PORTSMOUTH STL Wastewater Treatment Plant, Shelby County, Iowa

PORTSMOUTH STL is a municipal wastewater treatment plant located in Shelby County, Iowa, along State Highway 191. It serves a small community of 225 people, reflecting the rural character of the region. The plant operates under the regulatory framework of the U.S. Clean Water Act, which requires secondary treatment as the minimum standard for municipal wastewater facilities. The plant provides secondary treatment, a biological process that significantly reduces organic matter and suspended solids before discharge. With a designed capacity of 75.71 volume units and a similar discharge volume, the facility operates at full capacity to meet the needs of its service area. As a small-scale plant, it is subject to state-level permitting under the National Pollutant Discharge Elimination System (NPDES), which sets effluent limits to protect receiving waters. The treated effluent from PORTSMOUTH STL enters the local watershed, which drains into the Missouri River basin and ultimately the Mississippi River. This region is part of the larger Mississippi River drainage system, supporting diverse aquatic life and providing water for agricultural and recreational uses downstream. The plant's secondary treatment helps maintain water quality in this ecologically important river network.

The plant discharges into the local watershed within the Missouri River basin, which flows into the Mississippi River and eventually the Gulf of Mexico. This downstream water body chain supports a variety of fish and wildlife, including migratory birds and freshwater species. The region's agricultural landscape means the plant's nutrient removal helps reduce the risk of algal blooms in downstream waters.