Geohydrology and water chemistry of abandoned uranium mines and radiochemistry of spoil-material leachate, Monument Valley and Cameron areas, Arizona and Utah

Uranium mines in the Monument Valley area were established predominately in channel-fill deposits within the Shinarump Member of the Chinle Formation. The Shinarump Member yields ground water to wells and may yield water to the Moonlight and Radium Hill mines. In the study area near Cameron, uranium was mined from channel-fill deposits within the Petrified Forest Member of the Chinle Formation. Units of the Petrified Forest Member do not yield ground water to wells in the area, but fractures in the lower part of the Petrified Forest Member are probable pathways for upward flow of water from the Shinarump Member. Most of the mines receive water from surface inflow of rainfall runoff, but ground water also may be transmitted to open pits and drill holes in the subsurface through fractures or along faults in the Petrified Forest Member. Uranium-238 activities in shallow ground water from mines ranged from 150 to 14,000 picocuries per liter. Radionuclide activities in well and spring water were less than in shallow ground water near mines; however, in some samples, radionuclide activities in wells and springs were greater than activities in pit water. Uranium concentrations in leachate samples ranged from 20 to 7,700 micrograms per liter. Batch tests were done with material that was 2.00 millimeters and smaller. The radiochemistry of leachate from coarser material was not determined, and the specific rate and magnitude of radionuclide leaching depends on site-specific conditions that include the amounts of oxygen and organic material present, temperature, spoil mineralogy, and local ground-water composition.