The National Park Service on Monday said "geologic issues" had prevented drilling for the pipes, which would be set at 3,350 feet above sea level instead of at the level of the plant's current intake facility: 3,470 feet above sea level.

The Park Service intends to ensure future availability of cooling water for the coal-fired plant, located adjacent to the man-made lake.

Because of ongoing drought conditions, projections have indicated the lake level, now about 3,612 feet above sea level, could fall below the plant's current intake by 2009.

The drilling would accommodate five new intake tubes, each 150 feet long and 54 inches wide.

When Lake Powell is full, it measures 3,700 feet above sea level, said Park Service spokesman Kevin Schneider. In 2004, when the new intake tubes were first proposed, the lake level hit 3,573 feet above sea level.

The new environmental assessment will consider a drilling technique that wasn't considered at the time of the original study, Schneider said. The new study would be "pretty routine," necessary under federal regulations, he said.

Owen Lammers, spokesman for the Moab-based Living Rivers and Colorado Riverkeeper organization, in 2004 called the project a "boondoggle," dirty and a contributor to global warming.

Tuesday, he reaffirmed his position.

"We should be looking for opportunities to promote alternative [energy]," Lammers said.

Public comment will be accepted until July 25. They can be submitted online at parkplanning.nps.gov/glca; mailed to EcoPlan Associates, 701 W. Southern Ave., Suite 203, Mesa, Ariz., 85210; sent to dsmith@ecoplanz.com; or faxed to 480-733-6661.

- Patty Henetz