Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor

Power, Christopher

Abstract

Effective characterization and monitoring of subsurface processes associated with the remediation of sites contaminated by dense non-aqueous phase liquids (DNAPLs) remains a substantial environmental challenge. Geophysical techniques such as direct current (DC) resistivity and induced polarization (IP) offer the potential to considerably enhance our understanding of such complex phenomena occurring in the subsurface. However, despite extensive research highlighting the benefits of employing IP – in the time domain (DCIP) and/or frequency domain (spectral IP, SIP) – for contaminant investigations, more research is needed to understand the role of IP for monitoring DNAPL remediation. The goal of this thesis was to evaluate the DCIP and SIP techniques for tracking the remediation of DNAPLs. A novel combined DNAPL-DCIP model was developed, and realistic field-scale numerical simulations were performed, demonstrating that DCIP can provide valuable information on (i) subsurface lithology which controls DNAPL source zone architecture, and (ii) full-phase DNAPL mass removal over time via groundwater dissolution. Static laboratory column experiments highlighted the sensitivity of SIP to track changes in soils following the addition of remedial amendment fluids such as colloidal activated carbon (CAC) and subsequent destruction via smoldering combustion remediation. A suite of dynamic flow-through column experiments was then conducted to show the effectiveness of SIP to monitor temporal CAC progression in soils. In contrast, SIP had limited sensitivity to aqueous phase DNAPL and its adsorption to CAC. This thesis presents new work on evaluating DCIP and SIP at DNAPL-impacted sites, with a specific focus on the IP phenomena. The work contributes new knowledge to help clarify the potential role that these techniques could play in characterization and monitoring activities at DNAPL sites undergoing remediation.

Summary for Lay Audience

The chemicals that have been manufactured, used, and then disposed of by humans over years of urbanization and industrial activities can make their way into the ground where they can stay for many decades and continuously pollute soil and water. To clean up this pollution underground, we first need to know where it is and then be able to tell whether our clean-up strategies are working. Normally, we have drilled and dug our way into the ground to see what is happening, but this takes a lot of work, energy, and money. An attractive approach to this is the use of electrical detection techniques that can see these chemicals without going into the ground, much like a metal detector or x-ray. One popular electrical technique can tell us how resistive materials in the ground are to electrical current flow and how long these materials can hold an electrical charge. The work presented in this thesis investigates how well this technique can work to see the changes in the ground when a chemical is being cleaned up. This was done using a bunch of computer simulations and experiments in the laboratory on small samples of soils and chemicals. The results from this work show that this technique has good value to first locate and understand the pollution and how and why it is spread out the way it is. Then this technique can follow the changes in the ground after clean-up fluids are introduced and whether the clean-up is working or not. Overall, this thesis provides us with new information on the benefit of this technique and whether it helps us to locate and clean up pollution in the ground.

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