On January 14, the U.S. EPA released a Draft Risk Assessment on PFAS in biosolids The draft risk assessment is closed to public comment, but since its release, it has raised questions and concerns with wastewater treatment facility owners and operators. The findings of this assessment do not yet impose any new regulatory limits; however, understanding the assessment and its outcomes will benefit stakeholders’ long-term planning efforts.
In alignment with the 2021 PFAS Strategic Roadmap, EPA developed the Draft Sewage Sludge Risk Assessment for Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonic Acid (PFOS). Per EPA, the risk assessment “is key to determining the potential harm associated with human exposure to chemicals.” EPA further states that the “risk assessment will serve as the basis for determining whether regulation of PFOA and PFOS is appropriate” (EPA, PFAS Strategic Roadmap. 2021).
The draft risk assessment offers a preliminary evaluation of the potential human health and environmental risks associated with beneficial reuse, surface disposal of biosolids in a sludge monofill, and incineration of biosolids and sewage sludge containing PFOA and PFOS. Health risks were quantified for exposures related to biosolids land application and disposal in a sludge monofill. Health risks were qualitatively assessed for exposure from sewage sludge incineration, due to data gaps on destruction efficiency and combustion byproducts of PFOA and PFOS.
Specifically, it assesses the following scenarios:
The modeling approach in this risk assessment uses conservative exposure conditions for the following exposure pathways:
The assessment covers:
The preliminary findings of the Risk Assessment are meant to guide decisions impacted by risks from PFOA and PFOS in biosolids. The Risk Assessment does not model risks for the broader population beyond those near or directly reliant on the affected sites in the specified modeled scenarios.
Graphic by Woodard Curran
The Risk Assessment component for land application of biosolids focused on very particular exposure scenarios: that of farm families subsisting on either pastureland (for all meat, dairy, eggs) or home-grown crops (all fruits, vegetables, etc.), coupled with use of drinking water wells situated adjacent to land applications. The settings modeled are not relevant to the general American population or to the majority of biosolids land applications. The exposure assumptions regarding consumption rates for various farmed foods/meats, as well as fish assumed to be caught from the farm pond, reflect upper bound levels versus those for a typical person. Furthermore, the assumption that all the scenarios (farms, pastureland, landfilling, or reclamation) include drinking water wells directly adjacent to the assumed land application area versus complying with required setbacks adds to the assessment’s compounding conservatism. The use of these high-end settings in the risk assessment generates exceedingly low risk-based criteria. These criteria could be useful as a screening tool, but they are not reflective of the types of exposures and hence risks, for most land application scenarios.
Specifically, the vast majority of agricultural biosolids are applied to land used for producing animal feed, fiber, and/or fuel. Furthermore, very few Americans derive their entire meat, dairy, egg, fruit, and vegetable diet from pasture and crop land that receives biosolids application, and source their drinking water from a groundwater well adjacent to the land application site. Additional risk assessments could be performed to produce criteria reflective of the types of land applications and settings comprising the majority of agricultural biosolids usage.
The model concluded that concentrations as low as 1 part per billion (ppb) of PFOA and PFOS in biosolids used in land application pose a risk above the EPA’s acceptable threshold. While the report acknowledges that 1 ppb is on the low end of concentrations detected in biosolids, it fails to consider that background concentrations of PFOS and PFOA in surficial soils often exceed this value. Atmospheric deposition can result in PFOA and PFOS impacts in undeveloped areas far from point sources. For example, in an assessment of background soil concentrations of PFAS in Massachusetts (i), Woodard & Curran found up to 6 ppb of PFOS and 4.2 ppb of PFOA in soils from undeveloped land with no nearby sources. This has been further corroborated by a recent nationwide study entitled “National Collaborative Study on the Incidence and Mobility of PFAS Following Land Application of Biosolids” by the California Association of Sanitation Agencies collaborated on with the University of Arizona (ii). As such, while the model suggests 1 ppb of PFOA and PFOS in land application biosolids results in unacceptable risk, it overlooks the very likely presence of similar background concentrations of PFAS in “virgin” soils. The model’s assumption of 1 ppb PFOA/PFOS may be too conservative and unrealistic under typical environmental conditions. This observation highlights a significant limitation of the Risk Assessment.
Don’t panic. The biggest takeaway is that this document does not recommend any enforceable PFAS limit in biosolids. However, this much-anticipated study is the first of its kind and may lead to future regulations likely to be implemented at the state level.
Owners: As an owner, focus on the things that are within your control. Thoughtful programmatic preparation can replace millions of dollars of treatment technology right now. Focus on source reduction efforts and update or optimize your solids treatment trains.
If your NPDES permit is issued directly by EPA and you recently underwent a permit renewal, you have a new requirement to develop a PFAS industrial pretreatment program (IPP). Several other NPDES-delegated states are requiring this effort as well. Source reduction is the most economical and effective treatment method for reducing PFAS in biosolids and wastewater effluent—PFAS are challenging to treat once inside wastewater facilities. Start developing your PFAS IPP program to identify significant industrial PFAS contributors and heavy-loading sources from your publicly owned treatment works.
If your wastewater solids treatment equipment is more than 10 years old, it’s time to start planning for a solids upgrade. A recommended first step is to start with a planning-level effort focused on solids treatment. At a minimum, focus on driving for volume reduction by optimizing solids handling and treatment. Pursue additional contracts with biosolids haulers to diversify your options for end-use locations. Proactively engage with regulators to advocate for land application. Taking these actions will better prepare you for future regulations, should the time come.
Operators: As an operator working at the plant every day, your hands-on role is vital in managing biosolids at your facility. Your daily efforts contribute to public health protection and the sustainability of biosolids as a valuable resource.
As water industry professionals, we all have a responsibility to actively engage with regulators and the public to educate and spread the word about the sustainable practice of land application of biosolids. This collaborative effort will help ensure that biosolids continue to be a safe and beneficial resource.
For more information on the Draft Sewage Sludge Risk Assessment for Perfluorooctanoic Acid and Perfluorooctane Sulfonic Acid, read the full version of our paper at https://www.woodardcurran.com/epa-draft-risk-assessment-pfas-biosolids-what-to-know-2025/.
Woodard & Curran is an integrated science, engineering, design-build, and operations company specializing in water and environmental projects.
i: https://www.woodardcurran.com/pfas-in-massachusetts-background-soils/
ii: National Collaborative Study on the Incidence and Mobility of PFAS Following Land Application of Biosolids – https://casaweb.org/renewable-resources/pfas-1
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