Electrical resistivity surveys, like many other geophysical techniques, are noninvasive which is particularly attractive when penetration or disturbance of contaminated material is undesirable. This has allowed the technique to be used for identifying and mapping subsurface contaminants at geoenvironmental remediation sites. In addition to the applications mentioned above, resistivity has been shown to be an effective property for assessing changes in pore fluid composition for a given soil. Table 1 shows some typical values for saturated, contaminated soils. Resistivity values for a given material can also span multiple orders of magnitude. It is important to note from Figure 3 that there is significant overlap between different material types. Some examples of geomaterial resistivity or conductivity, the inverse of resistivity are provided in Figure 3. The broad applicability of electrical resistivity surveys has also led to its use for wide range of applications in geotechnical and geoenvironmental engineering including mapping geomorphologic features such as karsts Myat et al. Figure 1: Equipotential lines and current lines for electrode pairs in a homogeneous half-space from EPA, b. The assumed resistivity profile is iteratively updated until the calculated and measured apparent resistivity profiles sufficiently match.Īn example of software used to perform the inversion computations is shown in Figure 2. In general, an assumed resistivity profile is generated and used to calculate an apparent resistivity profile which is compared to the recorded field data.

Since the resistivity profile cannot be directly computed from apparent resistivity measurements, an inversion method must be used to estimate the resistivity profile e. More recent innovations use arrays of many probes for measuring cross-sections, or probes in grid patterns for tomography methods which allow 2D and 3D subsurface imaging.Įlectrical resistivity surveys directly provide an estimate of the apparent resistivity of the surveyed material. An example of this class of array is shown in Figure 1.

Based on the applied current and the measured voltage, the apparent electrical resistance of the subsurface can be measured. Wenner, Schlumberger, and dipole-dipole arrays. Two sets of probes are typically inserted vertically into the soil one set delivers a current into the soil and the second set measure the voltage differential over some distance i. Electrical resistivity surveys involve inserting electrodes directly into the ground surface and transmitting an electrical current into the soil which acts as a resistive medium.

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