In accordance with its agreement with the state of Michigan, Enbridge has completed a feasibility study to help ensure the continued protection of the Great Lakes.
The company worked collaboratively with state-appointed independent experts to assess the feasibility of three potential alternatives for the eventual replacement of the dual Line 5 pipelines under the Straits of Mackinac.
The team included qualified engineering consultants, specializing in tunneling, offshore pipelines and horizontal directional drilling, whom assessed potential options from design, compatibility, and logistical perspectives.
The options considered included: tunneling deep under the lakebed and placing the pipeline inside of the tunnel; trenching the lakebed and installing the pipeline within a secondary containment "pipe-in-a-pipe" system within the trench before covering it; and utilizing horizontal directional drilling to bore under the Straits lakebed and install the pipeline.
According to the study, the two feasible options for the potential replacement of Line 5 in the Straits include either placing the pipeline in a concrete-lined tunnel, or placing the pipeline inside a larger, secondary containment pipe, which would be buried.
The system in the second option would be laid in a trench near the shore and laid on the lakebed, with the pipe covered with rock to protect it at deeper depths. The study concludes that the third option was not feasible as the Straits crossing is too long for current horizontal directional drilling (HDD) capabilities. The approximately 4-mile crossing is more than double any comparable HDD crossing completed to date.
For a more in depth look, the study can be found here