By james art 
The murky brown Big Sioux River consistently gets poor marks for its water quality, but 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 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 an increased risk of certain cancers.
The federal government established new limits for 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 Great Sioux River can infiltrate wells near 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 has been found in wells near Ellsworth Air Force Base in Box Elder, as well as Sioux Falls Regional Airport and its Air National Guard base, where the chemicals were used in firefighting foam. The chemical has also been permanently detected in wells at National Guard facilities near Custer and in Rapid City, as well as 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 preliminary sample 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 report 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.
For South Dakota Spotlight: We use our journalistic spotlight to shine a light on critical issues facing South Dakota, analyze decisions made by state leaders and explain the consequences of their policies and the role of politics for South Dakotans. South Dakota Searchlight launched in 2022. We are an affiliate of States Newsrooma national 501(c)(3) nonprofit organization supported by grants and a coalition of donors and readers. Searchlight staff retains full editorial independence.