South Dakota Water District Expands PFAS Testing, Eyes Treatment Options for Big Sioux River
Why It Matters
South Dakota residents who rely on the Big Sioux River as a water source face growing uncertainty over the presence of per- and polyfluoroalkyl substances, commonly known as PFAS or “forever chemicals.” A regional water district is now expanding its testing efforts and weighing treatment options — a decision that carries significant implications for public health infrastructure and taxpayer costs across the region.
PFAS contamination in surface water sources has become one of the most pressing water quality challenges facing municipalities and rural water districts nationwide. Any treatment solution implemented along the Big Sioux River would likely represent a substantial financial undertaking for local ratepayers and government entities.
What Happened
A water district servicing communities along or near the Big Sioux River in South Dakota has announced plans to conduct additional testing for PFAS compounds in the waterway. Officials are also actively evaluating whether water treatment systems capable of filtering or neutralizing these persistent chemical compounds will need to be installed.
The decision to expand monitoring comes as water managers work to better understand the scope and concentration of PFAS contamination in one of the region’s most significant surface water sources. No specific timeline or cost estimate for potential treatment infrastructure has been publicly confirmed at this stage.
The Big Sioux River runs through eastern South Dakota and portions of neighboring states before joining the Missouri River, making contamination findings relevant not only to South Dakota communities but potentially to downstream users as well.
By the Numbers
4 parts per trillion (ppt) — The U.S. Environmental Protection Agency’s maximum contaminant level for individual PFAS compounds, including PFOA and PFOS, established under federal drinking water standards finalized in 2024.
Thousands of compounds — PFAS is not a single chemical but a family of more than 12,000 synthetic chemicals used in industrial and consumer products since the 1940s, making comprehensive testing a complex and ongoing process.
Billions of dollars — Estimated national cost for water systems to comply with federal PFAS drinking water standards, a burden that disproportionately falls on smaller and rural utilities.
Decades — The approximate persistence of PFAS compounds in the environment, which is why they are commonly referred to as “forever chemicals.” They do not break down naturally under normal conditions.
Multiple states — The Big Sioux River watershed spans South Dakota, Minnesota, and Iowa, meaning contamination monitoring in one state has cross-border relevance for regional water management.
Zoom Out
South Dakota’s water quality concerns over PFAS mirror a pattern playing out in communities across the country. The EPA’s landmark 2024 ruling setting enforceable limits on PFAS in public drinking water systems set off a wave of testing, compliance planning, and infrastructure investment from rural water districts to major metropolitan utilities.
Many states have struggled to balance the cost of PFAS remediation against already strained local budgets. Critics of federal PFAS regulations argue that the compliance mandates place an unreasonable financial burden on smaller water systems and rural ratepayers, with costs ultimately passed on to consumers in the form of higher water bills — a concern particularly relevant in agricultural and small-town communities like those along the Big Sioux River corridor.
Treatment technologies such as granular activated carbon filtration and reverse osmosis are capable of removing many PFAS compounds, but both require significant capital investment and ongoing operational costs that smaller districts find difficult to absorb without state or federal assistance.
What’s Next
The water district is expected to complete its expanded testing phase before making final recommendations on treatment infrastructure. Results from additional water sampling will help officials determine the concentration and distribution of PFAS compounds in the Big Sioux River and assess whether levels exceed federal thresholds that trigger mandatory action.
If treatment is deemed necessary, the district will likely need to seek funding assistance — potentially through federal infrastructure programs — to offset the capital costs involved. State legislators and water management officials in South Dakota may also weigh in as results become clearer.
Residents and local officials along the Big Sioux River corridor are encouraged to monitor updates from their water district as testing results become available. As scientific understanding of water systems and long-range planning continues to evolve — much like other large-scale infrastructure initiatives being tracked nationally, such as upcoming aerospace and environmental monitoring missions — local governments face mounting pressure to act decisively on water quality threats while keeping costs manageable for everyday ratepayers.