ExxonMobil also is a defendant in lawsuits by landowners in eastern Montana after a pipeline break in July 2011 dumped 63,000 gal of crude into the Yellowstone River, soiling about 70 miles of riverbank.

Plaintiffs won’t comment to reporters, but they charge the company with damage to property and livestock operations after its Silvertip pipeline broke during heavy flooding. It has since re-buried sections of the 12-in pipeline as much as 70 ft below the riverbed.

Jim Hall, former chairman of the National Transportation Safety Board, says a pipeline under a river like the Yellowstone “needs to be buried to a specific depth so the changes in water flow characteristics don’t affect the pipeline,” and the depth depends on each situation.

However, ExxonMobil spent $135 million on cleanup, $1.7 million on a PHSMA fine and $1.6 million in state fines.

While oil stains can still be observed on river rocks, the oil spilled in Montana is a lighter weight so the cleanup was faster and more complete.

The riverbanks and fields have been repaired or affected crops paid for, says Steve Lackman, Montana State University agricultural agent for Yellowstone County.

The good news: river water was not being used at that time for irrigation, though the area is heavily dependent on it, he says.

Critics have questioned the safety of transporting dilbit, which has more tar sands than conventional crude and might have a caustic effect on pipe. One possibility: a change in rules by PHMSA.

“We are working to better understand diluted bitumen,” says Damon Hill, PHMSA spokesman. The agency hired the National Academy of Sciences to determine if dilbit has a higher risk of release than other types of crude. That report is due in July.