Clean Water Action Council of Northeastern Wisconsin v. E.P.A.

EPA did not err in denying petitioners-environmental groups’ request to reject State of Wisconsin’s decision to reissue paper mill’s Title V operating permit, where petitioners argued that paper mill’s 2004 unopposed modification to said plant required that all emissions from said plant, including emissions from pre-1975 equipment previously incorporated into baseline, counted against state’s allowance that would have resulted in denial of permit. Clean Air Act is ambiguous as to appropriate treatment for plant's emissions from post-1975 modifications to plant’s equipment, and EPA was entitled to Chevron deference when it determined that only emissions attributable to 2004 modification count against Wisconsin’s pollutant allowance. Ct. further noted that petitioner’s stance would discourage future operational modifications to pollutant sources, even if those modifications would reduce pollution.