MONROE STP - Wastewater Treatment Plant in Monroe, Washington

MONROE STP is a municipal wastewater treatment plant located in Monroe, Washington, serving a population of about 17,330. The facility is situated in Snohomish County, part of the Pacific Northwest region known for its abundant rainfall and forested watersheds. The plant operates under the US Clean Water Act, which requires secondary treatment for municipal wastewater. For a community of this size, typical treatment includes biological processes followed by disinfection before discharge. The plant has a designed capacity of 1.00 million gallons per day. The treated effluent is discharged into the Skykomish River watershed, which flows into the Snohomish River and eventually reaches Puget Sound. This river system supports salmon runs and diverse aquatic life, making proper treatment essential for protecting downstream ecosystems and recreational uses.

The plant discharges into the Skykomish River, a tributary of the Snohomish River, which flows into Puget Sound. This watershed supports critical salmon habitat, including Chinook, coho, and steelhead populations. The region's high rainfall and forested landscape contribute to seasonal flow variations, requiring robust treatment to protect water quality during low-flow periods.