Ontario STP
2405 Malheur Dr, Ontario, OR 97914 · Malheur County · Publicly Owned Treatment Works
- Average flow
- 1.87 MGD
- 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 treating an average of 1.87 million gallons per day against a permitted design capacity of 3.06 MGD, serving about 11,515 residents. It discharges under NPDES permit OR0020621 (effective), which expires in January 2031, with 2 recorded violations in the last three years.
Treatment technology
One treatment structure or unit process identified at Ontario STP.
Available with a free Klarifi account
See the full treatment train at Ontario STP: structures, unit processes and planned upgrades, with exact unit counts.
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.
No verified contacts on file yet
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Nearby wastewater treatment plants in Oregon
Huntington · 25 mi away
0.15 MGD
North Powder · 82 mi away
0.05 MGD
Union · 92 mi away
0.14 MGD
Joseph · 93 mi away
0.15 MGD
Enterprise · 97 mi away
0.24 MGD
Mount Vernon · 108 mi away
0.02 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 October 26, 2026; facility record last updated February 16, 2025.
Wastewater terms: POTW · MGD · NPDES permit · Inflow and infiltration · Activated sludge · Oxidation ditch · all terms