Cleanup work continued on the Kalamzoo River almost a year after a July 2010 spill near Marshall, Mi. It was one of the largest oil spills in the history of the Midwest. (Joe Raymond/Associated Press)

The National Energy Board has asked Calgary-based Enbridge to provide documentation of improvements it has made since a massive oil spill in Marshall, Michigan two years ago.

Board inspectors visited the company's control centre in Edmonton a week ago as part of an increase in inspections the board announced following a damning report by U.S. authorities on the spill in the Kalamazoo River in July 2010.

In a letter sent Friday, the board asked for a copy of Enbridge's internal investigation into the pipeline rupture and documentation of the corrective actions it has taken.

The board also wants to know what improvements have been made to the company's in-line inspection program since the incident and it wants a copy of the control room management plan.

The investigation by the U.S. National Transportation Safety Board found a litany of errors in Enbridge's control centre that led to a spill of more than 20,000 barrels of oil into the Kalamazoo River.

According to the report, a segment of Line 6B ruptured during the final stages of a scheduled pipeline shutdown on July 25, 2010.

Even thoughmultiple alarms were set off at the control centre in Edmonton, staff believed it was because of a change in pressure due to the shutdown and not because of a rupture. After the 10-hour shutdown was finished, pipeline operations resumed.

"Leak-detection alarms were generated, but Enbridge staff continued to believe the alarms were the result of column separation, even though the Marshall area was relatively flat, without significant changes," the report said.

More than 17 hours after the rupture, a gas utility worker finally notified the Enbridge control centre about oil on the ground.

Inadequate training

The U.S. report concluded that, among other things, deficiencies in Enbridge's pipeline integrity and inadequate training of control centre personnel were to blame for the spill that affected more than 50 kilometres of waterways and wetlands and cost $800 million to clean up.

Since the Michigan spill, Enbridge says it has made multiple improvements to its pipeline integrity management, leak detection and control centre operations.

In an email sent to The Canadian Press last month, Northern Gateway President John Carruthers said Enbridge has now doubled the number of employees and contractors to detect leaks, added more control centre staff, improved training and technical support, and opened up a new control centre in Edmonton.

The oil giant has "revised and enhanced all procedures pertaining to decision making, handling pipeline startups and shutdowns, leak detection system alarms, communication protocols, and suspected column separations," the email says.

The company's proposed Northern Gateway pipeline from the Alberta oil sands to a tanker port on the B.C. coast is currently under review by a federal environmental assessment panel.