Oxidation ditches: wastewater treatment plants in California
33 plants · 17% of the state · 65 MGD reported by 23 plants
Klarifi identifies 33 publicly owned wastewater treatment plants with oxidation ditches in California, 17% of the 192 plants in the state (65 MGD reported by 23 plants). The largest is Regionwide Water Recycling System - Temescal Creek Discharge in Lake Elsinore at 19.76 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 | Regionwide Water Recycling System - Temescal Creek Discharge | Lake Elsinore | 19.76 | CA8000188 | Sep 2020 | 34 |
| 2 | Western Riverside Co Reg WWTP | Corona | 8.49 | CA8000316 | Jul 2020 | 46 |
| 3 | Corona WWTP 1 | Corona | 7.32 | CA8000383 | Jun 2025 | 9 |
| 4 | Lompoc Wastewater Plant | Lompoc | 6.37 | CA0048127 | Apr 2027 | 11 |
| 5 | Woodland WPCF | Woodland | 3.86 | CA0077950 | Mar 2030 | 2 |
| 6 | Brentwood Wastewater Treatment Plant | Brentwood | 2.88 | CA0082660 | May 2029 | 17 |
| 7 | Coachella Sd WWTP | Coachella | 2.77 | CA0104493 | Jun 2025 | 3 |
| 8 | Olivehurst WWTF | Olivehurst | 1.99 | CA0077836 | May 2026 | 25 |
| 9 | Ojai Valley WWTP | Ventura | 1.98 | CA0053961 | Jan 2029 | 289 |
| 10 | Imperial WWTP | Imperial | 1.4 | CA0104400 | Sep 2020 | 5 |
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 October 26, 2026.
Wastewater terms: Oxidation ditch · Activated sludge · Biological nutrient removal · Filter press · FOG · all terms