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Sioux City Finds Higher Levels Of Disinfection Chemicals In Its Water System

Courtesy of CDC
Water samples collected mid-August showed one of Sioux City’s eight testing sites for its water system was a little bit higher than the Environmental Protection Agency’s standard for trihalomethanes.";s:

Sioux City has been working to get its drinking water back to compliance after violating a drinking water standard for disinfection byproducts.
Water samples collected mid-August showed one of Sioux City’s eight testing sites for its water system was a little bit higher than the Environmental Protection Agency’s standard for trihalomethanes. These form when disinfectants like chlorine are used to take out pathogens from drinking water.

One testing site in Sioux City showed levels of .130 milligrams per liter in August. The EPA’s maximum contaminant level – the drinking water standard – is .080 milligrams per liter.

“We’re not taking it lightly. We’re doing what we can to decrease the levels of trihalomethanes as quickly as possible,” said Sioux City’s Water Plant Superintendent Brad Puetz.

Puetz said the city put out a notice to inform the public about the violation.

“We don’t feel that there’s any immediate health risks for anybody,” Puetz said.

Health effects like cancer can happen after long-term exposure to these chemicals. The city will continue to take samples to monitor the water. It started pulling water from deeper wells, Puetz said.

“Which cools the water down, reduces the amount of organics in the water that can react with the chlorine,” Puetz said.

Four factors form trihalomethanes: their disinfectant level, the water temperature, water age and amount of organics in the water. Puetz said he believes the Missouri River’s higher flow levels from this summer were a factor, along with warmer water temperatures and more organic compounds in the water.

Julie Sievers, an environmental specialist senior with the Iowa Department of Natural Resources said higher river flow levels mean increased organic matter in the water.

“They [Sioux City] also have very warm water temperature. Their temperature is some of the highest they’ve seen,” Sievers said. “And because August itself was cooler, water demand was down.”

Flows from Gavins Point Dam above the Missouri River at Sioux City were higher than average this summer.

Sievers said Sioux City took the proper course of action, responding immediately to the situation after it got its test results back for the sample, and putting out a public notice as required.

The city’s next routine sample is due in November, but the city is doing some earlier routine sampling to see if the levels are down, she said.

This is the first time Sioux City has exceeded the standard for trihalomethanes, but David Cwiertny, the director for the Center for Health Effects of Environmental Contamination at the University of Iowa, said this is not unusual nationwide.

“The reason we have disinfection byproducts is that we need to disinfect our water supplies,” Cwiertny said. “This is something that could happen in any water system just because it’s a byproduct of an absolutely necessary treatment step, which is adding something like a chemical disinfectant to kill pathogens that could make us sick acutely.”

Cwiertny said in some ways, trihalomethanes are a “necessary evil” because we have to disinfect our water, yet adding a chemical disinfectant can generate other chemicals.

“That’s part of that delicate balance that water providers have to find, is adding just enough chlorine as a disinfectant to kill the things we don’t want, but not generate enough of the things that we worry about like trihalomethanes,” Cwiertny said.

This story has been updated to clarify the higher river flow levels that officials believe increased the amount of trihalomethanes in the water.

Katie Peikes was a reporter for Iowa Public Radio from 2018 to 2023. She joined IPR as its first-ever Western Iowa reporter, and then served as the agricultural reporter.