Electrical Resistivity
Electrical or direct current methods measure the bulk resistivity of subsurface materials to determine geologic structure and/or physical properties of the subsurface materials. An electrical current is introduced directly into the ground through an evenly spaced string of current electrodes. The resulting voltage potential difference is measured between a pair of potential electrodes. The current and the potential electrodes are generally arranged in a linear pattern. The apparent resistivity is the bulk average resistivity of all soils and rock influencing the flow of current.
The Electrical Resistivity method is useful for the following:
- Lateral extent and thickness of landfills
- Determine depth to bedrock and overburden thickness
- Identify sinkholes
- Characterize subsurface hydrogeology
- Locate water bearing zones
- Paleochannel Delineation
- Determine depth to groundwater
- Evaluate electrical grounding characteristics
- Map stratigraphy
- Map clay aquitards
- Map salt-water intrusion
- Map vertical extent of certain types of soil and groundwater contamination
- Map faults
- Map lateral extent of conductive contaminant plumes
- Delineate disposal areas
Advantages
Substantial quantitative computer modeling is possible. The resulting models can provide accurate estimates of depths, thickness and electrical resistivities of subsurface layers. Surveys can be completed to depths of several hundred feet. Large distances can be covered in a relatively short period of time.
Limitations
Resistivity surveys require a fairly large area far removed from power lines and grounded metallic structures. Profiling surveys can be more labor intensive than some other geophysical survey methods.