Somonauk WWTP - Advanced Wastewater Treatment in Somonauk, Illinois

Somonauk WWTP is a municipal wastewater treatment plant located on North Gage Street in Somonauk, Illinois, within LaSalle County. The facility serves a population of approximately 1,430 residents, classifying it as a small-scale treatment operation under U.S. EPA guidelines. The plant employs advanced treatment processes, which go beyond secondary treatment to remove nutrients and other pollutants. With a designed capacity of 1,892.70 thousand cubic meters per year and an annual discharge volume of 476.96 thousand cubic meters, the plant operates well below its capacity, indicating room for future growth. As a U.S. facility, it operates under the Clean Water Act and is subject to National Pollutant Discharge Elimination System (NPDES) permitting, which sets effluent limits to protect water quality. The treated effluent is discharged into a local water body that ultimately drains into the Illinois River watershed, part of the larger Mississippi River basin. This region supports diverse aquatic life and provides critical habitat for migratory birds. The advanced treatment helps minimize nutrient loading, protecting downstream ecosystems from eutrophication.

The plant's discharge enters a tributary of the Illinois River, which flows into the Mississippi River and eventually the Gulf of Mexico. The Illinois River watershed supports diverse aquatic species and is an important migratory corridor for waterfowl. Advanced treatment at this facility helps reduce nutrient pollution, which is a key concern in the Mississippi River basin due to its contribution to the Gulf of Mexico hypoxic zone.