The Sierra Club and National Audubon Society had sought an injunction to stop construction. The environmental groups argued the U.S. Army Corps of Engineers improperly approved a Section 404 Clean Water Act permit for Turk. The Corps and SWEPCO disagreed, insisting the permit was properly issued.

In a separate complaint brought by the Hempstead County Hunting Club that deals with some of the same issues in the federal suit, the Supreme Court said it would address questions relating to state law. Key among them is whether the Arkansas Public Service Commission should be allowed to say whether Turk meets state standards. The PSC previously issued a certificate of environmental compatibility and public need for the baseload plant. The Supreme Court overturned the permit earlier this year. SWEPCO/AEP responded to that ruling by saying the small portion of the plant that was to serve Arkansas customers instead would be built as a merchant facility. Turk will supply SWEPCO customers in Texas and Oklahoma.

The Supreme Court did not indicate when it will answer the questions. The plant is scheduled for commercial operation in October 2012.