The disposal cell is excavated in phases. Two phases have been completed, each occupying about 45 acres. A portion of the third phase was excavated last spring and excavation of a second portion of this phase was completed this spring. Excavation depth is about 25 feet below the ground surface.
Tailings are end-dumped from the containers, loaded into dump trucks, and driven to the disposal area where they spread for compaction using a dozer. A sheep’s foot roller compacts them in place in the cell. Through the end of August 2017, about 8,783,800 tons of mill tailings and other contaminated materials have been disposed in the cell.
The cover on the disposal cell consists of multiple layers of soil and rock as illustrated in the diagram below. Interim cover is placed on portions of the cell once the final grade for tailings material has been met. Final cover layers have been installed over portions of the interim cover.
The rock for the biointrusion layer and the uppermost layer is being quarried to meet U.S. Nuclear Regulatory Commission specifications for durability, and is being hauled from Fremont Junction, Utah. All other cover layers come from material excavated on-site at Crescent Junction.
Diagram of cover layers for Crescent Junction disposal cell