Klarifi tracks 120 publicly owned wastewater treatment plants in South Dakota with a combined average flow of 26 MGD, serving about 179,280 residents. 6 plants treat more than 1 MGD and 1 more than 10 MGD; 107 use lagoon systems and 5 have digesters or biogas infrastructure. The largest is Rapid City Water Reclamation Facility in Rapid City at 10.62 MGD. 26 NPDES permits expire this year and 40 next year.
Every plant below links to a profile with average and design flow, treatment technology, the NPDES permit and its expiry, a three-year compliance snapshot and the capital projects planned in its city.
120 plant locations in South Dakota; dot size follows average flow.
NPDES permits and renewals in South Dakota
Every plant discharges under an NPDES permit that is renewed every five years, usually with tighter limits. The renewal year is the year a plant budgets for upgrades.
Largest wastewater treatment plants in South Dakota
The 25 largest publicly owned wastewater treatment plants in South Dakota by average flow, with NPDES permit, expiry, treatment technology and three-year violation count. Source: EPA ICIS-NPDES via Klarifi.
Klarifi tracks 120 publicly owned wastewater treatment plants in South Dakota with a combined average flow of 26 million gallons per day, serving about 179,280 residents. 6 of them treat more than 1 MGD and 1 more than 10 MGD.
Rapid City Water Reclamation Facility in Rapid City is the largest plant in South Dakota by average flow, treating about 10.62 MGD.
107 of South Dakota's plants use lagoon systems and 5 have biogas or anaerobic digestion infrastructure, based on Klarifi's aerial imagery review.
26 permits held by South Dakota plants expire in 2026 and 40 in 2027. Renewals typically bring new limits and trigger upgrade projects.
Sources and methodology
Flow, permit and violation figures come from the EPA's ICIS-NPDES discharge monitoring records. Population served comes from the Clean Watersheds Needs Survey 2022. Treatment structures are identified by Klarifi's review of aerial imagery, and capital improvement projects are extracted from published municipal budget documents. Violations are counted over the last three years of monitoring reports.
Data refreshed September 11, 2026.
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