The partially water-saturated soil region that extends from the Earth’s surface to the water table controls the access of nutrients and contaminants to the Earth’s aquifers. Understanding how dissolved chemicals mix and react when water infiltrates into these porous environments is thus critical. Despite infiltration being inherently dynamic, our understanding of mixing and reaction at the pore-scale is currently limited to steady flow. Leveraging recent breakthroughs by team members, this project aims to break new ground by characterizing and predicting mixing and reaction during water infiltration. The key outcome will be unique numerical data and theories revealing new laws for how air-water interface dynamics control mixing and reaction in porous media.