PLAIN STP - Advanced Wastewater Treatment Plant in Plain, Wisconsin

PLAIN STP is an advanced wastewater treatment facility located in Plain, Sauk County, Wisconsin. Serving a population of 805, the plant is part of the municipal infrastructure for this rural community in the Driftless Area of the Upper Midwest. The plant provides advanced treatment, which goes beyond secondary treatment to remove nutrients and other pollutants. With a daily discharge volume of 272.55 m³ and a designed capacity of 397.47 m³, it operates under the U.S. Clean Water Act, which requires NPDES permits for all point source discharges. Advanced treatment is typical for plants in sensitive watersheds or those requiring high effluent quality. The treated effluent is discharged into a local water body that ultimately drains to the Wisconsin River and then the Mississippi River. The plant plays a key role in protecting downstream aquatic ecosystems, including the Mississippi River basin, which supports diverse fish and wildlife.

The plant's discharge enters a tributary of the Wisconsin River, which flows into the Mississippi River. The Mississippi River basin is a major ecological corridor supporting hundreds of fish species and migratory birds. The advanced treatment helps reduce nutrient loading, which is critical for preventing hypoxia in the Gulf of Mexico.