Carrier Mills STP - Secondary Wastewater Treatment Plant in Saline County, Illinois

Carrier Mills STP is a municipal wastewater treatment plant located on Tuller Road in Saline County, Illinois, serving a population of approximately 2,300 residents. The plant operates under the regulatory framework of the United States Clean Water Act, which requires secondary treatment for municipal facilities of this scale. As a secondary treatment plant, it provides biological treatment to reduce organic pollutants and suspended solids before discharge. The plant has a designed capacity of 984.20 units and currently treats an average daily flow of 832.79 units, indicating it operates below its maximum capacity. Secondary treatment typically involves activated sludge or trickling filter systems. The plant is subject to National Pollutant Discharge Elimination System (NPDES) permits issued by the Illinois Environmental Protection Agency, which set effluent limits to protect water quality. The treated effluent is discharged to a receiving water body within the Ohio River basin, ultimately draining to the Mississippi River and the Gulf of Mexico. The plant plays a key role in protecting local streams and downstream aquatic ecosystems from untreated sewage. Its inland location and secondary treatment level align with standard practices for small communities in the region.

Carrier Mills STP discharges into a local tributary of the Saline River, which flows into the Ohio River and eventually the Mississippi River and Gulf of Mexico. The watershed supports diverse aquatic life and is part of a larger river system that provides habitat for fish and migratory birds. The plant's secondary treatment helps reduce nutrient and organic loading, protecting downstream water quality in this ecologically sensitive region.