O Fallon STP
O Fallon, IL · St Clair County · Publicly Owned Treatment Works
- Average flow
- 1.98 MGD
- Design flow
- 14.6 MGD
- NPDES permit
- IL0021636
- Effective
- Permit expires
- March 2031
- Population served
- 30,999
- CWNS 2022
O Fallon STP is a publicly owned wastewater treatment works in O Fallon, St Clair County, Illinois treating an average of 1.98 million gallons per day against a permitted design capacity of 14.6 MGD, serving about 30,999 residents. It discharges under NPDES permit IL0021636 (effective), which expires in March 2031, with 0 recorded violations in the last three years.
Treatment technology
Treatment structures identified at this facility. Exact unit counts are available in Klarifi.
Treatment structure data not yet analyzed for this facility.
Compliance snapshot (last 3 years)
- Total violations
- 0
- Effluent violations
- 0
Based on NPDES Discharge Monitoring Reports. Full violation history, parameters and discharge data available in the Klarifi platform.
Capital improvement projects in O Fallon
O Fallon's capital improvement plan lists 21 water, sewer and wastewater line items worth $32M starting 2026–2029. The largest budgeted items are shown here.
All water and sewer capital projects in O Fallon →
| Project | Budget | Years |
|---|---|---|
| South Cherry Street Rehabilitation | $4,000,000 | 2027–2027 |
| Watermain Replacement Program | $3,200,000 | 2026–2030 |
| Hickory and Walnut Street Rehabilitation | $3,150,000 | 2027–2028 |
| South Trunk Main Replacement Phase 3 | $2,100,000 | 2027–2028 |
| North Trunk Main Replacement Phase 2 | $2,100,000 | 2029–2030 |
Full project details — scope, funding source, engineering consultant and the decision-makers behind each project — are available in Klarifi, along with similar wastewater capital projects in other cities.
Key contacts
21 verified contacts for O Fallon STP, with validated emails and direct phone numbers.
Unlock 21 verified contacts (18 more than shown)
Names, validated emails and direct phone numbers for decision-makers at O Fallon STP, plus the full compliance history and discharge data.
Nearby wastewater treatment plants in Illinois
Lebanon · 3 mi away
0.37 MGD
Summerfield · 5 mi away
0.1 MGD
O Fallon · 6 mi away
1.75 MGD
O Fallon · 6 mi away
0.38 MGD
Mascoutah · 7 mi away
0.55 MGD
Belleville · 7 mi away
0.71 MGD
Swansea · 8 mi away
1 MGD
Trenton · 9 mi away
0.02 MGD
O Fallon 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 December 20, 2024.