The Gunnar Mine and mill site was the largest of some 38 now-abandoned uranium mines that were developed and operated in Northern Saskatchewan, Canada, during the Cold War years. During their operating lifetimes these mines produced large quantities of ore and tailings. The Gunnar mine (open pit and underground) produced over 5 million tonnes of uranium ore and nearly 4.4 million tonnes of mine tailings during its operations from 1955 through 1963. An estimated 2.2 to 2.7 million m3 of waste rock that was generated during the processing of the ore abuts the shores of Lake Athabasca, the 22nd largest lake in the world. After closure in the 1960s, the Gunnar site was abandoned with little to no decommissioning being done. The Saskatchewan Research Council has been contracted to manage the clean-up of these abandoned northern uranium mine and mill sites. The Gunnar Mine, because of the magnitude of tailings and waste rock, is subject to an environmental site assessment process regulated by both provincial and federal governments. This process requires a detailed study of the environmental impacts that have resulted from the mining activities and an analysis of projected impacts from remediation efforts. The environmental assessment process, specific site studies, and public involvement initiatives are all now well underway. Due to the many uncertainties associated with an abandoned site, an adaptive remediation approach, utilizing a decision tree, presented within the environmental assessment documents will be used as part of the site regulatory licensing. A critical early task was dealing with major public safety hazards on the site. The site originally included many buildings that were remnants of a community of approximately 800 people who once occupied the site. These buildings, many of which contained high levels of asbestos, had to be appropriately abated and demolished. Similarly, the original mine head frame and mill site buildings, many of which still contained the original machinery and equipment, also had to be dismantled. Remediation options for the accumulated demolition debris have been assessed, as have remediation options for the waste rock and tailings, all of which form part of the environmental assessment. The regulatory requirements include the environmental assessment processes, a complex public involvement strategy, and licensing from the Canadian Nuclear Safety Commission (CNSC) with the long-term goal of releasing the property in a remediated and stable state to the Province of Saskatchewan. Prescribed environmental and land-use endpoints will be determined based on the environmental assessment studies and remediation options analyzed and implemented. Ultimately, the site will be released into an institutional controls program that will allow long-term government management and monitoring.

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