Carlisle Boro STP - Wastewater Treatment Plant in Middlesex Township, Pennsylvania

Carlisle Boro STP is a municipal wastewater treatment plant located in Middlesex Township, Cumberland County, Pennsylvania. Serving a population of around 22,274, the facility is part of the region's wastewater infrastructure managed under state and federal regulations. As a U.S. plant, it operates under the National Pollutant Discharge Elimination System (NPDES) permit program, which sets effluent limits based on the Clean Water Act. For plants serving populations over 10,000, secondary treatment is typically required to reduce organic matter and suspended solids before discharge. The plant's treated effluent is discharged into a local waterway that ultimately drains into the Susquehanna River basin, which flows into the Chesapeake Bay. This makes the plant's performance important for downstream water quality and the health of the bay's ecosystem.

The plant discharges into a tributary of the Susquehanna River, which flows into the Chesapeake Bay, the largest estuary in the United States. The bay supports diverse aquatic life, including blue crabs, oysters, and migratory fish. Nutrient pollution from wastewater can contribute to algal blooms and hypoxia, making effective treatment critical for the bay's ecological balance.