Williamsville STP - Secondary Treatment Plant in Sangamon County, Illinois

Williamsville STP is a municipal wastewater treatment facility located on East Main Street in Sangamon County, Illinois, serving a population of 1,439. The plant operates under the U.S. Clean Water Act, which requires secondary treatment for municipal discharges to protect water quality. The facility provides secondary treatment, the standard level for domestic wastewater in the United States. With a designed capacity of 1,779.14 m³/day and an average discharge volume of 946.35 m³/day, the plant operates well within its capacity. As a small-scale facility, it is subject to National Pollutant Discharge Elimination System (NPDES) permitting, administered by the Illinois Environmental Protection Agency. The treated effluent is discharged into a local waterway that drains into the Sangamon River, a tributary of the Illinois River, which ultimately flows into the Mississippi River. The plant plays a key role in protecting downstream aquatic ecosystems and maintaining water quality in the Illinois River basin.

The plant discharges into a local stream that flows into the Sangamon River, part of the Illinois River watershed. The Illinois River is a major tributary of the Mississippi River, supporting diverse aquatic life and serving as an important migratory corridor for fish and waterfowl. The plant's secondary treatment helps reduce nutrient and organic loads, protecting downstream water quality in this agriculturally intensive region.