As DP supported investigation methodology, geo-log provides the newest high-resolution technology of the U.S. Company Geoprobe. Hydraulic Profiling Tool (HPT) is a system manufactured to evaluate the hydraulic behavior of subsurface soil. The tool is advanced through the subsurface while water is injected at a constant rate through a screen on the side of the probe. An in-line pressure sensor measures the pressure response of the soil to water injection. The pressure response identifies the relative ability of a soil to transmit water. Both pressure and flow rate are logged versus depth.

In situ testing of hydraulic conductivity can be performed by injecting water under a specified flow rate (ca. 300 ml/min) into the aquifer. The water flows into the layers in an easier or heavier way, depending on the hydraulic properties of the medium. The interpretation provides in a preliminary stage a relative profile of hydraulic conductivity. A Wenner array is integrated into the HPT probe allows the user to collect soil electrical conductivity (EC) data for lithologic interpretation.

By means of several slug tests the results are site-specific translated into absolute values of hydraulic conductivity. As a result, such a target oriented approach can lead to a more appropriate positioning of the soil and groundwater sampling ports, either as direct sampling procedures or through the means of groundwater monitoring wells.

Since the HPT pressure response is analogous to relative changes in the ability to transmit water (and therefore the relative change in dominant grain size), the HPT system can be used to identify potential contaminant migration pathways. Similarly, it can help identify zones for remedial material injection or provide qualitative guidance on how difficult injection may be in different zones of the formation.

The HPT system may be used to direct other investigation methods, such as soil and groundwater sampling and slug testing. HPT pressure response and EC data can help target zones of geologic and hydraulic interest, minimizing the number of soil and groundwater samples required to adequately develop a site conceptual model. Running the HPT and EC logs simultaneously provides independent confirmation of one log against the other for lithologic characterization.