Yoncalla STP - Secondary Wastewater Treatment in Douglas County, Oregon

Yoncalla STP (Sewage Treatment Plant) is a municipal wastewater facility located in Douglas County, Oregon, United States. It serves a small community of approximately 1,047 residents, reflecting its role as a local infrastructure asset in the rural Umpqua River basin. The plant is situated inland, away from coastal zones, and operates under the regulatory framework of the U.S. Clean Water Act. The plant provides secondary treatment, which is the standard level required by the U.S. EPA for municipal wastewater facilities. Its designed capacity is 984.20 volume units, with a current discharge volume of 794.94, indicating operational headroom. As a small-scale facility, it is subject to Oregon Department of Environmental Quality (DEQ) permits that enforce effluent limits to protect water quality. The treated effluent from Yoncalla STP ultimately drains into the Umpqua River watershed, which flows into the Pacific Ocean. The Umpqua River supports diverse aquatic life, including salmon and steelhead trout, making water quality protection critical. The plant's secondary treatment helps reduce organic pollutants and suspended solids before discharge, contributing to the ecological health of the downstream environment.

Yoncalla STP discharges into the Umpqua River basin, a major watershed in southwestern Oregon that drains into the Pacific Ocean. The Umpqua River is known for its rich biodiversity, including populations of Chinook salmon, coho salmon, and steelhead trout. The plant's secondary treatment process helps mitigate nutrient and pollutant loads, supporting the river's ecological integrity and recreational uses such as fishing and boating.