The Idaho EPA, in developing its SIP, determined that the maximum sulfur dioxide emissions that could be captured from zinc smelters with the currently available technology was 72 percent. The state...

The Idaho EPA, in developing its SIP, determined that the maximum sulfur dioxide emissions that could be captured from zinc smelters with the currently available technology was 72 percent. The state consequently adopted that standard for zinc smelters under the SIP. The federal EPA refused to accept that part of the SIP and promulgated an 82 percent standard. Did the federal EPA have authority to make such a change in the SIP?