After the dilbit gushed into the river, it began separating into its constituent parts. The heavy bitumen sank to the river bottom, leaving a mess that is still being cleaned up. Meanwhile, the chemical additives evaporated, creating a foul smell that lingered for days. People reported headaches, dizziness and nausea. No one could say with certainty what they should do. Federal officials at the scene didn’t know until weeks later that the pipeline was carrying dilbit, because federal law doesn’t require pipeline operators to reveal that information.

The 2010 spill could have been worse if it had reached Lake Michigan, as authorities originally feared it might. Lake Michigan supplies drinking water to more than 12 million people. Fortunately, the damage was restricted to a tributary creek and about 36 miles of the Kalamazoo, used primarily for recreation, not drinking water.

This close call hasn’t deterred the energy industry from announcing plans to build or repurpose more than 10,000 miles of pipelines to carry dilbit to the United States and global markets. That includes the controversial Canada-to-Texas Keystone XL pipeline, which would pass through the Ogallala aquifer, the nation’s largest drinking water aquifer. It supplies drinking water for eight states and about 30 percent of the groundwater used for irrigation.

The nation’s pipeline network was designed to handle conventional crude oil and is governed by laws and regulations that were written long before the unique risks and hazards associated with dilbit began to emerge. In fact, dilbit is exempt from an excise tax that pays for oil spill cleanups, because the 1980 law that created the tax did not consider bitumen from the “tar sands” to be crude oil.

After the spill, Congress passed new pipeline safety legislation, but it will take years for its modest provisions to have any impact. It does not require pipeline companies to reveal whether their lines are shipping dilbit. And while it does require a study of how dilbit affects pipeline corrosion, the scientists conducting that study met for the first time only last month, and their work is not likely to be completed before new pipelines are built or old ones are repurposed.