A U.S. probe into the rupture of an Enbridge Inc. pipeline uncovered concerns about rapid staff turnover and lack of experience among the company’s Edmonton control-room staff.

The rupture in July, 2010, spilled some 20,000 barrels of crude oil into the Kalamazoo River in southwestern Michigan.

The concerns were expressed in interviews with officials of the United States National Transportation Safety Board, and contained in transcripts released by the NTSB on Friday along with other documents and photos.

Asked about staff turnover, Enbridge spokeswoman Jennifer Varey did not comment specifically on that issue, but said the company is reviewing all of the material released by the NTSB.

“We have been working co-operatively with the NTSB from the beginning, so a lot of this is not information that is new to us or new perspectives,” Ms. Varey said on Monday.