Harrisburg STP Wastewater Treatment Plant, Harrisburg, Illinois

Harrisburg STP is a municipal wastewater treatment plant located in Harrisburg, Saline County, Illinois. The facility serves a population of about 9,832 people, classifying it as a small to medium agglomeration under U.S. regulatory standards. Under the U.S. Clean Water Act, municipal wastewater treatment plants of this scale are typically required to provide secondary treatment, which includes biological processes to reduce organic matter and suspended solids. The plant's discharge is regulated through a National Pollutant Discharge Elimination System (NPDES) permit issued by the Illinois Environmental Protection Agency, ensuring compliance with water quality standards. The treated effluent from Harrisburg STP is discharged into a local water body that ultimately drains into the Saline River, a tributary of the Ohio River. The Ohio River flows into the Mississippi River, which empties into the Gulf of Mexico. The plant plays a key role in protecting the Saline River watershed from nutrient pollution and pathogens, supporting aquatic life and downstream water quality.

Harrisburg STP discharges into a receiving water body that flows into the Saline River, part of the Ohio River basin. The Saline River supports diverse aquatic life and is used for recreation and fishing. Downstream, the Ohio River contributes to the Mississippi River system, which ultimately reaches the Gulf of Mexico. Protecting local water quality helps prevent nutrient loading and hypoxia in the Gulf.