HIGH RESOLUTION CHARACTERIZATION OF HYDRAULIC CONDUCTIVITY USING DIRECT-PUSH TECHNIQUES

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. In recent work at the extensively studied MADE site at Columbus Air Force Base, Mississippi, we have collected direct-push profiles at 66 locations, 21 using the HRK tool and the rest using a DPIL-only probe with an integrated electrical conductivity array. Applying the power-law transformation to both the HRK and DPIL-only data has yielded a laterally extensive 3D dataset of unprecedented vertical resolution. These data indicate K variations of eight orders of magnitude or more. We present geostatistical analysis and simulations of K in three intensively sampled subareas. The geostatistical simulations of the K data exhibit laterally persistent, sloping structural features with thicknesses on the order of a few tenths of a meter and larger whose character is consistent across realizations, due to the large quantity of conditioning data provide by the direct-push profiles. Our work at the MADE site has demonstrated the power of direct-push techniques 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.