A physiochemical analysis of the mechanisms for transport and retention of technetium (Tc-99) in unsaturated soils - 59050

Document available in abstract form only. Full text of publication follows: The transport of technetium (Tc-99), is of interest due to the potential for human exposure and impact on ecosystems. Technetium has been released to the environment through nuclear power production and nuclear fuel processing; as a result, further spreading of Tc-99 is a concern at DOE sites across the US. Specifically, technetium is a contaminant of concern at the Hanford Site in southeastern Washington, due to the magnitude of material that was disposed. The current body of work conducted on Tc- 99 has provided a wealth of information regarding the redox relationships, sorption, solubility, and stability of the mineral phases (Artinger et al., 2003; Beals and Hayes, 1995; Cui and Eriksen, 1996b; Gu and Schulz, 1991; Jaisi et al., 2009; Keith-Roach et al., 2003; Kumar et al., 2007), however little work has been conducted on the transport of technetium in unsaturated soils. Current conceptual models do not explain the persistence and presence of technetium in deep vadose zone environments such as the Hanford site. In an oxic reducing environment with low organic content the residence time of technetium is the soil would be expected to be low, due to its low sorption and high solubility. Surprisingly, nearly 50 years following the release of contamination into the site, much of the element has persisted in the subsurface. Using an integrated testing approach we examined the mechanisms for physical and chemical retention and transport of technetium. By employing transport and breakthrough curve analysis as well as pore water and sequential extractions, we evaluated transport behavior, technetium mineral association, and technetium leachability with regard to pore size distribution. (authors)