In 1983, the U.S. Department of Energy (DOE) and the Navajo Nation entered an agreement for surface cleanup of the Shiprock mill site. At the start of the cleanup project, radioactive materials at the site included uranium and vanadium mill tailings; radium, thorium, and uranium residues mixed with soil, a tailings pond area, several buildings and construction debris. In the cleanup, all radioactive materials at the former mill site were consolidated into one pile. Contaminated materials from 15 vicinity properties (residences, commercial buildings, and open land areas) were also placed in the pile. The pile was then stabilized in place as the permanent disposal cell structure.

About 2.8 million cubic yards of residual radioactive materials (RRM) from the Shiprock abandoned uranium mine site and the vicinity properties were entombed in the 77-acre on-site disposal cell. The cell’s cover is a three-layer, engineered structure 8.5 feet thick. A radon barrier placed directly on top of the contaminated material consists of a compacted sandy soil layer that is just less than six and a half feet thick on the top slopes, and seven feet thick on the side slopes of the encapsulated RRM. The barrier is covered by a six inch thick layer of granular rock designed to promote rapid runoff of precipitation and to prevent percolation through the cell. A system of rock-lined drainage ditches collects surface-water runoff and diverts it away from the completed cell structure.

The disposal cell is situated on a river terrace that slopes down to the flood plain of the San Juan River. There was no authorization to begin clean up of the contaminated ground water until 2003.

A plume of contaminated groundwater contains about 1.2 million cubic yards of cadmium, nitrate, radium, selenium, uranium, and net gross alpha. It extends beyond the former mill site boundaries and covers an irregularly shaped area more than one and a half miles long by about three quarters of a mile wide at its broadest dimensions.

Active remediation consists of pumping contaminated ground water from two extraction wells in the most contaminated part of the floodplain aquifer next to the San Juan River. This contaminated water is piped to a pond on the terrace and evaporated. Another 20 wells monitor contamination levels, to identify shifts in the migrating contamination. This water, along with water collected from at least four extraction wells in the sump area of the terrace, and water channeled from French drains (gravel trenches that direct groundwater) installed at “Many Devils Wash” and “Bob Lee Wash” is also piped to the evaporation pond on the terrace.

The U.S. DOE is responsible for long-term stewardship of the former Shiprock mill site, including all groundwater monitoring.