Oxidation ditches: wastewater treatment plants in Oregon
7 plants · 6% of the state · 55 MGD combined
Klarifi identifies 7 publicly owned wastewater treatment plants with oxidation ditches in Oregon, 6% of the 127 plants in the state (55 MGD combined). The largest is Willow Lake WWTP in Salem at 42.45 MGD.
Oxidation ditches are ring-shaped activated sludge reactors with long retention times, common at plants between 0.5 and 10 MGD. They are recognisable from the air by their looped channels and rely on surface aerators or brush rotors, which are frequent replacement and energy-efficiency projects.
The largest oxidation ditch plants in Oregon
| # | Facility | City | Avg flow (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| 1 | Willow Lake WWTP | Salem | 42.45 | ORL026409 | Dec 2030 | 2 |
| 2 | Mcminnville WWTP | Mcminnville | 4.99 | OR0034002 | Dec 2008 | 2 |
| 3 | Dallas WWTP | Rickreall | 2.77 | OR0020737 | Oct 2030 | 16 |
| 4 | Ashland WWTP | Ashland | 1.67 | OR0026255 | Jan 2027 | 13 |
| 5 | Seaside WWTP | Seaside | 1.65 | OR0020401 | Jul 2029 | 27 |
| 6 | Umatilla STP | Umatilla | 0.67 | OR0022306 | Dec 2027 | 0 |
| 7 | Myrtle Creek WWTP | Myrtle Creek | 0.6 | OR0028665 | Sep 2008 | 0 |
Contacts and project signals for every plant on this list
Klarifi adds verified decision-maker contacts, permit limits, discharge monitoring data and the capital projects planned in each city, filterable by technology, size and compliance record.
Other technologies in Oregon
Oxidation ditches in other states
Oxidation ditches in Oregon: 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: Oxidation ditch · Activated sludge · Biological nutrient removal · Equalization tank · Centrate · all terms