Phase 4 results reflect samples collected and analyzed in 2024 as part of the District’s ongoing PFAS sampling and analysis plan.
Similar to the first three phases, we tested for 33 PFAS compounds, as outlined by the Wisconsin Department of Natural Resources (WDNR). The District’s influent (incoming wastewater), effluent (outgoing, cleaned wastewater) and biosolids were tested.
Samples were collected using lab-accepted collection methodologies, and samples were analyzed by a lab certified by WDNR to conduct PFAS testing.
The sampling included:
Overall, the results align with expectations based on the characteristics of the District’s service area.
Released October 16, 2025
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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 33 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.
Table shows the flow-weighted composite of all forcemain influent for PFOA and PFOS for each month sampled in 2024.
A flow-weighted composite is a combined sample made up of influent from all force mains where the portion of the sample from each force main is proportional to the
force main flow contribution.
| 01/24 | 02/24 | 03/24 | 04/24 | 05/24 | 06/24 | 07/24 | 08/24 | 09/24 | 10/24 | 11/24 | 12/24 | Michigan Influent Study | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
PFOA (ppt) | 3.1 | 4.6 | 5.6 | 4.3 | 4.5 | 5.7 J | 6.1 | 4.9 | 4.0 | 5.3 | 7.0 | 4.9 | 4.6 |
PFOS (ppt) | 2.8 | 6.6 | 7.8 | <0.51 | 4.0 | 6.1 J | 8.1 | <0.58 | 3.8 | 4.4 | 19 | 4.0 | 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
| 01/24 | 02/24 | 03/24 | 03/24 Grab | 04/24 | 04/24 Grab | 05/24 | 05/24 Grab | 06/24 | 06/24 Grab | 07/24 | 07/24 Grab | 08/24 | 08/24 Grab | 09/24 | 10/24 | 11/24 | 12/24 | WDNR Surface Water Criteria | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
PFOA (ppt) | 6.5 | 8.4 | 7.7 | 7.5 | 7.2 | 6.5 | 7.7 | 8.2 | 10 | 9.3 | 9.4 | 9.1 | 8.3 | 8.3 | 6.6 | 7.7 | 9.2 | 6.5 | 95 |
PFOS (ppt) | 3.4 | 3.4 | 3.8 | 3.2 | 4.8 | 4.9 | 4.1 | 3.6 | 5.8 | 5.6 | 7.3 | 7.2 | 6.1 | 5.9 | 3.6 | 3.8 | 17 | 3.6 | 8 |
WDNR Surface Water Criteria for non-public drinking water sources included for comparison. Protocols for the determination of a need for a PFOS and PFOA minimization plan are specified in Wisconsin Administrative Code ch. NR 106.98(4), which states that if “at least 11 daily discharge concentrations of the substance are greater than the limit of detection, a PFOS and PFOA minimization plan is required for a permitted facility if the upper 99th percentile of the 30-day average discharge concentrations for PFOS and PFOA exceeds the applicable water quality based effluent limitation calculated under this subsection.” The upper 99th percentile of the 30-day average discharge concentrations was not calculated at this time because PFOS and PFOA monitoring requirements are not currently included in the District’s WPDES permit.
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 how to address PFAS in biosolids based on 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 2024 Metrogro (Class B biosolids) combined level is below 20 ppb. The 2024 Class A cake combined level is 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 pile made in 2022, 2023 and 2024, showing data for each year that same pile was sampled over time.
| 2022 | 2023 | 2024 | ||||
|---|---|---|---|---|---|---|
| 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)* |
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 |
2024 Class A Cake Pile + PFOS) | - | - | - | - | 20-32.6 | 29.5 |
Note that the sampling methods used for the Class A cake pile that was initially generated in 2022 are different than the sampling methods for the Class A cake piles generated in 2023 and 2024.
Table shows the Class A cake pile made and sampled in 2024. The combined median was calculated based on the four sums of PFOA and PFOS from the four quarterly samples collected.
| 05/24 | 06/24 | 09/24 | 12/24 | Combined Median of PFOS+PFOA | |
|---|---|---|---|---|---|
PFOA (ppb)* | 23 | 19 | 6 | 17 | |
PFOS (ppb) | 9.6 IJ | 12 | 14 IJ | 11 | |
Sum (PFOA + PFOS) | 32.6 | 31 | 20 | 28 | 29.5 |
Table shows the results of Class B Metrogro sampling and analysis in 2024. The combined median was calculated based on the four sums of PFOA and PFOS from the four quarterly samples collected.
| 03/24 | 06/24 | 09/24 | 12/24 | Combined median PFOA+PFOS | |
|---|---|---|---|---|---|
PFOA (ppb)* | 1.4 J | 1.4 J | <3.0 | 1.4 J | - |
PFOS (ppb) | 6.9 | 9.7 | 17 | 14 I J | - |
Sum (PFOA + PFOS) | 8.3 | 11.1 | 17 | 15.4 | 13.3 |
* 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.
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.
Through 2022, the District was engaged in phase 2 of its PFAS sampling plan. This provides preliminary results for PFOA and PFOS, two PFAS compounds.