DURHAM STP Wastewater Treatment Plant, Tigard, Oregon

DURHAM STP is a major wastewater treatment facility located in Tigard, Oregon, serving a population of approximately 363,059. It is situated in Washington County, within the Portland metropolitan area, and plays a critical role in managing wastewater from a densely populated suburban region. As a large agglomeration serving over 150,000 people, the plant is expected to meet advanced treatment standards under the U. S. Clean Water Act, which requires secondary treatment as a baseline and may necessitate tertiary treatment to protect sensitive water bodies. The facility operates under the National Pollutant Discharge Elimination System (NPDES) permit program, administered by the Oregon Department of Environmental Quality, ensuring compliance with discharge limits. The treated effluent is discharged into the Tualatin River, a tributary of the Willamette River, which flows north to join the Columbia River. This watershed supports diverse aquatic life, including salmon and steelhead, and is an important ecological corridor in the Pacific Northwest. The plant's operations are vital for maintaining water quality in this sensitive river system.

The DURHAM STP discharges into the Tualatin River, which flows into the Willamette River and then the Columbia River, ultimately reaching the Pacific Ocean. The Tualatin River watershed is ecologically sensitive, supporting runs of Chinook salmon, coho salmon, and steelhead trout. The river also provides habitat for native freshwater mussels and riparian bird species. Nutrient loading from wastewater can contribute to algal blooms and low dissolved oxygen, making advanced treatment important for protecting aquatic life.