Presenter: David Mays, associate professor, civil engineering, University of Colorado Denver
Topic: Reactive Transport, Dynamic Permeability and Feedback

Abstract
A host of biogeochemical processes occurs in soils and aquifers, such as mineral weathering, nutrient cycling, solute transport, in situ mining, and groundwater remediation. Soils and aquifers are porous media, which imposes two important constraints on the biogeochemistry. First, because porous media generally disallow turbulent flows, mixing is poor, which means that reactions are transport-limited. Second, because flow through porous media follows Darcy’s law, it depends on a crucial physical parameter called permeability, which determines how much flow results from a given difference in hydraulic head. Permeability has been recognized since the mid-1800s, but nearly 200 years later, we still have no reliable way of predicting it a priori. Permeability ranges over an incredible 13 orders of magnitude. Porous media have a great deal of spatial variability: In engineered porous media, homogeneous permeability is hard to create; in natural porous media, homogeneous permeability is virtually unknown. In addition to this spatial variability, permeability also manifests temporal variability from clogging processes including mineral precipitation, colloid filtration, biofilm growth, gas bubbles, and consolidation. Thus permeability is dynamic. And, to top it all off, permeability reflects a feedback process with reactive transport: High permeability regions have more transport, thus more reaction, which triggers clogging, which reduces the permeability, thus driving the flow and reactive transport elsewhere in the porous media. This seminar presents recent research on the fascinating and important topic of dynamic permeability. Starting with a background on clogging, we will review recent findings from experiments and simulations aimed at understanding reactive transport, dynamic permeability, and feedback. The reactive transport experiments offer new insight into the classic model reaction of sodium carbonate and calcium chloride forming calcium carbonate (i.e., calcite). In parallel, the simulations demonstrate a novel approach to infer dynamic permeability from sequential measurements of the groundwater velocity field, opening up a new avenue to study dynamic permeability through laboratory experiments with pore image velocimetry (PIV). The seminar will conclude with a few comments on future work and implications for biogeochemistry.

Bio
David Mays is an associate professor in the Department of Civil Engineering at the University of Colorado Denver. He earned his BS from the University of Pennsylvania in 1995, then taught high school through Teach for America and worked as a contractor at Los Alamos National Laboratory before earning his MS and PhD from the University of California Berkeley in 1999 and 2005, respectively. He has been at CU Denver since 2005, where he teaches fluid mechanics and hydrology, studies flow in porous media using ideas from complex systems science, leads the graduate track in Hydrologic, Environmental, and Sustainability Engineering (HESE) and advocates for broadening participation in engineering. He is a registered professional engineer (PE) in California and Colorado.