Coastal beaches are vital for recreation, tourism, and ecosystem health. However, they are increasingly threatened by fecal contaminants as indicated by high concentrations of fecal indicator bacteria (FIB). These bacteria can enter beach environments through human wastewater, stormwater runoff, and animal waste, accumulating in the sand and shallow groundwater. Natural coastal processes such as tides and waves can then mobilize and transport these contaminants across the land-sea boundary, posing risks to public health and marine ecosystems. This project will investigate how coastal hydrologic forces, including tidal fluctuations and wave action, influence the accumulation, movement, and discharge of FIB in beach aquifers. The research team will conduct fieldwork and groundwater sampling at two beaches in Hawaiʻi where FIB contamination is known to occur, and will develop advanced computer models to simulate how bacteria move through beach sediments. The findings will improve prediction and management of water quality risks in coastal zones. Broader benefits of the project include training two graduate students and engaging undergraduate students through the University of Hawaiʻi at Mānoa’s Undergraduate Research Opportunities Program. The team also plans to involve local communities through educational outreach and citizen science activities to support long-term coastal water stewardship in Hawaiʻi. Fecal contamination is an increasing concern in coastal beach environme