Alberta's Energy Resources Conservation Board has suspended the drilling of sour oil wells near Tomahawk, Alta., a village west of Edmonton.

The ERCB has decided to review the licences for nine wells granted to Calgary resource company Highpine Energy after tests on two wells drilled by another company in the same geological formation revealed higher-than-expected concentrations of toxic hydrogen sulfide.

In a letter to Jennifer Klimek, lawyer for a group of Tomahawk residents opposed to the Highpine proposal, the ERCB acknowledged it was aware the wells drilled by Grizzly Resources showed concentrations up to 21 per cent when they were supposed to have a concentration of less than 16 per cent.

The Highpine licence approvals were based on a 16-per-cent concentration level, Klimek said.

"We kept arguing at the hearings, 'You're using too low of a prediction,' and they kept saying, 'No don't worry about it. We've got it covered,'" Klimek said. "We've gone to four hearings, and every hearing we have challenged that and have lost and they said 'You're wrong it will never come in over 16 per cent.' So my clients are feeling a little, I guess, proven right here."

In the letter, the ERCB confirmed it has told Highpine it cannot act on any of its previously issued licences until the review is complete.

But Klimek wants the board to go one step further — cancel the current licences and starting the application process over again.

Klimek's clients have been fighting Highpine's proposals over concerns the wells would be drilled too close to the community and the elementary school, potentially putting students' safety at risk.

Despite those concerns, the ERCB approved the three Highpine wells closest to the school in December, albeit with conditions that limited work on two of the wells to days when school was not in session.

That decision was challenged by the Tomahawk residents, but in April it was upheld by the Alberta Court of Appeal.