COWICHE STP - Secondary Wastewater Treatment Plant in Cowiche, Washington

COWICHE STP is a municipal wastewater treatment facility located at 1120 Livengood Road in Cowiche, Washington, within Yakima County. The plant serves a small population of 996 residents, reflecting its role as a local infrastructure asset for this rural community in the Pacific Northwest. The plant provides secondary treatment, a standard level required under the U.S. Clean Water Act for facilities of this scale. Its designed capacity is 794.93 thousand cubic meters per year, with an annual discharge volume of 794.94 thousand cubic meters, indicating near-capacity operation. As a U.S. facility, it operates under an EPA National Pollutant Discharge Elimination System (NPDES) permit issued by the Washington State Department of Ecology, which sets effluent limits to protect water quality. The treated effluent is discharged into a nearby watercourse that flows into the Yakima River basin, part of the larger Columbia River watershed. The Yakima River supports diverse aquatic life and is an important resource for irrigation and recreation in central Washington. The plant's operations help maintain water quality in this semi-arid region where water resources are critical for both ecological and human uses.

The plant discharges into a tributary of the Yakima River, which flows into the Columbia River and ultimately reaches the Pacific Ocean. The Yakima River basin supports salmonid species, including steelhead and Chinook salmon, and is a vital water source for agriculture in the region. The plant's secondary treatment helps reduce organic pollutants and suspended solids, protecting downstream aquatic habitats in this water-scarce environment.