Assessment of the Hydraulic Profiling Tool for Lower Permeability Characterization

Abstract

The Hydraulic Profiling Tool (HPT) has become one of the most widely accepted approaches for obtaining vertical profiles of hydraulic conductivity (K) in environmental site investigations. The current tool, however, is limited to use in moderately permeable settings with a measurable K range of 0.03 to 25 m/d. In this work, we added a low‐flow injection system to standard HPT and modified the field profiling procedure so that it could be used more effectively in lower‐K settings. The modified lower‐K HPT was tested and evaluated against direct‐push slug tests at a field site in the Kansas River floodplain. Results indicated that when the injection rate was reduced, injection pressure decreased, which reduced the potential of injection‐induced formation alteration. A particular challenge of applying HPT in lower‐K zones is the large pressure generated by probe advancement; this can significantly affect the pressure signal measured at the injection screen. Our results showed that the impacts of advancement‐generated pressure could be mitigated by reducing the speed of probe advancement. Compared to K estimates by slug tests, the vertical variability in HPT K was much lower. The reduced variability in HPT K was likely due to formation alteration during probe advancement, as well as pressure interference from injections at previous depths and probe advancement at the bottom. Additional work, such as the use of a smaller‐diameter probe, is needed to further improve the performance of HPT in lower permeability zones.