CONTAMINANT TRANSPORT MODELING IN A HETEROGENEOUS ENVIRONMENT USING GEOPHYSICAL-BASED HYDRAULIC CONDUCTIVITY MEASUREMENTS

More than 2000 measurements of hydraulic conductivity in about 50 boreholes have been collected at the Macro-Dispersion Experiment (MADE) site in Columbus, Mississippi to quantify aquifer heterogeneity within an area of approximately 100 m by 250 m. This high-density measurement approach is practically infeasible in typical groundwater remediation sites with real contaminants. A natural-gradient tracer experiment from the MADE site is simulated using direct-current (DC) resistivity and ground-penetrating radar (GPR) data. A grid of 2D resistivity and GPR data was collected over a majority of the observed plume location. Hydraulic conductivity from one borehole collected during the original site characterization study is used to calibrate the geophysical data. A log-log relationship is derived for hydraulic conductivity from DC resistivity data, thereby providing a 3-D description of hydraulic conductivity. Four approaches are used to represent the hydraulic conductivity distribution, including: 1) A layered model with a homogeneous K value for each model layer derived from the borehole data, 2) A layered model similar to the first, but with resistivity derived hydraulic conductivity values, 3) A third model with ordinary kriging interpolation to fill in where geophysical data were not collected, and 4) A layered model again with K values derived from the borehole but with layer topography described by upper and lower boundaries of the main aquifer units mapped in a recent study. Each K distribution is used in an advection-dispersion model and a dual-domain mass transfer model to simulate the observed plume behavior. This study demonstrates that an extremely heterogeneous aquifer can be modeled with minimal hydrological data supplemented with geophysical data at least as well as previous models of the site using purely hydrologic data.