A sheep’s foot roller compacts the tailings in the disposal cell.
MILL TAILINGS REMOVAL
Sixteen million tons of uranium mill tailings 80 feet high stood on the banks of the Colorado River near Moab in southeast Utah, as a legacy to the former ore-processing site that operated for nearly three decades beginning in the mid-1950s. That is until April 2009, when the U.S. Department of Energy began moving the tailings by rail to an engineered disposal cell constructed 30 miles north near Crescent Junction, Utah. The mill tailings, a clayey sand-like material that remains after the uranium ore is processed, lie in a 130-acre pile on the 400-acre Moab site, which is located about a mile from the entrance to Arches National Park.
Under the DOE Moab Uranium Mill Tailings Remedial Action (UMTRA) Project, the tailings are being excavated and conditioned by mixing the drier sands with wetter slimes, then disked to achieve the optimal moisture content for compaction in the disposal cell. Loaders then place the tailings in metal containers that are radiologically surveyed and released before trucks haul them to the rail load out area that is located across a state highway and almost 160 feet above the tailings pile. Two gantry cranes load the containers onto the train which runs twice a day to the disposal site.
At the Crescent Junction site, reach stackers remove the containers from the train and place them on haul trucks for transport to the disposal cell. The container contents are dumped through an end gate and the tailings are placed in the cell using a sheep’s foot roller outfitted with a computer-aided global positioning system to monitor compaction. As of July 10, 2010, about 1.8 million tons of mill tailings had been transported to the disposal cell.
Tailings are excavated and conditioned on top of the pile.
GROUND WATER CLEANUP
When the uranium-ore processing site at Moab was in operation from 1956 to 1984, the tailings were slurried to an unlined impoundment that accumulated over time, forming a pile. Much of the excess water in the tailings pile drained into underlying soils, contaminating the ground water beneath the site. In addition to removing the mill tailings pile and other contaminated materials, the Moab Project scope includes remediation of the contaminated ground water. DOE installed an interim ground water remedial action system in stages beginning in 2003 to reduce contaminants from discharging to the Colorado River.
The interim action system lies between the base of the tailings pile and the river to remove contaminant mass and to protect the habitat areas along the riverbank from exposure to ammonia. To date, more than 155 million gallons of contaminated ground water has been extracted through the interim action system, including 640,000 pounds of ammonia and 2,800 pounds of uranium.
Gantry cranes at the Moab site rail load out place and remove containers from the train.
RECOVERY ACT BOOST
The Moab Project received about $108 million in American Recovery and Reinvestment Act (ARRA) funds. The project is using most of this money to accelerate the tailings removal. In April 2009, the project began shipping one train a day, 4 days a week. With ARRA money, the train shipments increased to 10 a week and, later, additional railcars extended the train lengths. The contractors hired more than 200 employees with ARRA funds to support a second work shift and to prepare maximum trainloads for shipment.
The Moab Project has accomplished many other ARRA-funded activities including construction of an underpass of a state highway to eliminate hundreds of potential daily interactions between project vehicles and public traffic. Construction of a container wash facility that became operational in April has substantially reduced the number of surveys for radioactivity that are required to ensure no contamination remains on the exterior of the containers before shipment. The installation of 11 extraction wells enhances remediation of ground water by focusing on contaminant mass removal closer to the tailings pile. Paving access and haul roads, rail load out areas at both sites, and the Moab site Support Area reduces wear on vehicles and minimizes road maintenance costs over the life of the project.
ARRA has funded the purchase of additional equipment, including a second American-made gantry crane for the Moab site to facilitate increasing the efficiency in loading and unloading containers from the railcars and to allow operations to continue if one crane is down for maintenance or repairs.
“Our focus now is on safe, sustained shipping,” said Moab Federal Project Director Donald Metzler. “We are looking forward to hitting the milestone of 2 million tons remove before mid-August.”
Tailings are end-dumped from the containers into the disposal cell.
For more information, visit Moab Project website at http://www.gjem.energy.gov/moab