Authors: Reszat, TR; Balding, G; Fawcett, M


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Reszat, TR, Balding, G & Fawcett, M 2009, 'Remediation of small scale uranium mining activities in the South Alligator Valley, Kakadu National Park', in AB Fourie & M Tibbett (eds), Mine Closure 2009: Proceedings of the Fourth International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 213-228,

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The director of National Parks has initiated works to remediate, over four years, 13 abandoned uranium mines and related sites in the Gunlom Aboriginal Land Trust (GLT) area located in the upper South Alligator River Valley of Kakadu National Park. There are two categories of abandoned uranium mines and related sites in the GLT area: namely, non-radiologically contaminated sites (termed Part A sites); and sites containing residual quantities of tailings and run-of-mine wastes with low levels of radiological contamination (termed Part B sites). The portion of the works discussed in this paper involves characterisation of the Part B sites and the design of an engineered containment facility suitable for low level radiologically contaminated materials. Site remediation and engineered containment design involved a comprehensive and critical assessment of both the waste sites and the containment area. Sites investigated and characterised included Battery Bund, El Sherana Mine, El Sherana Village, Palette Mine, tailings residues near Rockhole Creek, South Alligator Village and Weighbridge. Physical, geochemical and radiological material characterisation of waste was undertaken to assess which materials are at risk and require additional works to supplement previous remediation. Radiological assessment included gamma measurements and radiometric laboratory analyses. Geochemical assessment involved sampling and characterisation based on in-field gamma measurements and sampling of known waste materials from a non-radiological perspective. Geochemical characterisation of samples involved solids and leach extraction chemistry, and testing to assess acid rock drainage (ARD) potential. Laboratory geochemical and radiological results were assessed through geochemical modelling to predict pore-water speciation of all wastes and the likelihood of solute migration. Containment site assessment involved geochemical and radiological characterisation to obtain base-line conditions and considered geochemical mixing and speciation modelling to predict the effects of containment leachate on-site base-line chemistry, should migration of solutes occur. The containment was designed using industry best practice using site-specific physical characteristics to develop the optimum design option, and considered geotechnical, hydrological, erosional and geochemical processes. Design alternatives were considered using soil-atmosphere, seepage and regional groundwater modelling including full sensitivity analyses to ensure proper design specifications were met. The preferred design alternative includes a robust cover system to limit net percolation of water into the waste and consists of a thick growth medium underlain by a compacted clay layer (CCL). The containment is located in the vadose zone, 5 m above maximum groundwater levels, in low permeability, clay-rich materials, and includes a secondary containment method consisting of a CCL at the base of the waste. The design includes automated instrumentation for monitoring and surveillance including: soil suction, temperature, and moisture sensors throughout the profile; provision of radon gas egress monitoring though the cover system; vibrating wire piezometers and lysimeters at the base to assess seepage and pore-water pressures; cover erosion and runoff measurements; piezometers appropriately sited to intercept potential seepage and monitor hydraulic heads through the containment area; and meteorological instrumentation. Remediation of small scale uranium mining activities in the South Alligator Valley, Kakadu National Park T.R. Reszat et al. 214 Mine Closure 2009, Perth, Australia

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