If your pet poodle is an unreformed floor wetter, if your cat can't seem to make it to the litter box in time, you don't think twice  —  you ban the animal from the living room and keep it off the fancy furniture. It's the basic application of the precautionary principle, also known as common sense. Like pets, oil pipelines tend to leak and common sense should likewise apply.

Consider the Canada-based oil giant Enbridge and its history of embarrassing accidents. The worst occurred along Michigan's Kalamazoo River in 2010, when the company's Line 6b pipeline burst one summer day and sent 843,000 gallons of dirty diluted bitumen gurgling downstream for 39 miles. The clean-up cost was estimated at $1.2 billion. Later that year, an Enbridge pipeline leaked 250,000-gallons of crude in a suburb of Chicago. And, in early May, the Detroit Free Press reported that a 1980 Enbridge spill in Michigan's Hiawatha National Forest was not properly cleaned up, and that oil contaminants persisted on the forest floor, unbeknownst to the public, until 2011. According to the company's own reports, Enbridge has been responsible for more than 800 oil spills across North America since 2000.

That sticky trail of spews and spills leads us to the present, and to the latest of Enbridge's controversial pipelines. This one, known as Line 5, includes a pair of metal tubes that run through Michigan's Upper Peninsula, underwater across a wild, weather-beaten portion of the Great Lakes, and into the state's more populous lower region. A portion of the pipeline sits on the bottom of our country's most important fresh water resource, along a pristine and economically precious stretch called the Straits of Mackinac. It carries up to 20 million gallons of crude oil and gas every day.

Enbridge says the pipeline is safe. Company spokesman Ryan Duffy, in an emailed statement, asserts "Line 5, from an engineering and integrity perspective, is in excellent condition." It was "over-engineered when it was built to help it stand the test of time," he adds. "The standards to which it was constructed still meet or exceed today's standards for new pipeline construction."

For some, the outrageous gusher in Kalamazoo  —  the largest inland oil spill in United States history  —  contaminated Enbridge's reputation as much as it did local waterways. And so, despite the company's assurances, Michiganders are moving to lock up the living room and plastic wrap the upholstery. From municipal resolutions to a steady stream of letters, from damning reports to rallies to legal challenges, a growing group of Great Lakes residents want to shut down Line 5's underwater span, and soon.

I have spent many slow and satisfying summer days visiting the wild island country along Lake Huron's northern shores. The journey there never loses its splendor: You leave Michigan's Lower Peninsula and cross into the rugged north by way of the Mackinac Bridge, a towering monument to civil ingenuity and government largesse. From the bridge, look out in any direction, and you will see ubiquitous blue water, fresh and cold, interrupted here and there by low flat islands, rimmed by pine forest and rocky beach, crisscrossed by cargo ships and ferries and fishing boats. The water is packed with pike and perch and trout. The sky is full of gulls, cormorants, and the occasional osprey. The weather is unpredictable, the wind often gusting. In the winter, the ice is two, three, four feet thick. These are the Straits of Mackinac, the place where Lake Huron meets Lake Michigan and the two great peninsulas come closest to touching. This is where Line 5 resides.

The Mackinac Straits are the "worst possible place for an oil spill in the Great Lakes," according to Dave Schwab, a research scientist at the University of Michigan Water Center. The Straits are supremely complex. The currents there change direction regularly. "I can't think of any place that has more variable or stronger currents," Schwab says, and he has the data to prove it.

Overhead view of the Straits of Mackinac linking Lakes Michigan (left) and Huron (right) | (Louie Wannahocka/Wikimedia Commons)

In March, Schwab, an expert in hydrodynamic modeling, released a report that analyzed 840 different oil spill scenarios in the Straits of Mackinac. These scenarios, which account for different current conditions and spill volumes ranging from 5,000 to 25,000 barrels, paint a frightening picture of the potential devastation of a Line 5 rupture.

According to the report, approximately 700 miles of shoreline in Lake Michigan and Huron are vulnerable to being sullied by a 25,000-barrel spill, though no single incident would impact such a vast area. Rather, the worst individual case modeled by Schwab was a 25,000-barrel spill that alone could pollute 152 miles of Great Lakes shoreline. For 10,000- and 5,000-barrel spill volumes, the worst cases could impact 105 and 71 shoreline miles, respectively. Each scenario in the report is unique, suggesting the difficulty of planning for and properly containing a spill should the pipeline fail.

Schwab's study made headlines, but it's just one among many recent developments that have bubbled up from the debate over Line 5's future. The twin 20-inch pipelines began operating in 1953, and their continued presence in the Great Lakes is contingent on a state-sanctioned easement. Unlike most pipelines, which are under the jurisdiction of federal regulators, this easement allows Michigan an unusual level of control over the 4.5-mile underwater portion of Line 5. And it's this unique easement that environmentalists are hoping will help rid the Mackinac Straits of their peril.

"We are asking the state of Michigan to start the process for terminating the easement by putting Enbridge on notice," says Liz Kirkwood of the Michigan-based group For Love of Water, or FLOW. "It is easy for the attorney general and the governor to do this based on their legal authority and duty as public trustees of our water. They could shut down the pipeline."

In an April letter to Michigan Attorney General Bill Schuette and Governor Rick Snyder, Kirkwood's organization and its allies alleged that Enbridge is violating the terms of its 1953 agreement with the state. Among other assertions, the coalition says Line 5 contains manufacturing anomalies that breach the easement's pipeline wall thickness requirements. The letter also draws on Enbridge-provided data to conclude that the on-shore portion of one of the pipelines is corroded in nine different locations and that such corrosion is a "per se violation of the easement." With these arguments in hand, FLOW and its partners are calling on Michigan officials to cancel the underwater easement pending the results of a state-ordered pipeline risk and alternatives review currently underway.

Asked whether Schuette's office was investigating these serious accusations, spokeswoman Andrea Bitely said she could not comment. Nor would she say whether the state was considering closing down Line 5 while it waits for an independent third party to conduct the pipeline risk and alternatives analysis. The completion date of that analysis has yet to be determined. Bitely did, however, re-affirm the attorney general's vague but public declaration that the pipeline's "days are numbered."

Enbridge, in its defense, calls FLOW's allegations "scare tactics and fear mongering." Spokesman Ryan Duffy writes in an email that Line 5 is "in full compliance with all state and federal regulations, and with the easement requirements for the Straits of Mackinac Crossing." Questioned about the lingering distrust due to the Kalamazoo spill, he maintains that "the company has transformed its approach to safety, investing nearly $4 billion in enhanced monitoring, safer pipelines, and more staff to keep operations safe." According to state records, Enbridge has also been investing in Michigan lobbyists, spending more than $120,000 over the last six years to influence the Line 5 debate, among other issues.

Still, the lobbying blitz, a robust public relations presence, and promises about Line 5's safety don't seem to be taking hold. Local governments across Michigan want Enbridge to step away from the Straits. Some, like the city of Charlevoix, have passed resolutions calling on the state to permanently shut down the transport of crude oil through the underwater pipeline. Others, like Cheboygan County  —  not exactly an environmentalist mecca, I might add  —  have asked for a moratorium on the same until the risk analysis is complete. More than 30 such resolutions have been promulgated so far.

Business leaders are equally fearful of Enbridge's oil infrastructure. The Great Lakes region provides drinking water to over 30 million people, supports a fishery worth $7 billion, and is the basis for a $16 billion tourism economy.

"We just don't need to have a 64-year-old pipeline across the Straits of Mackinac with a high risk of having something happen to it," says Rich Bergmann, owner of Lake Charlevoix Brewing Company. "It would cause a needless catastrophe." Bergmann's company, a thriving beer manufacturer with 65 employees, draws its water from Lake Michigan and would be directly impacted by a Line 5 accident.

Enbridge, meanwhile, has 53 Michigan employees dedicated full-time to Line 5 and a total of 250 employees and contractors in the state, according to Duffy. The company says 30 percent of the crude oil Line 5 carries is delivered to Detroit-area refineries. Much of the rest ends up in Canada.

When you visit the shores of Lake Huron, the cobbled streets of Mackinac Island, or the boating corridors of the Les Cheneaux archipelago, when you see the fishermen in their motor boats or the old ladies selling whitefish in their roadside shops, when you sip a Charlevoix brew or cast for the sleek pike lingering under the dock, you can't help but think about the crude-filled tubes at the bottom of the big lake. You can't help but ask: When it comes to petroleum products, why does common sense hold so little sway?

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