Understanding the role of freeze-thaw processes on contaminant transport in the vadose zone

Freeze–thaw cycles are a defining feature of northern climates, yet their influence on groundwater recharge and water quality remains poorly understood. In the vadose zone, the freezing and melting of water in unsaturated porous media drives complex interactions between thermal, hydrologic, and mechanical processes. While these processes are ubiquitous in regions such as Wisconsin, significant knowledge gaps remain in how freeze–thaw dynamics control contaminant transport, remobilization, and dispersion.

This project seeks to establish a mechanistic understanding of how freeze–thaw cycles influence preferential flow, recharge timing, and solute transport in the vadose zone. We hypothesize that freeze–thaw cycling accelerates contaminant migration to groundwater through preferential flow pathways, while also extending breakthrough due to enhanced sorption from solute quenching during freezing. To test these hypotheses, we will conduct highly controlled laboratory experiments using a quasi-3D Hele-Shaw cell system designed to simulate porous media under freeze–thaw conditions.

The research is structured around three objectives: (1) quantify infiltration rates and preferential flow during transient melt events to determine how contaminants migrate into groundwater during mid-winter thaws; (2) measure solute transport during repeated freezing and melting cycles to evaluate the impacts on dispersion, breakthrough curves, and contaminant persistence; and (3) assess whether sorbing solutes such as PFAS experience enhanced retention due to concentrated liquid water lenses that form during freezing. These experiments will produce high-resolution datasets that are not achievable in field studies, allowing for quantification of the processes that govern contaminant fate during freeze–thaw conditions.

The outcomes of this project will advance the fundamental science of cryogenic–hydrologic coupling in unsaturated porous media and provide experimental benchmarks for the development of improved continuum-scale models of heat, water, and solute transport in cold-region vadose zones. This research will generate insights into how freeze–thaw processes control contaminant mobilization, recharge variability, and groundwater vulnerability in northern climates.