Oxidation ditches: wastewater treatment plants in California
33 plants · 17% of the state · 32 MGD reported by 19 plants
Klarifi identifies 33 publicly owned wastewater treatment plants with oxidation ditches in California, 17% of the 193 plants in the state (32 MGD reported by 19 plants). The largest is Western Riverside Co Reg WWTP in Corona at 8.54 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 California
| # | Facility | City | Avg flow (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| 1 | Western Riverside Co Reg WWTP | Corona | 8.54 | CA8000316 | Jul 2020 | 47 |
| 2 | Corona WWTP 1 | Corona | 7.64 | CA8000383 | Jun 2025 | 9 |
| 3 | Woodland WPCF | Woodland | 2.61 | CA0077950 | Mar 2030 | 2 |
| 4 | Olivehurst WWTF | Olivehurst | 1.99 | CA0077836 | May 2026 | 24 |
| 5 | Ojai Valley WWTP | Ventura | 1.56 | CA0053961 | Jan 2029 | 289 |
| 6 | Brentwood Wastewater Treatment Plant | Brentwood | 1.46 | CA0082660 | May 2029 | 17 |
| 7 | Imperial WWTP | Imperial | 1.4 | CA0104400 | Sep 2020 | 5 |
| 8 | Susanville Sd WWTP | Susanville | 1.02 | CA0102695 | Jul 2013 | 31 |
| 9 | Discovery Bay WWTP | Discovery Bay | 1.01 | CA0078590 | Jan 2030 | 5 |
| 10 | Pismo Beach WWTF | Pismo Beach | 0.93 | CA0048151 | Jan 2021 | 77 |
| 11 | Auburnna City Of | Auburn | 0.79 | CAC448871 | Nov 2022 | 2 |
| 12 | Live Oak City WWTP | Live Oak | 0.74 | CAC444735 | Nov 2022 | 14 |
| 13 | Corning Wastewater Treatment Plant | Corning | 0.63 | CA0004995 | May 2027 | 681 |
| 14 | Heber Pud WWTP | Heber | 0.48 | CA0104370 | Jun 2021 | 5 |
| 15 | Shasta Lake WWTF | Shasta Lake | 0.43 | CA0079511 | Jan 2026 | 30 |
| 16 | Lake Wildwood WWTP | Penn Valley | 0.35 | CAC439953 | Mar 2031 | 5 |
| 17 | Cottonwood WWTP | Cottonwood | 0.29 | CA0081507 | May 2029 | 78 |
| 18 | Westmorland WWTP | Westmorland | 0.2 | CA0105007 | Mar 2028 | 8 |
| 19 | Mariposa Pud WWTF | Mariposa | 0.16 | CAC441902 | Apr 2030 | 5 |
| 20 | Atwater Regional Wastewater Treatment Facility | Atwater | — | CAC422026 | Jul 2029 | 4 |
| 21 | Camrosa WRF | Camarillo | — | CA0059501 | Jul 2025 | 0 |
| 22 | City Of Lincoln WWTP | Lincoln | — | CA0084476 | May 2029 | 0 |
| 23 | City Of San Bernardino WRF | San Bernardino | — | CA0105392 | Dec 2022 | 115 |
| 24 | Coachella Sd WWTP | Coachella | — | CA0104493 | Jun 2025 | 3 |
| 25 | Colton WWTF | Colton | — | CA0105236 | Dec 2017 | 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 California
Oxidation ditches in other states
Oxidation ditches in California: 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.