Thermal effluent from the power sector: an analysis of once-through cooling system impacts on surface water temperature

In this study, we review federal datasets to assess the impacts of once-through power plant cooling systems on summer freshwater temperatures in the United States from 1996 to 2005. We find that maximum reported temperature discharges averaged 37 C (1996–2005) and were 9.5 C (1996–2000) to 10 C (2001–2005) higher than maximum reported intake temperatures during the summer. More than half of all power plant cooling systems report maximum temperature discharges that exceed 32 C and increase water temperatures enough to potentially impact aquatic life. However, current federal data on thermal discharges from power plants are insufficient to adequately assess their impact on in stream temperatures, or their subsequent effects on aquatic ecosystems and biodiversity. A preliminary analysis indicates that certain watersheds, primarily in the Southeastern and Midwestern United States, are good candidates for more focused study of power plant temperature impacts.