Castle Rock STP
118 Cummings St SW, Castle Rock, WA 98611 · Cowlitz County · Publicly Owned Treatment Works
- Average flow
- 0.37 MGD
- Design flow
- —
- NPDES permit
- WA0022683
- Effective
- Permit expires
- December 2028
- Population served
- 2,438
- CWNS 2022
Castle Rock STP is a publicly owned wastewater treatment works in Castle Rock, Cowlitz County, Washington treating an average of 0.37 million gallons per day, serving about 2,438 residents. It discharges under NPDES permit WA0022683 (effective), which expires in December 2028, with 1 recorded violation in the last three years.
Treatment technology
Treatment structures and unit processes at Castle Rock STP.
Treatment structure data not yet analyzed for this facility.
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 Castle Rock STP.
No verified contacts on file yet
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Nearby wastewater treatment plants in Washington
Toutle · 9 mi away
0.06 MGD
Ryderwood · 10 mi away
0.1 MGD
Longview · 11 mi away
17.43 MGD
Toledo · 12 mi away
0.1 MGD
Winlock · 15 mi away
0.54 MGD
Toledo · 15 mi away
0.002 MGD
Kalama · 18 mi away
0.49 MGD
Chehalis · 23 mi away
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Castle Rock 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 September 4, 2024.
Wastewater terms: POTW · MGD · NPDES permit · Inflow and infiltration · Oxidation ditch · Anaerobic digester · all terms