Uses, Advantages, Disadvantages

Uses, Advantages, Disadvantages

The electrical resistivity technique of geophysical exploration is one of the earliest methods. The Schlumberger brothers in France in the early part of the 20th Century did much of the early development.

The technique has been successfully employed for investigating:

· Groundwater depth

· Lithology favorable for groundwater

· Contamination of groundwater

· Depth to freshwater-saltwater interface

· Location of sinkholes and cavities

· Detection of fractures and dikes

· Thickness of overburden

· Geologic structure

· Archeological sites

· Electrical grounding of large electrical installation

· Electrical grounding of cell phone transmitting towers

· Electrical grounding of wind driven power generator towers

Advantages of the technique are:

· The equipment is light, portable and inexpensive

· Qualitative interpretation of the data is rapid and straightforward

· Field expenses are minimal

· It is flexible and can be used for various purposes and depths of investigation

· It can be used for both soundings and profiling

· Shallow investigations are rapid

Disadvantages of the technique are:

· Deep investigations require long cables and consume much field time

· Interpretation of complex geologic structures is difficult and ambiguous

· Presence of metal pipes, cables, fences and electrical grounds can complicate interpretation.

· Accuracy of depth determination is lower than with seismic techniques

The MiniRes and the GPR-Res also measure induced polarization. This additional information may be collected with only a few additional moments of field time at each observation setup. Since the same field setup is used, the only addition time required to make an IP observation is to press the blue IP switch and record the number. Newer units measure the IP reading at the same time as measuring resistance and there is no need to press an IP button.

Some of the advantages of having the IP data are:

· It can remove some of the ambiguity of interpretation. For example, the IP signal can allow you to distinguish between conductive clay and a conductive brackish saturated sand or gravel.

· It can detect corroding metals, such as an old pipeline or a valuable archeological artifact.

· It can be used to detect several types of mineral deposits.

· It can detect clays and the clays properties.

· See Appendix X note: "disturbed clays"

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