State and federal documents indicate that for years the Enbridge Line 5 pipeline under the Straits of Mackinac was out of compliance with easement rules that govern how far the twin pipes can span the lake bottom unsupported.

Although Enbridge's 1953 easement with the state of Michigan specifies the pipeline must have anchor supports across any gaps in the lakebed span greater than 75 feet, a 2003 survey identified 16 unsupported spans greater than 140 feet, with the longest being 224 feet on the east pipe and 286 feet on the west pipe.

The 286-foot unsupported span was nearly four times the allowable length.

The unsupported spans were identified in an October 2016 engineering report prepared by Kiefner & Associates for Enbridge as part of its negotiated settlement with the federal government over the 2010 Kalamazoo River oil spill.

Line 5 inspection reports submitted to a state pipeline board also document nearly 250 instances between 2005 and the most recent inspection in 2016 where unsupported spans on the twin lines have exceeded the 75-foot mark.

Enbridge says it has anchored all previously unsupported spans, but critics say the damage may already be done and that allowing such unsupported span lengths to go unattended for years may have irrevocably compromised the structural integrity of the pipeline, which carries light crude oil and natural gas liquids.

"Clearly, there was a huge period of time when Enbridge just ignored this thing," said Ed Timm, a retired Dow Chemical engineer with a PhD in fluid mechanics who authored an independent technical report on the pipeline integrity this year that was released by the National Wildlife Federation.

Timm believes the pipeline metal is worn out in historically unsupported points after being buffeted for 63 years of stronger currents in the Straits of Mackinac than Enbridge or federal regulators have previously accounted for.

In a report the state gave to independent contractors assessing the risk posed by the pipeline, Timm argued that currents near the straits bottom are higher velocity and more complex than the pipeline's original designers at Bechtel Corp. realized, and the combination of stress over time at key locations has fatigued the metal in ways that can't easily be seen or measured underwater.

Timm has spent three years studying Line 5 and claims that "based on all publicly available data" the company ignored unsupported spans of at least 150 feet until 16 years ago, meaning currents may have been hammering unanchored pipe sections of where the lakebed was washed out since it was installed in 1953.

Evidence of historic neglect in Timm's report includes a 2001 Enbridge application to the Michigan Department of Environmental Quality and U.S. Army Corps of Engineers asking for permission to place grout bags under unsupported spans of "too great a distance" in which an Enbridge engineer writes that "in order to maintain pipeline integrity and safety, these maintenance repairs can wait no longer."

Screenshot of the west leg of Enbridge Line 5 under the Straits of Mackinac that appears to show an area of bent pipe. Image from a June 2016 inspection.

Upon reviewing the June 2016 inspection video, Timm says there appears to be a section of the west pipe that is noticeably bent laterally.

Timm thinks the pipeline is "one peak current event" away from failure.

"This thing needs to be shut down and completely strip-searched with full access to Enbridge document databases so we know what's going on with this pipe," he said.

Jennifer McKay, policy specialist for Tip of the Mitt Watershed Council and member of the state's Pipeline Safety Advisory Board, said she "highly questions" the overall pipeline integrity given the unsupported spans disclosure and Enbridge's recent admission that the pipeline outer anti-corrosion coating has failed in several places.

"The lifespan of a pipeline is determined not only by how it's constructed, but by how it is operated and maintained," she said. "If it has not been properly maintained according to the design and safety specifications that were set for it, that calls into question if, in fact, that line is safe to operate currently and if there are any issues with structural integrity."

The pipeline board is holding its next meeting on June 12 at the Petoskey Middle School Auditorium. Discussion of past unsupported spans is not on the agenda, but DEQ spokesperson Melody Kindraka said "we are aware of this report and have shared it with the independent contractors who are preparing the risk and alternatives reports commissioned by the state."

Enbridge spokesperson Ryan Duffy said that inspection data "shows that the longer span lengths did not affect the integrity of the twin pipelines" in an email.

Enbridge has long argued that unsupported spans of 140-feet are safe. In the Kiefner & Associates report, the 140-foot mark is called the "criterion for taking corrective action" and characterizes the state's 75-foot requirement as "conservative."

Spans longer than 195 feet "would continue to be safe owing to several contributing factors, although it is difficult to precisely quantify the exact margins of safety offered by these factors in some cases," report author Michael Rosenfeld wrote.

Last fall, Enbridge installed four helical screw anchor supports on unsupported spans greater than 75 feet following an inspection. The company asked to install 18 more as a "proactive" measure but the state declined to allow the additional anchors, saying it wanted to wait for the conclusions in the two independent studies.

The board is awaiting the results of two state-ordered studies assessing the risk posed by the line, and alternatives to its crossing the straits bottom, which are being prepared by contractors and are expected to be released this month.

McKay said the state plans a public meeting on the draft reports on July 6.

Duffy said Enbridge is nonetheless planning to add those extra anchors.

"It is important to point out that currently all spans along Line 5 in the Straits are in full compliance with our easement agreement with the State. We continuously monitor and inspect this section of pipe to ensure its safe and reliable operations. Engineering analysis along with inspections have proven the pipeline is safe to continue operations. This summer we are planning to add 22 more steel anchor supports proactively on Line 5 to further ensure it is secure. More than a decade ago, Enbridge hired Kiefner and Associates to conduct an engineering analysis of the spans that cross the Straits of Mackinac. Surveys conducted in 2001 and 2003 identified some sections of the pipe longer than 140 feet. All spans longer than 140 feet were corrected by Enbridge using steel anchor supports."

Sen. Gary Peters, a Michigan Democrat, introduced legislation last week with Sen. Debbie Stabenow that would tighten up pipeline safety laws by raising the insurance liability cap on Line 5 and giving the U.S. Secretary of Transportation authority to shut down a pipeline not in compliance with operating requirements.

Peters said he's "obviously very concerned" by the Kiefner & Associates report.

"Clearly, there was violations of the easement during that time," he said.