DIAGONAL STL Wastewater Treatment Plant, Ringgold County, Iowa

DIAGONAL STL is a municipal wastewater treatment facility located in Ringgold County, Iowa, United States. The plant serves a small population of around 330 residents, reflecting its role in a rural community. As a secondary treatment plant, it provides biological treatment to reduce organic matter and suspended solids before discharge. The plant has a designed capacity of 151.42 units and currently treats an average daily flow of 75.71 units, operating well below its capacity. Under the U.S. Clean Water Act, such facilities are required to meet National Pollutant Discharge Elimination System (NPDES) permit limits, which are enforced by the Iowa Department of Natural Resources. Secondary treatment is the standard for municipal plants of this scale, ensuring compliance with federal effluent guidelines. The treated effluent is discharged to a local waterway, likely a tributary of the Missouri River basin, which ultimately drains to the Mississippi River and the Gulf of Mexico. The plant's operations help protect downstream water quality in this agriculturally intensive region, reducing nutrient and pathogen loads that could impact aquatic ecosystems and drinking water sources.

The plant discharges into a local stream within the Missouri River watershed, which flows into the Mississippi River and eventually the Gulf of Mexico. The region is dominated by agricultural land use, making nutrient management critical to prevent downstream eutrophication. The plant's secondary treatment reduces organic pollutants and helps maintain the ecological health of receiving waters, supporting aquatic life and recreational uses.