The roads don’t often go straight in northwest Wisconsin. They twist around wetlands, ponds, lakes, and rivers, making it a little tricky to find where the Line 61 oil pipeline crosses the St. Croix River and its tributaries. One might end up thigh-high in mucky cattail stands while hiking to river crossings, where brightly-colored posts stick out of the ground on either bank. There is no other sign of the river of oil flowing underfoot. Fish swim, birds feed, the water slips ceaselessly past.

By next year, there will be 50 million gallons of heavy crude per day flowing through the pipeline beneath the St. Croix River and its tributaries the Eau Claire, the Totogatic, the Namekagon, and all the countless creeks, ponds, and wetlands that flow into them.

River crossings are particularly risky for pipelines. A spill in moving water is many times more difficult to contain and clean up than on dry land, and the power of rivers increases the chance of a rupture.

Two oil pipelines have ruptured in the Yellowstone River in the past five years, together spilling more than 100,000 gallons of oil. Both breaks were blamed on the pipeline being exposed when the water carried away the soils that covered the pipe in the river. After that happened, floating debris and rushing water damaged the pipes and they ruptured.

Less than one percent of the oil spill in both incidents was collected.

Clean-up ‘virtually impossible’

Clean-up is never very successful, according to spill response leader Paul Peronard of the U.S. Environmental Protection Agency. “In good conditions, you get half the oil that hits the water,” he told VICE News in its recent “Pipeline Nation” documentary. Prevention is paramount.

“Since it is virtually impossible to clean up oil once it’s spilled into our waterways, our focus must be on spill prevention,” Scott Bosse of the nonprofit advocacy group American Rivers wrote after the Yellowstone River spill in January of this year. He pointed to burying pipelines deeper under rivers as a “common sense” step necessary to avoid the hazards of scour.

In a petition, American Rivers said burial depth regulations are “woefully inadequate.” Currently, federal law requires that under rivers 100 feet or wider, pipes must be buried four feet beneath the bottom. Under narrower rivers, there is no depth requirement. There is also no requirement that pipes remain buried after they are installed, although if a spill happens and the company failed to consider exposure, they can be fined.

According to Enbridge, when Line 61 was constructed in 2007 and 2008, it was buried “greater than five feet” deep under the St. Croix, Eau Claire, and Namekagon. Under the Totogatic, smaller than 100 feet, and a designated Wisconsin Wild River, Line 61 and the other pipelines in the corridor were buried “from near the surface to approximately two feet deep.”

The science of scour

The usual way to determine if that is deep enough to prevent exposure is to perform a scour analysis, looking at the river’s ability to dig down into its bed at the spot the pipeline crosses under it. Such studies take into account how much water is moving down the river at what speed, whether the bed is sand or gravel or rock, and most importantly, the 100-year flood level. Most major scour and pipeline damage occurs because of extreme flood events.

If those calculations showed the potential for greater scour than the legally-required burial depth, the pipe should be buried deeper.

“A prudent analysis would be that they do a scour analysis, and take the greater of the two depths,” said Dr. David Williams, a hydrologic engineer from Colorado who helps design pipeline river crossings. He said scour analysis is standard for pipeline crossings of medium to large rivers.

According to Enbridge spokesperson Becky Haase, Enbridge does not perform scour studies or flood analyses on the waterways its pipelines cross.

“There may be analysis of this completed during construction phases [so] specific erosion-control protections can be installed,” she wrote in an email, “but it is not done for our operational pipelines.”

If a pipe is exposed, the company might notice the problem during a visual inspection. Enbridge patrols by air every two weeks, said Haase, and on-the-ground patrols are at least that frequent, especially during floods.

Or it might not. The root-beer colored waters of these rivers could easily hide an exposed pipe until damage had already occurred.

“Pipeline scour is one of those things that has unknown potential,” Williams said. “Because you can have pipelines that are exposed and you never know it.”

Improved Enbridge efforts

The Pipeline and Hazardous Materials Safety Administration [PHMSA, pronounced “fim-sa”], requires pipe assessments in environmentally sensitive areas just once every five years. But it suggests pipeline operators patrol more regularly, checking for exposed sections of pipe and other problems along their lines. Although Haase said Enbridge checks Line 61 regularly, the company did not answer questions about the specific dates or findings of last patrols.

Haase emphasized that Enbridge has improved its efforts toward spill prevention since diluted bitumen from one of its pipes spilled into Michigan’s Kalamazoo River in 2010, the largest inland oil spill in American history.

“Since that day, Enbridge has completely overhauled its system with technological advances,” said Haase.

The company has increased the number of computer sensors, known as “smart pigs,” running through the pipes to check for corrosion, cracks, or other damage. That increase has led to a higher number of visual inspections and digs to check the integrity of pipes and repair them if needed.

Muddy waters

When it comes to pipe corrosion, the culprit in the Kalamazoo spill, Enbridge seems to have learned from its mistakes. But has it learned from the mistakes of others, especially when it comes to the river-specific risk of scour?

Only Enbridge really knows. The responsibility for assessing and handling risks along lines is left almost entirely up to the company, with few concrete standards.

“PHMSA’s regulations are written to say that the operator is responsible for protecting sensitive areas from failure of pipeline,” said Rebecca Craven of the Pipeline Safety Trust, a nonprofit watchdog group.

To illustrate, she cited a metaphor that circulates among staff at the trust. If pipeline operators were drivers and PHMSA regulations were speed limit signs, drivers passing through would not see numbered limits. They’d see a smiley face.

“It says, ‘Just don’t mess up,’” said Craven.

A PHMSA spokesperson wrote in an email that the agency does not have “specific records for each pipeline they inspect,” but would have inspected the pipeline after construction to ensure it met the four feet depth-of-cover requirement. With only about 120 inspectors for millions of miles of pipeline, the federal government is limited in what it can do.

The state and counties could help, by requiring key information about pipeline safety be publicly reported. Currently, Enbridge is not obligated to release specific information about patrol dates, findings, or depth of cover. Neither the Wisconsin Department of Natural Resources nor PHMSA could report how deeply Line 61 had been buried. Depth of cover was not mentioned in the environmental assessment conducted before the pipeline was built in 2006.

Stewardship of special rivers

The town of Gordon sits at the confluence of the Eau Claire and St. Croix Rivers. The Eau Claire lives up to its name, and is one of the few rivers in the area that is perfectly transparent, fed mostly by springs, not wetlands. Line 61 flows under it just above the town.

Gordon resident Bob Gile can recall the first fish his granddaughter caught from the DNR dock on the St. Croix River a couple years ago. “I would hate to see the rivers degraded to the point where that couldn’t happen for another little girl,” he said.

Before moving to the area 15 years ago, he continued, “I had never seen rivers that you could see all the way to bottom in, no matter what the depth. If that is lost, it will be more than a tragedy.”