Collaborative Research: Predicting Colloid Distribution in Subsurface Granular Media by Resolving Nanoscale Heterogeneity and Continuum-Scale Flow Field Topologic Impacts

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Protection of groundwater resources from pathogens and other contaminants, as well as cleanup of legacy contamination, requires the ability to predict the mobility of contaminants in groundwater systems. Under environmental conditions, interactions with media surfaces may lead some very small particles known as colloids to move far greater distances than expected, leaving practitioners of groundwater resource protection and remediation without a viable way to predict their transport. This work integrates measurements of nanoscale characteristics of surfaces with transport and modeling experiments within a pore-scale theoretical framework that can be used to better predict the mobility of colloids. In addition to developing modeling tools for researchers and training graduate students, the knowledge gained will be disseminated to the general public by working with middle and high school teachers, participating of informal community-level events, and collaborating on Learning Abroad classes. The observed transport behavior of colloids at the pore scale may be reproduced through inclusion of nanoscale heterogeneity in mechanistic trajectory simulations. Currently such representation is determined empirically via match to transport experiments but lacks testing on known nano-patterned surfaces. The proposed project will combine experimental observations of colloid interaction with nano-patterned surfaces and mechanistic trajectory simulations to address knowledge gaps on (1) relationships between discrete representations of nanoscale surface heterogeneities and measurable physicochemical surface characteristics and (2) mechanistic parameterization of the fate of colloids beyond the pore scale. Nano-pattern surfaces will be characterized using force-volume atomic force microscopy. Multi-grain micromodel experiments, both in the laboratory and in silico/computational, will elucidate links between pore scale flow fingering, accumulation of near surface colloids, depletion of a fast-attaching subpopulation of colloids, and deviation from expected retention profiles under unfavorable attachment conditions. Results will be integrated with state-of-the-art upscaling approaches to build consistent theoretical models to predict colloid transport processes at continuum scales. The proposed research will: 1) improve our theoretical understanding of colloid transport in groundwater and other unfavorable contexts to the benefit of water resource protection and remediation: 2) provide a suite of simulation tools for practitioners and researchers; 3) enhance graduate student education through short courses regarding particle transport and surface interaction; and 4) outreach a broader population regarding the role of particulates in trace element fate and transport in subsurface and surface aquatic systems. Outreach include engaging middle and high school science teachers during summer internships, participation in community-level events, such as Science Alive and Science Sunday, held at libraries and local parks, and collaboration on Learning Abroad classes in Ecuador.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.