As the landscape of regulation and treatment of per- and polyfluoroalkyl substances (PFAS) in stormwater rapidly evolves, municipalities and industries need sound advice on the latest research, upcoming regulations, and treatment innovations.

In this conversation, Brandon Steets, a Senior Principal Engineer at Geosyntec, discusses his background addressing PFAS in stormwater, the latest on the regulatory landscape, and what may be on the way in the future.

Brandon will present his talk, “PFAS in Stormwater | Updates on Research, Regulation, and Treatment Innovations,” at MuniCon 2025, focusing on best-management practice (BMP) research and effectiveness studies, permit compliance, source control, and other hot issues.

About the Speaker

Brandon is a Senior Principal and Licensed Chemical Engineer with more than 25 years of experience in NPDES regulations, water-quality modeling and monitoring, pollutant-source investigation, litigation, and stormwater BMP planning and design. Brandon addresses PFAS in stormwater for multiple precedent-setting sites, including aqueous film-forming foam-use sites, by evaluating their fate, transport, source control, and treatment.

Q&A

Can you tell us about your history working to address PFAS in stormwater management?

I’ve been a part of many Geosyntec projects focused on PFAS remediation of stormwater migration pathways. My role has involved permitting these discharges, as well as evaluating and recommending treatment or source control measures.

I have co-led several SERDP-funded research studies for the US Department of Defense on PFAS and stormwater. These studies include evaluating sediment recontamination, passive treatment using black carbon, active treatment using flocculants and electrocoagulation, and leaching from AFFF-impacted construction materials. I also worked with the State of California to develop a database for emerging contaminants in stormwater. Additionally, I’ve presented at over a dozen conferences on PFAS and stormwater and co-authored articles in Stormwater Solutions on the topic.

What are you seeing regarding PFAS in stormwater in a regulatory context?

PFAS is now being included in industrial stormwater NPDES permits as a monitored constituent, both for manufacturing facilities and other USEPA-identified PFAS-associated industries like airports. Permit limits for PFAS (or any constituent) are based on either technology performance or the water-quality standards.

The water-quality standards for a discharge depend on the beneficial use of the receiving water. For example, if you discharge into marine waters, the standards for PFAS are often based on aquatic toxicity, especially if human health criteria for fish consumption are not yet available. These standards are typically higher than those for urban stormwater, except where historic AFFF use or releases have occurred.

If you’re discharging into drinking water sources, like a lot of fresh waters across the United States, drinking water standards will apply. For PFAS, these standards are lower than the aquatic-toxicity criteria and typical urban stormwater concentrations, creating new risks for stormwater dischargers. Once permit limits are executed in stormwater-discharge permits, remedial interventions will become necessary when concentrations and discharges are found to be above those limits.

Are these regulations happening mostly on the Federal or state level, or both?

The standards for PFAS vary by state but must be at least as strict as federal USEPA standards and criteria. Several states have developed drinking water standards or maximum contaminant levels (MCLs) for PFAS, as well as aquatic toxicity and human health fish consumption criteria or advisory levels. In California, environmental screening levels for drinking water and aquatic toxicity have been available for a few years and may be used to set action levels or benchmarks for NPDES discharges. State MCLs close to USEPA’s MCLs are expected later this year and will likely form the basis of new enforceable NPDES permit limits. This is likely to affect individual industrial (wastewater and stormwater) and municipal wastewater permittees first.

Which is more effective for treating PFAS in stormwater: active or passive treatment systems?

Based on the physiochemical properties of most PFAS and the less efficient nature of passive treatment, passive stormwater best-management practices (BMPs) may have limited effectiveness in most circumstances. However, they might work if stormwater has low dissolved organic carbon, and the media filter BMP includes effective pretreatment, substantial carbon, hydraulic retention time controls, and design for efficient media changeout.

In most PFAS cleanup sites where stormwater remediation is required, active treatment systems are needed due to high influent concentrations and high removal needs (like 2 log or higher). These systems are powered, use pressurized tanks, provide equalization storage, and include robust pretreatment, like chemical-flocculant addition or ultrafiltration, and GAC and/or ion exchange.

For PFAS above typical urban stormwater levels, active treatment is generally more cost-effective over time. But for municipal stormwater with typical urban background concentrations, if <1 log PFAS removal is desired, well-designed passive treatment is an option. This could make sense where stormwater discharges or infiltrates sensitive waters that receive little treatment prior to drinking water use.

How is the overall effectiveness of our current methods of PFAS treatment?

Nothing is 100% effective, and every chemical breaks through sometime. Passive systems are inherently less efficient at removing and retaining chemicals through filtration media, so they will have limits to how much they can remove. As a result, they are only effective for low influent concentrations. On the other hand, active treatment systems like those that we are using for certain industrial clients can achieve a multi-log reduction of PFAS.

What key questions remain, and lessons learned from the research arena are informing your current PFAS in stormwater work?

I think sediment recontamination risks for the more hydrophobic PFAS, like PFOS, require more study. For AFFF-use sites, PFAS leaching into stormwater will be an ongoing challenge for decades unless the source is removed, capped, stabilized, or the stormwater is treated. Stabilization products require further field demonstration though.

More work is needed to evaluate risks to groundwater from urban stormwater infiltration, much of which receives minimal pretreatment, and from a lack of adequate maintenance. A key takeaway I’ve had for PFAS remediation sites is that the stormwater-migration pathway, compared to other traditional offsite migration pathways like groundwater, is much faster, allowing little time for lengthy characterization and remedial alternatives evaluation phases, so interim mitigation actions are prudent.

What are the top takeaways that you’d like for the audience to have from your presentation at MuniCon 2025?

If your industrial site is considered a PFAS-associated industry by a regulator, you’re likely to get PFAS-monitoring requirements soon, followed by PFAS benchmarks or numeric limits, especially if you have an individual permit. This will often drive treatment for dischargers to drinking water sources, and these long-term compliance costs may be driven more by operations and maintenance than capital costs (and O&M costs are often overlooked or underestimated during remedial planning).

For municipal stormwater agencies, numeric limits for pollutants are less common except through total maximum daily loads (TMDLs). And setting 303(d) listings and developing TMDLs can take decades. So, we’re unlikely to see PFAS numeric limits in MS4 permits anytime soon.

But there are certain things that you may want to do now to be proactive. These things could include monitoring to understand the extent of the issue in your discharges and receiving waters and identifying sources within your drainage areas (like publicly owned treatment works and certain PFAS-associated industries). You can also identify where you discharge to drinking-water bodies (whether that’s a reservoir or groundwater that’s used for water supplies), evaluate risks to receptors, and weigh the costs and benefits of treating stormwater discharges versus implementing point-of-use treatment.