Integration of Field Investigations and an Innovative Modelling Tool to Prioritize Closure Strategies for an Abandoned Uranium Mine

Abstract

The Gunnar Mine was a uranium mine located in northern Saskatchewan, Canada, on the north shore of Lake Athabasca. It operated as an open pit and underground mine from 1951-1963. The Saskatchewan Research Council began decommissioning at site in 2010. EcoMetrix supported the evaluation of decommissioning options for the Gunnar Mine site by considering the potential source loadings of trace metals and radionuclides from the site, and the potential effects of these loadings on downstream water quality. The evaluation of decommissioning options should be: 1. based on appropriate site data that accurately characterizes the mine source loadings; 2. holistic and account for all potential mine source loadings so as to prioritize sources based on net benefit to downstream water quality; and 3. clear and understandable to a broad group of stakeholders. Field investigations were utilized in the development of a site specific water quality model; MineMod. The model was developed with three objectives: 1. to assess the water quality that would result from preferred closure options; 2. to identify any issues that may require additional management; and 3. to assess the required efficiency of potential mitigation activities for closure. Several conditions representing preferred closure options were built into the model. The model was developed and calibrated using operating data on flows and concentrations from known sources. Numerous sensitivity analyses were completed within the model to identify the key controls on the radium-226, uranium, arsenic, and lead concentrations in discharge from the site, as well as to understand how various mitigation strategies would influence water quality post- closure.Model results showed that waste rock represents the greatest potential loading of radium-226, uranium, arsenic, and lead to downstream waterbodies. Overall, the model results using MineMod provides a path forward in assessing potential remediation strategies and subsequent trade off studies.