Improved hydrogeophysical characterization and monitoring through parallel modeling and inversion of time-domain resistivity andinduced-polarization data

Abstract

Electrical geophysical methods have found wide use in the growing discipline of hydrogeophysics for characterizing the electrical properties of the subsurface and for monitoring subsurface processes in terms of the spatiotemporal changes in subsurface conductivity, chargeability, and source currents they govern. Presently, multichannel and multielectrode data collections systems can collect large data sets in relatively short periods of time. Practitioners, however, often are unable to fully utilize these large data sets and the information they contain because of standard desktop-computer processing limitations. These limitations can be addressed by utilizing the storage and processing capabilities of parallel computing environments. We have developed a parallel distributed-memory forward and inverse modeling algorithm for analyzing resistivity and time-domain induced polar-ization (IP) data. The primary components of the parallel computations include distributed computation of the pole solutions in forward mode, distributed storage and computation of the Jacobian matrix in inverse mode, and parallel execution of the inverse equation solver. We have tested the corresponding parallel code in three efforts: (1) resistivity characterization of the Hanford 300 Area Integrated Field Research Challenge site in Hanford, Washington, U.S.A., (2) resistivity characterization of a volcanic island in the southern Tyrrhenian Sea in Italy, and (3) resistivity and IP monitoring of biostimulation at a Superfund site in Brandywine, Maryland, U.S.A. Inverse analysis of each of these data sets would be limited or impossible in a standard serial computing environment, which underscores the need for parallel high-performance computing to fully utilize the potential of electrical geophysical methods in hydrogeophysical applications.

Complex conductivity of soils

“…It extends the classical Direct Current (DC) resistivity method, which has been broadly used in hydrogeophysics in the last two decades (e.g., Johnson et al [2010]; Binley et al [2015]). In spectral induced polarization, the frequency dependence of both electrical resistivity and the phase shift between the electrical field and the current are independently measured and analyzed over a range of frequencies (e.g., Kemna et al [2012]).…”

Electrical Resistivity Imaging and the Saline Water Interface in High-Quality Coastal Aquifers

“…Optimized arrays have potential to reduce time-of-acquisition with improved resolution Ishola et al (2015) and Loke et al (2014a Joint/collaborative groundwater and ERI inversion Joint/collaborative groundwater flow and transport modeling, coupled with geo-electrical inversion of ERI data, has potential to improve spatial and temporal resolution of the seawater wedge, mixing zone and fresh groundwater. Also inversion outcomes based on continuous monitoring of wells and ERI transects can then be used to better predict future movements of the seawater interface under various abstraction scenarios Beaujean et al (2014), Johnson et al (2010) and Nguyen et al (2009) Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creat iveco mmons .org/licen ses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.…”

Re-Inversion of Surface Electrical Resistivity Tomography Data from the Hanford Site B-Complex

“…Recognizing these limitations and the potential for enhanced ERT characterization and time-lapse imaging at contaminated sites, a joint effort was initiated in 2007 by the U.S. Department of Energy (DOE) Office of Science, with later support from the DOE Office of Environmental Management and the U.S. Department of Defense, to develop a high-performance distributed memory parallel 3D ERT inversion code capable of optimally processing large ERT data sets. The culmination of this effort was the development of E4D (Johnson et al 2010(Johnson et al , 2012. The Hanford Site is a former weapons grade plutonium production facility that was initiated in 1942 as part of the Manhattan Project, and was operated until the early 1990s.…”

“…Effectively inverting a data set of this size with optimal imaging resolution is a significant computational challenge. Johnson et al (2010) presented a scalable ERT inversion algorithm, E4D, which enables large ERT data sets to be inverted on parallel distributed memory computing systems. The algorithm is based on a finite element solution to the Poisson equation on an unstructured tetrahedral mesh (Gunther et al 2006), enabling optimal mesh configurations that honor surface topography, known boundaries or subsurface structures, and with efficient refinement around the electrodes.…”