title: Evaluating four-dimensional time-lapse electrical resistivity tomography for monitoring DNAPL source zone remediation.
abstract: Practical, non-invasive tools do not currently exist for mapping the remediation of dense non-aqueous phase liquids (DNAPLs). Electrical resistivity tomography (ERT) exhibits significant potential but has not yet become a practitioner's tool due to challenges in interpreting the survey results at real sites. This study explores the effectiveness of recently developed four-dimensional (4D, i.e., 3D space plus time) time-lapse surface ERT to monitor DNAPL source zone remediation. A laboratory experiment demonstrated the approach for mapping a changing NAPL distribution over time. A recently developed DNAPL-ERT numerical model was then employed to independently simulate the experiment, providing confidence that the DNAPL-ERT model is a reliable tool for simulating real systems. The numerical model was then used to evaluate the potential for this approach at the field scale. Four DNAPL source zones, exhibiting a range of complexity, were initially simulated, followed by modeled time-lapse ERT monitoring of complete DNAPL remediation by enhanced dissolution. 4D ERT inversion provided estimates of the regions of the source zone experiencing mass reduction with time. Results show that 4D time-lapse ERT has significant potential to map both the outline and the center of mass of the evolving treated portion of the source zone to within a few meters in each direction. In addition, the technique can provide a reasonable, albeit conservative, estimate of the DNAPL volume remediated with time: 25% underestimation in the upper 2m and up to 50% underestimation at late time between 2 and 4m depth. The technique is less reliable for identifying cleanup of DNAPL stringers outside the main DNAPL body. Overall, this study demonstrates that 4D time-lapse ERT has potential for mapping where and how quickly DNAPL mass changes in real time during site remediation.
authors.affiliation: Department of Civil and Environmental Engineering, University of Western Ontario, London, Ontario, N6A 3K7, Canada. Electronic address: cpower9@uwo.ca.
authors.forename: Christopher
authors.initials: C
authors.lastname: Power
authors.affiliation: Department of Civil and Environmental Engineering, University of Western Ontario, London, Ontario, N6A 3K7, Canada. Electronic address: jgerhard@uwo.ca.
authors.forename: Jason I
authors.initials: JI
authors.lastname: Gerhard
authors.affiliation: Department of Geophysics, Colorado School of Mines, Golden, CO, 80401, USA. Electronic address: marios.karaoulis@gmail.com.
authors.forename: Marios
authors.initials: M
authors.lastname: Karaoulis
authors.affiliation: Department of Geophysics, Aristotle University of Thessaloniki, 54124, Thessaloniki, Greece. Electronic address: tsourlos@geo.auth.gr.
authors.forename: Panagiotis
authors.initials: P
authors.lastname: Tsourlos
authors.affiliation: School of Engineering, The University of Edinburgh, Edinburgh, EH9 3JL, UK. Electronic address: a.giannopoulos@ed.ac.uk.
authors.forename: Antonios
authors.initials: A
authors.lastname: Giannopoulos
mesh_terms: D004553:Electric Conductivity; D004784:Environmental Monitoring / Q000379:methods*; D052918:Environmental Restoration and Remediation; D060587:Groundwater / Q000737:chemistry; D008962:Models, Theoretical; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D014874:Water Pollutants, Chemical
keywords: 4D time-lapse monitoring; DNAPL; Electrical resistivity tomography; Geophysics; Remediation