Grey water footprints of US thermoelectric power plants from 2010-2016

Water demands for power generation within the energy-water nexus focus on both consumptive and withdrawn water for thermoelectric power plant cooling. However, the consumptive-based approach of water footprinting is incongruent with withdrawn water. Grey water footprints of thermoelectric power plants associated with thermal pollution offer a proxy method to integrate the consumptive (blue) water footprint concept with withdrawn water. In this study, we compute the monthly grey water footprints of thermoelectric power plants from 2010-2016 in the United States. The calculation of grey water footprint relies on return flow and temperature effluent data, which are available through the Energy Information Administration. However, in cases where these data are unavailable, we present a model for estimating grey water footprints based on fuel type, return flow, and generation. Grey water footprints show a peak in the winter and summer months with lower volumes in the spring and fall. Additionally, the national grey water footprint was 18% greater in 2016 than 2010 (408 km(3) versus 347 km(3)), peaking in 2015 at 505 km(3). Grey water footprints of electricity generally occur in the eastern area of the United States, where once-through cooling systems are most prevalent. We discuss the potential of grey water footprints as a policy tool for assessing aquatic ecosystem impacts of thermal pollution. Our study provides the first quantification of grey water footprints due to thermoelectric power plant pollution in the United States and provides a means of estimating grey water footprints with limited data.