CALGARY — The National Energy Board is giving Imperial Oil until the end of 2022 to start building the long-delayed Mackenzie Gas Project, a pipeline that would ship natural gas from the Northwest Territories to northern Alberta.The board originally approved the project in December 2010 and the federal cabinet of then-prime minister Stephen Harper sanctioned it the next year.But one of the conditions was that construction had to start by the end of 2015.East coast ‘renaissance’: Oil producers flock to area, committing $1.2B in parcels after law changeFormer NEB chair says politicians should stay out of pipeline reviews as energy watchdog comes under siegeLast year, Imperial Oil (TSX:IMO) asked the board for a seven-year extension on that deadline because low gas prices had forced the companies behind the project to delay development.In granting approval of the extension, the board said the project was still in the public interest.The decision now goes to the federal cabinet of Prime Minister Justin Trudeau for final approval.The natural gas market has been transformed since proponents first filed for regulatory approval more than a decade ago, with shale formations in Canada and the United States providing a closer, cheaper and more abundant source of natural gas.Premier Bob McLeod of the Northwest Territories has been a supporter of the project, saying it would bring prosperity to the North, but some groups have opposed it on environmental grounds.The proposed $16.1 billion pipeline would run 1,200 kilometres from gas fields near the coast of the Beaufort Sea to the northern Alberta boundary, where it would link up with existing gas pipelines.