impoundment.
Atlas "placed an interim cover over the tailings pile in 1995," the DOE adds.
The department has been preparing an environmental impact statement about what to do with the tailings, which at the closest point reach to within about 1,000 feet of the river.
Gov. Jon Huntsman Jr. recently wrote to the DOE expressing his determination that the pile should be hauled away from the river as soon as possible.
"Recent flooding in the St. George and Santa Clara regions of Utah also demonstrated the swift and immense force of moving water in the desert," he wrote.
Huntsman's concerns are backed by studies, including one published in December 2003 by Solomon and Philip Gardner, a graduate student at the U.
DOE studies found ammonia and uranium in gravel below the Matheson Wetlands Preserve across the river, the researchers wrote.
"The magnitude of these concentrations and the location of the highest values suggest that groundwater from the mill tailings is flowing under the Colorado River and impacting groundwater" beneath the preserve, they added.
"We believe that there are fluids that have migrated underneath the river," Solomon said in a telephone interview.
Contrary to earlier expectations of the DOE, the river was not a barrier to the flow. A lot of contaminated fluids are discharging into the Colorado, he added. But some of it goes under the river to the Moab side.
Whether this occurs depends on the amount of water in the river and how much groundwater pumping is going on.
When the uranium mill was working, operators leached out material they needed by pouring fluids on the tailings. This caused material to leak out of the pile.
"They were pushing fluids beneath the river toward Moab," he said. Now that operations have ceased, whether the flow is still occurring "is a little uncertain."
The study uncovered "very, very permeable gravel deposits beneath the mill tailings, beneath the river and beneath the entire Matheson Wetlands Preserve," Solomon added.
The layer amounts to a hydrological "superhighway." It's a pathway along which groundwater can migrate under the river. If enough pumping takes place on the tailings side, water might flow toward it. If the reverse is true, water could flow from the tailings toward Moab.
The "very coarse gravels" show that the Colorado River has flooded in the past, bringing in gravel and boulders. "The river has migrated laterally over very large distances through geologic time," he said.
Above the gravel is about 15 feet of fine, silty material. The tailings are on top of the silt, approaching within 1,000 feet of the river in one place.
The tailings amount to "a house that's literally built on sands and silts," Solomon said. "They're not founded on any really competent material," meaning they could easily wash away.
At 24 and 30 feet below the surface, geologists uncovered organic material. A lab in Florida checked the age of the wood and peat through carbon dating.
Radiocarbon dates for samples from the two floods ranged between 1860 and 1980 for the most recent, and between 990 and 1090 AD for the earlier material. That is about when flood waters carried them in.
The samples were taken from a bore hole on the Moab side of the river. But the debris indicate the river's violence throughout the zone.
The report by Gardner and Solomon explains, "The radiocarbon ages of these two samples indicate that there have been two flood events in the last 1,000 years that have scoured down to 24 and 30 feet below present land surface, respectively, at a distance of more than 260 feet from the present river channel."
During January's flooding, the Santa Clara River in southwestern Utah rapidly ate away at its banks.
"The biggest meander was 700 feet," said Jan Sandberg, engineer for the city of St. George. "There was a lot of meandering in lots of areas."
"In the city of Santa Clara, it took a huge bite, took out a bunch of prime real estate," said Dean Cox, emergency services director for Washington County.
An erosion of 700 feet would not quite bring the Colorado River onto the Moab tailings. But the Santa Clara destruction happened with just one flood, and that river is far smaller than the Colorado.
If a big enough flood were to race through the Colorado, said Dianne Nielson, executive director of the Utah Department of Environmental Quality, "We're going to have uranium mill tailings strewn along the banks and sandbars along that river for distances downstream."
E-mail: [email protected]