Per- and polyfluoroalkyl substance (PFAS) compounds are quickly becoming known as “forever compounds”, and as regulators rush to develop guidelines for various media and understand their toxicity, assessors and researchers strive to understand their fate and transport in various environments. These two key components need to be brought together in order to effectively manage risks and develop site strategies, particularly in dynamic environments such as aquatic ecosystems. An additional challenge comes when there are regulatory and public pressures to make rapid site strategy decisions based on limited information. This presentation will present a unique case study of an unconventional, multi-pronged site strategy developed in response to a release of PFAS-containing firefighting foam and other contaminants to a riverine environment. The fire involved the ignition of rubber at an industrial facility. The run-off from the firefighting activities entered the storm sewer system and discharged to a nearby creek that drained through a largely agricultural area. Public and regulator concern for both human and ecological receptors was high, and regulatory orders were promptly issued. This spawned an emergency containment program, along with the rapid assessment of surface water and potable groundwater impacts to help define the extent and magnitude of the release and inform future containment and clean up actions. Selected PFAS compounds and other contaminants were found in surface water several kilometres downstream of the site, necessitating surface water management measures to mitigate further spread, and implementation of a robust surface water sampling and assessment program. While this program facilitated defining the contamination extent, challenges to site decisioning arose from knowledge gaps related to PFAS fate and transport, PFAS toxicity to aquatic communities, additive toxicity from PFAS and other contaminants, and other potential historical contaminating activities in the area that could have been contributing to the observed contaminant signature. As such, the need for additional clean-up and/or risk management in response to the fire release was uncertain. Given that active remedial strategies for aquatic environments (e.g., dredging, containment) are costly, intrusive and can have a reduced net environmental benefit compared to a longer-term, natural recovery solution, a multi-pronged site assessment and management strategy was then developed as follows: Evaluation of background conditions to establish the limits of the contribution of the fire to the contamination. This helped to reduce the footprint requiring management/remediation. Completion of a risk evaluation that combined incidental observations and available toxicological literature values to assess the potential for risks to the aquatic community. Implementation of a longer-term monitoring program of both surface water and sediment over time to confirm the natural recovery of the system In addition to providing a sustainable and long-term solution to assessing and managing the contamination from the fire, this strategy proved effective at addressing public and regulatory concerns, limiting remedial costs, and advancing the site towards closure in a reasonable timeframe. Tiana Robinson, Senior Hydrogeologist, Principal and Discipline Leader, Stantec Tiana Robinson is a Senior Hydrogeologist, Principal and Discipline Leader based out of Stantec’s Waterloo office. She has over thirteen years’ experience in site management and remediation; conducting and managing environmental site assessment; soil, sediment, and groundwater remediation; contaminant hydrogeology; excess materials and waste management; spill response; and, risk assessment projects in a variety of client service areas across Canada and the U.S. Through these projects, Tiana has fulfilled multiple roles, including technical lead, project management, client management, regulatory and stakeholder consultations, and litigation support. She holds a B.Sc. in Geology from the University of Minnesota and an M.Sc. in Earth Sciences from the University of Waterloo. Tiana is a Qualified Person Environmental Site Assessments under Ontario Regulation 153/04 and is registered as a Practicing Member of the Association of Professional Geoscientists of Ontario and the Association of Professional Engineers and Geoscientists of Alberta.