Winlock S_T Facility Wastewater Treatment Plant, Winlock, Washington

The Winlock S_T Facility is a municipal wastewater treatment plant located in Winlock, Lewis County, Washington. It serves a small community of approximately 1,340 residents, reflecting its role in managing domestic wastewater for this rural area. The plant provides secondary treatment, which is the standard biological treatment process required under the U.S. Clean Water Act for most municipal facilities. With a designed capacity of 1,892.70 thousand gallons per day and an actual discharge volume of 450.46 thousand gallons per day, the plant operates well below its capacity, indicating room for future growth. The treated effluent is discharged into a local waterway that ultimately drains into the Cowlitz River, a tributary of the Columbia River. This river system supports diverse aquatic life and is important for regional salmon runs. The plant's operations are regulated under the National Pollutant Discharge Elimination System (NPDES) to protect downstream water quality.

The plant discharges into a tributary of the Cowlitz River, which flows into the Columbia River and then to the Pacific Ocean. The Cowlitz River supports critical salmon and steelhead habitats, making water quality protection essential for these migratory fish species. The surrounding watershed is primarily forested and agricultural, with the plant's effluent contributing to base flows during dry periods.