Water Resources Professional Project Reports

Document Type

Technical Report

Publication Date



The U.S. Environmental Protection Agency (EPA) has conducted risk assessments to quantify uranium exposure at inactive mining areas on the Navajo Nation. These evaluations include drinking water from domestic and agricultural sources dating back to the late 1990s because public water services were not entirely available in the mining districts at the time. This research reviews the radionuclide concentrations in the water samples determined by the EPA in 2000 to identify potential sources of water contamination. The inconsistencies of the radionuclide concentrations relative to their natural activities were initially observed. The concentrations of 234U and 210Pb tend to be higher than their parent nuclide in majority of the samples. The radionuclide distributions in the samples were compared using a non-parametric statistic test, the Mann-Whitney test. For instance, the results of the analysis for the distribution of 234U concentrations did not reflect the concentrations of 238U in water samples, and their behavior cannot be explained by the natural decay of 238U series (separated by decay of 234Th and 234Pa). Also, the water samples frequently contained higher or lower 235U ratio than its natural isotopic ratio of 0.72% ± 0.10%. The difference to the natural ratio can only be explained by errors in isotopic measurement, otherwise it would indicate that the mining areas were contaminated with enriched or depleted uranium. Based on these analyses, it is concluded that there may be errors in measurement of radionuclide or other sources of water contamination may exist in addition to the natural leaching processes (rain water) from mine tailings or solid material from mine areas transported by natural processes to groundwater and surface water.

Language (ISO)



EPA, Uranium exposure, Navajo Nation, radionuclide


A Professional Project Report submitted in partial fulfillment of the requirements for the degree of Master of Water Resources, Water Resources Program, University of New Mexico.