Full-resolution 3D GPR and Direct-Push K Data Reveal Distinct Hydrostratigraphic Zones at the MADE Site

The Macrodispersion Experiment (MADE) site at Columbus Air Force Base in Mississippi, USA, has been a natural laboratory for the study of transport through heterogeneous aquifers for over 25 years. Natural-gradient tracer tests conducted at this site resulted in highly asymmetrical mass distributions that cannot be explained using classical advection-dispersion theory. During several large-scale tracers tests it was observed that considerable tracer remained trapped around the source area. To improve transport simulations through highly heterogeneous aquifers such as at the MADE site it is important to characterize both the vertical and horizontal variations of aquifer properties in sufficient detail. We collected 3D Ground Penetrating Radar (GPR) data cubes and direct-push High Resolution Hydraulic Conductivity (HRK) profiles in different areas of the MADE site. The GPR data were used to characterize depositional environments and their lateral extensions, while HRK data were used to define high-resolution vertical variability in hydraulic conductivity. Both datasets were statistically analyzed and used for integrated analysis of the site hydrostratigraphy. Our results reveal distinct differences in depositional environments for the near-source, central, and downgradient portions of the natural-gradient tracer plumes. The integration of GPR and HRK provides insight into the distribution of large-scale hydrostratigraphic units, which can be used for improved understanding of contaminant transport.