GEOCENTRIFUGE APPLICATIONS TO SOLUTE TRANSPORT IN THE VADOSE ZONE

Improved models of contaminant migration in heterogeneous, variably saturated porous media are required to better define the long-term stewardship requirements for U.S. Department of Energy (DOE) lands and to design effective vadose-zone remediation strategies that significantly decrease contaminant migration. To better understand contaminant migration processes, we have been using of the 2-meter radius geocentrifuge capabilities at the Idaho National Engineering and Environmental Laboratory (INEEL) to conduct unsaturated reactive transport experiments. The experimental approach using the geocentrifuge provides data in a much shorter time period than conventional methods allowing us to complete more experiments and explore a wider range of moisture contents. Through our review of the theory of unsaturated flow in the geocentrifuge, we have derived an expression for the fluid potential in a centrifugal field that is different from the expression in constant gravity field. This difference suggests that caution should be used in applying simple scaling laws. Collaborating with others, we have developed numerical tools that allow us to simulate flow and transport in a centrifugal field. We have designed and constructed an in-flight fraction collector system capable of withstanding the acceleration on the geocentrifuge. We have also improved the design of a soil moisture probe making it more suitable for column experiments. Tracer tests conducted on the geocentrifuge demonstrate the detailed information can be obtained in-flight in relatively short time periods of time. Through the use of our work on flow under enhanced acceleration, modified models, and improved experimental techniques, we are continuing to improve our analysis of vadose-zone transport experiments on the geocentrifuge.