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The Washington Department of Ecology (“WDE”) released a September 2025 document titled:
Assessment of PFAS Levels in Washington State Biosolids (“Assessment”).
See Publication 25-07-057.
The Assessment documents the results of a study that WDE undertook in 2024 to assess PFAS concentrations in biosolids generated by 44 wastewater treatment plants in Washington State.
Participating facilities are stated to have varied by:
- Size.
- Location.
- Types of residential and industrial inputs received.
The stated goals of the study were to:
- Begin collecting data on the levels of PFAS concentrations in Washington biosolids, and
- Gain a better understanding of the sampling process for U.S. Environmental Protection Agency (“EPA”) Method 1633.
Authors of the Assessment include:
- Mounia Sassi.
- Emily Kijowski.
- Amber Corfman.
The abstract section of the Assessment notes in part:
- Limitation with using EPA Method 1633 for liquid biosolids that were less than 5% solids was identified.
- The limitation affected seven of the participating WWTPs’ results.
- The results from the remaining 37 WWTPs show PFOS and PFOA concentrations in the biosolids were relatively low.
- Samples from these facilities all contained less than 60 ppb (parts per billion) PFOS, and less than 20 ppb PFOA.
A caveat in the Abstract section notes:
…While this study allowed us to gather initial data on PFAS levels in Washington biosolids, it was limited in scope. Additional data is needed both in frequency and location to inform future policy decisions. The passing of Senate Bill 5033 “Concerning sampling or testing of biosolids for PFAS chemicals”6 (SB 5033), during the 2025 legislative session will help Ecology gather additional data.
A copy of the Assessment can be downloaded here.
