Key document could help wrap up Yellowstone spill probe

A key document that reveals the reason behind the pipeline break that caused an oil spill in the Yellowstone River last year is expected to help conclude a federal investigation into the July 2011 incident.

The Pipeline and Hazardous Materials Safety Administration recently received the metallurgical report from Exxon Mobil Corp. that details the cause of the leak, said the regulator's Western region director, Chris Hoidal. He said that the documents are not open to the public but that there "were no surprises in the report." He didn't say what the cause of the leak was, but he said internal pipeline corrosion wasn't it.

Some officials have speculated the pipeline was damaged by debris after high waters exposed it. But an official cause has not been released.

Fifteen hundred barrels of oil were spilled into the Montana waterway, and it took nearly an hour to shut down the pipeline. Despite months of efforts to clean up the spill, only 1 percent of the oil was recovered.

Exxon Mobil has now buried that pipeline and two others dozens of feet below the riverbed, and other companies have done the same with pipelines that may not sit deep enough underground.

Hoidal said a decision on whether the company will face penalties will likely be made by the end of next month, when the investigation is expected to wrap up.