Stormwater runoff is an underappreciated but significant pathway for PFAS transport through the environment and into drinking water supplies. As rain moves across urban surfaces — rooftops, roads, parking lots, and industrial areas — it picks up PFAS from a variety of sources and carries them into storm drains, surface water bodies, and ultimately groundwater. Managing this diffuse PFAS source presents unique challenges compared to point-source contamination from industrial facilities.
PFAS Sources in Urban Stormwater
Multiple sources contribute PFAS to urban stormwater:
Building materials: Architectural coatings, treated fabrics, and certain roofing materials containing PFAS shed these compounds when exposed to rain. Studies of roof runoff have found elevated PFAS concentrations, particularly in areas with older PFAS-containing materials.
Road surfaces and traffic: Road markings, tire and brake materials, and fuel combustion byproducts can all contribute PFAS to road runoff. PFAS have been detected in tire debris, which fragments into fine particles that wash off road surfaces during rain events.
Fire suppression system discharges: Urban fire departments use AFFF (aqueous film-forming foam) for certain fire types. Accidental discharges, equipment testing, and training exercises release PFAS-laden foam that enters storm drains.
Industrial area runoff: Facilities that use or manufacture PFAS may have surface contamination that washes off during rain events, contributing to area stormwater loads.
Atmospheric deposition: PFAS can travel through air and deposit on urban surfaces during dry periods, then wash off during rain — a phenomenon documented in studies of urban-area PFAS loadings.
PFAS Concentrations in Urban Stormwater
Published studies of urban stormwater PFAS concentrations show considerable variability, but concentrations in the range of 10–1,000 ng/L (ppt) are common, with occasional peaks exceeding this range near fire stations, industrial areas, or following fire events. These concentrations, while below typical drinking water standards, contribute to cumulative loading in receiving water bodies.
A particularly well-studied case is the San Francisco Bay Area, where stormwater PFAS inputs have been quantified as a significant contribution to bay water contamination — affecting fish consumption advisories and potentially drinking water supplies that draw from the Bay watershed.
Treatment of PFAS in Stormwater
Treating PFAS in stormwater is far more challenging than point-source treatment because:
- Stormwater volumes are massive and highly variable — systems must handle peak flows that can be 100× base conditions
- PFAS concentrations are relatively dilute, making treatment economics challenging
- Stormwater is typically managed through large infrastructure designed for volume control, not contaminant removal
Emerging approaches include:
Bioretention cells with amended media: Conventional bioretention (rain gardens) do not remove PFAS, but research shows that amending the media with activated carbon or ion exchange resin significantly improves PFAS retention. Field pilot studies have shown 50–90% PFAS reduction through amended bioretention.
Constructed wetlands with media amendments: Similar principles applied at larger scale for treating stormwater before it enters sensitive receiving waters.
End-of-pipe treatment: For high-volume, lower-concentration stormwater, granular activated carbon contactors or ion exchange columns can provide meaningful PFAS reduction.
Implications for Drinking Water Utilities
Utilities that draw from surface water bodies receiving PFAS-laden stormwater face seasonal and event-driven PFAS concentration spikes. Conventional water treatment (coagulation, sedimentation, filtration, disinfection) does not remove PFAS. Utilities in affected areas are increasingly evaluating or implementing advanced treatment — primarily granular activated carbon contactors and/or membrane treatment — as additional barriers.
For households served by these utilities, point-of-use reverse osmosis or certified activated carbon systems provide a reliable final barrier against variable PFAS levels in the tap water supply.