Portions of the Navajo Nation are on geologic formations rich in radioactive uranium ores. Beginning in the 1940s, widespread mining and milling of uranium ore for national defense and energy purposes on Navajo tribal lands led to a legacy of abandoned uranium mines (AUMs). The A&B No. 3 AUM (Site) is one of approximately 520 AUMs located on the Navajo Nation. The Site is a reclaimed surface mine covering approximately 22.5 acres located on tribal trust land of the Navajo Indian Reservation. The mine was identified as being operational from 1954 to 1955. While operational, the mine had a total production volume of 586 tons.
During screening assessments, many small waste piles were observed throughout the Site with larger piles sloping towards the Little Colorado River. The gamma radiation measurements collected at the waste piles were found at maximum levels ranging from approximately 40,000 cpm to 640,000 cpm. In comparison, the average measured background gamma radiation activity for the area was 17,198 cpm. Over 50 residential structures are located within ½ mile south of the Site and the closest is within 300 feet of the Site boundary.
The Region IX Emergency Response Section initiated a time-critical removal action in August 2014 to install signage to warn of the nearby hazards and discourage trespass.
