Characterization of calculation of in-situ retardation factors of Contaminant Transport Using Naturally- Occurring U-Series Disequilibria timescales.

This progress report outlines the ongoing research focused on quantifying contaminant transport rates in fracture-rock systems using naturally occurring uranium-series radionuclides. The objective is to assess the adsorption-desorption and transport mechanisms of radioactive contaminants, as well as fluid transport and rock dissolution, particularly at the Idaho Environmental and Engineering Laboratory (INEEL) site. The methodology includes determining the natural distribution of uranium, thorium, protactinium, and radium isotopes in rock minerals, fluids, and absorbed phases in both saturated and unsaturated zones, alongside employing a statistical analysis-based model to study rock/water interactions. Initial results from the August sampling trip indicated successful collection of samples necessary to meet project goals, despite delays in funding the University of Southern California's involvement, which had temporarily stalled sample collection efforts. Continued efforts include additional uranium analyses, collection of large-volume samples, and initial analyses of uranium-and thorium-series nuclides. The project findings suggest significant implications for understanding the mobility of radioactive contaminants constrained by the hydrogeologic features of fracture-rock systems.