CHARACTERIZING SMALL-SCALE HETEROGENEITIES AT THE MADE SITE USING SEDIMENTOLOGICAL, HYDRAULIC, AND TRACER DATA

The Macro-Dispersion Experiment site, more commonly referred to as the MADE site, in Columbus, Mississippi has become a natural laboratory for studying the effect of aquifer heterogeneities on contaminant transport. Since the early 1990s, the data collected at the MADE site has been used extensively by numerous researchers around the world to gain insights into contaminant transport processes in highly heterogeneous aquifers. Analysis of three previous natural-gradient tracer tests and a recent forced-gradient tracer test has shown that solute transport at the MADE site is dominated by preferential flowpaths arising from small-scale heterogeneities, leading to well-documented dual-porosity phenomena. This presentation will provide an overview of several more recent efforts aimed at characterizing the nature and geometry of these preferential flowpaths at the MADE site. These efforts include a detailed grain-size analysis of 20 closely-spaced soil cores, a dye-tracing investigation, and a proof-of-concept application of direct-push hydraulic profiling. The results of these studies have shed some new lights on the characteristics of small-scale heterogeneities at the MADE site and will provide a more solid footing for development of improved mathematical modeling tools for accounting the effect of small-scale heterogeneities on solute transport.