| A large column (108 cm in length with an inner diameter of 45 cm) of heterogeneous aquifer sediment collected from a shallow glacial drift deposit in northern East Lansing, MI was characterized to obtain high-resolution estimates of hydraulic conductivity. The characterization was accomplished through a series of tracer transport experiments, visual observations, and physical measurements. Bromide, fluorescein and tritium were used as the tracers for this project and all displayed asymmetrical breakthrough curves (BTC's). Also, the tritium tracer test had a slightly delayed BTC peak time which was attributed to molecular mass differences of the tracers with associated differential diffusion rates, as described by Ewers (1997). The physical measurements taken of the aquifer sediment provided high-resolution estimates of hydraulic conductivity and porosity enabling a more accurate groundwater flow and solute transport computer model to be created than was possible prior to this characterization. The numerical simulations allowed for the dominant physical processes (i.e. advection and diffusion) to be studied in a carefully controlled laboratory experiment in which the boundary conditions are known. Specifically, this study focuses on the effect of centimeter to decimeter scale heterogeneities on the flow and transport of conservative tracers. |
