Designer waste landform modelling and design - Rum Jungle Mine

摘要

Rum Jungle is a former uranium mine site near Batchelor in the Northern Territory. Historical mining activities at the site between 1952 and 1971 have led to ongoing and adverse impacts on the surrounding environment. Sulfidic mine waste is prevalent in the Main and Intermediate Waste Rock Dumps (WRDs) and consequently, Acid and Metalliferous Drainage (AMD) is a problem. Even though a technical assessment after rehabilitation determined that the engineering and environmental criteria were met, ongoing impacts have led to contemporary water quality standards not being met in the East Branch of the Finniss River and soils around the site, and led to poor vegetation establishment and coverage. The Department of Mines and Energy (DME) is directing a collaborative, multi-phased rehabilitation planning process for the site. The Former Rum Jungle Mine Site Conceptual Rehabilitation Plan (CRP) (2013) outlines the objectives, the rehabilitation approach and preferred rehabilitation strategy for the mine site. Objectives for the site are to provide geotechnical and geochemical stability so as to allow for sustainable land uses by traditional Aboriginal owners of the site. To achieve these objectives, it is proposed to relocate all existing above ground WRDs, to either backfill the Main Pit void, or a single, stable and aesthetic waste storage facility (WSF) which will be constructed on site. Development of the strategic approach and detailed design of civil engineering works is currently underway to manage geochemically and radiologically active mine waste prevalent across the site. O'Kane Consultants Pty. Ltd. (OKC) is preparing rehabilitation designs for the overall site, supported by various (ongoing) technical assessments for the WSF and Main Pit. The detailed numerical modelling includes a material balance assessment, waste placement and oxygen ingress modelling, waste wetting up and drain down modelling, cover system and landform evolution modelling. The control of surface water, seepage, and erosion in the long-term and during construction is central to achieving the rehabilitation objectives. As such, assessment of the proposed WSF geometric design methodology by the practical implementation of landform evolution models, including Water Erosion Prediction Project (WEPP), SIBERIA and CAESAR-Lisflood is being completed. These models are used in conjunction with sophisticated terrain modelling software (Civil 3D) to assess future stability based on surface materials and desired landform geometry. The assessment methodology is based on lab testing and observations of erosion on existing landforms, and the validation adds confidence to the assessment. This enables improved aesthetic design for the proposed WSF, an important design objective, and can provide confidence in stability of the landform over long timeframes.