Ontario STP
Ontario, OR · Malheur County · Publicly Owned Treatment Works
- Average flow
- —
- Design flow
- 3.06 MGD
- NPDES permit
- OR0020621
- Effective
- Permit expires
- January 2031
- Population served
- 11,515
- CWNS 2022
Ontario STP is a publicly owned wastewater treatment works in Ontario, Malheur County, Oregon, serving about 11,515 residents. Treatment on site includes aerated lagoons. It discharges under NPDES permit OR0020621 (effective), which expires in January 2031, with 2 recorded violations in the last three years.
Treatment technology
Treatment structures identified at this facility. Exact unit counts are available in Klarifi.
Aerated lagoons
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Compliance snapshot (last 3 years)
- Total violations
- 2
- Effluent violations
- 0
Based on NPDES Discharge Monitoring Reports. Full violation history, parameters and discharge data available in the Klarifi platform.
Key contacts
Decision-makers at Ontario STP.
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Nearby wastewater treatment plants in Oregon
Huntington · 25 mi away
0.04 MGD
North Powder · 82 mi away
0.04 MGD
Union · 92 mi away
0.12 MGD
Joseph · 93 mi away
0.12 MGD
Enterprise · 97 mi away
0.24 MGD
Mount Vernon · 108 mi away
0.03 MGD
Wallowa · 109 mi away
0.1 MGD
Long Creek · 114 mi away
0.03 MGD
Ontario STP: frequently asked 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; facility record last updated February 16, 2025.