Doctor of Philosophy
Civil and Environmental Engineering
Dr. Jason Gerhard
Cleaning up sites contaminated with dense non-aqueous phase liquids (DNAPLs) remains a challenging geoenvironmental problem. The performance of site remediation methods is difficult to assess without a practical, non-destructive technique to map where and how quickly DNAPL mass is being reduced. The promise of electrical resistivity tomography (ERT) in this context has not been realized, in part because traditional ERT methods were used to solve the near-impossible problem of mapping the initial DNAPL outline. However, new developments in ERT have emerged that focus on resolving subsurface changes over time. The objective of this work was to evaluate the potential of time-lapse ERT for mapping DNAPL mass reduction during remediation. A new numerical model was developed to explore this potential at the field scale, generating realistic DNAPL scenarios and predicting the response of an ERT survey. Central to the model was the development of a novel linkage between hydrogeological and geoelectrical properties. Sensitivity studies conducted at a variety of scales demonstrated that the linkage routine is robust and the DNAPL-ERT model is a valuable research tool. Moving forward to consider site applications, a new time-lapse method, four-dimensional (4D, three spatial dimensions plus time) ERT, was identified as highly promising. A laboratory experiment was conducted that demonstrated, for the first time, the effectiveness of 4D ERT applied at the surface for mapping an evolving DNAPL distribution. Independent simulation of the experiment demonstrated the reliability of the DNAPL-ERT model for simulating real systems. The numerical model was then used to explore the 4D surface ERT approach at the field scale for monitoring a range of realistic DNAPL remediation scenarios. The approach showed excellent potential for mapping shallow DNAPL changes but deeper changes were not as well resolved. To overcome this limitation, a new surface-to-horizontal borehole (S2HB) ERT configuration was proposed. The potential benefit of this innovation was first demonstrated by using the numerical model to compare surface ERT to S2HB ERT for a realistic, field scale DNAPL scenario with remediation at depth. A second laboratory experiment then demonstrated that this new configuration does better resolve changes in DNAPL distribution relative to surface ERT, particularly at depth. Independent simulation of the experiment showed that S2HB ERT is reliably modelled. Overall, this research has substantially advanced ERT in the context of DNAPL sites, with novel contributions to theory, modelling, demonstrations with physical systems, and simulations of realistic field scenarios. As a whole, this work demonstrates that, with these innovations, ERT exhibits significant potential as a DNAPL remediation site monitoring tool.
Power, Christopher, "Electrical Resistivity Tomography for Mapping Subsurface Remediation" (2014). Electronic Thesis and Dissertation Repository. 2078.