The National Energy Board has given Enbridge Inc. the go-ahead to start sending oil from Western Canada through its Line 9 pipeline from Sarnia, Ont., to Montreal.

Line 9 is a pipe, about 76 centimetres in diameter, that runs parallel to Highway 401 in eastern Ontario, through communities including Cornwall, Brockville and Kingston. Further west, it goes through heavily urbanized parts of Toronto and on to Sarnia, Ont.

It was built in 1976 to carry oil eastward, but for the last 17 years was allowed to transport foreign oil westward.

Enbridge intends to reverse the flow yet again to send oil from Western Canada to refineries in Quebec.

Many people spoke out in 2013 at the public hearing for the eastern section of the pipeline between North Westover, Ont., and Montreal, concerned about the heavier oil it would transport and the 60,000 extra barrels a day the company wanted it to carry. They said they feared oil leaks or spills.

The regulator approved the company's application for the reversal in March 2014, with conditions.

No specified date for return to service

Its startup has been delayed over environmental concerns, such as the protection of water crossings along the route. In recent months, Enbridge did high-pressure water testing on three portions of the line, including between Brockville and Kingston.

"The successful hydrotests confirm the NEB's confidence in the integrity of the pipeline and its confidence that the line can safely be returned to operation," the regulator said in a media release late Wednesday.

Having passed the last hurdle, Enbridge can now start operating Line 9 from west to east, though spokesman Graham White said in a statement there is no specified date for its return to service.

The pipeline has not carried oil in over a year, as the company worked to fulfil its regulatory requirements.

Enbridge has done more than 900 digs for inspection, repair and maintenance in past year and a half, and has installed extra valves "to further enhance Line 9's safety standards along water courses and other sensitive areas," White said.

The NEB underscored that when Line 9 does start carrying oil again, it has imposed strict conditions for the first year that include ground patrols every two weeks and integrity testing of the pipeline every three months.

As an extra layer of safety, Enbridge must limit the pressure of the pipeline for that first year, the regulator said.