Birch Bay STP - Cottonwood Beach, Washington Wastewater Treatment Plant

Birch Bay STP is a municipal wastewater treatment plant located in Cottonwood Beach, Washington, within Whatcom County. The facility serves a population of approximately 5,500 residents and has a designed capacity of 1.00 million gallons per day, reflecting its role as a small to medium-scale treatment facility in the Pacific Northwest region. As a US-based plant, Birch Bay STP operates under the regulatory framework of the Clean Water Act, administered through the National Pollutant Discharge Elimination System (NPDES) permit program. For a plant of this size serving a coastal community, secondary treatment is typically required to meet water quality standards before discharge. The regulatory context ensures compliance with federal and state effluent limits. The plant's treated effluent is discharged into the local watershed, which ultimately drains to the Strait of Georgia via Birch Bay and the Salish Sea. This coastal environment supports diverse marine life, including salmon runs and shellfish beds, making proper treatment essential for protecting downstream ecosystems and recreational water quality.

Birch Bay STP discharges into Birch Bay, a coastal embayment of the Strait of Georgia in the Salish Sea. This marine environment supports ecologically sensitive habitats, including eelgrass beds and shellfish growing areas, which are vulnerable to nutrient pollution and pathogens. The plant's location within 50 km of the coast underscores the importance of effective treatment to protect downstream marine ecosystems and public health.