One of the great challenges in making accurate predictions of reactive contaminant transport in subsurface flows is accounting for the impact of geological heterogeneity. For many real life scenarios, prediction using traditional approaches that are valid in homogeneous environments simply cannot capture many of the complex features that have been observed in field and laboratory experiments. For the case of non-reactive contaminants, several promising theoretical methods have emerged. Predicting chemical reactions in subsurface flows is by its nature a more complex problem and it is not clear whether the novel methods put forth for non-reactive contaminants offer the same potential for success in this area. This project aims to address the applicability of methods designed for conservative transport to the problem of predicting non-conservative transport. Specifically, the reasons for lack of predictive capability and the needed improvement in the mathematical description(s) is a primary focus of this research. These concerns will be addressed using theory, numerical simulations and laboratory experiments in a synergistic manner. The first part of this work will focus on studying mixing, which is a fundamental driver of reactions. Numerical and laboratory experiments will be conducted in constructed heterogeneous porous media and comparisons between theoretical predictions and experimental data will highlight limitations in one or both of these approaches (modeling and laboratory). The experimental data will help to identify when and how fundamental assumptions associated with the theoretical models fail with the ultimate aim of circumventing limiting assumptions in the theory. The second part of this work focuses on studying chemical reactions, again via experiments and theory, to determine whether incorporating mixing, by itself, in a theoretical model is sufficient to improve prediction of reactive transport, or whether modifications of mixing and mechanisms related to chemical reactions will be necessary additions to existing models.
Current predictive tools and methods often provide policy makers, legal authorities, stakeholders and managers with unreliable information when it comes to making decisions regarding contaminants that undergo chemical reactions in groundwater systems. For a resource as valuable as water, which is already strained in many parts of the world, this can give rise to great concern. One specific goal of this work is to improve the current theoretical understanding of reactive contaminant transport in groundwater systems. The successful completion of this project holds substantial promise to provide the hydrological and environmental engineering communities with new, substantially improved, tools. These tools will allow experts to better assess and design strategies for cleanup and remediation at already contaminated sites. It will also provide more reliable information to allow for better management and protection strategies of existing groundwater resources and hopefully help guide decision makers in the development of future groundwater policies. Finally, this research will involve research experiences for both undergraduate and graduate students at the University of Notre Dame.