Water temperature duration curves for thermoelectric power plant mixing zone analysis

Thermoelectric power plants, constituting the largest withdrawals of fresh water in the United States, can cause thermal pollution in waterways via elevated temperature effluent. Thermal pollution can contribute to shifts in aquatic ecosystems, with many aquatic ecosystems already threatened by climate change. Thermal pollution can be quantified, via mixing models, to create a corresponding temperature duration curve (TDC). To demonstrate and compare TDCs, a scenario analysis was conducted using Energy Information Administration (EIA) power plant data and USGS river data. Thermal pollution on a medium and large river from small (300 MW), medium (650 MW), and large (1,575 MW) coal-fired, open-loop cooled power plants generated distinct temperature conditions. Overall, results show that the size of the receiving waterway and the temperature difference between intake and discharge water, ΔT, are the largest factors that influence TDCs. TDCs can inform thermoelectric power plant operational decision making, particularly in regards to regulatory mixing zones (RMZs), and also be used as a predictive tool in risk assessment, both with respect to power plants and aquatic ecosystems.