Investigating Uranium Isotopic Ratios and Activity Ratios in Groundwaters in the State of Idaho

Analyzing uranium isotopic and activity ratios can give valuable information for hydrologic and environmental studies such as insights to weathering processes, estimating water mixing ratios, and identifying water sources. The authors employed an inductively coupled plasma mass spectrometer (ICP-MS) to perform environmental level concentration measurements of isotopic uranium on 380 groundwater samples from various locations within the state of Idaho. The U:U uranium activity ratios (UAR) for these samples range between 0.91 and 6.21, which suggests that the parent U is not in equilibrium with its decay product U. The U:U isotopic ratio was also measured for each sample to confirm that there was no depleted or enriched uranium present. All 380 samples exhibited the natural isotopic ratios of U and U isotopes. Therefore, it was concluded that the U:U UARs reflect natural variations in the Idaho groundwater systems.