Old Weedon mine site undergoes reclamation

It cost almost $4 million to reclaim an old copper mine site at Weedon, Que., about 100 km east of Sherbrooke.

The work at the old mine site, which was fully operational in the 1950s, was wrapped up in four months. Completed in the autumn of 1993, the project was the largest of its type in the province. (Final acceptance of the work was given in June of this year.)

The contract called for the restoration to last for at least 20 years; according to the president of Archer Consulting Engineers of Montreal, George Archer, the cleanup should last much longer.

Left over from the former mining operations were two tailings ponds (A and B) and mounds of crushed waste rock and pyritic material. It is estimated that between 1952 and 1959, 425,000 tonnes of tailings were deposited in the two ponds.

The barrier surrounding pond A had broken over time, allowing the tailings to spread over an area 1 square km in size and to contaminate the nearby Rat River. A study in 1986 indicated a low on-site pH of 2.7 and the presence of rich concentrations of heavy metals.

On-site preparatory work was undertaken in August and September, 1992. From 16 tenders submitted in November of that year, Societe Desourdy 1949 Inc. was awarded the contract. The actual restoration work was performed between the end of May and the end of September in 1993, at a cost of $3.8 million. Capping, using a 1.5-mm, high-density, polyethylene membrane to prevent contact with oxygen and unwanted chemical reactions, was chosen as the method of containment; after capping, a metre-thick protective layer of soil was applied and then seeded.

Pond B, the smaller of the two tailings areas, was capped in place; the surface area of pond B is about 12,000 sq. metres.

Pond A was considered re-usable. It was decided to construct a new water-tight dyke around the pond. All of the loose tailings and pyritic material were poured into pond A (because of its size, the pond was sub-divided into four cells for easier filling), which was then capped. The surface area of pond A is about 54,000 sq. metres.

In all, more than 300,000 cubic metres of contaminated material (representing 90-95% of all such on-site material) was capped. Two areas not excavated were along the banks of the Rat River and where existing vegetation had remained healthy; it was judged that the concentration of contamination in these areas was weak, that the excavation would be difficult and that such work might cause even more damage to the local

environment.