A Modified Approach for Direct-Push Hydraulic Profiling in Formations of Moderate to High Hydraulic Conductivity

Spatial variations in hydraulic conductivity (K) are a primary control on solute movement in groundwater. Characterization of these variations, however, has proven to be difficult. Over the last two decades, significant progress has been made in utilizing direct-push (DP) technology to characterize K variations in shallow unconsolidated settings. Initial efforts were focused on the adaptation of conventional well testing methods to DP equipment, but more recent efforts have been directed at the development of approaches that better exploit DP capabilities. The continuous Direct-Push Injection Logger (DPIL) was designed to provide high-resolution (centimeter scale) information about relative variations in K. Water is injected continuously through a screened port while the probe is advanced and the pressure response is monitored behind the screen. The profile of the ratio of injection rate to pressure (DPIL ratio) reflects vertical variations in K. Since the DPIL only provides qualitative K information, methods are needed for transforming DPIL ratios into K estimates. These methods typically involve correlations with nearby K data, which can introduce considerable uncertainty into the transformed K estimates. The High-Resolution K (HRK) tool was designed to reduce this uncertainty by co-locating the high-resolution DPIL profiling with the direct-push permeameter (DPP - Butler et al., 2007) tool. The collocation of K estimates obtained from DPP hydraulic tests with the high-resolution DPIL-ratio data allows the DPIL profile to be directly transformed into K estimates through a calibration procedure. This procedure uses a numerical model to account for the DPIL data at their acquired resolution, circumventing the need for upscaling. Previously, Liu et al. (2009) developed an HRK tool with an upper DPIL-K limit of 10 m/d, which was primarily imposed by frictional losses caused by the small diameter of the DPIL injection tubing. Although increasing the tubing diameter allowed use of higher injection rates, those higher rates resulted in significant nonlinear flow losses that could greatly exceed the formation pressure responses in higher-K zones. In order to assess and correct for these flow losses during DPIL profiling and thereby increase the upper K limit of the HRK, we have developed an approach based on the step drawdown test procedure commonly used to characterize well losses in high-capacity pumping wells. Flow losses are characterized in pre- and post-profiling calibrations, as well as at two to three depth intervals during probe advancement, and then removed from the DPIL data. The removal of these line losses allows the DPIL-K limit to be extended upward by a factor of six (60 m/d), thus increasing the utility of the tool in permeable settings. The modified HRK approach was applied in a coarse sand and gravel aquifer at a field site located in the floodplain of the Kansas River in northeast Kansas. The results of that application demonstrate that this method can be used to characterize K in heterogeneous aquifers at a profiling resolution and speed that has not previously been possible.