Ryderwood STP
Ryderwood, WA · Cowlitz County · Publicly Owned Treatment Works
- Average flow
- —
- Design flow
- —
- NPDES permit
- WA0038695
- Effective
- Permit expires
- September 2029
- Population served
- 435
- CWNS 2022
Ryderwood STP is a publicly owned wastewater treatment works in Ryderwood, Cowlitz County, Washington, serving about 435 residents. Treatment on site includes aerated lagoons. It discharges under NPDES permit WA0038695 (effective), which expires in September 2029, with 16 recorded violations in the last three years.
Treatment technology
Treatment structures identified at this facility. Exact unit counts are available in Klarifi.
Aerated lagoons
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Compliance snapshot (last 3 years)
- Total violations
- 16
- Effluent violations
- 6
Based on NPDES Discharge Monitoring Reports. Full violation history, parameters and discharge data available in the Klarifi platform.
Key contacts
1 verified contact for Ryderwood STP, with validated emails and direct phone numbers.
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Names, validated emails and direct phone numbers for decision-makers at Ryderwood STP, plus the full compliance history and discharge data.
Nearby wastewater treatment plants in Washington
Winlock · 9 mi away
0.15 MGD
Toutle · 16 mi away
0.06 MGD
Longview · 20 mi away
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Chehalis · 20 mi away
0.03 MGD
Rochester · 29 mi away
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Littlerock · 35 mi away
0.04 MGD
Ridgefield · 41 mi away
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Ilwaco · 43 mi away
0.15 MGD
Ryderwood 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 April 13, 2025.