MCLEAN STP Wastewater Treatment Plant, McLean County, Illinois

MCLEAN STP is a municipal wastewater treatment plant located in McLean County, Illinois, United States. The facility serves a small population of 874 residents and operates under secondary treatment standards, which is the minimum required by the US Clean Water Act for municipal plants of this scale. The plant has a designed capacity of 757.08 volume units and currently discharges 567.81 volume units, indicating it operates below its capacity. As a US facility, it is regulated under the National Pollutant Discharge Elimination System (NPDES) permit program, which sets effluent limits to protect water quality. The treated effluent from MCLEAN STP is discharged into a local waterway that ultimately drains into the Mississippi River basin. This region is part of the larger Illinois River watershed, which supports diverse aquatic life and provides important habitat for migratory birds and fish species.

The plant discharges into a tributary of the Illinois River, which flows into the Mississippi River and eventually the Gulf of Mexico. The watershed supports a mix of agricultural and natural landscapes, and the plant's secondary treatment helps reduce nutrient loads that could contribute to downstream hypoxia in the Gulf.