Navajo Nation Uranium Assessments

Beginning in the 1940s, widespread mining and milling of uranium ore for national defense and energy purposes on Navajo tribal lands across Arizona, New Mexico and Utah led to a legacy of more than 500 abandoned uranium mines (AUMs) that threaten human, livestock and environmental health. The Skyline Mine, one of many AUMs that WSP addressed, was a high-priority site with gamma radiation activity measuring two times the naturally occurring level.

In the 1990s, portions of the Skyline AUM were closed by the Navajo Nation Abandoned Mine Land program, which focused on immediate physical hazards like sealing mine portals and consolidating and capping loose mine waste. However, inaccessible mine tailings were not removed because of onerous terrain, and the remaining elevated levels of gamma activity continued to affect area water sources.

 WSP conducted a site visit to delineate the extent of contamination and — using field observations input from EPA and Navajo Nation EPA and gamma radiation measurements — developed a time-critical Quality Assurance sampling plan for removal assessment activities. We conducted a three-phased sampling effort, modeled exposure scenarios and studied impacts resulting from removal scenarios.

The selected remedy called for removal and disposal of 25,000 cubic yards of radioactive mine waste in a repository. Because traditional repository design leads to the accumulation of contaminated leachate, which must be actively managed and is a risk for release to groundwater, WSP designed and oversaw the installation of an evapotranspirative repository that eliminated leachate generation.

The Skyline Mine was one of the first full mines cleaned up under the AUM program and served as an example for best practices in sampling and removal strategies. In the area surrounding the Skyline Mine, Navajo Nation residents have been able to return the land to economically important grazing activities.