Results continue to show low concentrations of PFAS; wastewater testing provides a snapshot of a community’s PFAS levels, contributions
MADISON — 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. The results show that PFAS concentrations continue to be minimal and likely reflect background levels of historical PFAS persisting in local waters.
“The District has set the bar Wisconsin and the nation for testing for PFAS in the wastewater cycle, both what we receive and what we recover and return to the environment,” says Michael Mucha, Chief Engineer and Director of Madison Metropolitan Sewerage District. “Testing wastewater for these compounds provides a snapshot of the community, and while we continue to find low concentrations of PFAS through our sampling and analysis work, we are committed to learning more and positively contributing to reducing PFAS in the environment where we can.”
In Spring 2021, the District initiated its PFAS sampling and analysis plan to understand the presence of PFAS in its influent (incoming wastewater), effluent (cleaned, outgoing water), and biosolids. The first phase was a snapshot of the baseline types and amounts of PFAS present in the wastewater cycle, and these results were made available in September 2021. Phase 2, which started in early 2022, was designed to start filling data gaps identified in a fate and transport review and answer key questions from the Phase 1 sample analysis.
More specifically, Phase 2 committed to recurring 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. A brief summary of the results follows; complete results are available here. The reported results focus on PFOA and PFOS; these are two of the most common types of PFAS and the only compounds for which there are currently state-level regulations.
Influent
The District receives about 36 million gallons of influent, or raw wastewater, daily from 407,000 homes and businesses. The low levels of PFAS found in the District’s influent directly reflect individuals’ and businesses’ contributions through the products they choose to use and consume and, notably, historical and persistent levels of these chemicals in our air, water and bodies. Through monthly samples, results from Phase 2 show PFOA and PFOS levels remain similar to the 2021 results and align with a comprehensive influent study of more than 40 wastewater treatment plants in Michigan.
“The levels we see in our influent are close to background levels and typical for what you would see in a residential area,” says Martye Griffin, Director of Ecosystems Services for the District. “Because we don’t generate PFAS and our service area does not have any highly concentrated sources that manufacture, create or use PFAS compounds, reducing PFAS levels further will be challenging and need to be driven by producers committing to curbing the use of PFAS in products that are used by the residents of our service area.”
Effluent
In the Summer of 2022, the Wisconsin Department of Natural Resources established water quality criteria for the state’s surface waters for PFOA, 95 parts per trillion (ppt) and PFOS, 8 ppt. Phase 2 sampling results of the District’s effluent, which is cleaned and treated wastewater returned to local waterways, show similar PFOA and PFOS effluent levels compared to Phase 1. These levels are below the WDNR water quality standards applicable to the District’s ability to discharge to receiving streams.
Biosolids
The District produces two types of biosolids: Metrogro, a Class B liquid that the District applies to local fields as a beneficial fertilizer, and Class A cake, a semi-dry, limited-use product that undergoes additional dewatering and digestion processes.
A key part of the Phase 2 testing was further investigating the District’s biosolids, specifically how they change over time and through various processes. A critical discovery from Phase 2 is that PFAS levels in Class A cake change over time. It is believed this is due to a class of compounds known as PFAS precursors, which are less stable compounds that undergo transformation or degradation to PFAS compounds.
The WDNR currently has a draft interim strategy that provides guidelines for the land application of PFAS-containing biosolids. The interim strategy utilizes a stepped approach; the higher the PFAS levels, the more action is required. The District’s combined PFOA and PFOS levels for Metrogro, which represents the overwhelming majority of the District’s biosolids, do not rise to the level of triggering the first step of WDNR’s strategy.
“The District maintains high standards for its biosolids products to ensure the health and safety of the environment, residents and local waterways so we can continue to provide this valuable resource to local growers,” says Griffin. “The latest results show that local growers and their neighbors can take comfort in knowing that PFAS levels in our Metrogro product are minimal and stable.”
The District is committed to continuing its PFAS sampling and analysis program for the foreseeable future. The District anticipates that the state water quality standards for PFOA and PFOS will be included in its next permit.
“The District is not required to do PFAS sampling and analysis, but we understand our duty to positively contribute to building the PFAS knowledge base,” says Mucha. “This work underscores our commitment to be a strong community partner and a steward of our shared resources.”