After floodwaters breached the property’s lowest elevations in May 2011, UMTRA crews raised and reinforced the first of three berms that protect the southern toe of the tailings pile.
They also recontoured an already-decontaminated area to the east, which allows for more gradual and less erosive flooding that builds up nutrients in the soil, according to a new U.S. Department of Energy (DOE) report.
“Because of the experiences of 2011, they’ve done a lot more to prepare for flooding,” Grand County UMTRA Liaison Lee Shenton said.
“The pile is well-defended,” he added. “The site is better contoured to defend against floodwaters … and now the berm has been improved to defend other parts of the site.”
While the river has been calm for the last two years, above-average runoff from the mountains of west-central Colorado could put those improvements to the test later this month.
The Colorado River Basin Forecast Center is projecting that river flows at the closest official gauging station near Cisco will crest at about 35,000 cubic feet per second (cfs) by late May. In comparison, peak flows reached 48,600 cfs during the 2011 floods, and the river typically peaked at about 27,500 cfs over a 30-year average, according to Shenton.
Based on the forecast center’s recent projections, Moab UMTRA Project Director Don Metzler isn’t expecting a repeat of the last major flood event.
“I don’t think it’s going to be nearly as high as (it was) in 2011,” Metzler said last month.
But the DOE and its contractors are still taking precautions in the event that the river spills over its banks.
A newly revised flood mitigation plan for the site outlines the steps that contractors should take each time the river flows above specific trigger points, which range from 15,000 cfs to 35,000 cfs and beyond.
At each of those trigger points, for instance, contractors will visually inspect each berm and make any repairs, if needed.
“We’re going to be as prepared as we can be,” Metzler said.
The DOE recently updated its project website at: www.gjem.energy.gov/moab/ to outline the steps it’s taking, and Shenton said that Metzler and his team will keep the community up to date in the event of any flooding.
“If the waters do flow over the banks, they will keep the public aware of what’s happening,” he said. “They are ready and willing to give updates.”
Although the Colorado River loses much of its erosive power when it enters the valley and widens out, occasional floods are not unheard of, since 160 acres on the 480-acre site lie within the 100-year floodplain.
The river has surged past 40,000 cfs in 12 of the last 50 years, and waters from the normally dry Moab Wash also flow east of the protected tailings pile after major storm events, according to the DOE’s flood plan.
During the most recent flood in 2011, rising waters breached a berm along the riverbank on May 30, and they continued to rise over the next eight days. On June 8, 2011, low-velocity floodwaters spilled over the lower tailings pile berm into an area where concentrations of radium-226 exceed federal standards, according to a DOE flood response summary.
After the floodwaters receded, surveyors found elevated levels of radioactivity in the top six inches of soil within a 240-foot by 20-foot area near the lower tailings pile berm.
The site has long since been cleaned up, and a follow-up survey found that it was free of any contamination, according to the DOE’s flood response summary.
Another low spot to the south of the tailings pile remained under water until late-August 2011; it has since been filled in with an estimated 30,000 cubic yards of free soil from the Lion’s Park Transit Hub.
“To get that with no charge was just a huge benefit to the project,” Metzler said.
All in all, Shenton believes the work that has been done in the last three years will effectively keep 2011-level floodwaters away from the three tailings pile berms.
“Even at close to 50,000 cubic feet per second, it should still be good,” he said.
For more information about the project’s flood mitigation plan, go to: www.gjem.energy.gov/moab/documents/FloodMitigationPlan_Rev3.pdf.