ONARGA STW - Advanced Wastewater Treatment Plant in Onarga, Illinois

ONARGA STW is a municipal wastewater treatment facility located in Onarga, Iroquois County, Illinois, United States. The plant serves a population of approximately 1,368 residents and operates with advanced treatment capabilities, ensuring high-quality effluent discharge. As an advanced treatment plant, ONARGA STW likely employs processes beyond secondary treatment to remove nutrients and other pollutants. The plant has a designed capacity of 946.35 m³/day and currently discharges 662.45 m³/day, indicating it operates below its maximum capacity. Under the US Clean Water Act, such facilities must comply with National Pollutant Discharge Elimination System (NPDES) permits issued by the Illinois Environmental Protection Agency, which set effluent limits to protect water quality. The treated wastewater from ONARGA STW is discharged into local waterways that ultimately drain into the Mississippi River basin. The plant's advanced treatment helps protect downstream ecosystems, including the Illinois River and the Mississippi River, which support diverse aquatic life and provide drinking water for millions. The facility plays a key role in maintaining water quality in the region.

ONARGA STW discharges into local streams that flow into the Iroquois River, a tributary of the Kankakee River, which joins the Illinois River and eventually the Mississippi River. The Mississippi River basin is a major ecological corridor supporting diverse fish, bird, and plant species. Advanced treatment at this plant helps reduce nutrient loading, which is critical for preventing hypoxia in the Gulf of Mexico.