Environmentalists, the Michigan Attorney General, and many others are keeping an eye on every step of the process of replacing Line 5 at the Straits of Mackinac. Enbridge’s Line 5 is the pipeline that crosses the Upper and Lower peninsulas of Michigan to transport oil and liquid natural gases to Canada.

But there’s another place where Line 5 is going under a body of water that’s part of the Great Lakes. Enbridge is replacing that pipeline under the St. Clair River just south of Lake Huron.

A spokesman for Enbridge says this is all part of trying to allay any concerns about the safety of Line 5.

“Well, it really goes back to our agreement with the state. And this is one part of those agreements where we are going above and beyond for safety, really, and just making what's been a safe pipeline there even safer and doing what we call a horizontal directional drill that will move the pipeline below the lake bed,” said Ryan Duffy with Enbridge.

The existing 65-year-old pipeline was installed in a trench dug five feet below the riverbed. The new 2,800 foot section of 30-inch diameter pipe will be deeper.

“It'll be about 30 feet or so below the lake bed there at the St. Clair River,” Duffy said.

Enbridge will be using Horizontal Directional Drilling. Machinery will bore a hole underground. From the U.S. side of the river, the completely welded length of the pipeline will then be pulled through the bore hole.

Enbridge says the old pipe is safe. So why is it replacing it?

Duffy explained it would be even safer deeper in the ground, adding, “You also wouldn't have the chance of any kind of product ever getting out into the water because it is buried into the riverbed.”

That last statement might be disputed.

The substrate in that area along the St. Clair River is Bedford Shale and Antrim Shale. Bedford Shale is described by the U.S. Geological Survey as “silty shale.” It becomes siltier and sandier in its upper layers. But that rock is actually farther below the level where the Line 5 pipe will be installed.

The pipe will actually be buried in a higher layer of what’s called Blue Clay. Clay is often used to line retention ponds and landfills, so it would offer some protection between the pipe and the river if it ruptured. But, whether that means oil wouldn’t have any chance of getting into the water would not seem to be certain.

Enbridge’s Ryan Duffy also says there will be automatic shutoff valves on both the U.S. and Canadian sides of the river.

Crews are doing some preliminary work on the Canadian side right now. Next month they plan to start welding the length of pipe which will take some time.

Just nine years ago Enbridge used the same method to replace the length of Line 6B under the St. Clair River right next to where its crews are working now. You might remember Line 6B was the pipeline that leaked hundreds of thousands of gallons of oil into a creek and eventually the Kalamazoo River near Marshall in 2010. It was the largest inland oil spill in U.S. history.

Full disclosure: Enbridge is a corporate supporter of Michigan Radio.

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