Wastewater Treatment Plants in Idaho
94 facilities · 94 MGD combined flow
Klarifi tracks 94 publicly owned wastewater treatment plants in Idaho with a combined average flow of 94 MGD, serving about 879,926 residents. 13 plants treat more than 1 MGD and 1 more than 10 MGD; 64 use lagoon systems and 7 have digesters or biogas infrastructure. The largest is West Boise WWTP in Garden City at 62 MGD. 6 NPDES permits expire this year and 4 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.
94 plant locations in Idaho; dot size follows average flow.
NPDES permits and renewals in Idaho
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 Idaho
| Facility | City | Avg flow (MGD) | Design (MGD) | NPDES permit | Expires | Technology | Violations (3y) |
|---|---|---|---|---|---|---|---|
| West Boise WWTP | Garden City | 62 | 24 | ID0023981 | Jun 2027 | Clarifiers, Uncovered lagoons, Biogas silos | 9 |
| Pocatello City WWTP | Pocatello | 6.79 | 12 | ID0021784 | Aug 2017 | Clarifiers, Uncovered lagoons, Biogas silos | 8 |
| Jerome WWTP | Jerome | 3.59 | 3 | ID0020168 | Jun 2015 | Clarifiers, Biogas silos | 4 |
| Lewiston WWTP | Lewiston | 3.31 | 5.7 | ID0022055 | Jan 2021 | Clarifiers, Biogas silos, Biogas balloons | 0 |
| Oxbow WWTP | Shelley | 1.93 | 2 | ID0020133 | May 2019 | — | 0 |
| Emmett WWTP | Emmett | 1.76 | 5.7 | ID0020311 | Jan 2007 | Uncovered lagoons | 2 |
| Star WWTP | Star | 1.58 | 1.85 | ID0023591 | Apr 2020 | Aerated lagoons | 0 |
| Page WWTP | Smelterville | 1.36 | 4.3 | ID0021300 | Sep 2018 | Clarifiers, Aerated lagoons, Uncovered lagoons | 1 |
| Kuna North WWTP | Meridian | 1.23 | 3.5 | ID0028355 | May 2014 | — | 5 |
| Rigby WWTP | Rigby | 1.2 | 0.53 | ID0020010 | Dec 2021 | Clarifiers, Carrousels / oxidation ditches | 9 |
| Salmon Sewage Lagoon | Salmon | 1.02 | 0.45 | ID0020001 | May 2026 | Aerated lagoons, Uncovered lagoons | 0 |
| Ketchum Sun Valley WWTP | Ketchum | 1.02 | 4 | ID0020281 | Jul 2017 | Biogas balloons | 0 |
| Payette WWTP | Payette | 1 | 2.88 | ID0020672 | Oct 2019 | Clarifiers, Carrousels / oxidation ditches | 1 |
| Soda Springs WWTP | Soda Springs | 0.86 | 1.7 | ID0020818 | Jun 2025 | — | 1 |
| Moscow STP | Moscow | 0.85 | 4 | ID0021491 | Jan 2031 | Clarifiers, Carrousels / oxidation ditches | 0 |
| Heyburn WWTP | Heyburn | 0.71 | 0.66 | ID0020940 | Jan 2007 | Clarifiers, Carrousels / oxidation ditches | 17 |
| American Falls WWTP | American Falls | 0.53 | 0.9 | ID0020753 | Jul 2019 | — | 2 |
| Homedale WWTP | Homedale | 0.5 | 0.65 | ID0020427 | Sep 2018 | Covered lagoons, Uncovered lagoons | 18 |
| Driggs WWTP | Driggs | 0.39 | 0.6 | ID0020141 | Dec 2015 | Aerated lagoons | 163 |
| Grangeville WWTP | Grangeville | 0.39 | 0.88 | ID0020036 | Apr 2025 | Clarifiers, Carrousels / oxidation ditches | 3 |
| Buhl WWTP | Buhl | 0.29 | 0.67 | ID0020664 | Oct 2012 | Clarifiers, Uncovered lagoons, Carrousels / oxidation ditches | 2 |
| St Anthony Sewage Lagoon | Saint Anthony | 0.26 | 0.8 | ID0020401 | Nov 2014 | Aerated lagoons | 7 |
| Aberdeen WWTP | Aberdeen | 0.2 | 0.6 | ID0020176 | Feb 2021 | Clarifiers | 18 |
| Shoshone WWTP | Shoshone | 0.13 | 0.53 | ID0023728 | Apr 2024 | Uncovered lagoons | 22 |
| Council WWTP | Council | 0.12 | 0.4 | ID0020087 | Aug 2025 | Aerated lagoons, Uncovered lagoons | 3 |
Idaho plants by treatment technology
All 94 plants in Idaho
Wastewater treatment in Idaho: 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 September 11, 2026.