Staff Directory

Flow and Transport Modeling for Closure of Pit 3 at the Ranger Uranium Mine

Client: Energy Resources of Australia Ltd.
Location: Northern Territory, Australia

Challenge. Evaluate impacts on water resources from various alternatives for closing a large open pit at a mine site located inside a National Park and upstream of UNESCO world heritage wetlands.

Project-Ranger-MineSolution. INTERA’s modeling expertise was used to support the development and optimization of mine closure strategies. A major part of this work included developing and applying a groundwater flow and solute transport model to facilitate closure planning for one of the mine’s large open pits. The model was used to evaluate various pit closure scenarios based on predictions of potential solute loadings from the pit to nearby surface water resources. We also applied a systems assessment methodology to evaluate the effectiveness of a selected closure scenario in preventing waste tailings, which are being used to backfill the pit, from adversely impacting surface water and groundwater resources over the next 10,000 years. These tools played a key role in establishing support and approval from regulators and other stakeholders for the recommended closure strategy.

Providing modeling and technical support for closure of existing Ranger mine workings within the lands of traditional owners and the Kakadu National Park. Efforts focused on determining cost-effective final disposition of mine wastes that secures approval from stakeholders. As lead modeler, developed conceptual and numerical modeling tools to assess solute loading from Ranger Pit 1 and Pit 3 to the nearby creeks that flow into world heritage wetlands. Directed a team to create a new conceptual model in collaboration with Australia’s Commonwealth Scientific and Industrial Research Organization and

construct and calibrate a new three-dimensional MODFLOW SURFACT flow model. Created a digital model of the key hydrolithologic units using Leapfrog Hydro, bore logs, and GIS and Vulcan data products. Created and applied three-dimensional flow and solute transport models with MODFLOW SURFACT to assess the potential impacts on the creek from different closure designs for Pit 3 and a single design for Pit 1. Completed assessments of dense brine emplacement using FEFLOW and MODFLOW-SURFACT that were used by ERA engineers to choose an appropriate brine disposal method with savings of many hundreds of millions of dollars. Presented results in 2012, 2013, and 2014 to Australia’s Office of the Supervising Scientist, which is tasked with ensuring environmental compliance at the Ranger Mine. Collaborated with INTERA geochemists to reduce uncertainty in solute leaching from waste rock.