Flare stacks located at Alliance’s mainline block valve site near Arcola, Sask., are shown in this August 9, 2015, handout photo. It could take several days to dispose of hazardous gas that mistakenly got into a major Canada-U.S. natural gas pipeline. Alliance Pipeline, whose B.C.-to-Chicago system has been shut since Friday, starting burning off the gas at two locations in southeastern Saskatchewan on Sunday. THE CANADIAN PRESS/HO - Alliance Pipeline

CALGARY - It could take several days to dispose of hazardous gas that mistakenly got into a major Canada-U.S. natural gas pipeline.

Alliance Pipeline, whose B.C.-to-Chicago system has been shut since Friday, started burning off the gas at two locations in southeastern Saskatchewan on Sunday.

In an online notice, Alliance said flaring was the safest way to get rid of the gas that was contaminated with poisonous hydrogen sulphide, or H2S.

It said people in the Alameda and Arcola areas of Saskatchewan may see and hear the gas being burned, but it shouldn't have any odour. Residents are being asked to avoid the immediate area as a precaution.

Tony Straquadine, manager of commercial and government affairs at Alliance, said crews are working around the clock at the two Saskatchewan flare sites.

Meanwhile, Alliance is lining up gas supplies to put into the pipe once it's ready to start up again.

"Our goal is to get back into service just as quickly as we can to serve our customers," he said.

Natural gas processor and transporter Keyera Corp. (TSX:KEY) said Friday that the toxic gas got into the Alliance pipeline after a "brief operational upset" at its Simonette gas plant in northwestern Alberta two days earlier.

Among the services Simonette provides to customers is "sour gas sweetening," or handling gas from deposits that naturally contain H2S.

Keyera spokesman Nick Kuzyk said some of its customers' gas has been diverted to a different system operated by TransCanada (TSX:TRP), but there's a limited amount of room.

It's not known yet what caused the problem at Simonette or how much H2S got into the Alliance system as a result, said Kuzyk.

"There's some data that we are able to extract from the detection equipment that we can analyze over the course of this week, once everything's back up and running," he said. "That's still to be determined, but priority number 1 is getting Alliance back up and running."

A number of producers have had their operations hampered by the Alliance closure, most recently Athabasca Oil (TSX:ATH), which has suspended some 4,200 barrels a day of light oil output while shifting other production onto the TransCanada system. Athabasca is affected because gas is produced along with oil at its operations.

Other affected producers include Seven Generations Energy (TSX:VII), RMP Energy (TSX:RMP), NuVista Energy (TSX:NVA), Cequence Energy (TSX:CQE), Crew Energy (TSX:CR) and Vermilion Energy (TSX:VET).

The Alliance Pipeline is jointly owned by an Enbridge affiliate (TSX:ENF) and Veresen (TSX:VSN).

The line runs 3,848 kilometres and ships 1.6 billion cubic feet of gas a day.

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News from © The Canadian Press, 2015