Conceptual models have been identified as one of the sources of uncertainty in the interpretation and prediction of contaminant migration through the vadose zone at Hanford. Current conceptual models are limited partly because they often do not account for the random heterogeneity that occurs under the extremes of very nonlinear flow behavior typical of the Hanford vadose zone. Over the last two years significant progress has been made in characterizing physical heterogeneity and in the development of techniques for incorporating this heterogeneity into predictive and inverse models for field-scale subsurface flow. One of the remaining pieces of the puzzle is the impact of heterogeneity on the distribution of reactive contaminants. Reactive transport occurs over a wide range of spatial and temporal scales. However, the manner in which the various subsurface physical and chemical processes interact to influence transport is not very well understood. Hydrogeologic characterization and model analysis, however, have traditionally focused on measurement of physical properties and predicting the effects of variability in these properties on flow and transport. As a result, the role of geochemical heterogeneity on solute transport has remained largely unexplored. This project will use a combination of geophysical and soil physics techniques to investigate the …