Evaluating four-dimensional time-lapse electrical resistivity tomography for monitoring DNAPL source zone remediation

Christopher Power; Jason I Gerhard; Marios Karaoulis; Panagiotis Tsourlos; Antonios Giannopoulos

doi:10.1016/j.jconhyd.2014.04.004

Evaluating four-dimensional time-lapse electrical resistivity tomography for monitoring DNAPL source zone remediation

J Contam Hydrol. 2014 Jul:162-163:27-46. doi: 10.1016/j.jconhyd.2014.04.004. Epub 2014 May 5.

Authors

Christopher Power¹, Jason I Gerhard², Marios Karaoulis³, Panagiotis Tsourlos⁴, Antonios Giannopoulos⁵

Affiliations

¹ Department of Civil and Environmental Engineering, University of Western Ontario, London, Ontario, N6A 3K7, Canada. Electronic address: cpower9@uwo.ca.
² Department of Civil and Environmental Engineering, University of Western Ontario, London, Ontario, N6A 3K7, Canada. Electronic address: jgerhard@uwo.ca.
³ Department of Geophysics, Colorado School of Mines, Golden, CO, 80401, USA. Electronic address: marios.karaoulis@gmail.com.
⁴ Department of Geophysics, Aristotle University of Thessaloniki, 54124, Thessaloniki, Greece. Electronic address: tsourlos@geo.auth.gr.
⁵ School of Engineering, The University of Edinburgh, Edinburgh, EH9 3JL, UK. Electronic address: a.giannopoulos@ed.ac.uk.

PMID: 24854903
DOI: 10.1016/j.jconhyd.2014.04.004

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.

Keywords: 4D time-lapse monitoring; DNAPL; Electrical resistivity tomography; Geophysics; Remediation.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Electric Conductivity*
Environmental Monitoring / methods*
Environmental Restoration and Remediation*
Groundwater / chemistry
Models, Theoretical
Water Pollutants, Chemical / analysis*

Substances

Water Pollutants, Chemical