Mixing is the fundamental process that leads to the dilution of solutes and brings chemical species into contact with one another. It is a key driver of biogeochemical reactions in hydrologic systems. Flows through the Earth's subsurface are by their nature complex due to the ubiquitous occurrence of heterogeneity at multiple scales. At the millimeter scale the fluid must move through complex porous architectures. At meter to kilometer scales heterogeneity in the geologic makeup of an aquifer becomes important. Each of these heterogeneities acts in such a way as to distort the shape of solute plumes, which can have a strong influence on how quickly and where mixing will occur. Since mixing strongly affects how substances dilute and react, a better understanding of mixing is necessary to ultimately accurately predict movement of both inert and reactive solutes. The overarching goal of this work is to develop an improved theoretical framework of how heterogeneity affects mixing. This will be done by computationally simulating flow and transport through a variety of synthetic and realistic small-scale pore structures as well as larger scale geologically heterogeneous configurations. Simultaneously, theoretical descriptions of mixing, driven by observations from the computational experiments, will be developed. Ultimately, to validate these theoretical developments, the theory will be tested on data from previous laboratory experiments that explore mixing and mixing-driven phenomena.
Despite our image of Earth as "the water planet," global supplies of uncontaminated surface and groundwater are indispensable, yet fragile, natural resources. Threats to freshwater supplies in the form of contamination must be understood to assure sustainable supplies, as well as to guide effective remediation and future development. However conventional models that do not account for heterogeneity (i.e. the natural variability in the geologic makeup of aquifers) are inadequate. For example, studies by the National Research Council show that court-ordered remediation strategies can fail to adequately remediate polluted sites 90% of the time. The models and novel theoretical description provided by this work, incorporating the influence of heterogeneity, will ultimately provide policy makers, legal authorities, stakeholders and managers with improved tools to better design and assess remediation strategies and protect current water resources. Additionally, to ensure the success of approaches to making water use more sustainable, a broader understanding of groundwater and contamination processes is needed by the general public. To this end, exploiting novel advances in computer tablet technology, this project will develop educational tablet 'apps' for hydrology education aimed at K-12 and the general public. The work will be conducted in close collaboration with local primary, middle and high school teachers. At the university level new courses on flow, transport, mixing and reactions in heterogeneous subsurface environments will be developed. This will include the development of openly shared online video resources to aid in conveying complex phenomena in a tangible manner.
Project leader: Diogo Bolster