Over the last month, Enbridge has been working to secure their two 20-inch pipelines to the lake bottom, and weather permitting, officials say they should finish their work over the next few days.
Enbridge’s Line 5 pipeline runs 645 miles from Superior, Wisconsin to Sarnia, Ontario. At the Straits, the single 30-inch pipeline splits into two 20-inch pipelines.
Enbridge says Line 5 carries natural gas liquids and light crude oils. They say it does not carry the heavy dilbit crude that proved so difficult to clean up in the Kalamazoo River oil spill.
This section of Line 5 was built on the bottom of the Straits of Mackinac 61 years ago – right before construction started on the Mackinac Bridge.
Michigan’s 1953 easement with Enbridge lays out all kinds of technical specifications, including operating pressures, specifications for the type of steel used to build the pipeline, automatic shut-off valves at either end, and specifications for maximum unsupported span lengths.
From the easement:
The maximum span or length of pipe unsupported shall not exceed seventy-five (75) feet.
For a state that has suffered through the biggest inland oil spill in North America from an Enbridge pipeline, environmental groups and others have raised concerns about the condition of Enbridge's pipeline running through the Great Lakes.
This past spring, state Attorney General Bill Schuette, and MDEQ chief Dan Wyant requested specific information from the company under the terms of the state's easement agreement.
In their response, Enbridge said there were a few spans that exceeded the 75 foot requirement, but that they were working to resolve this issue by installing “ten-foot-long steel screws that are augured into the lake bed on either side of the lines and holds a steel saddle that permanently supports the line.”
They’ve been doing this work, they wrote, since 2002, and they planned to install up to 42 additional anchors this summer.
How do they do this with sections of pipeline that are more than 200 feet underwater?
In this video, the project manager for Ballard Marine Construction, Chris Bauer, explains how they do their work:
http://youtu.be/RrX2Ysh0qe4
Divers in the Straits of Mackinac have to battle currents at the bottom as if they were in a river.
Here’s dive captain Jim Hebert explaining what it’s like for one of his divers at the bottom. He says they’ve measured current speeds at more than 3.5 miles per hour at the bottom:
The dynamic lake bed
And these currents are what make keeping the unsupported pipeline span lengths at 75 feet or less so challenging.
Some sections of the pipeline are supported by the lake bottom, but currents can wash away parts of the lake bed.
Tom Prew is a region engineer for Enbridge. He says the company has been monitoring the outside of the pipeline using an underwater “remotely operated vehicle” every two years. This ROV can find where the washouts have occurred.
"... we'll replace that lost soil with a mechanical support, so that the pipe is safely fastened to the bottom of the lake."
“And we come back, and we’ll replace that lost soil with a mechanical support, so that the pipe is safely fastened to the bottom of the lake.” said Prew.
Prew says once they’re done with this summer’s work, the pipeline will meet the easement agreement.
“Before the project started, we were in the 90 foot range, and once this project’s done, we won’t have anything over 73 feet.”
Prew says the spans they’ll have in place now are well within what they consider to be safe for this pipeline. The company says this pipeline would be safe with spans up to 140 feet.
It's not flat at the bottom
The lake bed under the Straits is very uneven with hills and deep valleys. You get the idea by looking at this wood carved map:
In their report, Sunken Hazard, the National Wildlife Federation raised concerns about this:
The pipeline suspends over a 250-300 foot-deep, quarter-mile-wide, underwater canyon with steep walls. The tension on that section of the line is likely to be severe—but neither Enbridge nor the government will release any information about how that segment of the pipeline is supported.
Tom Prew says he wished the NWF had contacted him before writing this.
He says the pipeline follows the uneven contour of the lake bed, and is not suspended over a quarter-mile wide deep canyon. He says the lines are mostly two or three feet off the bottom, and that at most, the line is suspended eight to ten feet above the bottom.
Beth Wallace, one of the report’s preparers, said they did try to reach out to Enbridge prior to publishing, but she said the company denied their request for more information citing national security reasons.
Wallace and other pipeline watchdog groups say they hope Enbridge becomes more transparent about the condition of Line 5 running through the Straits – a line the company says is in excellent condition.
This is a story we’re continuing to look at for our M I Curious project. Watch for updates in the coming weeks.
