(August 25, 2023, 3:59 PM EDT) -- DENVER — In disapproving a portion of Wyoming’s state implementation plan (SIP) for reducing emissions at several power plants within its borders, the U.S. Environmental Protection Agency incorrectly treated some of its discretionary guidelines as mandatory, a 10th Circuit U.S. Court of Appeals panel found in vacating a portion of the agency’s final rule on the SIP....