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Wausau commission sets 4 ppt trigger for PFAS carbon change-outs, directs staff flexibility on timing
Summary
The commission accepted staff recommendations to operate the granular-activated carbon (GAC) system toward a 4 parts-per-trillion trigger for PFOA/PFOS to guide future change-outs and to collect operational data, while allowing staff latitude on exact timing and logistics.
The Water Works Commission on Tuesday accepted staff recommendations to use 4 parts per trillion (ppt) for PFOA and PFOS as the operational trigger for planning granular-activated carbon (GAC) change-outs and to give staff flexibility on timing to collect data and stage replacements economically.
Scott, the water operations supervisor, summarized regulatory context: the U.S. Environmental Protection Agency has proposed a 4 ppt level for PFOA and PFOS, and state agencies currently reference higher numeric levels in certain contexts. Scott told commissioners the commission's GAC lead-lag configuration provides a nondetect result when operating properly and that change-outs cost about $1 million per event. He said running the system toward the 4 ppt trigger will help staff collect data on breakthrough timing and schedule the most cost-effective change-outs.
An outside commenter, Mr. Robinson, who participates in state advisory work, advised the commission that the 4 ppt values for PFOA and PFOS remain embedded in federal proposals and that the EPA delayed the compliance date for many systems. "The 4 parts per trillion has been embedded for PFOA and PFOS," Robinson said, noting the agency delayed the effective compliance date to give systems time to comply. Robinson described the city's lead-lag vessel approach for GAC and cautioned against lowering standards that could increase PFAS loading to wastewater treatment or biosolids.
Commissioner discussion acknowledged testing accuracy and seasonality factors that affect loading and breakthrough. Staff said they are currently testing monthly and that accuracy improves at and above the 4 ppt level; staff asked for discretion on timing to avoid, for example, undertaking a change-out during winter when logistics and costs are higher.
Commissioner Hadley moved to accept Scott's recommendation to operate the GAC system toward a 4 ppt trigger and to give staff flexibility on timing for change-outs; Commissioner Gellhar seconded. The motion passed by voice vote.
The commission directed staff to continue monthly monitoring, use the 4 ppt trigger to inform operational decisions, and return with data or recommended change-out schedules as needed. Staff noted the city previously used ion-exchange resin at the old plant but that resin showed short service life for PFAS removal and that the current GAC system was installed to provide longer-term control.
