Phase 3 results reflects samples collected and analyzed in 2023 as part of the District’s ongoing PFAS sampling and analysis plan.
Similar to the first two 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.
In Phase 2, the District began recurrent testing to begin generating a temporal data set to provide a more holistic view of the types and amounts of PFAS in our influent, effluent and biosolids. Phase 3 continued this temporal monitoring approach to expand the data set. A key change in Phase 3 was that we refined its sampling methodology for Class A biosolids for the best representative sample and to better align with anticipated future monitoring requirements. Influent and effluent were tested monthly, and biosolids quarterly.
Samples were collected by a consultant, TRC, using lab-accepted collection methodologies, and samples were analyzed by a lab certified by WDNR to conduct PFAS testing.
Overall, the results remain as expected based on the characteristics of the District’s service area.
Released August 19, 2024
If you have difficulty reading these charts on a mobile device,
download this summary document.
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 all of the 33 compounds tested, the types of PFAS found in local wastewater is 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 2023. 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.
| 01/23 | 02/23 | 03/23 | 04/23 | 05/23 | 06/23 | 07/23 | 09/23 | 10/23 | 11/23 | 12/23 | Michigan Influent Study | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
PFOA (ppt) | 4.2 J | 6.3 J | 6.0 | 6.0 | 4.5 | 4.1 J+ | 8.8 | 5.0 | 3.7 | 5.1 | 3.9 | 4.6 |
PFOS (ppt) | 6.5 J | 7.9 J | 6.3 | 6.9 | 5.0 | 4.3 | <0.47 | 5.0 | 2.6 | 4.0 | 4.0 | 7.5 |
J = estimated; when the value is below the level of detection and the established capabilities of the instrument, it is considered estimated.
J+ = estimated with high bias.
August 2023 = No August influent data. Laboratory analysis was cancelled due to shipping delays and misrouting causing the sample to arrive at the laboratory above the required temperature range.
Michigan Influent Study data included for comparison.
The District cleans wastewater to river-quality water and returns it to local waterways.
The Department of Natural Resources approved surface water criteria for levels of PFOA and PFOS in Summer 2022. These criteria establish a threshold beyond which certain pollution minimization efforts must be undertaken. Our testing reveals PFOA and PFOS levels in the District’s effluent are lower than WDNR’s surface water criteria.
The waterways the District discharges to are not drinking water sources.
Table shows the effluent concentration for PFOA and PFOS for each month sampled in 2023
| 01/23 | 02/23 | 03/23 | 04/23 | 05/23 | 06/23 | 07/23 | 09/23 | 10/23 | 11/23 | 12/23 | WDNR Surface Water Criteria | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
PFOA (ppt) | 16.8 | 8.6 J | 9.3 | 12 | 11 | 7.4 J+ | 12 | 7.8 | 7.2 | 8.0 | 8.6 | 95 |
PFOS (ppt) | 4.1 | 5.6 J+ | 5.5 | 5.4 | 5.6 | 3.8 | 4.9 | 5.2 | 3.2 | 4.0 | 4.3 | 8 |
J = estimated; when the value is below the level of detection and the established capabilities of the instrument, it is considered estimated.
J+ = estimated with high bias.
August 2023 = No August influent data. Laboratory analysis was cancelled due to shipping delays and misrouting causing the sample to arrive at the laboratory above the required temperature range.
WDNR Surface Water Criteria for non-public drinking water sources included for comparison.
WDNR Surface Water Criteria for non-public drinking water sources included for comparison.
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 District’s combined level in PFOA and PFOS falls into WDNR’s lowest category of 50 ppb and lower. Please see the interim strategy document for details.
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 for cake made in 2022, sampled again in 2023.
| March 2023 | June 2023 | September 2023 | December 2023 | Combined median PFOA+PFOS | |
|---|---|---|---|---|---|
PFOA (ppb)* | 6.1 | 6.0 J+ | 9.2 | 16 | |
PFOS (ppb) | 11 | <0.95 | 9.9 | 13 IJ | |
Sum (PFOA + PFOS) | 17.1 | 6 | 19.1 | 29 | 18.1 |
The combined median was calculated based on the four sums of PFOA and PFOS from the four quarterly samples collected
Table shows the Class A cake pile for cake made in 2023. Note that the sampling schedule was only twice in 2023, the first event was when the pile passed bacteria testing for land application and the second sampling event was one quarter later, which reflected the goal of the 2023 sampling to assess sample collection methods to improve data quality for monitoring. Each event sampled different areas of the pile: shallow (S), middle (M) and deep (D). All results are shown below.
| July S-1 | July S-2 | July S-3 | July S-4 | July M | July D-1 | July D-2 | Oct S-1 | Oct S-2 | Oct S-3 | Oct S-4 | Oct M | Oct D-1 | Oct D-2 | Combined median PFOA+PFOS | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
PFOA (ppb)* | 23 | 7.0 | 3.5 | 3.1 J | 4.0 | 2.7 J | 3.3 J | 6.0 | 3.2 | 2.3 J | 3.0 J | 5.6 | 3.0 J | 3.2 J | |
PFOS (ppb) | <0.51 | <0.60 | <0.68 | <0.70 | <0.70 | <0.84 | <0.87 | 13 | 14 | 12 | 13 | 13 | 15 | 15 | |
Sum (PFOA + PFOS) | 23 | 7 | 3.5 | 3.1 | 4 | 2.7 | 3.3 | 19 | 17.2 | 14.3 | 16 | 18.6 | 18 | 18.2 | 15.1 |
The combined median was calculated as the median of the 14 sums of PFOA and PFOS for all 14 samples collected during 2023.
| March 2023 | June 2023 | September 2023 | December 2023 | Combined median PFOA+PFOS | |
|---|---|---|---|---|---|
PFOA (ppb)* | 1.3 J | 1.5 J | 0.92 J | <7.8 | |
PFOS (ppb) | 9.7 IJ | <0.70 | 8.9 IJ | 10 IJ | |
Sum (PFOA + PFOS) | 11 | 1.5 | 9.82 | 10 | 9.91 |
The combined median was calculated based on the four sums of PFOA and PFOS from the four quarterly samples collected
* Duplicate samples were taken.
J = Estimated; when the value is below the level of detection and the established capabilities of the instrument, it is considered estimated.
I = Ion transition ratio did not meet certain limits and is outside the quality control window.
* 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.
Sign up to stay up to date on on the District’s PFAS work, including sampling and analysis results once available.