When It Rains, It PFAS: Stormwater as a Contamination Pathway
Stormwater runoff—rain and snowmelt flowing over impervious surfaces and contaminated land before reaching waterways—has emerged as a major PFAS transport pathway that traditional urban water management infrastructure is wholly unprepared to address. Unlike point source industrial discharges, which can be regulated through specific facility permits, stormwater PFAS loading is a diffuse, variable source that requires fundamentally different regulatory and technical approaches. Cities, counties, and stormwater agencies are grappling with PFAS in stormwater under regulatory frameworks designed for a different chemical era.
PFAS Sources in the Urban Stormwater Environment
Multiple PFAS sources contribute to urban stormwater contamination. PFAS-treated asphalt and pavement sealants applied to parking lots and driveways release PFAS compounds to stormwater as the coating degrades over time. PFAS-treated textiles—from outdoor furniture to clothing to building materials—shed PFAS to rainwater through surface contact. Industrial areas, former dry cleaning facilities, and automotive service centers contribute PFAS to stormwater through contaminated soil leaching during rain events.
Firefighting training and response activities represent episodic but high-concentration PFAS stormwater loading events. AFFF releases during fire suppression activities at commercial and industrial fires can introduce large PFAS masses directly to stormwater drainage systems, potentially impacting receiving water bodies acutely as well as depositing residual PFAS in drainage infrastructure that continues to leach to subsequent rain events.
Stormwater Permit Limitations and Regulatory Gaps
Municipal Separate Storm Sewer System (MS4) permits under the Clean Water Act govern stormwater discharges from municipal drainage systems. These permits typically require best management practices (BMPs) for controlling conventional pollutants—sediment, nutrients, trash—but have rarely included PFAS-specific requirements. As water quality standards for receiving water bodies incorporate PFAS limits, MS4 permit writers face the challenge of requiring PFAS control from a diffuse, multi-source stormwater system for which no established “best management practice” for PFAS reduction exists.
Industrial stormwater permits under the Multi-Sector General Permit (MSGP) are beginning to incorporate PFAS monitoring requirements for sectors with known PFAS use. The EPA’s 2021 MSGP updates included PFAS monitoring benchmarks for aerospace manufacturing, metal finishing, and other PFAS-intensive sectors—marking the first time PFAS appeared in stormwater permit conditions at the federal level.
Treatment Technologies for PFAS in Stormwater
Treatment of PFAS in stormwater faces challenges unique to this matrix: highly variable flows, complex chemical mixtures, dilute PFAS concentrations, and the absence of centralized treatment infrastructure for managing large stormwater volumes. Granular activated carbon (GAC) systems deployed in stormwater detention basins or inline treatment systems can remove PFAS from stormwater, but carbon exhaustion rates at low PFAS concentrations result in high operating costs relative to mass of PFAS removed. Research is underway on novel sorbent materials, electrocoagulation, and constructed wetland systems incorporating reactive media that may improve stormwater PFAS treatment economics—but no widely deployed, cost-effective solution yet exists at the scale needed for urban stormwater systems.