The 37 largest wastewater treatment plants in South Dakota
Ranked by average flow · 33 MGD combined · 100% of the state's reported flow
Rapid City Water Reclamation Facility in Rapid City is the largest publicly owned wastewater treatment plant in South Dakota by reported average flow, treating about 9.62 million gallons per day. The 37 plants below treat 33 MGD between them, 100% of the flow reported by all 130 plants in the state, and serve about 154,295 people. Every plant links to its profile with permit and compliance data. Treatment technology is shown with a free Klarifi account.
| # | Facility | City | Avg flow (MGD) | Population | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|---|
| 1 | Rapid City Water Reclamation Facility | Rapid City | 9.62 | 96,450 | SD0023574 | Jun 2022 | 4 |
| 2 | Huron, City Of | Huron | 4.88 | — | SD0023434 | Jun 2027 | 21 |
| 3 | Watertown, City Of | Watertown | 3.89 | 25,026 | SD0028614 | Jun 2018 | 1 |
| 4 | Wilmot, City Of | Wilmot | 2.35 | — | SD0021024 | May 2027 | 24 |
| 5 | Lead - Deadwood Sanitary District | Deadwood | 1.65 | 3,290 | SD0020796 | Jun 2020 | 2 |
| 6 | Pierre, City Of | Pierre | 1.49 | — | SD0020176 | Jun 2027 | 3 |
| 7 | Spearfish, City Of (wtp) | Spearfish | 1.18 | 12,193 | SDG860058 | Oct 2027 | 4 |
| 8 | Canton, City Of | Canton | 1.08 | — | SD0022489 | Dec 2023 | 25 |
| 9 | Vermillion, City Of | Vermillion | 1.06 | — | SD0020061 | Sep 2017 | 2 |
| 10 | Hartford, City Of | Hartford | 0.87 | 4,128 | SD0021750 | Dec 2024 | 117 |
| 11 | Frederick, Town Of | Frederick | 0.53 | — | SD0022152 | Sep 2024 | 49 |
| 12 | Harrisburg - City Of | Harrisburg, City Of | 0.48 | — | SD0023728 | Jun 2031 | 0 |
| 13 | Hot Springs, City Of | Hot Springs | 0.43 | — | SD0022918 | Dec 2017 | 1 |
| 14 | Volga, City Of | Volga, City Of | 0.39 | — | SD0021920 | Dec 2028 | 36 |
| 15 | Oacoma, Town Of | Oacoma | 0.39 | — | SD0020737 | Dec 2027 | 5 |
| 16 | Beresford, City Of | Beresford | 0.3 | — | SD0020079 | May 2031 | 5 |
| 17 | Freeman, City Of | Freeman | 0.29 | — | SD0022110 | Jun 2027 | 3 |
| 18 | Summerset, City Of | Summerset | 0.21 | 2,477 | SD0027758 | Apr 2031 | 0 |
| 19 | Whitewood Water | Whitewood | 0.2 | — | SD0021466 | Feb 2023 | 4 |
| 20 | Wagner, City Of | Wagner | 0.2 | — | SD0020184 | Sep 2029 | 5 |
| 21 | Dell Rapids, City Of | Dell Rapids | 0.2 | 3,949 | SD0022101 | Sep 2019 | 1 |
| 22 | Hill City, City Of | Hill City | 0.17 | — | SD0020885 | Feb 2027 | 1 |
| 23 | Mobridge, City Of | Mobridge | 0.17 | — | SD0020028 | Jun 2024 | 0 |
| 24 | Lennox, City Of | Lennox | 0.16 | — | SD0021768 | Dec 2027 | 3 |
| 25 | Iroquois, City Of | Iroquois | 0.14 | — | SDG922438 | Aug 2026 | 33 |
| 26 | Platte, City Of | Platte | 0.14 | 1,425 | SD0020354 | Dec 2028 | 130 |
| 27 | North Sioux City, City Of (wtp) | North Sioux City | 0.1 | 5,061 | SD0020567 | Dec 2030 | 7 |
| 28 | Springfield, City Of | Springfield | 0.1 | — | SD0028647 | Sep 2029 | 120 |
| 29 | Keystone, Town Of | Keystone | 0.1 | — | SD0024007 | Jun 2025 | 21 |
| 30 | Roslyn, Town Of | Roslyn | 0.07 | — | SD0022802 | Dec 2028 | 3 |
| 31 | Labolt, Town Of | Labolt | 0.06 | — | SDG926662 | Aug 2026 | 114 |
| 32 | Claremont, Town Of | Claremont | 0.05 | — | SDG922314 | Aug 2026 | 128 |
| 33 | Herreid, City Of | Herreid | 0.03 | — | SD0022900 | Apr 2028 | 0 |
| 34 | Hermosa - Town Of | Hermosa | 0.02 | 296 | SD0022349 | Jun 2030 | 18 |
| 35 | Worthing, City Of | Worthing | 0.02 | — | SD0021474 | Jan 2027 | 34 |
| 36 | Grand River Casino And Resort | Mobridge | 0.01 | — | NDG589306 | Mar 2027 | 16 |
| 37 | Elkton, City Of | Elkton, City Of | 0.01 | — | SD0020788 | Jun 2024 | 17 |
Treatment technology for each plant is shown with a free Klarifi account. Create one →
Largest plants in South Dakota: questions
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 October 26, 2026.
Wastewater terms: WWTP · POTW · MGD · NPDES permit · Inflow and infiltration · Sludge dewatering · all terms
Cite this page
Journalists, researchers and educators are welcome to quote these figures. Please credit Klarifi as the source and link to this page.
Klarifi. “Largest wastewater treatment plants in South Dakota (2026).” Updated October 26, 2026. https://klarifi.io/facilities/south-dakota/largestNeed a custom cut of the data for a state, a county or a list of plants? Email info@klarifi.io.