An air permitting case in Wisconsin's District IV Court of Appeals was recently decided. The case involved a Sierra Club challenge to the Prevention of Significant Deterioration (PSD) permit issued for the Weston 4 power plant in Marathon County, WI. The Sierra Club challenged the Best Available Control Technology (BACT) determinations made by the Wisconsin Department of Natural Resources (WDNR) for sulfur dioxide (SO2), nitrogen oxides (NOx), and opacity. The court gave deference to DNR's interpretation and application of the underlying statutes and regulations, and decided in favor of the WDNR's actions in all but one of the areas of appeal. This one area dealt with the setting of a BACT limit for opacity for the coal fired power plant. While this may seem odd to the student of the federal PSD program that a BACT limit for opacity would be required since opacity is not considered a regulated pollutant under the PSD program), the court reasoned that BACT under Wisconsin's NR 405.02(7) is defined to include a visible emissions standard (in this regard it is similar to the definition of BACT in the federal rules), and that WDNR could not ignore the plain reading of its rules. The case was remanded for further proceedings. Read the decision here.