Mainland STP
Harleysville, PA · Montgomery County · Publicly Owned Treatment Works
- Average flow
- 0.5 MGD
- Design flow
- 0.9 MGD
- NPDES permit
- PA0056413
- Effective
- Permit expires
- November 2026
- Population served
- —
- CWNS 2022
Mainland STP is a publicly owned wastewater treatment works in Harleysville, Montgomery County, Pennsylvania treating an average of 0.5 million gallons per day against a permitted design capacity of 0.9 MGD. Treatment on site includes clarifiers, carrousels / oxidation ditches. It discharges under NPDES permit PA0056413 (effective), which expires in November 2026, with 10 recorded violations in the last three years.
Treatment technology
Treatment structures identified at this facility. Exact unit counts are available in Klarifi.
Compliance snapshot (last 3 years)
- Total violations
- 10
- Effluent violations
- 10
Based on NPDES Discharge Monitoring Reports. Full violation history, parameters and discharge data available in the Klarifi platform.
Key contacts
Decision-makers at Mainland STP.
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Nearby wastewater treatment plants in Pennsylvania
Lansdale · 2 mi away
2.85 MGD
Harleysville · 3 mi away
0.32 MGD
Souderton · 3 mi away
0.94 MGD
Lansdale · 4 mi away
2.15 MGD
Worcester · 4 mi away
0.14 MGD
Zieglersville · 5 mi away
0.13 MGD
Schwenksville · 6 mi away
0.09 MGD
North Wales · 6 mi away
2.21 MGD
Mainland 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 November 28, 2025.