Evaluation of Ecological Risks and Benefits of Revegetation of the Thetford Mines- Phase 1 - Final Report

Final Report

EXECUTIVE SUMMARY

The Mine Closure and Ecosystem Risk Management Program was tasked to contribute to the improvement of the environmental performance of the asbestos mining industry in the Thetford Mines area. The project proposal was approved in May 2010. The first interim report (MMSL 11-040), a literature review, was completed in July 2010. This is the second and final report outlining the major findings from the two field trips and the results of the laboratory pot trials.

Revegetation may help to slow down the erosion processes in unattended asbestos tailings that may, in the long term, deteriorate the quality of the surrounding air, water and soil. The scope of this project is confined to phase 1 of a multi-stage evaluation. It includes a literature review to identify knowledge gaps and a laboratory study of vegetation on tailings sampled from selected waste piles in Thetford Mines.

In the laboratory study, artificial water and light exposure was used to simulate natural rain erosion of the bare tailings. The risks of erosion are identified to mainly lie in two aspects—water loss to leachate and magnesium mobility from the tailings piles to the surrounding environment and beyond. It is also found that nickel in the tailings remains bound by the mineral lattice and will not pollute the water as long as the tailings remain alkaline.

The laboratory pot trials have generated data to support the evaluation of the benefits of establishing vegetation covers on tailings in terms of carbon capture and nitrogen fixation. The pot trials indicate that planting vegetation helps in fixing nitrogen and capturing carbon dioxide. The most efficient treatments for biomass production, nitrogen fixation, and carbon capture have been identified.

Although the chemical aspects of the revegetation problems have been further clarified and mostly addressed, the physical features of the tailings piles, mainly the steep slopes and the hard crust formed on the surface, remain the major challenges in the attempt to establish vegetation covers. In addition, the risk of asbestos fiber remobilization arising from any actual revegetation work is yet to be addressed.

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