What is the address of Ryderwood STP?

The address on the plant’s EPA facility record is 602 6th St W, Ryderwood, WA 98581, in Cowlitz County. Its coordinates are 46.3814, -123.0482. For some plants the record holds the utility’s mailing address rather than the plant gate.

How much wastewater does Ryderwood STP treat?

Ryderwood STP treats an average of 0.1 MGD.

What treatment technology does Ryderwood STP use?

Klarifi has identified one treatment structure or unit process at the Ryderwood facility. The full treatment train, with exact unit counts, is shown in Klarifi with a free account.

What is the NPDES permit for Ryderwood STP?

The facility discharges under NPDES permit WA0038695, currently effective, expiring September 2029.

Is Ryderwood STP in compliance?

Discharge monitoring reports show 16 violations at Ryderwood STP in the last three years, 6 of them effluent limit exceedances. The full history is available in Klarifi.

Who operates Ryderwood STP and how do I contact them?

Ryderwood STP is a publicly owned treatment works in Ryderwood, Washington. Klarifi lists 1 verified decision-maker contact for this facility, available with a free trial.

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Ryderwood STP

602 6th St W, Ryderwood, WA 98581 · Cowlitz County · Publicly Owned Treatment Works

Average flow: 0.1 MGD

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 treating an average of 0.1 million gallons per day, serving about 435 residents. It discharges under NPDES permit WA0038695 (effective), which expires in September 2029, with 16 recorded violations in the last three years.

Treatment technology

One treatment structure or unit process identified at Ryderwood STP.

Available with a free Klarifi account

See the full treatment train at Ryderwood STP: structures, unit processes and planned upgrades, with exact unit counts.

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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.

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Nearby wastewater treatment plants in Washington

Winlock Wastewater Treatment Plant

Winlock · 9 mi away

0.54 MGD

Toledo STP

Toledo · 10 mi away

0.1 MGD

Castle Rock STP

Castle Rock · 10 mi away

0.37 MGD

Cowlitz Indian Tribe - Lewis County WWTF

Toledo · 13 mi away

0.002 MGD

Toutle STP

Toutle · 16 mi away

0.06 MGD

Pe Ell STP

Pe Ell · 18 mi away

0.31 MGD

Three Rivers Regional WWTP

Longview · 20 mi away

17.43 MGD

Onalaska Wastewater Treatment Plant

Chehalis · 20 mi away

0.07 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 October 26, 2026; facility record last updated April 13, 2025.

Wastewater terms: POTW · MGD · NPDES permit · Inflow and infiltration · Ozonation · Activated sludge · all terms

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