There are many international guidelines, state regulations and technical standards relating to tailings disposal. In addition, the larger mining companies have their own in-house standards and design rules with competent personnel in charge of their operations. Sound embankment design methods can be used by most designers familiar with earth dam design.
The paper gives a listing of many of the current sources of information and guidance available, with some comments by the author on their perceived relevance to the Australian mining industry. Despite the availability of a number of other guidelines at the time, the need for Australian Guidelines was recognised in the mid 1990s and the reasons for the development of the 1999 ANCOLD Tailings Guideline are explained.
Perhaps the best recognition of the need for the original ANCOLD guideline is the degree to which it has been adopted since publishing the 1999 edition. It is in almost universal use in the Australian mining industry and is recognised as providing appropriate and acceptable standards by all state governments. Its use is recognised and sometimes even specified by a number of neighbouring countries and it is also recognised internationally when used by Australian companies with overseas operations.
The reasons for this wide acceptance are described. However, there are some areas where more recent developments have led to the Guidelines becoming dated and improved international guidelines have been published since 1999. The need for a revised ANCOLD guideline and its elevance is then described.
Keywords: Tailings, dams, mining, guidelines
Giovanni De Cataldo
The ANCOLD Guidelines on Dam Safety Management August 2003 were formulated to ensure that dam owners adopt a responsible approach towards the safe operation and maintenance of their dams.
Is it possible to safely, responsibly and acceptably work outside the regulatory Guidelines/Requirements?
The challenge for dam owners now and into the future in meeting stringent standards, is to cost effectively manage their assets within available financial constraints whilst minimising risks and maintaining acceptable levels of safety.
With the continuing drought and suppressed storage levels in most dams, the risk to downstream communities and to the environment from dam failure is significantly reduced.
Based on various studies, investigations, internal workshops and external “Expert Panel” reviews, this paper puts forward a case for a sound and responsible risk-based approach to routine visual and surveillance monitoring frequencies at varying storage levels for “Sunny Day” conditions and compares it against traditional ANCOLD standards which are based solely on consequences.
Keywords: State Water Corporation, ANCOLD guidelines, risk-based approach, dam safety, regulator.
David Ryan, Simone Gillespie
The Burdekin Falls Dam is the largest of the 19 dams owned by SunWater. The dam is located on the Burdekin River at AMTD 159.3km, approximately 210 km south of Townsville and supplies water for irrigation, urban and industrial development in the lower Burdekin Region. The dam has such unique features as the largest spillway of any dam in Australia and a catchment area of 114,770 km2, which is equivalent to about 1.7 times the land area of Tasmania. It is proposed to raise the dam to provide a more certain water supply for the North Queensland region. This paper outlines the features of the existing structure, the influence of the revised hydrology since the time of its construction and the options considered in the planning and design of the raised structure.
Keywords: Burdekin Falls Dam, unique features, spillway, fuse plug.
David Brett, Bruce Brown, Imran Gillani, David Williams
This paper reports the direction of a current review of the 1999 ANCOLD Guidelines on Design, Construction and Operation of Tailings Dams. A sub-committee has been formed and has determined that the majority of the current guidelines need only minor editing but that additional attention is required to the concepts of risk and design for closure.
Major mining companies recognise that effective operation and closure of their tailings facilities are fundamental to their continued business from financial and political aspects. Risk needs to be managed throughout the life cycle of a TSF through planning, design, operation, closure and post-closure. Various methods are used to assess the “consequence category” of a TSF. This then determines design and operational criteria. Risks are identified and controls developed to limit these to acceptable levels.
The involvement in the sub-committee of representatives of the mining industry gives an industry perspective to this issue. This includes determination of acceptable risk levels and how to manage operations to achieve them.
The current ANCOLD Guidelines are very limited in terms of guidance for closure and possible abandonment of TSFs. However this area is perhaps the most critical from an economic and environmental perspective. The issues to be faced at closure and post-closure should be considered at the planning and design phases. The paper outlines some of the post closure cases that might need to be considered in design.
Keywords: guidelines, tailings dams, ANCOLD
Robert Kingsland, Glen Burton
The management and closure of tailings dams can present mines with a trailing liability potentially extending well beyond the life of the mine. The dilemma faced by mine operators is that a tailings storage facility (TSF) is usually required to be in service up until the last product is mined and processed, but the stored tailings may be too weak to support the capping of those facilities for some years after the last tailings deposition. This paper presents the authors’ experience in the geotechnical characterisation of tailings and failure mode analysis required for tailings dams cover design, with particular reference to coal mines in the Hunter Valley. Techniques for field and laboratory determination of strength and consolidation parameters are presented. Failure modes for capping cover and displacement cover alternatives are discussed. Alternative cover techniques including strategies for improving and/or accelerating tailings strength gain are also discussed. Finally, areas needing further study are noted.
Keywords: tailings storage facilities, tailings dams, closure, capping, cover design.
Peter Cordi, Paul Fuller
Tallowa Dam was completed in 1977 at the junction of the Shoalhaven and Kangaroo Rivers in the southern highlands of NSW to provide a pumping pool for water supply transfers to Sydney. These transfers were made only during drought periods, at which time limited and fixed environmental flow releases from a low level outlet were made to the downstream Shoalhaven River. After extensive consultation with the local community the Government decided in 2006 to commence transfers earlier in the drought cycle, and release variable amounts of surface water to improve river health during transfer periods. In addition, Tallowa Dam was identified as having a significant impact on fish passage, as many species migrate to the estuary during their life cycle, and approximately 75% of the viable fish habitat was upstream of the dam. This project involved the design and construction of works to be retrofitted to the dam to address both issues. A surface water release slide gate in the spillway, a low friction coating on the spillway, and a downstream weir were constructed to release environmental flows and allow safe downstream fish passage. A new fish attraction flow outlet was drilled through the dam wall, and a fish attraction chamber and a travelling bucket fish lift was installed for upstream fish passage.
Keywords: environmental flows, fish passage, Shoalhaven River, construction.