Land Theme Report
Australia State of the Environment Report 2001 (Theme Report)
Prepared by: Ann Hamblin, Bureau of Rural Sciences, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06748 5
Soil and land pollution (continued)
Condition
What is the condition surrounding current mining and mineral processing sites? [L Indicator 6.4 and 6.5]
Australia earns much more from minerals and energy exports than from rural products (A$38 billion and A$24billion respectively in 1999-2000), yet the area of land affected by the whole energy and mineral sector is tiny by comparison. However, some types of mining operation can have a large effect beyond the mine site itself. The mining industry has made vigorous efforts to manage operations to high environmental standards, in collaboration with government agencies.
About 375 companies have mining operations across Australia, of which about 50 produce nearly 90% of the mineral value. State and Territory EPAs and mines departments regulate all mining. The Australian Minerals and Energy Environment Foundation, created in 1991, and funded through combined company and government sponsorship, provides a wide range of information, conferences, scholarships and awards to stimulate best practice community consultation; ecological components; planning; rehabilitation; and noise, dust, tailings, waste and water management. Its activities, and those of CSIRO, ANSTO, and other specialised research centres, assist companies to improve their environmental management, site design, monitoring, safety and rehabilitation after mining operations cease.
The 1996 Code of Environmental Management, updated as Code 2000
In 1996 the Australian Minerals Council developed an environmental management code aimed at changing values and behaviour in the industry. Signatories accept environmental responsibility, integrate environmental management with all operations, and minimise environmental impacts. The revised code now commits companies to producing an annual public environmental report, progressively implementing all features of the code wherever they practice, and verify the results with an accredited auditor every three years.
By May 2000, 50 companies, representing over 85% of the minerals industry, had signed the Australian Minerals Industry Code of Environmental Management; of these, 34 have produced a first report.
Mine condition and management
The following case studies illustrate how the mining industry deals with a range of environmental issues.
Acid drainage
Acid drainage is one of the most technically challenging problems facing the mining industry. It occurs as a consequence of the oxidation of sulphide minerals and subsequent leaching by rainfall and transport in drainage waters. The most threatening situations occur where acid drainage dissolves and incorporates other minerals, such as heavy metals, including radioactive ones. Whenever new sulfide-rich minerals and coal deposits are mined, the potential risk of acid drainage is high. Some of the highest impacts in the past have come from abandoned mines at Rum Jungle (NT), Captains Flat (NSW) and Mt Morgan (Queensland), and the still operational mine at Mt Lyell (Tasmania). Remedial action at such sites has substantially reduced their impact and has overcome most of these problems.
An example of an operating mine dealing with this problem is the Gregory open cut (strip) coal mine in the Bowen Basin, central Queensland. From the first exploration of the site in the late 1970s, it was recognised that acid drainage would be a problem, and the mine was designed to minimise acid generation and impact.
Norwich Park mine in the Bowen Basin.
Note: Topsoil removed prior to mining is spread over mined land. This view shows stockpiles of topsoil, with good grass and shrub growth after rehabilitation in the foreground.
Source: BHP
All wastes are managed to reduce their potential to generate acid drainage. The fine wastes from coal washing, tailings, are deposited as a slurry, under water, with the water recovered and reused in coal washing, after neutralising with lime. Coarse waste products are returned to mine pits, which are then covered with spoil. This negates the need for special reject dumps and their subsequent rehabilitation. Selective handling is used to locate and place pyrite layers into deep parts of the mine, which are then covered in spoil before revegetation is undertaken. All drainage is captured and reused, because of the potential threat of acid drainage occurring in any water used.
Dealing with cyanide
Telfer Gold Mine is located 485 km south-east of Port Hedland in the north of Western Australia, in the Great Sandy Desert. The mine produces 5 million ounces of gold per year. It uses the 'carbon-in-leach' process that extracts gold with cyanide, after concentrating the sulfide ore by flotation. Risk analysis demonstrated potential for ground water pollution and, faunal deaths. This could occur from bursting pipes, and leakage of tailings storage. Consequently the leach pads are constructed on an impermeable base, and any potential leakage is monitored by 20 surrounding bores. All ponds, dumps and pads are designed to take a 1-in-50-year rainfall event. A supplementary retention pond has been constructed to cover extreme events. No cyanide has been detected in any bore over 12 years of monitoring.
Rehabilitation after mining mineral sands
Eneabba Mineral Sands mine is 300 km north of Perth, and is a surface strip mine extracting titanium and rutile by wet dredging. A total of 1200 ha has been rehabilitated to the original low heathland vegetation, which contains very high numbers of species endemic to WA.
A full botanical survey is carried out before mining, and seeds collected. Topsoil is stripped and placed in properly sequenced layers where it is stockpiled. Rehabilitation of earthworks recreates the subsoil surface, and topsoil is then replaced and mulched and a cover crop is sown with native seeds incorporated. The cover crop protects germinating seedlings. Many seeds are recalcitrant propagators, and require special pre-treatment, such as exposure to smoke from burning bush, or firing in mulch. Research has been undertaken to assist propagation of the full range of original species.
Radiation sites
Radiation is an issue for uranium mines and some mineral sands mines that extract minerals such as monozite and zircon. There are three mines in Australia that currently mine uranium. The longest established are Ranger mine in the Northern Territory, surrounded by Kakadu National Park; and Olympic Dam, in arid pastoral country in the north of South Australia. The Commonwealth's Office of the Supervising Scientist was established to supervise the environmental aspects of uranium mining in the Alligator Rivers region that includes Ranger. Ranger is also subject to regulation by the Northern Territory Government whilst Olympic Dam is regulated by South Australian government agencies. In addition the Australian Radiation Protection and Nuclear Safety Authority (ARPANSA) issues licences to operate and is responsible for guidelines on human health issues in association with the NHMRC. As with other mine sites, monitoring of the sites for acid drainage is carried out regularly. Current operations are carried out to very strict standards, but former operations have left legacies of environmental contamination. For example at Rum Jungle, after mine closure in 1961, a combination of both tailings and acid mine drainage waters to the Finniss River impacted on the downstream environment for about 16 kilometres. During the mid-1980s an extensive rehabilitation program relocated tailings and waste materials to secure containments, including a former open cut. Other work included capping of waste rock stockpiles, and revegetation of the site. The Finniss River downstream of the mine has recovered well.
Ranger
The Ranger mine site extends over approximately 6 km 2 and includes extensive waste rock dumps, low-grade ore stockpiles and a 1 km 2 tailings dam. Rainfall runoff, which may not meet water quality criteria for direct release, is directed into retention ponds designed to accommodate the very high rainfall in the wet season. Some of the better quality wastewater is used to irrigate vegetation around the mine site in the dry season. The composition of the water is monitored regularly and a comprehensive monitoring program checks the quality of both ground and surface water, as well as atmosphere, soil and vegetation around the site. Since 1997, tailings have been deposited in the worked-out Pit 1 rather than the tailings dam, which is now used as an evaporation pond. When the site is rehabilitated, all the tailings in the tailings dam will be returned to the pit that will then be capped and revegetated.
Operations at Olympic Dam, a modern and sophisticated complex of mining, processing and rehabilitation activity.
Source: Western Mining Corporation Ltd
Olympic Dam
This mine is the largest in Australia. It is an underground mine, with over 200 km of shafts and tunnels. The principal metals extracted are copper and uranium oxide concentrate, with smaller amounts of gold and silver. The acid tailings are pumped out into sealed settling ponds, which presently cover 380 ha. Workers at Olympic Dam metallurgical processing plant and mine are located in the purpose-built township of Roxby Downs, which is 16 km south of the Olympic Dam operations, and has a population of about 4500. The mine site is open to tourists and environmental officers work with local community members on a range of ecosystem management issues. The company, WMC, is a signatory to the Australian Minerals Industry Code, and has recently completed an ambitious expansion plan that required stringent environmental impact assessment. This expansion more than doubled the production of copper from 85 000 to 200 000 tonnes of copper per annum, with associated increase in the other metals produced.
When mine shafts are exhausted they are filled with cemented waste rock (mullock) and other waste products to reduce the amount of above ground materials. One of the main pressures on the environment comes from the use of artesian water to run the operation and supply the township. However, from a total of 425 ML/day of water entering the South Australian part of the Great Artesian Basin, Olympic Dam and Roxby Downs use about 32 ML/day, compared with pastoral bore usage of 110 ML/day.
Tailings disposal areas are a potential hazard at any time, and on the scale of this operation they need very high engineering standards. The tailings waste streams and tailings liquor evaporation systems are designed in a closed loop and conservatively engineered to minimise the possibility of failure. Such structural failures have occurred in other countries and companies. The tailings liquor evaporation pond system is designed so that there is no discharge of water from the mine site. The environmental plan requires reporting of all spillages. In 1999-2000 there were no toxic spills or radioactive leakages, but a few saline water and hydrocarbon spills occurred.
Chemical analysis of the emissions from all operations at Olympic Dam are now posted in the National Pollutant Inventory and on WMC 's website.
Implications
Australia's low level of population density, lack of past industrial economy, and highly urbanised population distribution mean that we have little of the types of highly toxic waste disposal problems of other OECD countries, and very large tracts of land that have had very little anthropogenic input. However, there are still many contaminated sites, including some, such as the Olympic site in Sydney, in populated areas. This issue is covered more fully in the Human Settlements Theme Report.
| Substance | NPI emission estimates (t/year) | Main sources |
|---|---|---|
| Arsenic and compounds | 67 | waste stream |
| Chromium and compounds | 0.017 | waste stream |
| Particulate matter | 98 | combustion, stockpiles, vehicle emissions, ventilation |
| Polycyclic aromatic hydrocarbons | 5.5 | diluent usage (process chemicals) |
| Sulfuric acid | 979 | waste stream (process chemicals) |
The mining and mineral processing industries are highly organised in their approach to environmental (and safety) management. As with petrochemical and industrial chemical industries this is critical from an occupational health and safety aspect, because of the potential dangers in their activities. However, these industries have also found that being good environmental corporate citizens pays, in terms of public relations and cost savings (in operational and restoration expenditure). The cohesiveness of the industries and their commercial focus have made it easier for them to address such issues than is the case for some rural industry sectors.