Oxidation ditches: wastewater treatment plants in Washington
38 plants · 30% of the state · 2 MGD reported by 8 plants
Klarifi identifies 38 publicly owned wastewater treatment plants with oxidation ditches in Washington, 30% of the 125 plants in the state (2 MGD reported by 8 plants). The largest is Omak Wastewater Treatment Plant in Omak at 0.53 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 Washington
| # | Facility | City | Avg flow (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| 1 | Omak Wastewater Treatment Plant | Omak | 0.53 | WA0020940 | Dec 2020 | 0 |
| 2 | Medical Lake WWTP | Medical Lake | 0.27 | WA0021148 | Jul 2019 | 13 |
| 3 | Chewelah WWTP | Chewelah | 0.19 | WA0023604 | Nov 2016 | 1 |
| 4 | Brewster STP | Brewster | 0.18 | WA0021008 | Jan 2021 | 0 |
| 5 | Tulalip Wastewater Treatment Plant | Marysville | 0.17 | WA0024805 | Oct 2014 | 1 |
| 6 | Pacific Beach STP | Pacific Beach | 0.09 | WA0037095 | Aug 2030 | 37 |
| 7 | Asotin STP | Clarkston | 0.08 | WA0020818 | Aug 2023 | 1 |
| 8 | Toutle STP | Toutle | 0.06 | WA0037770 | Jun 2030 | 7 |
| 9 | Bingen POTW | Bingen | — | WA0022373 | Jun 2019 | 13 |
| 10 | Bridgeport WWTP | Bridgeport | — | WA0024066 | Jul 2030 | 0 |
| 11 | Entiat POTW | Entiat | — | WA0051276 | Jul 2022 | 27 |
| 12 | Everson WWTP | Everson | — | WA0020435 | Sep 2022 | 0 |
| 13 | Grand Coulee WWTP | Grand Coulee | — | WA0044857 | Dec 2014 | 0 |
| 14 | Grand Mound STP | Rochester | — | WA0042099 | Feb 2029 | 3 |
| 15 | Grandview Wastewater Treatment Plant | Grandview | — | WA0052205 | Dec 2024 | 195 |
| 16 | Granger POTW | Granger | — | WA0022691 | Aug 2031 | 210 |
| 17 | Granite Falls STP | Granite Falls | — | WA0021130 | Jul 2025 | 6 |
| 18 | Hoquiam STP | Hoquiam | — | WA0020915 | Oct 2030 | 0 |
| 19 | Kitsap Cnty Kingston WWTP | Kingston | — | WA0032077 | Nov 2020 | 0 |
| 20 | La Conner STP | Mount Vernon | — | WA0022446 | Feb 2024 | 9 |
| 21 | Leavenworth STP | Leavenworth | — | WA0020974 | Aug 2020 | 0 |
| 22 | Lynden STP | Lynden | — | WA0022578 | Oct 2022 | 6 |
| 23 | Mabton Wastewater Treatment Plant | Mabton | — | WA0020648 | Jul 2031 | 0 |
| 24 | Naches STP | Naches | — | WA0022586 | Sep 2019 | 41 |
| 25 | Newport WWTP | Newport | — | WA0022322 | Apr 2013 | 21 |
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 Washington
Oxidation ditches in other states
Oxidation ditches in Washington: 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.