People who remain evacuated from their homes were told at a meeting on Tuesday that they won‘t be able to return to their dwellings for at least a year.
Ministry of the Environment officials said significant decontamination work is still required in the epicentre of the disaster once known as the "red zone."
They said if the soil is too contaminated, some residents may never be able to return to their homes.
Earlier Tuesday, police transferred control of the hardest hit area to the city, which has hired a security company to keep watch on the devastated downtown zone.
A train hauling crude oil derailed and exploded in Lac-Megantic on July 6, destroying much of the downtown core and killing at least 47 people.
Both the Quebec provincial police and the Transportation Safety Board of Canada continue to investigate the disaster.
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