Wausau utility debates when to replace PFAS-filtering carbon as levels rise

Wausau Waterworks staff told the Waterworks Commission on Aug. 5 they are seeing early breakthrough of PFOA and PFOS in the GAC treatment vessels and asked the commission whether to trigger a media replacement now or wait until a regulatory-level trigger is reached.

The issue matters because the city built a new treatment train with 12 tall vessels to remove PFAS, and replacing the carbon in all vessels would cost in the low seven figures. The choice affects near-term operating budgets, ratepayer bills and compliance planning as federal and state guidance evolves.

Staff consultant Susan (Donahue) said the project was designed for flexibility and "ultimately, we, selected the alternative 1, which was 12 tall vessels for granular activated carbon." She described the vessels as operating in a lead–lag configuration that lets the utility rotate media between a working bed and a lag bed. Staff samples 18 PFAS compounds at multiple ports in each vessel and reported that PFOA and PFOS are the compounds showing the most movement through the beds.

The utility director noted federal, state and health-agency guidance currently differ, saying, "The EPA has a recommendation right now. They're established a recommendation of 4 parts per trillion." Staff summarized the applicable thresholds discussed in the meeting: Wisconsin Department of Natural Resources (DNR) has a historical enforcement level of 70 parts per trillion, the state Department of Health Services (DHS) has advised 20 parts per trillion and EPA's proposed maximum contaminant level is 4 parts per trillion. Staff said DNR currently expects utilities to publicly notify customers when results exceed 20 parts per trillion, which can create public anxiety.

Technical and cost details presented to the commission: - The treatment system placed in service in November uses 12 tall vessels sized so the city can use GAC, ion exchange or emerging media such as Fluorozorb. - Sampling indicates influent (raw) PFAS concentrations in Wausau wells of roughly 30–40 parts per trillion combined for certain compounds; PFOA and PFOS are the primary concerns. - Staff presented modeled replacement scenarios for replacing media in all vessels that ranged roughly from about $1.3 million to $1.8 million for new virgin carbon; reactivated carbon could offer ~20–30% savings in some scenarios. - Staff said one-time federal congressionally directed funds of about $1.7 million are available to the city to help cover the first changeout. - With current staffing and procedures, staff estimated they could change roughly one vessel per month; a multi-vessel changeout could therefore take several months to complete.

Staff recommended using an internal trigger based on the EPA's 4 parts-per-trillion value to schedule changeouts and to gather additional operating data while avoiding premature replacement. The utility said some vessels (referred to as systems 5 and 6 in the presentation) appear to be loading more quickly and could reach the 4 ppt level within two to three months.

Commissioners pressed staff on alternatives and timing. Staff said the utility could pilot alternative media—Fluorozorb—or test different brands of carbon; a full pilot of a new media could take about a year, while switching to a different NSF-60–certified carbon brand could be done full scale more quickly. Staff also noted DNR does not preapprove media changeouts but requires NSF-60 certification for materials.

No formal policy or procurement decision was made at the Aug. 5 meeting. The commission asked staff to refine cost estimates, provide additional sampling and operational data, and return with a recommendation at a future meeting. Staff agreed to prepare refined cost estimates and to provide data to commissioners in the coming weeks. The item was left for further consideration with staff direction to return with more information.

Community and downstream concerns were noted: wastewater staff reminded the commission that PFAS testing will be required in the plant's new discharge permit term and that higher PFAS in collection-system flows could affect wastewater compliance and minimization planning.

The commission and staff scheduled additional discussion and offered to arrange a plant tour for commissioners to view the vessels and sampling ports in person.