In Alaska Department of Environmental Conservation v. EPA, 540 U.S. 461 (2004), the Court held that even where a State administers a Part C permitting program pursuant to an approved state implementation plan ("SIP"), Congress vested EPA with a broad oversight role in 167 to ensure that Prevention of Significant Deterioration of Air Quality (PSD) permits comply with statutory requirements. The Court described the PSD permitting requirements as applying directly to stationary sources through CAA 165(a) and, although recognizing that Alaskas SIP imposed analogous requirements, continued to look to Part C, rather than the SIP, for the governing provisions. See id. at 472-73, 484-85.