At last report the Alliance Pipeline System was still closed preventing the average transportation of 1.6 billion cubic feet per day of liquids rich natural gas from Northeastern B.C. and North Dakota, to the Chicago area.

The pipeline operator is Calgary based Keyera Corporation, and it says a brief operational error during maintenance activity last Wednesday morning allowed poisonous hydrogen sulphide to enter the main line at a gas plant located about 60 kilometers southwest of Valleyview.

The plant is designed to remove sulphur from as much as 250 million cubic feet of sour gas per day, and Keyera President David Smith is quoted as saying “Under normal operation there are a number of different fail-safes that would catch this, but it appears in this case they didn’t work the way they should have”.

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However, the H2S was detected by monitoring equipment after the release was reported and Alliance says the incident is the first for the fourteen year old system.

The pipeline is a jointly owned by an affiliate of Enbridge and Veresen, and Alliance closed the nearly four thousand kilometre system Friday morning, without saying, how much H2S had entered the line, or giving any clear indication how long it’s expected to take to remove it.

The tainted gas was stopped in Southeastern Saskatchewan and targeted for disposal by flaring at a compressor station east of Estevan, and Alliance says there’s no public health risk provided it stays in the system.

It also notified shipping companies to make alternative short term arrangements to move their natural gas, and reports indicate at least four did—including Crew Energy—which halted production in the Montney.

The outage is the latest to hit Calgary-based producers after a winter of unplanned and maintenance shutdowns on TransCanada and Spectra Energy gathering lines which also reduced production for companies here in Northeastern B.C. and Northwestern Alberta.