EPA approved NR § 216.21(4)(a). However, we need not decide whether the EPA approved this specific provision of Wisconsin’s WPDES scheme because, even if Flambeau’s permit were legally invalid, we cannot, consistent with the requirements of due process, impose a penalty on Flambeau for complying with what Wisconsin deemed a valid WPDES permit. Informed by basic principles of due process, it is “a cardinal rule of administrative law” that a regulated party must be given “fair warning” of what conduct is prohibited or required of it. Rollins Envtl. Servs. (NJ), Inc. v. United States EPA 937 F.2d 649, 655 (D.C.Cir.1991) (Edwards, J., dissenting in part and concurring in part) (internal quotation marks omitted); see also United States v. Cinergy Corp., 623 F.3d 455, 458-59 (7th Cir.2010) (<HOLDING>); United States v. Trident Seafoods Corp., 60
holding that epa rule relating to repair of cars not in compliance with clean air act was interpretative not legislative rule and thus not subject to apa notice and comment procedures holding that defendant could not be sanctioned and found to have violated the clean air act when it complied with regu lations as codified despite having knowledge that the epa requested amendment of the regulations to prohibit defendants conduct holding that the government did not have to prove that the defendant knew that his acts violated the clean water act but merely that he was aware of the conduct that resulted in the permits violation holding the epa could regulate air pollutants under the clean air act solely on the basis of the pollutants risk to human health holding in a case involving the clean air act asbestos workpractice standards that knowingly violates does not require knowledge of the illegality of ones conduct