Arsenic Trioxide and Other Underground Issues

The greatest challenge associated with the remediation of Giant Mine is the 237,000 tonnes of highly toxic arsenic trioxide waste stored underground. Effective, long-term management of that material is one of Aboriginal Affairs and Northern Development Canada's top priorities for Giant Mine. There are 15 purpose-built chambers and mined out stopes, 14 of which contain approximately 237,000 tonnes of arsenic trioxide waste. Cement bulkheads, which act as plugs, seal the openings to these chambers and stopes. The arsenic trioxide waste is completely surrounded by solid rock. These will be further contained using the frozen block method.

A mine worker examines an underground pool of water at the Giant Mine site

Arsenic is also naturally occurring in the rock at Giant Mine. When that rock was crushed and mined out, more arsenic was exposed to the environment. There are large sections of the underground mine that have been backfilled with waste rock and tailings. Although the concentration of arsenic in these sources is hundreds of times lower than in the arsenic trioxide waste in the storage chambers, the large volumes mean that they also have the potential to contaminate the surrounding groundwater.

Some of those areas will be frozen as part of the frozen block method. However, water treatment will be required for the long-term to treat the minewater that comes into contact with this material.

Surface openings to the underground pose hazards to humans and wildlife through inadvertent or deliberate access. These openings will be sealed when they are no longer used for mine access or ventilation. Access to mine openings that still serve a purpose will be controlled with a lockable gate/door.