WWTF Sampling Obligations Kick-in Under Minnesota’s Biosolids PFAS Strategy

Originally published in the November 2025 issue of Bench & Bar of Minnesota Environmental Law Update, Minnesota State Bar Association.

Pursuant to Minnesota’s Biosolids PFAS Strategy, all Minnesota wastewater treatment facilities (WWTFs) that land apply any amount of biosolids must, as of September 1, 2025, collect at least one biosolids sample per cropping year and analyze it for PFAS content before land applying the biosolids. 

In its 2024 session, the Minnesota Legislature passed a law requiring MPCA to “develop a strategy to require sewage sludge prepared for application to land in Minnesota to be analyzed…for the [PFAS] by December 31, 2024, and begin implementing this strategy in water discharge permits thereafter.” Pursuant to this mandate, MPCA issued a draft Biosolids PFAS Strategy in December 2024 and finalized the Strategy early in 2025. In July 2025, the agency issued a slightly more detailed version of the strategy.

MPCA’s Strategy builds upon the agency’s 2022 PFAS Monitoring Strategy, pursuant to which many Minnesota WWTFs have collected PFAS water quality samples. Under the Biosolids PFAS Strategy, WWTFs that land apply biosolids must collect “one biosolids sample per cropping year (September 1 through August 31) and analyze it for PFAS prior to land application.” The actions the WWTFs must take based on the sampling results depend upon the whether concentrations of either perfluorooctanic acid (PFOA) or perfluorooctane sulfonate (PFOS) exceed certain thresholds, as follows:

• Tier 1 (≤20 µg/kg): Notify landowners and farmers (if different from the landowner) that PFAS sampling was conducted and that results are available upon request.
• Tier 2 (21–50 µg/kg): Provide sampling results to landowners and farmers, initiate or continue source-identification and -reduction work (encouraged, not required), track cumulative application rates on each site and report the information to MPCA.
• Tier 3 (51–124 µg/kg): Provide sampling results and MPCA contact information to landowners and farmers, initiate source-identification and -reduction work by generating, submitting and implementing a PFAS PMP within 180 days, reduce the loading of land-applied biosolids to 1.5 dry tons per acre, track cumulative application rates on each site and report the information to MPCA, and plan for alternative management options for biosolids, as appropriate.
• Tier 4 (≥125 µg/kg): These biosolids are considered “industrially impacted” and may not be land applied. The WWTF must: notify MPCA within 10 days of receiving the results, initiate source-identification and -reduction work by generating, submitting and implementing a PFAS PMP within 180 days, and sample its wastewater plant effluent and have it analyzed for PFAS, if not already required by its NPDES/SDS Permit.

MPCA’s Biosolids PFAS Strategy also creates an “Exceptional Quality” category of biosolids, which can be sold for domestic use. These biosolids must meet stricter PFAS thresholds (≤20 µg/kg combined for PFOA and PFOS) and the WWTF must demonstrate compliance through quarterly sampling.

MPCA indicated that biosolids PFAS requirements will be added to the WWTFs’ NPDES/SDS permits as they are reissued. The agency also noted that it will continue to reevaluate its Strategy as the science and federal regulatory requirements evolve.

With the implementation of MPCA’s Biosolids PFAS Strategy, Minnesota joins a growing number of states that have established requirements to control PFAS in biosolids. In January 2025, the federal Environmental Protection Agency (EPA) under the Biden administration issued a Draft Risk Assessment for PFOA and PFOS in Biosolids. Once finalized the risk assessment could form the basis of federal Clean Water Act regulations governing PFAS in biosolids. However, since the change of administration, the EPA has not finalized the assessment and has expressed an interest in reevaluating the science underlying the assessment. (Inside PFAS Policy, 7-31-2025.)