MOSIER STP Wastewater Treatment Plant, Wasco County, Oregon

MOSIER STP is a municipal wastewater treatment plant located in Wasco County, Oregon, United States. The facility serves a small population of 430 residents, reflecting its role in a rural community. As a secondary treatment plant, it provides biological treatment to remove organic matter and suspended solids from wastewater. The plant's designed capacity is 321.76 units, and it currently discharges 113.56 units of treated effluent. Under the U.S. Clean Water Act, facilities of this scale are typically regulated through National Pollutant Discharge Elimination System (NPDES) permits issued by the Oregon Department of Environmental Quality. These permits set effluent limits to protect water quality in receiving waters. The treated effluent from MOSIER STP is discharged into a local water body, which ultimately drains into the Columbia River basin. The Columbia River is a major Pacific Northwest waterway that flows into the Pacific Ocean. The plant's operations help protect downstream aquatic ecosystems, including salmon and steelhead habitats that are ecologically and economically significant.

The treated effluent from MOSIER STP enters a local water body that is part of the Columbia River watershed. The Columbia River flows westward through Oregon and Washington before emptying into the Pacific Ocean. This river system supports diverse aquatic life, including several species of salmon and trout that are important for both ecological balance and regional fisheries. The plant's secondary treatment helps reduce nutrient and pollutant loads, contributing to the health of downstream waters.