Oconomowoc utility staff brief council on chlorine, fluoride and orthophosphate use and monitoring

City of Oconomowoc utility staff on Tuesday briefed the common council on the chemicals the utility adds to drinking water, how they monitor doses and the safety measures they use.

Scott Osborne, the water superintendent, told the council the utility doses gas chlorine for disinfection, fluoride to help prevent tooth decay and a blended orthophosphate product (AquaMag) for corrosion control and iron sequestration. “We dose at our 3 spots there between 1.5 and 3.3 milligrams per liter,” Osborne said of chlorine, and he said the utility follows current fluoride dosing recommendations of 0.7 milligrams per liter. He described orthophosphate dosing in the range the utility uses and said orthophosphate was added in the mid-1990s after a Wisconsin Department of Natural Resources corrosion-control study recommended a sequestering chemical.

The council was given details about daily and periodic monitoring. Osborne said crews visit each chemical feed site every day, record pumped volumes and chemical consumption, and enter data into spreadsheets used to check that dosages stay within required parameters. “All our water operators are first class operators certified. They have annual training requirements,” Osborne said. He added the utility runs split samples with the state lab each month for fluoride, tests fluoride in-house daily, and samples sources and residuals multiple times per week for iron, phosphate and chlorine.

Osborne told the council that the city’s budget for water treatment chemicals for the year is about $100,000, with roughly 70% used for orthophosphate, 25% for chlorine and a small share for fluoride. He described recent equipment changes, including switching from floor-scale day tanks to enclosed “tank-in-tank” secondary containment and installing radar-level monitoring on some tanks to reduce spill risk.

Council members asked follow-up questions about alternatives and monitoring. Alderman Rosick said he had shared a report from the National Toxicology Program and raised concerns about exposure levels. “Exposure above the 1.5 milligrams per liter is considered toxic to children and can actually reduce, you know, brain development and cognition,” Rosick said, urging careful review of health studies and multiple exposure sources such as toothpaste and mouthwash.

Osborne and others explained the local picture: the utility’s naturally occurring fluoride in source water is very low, the system’s fluoride dosing target is 0.7 mg/L and the EPA’s maximum contaminant level (MCL) for fluoride is 4 mg/L. Osborne said the city’s fluoride levels are well below the values cited in recent studies. He also emphasized that orthophosphate use is tied to corrosion-control goals: it forms a protective coating to limit lead and copper release from pipes.

Council members also pressed staff on alarms and automated monitoring. Rosick asked the utility to investigate SCADA (supervisory control and data acquisition) upgrades that would alarm if feeders over- or under-dose. Osborne said there are options, including continuous analyzers at each site or setting alarms on radar-level devices that detect unusually fast chemical consumption; staff will investigate costs and report back.

Several council members and Osborne returned repeatedly to service-line replacement as a long-term way to reduce orthophosphate needs. Osborne said the city still has “over 700 lead service lines.” He reported the utility has changed out about 1,000 meters since last June and aims to change 2,600 meters by the end of 2026; he described the city’s ongoing program to replace public-side lead laterals during annual street projects and said financing for private-side replacements remains a challenge.

There was no formal council action at the meeting. Staff listed next steps: continue daily monitoring and safety training; investigate SCADA and alarm options; continue permitting and planning for Well 8 and an iron-filtration pump station scheduled to start pumping near Thanksgiving; continue replacing public-side lead laterals during street projects; and provide follow-up information to the council on requests made during the meeting.

The council asked staff to compile requested technical information, cost estimates for SCADA alarms and options for reducing fluoride or changing fluoride dosing, and return to a future meeting or committee for further discussion.