Mattoon STP Wastewater Treatment Plant, Mattoon, Illinois

Mattoon STP is a municipal wastewater treatment plant located at 780 South 5th Place in Mattoon, Coles County, Illinois. The facility serves an estimated population of 20,439, placing it in the medium-agglomeration category for US wastewater infrastructure. As a US-based plant, Mattoon STP operates under the Clean Water Act and is subject to National Pollutant Discharge Elimination System (NPDES) permitting, typically administered by the Illinois Environmental Protection Agency. For plants serving populations of this scale, secondary treatment is the standard requirement, with additional nutrient controls possible depending on the receiving water body's sensitivity. The plant's treated effluent discharges into a local waterway within the Mississippi River basin, ultimately draining to the Gulf of Mexico. The downstream environment includes the Mississippi River system, which supports diverse aquatic life and is a major migratory corridor for birds and fish.

Mattoon STP discharges into a tributary of the Embarras River, which flows into the Wabash River and then the Ohio River, part of the vast Mississippi River basin. The Mississippi River system drains to the Gulf of Mexico, where nutrient loading from wastewater and agricultural runoff contributes to seasonal hypoxic zones. The local watershed supports diverse aquatic species and provides habitat for migratory waterfowl.