Best Available Science – Critical Areas

Per-and Polyfluoroalkyl Substances (PFAS) in Urban Stormwater Runoff: Insights from a Roadside Rain Garden
Water 2025, 17, 2982
Saleh, H., Sarkar, D., Zhang, Z., Boufadel, M. and Datta, R., 2025

• ​The study found rain gardens do not alter PFAS concentrations; highlighting the limitations of filtering persistent and mobile contaminants like PFAS.
• Findings underscore the ineffectiveness of conventional green infrastructure for PFAS mitigation and the urgent need for development of advanced treatment technologies integrated into urban stormwater management.

Greater Lake Washington Watershed PFAS Survey: Final Report
Publication 25-03-008
Washington State Department of Ecology, Olympia
Wong, S. and D. Escobedo. 2025.

• PFAS were detected throughout the watershed in nearly all sample types and locations, indicating widespread distribution rather than being confined to a few point sources.
• Stormwater and groundwater pathways are important contributors to PFAS loading to the lake, underscoring the need to evaluate urban land use, runoff controls, and infiltration practices.

Stormwater discharges affect PFAS occurrence, concentrations, and spatial distribution in water and bottom sediment of urban streams
Water Research, 271, p.122973
Kali, S.E., Österlund, H., Viklander, M. and Blecken, G.T., 2025

• Stormwater runoff is a significant pathway for PFAS transport from urban landscapes.
• Urban stormwater impacts occur even in smaller cities without large industrial sources, indicating widespread urban runoff contamination.
• Findings support the need for improved stormwater treatment and source controls to reduce PFAS inputs to aquatic environments.

EPA’s Emerging contaminants in wastewater and receiving surface water environments
EPA Publication 5003
2025

• Conventional treatment processes vary in their effectiveness for different classes of emerging contaminants. Some compounds are substantially reduced during treatment, while others pass through largely unchanged.
• The variation in removal efficiency highlights the limitations of conventional treatment technologies in addressing the full suite of emerging contaminants.
• Conventional treatments do not reliably remove PFAS. Unlike most other contaminant groups, PFAS showed little removal and often increased in concentration from influent to effluent, indicating transformation, desorption, or precursor breakdown during treatment rather than effective removal,

PFAS in stormwater control measures: Removal, distribution, and long-term fate
Water Research, p.124795
Gómez-Ávila, C., Hussain, T., Rao, B., Pitt, R., Guelfo, J., Zhou, H. and Reible, D., 2025

• Dissolved PFAS are not removed by conventional stormwater treatment.
• Particulate bound PFAS are more likely to be better controlled.
• Sediment resuspension can cause release of particulate-bound PFAS.

Per- and Polyfluoroalkyl Substances (PFAS) Occurrence and Contaminant Background Support Document for the Final PFAS National Primary Drinking Water Regulation
U.S. Environmental Protection Agency 2024

• The report examines how often PFAS appear individually and together in water supplies, informing EPA’s decision to regulate both individual compounds and mixtures through a “hazard index” approach.
• Report provides the evidence necessary for EPA to justify new enforceable drinking water limits, blending scientific occurrence data with regulatory requirements under the Safe Drinking Water Act.

PFAS National Primary Drinking Water Regulation
Federal Register Notice

• Drinking water is one of several ways people can be exposed to PFAS. The EPA’s examination of drinking water data shows that different PFAS can often be found together and in varying combinations as mixtures. Additionally, decades of research demonstrates that exposure to mixtures of different chemicals can elicit dose-additive health effects: even if the individual chemicals are each present at levels considered ‘‘safe,’’ the mixture may cause significant adverse health effects.
• Individual Maximum Contaminant Levels (MCLs)
  a. Perfluorooctanoic acid (PFOA) MCL = 4.0 nanograms per liter or parts per trillion (ng/L or ppt)
  b. Perfluorooctane sulfonic acid (PFOS) MCL = 4.0 ng/L
  c. Perfluorohexane sulfonic acid (PFHxS) MCL = 10 ng/L
  d. Perfluorononanoic acid (PFNA) MCL = 10 ng/L
  e. Hexafluoropropylene oxide dimer acid (HFPO–DA) MCL = 10 ng/L

REVISED FINAL RESULTS OF SUPPLEMENTAL STORMWATER MONITORING FOR PFAS, MADRONA K-8 SCHOOL REPLACEMENT PROJECT, EDMONDS, WASHINGTON
Letter Report to Edmonds School District
Shannon & Wilson. 2024.

• Multiple PFAS compounds were detected in stormwater at two sample locations on the Madrona School site, including commonly encountered short-chain acids (e.g., PFBA, PFHxA) and regulated legacy compounds (PFOA, PFOS).
• Stormwater PFOA concentrations exceeded Washington’s drinking water state action level and comparable MTCA groundwater benchmark.

Storms mobilize organophosphate esters, bisphenols, PFASs, and vehicle-derived contaminants to San Francisco Bay watersheds
Environmental Science: Processes & Impacts, 26(10), pp.1760-1779
Peter, K.T., Gilbreath, A., Gonzalez, M., Tian, Z., Wong, A., Yee, D., Miller, E.L., Avellaneda, P.M., Chen, D., Patterson, A. and Fitzgerald, N., 2024

• Stormwater is a major transport pathway for a complex mixture of emerging organic contaminants to aquatic ecosystems, especially in urbanized areas.
• Urban stormwater sites had significantly higher contaminant levels than less developed reference sites, pointing to urban land use as major sources.

Maximum Contaminant Level Goals for Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonic Acid (PFOS) in Drinking Water
EPA-815-R-24-010. Office of Water
U.S. Environmental Protection Agency. 2024

• Federal Regulations set the Maximum Contaminant Level Goal (MCLG) for PFOA and PFOS is zero. While the MCLG is zero, the enforceable Maximum Contaminant Level (MCL) for both PFOA and PFOS is set at 4.0 parts per trillion (ppt). The MCLG of zero reflects scientific findings that there is no level of exposure to these two chemicals without risk of health impacts, including certain cancers.
• The U.S. Environmental Protection Agency (EPA) finalized the first-ever National Primary Drinking Water Regulation for six per- and polyfluoroalkyl substances (PFAS) in April 2024.

Guidance for Investigating and Remediating PFAS Contamination in Washington State
WA Dept of Ecology
2023

• PFAS compounds meet the definition of a hazardous substance under Washington’s Model Toxics Control Act (MTCA).
  
  The toxicology of PFAS is currently an area of intense research. As new toxicological information emerges, MTCA cleanup levels for PFOS and PFOA may change and regulatory levels for other PFAS compounds may become available.
• Analytical and remediation technologies for PFAS continue to improve, so the guidance is considered living and subject to update.

Review of contaminants of potential human health concern in wastewater and stormwater
Science for Communities, pp.1-232
Coxon, S. and Eaton, C., 2023

• Stormwater runoff also plays a significant role in transporting PFAS to surface waters, particularly in urbanized areas where PFAS-containing materials and dust accumulate on impervious surfaces.
• PFAS are highly persistent and resistant to degradation, leading to their accumulation in aquatic environments and soils.

Olympic View Water & Sewer District 2023 Watershed Protection Plan

• Prohibiting the use of underground injection (UIC) wells within the watershed and wellhead protection areas is a regulatory measure that land use agencies should use as a means of minimizing the potential for contamination of and protection of the Deer Creek water supply.
• The Washington State Department of Health assigned the Deer Creek aquifer a high susceptibility rating to indicate the vulnerability of and potential severity of certain pollutants entering the water source – – based on geologic and land-use factors influencing contaminant entry pathways.

Per-and polyfluoroalkyl substances (PFAS) are emerging contaminants: Review of sources, contaminations, and awareness
Acad. Res. J. of Nat. and Pub. Health. 2023, 2, 86-91
Chowdhurya, S., 2023

• It is important to regulate PFAS conveyance to avoid future consequences of damaging human health and the environment.
• It is important for to regulate PFAS to avoid any future consequences of damaging our health and the environment.
• Stormwater collected from residential rooftops contained higher concentrations of PFAS than what is recommended by the EPA for human safety.

PFAS Technical and Regulatory Guidance Document
Interstate Technology & Regulatory Council’s, September 2023

• Infiltration-based stormwater BMPs may unintentionally concentrate or mobilize PFAS, especially into drinking water aquifers.
• Long-chain PFAS tend to sorb to solids, while short-chain PFAS are more mobile and difficult to remove, increasing long-term exposure risks.
• Emphasizes drinking water aquifers and sources as a top priority for protection.

Predicted aquatic exposure effects from a national urban stormwater study
Environmental Science: Water Research & Technology, 9(12), pp.3191-3199
Bradley, P.M., Romanok, K.M., Smalling, K.L., Masoner, J.R., Kolpin, D.W. and Gordon, S.E., 2023

• Stormwater discharges can generate localized, extensive contaminant mixtures whose ecological risks are likely higher than documented due to unmeasured chemicals and below-detection exposures.
• Current monitoring and risk evaluation focus on limited chemical lists probably underrepresent true ecological risk of contamination – underscoring the need for broader chemical assessment and improved stormwater mitigation strategies

Guidance on PFAS Exposure, Testing, and Clinical Follow-Up
Washington, DC: The National Academies Press
National Academies of Sciences, Engineering, and Medicine. 2022. https://doi.org/10.17226/26156.

• PFAS are widespread, persistent chemicals found in the environment and have potential associations with various adverse health outcomes. There are more than 12,000 different PFAS compounds and are used in thousands of products because they have desirable chemical properties that impart oil and water repellency, friction reduction, and temperature resistance.
• Because there are “no established medical treatments to remove PFAS from the body,” reducing PFAS exposure is the primary means of risk reduction.

PFAS molecules: a major concern for the human health and the environment
Toxics, 10(2), p.44
Panieri, E., Baralic, K., Djukic-Cosic, D., Buha Djordjevic, A. and Saso, L., 2022

• PFAS) are a large family of over 4,700 synthetic chemicals known for their chemical and thermal stability and amphipathic (water- and oil-repelling) properties. These traits have led to their widespread use in industrial applications and consumer products for nearly six decades
• Significant advances are expected to emerge from the identification of the most effective remediation technologies to remove PFAS in the environmental media in a cost-effective and environmentally sustainable way.
• There are major gaps in understanding PFAS mixtures’ toxicity, environmental behavior, and long-term health effects; regulatory, and technological responses to mitigate their impact are needed..

Per- and Polyfluoroalkyl Substances Chemical Action Plan
WA Dept of Ecology
2022

• Prevent PFAS from entering groundwater and surface waters that serve as drinking water sources.
• PFAS meet the definition of hazardous substances under Washington’s Model Toxics Control Act (MTCA). This classification means PFAS releases that could threaten drinking water must be reported and addressed under cleanup laws, which helps prevent further contamination of drinking water sources.

Rechargeable stormwater biofilters: In situ regeneration of PFAS removal capacity by using a cationic polymer, polydiallyldimethylammonium chloride
Journal of Cleaner Production, 375, p.134244
Borthakur, A., Das, T.K., Zhang, Y., Libbert, S., Prehn, S., Ramos, P., Dooley, G., Blotevogel, J., Mahendra, S. and Mohanty, S.K., 2022

• Conventional stormwater biofilter media such as sand and compost have limited capacity to remove PFAS due to the exhaustion of attachment sites with pollutants and other stormwater constituents. Replacing exhausted filter media is expensive whereas in situ regeneration of their adsorption capacity can be cost-effective.
• The result indicates the application of the cationic polymer can help remove short-chain PFAS, the ones that are most difficult to remove by typical organic amendments such as activated carbon and biochar.

Addressing urgent questions for PFAS in the 21st century
Environmental Science & Technology, 55(19), pp.12755-12765
Ng, C., Cousins, I.T., DeWitt, J.C., Glüge, J., Goldenman, G., Herzke, D., Lohmann, R., Miller, M., Patton, S., Scheringer, M. and Trier, X., 2021

• Despite decades of research on PFAS, fundamental obstacles remain to addressing contamination by these chemicals and their associated impacts on environmental quality and human health.
• The lack of historical and ongoing production, use, and emissions data on PFAS is a central scientific barrier. Without such PFAS data, society will fail to protect its members from unknown exposures until or even after harmful and irreversible effects are discovered.

Critical Aquifer Recharge Areas (CARA) – Guidance
WA Dept of Ecology
2021

• The Growth Management Act requires protection of public groundwater drinking supplies so that contamination events and their associated costs can be prevented.
• Shallow, unconfined aquifers are more susceptible to contamination. When water can move readily through the ground, it can carry contaminants to groundwater more quickly. Sandy, shallow unconfined aquifers are more susceptible than deep aquifers that are overlain by an aquitard.
• It is important to remove stormwater contaminants so that groundwater does not become polluted.
• PFAS are a large group of perfluorinated and polyfluorinated alkyl substances. These very stable, manufactured chemicals remain in the environment for a long time without breaking down, and some of them build up in people and the environment.
• PFAS are water soluble and highly mobile, meaning they can easily contaminate groundwater and can be hard to filter out. Many PFAS transform into highly persistent perfluorinated chemicals in the environment. There are no natural processes that can break down these substances. Exposures could continue for hundreds or thousands of years

Loading, transport, and treatment of emerging chemical and biological contaminants of concern in stormwater
Water Science and Technology, 83(12), pp.2863-2885
Saifur, S. and Gardner, C.M., 2021.

• Stormwater is a source of pollution that is largely uncontrolled in both rural and urban watersheds and increasingly recognized as a significant pathway for contaminants to enter groundwater.
• Stormwater historically has been managed for conventional pollutants such as nutrients and heavy metals, but emerging contaminants such as PFAS, which have not been traditionally regulated or fully understood, are present in stormwater and represent risks to human health.
• Emerging contaminants, such as PFAS, can exert a range of effects, often at low concentrations, that are not fully addressed by traditional stormwater management practices.
  Research is needed on advanced treatment technology to determine if it is truly protective of ecological or human health.

PFAS exposure pathways for humans and wildlife: a synthesis of current knowledge and key gaps in understanding
Environmental toxicology and chemistry, 40(3), pp.631-657
De Silva, A.O., Armitage, J.M., Bruton, T.A., Dassuncao, C., Heiger‐Bernays, W., Hu, X.C., Kärrman, A., Kelly, B., Ng, C., Robuck, A. and Sun, M., 2021

• Drinking water has been established as the major human exposure source for PFAS.
• A major focus of past PFAS research has been contaminated sites where the highest concentrations in the environment and biota are often found. Moving forward, a better understanding of atmospheric PFAS sources and potential resulting exposures is needed, particularly as treatment systems are introduced for contaminated drinking water supplies. 
• Additional research is needed to characterize the fraction of exposure originating from precursors that degrade into terminal PFAAs that have been linked to adverse health effects.

Minimizing the environmental impact of PFAS by using specialized coagulants for the treatment of PFAS polluted waters and for the decontamination of firefighting equipment
Emerging Contaminants, 7, pp.63-76
Cornelsen, M., Weber, R. and Panglisch, S., 2021

• PFAS pollution poses serious health and ecological risks and is difficult to remediate with traditional treatment methods. Some PFAS are linked to carcinogenic, immunotoxic, and endocrine-disrupting effects, and exposure reduction is critical.
• Traditional treatment technologies alone often fall short. Well-known methods of water treatment, especially the use of materials for adsorption and ion exchange, can often neither guarantee satisfactory cleaning results nor economically justifiable filter running times. Their combination with a pre-precipitation stage using specialized precipitants can significantly optimize treatment successes.

An overview of per-and polyfluoroalkyl substances (PFAS) in the environment: Source, fate, risk and regulations
Water, 12(12), p.3590
Abunada, Z., Alazaiza, M.Y. and Bashir, M.J., 2020

• PFAS are persistent environmental contaminants with widespread distribution and potential health risks. Despite increased research and evolving regulations, significant uncertainties remain about exposure pathways, health impacts, and effective remediation.
• Various PFAS removal methods including adsorption (e.g., granular activated carbon), membrane technologies (e.g., nanofiltration and reverse osmosis), and advanced oxidation/sonochemical techniques have limitations such as incomplete removal, problematic brine waste, and high costs.
• Regulating PFAS is complex due to scientific uncertainties, differing toxicological data, and varied national/regional approaches.

PFAS environmental pollution and antioxidant responses: an overview of the impact on human field
International journal of environmental research and public health, 17(21), p.8020
Bonato, M., Corrà, F., Bellio, M., Guidolin, L., Tallandini, L., Irato, P. and Santovito, G., 2020

• Although many PFAS have been phased out, their persistence and ongoing use of replacement PFAS compounds pose long-term risks to human health and ecosystems.
• Epidemiological studies have linked PFAS exposure to a range of adverse health outcomes in humans, including: infertility and reproductive effects; hormonal disruption; thyroid, liver, and kidney disorders; and, metabolic dysfunctions.

Olympic View Water and Sewer District Wellhead Protection Area Delineation – Deer Creek Springs and 228th Street Wellfield
Robinson-Noble Report
Wills, M.T. 2018

• The Qva aquifer is a relatively shallow system which is directly exposed at the surface in many places within the Deer Creek CARA and extra protection is recommended. As such, a buffer zone is also recommended.
• There is cause for additional concern in the areas where the Qva is mapped as the surficial geologic unit. The Qva aquifer has no natural geologic protection in these locations and is highly vulnerable to impact from various activities that may occur within these areas. As such, additional precautions are warranted for these specific areas.

Treatment of poly-and perfluoroalkyl substances in US full-scale water treatment systems
Water research, 51, pp.246-255
Appleman, T.D., Higgins, C.P., Quiñones, O., Vanderford, B.J., Kolstad, C., Zeigler-Holady, J.C. and Dickenson, E.R., 2014

• Standard drinking water treatment processes have limited to no effectiveness for PFAS removal.
• Advanced treatment such as Reverse Osmosis reduces PFAS across all types, but is more costly and operationally intensive than conventional technologies. Adsorption methods can reduce many PFAS, especially longer-chain ones, but performance varies with PFAS chemistry and operational conditions.