About 99% of global unfrozen freshwater is stored in groundwater systems, and about 75% of near-surface groundwater aquifers on earth are fractured. Recent field studies have shown the presence of emerging contaminants such as microplastics, viruses, and harmful bacteria in groundwater, and fractures are often major pathways through which contaminants migrate long distances at anomalously fast rates. However, conventional groundwater models ignore fracture flow, and as a result, often fail to predict contaminant transport in the subsurface. To secure sustainable water resources, there is urgent need for a new model that predicts flow and transport in fractured media. This project presents an integrated research, education, and outreach plan that will advance the current practices of modeling fractured media and teaching fractured rock hydrogeology. This project will first combine visual laboratory experiments and direct numerical simulations to elucidate fundamental physical laws that govern flow and transport at single fracture scales. The identified key single-fracture scale processes will then be incorporated into field-scale models. Finally, the developed models will be validated through field experiments at a fractured aquifer site. The project has three major outreach and teaching activities that are directly synergistic with the proposed research: (i) a professional hydrogeologists’ working group will be formed to bridge the gap between academia, industry, and government agencies in the area of fractured rock hydrogeology, (ii) visual groundwater teaching tools will be developed for K-12 and college-level education, and lastly (iii) accessible modules based on a contaminated fractured aquifer site will be developed for a new urban field course.

Conventional groundwater models often treat aquifers as two-dimensional continuous porous media, thereby missing critical complexities that govern flow and transport in fractured aquifers. Recent studies have shown that complex three-dimensional (3D) flows can alter the overall mixing and reaction dynamics up to the field scale, but the underlying processes and how they scale up in fracture networks are still not well understood. This project will establish a mechanistic understanding of 3D flow effects on Transport, Mixing, and Reaction (TMR) at single-fracture scales and translate that knowledge across scales to predict processes at fracture network scales. This project first combines visual laboratory experiments and direct numerical simulations to elucidate how the interplay between fracture heterogeneity (e.g., fracture roughness and aperture variability) and flow boundary conditions (Reynolds number) controls 3D flows and TMR at single fracture scales. The single-fracture scale processes will then be incorporated into fracture network-scale models, and an upscaled modeling framework that predicts TMR will be developed. A comprehensive data set will be generated and analyzed with machine-learning-based methods to yield a powerful map that links upscaled model parameters to key medium properties and flow conditions. The developed upscaled model will be validated through controlled field tracer experiments at a fractured aquifer site. Overall, this project will transform how we understand and model fractured media and will provide a new foundation for modeling coupled biogeochemistry and fluid flow.

This proposal is co-funded by the Hydrologic Sciences and Education and Human Resources programs in the Division of Earth Sciences.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

National Science Foundation (NSF)
Division of Earth Sciences (EAR)
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Laura Lautz
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University of Minnesota Twin Cities
United States
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