ST CLAIR STP Wastewater Treatment Plant, Saint Clair County, Illinois

ST CLAIR STP is a municipal wastewater treatment plant located in Saint Clair County, Illinois, United States. The facility serves a population of approximately 14,253 residents, placing it in the small-to-medium agglomeration category. As part of the state's wastewater infrastructure, it plays a key role in managing sanitary sewage from the surrounding community. The plant operates under the regulatory framework of the US Clean Water Act, administered by the Illinois Environmental Protection Agency. For facilities of this scale, secondary treatment is typically required to meet effluent limits for biochemical oxygen demand and total suspended solids. The plant is expected to comply with National Pollutant Discharge Elimination System (NPDES) permit requirements. The treated effluent from ST CLAIR STP is discharged into local waterways that ultimately drain into the Mississippi River basin. The Mississippi River system supports diverse aquatic life and provides drinking water for millions downstream. Proper treatment at this facility helps protect water quality in the region's extensive river network.

The plant discharges into tributaries of the Mississippi River, which flows southward to the Gulf of Mexico. The Mississippi River basin is one of the largest watersheds in North America, supporting a wide range of fish species and migratory birds. Effective wastewater treatment is crucial to prevent nutrient loading that could contribute to hypoxia in the Gulf of Mexico.