MASS TRANSPORT OF HALIDE AND BENZOATE TRACERS TO CHARACTERIZE GROUNDWATER VELOCITY, DISPERSIVITY, AND MATRIX DIFFUSION IN A URANIUM-CONTAMINATED AQUIFER

The concentration of uranium in groundwater at a former mill tailings site persists above levels as predicted by a site-wide model. It is hypothesized that the mass transport mechanisms that control the concentration of uranium in groundwater need to be further characterized to better inform a revised site-wide model. To this end, an in-situ tracer test was conducted using chloride and pentafluorobenzoate; the former being a non-reactive tracer to characterize groundwater velocity and dispersivity, the latter being a relatively low-diffusion tracer to elucidate matrix diffusion. A 100-gallon solution of tracer-amended water was injected into a single well and was tracked over several weeks in two down-gradient transects of observation wells. The two-dimensional center of mass of both tracers will be quantified, visualized, and compared across snap shots in time to characterize groundwater velocity, dispersivity, and matrix diffusion. The results of these data will be discussed in terms of better informing a revised site-wide model.