In the Mix: Pollution Remediation and Prevention in Groundwater Systems
There is an old adage in real estate that identifies the most important thing in purchasing a home or business: “Location. Location. Location.” The same can be said of global groundwater supplies in that the location of the water, as well as the interaction of chemical species located within the water, affect its potability. Of course, remediating a specific hydrologic system is not as simple as moving across town. It involves understanding how different solids and liquids react when they come into contact with one another as they flow through the Earth’s subsurface and how that mix drives chemical reactions.
Whether speaking of a single homeowner, a community, or an entire country, the availability of clean water impacts quality of life. However, anything that comes in contact with the water can affect its quality — from the millimeter scale as water moves through complex porous architectures in the Earth’s subsurface through the kilometer scale, which makes up entire aquifers. Mixing, the process that dilutes solutes in a fluid or at the very least dissipates them throughout the fluid and allows them to be transported across a greater volume of the water’s flow field, also brings them into contact with a range of other chemical species within the water. How these species react to one another is controlled by the mixing process, which is influenced by the variety of species themselves, the velocity of the flow of the system, as well as the location of the hydrologic system in general.
In a project funded by the National Science Foundation’s Early Career Development program, Diogo Bolster, assistant professor of civil & environmental engineering & earth sciences, is developing an improved framework of how mixing affects the dilution, reaction, and transport of materials and pollutants in the environment. This is critical as studies by the National Research Council confirm that current remediation strategies fail to adequately remediate polluted sites as much as 90 percent of the time. The challenge is not that engineers and scientists do not understand general mixing and chemical reactions on the local scale in a well-mixed, controlled reactor; that is much easier to predict. Rather it is that real environmental systems are complex: nothing in the real world is uniform and homogeneous. Physical and chemical heterogenity, uibiquitous in the natural environment, changes mixing and reaction patterns. Thus, they exhibit atypical behaviors that are not consistent with observations from controlled homogeneous lab experiments, including turbulent environmental flows, sediment transport, and irreversible biomolecular reactions.
Using a variety of synthetic and realistic small-scale pore structures, as well as large-scale configurations, Bolster and his team are conducting computational experiments to validate their findings from the data they obtained in previous project, which were focused on mixing and mixing-driven phenomena. The information they glean could assist in the development of additional tools to assess and design improved protection strategies for water resources not yet compromised as well as new remediation strategies for already affected areas. The information will also be used to develop educational applications for K-12 educational applications and an openly shared online video resource to help generate a broader, public understanding of groundwater and contamination processes.
Paster, A.; Bolster, D.; and Benson, D.A., “Connecting the Dots: Semi-analytical and Random Walk Numerical Solutions of the Diffusion-Reaction Equation with Stochastic Initial Conditions,” Journal of Computational Physics, 2014, 263, 91-112.
Ding, D.; Benson, D. A.; Paster, A.; and Bolster, D., “Modeling Biomolecular Reactions and Transport in Porous Media via Particle Tracking,” Advances in Water Resources, 2012, 53, 56-65.
Castro, E.; Fernandez-Garcia, D.; Carrera, J.; and Bolster, D., “Visualization of Mixing Processes in a Heterogeneous Sand Box Aquifer,” Environmental Science and Technology, 2012, 46, 6, 3228-3235.
Bolster, D.; deAnna, P.; Benson, D. A.; and Tartakovsky, D.M., “Incomplete Mixing and Reactions with Fractional Dispersion,” Advances in Water Resources, 2012, 37, 86-93.
Bolster, D.; Barahona, M.; Dentz, M.; Fernandez-Garcia, D.; Sanchez-Villa, X.; Trichero, P.; Valhondo, C.; and Tartakovsky, D.M., “Probabilistic Risk Assessment Applied to Contamination Scenarios in Porous Media,” Water Resources Research, 2009, 45, 6, W06413, doi:10.1029/2008WR007551.