Cromwell Lagoon Wastewater Treatment Plant, Union County, Iowa

Cromwell Lagoon is an advanced wastewater treatment facility located in rural Union County, Iowa, United States. The plant serves a small population of 107 residents, reflecting its role in a sparsely populated agricultural region. As an advanced treatment plant, Cromwell Lagoon goes beyond secondary treatment standards, providing enhanced nutrient removal and pathogen reduction. This level of treatment is typical for facilities in sensitive watersheds or those requiring high effluent quality under the U.S. Clean Water Act, which mandates National Pollutant Discharge Elimination System (NPDES) permits for all point-source discharges. The plant discharges 37.85 cubic meters of treated wastewater per day into local waterways that ultimately drain into the Missouri River basin. The advanced treatment helps protect downstream aquatic ecosystems and supports water quality in the region's streams and rivers.

Cromwell Lagoon discharges into local streams that flow toward the Missouri River, a major tributary of the Mississippi River. The surrounding watershed is predominantly agricultural, with row crops and livestock operations. Advanced treatment at this plant helps reduce nutrient loading, which is critical for preventing algal blooms and maintaining dissolved oxygen levels in downstream waters that support diverse fish and invertebrate communities.