Frozen Block Method

The 15 underground chambers and stopes containing the arsenic trioxide dust will be carefully frozen using an active freezing system — a system that is very similar to what is used to freeze the ice in indoor rinks.

A super-cooled liquid will be circulated through a series of underground pipes to freeze the designated areas around and within each of the chambers and stopes. This will create an impenetrable barrier that will prevent water from entering the chambers and arsenic from leaving the chambers.

The freezing will occur in stages over a number of years to ensure that the chambers and surrounding rock are completely frozen. The department will ensure that the site is safely managed throughout the entire process, and regular monitoring of the chambers and stopes will continue long-term after the remediation is complete.

The blocks will be kept frozen over the long term by using thermosyphons, which are tall, metal tubular devices that take heat out of the ground. Thermosyphons are self-sustaining, meaning they do not require an external source of power.

Thermosyphons are commonly used in the North to keep ground frozen. For example, thermosyphons are used in the parking lot of the NWT Legislative Assembly to prevent thawing of the natural permafrost. They are also used to maintain frozen core dams at the Ekati Diamond Mine in the NWT.

The Freeze Optimization Study

While the remediation plan undergoes an environmental assessment, Aboriginal Affairs and Northern Development Canada has been able to proceed with a Freeze Optimization Study at Giant Mine. This study is a small-scale test of the frozen process which was proposed in the remediation plan. The Mackenzie Valley Environmental Impact Review Board    removed the study from the scope of the environmental assessment and the Project Team anticipates that the results will help inform the regulatory review process. Construction for the Freeze Optimization Study has been ongoing since June 2009.

The study will be used to inform the environmental assessment process and provide information about the operation such as power requirements, rate of freezing, as well as more accurate cost estimates.

In January 2011, the Study is planned to move from the construction to the operational phase. This is the portion of the project where the freeze plants become operational and begin to freeze the rock around the underground arsenic chamber.

Stay tuned for updates on the Freeze Optimization Study from the Project Team at community meetings and in the media.

Frozen Block Method