Alton STP Wastewater Treatment Plant | Alton, Illinois

Alton STP is a municipal wastewater treatment facility located at 198 Chessen Lane in Alton, Madison County, Illinois. The plant serves a population of around 53,721 residents, placing it in the medium-agglomeration category for US wastewater infrastructure. As a US facility, Alton 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. Plants of this scale are generally expected to provide secondary treatment as a minimum standard, with potential nutrient removal requirements depending on the receiving water body's sensitivity. The plant's treated effluent is discharged into the Mississippi River watershed, which ultimately drains to the Gulf of Mexico. This downstream environment includes ecologically significant habitats such as the Mississippi River's floodplain and delta, which support diverse aquatic life and migratory bird populations. The plant's performance contributes to local water quality and the broader health of the Mississippi River basin.

Alton STP discharges into the Mississippi River, a major waterway that flows south to the Gulf of Mexico. The river supports a rich ecosystem including fish, mussels, and waterfowl, and its floodplain provides critical habitat. Downstream, the Mississippi River Delta is an ecologically sensitive area that depends on balanced nutrient loads to prevent hypoxia zones in the Gulf.