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.