Characterization of ²³⁴U/²³⁸U Activity Ratios and Potential Inorganic Uranium Complexation Species in Unregulated Water Sources in the Southwest Region of the Navajo Reservation

Extensive uranium mining occurred from the mid- to late-1900s on Navajo tribal lands in Northern Arizona, an area rich in natural uranium. In this study, water samples from unregulated sources on the Navajo Reservation were analyzed to determine elemental uranium concentration, ²³⁴U/²³⁸U activity ratios, and existing inorganic anions. These data provide a more complete understanding of uranium source and the formation of potential uranium complexes. Results of the current studies suggest that some wells on the Navajo Nation have uranium concentrations near or above the U.S. Environmental Protection Agency guideline of 30μg/l. The ²³⁴U/²³⁸U activity ratios were similar for water wells located near mining sites with ratios of 1-1.5, and for those from the control, activity ratios were observed at 2.5-4.5. Two wells were observed to have high uranium and bicarbonate content suggesting the presence of uranyl carbonate species that may increase the solubility of uranium.