Risks addressed at Giant Mine prior to remediation
The Giant Mine Remediation Project team regularly identifies site elements that require immediate action to keep the environment, workers, and public safe. This includes underground stabilization and deconstruction of infrastructure
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How are risks addressed and dealt with?
The Project team uses the same methods that are used in many other areas of industry and business to identify, prioritize, and manage risks. The main tool that is used is called a qualitative risk assessment.
A qualitative risk assessment looks at possible events and evaluates them based on:
- how likely they are to occur
- environmental risks
- social risks
- health risks
- financial risks
Using these assessments, the Project team identifies ways to reduce the severity of potential risks. Risk assessments take place quarterly, and upon completion of a major change in the project, such as when the Roaster complex was deconstructed.
Work completed to date
Underground stabilization work
Stabilizing the underground reduces risks at the Giant Mine site. It helps keep the underground from flooding and rock from collapsing or sinking above mined-out voids.
In 2013, the Project Team received a Type B water licence from the Mackenzie Valley Land and Water Board in support of the Site Stabilization Plan. This plan includes stabilizing parts of the underground. The final work plans and waste management plans were approved in September 2013.
The general process for stabilizing the underground involves drilling boreholes for various purposes, including monitoring. A backfill product was pumped underground, via the boreholes, to fill the empty spaces.
The backfill product was made mostly from tailings already on site. The Project team conducted a short testing program to find the most appropriate mix of tailings and other material. Materials used in the tests included:
- fly ash and other binders
The backfill product is a paste. This paste was pumped underground. It hardened and filled the void inside each stope, helping to stabilize the mine structure.
While most voids identified as needing to be addressed under the Site Stabilization Plan have been filled, work remains to fill stope complex C5-09. The project is currently working on the plan to fill it. A contractor conducted assessment work over the summer of 2016, and further work and tendering took place throughout 2017. Anticipated completion of the backfill program is October 2018.
This work falls under existing site-wide emergency, and health and safety plans. The Project team will continue to monitor air quality through its site and community networks with additional oversight by independent third parties.
Deconstruction is not the same as demolition. Deconstruction involves many more controls while taking down structures in a systematic, orderly way. This is done to maximize work safety and minimize potential accidents or the release of contaminants. Due to the nature of the buildings on the Giant Mine site, they are deconstructed according to very strict and specific procedures.
Health and safety protocols during deconstruction
Safety and preserving the environment are top priorities during any deconstruction work. Air quality monitoring takes place through all phases of any deconstruction. The Project team ensures oversight by independent third parties when removing infrastructure. In addition to air stations at work sites, dedicated air monitoring continues at the Giant Mine boundary and at fixed locations in the community. Workers wore personal protective equipment during all deconstruction work.
Parsons Canada Ltd decontaminated and deconstructed the roaster complex, starting in June 2013. They largely completed the work by December 2014, with final tasks completed in June 2015. Parsons worked with Yellowknife-based companies Det'on Cho Corporation and Det'on Cho Nahanni. They also work with Tervita, Enviro-Vac, Williams Engineering, and International Chimney.
The project started with a structural check. This helped the contractor finalize the safest way to proceed with the plan. Scaffolding was then installed before each structure was sealed with shrink wrap to prevent air from escaping.
Roaster complex decontamination
Before the roaster complex was taken down, it was decontaminated. This was done to keep workers and the environment safe. Workers used negative air pressure inside each building to draw air, potential contaminants, and dust inward. This prevented potential contaminants from leaking into the environment. All the air inside each shrink-wrapped enclosure was filtered prior to release.
The initial process of removing arsenic and asbestos was done with a specially-designed hazardous debris vacuum. The vacuum picked up the contaminants and placed them in sealed bags. This ensured the material did not come into contact with the atmosphere. Surfaces inside the buildings were washed, inspected, and tested to confirm they were fully decontaminated. All material collected was packaged, cleaned, and removed from the structure.
Arsenic waste was safely and securely stored on site for disposal. The Project team will manage this waste until remediation can begin. Non-arsenic hazardous waste was safely packaged, transported, and disposed outside the Northwest Territories according to regulations. The water used to control dust was captured, treated by the site's effluent treatment plan, and discharged. No untreated waste water was discharged into the environment.
Roaster complex deconstruction
The roaster complex was cleaned of hazardous materials before deconstruction. The structures were dismantled in a step-by-step and controlled way. Workers used specialized equipment and techniques to ensure their safety, as well as that of the environment. While the structure was covered with shrink wrap, all of the interior contents were removed. Following that, the roof and building siding were removed.
Once the interior was cleared and portions of the structure were taken down, the shrink wrap was removed. The remaining portions of the building were then dismantled. The bulk of the Roaster Deconstruction Project was completed in 2014. Contractors returned to the site in June 2015 to complete the remaining work.
Constructed in 1949, the C-Shaft Head Frame towered above Giant Mine for 66 years. In October 2015, the Project team needed to dismantle this structure to eliminate safety risks to workers and nearby infrastructure.
Work to deconstruct the head frame was a part of the C-Shaft Complex Deconstruction Project. It included dismantling five structures in the complex:
- the screen house
- the conveyor galleries
- the crusher house
- the trestle
- the head frame
Site assessments of these structures confirmed they had deteriorated to an unsafe state. The head frame itself posed unacceptable on-site risks, including risk of injury to site personnel and causing potential power loss to the Freeze Optimization Study. The deconstruction work successfully eliminated these risks.
Work began on September 18, 2015. The last structure – the head frame – was down by October 28 of the same year. The C-Shaft remains. It is a narrow, vertical hole, approximately 650 metres deep. In November 2015, workers installed a steel cap over the opening. This will protect infrastructure and act as a safety measure, while allowing air circulation through the mine.
A-Shaft Head Frame, curling club, and assay lab deconstruction
In summer 2015, the Project team found more site structures had deteriorated to unsafe conditions. The team determined the A-Shaft Head Frame, curling club, and assay lab posed unacceptable risks and had to be dismantled. The three buildings were dismantled in the fall of 2016.
Many of the structures contained asbestos and other hazardous construction materials. The assay lab also contained chemicals. The Project team developed standard operating procedures to safely manage this material.
Hazardous waste materials were safely packaged, transported, and disposed outside the Northwest Territories according to all applicable regulations. Non-hazardous waste materials, as well as some lead-painted items, are being safely stored on site within the project work area. Ongoing management of this waste will continue until full remediation can begin.
A temporary cap was initially placed over A-Shaft, which is a narrow, vertical hole, hundreds of metres deep. In November 2016, a steel cap was installed to protect infrastructure and act as a safety measure, while allowing air circulation through the mine. A fence was installed around the cap. An associated building, the A-Shaft powerhouse, remains standing. It is structurally sound.
The Akaitcho Head Frame is the only head frame still standing at the Giant Mine site. It will be addressed as part of the final remediation plan, unless future structural assessments indicate an unacceptable risk.
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