North Castle T SD STP - Advanced Wastewater Treatment in Armonk, New York

North Castle T SD STP is a municipal wastewater treatment facility located in Armonk, a hamlet within the Town of North Castle in Westchester County, New York. The plant serves a population of approximately 2,600 residents, providing advanced treatment to protect local water quality. The plant operates under the U.S. Clean Water Act, which requires National Pollutant Discharge Elimination System (NPDES) permits for all discharges. As an advanced treatment facility, it goes beyond secondary treatment standards to remove additional nutrients and pollutants, reflecting the regulatory expectations for sensitive watersheds in the New York metropolitan area. The treated effluent is discharged into local waterways that ultimately drain into the Long Island Sound, a vital estuary supporting diverse marine life and recreational activities. The plant's advanced treatment helps reduce nutrient loading, which is critical for preventing eutrophication and maintaining the ecological health of the Sound.

The plant discharges into the Byram River watershed, which flows south into the Long Island Sound. The Sound is a major estuary that supports commercial and recreational fisheries, migratory birds, and marine habitats. Advanced treatment at this plant helps control nitrogen and phosphorus levels, reducing the risk of harmful algal blooms and hypoxia in downstream waters.