The electrical properties of the subsurface vary with the ground material, the presence and saturation level of fluids, and the presence of buried objects. By employing different electrode configurations it is possible to determine the apparent resistivity at various locations and depths. Comparison with computer models makes it possible to solve for the subsurface resisitivity distribution, and hence identify any anomalous areas or features. As different rocks/objects/saturating fluids exhibit different values of electrical resistivity, it is possible to map their distribution.
The introduction of multi-electrode and computer controlled systems allow semi-automated surveys, allowing large data sets to be collected more quickly and at reduced cost. Three-dimensional surveys, which are invaluable when surveying complex geological / man-made features, are now a practical and cost effective tool.
RSK Geophysics routinely employ state of the art processing software which allow forward modelling and inversions of resisitivity data using complex mathematical algorithms.
Electrical Resistivity Tomography (ERT) Applications
- Locating extent and depth of buried landfills
- Mapping and monitoring leachate plumes
- Mapping and monitoring groundwater pollution
- Determination of depth to bedrock
- Locating dissolution features
- Stratigraphic mapping
- Locating buried channels, dykes, ore bodies and other geological features
- Slope stability assessments
- Cross-hole tomography
- Time-lapse infiltration studies
- Assessment of aquifer heterogeneity
Other electrical techniques:
1D Resistivity Sounding
In addional to 2D and 3D resisitivity profiling, we also undertake simple 1D soil resisitivity sounding profiles with the use of a pair of current electrodes and measuring the potential gradient within the subsurface. By increasing the spacing of the electrodes, the depth of the invesitgation below the centre point is increased. Read more...
Self Potential Imaging
Self potentials are measurements of the difference in natural ground potentials between two points on the ground surface. They can be generated by a number of different sources including groundwater flow, mineral deposits and chemical diffusion. Read more...
Self potentials measured can vary from less than a millivolt to over one volt, and the sign (+/-) of the potential is a diagnostic factor in the interpretation of SP anomalies. Although there are many sources of self potentials, the common factor among them is groundwater. The potentials are generated by the flow of water, by water acting as an electrolyte and as a solvent of different minerals and compounds.
The SP technique can be used for a variety of applications including:
Induced polarisation (IP) imaging is a complementary technique to electrical resistivity imaging and is concerned with the capacitance (how much energy is stored) of the subsurface. In conjunction with resistivity, IP imaging can provide additional discrimination of subsurface materials. Read more...
- Hydrogeological investigations (eg groundwater flow determination, contaminant transportation)
- Locating massive sulphide ore bodies
- Landfill delineation
- Leak detection in reservoirs and dams
- Geothermal surveys