Induced polarization (IP) imaging is a promising tool in engineering and environmental studies. Application of this technique for near-surface investigations has previously been limited by incomplete understanding of the physicochemical controls on the IP response, together with a lack of appropriate methods for data inversion. As laboratory studies have shown, description of IP in terms of complex electrical conductivity enables access to various structural characteristics pertinent to practical issues such as subsurface lithology definition, hydraulic permeability estimation, or hydrocarbon contaminant mapping. In particular, analysis in terms of real and imaginary conductivity components offers improved lithological characterization, since surface polarization effects are separated from electrolytic and surface conduction effects. An Occam-type IP inversion algorithm based on complex algebra is described which accounts for these advances in IP interpretation by directly solving for complex conductivity. Results from crosshole applications at two case study sites demonstrate the suitability of the IP imaging approach for subsurface characterization. In the first case study, the imaging results correlate with the observed complex sequence of Quaternary sediments at a waste disposal site. Characterization of the polarizability of these sediments offers significant value in lithological differentiation. In the second case study, the results of IP imaging at a hydrocarbon-contaminated site illustrate the potential of the method in environmental studies. The hydrocarbon location is clearly evident from the IP image, and a markedly different response is observed at an uncontaminated region of the site. By adopting empirical structural‐electrical relationships, images of textural and hydraulic properties are estimated as a step toward improved quantitative characterization. The success of the method for these contrasting applications supports further investigation into understanding the physical and chemical processes that control observed IP.

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Crosshole IP imaging for engineering and environmental applications

A model is proposed regarding the polarization of dispersed metallic conductors (e.g., pyrite and magnetite) in porous media free of redox-active ionic species in the pore water. We studied two cases corresponding to having a background material with or without chargeability. The model was based on the polarization mechanism of a single particle using well-established bounds for the reflection coefficient entering the definition of the dipole moment of the metallic grains. We used the Maxwell-Clausius-Mossotti mixing equation to obtain the complex conductivity of the mixture of dispersed metallic particles in the background porous material composed of the pore water and the insulating grains coated by an electric double-layer. This equation can be generalized to a mixture of various types of metallic particles (with their own properties) dispersed in the background porous material. Our model led to a very simple linear relationship between the chargeability and the volume content of metallic parti...

Induced polarization response of porous media with metallic particles — Part 1: A theory for disseminated semiconductors

Electrical methods using active sources (direct current (DC) resistivity and induced polarization (IP)) are probably the most widely used near-surface geophysical techniques, particularly for environmental investigations. After first providing a brief historical perspective on the development of these methods, we present a range of field investigation approaches, including surface-based imaging and borehole-based imaging. Forward and inverse modeling approaches are reviewed and a general framework for modeling is presented, including the analysis of time-lapse data and image appraisal. Throughout the chapter, we offer some guidelines on the measurement and modeling of DC resistivity and IP data. Finally, some perspectives on future developments of these methods are offered.

Tools and Techniques: Electrical Methods

Several laboratory and scaled model investigations suggest that organic contaminants affect the surface electrical properties of exposed soils/rocks and therefore produce measurable induced polarization IP signatures. However, there is little field evidence of an IP methodology for contaminant mapping. A2D time-domain IP method is developed for mapping the FS12 contaminant plume at the Massachusetts Military Reservation MMR located in Cape Cod, Massachusetts. The FS-12 plume consists of approximately 265 m 3 of fuel that erupted from a broken underground pipeline in the early 1970s. Benzene and ethylene dibromide EDB are the primary contaminants at FS-12, with concentrations exceeding the allowed maximum concentration levels MCL, while other constituents of the plume did not exceed their MCL. Therefore, the contaminants of interest are benzene and EDB, partly because of their health risk and partly because they present the highest concentrations 2400 and 1000 g/L, respectively among the plume constituents and are therefore more likely to be related to the polarization source. IP data were acquired along a survey line that partially transects the plume extending over contaminated and uncontaminated zones and were inverted to give 2D resistivity and chargeability plots to 100 m depth and a horizontal extent of 400 m. By separately inverting IP data derived from time windows located at short and long decay times, a timedomain gross spectral chargeability difference is produced. Both the chargeability and gross spectral chargeability difference show good agreement with the known location of the plume from monitoring wells, with the IP chargeability section suggesting contaminant distribution detail that cannot otherwise be inferred from the sparse borehole distribution.

Induced-polarization detection and mapping of contaminant plumes

https://hal.archives-ouvertes.fr/hal-02324339/document

Complex conductivity of volcanic rocks and the geophysical mapping of alteration in volcanoes

Laboratory experiments have shown certain fundamental relationships concerning the induction of a polarization potential on a metallic body in an electrolyte. The potential induced is a linear function of the potential drop across the body in the energizing field up to a saturation potential of 1.2 volts. Diffusion of ions and chemical action are the predominant factors which determine the rate of growth or decay of the polarization potential. Polarization occurs only at the boundaries of electrically conducting minerals. The results of the laboratory experiments provide an explanation of the induced polarization potential of a homogeneous, uniformly mineralized earth. This potential falls off as 1/r from a point electrode. Induced polarization susceptibility is defined and a method of analyzing field data is described. Field measurements over two mineralized zones (pyrrhotite and magnetite) substantiate the theory as developed.

David Franklin Bleil

Papers

Induced polarization; a method of geophysical prospecting

Induced Polarization: a Method of Geophysical Prospecting.