Authors: Amoah, N; Phillips, J; Vlahos, S

Cite As:
Amoah, N, Phillips, J & Vlahos, S 2006, 'Investigation of Hydrological Behaviour of In Situ Bauxite Residue for Closure and Rehabilitation Design', in AB Fourie & M Tibbett (eds), Proceedings of the First International Seminar on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 441-451.

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Over 20 million m³ of residue from the alumina refining industry are produced in Western Australia each year. The residue is normally stored in engineered earth impoundments termed as Tailings Storage Facilities (TSFs). In recent years the closure and rehabilitation of such TSFs have become a very important aspect of overall strategic plans of many mining operations. The slurry deposition method of tailings disposal results in considerable volumes of water being deposited with tailings, some of which is still retained within the tailings deposit even after closure. It is important to know the future behaviour of this water, particularly if it is contaminated. Water can influence the closure of a tailings system in several ways including the following: • Waterlogging of the surface. • Capillary rise of contaminated water. • Major settlements of the tailings surface if the water table within the residue falls. • Underseepage which may infiltrate groundwater or need interception/treatment. • Rainfall infiltration may dissolve contained salts. At Worsley Alumina Refinery, the first Bauxite Residue Disposal Area (BRDA 1) was constructed in 1984. Residue deposition continued with the various stages of embankment raising. BRDA 1 reached the final design height in 1995. The total footprint covers 75 ha. The upper surface covers 50 ha, has a maximum depth of residue of about 45 m and contains caustic residue and approved refinery wastes. The hydrological behaviour of the tailings in BRDA 1 has undergone intense study in recent years. One of the primary aims has been to develop a conceptual model that could be used to predict the rate and quantity of liquor movement through the residue into the underdrainage system and to allow the estimation of potential liquor quantities to be treated after closure of the refinery. As part of closure design, adequate knowledge of this was required for the evaluation and design of a capping system for the BRDA. Investigations consisted of detailed instrumentation, several years of in situ monitoring, drilling, in situ testing and laboratory tests to characterise both the geotechnical and hydrological behaviour of the bauxite residue. The importance of rainfall penetration and its relationship with a perched and long-term watertable was examined. A predictive model was developed using the interrelationship between these factors to determine the impact on closure and rehabilitation design. Mine Closure 2006 ― Andy Fourie and Mark Tibbett (eds) © 2006 Australian Centre for Geomechanics, Perth, ISBN 0-9756756-6-4 Mine Closure 2006, Perth, Australia 441

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