Asotin STP
Clarkston, WA · Asotin County · Publicly Owned Treatment Works
- Average flow
- 0.08 MGD
- Design flow
- 0.33 MGD
- NPDES permit
- WA0020818
- Effective
- Permit expires
- August 2023
- Population served
- 1,437
- CWNS 2022
Asotin STP is a publicly owned wastewater treatment works in Clarkston, Asotin County, Washington treating an average of 0.08 million gallons per day against a permitted design capacity of 0.33 MGD, serving about 1,437 residents. Treatment on site includes clarifiers, uncovered lagoons, carrousels / oxidation ditches. It discharges under NPDES permit WA0020818 (effective), which expires in August 2023, with 1 recorded violation in the last three years.
Treatment technology
Treatment structures identified at this facility. Exact unit counts are available in Klarifi.
Clarifiers
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Uncovered lagoons
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Carrousels / oxidation ditches
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Compliance snapshot (last 3 years)
- Total violations
- 1
- Effluent violations
- 1
Based on NPDES Discharge Monitoring Reports. Full violation history, parameters and discharge data available in the Klarifi platform.
Key contacts
Decision-makers at Asotin STP.
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Nearby wastewater treatment plants in Washington
Clarkston · 6 mi away
0.71 MGD
Colton · 16 mi away
—
Pullman · 27 mi away
2.13 MGD
Pomeroy · 28 mi away
0.09 MGD
Palouse · 39 mi away
0.04 MGD
Colfax · 41 mi away
—
Dayton · 45 mi away
0.19 MGD
Waitsburg · 53 mi away
—
Asotin 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 20, 2025.