CALUMET STL Wastewater Treatment Plant, O'Brien County, Iowa

CALUMET STL is a municipal wastewater treatment facility located on 480th Street in O'Brien County, Iowa, United States. The plant serves a small community of approximately 170 residents, reflecting its role in rural wastewater management. The plant provides secondary treatment, which is the standard level required under the U.S. Clean Water Act for most municipal facilities. With a designed capacity of 94.64 cubic meters per day, it operates at full capacity based on reported discharge volumes. The plant is regulated under the National Pollutant Discharge Elimination System (NPDES) permit program, administered by the Iowa Department of Natural Resources. The treated effluent is discharged into local waterways that drain into the Missouri River watershed, ultimately reaching the Mississippi River and the Gulf of Mexico. The plant's operations help protect downstream water quality in this agriculturally intensive region.

The plant discharges into streams within the Missouri River basin, which flows into the Mississippi River and eventually the Gulf of Mexico. This region is dominated by agricultural land use, and the plant's secondary treatment helps reduce nutrient and organic pollutant loads that could contribute to hypoxia in the Gulf. The local watershed supports diverse aquatic life and is an important part of the Mississippi Flyway for migratory birds.