By james art 
Jenny Kozak, a master’s student in South Dakota Mines, pours water from the Big Sioux River into a collection bottle on Sept. 26 near Eagan. The sample will be tested for PFAS compounds. (Makenzie Huber/South Dakota Searchlight)
The murky Big Sioux River consistently gets bad marks for this water qualitybut eastern South Dakota’s water systems near the river don’t know if that pollution involves “perpetual chemicals.”
To find out, South Dakota mine researchers are testing for per- and polyfluoroalkyl substances (PFAS) at the behest of the East Dakota Water Development District.
The study will cost the district at least $100,000 to test 11 sites from northeastern South Dakota to the Iowa border past Sioux Falls, including four more samples in 2025.
“Ideally, we won’t find anything and we’ll have spent a lot of money to do it,” said Jay Gilbertson, district manager. “But right now we don’t know if there are PFAS in the river. It’s hard to be proactive and plan if you don’t have information.”
A a separate, federally funded project through the South Dakota Department of Agriculture and Natural Resources was announced earlier this year to assess and clean up contaminated sites in South Dakota. Falls Park, Quarry Lake and the former wreck site south of the Sioux Empire Fairgrounds in Sioux Falls are being tested for PFAS and other contaminants that pose a risk to the Greater Sioux River. The project is in the planning phase, and testing has not yet begun.
The chemicals have been used in industry and consumer products since the 1940s and do not break down easily in the environment or in the human body. Research shows that PFAS exposure may be associated with negative developmental and reproductive effects and increased risk of certain cancers.
The federal government set new boundaries on certain types of PFAS in drinking water earlier this year. These restrictions apply specifically to purified drinking water. Restrictions do not apply to chemicals found in waterways.
Water treatment plants along the Big Sioux River can draw directly from the river or from underground wells near the river. Sioux Falls is the only water system that draws water from the Big Sioux River, but the city rarely uses the river as a water source.
An ongoing study shows that under the right conditions, water from the Big Sioux River can penetrate wells by the river.
Gilbertson saw treatment plants in southeastern South Dakota along the Big Sioux River several years ago experience hard water inflow into their systems. He said the culprit is Poinsett Lake, near Watertown, which has started dumping water into the Big Sioux that seeps into underground wells used by some downstream treatment plants.
That’s why it’s “better to go look for it,” Gilbertson said, so treatment plants can prepare solutions before pollution becomes a crisis.
If PFAS is found in the Big Sioux River, the water district can notify public water suppliers, Gilbertson added.
“Perhaps we will tell them, if they can, not to use the well that is so near the river; reactivate one a little further out,” Gilbertson said. “As a result, they may not technically have a problem and have to stop serving customers because they stopped using the water before it became a problem.”
PFAS was detected in wells near Ellsworth Air Force Base in Box Elder, as well as Sioux Falls Regional Airport and the co-located Air National Guard base, where the chemicals were used in firefighting foam. The chemical has forever been found in wells at National Guard facilities near Custer and in Rapid City and three private wells in South Dakota.
Sioux Falls shut down 21 of its wells suspected of being contaminated with PFAS after the discovery. Since then, all raw water samples — which can sometimes include the Big Sioux River — have been tested for PFAS compounds, Sioux Falls Superintendent Chris Myers said in an emailed statement. The city has not detected PFAS in these sources.
But even if Sioux Falls doesn’t detect PFAS in river tests, that doesn’t mean there aren’t PFAS in the river: It just means it’s not immediately upstream, Gilbertson said.
“It doesn’t necessarily rule out it being from the upper basin or below the city,” he added.
Most recently a preview of Drinking water at Mount Rushmore National Memorial had PFAS levels more than twice the new federal limit.
The South Dakota Rural Water Systems Association is testing 40 rural water systems across the state for PFAS chemicals in cooperation with the EPA. Cities also test their water and submitting it to the EPA.
Lisa Kunza, associate professor of chemistry, biology and health sciences and director of the Center for Sustainable Solutions at South Dakota Mines in Rapid City, helped collect the initial samples from the Big Sioux River in September.
Kunza and her team investigate the impact of PFAS contamination on water resources, agriculture and human health. They look for 40 PFAS compounds in the water. She said initial test results could take a month to several months to come back from the lab.
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