HILLSBORO STL Wastewater Treatment Plant, Henry County, Iowa

HILLSBORO STL is a municipal wastewater treatment plant located on Ash Avenue in Henry County, Iowa, United States. The facility serves a small population of 151 residents, reflecting its role as a local-scale treatment system in a rural setting. The plant provides secondary treatment, a standard level required under the U.S. Clean Water Act for most municipal facilities. Its designed capacity is 75.71 units, matching the current discharge volume, indicating full utilization. As a small plant, it operates under a National Pollutant Discharge Elimination System (NPDES) permit issued by the Iowa Department of Natural Resources, which sets effluent limits to protect water quality. The treated effluent is discharged into a local waterway within the Mississippi River basin, which ultimately drains to the Gulf of Mexico. The plant's operations help maintain the ecological health of downstream waters, supporting aquatic life and recreational uses in the region.

The plant discharges into a tributary of the Mississippi River, which flows into the Gulf of Mexico. This watershed supports diverse aquatic ecosystems and is part of the larger Mississippi River Basin, a critical migratory corridor for birds and fish. The plant's secondary treatment helps reduce nutrient loads, contributing to efforts to mitigate the Gulf of Mexico hypoxic zone.