Wednesday, April 14, 2010: 3:10 p.m.
Continental C (Westin Tabor Center, Denver)
Spatial variations in hydraulic conductivity (K) play an important role in subsurface contaminant transport. There is a critical need to develop field methods that characterize those variations at a resolution appropriate for quantifying transport in heterogeneous formations. Direct-push (DP) methods have shown much promise in this regard. Over the past decade, methods have progressed from empirical relationships based on cone penetrometer or electrical conductivity logs to variants of the slug test to a new generation of methods that provides reliable K estimates at an unprecedented resolution and speed. In the last year, we have developed a new tool, the high-resolution K (HRK) probe, for obtaining K estimates at a vertical resolution as fine as 0.015 m. This tool is the product of coupling the direct-push permeameter (DPP) and the direct-push injection logger (DPIL) into a single probe. The DPP is a small-diameter probe with a short screen and two pressure transducers set into the DP rod. Short injection tests are performed at a given depth and K is estimated from pressure responses. The DPP resolution for practical applications is currently ≈ 0.4 m. The DPIL is a probe with a small screened port through which water is injected while the pressure response is monitored behind the screen. The injection logging process is conducted continuously at a 0.015-m resolution as the tool is advanced, creating a profile of the ratio of injection rate to pressure that is reflective of vertical variations in K. The HRK probe provides high-resolution K estimates by using DPP results to transform the co-located high-resolution DPIL ratios into K estimates. A recent field demonstration at the extensively studied MADE site in Mississippi demonstrated that a series of HRK profiles across a site can provide invaluable hydrostratigraphic insights, particularly when coupled with site-appropriate high-resolution geophysical methods.