Currently, many remediation approaches are financially prohibitive or unrealistic to remediate deep, persistent dilute plumes of chlorinated ethylenes. This thesis outlines a new remediation approach designed to increase the residence time of in-situ dense chemical oxidants. This will be accomplished through the manipulation of the viscosity of the remediation chemicals and by taking advantage of natural aquifer heterogeneities. Dense chemical oxidants have advantages over more traditional remediation systems because they are relatively affordable, they require little maintenance, and they can be placed in targeted areas to maximize their effectiveness. Because they can be used to target specific areas, dense chemical oxidants have the ability to mitigate large, deep volatile organic compound (VOCs) plumes in aquifers. I postulate that the use of dense chemical oxidants can be enhanced further with the development of methods that will allow for the slow release of remediation chemicals over an extended period of time.
The first chapter identifies the problems addressed in this thesis. The second chapter analyzes the effect of heterogeneities on the movement of hypersaline solutions and demonstrates the modeling of dense, viscous solutions. The third chapter investigates the movement of dense solutions by gravity alone. The final chapter provides a general conclusion to the thesis. This thesis is part of a larger body of work funded by the Strategic Environmental Research and Development Program (SERDP), which is funded by the United States Department of Defense, Department of Energy, and Environmental Protection Agency.
In chapter 2, it was found that the lenticular media used in the experiments of Schincariol and Schwartz (1990) actually decreased solute residence time due to the high permeability of highly permeable lenses. These high permeability lenses also prevented the downward transport of plumes. One advantage found in this media, however, was that these lenses enhanced solute mixing. This is important because mixing helps spread remediation chemicals throughout larger portions of a contaminated aquifer. Results from chapter 2 also found that the variable-density flow and transport numerical model, MITSU3D (Ibaraki, 1998), was appropriate to model the dense, viscous solutions created by silica grout and that a long-term source of oxidant could be produced using silica grout to increase the viscosity of the remediation chemicals.
Results of chapter 3 analyzed the importance of permeability, instabilities, heterogeneous lenses, and source zone size on the movement of dense solutions by gravity alone in a media with alternating high and low permeable layers. It was found that the permeability of the less permeable layer played a significant role in plume development by slowing the downward transport of dense fluid. Lenses were also shown to significantly affect results by acting as conduits for the mixing and guidance of dense fluid. Instabilities and source zone size were shown to have only marginal effects on plume development.