Consequences of proposed changes to clean water act thermal discharge requirements

Abstract

This paper summarizes three studies that examined the economic and environmental impact on the power industry of: a) limiting thermal mixing zones to 1,000 feet (∼305 m), and b) eliminating the Clean Water Act (CWA) §316(a) variance. Both of these proposed changes were included in S. 1081, a 1991 Senate bill to reauthorize the CWA. The bill would not have provided for grandfathering plants already using the variance or mixing zones larger than 305 m. Each of the two changes to the existing thermal discharge requirements were independently evaluated. Power companies were asked what they would do if these two changes were imposed. Most plants affected by the proposed changes would retrofit cooling towers and some would retrofit diffusers. Assuming that all affected plants would proportionally follow the same options as the surveyed plants, the estimated capital cost of retrofitting cooling towers or diffusers at all affected plants ranges from $21.4 to 24.4 billion. Both cooling towers and diffusers exert a 1%–5.8 % energy penalty on a plant's output. Consequently, the power companies must generate additional power if they install those technologies. The estimated cost of the additional power ranges from $10 to 18.4 billion over 20 years. Generation of the extra power would emit over 7.3 billion kg per year of additional carbon dioxide. Operation of the new cooling towers would cause more than 94.5 m3 per second of additional evaporation. Neither the restricted mixing zone size nor the elimination of the §316(a) variance was adopted into law. More recent proposed changes to the Clean Water Act have not included either of these provisions, but in the future, other Congresses might attempt to reintroduce these types of changes.