The HPT allows the creation of fast, continuous real-time profiles of soil hydraulic properties in both fine- and coarse-grained material. The HPT uses a sensitive, downhole transducer to measure the pressure response of the soil to injection of water. One primary use of this tool is to locate and define preferential migration pathways for contaminants in the subsurface. It can also be used to target zones for injection of remediation material. In addition, the HPT can be used to select well screen intervals, evaluate locations to conduct slug tests, and measure static water conditions across a site.

HPT is designed to evaluate the hydraulic behavior of unconsolidated materials. As the probe is pushed or hammered, clean water is pumped through a screen on the side of the HPT probe at a low flow rate. Injection pressure, which is monitored and plotted with depth in real time, is an indication of the hydraulic properties of the soil. That is, a relatively low pressure response would indicate a relatively large grain size and the ability to easily transmit water. A relatively high pressure response, however, would indicate a relatively small grain size and the lack of ability to transmit water. Since the pressure transducer is located downhole, the HPT system also can be used to collect profiles of static water pressure data, which can be used to calculate static water levels. 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. Static water level calculations can be made using static pressure and depth data from response testing, as well as pre- and post-test response data measured at the top of the reference tube at zero flow. Since the HPT system uses an absolute pressure transducer to measure in-situ pressures, pre- and post-test data must be changed to reference atmospheric pressure.

A Wenner array is integrated into the HPT probe. This allows a user to collect soil electrical conductivity (EC) data for lithologic interpretation. Generally, EC is inversely proportional to particle size. That is, clays usually have higher conductivity than sands. Another rule of thumb is the smaller the particle size of the soil, the lower the permeability. Thus, EC measurements yield important lithological information and identify the locations permeable and non-permeable zones. However, other factors can affect EC, such as mineralogy and pore water chemistry (brines, extreme pH). Conversely, the HPT pressure response is independent of the chemical and mineralogical factors.

HPT’s features include:
  • Fast, continuous, real-time profiling of soil hydraulic properties
  • Use in both fine- and coarse-grained material
  • Use in both saturated and unsaturated conditions
  • Built to withstand percussion driving
  • Collects static water level data
  • Provides a simultaneous log of electrical conductivity with integrated Wenner array
  • Sensitive, downhole transducer measures pressure response of soil to injection of water
  • Parameters are displayed and stored on the field instrument for future analysis
Advantages of using Soil Conductivity are:
  • Rapid logging of soil lithology in saturated and/or unsaturated zones
  • Eliminates all soil cuttings and waste
  • Dramatically reduces the time and cost of site characterization
  • Identifies target treatment intervals for in-situ groundwater remediation
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