In a letter to Wisconsin DNR, providing comments on an air permit for a wastewater treatment facility, EPA Region V has required the state to consider combined cycle natural gas turbines as a best available control technology ("BACT") for cutting greenhouse gas ("GHG") emissions. EPA's says that because the combined-cycle technology is more energy efficient than a simple-cycle turbine, and therefore emits less GHGs, it should be considered under the BACT analysis. However, it is also worth noting that combined-cycle turbines are significantly more costly.

Under the Clean Air Act, BACT mandates that permit writers consider other technologies that have been used for reducing emissions, and either require them in the permit or explain why they are infeasible. Thus, by means of simply prodding state agencies, EPA could be effectively establishing a requirement for every CAA prevention of significant deterioration ("PSD") BACT review in the nation.