Stormwater as a PFAS Transport Pathway
Urban stormwater collects PFAS from treated impervious surfaces — parking lots coated with PFAS sealers, buildings with PFAS-treated exterior surfaces, and roads where PFAS-containing tire wear particles and road paint accumulate. Rain and snowmelt mobilize these accumulated PFAS and transport them through storm drain systems to receiving water bodies.
Stormwater from fire training areas and airports where AFFF was used carries extremely high PFAS concentrations — particularly during first-flush events when rain mobilizes PFAS accumulated on surfaces between rain events. Stormwater from these source areas can contain PFAS at parts-per-billion levels, orders of magnitude above drinking water standards.
Regulatory Framework for PFAS in Stormwater
Stormwater from industrial facilities is regulated under NPDES (National Pollutant Discharge Elimination System) permits through the Clean Water Act. Industrial stormwater general permits are being updated to include PFAS monitoring and, in some jurisdictions, PFAS treatment requirements for high-risk industrial categories.
Municipal separate storm sewer systems (MS4s) — the storm drains in cities and suburbs — face growing pressure to address PFAS in their stormwater programs. EPA is developing guidance on PFAS best management practices for MS4 permits, and some state programs are already requiring PFAS monitoring and source control in MS4 permits for communities near known PFAS sources.
Treatment Technologies for PFAS Stormwater
Conventional stormwater treatment — detention basins, vegetated swales, and bioretention cells — does not effectively remove PFAS. Specialized treatment technologies including GAC, ion exchange, and constructed wetlands with PFAS-adsorbing media are being adapted for stormwater applications, but the variable flow rates and dilute concentrations characteristic of stormwater create technical challenges.
Source control — preventing PFAS from reaching stormwater in the first place — is the most cost-effective approach. Prohibiting PFAS-based products in areas where runoff enters drinking water sources, transitioning away from PFAS-treated pavement sealers and surface coatings, and managing AFFF legacy contamination at source areas reduces the stormwater PFAS load without requiring end-of-pipe treatment.