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.