Enbridge endorses two alternatives for Great Lakes pipeline replacement

Enbridge Inc on Friday endorsedeither an underwater tunnel or trench to replace a section ofits 65-year-old energy pipeline that travels under a stretch ofthe U.S. Great Lakes in Michigan.

Some local officials want the line removed to prevent thepotential for a spill into lake waters. The state of Michiganproposed moving the line into a tunnel under the lake bed andasked the company to evaluate it and other alternatives.

The Canadian pipeline operator said a tunnel would costbetween $350 million and $500 million and take five to six yearsto assemble.

A concrete-lined tunnel built as much as 100 feet below thelake bed and 350 feet below the surface of the lake wouldprevent an oil spill from reaching the water, the company said.

The alternative, an open-cut trench, would cost between $250million and $300 million and take four to five years to build,the company said.

That method would prevent spills by constructing a second36-inch outer pipe around a 30-inch energy pipeline. The outerpipe would have a leak detection system, Enbridge said.

Building either a tunnel and a trench would require 15 stateand federal permits, with oversight by the Army Corps ofEngineers and Michigan environmental agencies.

In April, the pipeline was damaged by a boat anchor, raisingfears of a potential spill in an environmentally sensitive area.

The 20-inch Line 5 pipeline carries crude oil and naturalgas liquids on twin lines running from Superior, Wisconsin, toSarnia, Ontario. A portion of it runs 4.5 miles (7.2 km) underthe Straits of Mackinac, which links Lake Michigan and LakeHuron.

Enbridge concluded that one proposed option, usinghorizontal directional drilling to push a pipe underground, wasnot technically feasible.

(Reporting by Collin EatonEditing by Bill Berkrot and Cynthia Osterman)