ELMA STP Wastewater Treatment Plant, Elma, Washington

ELMA STP is a municipal wastewater treatment plant located in Elma, Washington, within Grays Harbor County. The facility serves a population of approximately 3,540 residents and operates under the regulatory framework of the U.S. Clean Water Act, which requires National Pollutant Discharge Elimination System (NPDES) permits for discharges to surface waters. The plant provides secondary treatment, a standard level for municipal facilities in the United States that removes biodegradable organic matter and suspended solids. With a designed capacity of 1,816.99 million gallons per year and an actual discharge volume of 791.15 million gallons per year, the plant operates well within its capacity. The treated effluent is discharged into a receiving water body that ultimately drains to the Chehalis River and then to Grays Harbor, an estuary on the Pacific coast. This watershed supports diverse aquatic life, including salmon runs, and the plant's discharge is regulated to protect downstream water quality and ecological health.

The plant discharges into a tributary of the Chehalis River, which flows into Grays Harbor, a large estuary on the Washington coast. This estuary is a critical habitat for salmon, steelhead, and migratory birds. The plant's secondary treatment helps reduce nutrient and pollutant loads to protect this sensitive ecosystem.