City official: Guard base contaminated Sioux City drinking water

There are small amounts of so-called “forever chemicals” in Sioux City’s treated drinking water, and the likely source of contamination is an Iowa Air National Guard base, said Brad Puetz, utilities director for Sioux City.

An analysis of groundwater in the area about three years ago revealed perfluoroalkyl and polyfluoroalkyl substances — commonly called PFAS — in concentrations that were more than 100 times a health safety threshold set by the U.S. Environmental Protection Agency, according to Iowa Public Radio.

In December, the Iowa Department of Natural Resources tested a city well about a mile and a half west of that base and found two prominent PFAS in a total concentration of 9.1 parts per trillion in the groundwater.

The federal health advisory is 70 parts per trillion. Tests at the base showed concentrations of up to 8,610 parts per trillion.

“We’re pretty confident the source is the firefighting foam from the air base,” Puetz said.

PFAS have been used in non-stick and stain-resistant products and firefighting foams, among others. Research has shown they can cause cancers in people who ingest them, and that they persist indefinitely in the environment.

DNR tests of finished drinking water from one of the city’s two treatment plants found PFAS in a slightly higher concentration than in the untreated water.

The Southbridge Regional Water Treatment Plant accounts for about a quarter of the city’s total water capacity, and it only draws water from the contaminated well, Puetz said. The plant is located on the city’s south side, but its water commingles with treated water from the other plant.

The city will test its drinking water every three months to be sure the rate of contamination doesn’t increase. Water at the other treatment plant had no detectable amounts of PFAS.

“I think we’ve got a good handle on what’s there and what needs to be dealt with,” Puetz said.

The tests in Sioux City were part of statewide sampling the DNR is using to determine the prevalence of PFAS in drinking water. Contaminations have also been found in Ames, Rock Valley and West Des Moines.

Tom Van Maanen, city administrator for Rock Valley, said the city’s shallow wells were likely contaminated by the nearby Rock River. A firefighter training area is thought to be the contamination source in Ames, and West Des Moines Water Works officials have not indicated a suspected source.

Sioux City has also had trouble with its wastewater in recent years. The DNR filed suit this month against the city and alleged it has repeatedly failed to ensure it isn’t discharging excessive amounts of harmful bacteria and treatment chemicals into the Missouri River.