CALGARY, Alberta -- Part of the shut Enbridge Inc (ENB.TO) 2A pipeline will need to be drained for several days, Canada's National Energy Board said on Tuesday, without giving an estimation of when it will be back online.

The 959-km (586-mile) pipeline, which transports light crude as well as condensate between Edmonton and Hardisty in the province of Alberta, was shut following a leak in Strathcona County last week.

Enbridge has said the line was struck during unrelated construction activity in the area by TransCanada Corp (TRP.TO) and its contractor, the privately held Ledcor Group of Companies.

Enbridge reported about 200 cubic meters (7,063 cubic feet) of oil condensate was released, according to the NEB.

The exact circumstances of the strike were not immediately clear. TransCanada said "a release was detected" when its crews were working on the construction of the Grand Rapids pipeline, which passes through the Strathcona area.

"An internal investigation is being conducted to determine what occurred," said spokesman Terry Cunha.

Ledcor did not immediately respond to a request for comment.

The NEB said about 490 cubic meters of oil condensate had been recovered to date. ‎The total amount recovered will exceed the amount initially released because 20 km of the 24-inch (61 cm) 2A pipeline will require draining, the regulator said.

It was not immediately clear why the line needs to be drained.

The regulator said there was no public impact, and no worker safety incidents were reported.

"No NEB enforcement actions have been taken as the incident is still being investigated," the regulator said.

The NEB referred questions to Enbridge, which said it had no immediate comment beyond what it said on Monday.

At that time, Enbridge said downstream operations were "normal," but there was no estimated date for restarting the line. The company will work with customers to mitigate any impact on their operations, it said.

A shipper on Line 2A said his company's volumes so far were not affected.