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|WMC Limited (WMC) has progressively introduced process changes at its Olympic Dam mine site and processing plant in the arid north of South Australia to reduce its water consumption per unit of production, and is continuing to investigate further water conservation possibilities.
WMC is one of Australia's largest mining companies. Its main business is the discovery, development and processing of mineral resources.
The company owns huge underground reserves of copper, uranium, silver and gold at Olympic Dam in South Australia, and has invested some 1.1 billion Australian dollars in an integrated underground mine and processing plant to extract these minerals. The company produces refined copper, gold and silver, and uranium oxide concentrate and in 1998 planned to spend a further 1.6 billion dollars to significantly expand operations.
The mine is close to the rim of the Great Artesian Basin, which covers 1.7 million square kilometres in the Northern Territory and three Australian States. The Basin is one of the largest sedimentary basins in the world. It is estimated that 425 million litres of water flow into the South Australian section of the Basin each day. The overall flow is so large that water under pressure seeps to the surface in mound springs throughout several regions of arid South Australia. These springs are of high conservation significance, and WMC has a comprehensive monitoring program for the springs and also the bores in the south-west region of the Basin.
Location of Olympic Dam mine
The mining operations currently use 13.4 million litres of water a day (1998), while the nearby town of Roxby Downs, which was built to support the operations, uses another 1.6 million litres. Roxby Downs has developed to be an important regional centre.
In the 1980s, water was extracted from a single borefield located 110 kilometres from the mine and town. The water requires desalinisation before it is suitable for human consumption or can be used for plant processes at Olympic Dam. An extensive monitoring program ensures that impacts on mound springs on the southern rim of the Great Artesian Basin are minimised.
In 1995, the company applied for permission to begin drawing water from a second borefield a further 90 kilometres into the Basin. The goal was to reduce withdrawal pressures on the original borefield and to ensure an additional water supply for expansion of mine operations.
The project was approved and implemented in 1996. WMC now has approval to abstract water within licensed draw-down limits, which have been estimated by hydro-geological modeling to be equivalent to approximately 42 million litres a day. One of the conditions for approval was that WMC should monitor carefully the water flows to nearby water mounds. Further, the company is committed to minimise its withdrawals, to conserve water and to recycle whenever possible.
Water supply system site plan
Since 1997, the overall approach to reducing water consumption at Olympic Dam has been to:
Various processes were and are being modified so that less water is used in flotation and separation of the minerals from the ore. This has included:
Since 1998, WMC has also worked closely with the 3,000 residents of Roxby Downs in water conservation activities, such as:
For individuals and companies living and operating in an arid climate such as South Australia, water conservation and management is an important consideration. WMC recognises its responsibilities to assist with management of the Great Artesian Basin and is strongly committed to minimising its withdrawals, to conserve water and recycle whenever possible.
Because of the relatively high cost of water, WMC has considerable incentive to minimise its own use, and to encourage residents also to be water conscious. As at 1998, the unit cost of water for the project was A$1.61 per kilolitre for general process water, and A$2.40 per kilolitre for potable quality water. This compares with the cost, i.e. $0.88 per kilolitre, charged by the South Australian Government to other users. It is a company decision that water be sold to Roxby Downs residents at the same rate as paid elsewhere in the State.
Mound spring water monitoring
The main barriers to further water conservation are process constraints and the capital and operating costs of recycling equipment.
Owing to the high cost of supply, the processing facilities at Olympic Dam were designed and built, and are being operated, to be efficient in the use of water. However, the continuous reuse of process water results in the build-up of salts (particularly chlorides) and other contaminants, which originate either from the initial water source or from the ore or process chemicals used. Eventually the concentrations of some salts and other contaminants become so high that they have detrimental effects on process efficiency.
WMC will continue to research and develop methods to reduce consumption and to encourage water conservation through educational programmes for employees and other Roxby Downs residents.
The costs of water conservation initiatives within the plant are many times higher than the cost of equivalent potential water savings in the pastoral industry. WMC has therefore offered to assist pastoralists in the borefields region to more efficiently utilise their water by providing assistance for the closure of boredrains and their replacement with piping, tank and trough systems.
The response to this initiative has been well received by pastoralists in the region. The potential water savings identified are between 14.6 and 23.8 million litres per day. This is significantly greater than any potential water savings available at the mine and town. However the company is continuing to investigate possible further cleaner production initiatives available at the mine and plant.
Senior Environmental Scientist
WMC ODC Pty Ltd
PO Box 150
Roxby Downs SA 5725
Ph: 08 8671 8558
Fax: 08 8671 0179
WMC's cleaner production initiatives were featured in Industry, Fresh Water, Sustainable Development, World Business Council for Sustainable Development, UNEP, April 1998.
Casestudy initially produced: 1997 by the Environment Management Industry Association of Australia
Last reviewed: May 2001