The City of Portland constructed the Tryon Creek Wastewater Treatment Plant (TCWTP) in 1965 within the Lake Oswego city limits next to the Willamette River. The plant treats sewage collected from parts of southwest Portland, unincorporated areas of Multnomah and Clackamas counties, and the City of Lake Oswego.
Environmental Services owns and operates the TCWTP, although the plant treats wastewater from sewer customers of both the City of Portland and the City of Lake Oswego under an inter-city contract.
Tryon Creek is an activated sludge, secondary treatment plant. It’s about one-tenth the size of Portland’s Columbia Boulevard Wastewater Treatment Plant.
The city designed the TCWTP for an average flow of 8.3 million gallons per day with the ability to treat hourly peak flows of up to 35 million gallons per day for short periods. Roughly one-third of that flow comes from the City of Portland’s Tryon Creek basin via the 30-inch Tryon Creek Interceptor. The rest of the flow comes from the City of Lake Oswego sewer service area through a 24-inch sewer line.
The TCWTP has a National Pollutant Discharge Elimination System (NPDES) permit to discharge treated effluent to the Willamette River.