The EPA has begun cleanup work at the Lukachukai Mining District Superfund Site on the Navajo Nation, where uranium mining left decades of contamination. The agency said crews will remove thousands of cubic yards of uranium-contaminated waste rock from the Mesa V complex and place it in a newly built engineered repository designed to prevent further erosion or groundwater contamination. The project is expected to take about a year to complete. Officials said the area is used for grazing and other activities by Navajo families, and the cleanup will help reduce risks from exposure to radioactive materials.