Extreme Flooding in Southern Alberta Causes Deadly Sour Gas Leak

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A sour gas leak from a natural gas pipeline put the flood-ravaged southern Alberta community of Turner Valley on evacuation alert yesterday.

The town of 2100 is 60 km southwest of Calgary and is amidst the many communities in the area that are suffering from the worst flooding in decades.

The pipeline belonged to Legacy Oil + Gas Inc, who said in a statement yesterday that they were in the process of shutting down when a piece of debris hit the line.

“Recent heavy rains and spring run-off in southern Alberta caused a flooding of the Sheep River.  As a precautionary measure, Legacy was in the process of shutting in production in the Turner Valley Field when a natural gas well, Royalite 19, located at 5-6-20-2W5M in the southwest corner of the town of Turner Valley, had a flow line rupture due to impacts from trees and other debris in the rising flood water.”

Athough the production has been shut down, rising water levels have made it impossible to seal the leak without significant risk to human life.

“There still is a small amount of flow coming from the line – we don’t have an exact number – and we will get somebody in there … to shut off that well as soon as it’s safe to do so,” CFO Matt Janisch told Global News.

“There’s still a lot of water and it’s moving very quickly and there’s a lot of debris, so we’re erring on the side of safety.”

According to Alberta Energy sour gas is, “natural gas containing more than one percent hydrogen sulphide (H2S) and in low concentrations is identifiable by a strong 'rotten eggs' smell. It is commonly found in deep, high-pressure natural gas deposits such as those in the foothills of Alberta's Rocky Mountains region.”

“H2S is toxic to humans and animals at very low concentrations. At concentrations between 10 – 750 ppm H2S becomes increasingly toxic.  It is deadly to humans in concentrations of greater than 750 ppm. Most people can smell the distinctive 'rotten eggs' odour of the gas at concentrations between 0.1 and 0.3 ppm. At concentrations of 20 ppm or more, people may begin to experience slight discomfort in the eyes and nasal passages, and workers are required to wear breathing apparatus. At higher levels, around 100 ppm, the gas becomes more dangerous because it quickly numbs the sense of smell. Health effects such as dizziness and slight respiratory difficulties begin with exposure for an hour at 150 ppm, and fatalities can result from exposure to levels above 750 ppm unless the person is immediately evacuated and resuscitated.”

Approximately one-third of Alberta’s natural gas contains hydrogen sulfide. The province contains about 6000 sour gas wells, 18,000 kilometres of sour gas pipelines and  approximately 250 processing plants.

Sour gas leaks are a common occurrence in Alberta. There have been approximately forty sour gas leaks from companies near Turner Valley alone since 1975. In January, a sour gas leak near Grand Prairie forced RCMP to close a 100 km stretch of Highway 40.  

Image Credit: Twitter via @RyanBlondia