Miller Creek STP | Normandy Park, Washington Wastewater Treatment Plant

Miller Creek STP is a municipal wastewater treatment plant located in Normandy Park, Washington, serving a population of approximately 31,104 people. The plant is situated in King County, within the Puget Sound region, and operates under the regulatory framework of the U.S. Clean Water Act, which requires National Pollutant Discharge Elimination System (NPDES) permits for all discharges to surface waters. The plant has a designed capacity of 1.00 million gallons per day, indicating it is sized for a medium-sized community. Plants of this scale in Washington typically employ secondary treatment, which is the minimum standard under the Clean Water Act for municipal wastewater. The plant's proximity to the coast (within 50 km) may necessitate additional nutrient removal to protect marine water quality. Miller Creek STP discharges treated effluent into the Puget Sound basin, which ultimately drains into the Pacific Ocean via the Strait of Juan de Fuca. The receiving waters support diverse aquatic life, including salmon runs and marine mammals. The plant plays a key role in protecting the ecological health of this sensitive estuarine environment.

The plant discharges into the Puget Sound watershed, a large estuarine system connected to the Pacific Ocean via the Strait of Juan de Fuca. Puget Sound supports critical habitats for salmon, orcas, and other marine species. The region is ecologically sensitive due to urban runoff and industrial activities, making effective wastewater treatment essential for maintaining water quality and biodiversity.