A New Method for Rapid, High-Resolution Characterization of Hydraulic Conductivity: Application to Solute Transport at the MADE Site

A new direct-push probe has been developed for the high-resolution characterization of hydraulic conductivity (K) in shallow unconsolidated formations. This high-resolution K (HRK) tool couples the direct-push permeameter (DPP) and direct-push injection logger (DPIL) into a single probe. The DPP provides reliable K estimates for approximately 0.4 m thick intervals through a series of small-scale injection tests, while the DPIL provides a ratio of injection rate to injection pressure, a qualitative indicator of K, at a 0.015-m resolution during continuous probe advancement. Coupling these into a single tool allows collection of collocated data, enabling a power-law relationship to be developed for directly estimating K from the DPIL ratio. The HRK tool was recently applied at the extensively studied MADE site in Mississippi, where a total of eleven profiles were obtained with K varying up to seven orders of magnitude in individual profiles. Six profiles were performed in the vicinity of a recent single-well injection-withdrawal (SWIW) bromide tracer test. From these profiles, a local wedge-shaped high-K zone was identified in the upper part of the aquifer in the tracer test area. By incorporating the K information from these profiles into the analysis model, the match between the observed and simulated SWIW tracer behaviors was significantly improved. Our initial work at the MADE site has demonstrated the power of the HRK tool to rapidly characterize K variations in highly heterogeneous systems at a resolution (0.015 m) that has not previously been possible, providing a new means to address unresolved issues of solute transport in highly heterogeneous aquifers.