The head of Imperial Oil has heard how the spill of oilsands wastewater from its Kearl mine north of Fort McMurray, Alta., created fear in downstream communities.

Brad Corson is testifying before the House of Commons environment and sustainability committee about why there was a nine-month delay for First Nations and governments to find out about contaminated groundwater that was found seeping from a tailings pond.

Laila Goodridge, the Conservative member of Parliament for Fort McMurray, says people were deeply afraid about the releases.

She says there were weeks when rumours flew before the six area First Nations were told about what had happened.

Corson apologized for the releases, which have exceeded guidelines for some toxic chemicals near the release sites, and says Imperial failed in its duty to the Indigenous communities and promises to work to rebuild trust.

The environmental group Greenpeace is calling for Imperial Oil to be charged over releases of the toxic wastewater.