Spectral Induced Polarization Survey Research Articles

3D electrode configurations for spectral induced polarization surveys of landfills

There is growing interest in the use of spectral induced polarization (SIP) surveys to characterize the near-surface environment. Few attempts have been made to perform field SIP surveys in a 3D configuration; when done, they are typically conducted using a series of parallel 2D electrode lines with collinear measurements. However, such measurements are limited in the resolution between the lines which is critical in the case of heterogeneous subsurface conditions, such as in landfills. To overcome this, we investigate here the enhanced resolution in SIP measurements through true 3D measurements, i.e., the resolving capabilities of different electrode configurations distributed across measuring planes. First, we investigate, through a synthetic study, the difference between results from using 2D parallel collinear electrode arrays and true 3D configurations. Second, we collected SIP data (in the frequency range between 1 and 240 Hz) using 2D and 3D configurations in two landfills to evaluate the application of our results in real field conditions. Both the synthetic and the field experiments demonstrate that measurements of parallel 2D collinear arrays result in the creation of artifacts and the loss of resolution in the 3D structure, especially of polarizable features. In contrast, the 3D configurations are able to resolve polarizable anomalies in synthetic and field measurements, resulting in a better delineation of the geometry of waste units. Our results also demonstrate that 3D configurations are better suited to recover the frequency-dependence of the electrical properties; thus, permitting an improved interpretation of waste composition and the quantification of waste volume.

Spectral Induced Polarization Survey with Distributed Array System for Mineral Exploration: Case Study in Saudi Arabia

The Saudi Arabian Glass Earth Pilot Project is a geophysical exploration program to explore the upper crust of the Kingdom for minerals, groundwater, and geothermal resources as well as strictly academic investigations. The project began with over 8000 km2 of green-field area. Airborne geophysics including electromagnetic (EM), magnetics, and gravity were used to develop several high priority targets for ground follow-up. Based on the results of airborne survey, a spectral induced polarization (SIP) survey was completed over one of the prospective targets. The field data were collected with a distributed array system, which has the potential for strong inductive coupling. This was examined in a synthetic study, and it was determined that with the geometries and conductivities in the field survey, the inductive coupling effect may be visible in the data. In this study, we also confirmed that time domain is vastly superior to frequency domain for avoiding inductive coupling, that measuring decays from 50 ms to 2 s allow discrimination of time constants from 1 ms to 5 s, and the relaxation parameter C is strongly coupled to intrinsic chargeability. We developed a method to fully include all 3D EM effects in the inversion of induced polarization (IP) data. The field SIP data were inverted using the generalized effective-medium theory of induced polarization (GEMTIP) in conjunction with an integral equation-based modeling and inversion methods. These methods can replicate all inductive coupling and EM effects, which removes one significant barrier to inversion of large bandwidth spectral IP data. The results of this inversion were interpreted and compared with results of drill hole set up in the survey area. The drill hole intersected significant mineralization which is currently being further investigated. The project can be considered a technical success, validating the methods and effective-medium inversion technique used for the project.

Inversion of time-domain induced polarization data based on time-lapse concept

Induced polarization (IP) surveys, measuring overvoltage phenomena of the medium, are widely and increasingly performed not only for exploration of mineral resources but also for engineering applications. Among several IP survey methods such as time-domain, frequency-domain and spectral IP surveys, this study introduces a noble inversion method for time-domain IP data to recover the chargeability structure of target medium. The inversion method employs the concept of 4D inversion of time-lapse resistivity data sets, considering the fact that measured voltage in time-domain IP survey is distorted by IP effects to increase from the instantaneous voltage measured at the moment the source current injection starts. Even though the increase is saturated very fast, we can consider the saturated and instantaneous voltages as a time-lapse data set. The 4D inversion method is one of the most powerful method for inverting time-lapse resistivity data sets. Using the developed IP inversion algorithm, we invert not only synthetic but also field IP data to show the effectiveness of the proposed method by comparing the recovered chargeability models with those from linear inversion that was used for the inversion of the field data in a previous study. Numerical results confirm that the proposed inversion method generates reliable chargeability models even though the anomalous bodies have large IP effects.

Time‐lapse spectral induced polarization imaging of stimulated uranium bioremediation

ABSTRACTTomographic measurements of the spectral induced polarization (SIP) response of aquifer sediments were conducted at the U.S. Department of Energy’s (DOE) Integrated Field Research Challenge site (IFRC) in Rifle, Colorado (USA), where biostimulation research is ongoing with the purpose to immobilize uranium in tailings‐contaminated groundwater. The aims of the SIP surveys were to (a) collect data over a sufficiently broad bandwidth so as to determine the characteristic frequency of the spectral response (at which the strongest polarization response takes places), (b) investigate the distribution of spectral parameters (e.g., characteristic time constant) in an imaging framework and (c) evaluate the potential of these images to delineate changes in the hydraulic properties of the aquifer. Careful field procedures provided high‐quality SIP data from 0.060–256 Hz for three different periods during the remediation experiment. Data quality was evaluated by means of analysis of the discrepancy between normal and reciprocal measurements. A Cole‐Cole model was fitted to pixel values extracted from the inverted images in order to assess changes in the SIP response – particularly in time constant () and chargeability (m) – due to processes accompanying the stimulation of subsurface microbial activity. A significant increase in both and m was observed after halting acetate injection, consistent with the accumulation of semi‐conductive minerals (e.g., FeS) during biostimulation and the post‐injection rebound in aqueous Fe(II). The reliability of the imaged spectral parameters was assessed by means of a numerical study.

CR1Dinv: A Matlab program to invert 1D spectral induced polarization data for the Cole–Cole model including electromagnetic effects

An inversion code has been constructed using Matlab, to recover 1D parameters of the Cole–Cole model from spectral induced polarization data. In a spectral induced polarization survey, impedances are recorded at various frequencies. Both induced polarization and electromagnetic coupling effects occur simultaneously over the experimental frequency bandwidth, and these become progressively more dominant when the frequency increases. We used the CR1Dmod code published by Ingeman-Nielsen and Baumgartner [2006]. This code solves for electromagnetic responses, in the presence of complex resistivity effects in a 1D Earth. In this paper, a homotopy method has been designed by the authors to overcome the local convergence problem of normal iterative methods. In addition, in order to further condition the inverse problem, we incorporated standard Gauss–Newton (or quasi-Newton) methods. Graphical user interfaces enable straightforward entering of the data and the a priori model, as well as the cable configuration. Two synthetic examples are presented, showing that the spectral parameters can be recovered from multifrequency, complex resistivity data.

Three‐dimensional self‐potential inversion for subsurface DNAPL contaminant detection at the Savannah River Site, South Carolina

Self‐potential (SP) data are collected over an area of approximately 250 m2 at the Department of Energy Savannah River Site where there is known subsurface dense nonaqueous phase liquid (DNAPL) contamination. Nonpolarizing electrodes are used to measure the SP signal on a two‐dimensional (2‐D) surface grid with 2‐m spacing in both horizontal directions, and four borehole arrays with 3.7‐m electrode spacing and 25.6‐m total depth. The primary contaminants, tetrachloroethylene (PCE) and trichloroethylene (TCE), are known to undergo redox reactions in the environment. Variations in the subsurface redox conditions are proposed as an electrochemical source for the SP signals measured in this investigation. A 3‐D self‐potential inversion algorithm is used to find an electrical current source model, taking into account the resistivity structure derived from a 3‐D spectral induced polarization survey at the same field location. The sources and sinks of electrical current can be related to the zones of relative high or low redox potential and are therefore interpreted in the context of contaminated areas. These results are reasonably correlated with DNAPL concentration data obtained from several ground‐truth well measurements, indicating that the SP sources can be an indicator of contaminated areas where electrochemical source mechanisms are active. In several cases, however, the SP sources and contaminant concentrations are not correlated, reflecting the spatial variability of biogeochemical parameters in the Earth that control the SP response in addition to concentration. More extensive geochemical ground‐truth information is therefore needed to validate the self‐potential source inversion methodology and develop it as a predictive tool in the context of contaminated sites.

Investigation of a Bronze Age plankway by spectral induced polarization

AbstractThe induced polarization (IP) method was developed originally for ore exploration. The transition from electronic to electrolytic conduction causes strong polarization effects in ores. However, other porous materials also exhibit polarization effects. They are caused by electrochemical processes at the internal interface between the pore fluid and the mineral grains. Although these effects are one to two orders smaller in size, modern IP equipment is able to resolve these phenomena. Spectral induced polarization (SIP) investigates the polarization effect in a wide frequency range. As a SIP measurement has an identical setup to conventional resistivity survey, a multichannel geoelectrical instrument (SIP‐256) was developed that is able to measure both apparent resistivity and the polarization effect using a multi‐electrode array.The Federsee bog near Lake Konstanz with its optimal preservation conditions is of international importance for archaeology. Pile dwelling settlements dating back to the eneolithicum have been revealed. Wood samples of a Bronze Age plankway (1500–1400 BC) were collected and investigated. The astonishing result of the laboratory measurements was that the samples showed a remarkable polarization effect in the classic frequency range of IP. Wood therefore can be regarded as a polarizable material. As a consequence a SIP survey was performed in order to investigate the plankway. The SIP survey was carried out in a frequency range from 1 to 60 Hz, where the maximum polarization effect in the laboratory was observed. Two profiles were measured, one parallel and one perpendicular to the plankway. In contrast to the result of the resistivity measurement, the plankway could be identified by weakly increased polarization effects. Copyright © 2002 John Wiley & Sons, Ltd.

Induced-polarization modelling using complex electrical conductivities

A numerical technique for induced-polarization (IP) modelling of arbitrary 2-D or 3-D distributions of electrical conductivity is developed. This technique is based on the premise that, due to polarization effects, the conductivity is complex. Complex finite-difference equations are obtained for the complex potential by an elemental volume discretization. The accuracy of the discretization is improved by the application of asymptotic boundary conditions and singularity removal. The resulting linear set of complex equations is symmetric. It is solved by a generalized conjugate gradient method which is speeded up by pre-conditioning techniques. A compact storage scheme fully utilizes the sparsity and the symmetry of the matrix. The complex arithmetic ensures that the resulting values of amplitude and phase angle of apparent resistivity can be directly compared with the measured quantities of a spectral IP survey. Models of a layered half-space and of a buried cube are chosen to demonstrate the good agreement of the apparent resistivity curves with the results from other numerical techniques.

Effects of Pipelines on Spectral Induced-Polarization Surveys

The formal electromagnetic coupling solution for a dipole-dipole electrode array configuration has been modified to include cultural coupling in a uniform conducting half-space. Solutions are obtained for survey lines oriented at an arbitrary position and angle with respect to a cylindrical structure. The convergence properties of the general mutual impedance solution are analyzed using a low-frequency approximation which is useful in predicting cultural anomalies in the frequency range of spectral IP surveys as long as all significant dimensions are less than one skin depth. Both interfacial polarization and induced currents in the cylindrical conductor are considered in examining the behaviour of the overall spectrum as seen by an external observer. Spectral responses for dipole-dipole arrays oriented perpendicular and parallel to the buried conductor show that the phase shift is the most diagnostic parameter for pipe depth and survey data distortion. The results also show that field survey procedures can be devised to minimize such interference effects when the pipe position is known.