Greencastle WWTP - Sullivan County, Missouri Wastewater Treatment Plant

Greencastle WWTP is a municipal wastewater treatment facility located on Ivan Drive in Sullivan County, Missouri, serving a small population of 275 residents. The plant provides secondary treatment, a standard level for small communities in the United States. The plant has a designed capacity of 98.42 million gallons per year and discharges approximately 75.71 million gallons of treated wastewater annually. As a US facility, it operates under the Clean Water Act and is subject to National Pollutant Discharge Elimination System (NPDES) permits issued by the Missouri Department of Natural Resources, which set effluent limits to protect water quality. The treated effluent from Greencastle WWTP is discharged into a local waterway that ultimately drains into the Mississippi River basin. This watershed supports diverse aquatic life and provides drinking water for downstream communities. The plant's secondary treatment helps reduce organic pollutants and suspended solids before discharge.

The plant discharges into a tributary of the Mississippi River basin, which flows into the Gulf of Mexico. The local watershed supports aquatic ecosystems and is part of a larger drainage network that includes important fish habitats and migratory bird corridors. Nutrient management is a key concern in the Mississippi basin due to its contribution to the Gulf of Mexico hypoxic zone.