These results reflect samples collected and analyzed in 2025 as part of the District’s ongoing PFAS sampling and analysis plan.
2025 is the fifth year of the District’s sampling and analysis, which tested for 40 PFAS compounds; this is in accordance with WDNR requirements. The District’s influent (incoming wastewater), effluent (outgoing, cleaned wastewater) and biosolids were tested as follows:
Samples were collected using lab-accepted collection methodologies, and samples were analyzed by a lab certified by WDNR to conduct PFAS testing.
Overall, the 2025 results align with expectations based on the characteristics of the District’s service area.
Released August 27, 2026
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The District tested influent from each of its five large sewer pipes, called forcemains, which aggregate wastewater from the service area and deliver it to the plant.
Examining the 40 compounds tested, the types of PFAS found in local wastewater are consistent with results from other municipal wastewater treatment plants in urbanized areas without significant industrial sources.
| 01/25 | 02/25 | 03/25 | 04/25 | 05/25 | 06/25 | 07/25 | 08/25 | 09/24 | 10/25 | 11/25 | 12/24 | Michigan Influent Study | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
PFOA (ppt) | 4.9 | 4.1 | 4.3 | 5.3 | 6.2 | 5.2 | 5.2 | 7.7 | 4.7 | 5.2 | 5.4 | 4.9 | 4.6 |
PFOS (ppt) | 7.3IJ | 4.5IJ | 7.9IJ | 7.9IJ | 8.0 | <0.22 | 8.8 | 7.7 | 5.2 | 4.1 | 4.8 | 6.2IJ | 7.5 |
Michigan Influent Study data included for comparison.
The District cleans wastewater to river-quality water and returns it to a local waterway.
The effluent from the Nine Springs Wastewater Treatment Plant is discharged into waters that are not classified as a public water supply; therefore, the relevant surface water criterion for PFOA is 95 ng/L and PFOS is 8 ng/L.
Our testing reveals PFOA and PFOS levels in the District’s effluent are lower than WDNR’s surface water criteria.
Table shows the effluent concentration for PFOA and PFOS for each month sampled in 2024
| 01/25 #1 | 01/25 #2 | 01/25 #3 | 01/25 #4 | 02/25 | 03/25 | 04/25 | 05/25 | 06/25 | 07/25 | 08/25 | 09/25 | 10/25 | 11/25 | 12/25 | WDNR Surface Water Criteria | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
PFOA (ppt) | 5.4 | 5.8 | 5.6 | 4.8 | 4.5 | 5.5 | 7.0 | 6.8 | 6.6 | 6.9 | 9.4 | 7.1 | 7.1 | 7.7 | 5.6 | 95 |
PFOS (ppt) | 2.5 | 2.4 | 2.2 | 2.5 | 1.8 | 2.6 | 3.6 | 3.1 | 3.5 | 3.8 | 5.5 | 6.1 | 2.9 | 3.1 | 3.4 | 8 |
The District produces two biosolids products. The primary product is Metrogro, a liquid Class B biosolids product that is land-applied to local farm fields as a valuable, nutrient-rich fertilizer. The District also produces a small amount of Class A cake.
WDNR has not established PFAS standards but has published an interim strategy for land application of biosolids containing PFAS. The guidance provides a decision-making process for addressing PFAS in biosolids based on the combined concentration levels of PFOA and PFOS. The lowest category is below 20 ppb, the second category is above 20ppb but below 50 ppb. The combined level of 2025 Metrogro (Class B biosolids) is below 20 ppb. The 2025 Class A cake combined level is marginally above 20ppb but below 50 ppb
Land application of Metrogro is the most cost-effective and environmentally friendly way for the District to dispose of the solid waste recovered from wastewater. Alternatives such as landfilling or incineration are costly and have additional impacts on the environment and human health.
Table shows the Class A cake piles made in 2022 through 2025, with data for each year that same pile was sampled over time.
| 2022 | 2023 | 2024 | 2025 | |||||
|---|---|---|---|---|---|---|---|---|
| Year Generated | Range PFOS + PFOA (ppb)* | Median PFOS + PFOA (ppb)* | Range PFOS + PFOA (ppb)* | Median PFOS + PFOA (ppb)* | Range PFOS + PFOA (ppb)* | Median PFOS + PFOA (ppb)* | Range PFOS + PFOA (ppb)* | Median PFOS + PFOA (ppb)* |
2022 Class A Cake Pile | 11.4-45 | 38 | 6-29 | 18.1 | 35-52 | 43 | ** | ** |
2023 Class A Cake Pile | - | - | 2.7-23 | 15.1 | 20-66 | 29 | 33.9-75 | 58 |
2024 Class A Cake Pile | - | - | - | - | 20-32.6 | 29.5 | 18.1-42 | 28.6 |
2025 Class A Cake Pile | 16.2-22 | 21 | ||||||
**No longer sampled in 2025.
Table shows the Class A cake pile made and sampled in 2025. The median was calculated from the sums of PFOA and PFOS across the four quarterly samples collected.
| 07/25 | 09/25 | 12/25 | Median of PFOS+PFOA | |
|---|---|---|---|---|
PFOA (ppb)* | 14 | 10 | 7.7 | |
PFOS (ppb) | 8 | 11 | 8.5 | |
Sum (PFOA + PFOS) | 22 | 21 | 16.2 | 21 |
Table shows the results of Class B Metrogro sampling and analysis in 2025. The median was calculated from the four sums of PFOA and PFOS across the four quarterly samples collected.
| 03/25 | 06/25 | 09/25 | 12/25 | Median PFOA+PFOS | |
|---|---|---|---|---|---|
PFOA (ppb)* | 1.3J | 1.1J | <2.1 | 0.91J | - |
PFOS (ppb) | 8.1 | 7.7 | 7.5 | 5.1 | - |
Sum (PFOA + PFOS) | 9.4 | 8.8 | 7.5 | 6.01 | 8.15 |
* In the full report, numbers are reported as ug/kg, which is the same as ppb, or parts per billion. For context on ppb equivalents, see our About PFAS page.
For additional information about what the District is doing to address PFAS, check out the information below.
The District's initial look at PFAS, including action steps. June 2019
A look at how PFAS move through the environment and cycles through wastewater treatments plants and their effluent. Produced by District consultant, TRC, February 2020.
Guidance and procedures for conducting a comprehensive PFAS sampling plan. Produced by District consultant TRC, February 2020.
Results from Madison Metropolitan Sewerage District’s 2024 PFAS sampling and analysis show low levels of PFAS in the local wastewater system.
Madison Metropolitan Sewerage District recently shared the results of its Phase 2 sampling and analysis of PFAS, or per- and polyfluoroalkyl substances, in the local wastewater cycle.