Foam use by the South Dakota Air National Guard and Sioux Falls Fire Department is the cause.
City engineer Tim Stefanich, who oversees the water system, conceded “there was a little bit of time in between” finding the contamination, determining its source and deciding to shut off affected wells.
In 2014, the city tested for PFAS as part of an EPA-mandated water sampling program.
Today, the 19 offline wells are no longer sampled, but water leaving the city’s purification plant is sampled monthly.
But unlike Box Elder, where training, testing and emergency response activities at Ellsworth Air Force Base led to contamination, two culprits are responsible for the contamination in Sioux Falls.
Of the 17 wells sampled for PFOA/PFOS, 12 had concentrations above the EPA level, including one well 3,500 times that level.
Six of the 10 municipal wells with PFOA/PFOS above the EPA level are marked in the Air Guard’s report.
Lubbers and Stefanich balked at providing the exact location of the other four wells, but Stefanich described one well as north of the airport terminal, and the three others as west and northwest of well 10, which had detections 200 times the EPA advisory level.
With no PFAS detections in raw water entering the treatment plant since 2016, Lubbers and Stefanich believe they have the situation under control.
The Lewis and Clark Regional Water system, a nonprofit, wholesale provider of treated water that Sioux Falls uses for the other half of its drinking water needs, is also tested and has no reported detections.