Quantification of the Impact of Hydrologic Controls on Anomalous Solute Transport and Mixing Dynamics in Partially Saturated Porous Media

As groundwater moves through the subsurface, it often undergoes chemical reactions as it mixes with other chemically distinct waters, which can facilitate the breakdown of pollutants into less harmful substances. These critical processes of mixing and reaction are significantly influenced by unsaturated conditions, where soil and sediment layers contain phases other than water, such as air or gas, within their pores. This project aims to investigate and quantify how flow, transport, and mixing are impacted by unsaturated conditions in subsurface hydrologic systems. Specifically, the project will use new experimental imaging methods in 3D-printed soil structures and novel numerical simulations to visualize and predict how fluids interact and explore how variations in water content and the physical characteristics of the porous matrix influence mixing and reaction outcomes. Collectively, this research will provide a robust scientific foundation for water resource management and advancing water science, ensuring the protection and sustainability of groundwater resources. Moreover, the project will facilitate impactful educational and training opportunities for students across all levels, complemented by public outreach and initiatives to enhance STEM education. This project will develop and use novel experimental techniques and mathematical models aimed at understanding the complexities of reactive transport in partially saturated porous media. The research focuses on investigating and quantifying the interrelated phenomena of anomalous transport, mixing, and chemical reaction in unsaturated porous media, combining pore- and Darcy-scale visual laboratory experiments and direct numerical simulations. The primary objectives include: 1) Investigating the effects of flow dynamics, medium heterogeneity, and the distribution of fluid phases on solute transport and dispersion using experimental observations in three-dimensional porous media. 2) Utilizing experimental data to assess the role of saturation in promoting reaction hotspots and enhancing mixing processes. 3) Employing pore-scale properties, flow and transport statistics, and reaction rates in reactive transport models to mechanistically describe and predict mixing and reaction. The project results will be relevant for the improved prediction and management of contamination of water resources that rely on the transport and mixing of chemicals to target polluted locations. This award is co-funded by the Hydrologic Sciences program and Established Program to Stimulate Competitive Research (EPSCoR). 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.