South Dakota Private Well Water Quality 2026

Ellsworth Air Force Base: South Dakota’s Defining PFAS Crisis

The defining source of PFAS contamination in South Dakota’s private wells is Ellsworth Air Force Base, located six miles east of Rapid City near Box Elder. The US Air Force first detected PFAS in groundwater at Ellsworth in 2011, but contamination of local private drinking water wells was not confirmed until 2016. Testing by the Air Force found at least 23 private wells above EPA safety limits, serving more than 130 residences — with PFOS concentrations as high as 4,680 parts per trillion and PFOA concentrations up to 320 ppt. The federal limit as of April 2024 is 4 ppt for each, meaning some wells exceeded it by more than 1,000 times. On-base soil and groundwater contamination reached 551,000 ppt according to analysis of military records by Northeastern University and EWG.

The PFAS contamination plume is estimated at approximately 25 miles long, according to the EPA’s Superfund site assessment. The Air Force initially provided bottled water to affected households, then installed treatment systems at impacted residences. More recently, Box Elder, the Ellsworth Development Authority and Rapid City partnered on a $12.5 million pipeline — funded by the US Air Force — to transport water from Rapid City to approximately 35 of the most affected properties. Construction began in 2024. Despite these remediation efforts, the Air Force has stated that the full extent of PFAS contamination at Ellsworth is still being investigated.

Ellsworth is not the only military source of PFAS contamination in the state. PFAS has been detected at National Guard facilities near Custer and Rapid City, and at the Sioux Falls Regional Airport co-located with the South Dakota Air National Guard base, where groundwater and soil contamination reached a combined 255,100 ppt in 2018. In the Black Hills, a 2023 test of Mount Rushmore National Memorial’s drinking water found PFOS at 9.8 ppt — more than twice the 4 ppt federal limit — with the source unknown. Sioux Falls received a $37.2 million settlement from 3M and DuPont in 2025 over PFAS contamination of its municipal wells.

PFAS in Rural and Tribal Wells

Beyond the military base hotspots, a 2023 USGS study testing both public and private well systems found PFAS in three South Dakota private wells — all located in or near Native American Reservation communities in western South Dakota, in counties including Dewey, Ziebach, Oglala Lakota, Bennett and Jackson. Two wells tested positive for PFBS at 2,700 ppt and 13,200 ppt respectively; a third tested at 84,000 ppt for PFBA. Each of these detections exceeded the EPA interim health advisories in force at the time, which were set near zero for PFOS and PFOA.

These tribal area detections highlight a concern that extends beyond the immediate Ellsworth plume: rural and Indigenous communities across western South Dakota may have private wells with PFAS contamination that has never been formally tested, given that private wells carry no federal or state mandatory testing requirements.

A 2024 study by South Dakota Mines, commissioned by the East Dakota Water Development District, was also underway to test 11 sites along the Big Sioux River from northeast South Dakota to the Iowa border — seeking to determine whether PFAS has infiltrated the river and, from there, wells drawing from riverbank aquifers downstream.

Nitrate, Arsenic and Uranium in South Dakota Well Water

PFAS aside, South Dakota well owners face several serious naturally occurring and agricultural contamination risks. EWG analysis found that 234 public water systems serving approximately 458,500 people had contaminant levels exceeding health guidelines for nitrate, and 37 systems serving around 201,000 people exceeded health guidelines for arsenic — though most remained within federal legal limits. For private well owners, whose water is untested by any authority, the picture is likely worse.

Nitrate is a persistent concern in South Dakota’s agricultural heartland. Fertiliser runoff from farming and livestock operations contaminates shallow groundwater, particularly in the eastern part of the state. High nitrate levels are especially dangerous for infants under six months, potentially causing the life-threatening condition known as “blue baby syndrome.” South Dakota law requires new domestic wells to be tested for nitrate before use under the Centennial Environmental Protection Act — but existing wells carry no ongoing mandatory testing requirement.

Arsenic is naturally elevated in parts of South Dakota due to geology, particularly in western South Dakota’s Black Hills region and areas with mineralised rock. The DrillerDB guide for South Dakota well owners notes elevated arsenic in western areas specifically. Arsenic is colourless and tasteless and can only be detected through laboratory testing. Long-term exposure is linked to cancers of the bladder, lungs, liver, skin and kidneys.

Uranium and radium are also documented concerns in South Dakota’s water. EWG data found 210 public water systems serving around 220,000 people had unhealthful levels of radium or uranium based on health guidelines. Areas near historic uranium mining and exploration in western South Dakota are at elevated risk for these contaminants in well water — the state’s own 2024 integrated water quality report notes that monitoring stations near uranium mining areas are specifically tested for arsenic, uranium and radium.

Regulatory Situation for South Dakota Well Owners

Private residential wells in South Dakota are not regulated under the federal Safe Drinking Water Act, and the state has no enforceable MCLs (maximum contaminant levels) for private well water. South Dakota DANR (Department of Agriculture and Natural Resources) oversees the state’s drinking water programme — but its authority extends only to public water systems, not private wells.

Under South Dakota law, new domestic wells must be tested for coliform bacteria and nitrate before use — this is one of the stronger new-well requirements in the region. However, there is no requirement for ongoing testing of existing private wells, and no requirement to test for PFAS, arsenic, uranium or other contaminants beyond the initial bacteria and nitrate check. Testing and treatment of your own well is entirely your responsibility as a homeowner.

For PFAS specifically, South Dakota has no state MCLs. The federal EPA MCLs of 4 ppt for PFOA and PFOS, finalised in April 2024, apply only to public water systems — not private wells. The Trump administration announced in 2025 plans to delay enforcement of these limits until 2031 and is reconsidering rules for some types of PFAS, though the MCLs remain in force and public systems are required to comply.

Check our South Dakota municipal water quality page for city-by-city tap water data, our Sioux Falls water quality page for detail on PFAS issues affecting the city’s public supply, or use our live boil water notice tracker for active advisories across the state.

Known High-Risk Areas in South Dakota

If you live near any of the following locations, well water testing is urgent — not precautionary.

How to Test Your South Dakota Well Water — and What to Do Next

Every South Dakota private well owner should test their water — the combination of military PFAS plumes, agricultural nitrate, naturally occurring arsenic and uranium, and a lack of any mandatory ongoing testing means that well water conditions are essentially unknown until tested.

If you live within 30 miles of Ellsworth Air Force Base, the Sioux Falls Regional Airport, or any National Guard facility in the state, PFAS testing should be treated as urgent. Contact your county health department or use DANR’s certified laboratory list at danr.sd.gov. For properties near military installations, the Air Force has coordinated bottled water and treatment system programmes for the most severely affected households — contact EPA Region 8 or ATSDR if you believe your well may be in a contamination zone.

For filter options, our well water filter guide covers reverse osmosis systems for PFAS, arsenic and uranium, UV disinfection for bacteria, and whole-house well systems for comprehensive protection. You can also browse our full water filter solutions page or check your ZIP code for local water quality context.

For nearby state well water risks, see our pages on Ohio wells and Michigan wells. Return to the private well water directory to find your state.