Repost from The Montreal Gazette
Contamination in Lac-Mégantic may be less than original estimate: studyBy Michelle Lalonde, THE GAZETTE – July 31, 2014
Estimates of soil contamination at Lac-Mégantic after last summer’s deadly train derailment may have been exaggerated, according to a new study commissioned by the provincial environment department.
Envisol Canada Inc., a Montreal-based engineering firm that specializes in geostatistical studies of contaminated sites, re-examined data collected in Lac-Mégantic in 2013. The firm used 3D mapping to visualize contamination dispersion to re-estimate contaminated soil volumes.
An earlier estimate of contaminated soil in the worst-hit area of downtown Lac-Mégantic — using the traditional method, known as the Thyssen Polygons method — was 126,300 cubic metres. The geostatistical method found between 64,000 and 92,000 cubic metres of contaminated soil in the same area.
“With this method we can look at the migration of contamination in specific topology and geology,” said Sara Godoy, a contaminated site consultant with Envisol who worked on the study.
She explained that the geostatistical method, which is used widely by mining companies to analyze the commercial viability of sites and has been evolving since the 1950s, is more scientific and considers more variables than the Polygons method.
It is more expensive because of the equipment and expertise required, but she said it can save money in the long run by pinpointing contaminated areas with more accuracy and avoiding unnecessary decontamination work.
An estimated 6 million litres of crude oil spilled out of the runaway freight train that rolled into downtown Lac-Mégantic on July 6 and burst into flames. The fire killed 47 people, destroyed the downtown area of the tourist town and caused extensive environmental damage to soil and waterways.
Two other reports released last year by the Environment Department indicated a total of 558,000 tonnes of contaminated soil will have to be removed and replaced in downtown Lac-Mégantic.
By the end of October, 75,000 cubic metres of soil had been excavated from the town and moved to a storage and treatment site. The Environment Department has said soil decontamination work could cost between $75 million and $100 million.
The Envisol study recommends the Environment Department conduct further research into whether the province should be using the geostatistical method to characterize soil contamination in the event of significant oil spills in the future.