Investigators are probing how low concentrations of sour gas leaked into rural residential lines in the Olds area on Wednesday.
Gas was detected in a transmission line serving 240 customers.
No evacuations were necessary and no injuries or illnesses have been reported. One minor odour complaint was received.
Davis Sheremata, communications officer with the Energy Resources Conservation Board, said most of the readings in the lines were trace amounts of up to eight parts per million.
“For seniors, children, people with respiratory concerns it was not something you would want them exposed to. It was unlikely that anyone was injured, but still it would not have been an acceptable situation,” Sheremata said on Thursday.
“Alberta Workplace health and safety mandates workers can be exposed up to 10 parts per million continuously for eight hours without having to wear breathing apparatus.”
At about 10 a.m. on Wednesday, a well licensed to Anderson Energy Ltd. allowed sour gas to enter a sweet gas pipeline running into the Husky Energy Netook gas plant just north of Olds, which fed into the transmission line to the Foothills Natural Gas Co-op.
Monitoring equipment quickly detected the sour gas and Foothills staff began purging their high pressure lines that distribute gas into low-pressure lines that run directly to customers.
The ERCB is investigating how the sour gas entered the distribution lines and why sour gas controls at three locations did not work.
“At every step, you have control systems to control the flow of sour gas and to detect sour gas. Control systems were in place the question is why they didn’t prevent what happened,” Sheremata said.
“Obviously, we are very concerned. This is a situation we’ve never seen before and never want to see again.”
Foothillls staff contacted each customer on Wednesday by phone to advise them temporary shortages of natural gas service were possible due to the purge.
In the afternoon, trace amounts of sour gas was still detected in some low pressure lines.
“This morning, we’ve been informed detection points throughout the Foothills natural gas system were showing no readings.
“There is still concern there might be trace amounts of sour gas here and there so Foothills is still monitoring the situation very closely.”
Customers detecting any odours or have any concerns or questions can call Foothills Natural Gas Co-op at 403-556-3007.