Giant Mine State of Knowledge Review: Plain Language Summary Toxic arsenic trioxide dust is currently as stopes) at the mine site since the early stored underground at the former Giant 1950s. Mine. The Giant Mine Oversight Board During the 50 years of operation, the mine contracted Arcadis to research and assess produced 237,000 tonnes of arsenic technologies that could be used to manage trioxide dust. The dust stored at the site the dust. The report that was produced is would fill Yellowknife’s Precambrian called a State of Knowledge Review. The Building (an 11-storey high rise) seven following is a plain language summary of times. The dust is, on average, about 60% the Arcadis review. arsenic trioxide by weight. Background Arsenic trioxide can dissolve in water. If it was dissolved in water, the arsenic The former Giant Mine is on Great Slave trioxide would be a risk to people and the Lake about five kilometres north of environment if it makes its way to Great Yellowknife, in the Northwest Territories. Slave Lake and Baker Creek, which runs Gold was mined from the site from 1948 through the mine site. until 1999, when the owner, Royal Oak Mines, declared bankruptcy. Indigenous The Giant Mine Remediation Project Team and Northern Affairs Canada (INAC) and began the process of evaluating the Government of the Northwest approaches that could be used to manage Territories (GNWT) took on responsibility the arsenic trioxide dust in 2000. After for managing the site, including the considering more than 50 technologies, environmental risks. INAC and the GNWT the Project Team decided that the “frozen are planning to manage those risks by block method” was the best option. In implementing the Giant Mine Remediation 2013, the Mackenzie Valley Project. Environmental Impact Review Board approved the frozen block option but The gold-bearing rock at Giant Mine there were several important conditions: includes arsenopyrite, a mineral that contains arsenic. Dust, made up mostly of 1. The frozen block option was arsenic trioxide, was created when the approved for a maximum of 100 rock, or ore, was processed to produce years; gold. That dust has been stored 2. An independent body was underground in specially-built vaults or in necessary to oversee the previously mined-out chambers (known remediation project; and Giant Mine State of Knowledge Review Summary, September 2017 arcadis.com 1 3. The oversight body needed to arsenic trioxide research program. As a initiate research into more first step, it was decided that a State of permanent arsenic trioxide Knowledge Review should be performed management solutions. to evaluate the current status of methods that could be used to manage arsenic The Giant Mine Oversight Board (GMOB) trioxide. GMOB contracted Arcadis to was established in 2015 to oversee the perform the State of Knowledge Review, remediation project. GMOB is also which is summarized below. beginning the process of designing its Research Method Arcadis reviewed various potential permanence of operation and treatment solutions. It looked at the 50 maintenance. technologies previously evaluated and the Figure 1 shows all the different factors and likelihood of success. It then looked more the importance given to each one. Teams closely at a shorter list of potential ways of experts scored the different solutions. to: Arcadis obtained information in Canada • manage the arsenic trioxide dust and elsewhere from government agencies, where it is now; research organizations, universities and • remove the dust from underground business. at Giant mine; Time required for Completion • stabilize and Ease of implementation, 2.6% 2.6% Compatibility with process the Pilot Testing/Design/Pre- Cold Climates, 2.6% Installation Requirements, dust; and 2.6% • store the dust. Confidence in Expected Effectiveness (Long Results, 2.6% Term Risk/ To determine the Permanence) 26.3% most promising Independent, Standalone Cost options, Arcadis Technology 7.9% considered several 2.6% factors. It gave the OMM most weight to such Compatibility with Requirements Future Uses 13.2% things as long-term 7.9% effectiveness, safety Practicality of Actions in Short Term/Health & Safety for people and the Case of Failure Risk Technical Maturity 7.9% 13.2% environment, 7.9% minimizing the risks Figure 1: Scoring Criteria Contribution by Percent and increasing the Giant Mine State of Knowledge Review Summary, September 2017 arcadis.com 2 Findings for processing. In the past 15 years, technology developments using remote- Keeping the arsenic trioxide controlled mining equipment have made underground the mining option safer for workers. Two methods for keeping the arsenic trioxide dust where it is now were Remote Mechanical Mining Methods examined. Due to the complexity of the stopes and chambers, it is likely that several different Frozen Block mining methods would be needed to The frozen block method keeps the arsenic effectively remove the arsenic trioxide dust in place by freezing the ground dust from underground. While technology around it. Because the ground is frozen, has made mining safer, it is still high-risk. water is unable to dissolve the arsenic Therefore, mining still scores low in the dust. The frozen block is the highest safety category. scoring method for keeping the arsenic trioxide dust in place and is now being Hydraulic Borehole Mining applied at the mine site. This method Hydraulic borehole mining was scored scored well for both technical soundness separately because it might be able to and for safety. remove nearly all of the dust. This process uses high-pressure liquid or steam to Nano-Scale Zero-Valent Iron remove the dust in a safer way than other Nano-scale zero-valent iron refers to very mining methods. It scored the highest of small iron particles that can potentially the mining methods, and highest overall. stop arsenic trioxide from escaping into However, because this is only a removal groundwater. The particles would be method, it would need to be combined mixed with a liquid and injected into the with a process to stabilize the dust. ground surrounding the dust storage areas. This would create a barrier to Treating the arsenic trioxide dust once arsenic movement. While this technology removed from underground has been used at other contaminated sites, Once the arsenic trioxide dust is removed the experts determined that it would be from underground, it would need to be difficult to use for Giant Mine, and made safe for people, the land and water. probably not work as the only solution. A number of ways to treat the dust were reviewed. Removing the arsenic trioxide dust from underground Dust removal or mining would remove the arsenic trioxide dust from underground Giant Mine State of Knowledge Review Summary, September 2017 arcadis.com 3 Vitrification Vitrification is a process for encasing Arsenic Recycle Stream Exhaust + the arsenic trioxide dust in glass. The Glass- making arsenic dust would be mixed with material Air filter glass-making material and then heated in a furnace. The glass captures the dust so it can’t dissolve into water (Figure Pre-processing and 1200ºC Glass Product 2). Drying Furnace This method was the best performing Figure 2: Vitrification Process treatment method for arsenic trioxide dust removed from underground. It scored Cement Paste Backfill well because the glass is expected to be Cement paste backfill is a type of cement very stable. stabilization where a paste of cement and Cement Stabilization dust is made. This paste can be pumped, Cement stabilization would combine which helps move the dust safely. The cement with the dust to keep the arsenic cement paste would not be as strong as the trioxide from moving. Experts concluded solid blocks created through cement that this method could work if the cement stabilization. It was assumed that after were stored in large blocks, keeping the stabilization the arsenic trioxide dust arsenic away from groundwater and would be pumped back underground. surface water. This method would use large amounts of cement, making it costly. Biological Arsenic Precipitation Bacteria can make stable arsenic minerals Mineral Precipitation under the right conditions. This Arcadis evaluated the possibility of technology is newer and not as well converting the arsenic trioxide into stable studied as mineral precipitation. It would natural arsenic minerals that do not easily also require an above-ground treatment dissolve in water. Mineral precipitation is plant. Some minerals formed in this way used to process arsenic waste at other are not as stable as the ones formed using mines around the world using different mineral precipitation and new processes methods. The treatment would occur are being developed. Arcadis examined above ground in a treatment plant. Two this method under both low, or no, oxygen different groups evaluated this technology (reductive) and higher oxygen (oxidative) as a way to confirm quality control of the conditions. research method and findings. Giant Mine State of Knowledge Review Summary, September 2017 arcadis.com 4 Underground Disposal Ranking of Reviewed Only one method of underground storage Technologies of the processed arsenic trioxide dust was The frozen block method was the highest- studied. scoring method for keeping the dust in the current location underground. It also got Sand Shell Purpose-Built Vault the second-highest score for the The sand shell purpose-built vault was stabilization/treatment methods. The evaluated as a possible underground highest-ranking dust removal method was storage option. The treated dust would be hydraulic borehole mining, and the moved to new underground concrete highest-scoring treatment method was vaults surrounded by sand and/or gravel vitrification, or encasing the dust in glass. to provide protection from ground movement (Figure 3). The overall scores are summarized in Figure 4. Arcadis gave each method a This method scored well but needs to be score on a scale of 1 to 10.