Human-made chemicals in the environment can flow through soils to contaminate groundwater that is critical to daily life and the Nation?s prosperity. In the ground, many such contaminants are active at surfaces of solid particles and the interfaces between air and water. Because of this surface-activity, significant amounts of toxic chemicals can accumulate in the spaces between air and water in soils and cause long-term threats to essential groundwater. While most of the air?water interfaces in soils are from thin water films on soil-grain surfaces, how the surface-active contaminants and thin water films interact is still not well understood. Researchers will investigate the processes that govern these complex interactions to improve the tools that scientists use to predict and to assess the contamination risks from human-made chemicals such as the perfluoroalkyl and polyfluoroalkyl substances commonly known as PFAS. The results of this research will lead to more effective cleanup strategies to reduce harm to human health from PFAS and similar contaminants. The scientists will use this research on groundwater PFAS contamination as a resource to collaborate with and support high school teachers with innovative curriculum tools, and training to engage Arizona high-school students, advance their interest in STEM, and enhance their experiential and critical thinking skills. The project goals are to advance the fundamental understanding of the thin-film-mediated retention and mass-transfer processes for surface-active contaminants in vadose zones and to develop a cross-scale framework that incorporates this new information to improve macroscopic transport models. The research will combine thin-film theory, experimental image characterization, and multiscale modeling approaches. The methodological approaches to differentiate the thin-film and bulk capillary air?water interfaces in soils will potentially transform how hydrologists conceptualize the movement of surface-active contaminants in vadose zones. The PI will partner with the University of Arizona?s cooperative-extension Arizona Project WET for Water Education, a STEM teacher in a Tucson public school, and a College of Education professor. Together, the project education team will develop, test, and formalize a fully inquiry-based educational program that involves hands-on experiences in building and using physical and digital models for deepening understanding and problem solving. The formalized educational program will be available to all high schools in Arizona via the existing infrastructure of Arizona Project WET supported by Tucson Water and the Arizona Department of Water Resources. This award is co-funded by the Hydrologic Sciences and Environmental Engineering programs 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.