A Model for Relating Environmental Variation to Water Permit Violations at Thermoelectric Facilities

A regression model is presented which relates cooling water withdrawal rates and discharge temperatures at two mid-size thermoelectric facilities to electricity demand and ambient air temperature using historical data. Both facilities employ open-loop cooling systems, which have substantial water demands. Open-loop facilities comprise roughly one third of U.S. generation capacity. High water demands put facilities and downstream aquatic habitats at risk during heat waves and droughts, and put facility managers in a position to decide between reducing their power generation and violating their permit limits. National Pollutant Discharge Elimination System (NPDES) permits place limits on cooling water withdrawals and effluent (discharge) temperatures. Human health is put at risk when power plants fail to generate electricity. The flora and fauna of receiving waters are put at risk when effluent temperatures and/or withdrawal rates are too high. Two power plants in Massachusetts were chosen as suitable case studies. A multi-decadal database of daily air temperatures, and monthly electricity generation values, water withdrawal rates, and industrial wastewater discharge temperatures was compiled from National Climate Data Center records, Energy Information Administration records, and state environmental records. Results of a multiple linear regression analysis suggest that air temperature and electricity demand are useful predictors of effluent temperatures, but poor predictors of water withdrawal rates