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Supervising Scientist Report 126
Koehnken L
Supervising Scientist, 1997
ISSN 1325-1554
ISBN 0 642 24326 3
The following abstract, executive summary or foreword/preface is reproduced here from the full report. The full report is available online in PDF or can be ordered in hard copy or CD from Publications, Supervising Scientist Division. See our publication ordering page for further instructions.
Copper has been mined and processed at the Mount Lyell mine at Queenstown in western Tasmania for a century but it was not until Copper Mines of Tasmania (CMT) took the Mount Lyell mine over in 1994 that more than scant regard was paid to protecting the environment.
Historically the mine was an economic focal point for western Tasmanian development, with towns, railways and governments all dependent on its fate. But the environmental impact and costs of this prosperity were high. With 'new' industries on the west coast such as ecotourism and aquaculture, which depend on a 'clean' environment, the existing and continuing pollution from historic mining practices is unacceptable to society and remediation solutions are needed.
The environmental impacts include:
Smelting ended in the 1960s and CMT has built a dam to contain tailings. CMT's modern environmental management plan is based on 'Best Practice Environmental Management' principles.
The Mount Lyell Remediation Research and Demonstration Program (MLRRDP) has collected technical information and designed a remediation plan to redress environmental damage relating to Mount Lyell activities. The MLRRDP is one of Australia's most comprehensive responses to large-scale environmental damage. The Program's field trials have studied cost-effective ways to reverse the environmental damage affecting Mount Lyell, Macquarie Harbour and the King and Queen Rivers.
The Program is of national and international significance as an example of responsible environmental management and it also has strong local significance to the economy and quality of life for the west coast of Tasmania.
The Commonwealth (through the Supervising Scientist, part of Environment Australia) and Tasmanian Governments (Department of Environment and Land Management [DELM]) jointly managed the MLRRDP and have provided a total $2 million for research, field trials/reports, as well as community consultation/education and administration for two and a half years.
This report summarises MLRRDP outcomes. The findings will help Government and CMT redress environmental damage in the region.
The program had extensive community participation in all phases through its Consultative Committee (consisting of all stakeholders in the region) plus public meetings and newsletters.
Early on, public input was grafted onto the technical expertise of the Supervising Scientist and DELM to create the Environmental Quality Objectives of the MLRRDP and design 16 investigative projects for environmental information about the affected areas. This enabled an accurate assessment of the state of these regions and the basis of a cost-effective remediation plan targeting primary pollution sources.
The projects overwhelmingly identified the lease site as the major source of acid drainage related pollutants affecting the rivers and harbour, with metals contamination from tailing and slag deposits being very minor in comparison.
Within the lease site, the North Lyell Tunnel has water derived in part from underground workings and has approximately 78% of the lease site copper loading. Discharge from other tunnels and waste rock dumps accounts for 21%. The remaining 1% is from smaller sources.
Downstream, chemical modelling and toxicological testing indicates that 95% to 99% of the acid drainage from the site must be neutralised or stemmed for the resultant water quality to meet downstream environmental quality objectives. Contaminated sediments in the King River and Macquarie Harbour contribute relatively little of the total pollutant load entering the harbour, and it is clear the priority for remediation should be the lease site. The Queen and lower King Rivers (but not their tributaries) are essentially lifeless due to acidity and high metal concentrations. The biological communities in Macquarie Harbour are impoverished compared with coastal embayments elsewhere in south-eastern Australia. However, Macquarie Harbour waters are less toxic than would be expected from the concentrations of copper present. This is because other constituents of the water chemistry hold a proportion of the copper in inactive forms.
Two principal lease site remediation alternatives have been identified which would achieve the downstream Environmental Quality Objectives:
The options were assessed for: effectiveness, feasibility, cost, social acceptability, flexibility and impact of mine closure/development. Neutralising all acid drainage sources is recommended in conjunction with water diversion works which minimise the production of acid drainage. Neutralisation is a flexible system with options for staged implementation, using mine tailings in the neutralising process. A copper recovery system, such as solvent extraction/electro winning (SX/EW) is also recommended as it has potential cost offsets.
The MLRRDP has also identified and trialed remediation options suitable for small acid drainage sources, particularly those not easily diverted to a central collection point, or those not linking with the Queen River. Covering the Magazine Creek waste rock dump and the installing a successive alkalinity producing system (SAPS) have both been very effective in reducing acid drainage, and could be incorporated as supplementary measures to the large-scale lease site water management plan is developed.
While remediation must focus on the lease site, downstream revegetation trials (established to determine the most successful riverbank revegetation methods) need monitoring. Community-based groups should be encouraged to help implement revegetation works.
The cost of remediating the lease site may appear substantial at first: neutralising all acid drainage sources requires capital expenditure exceeding $10 million, with yearly operating costs around $2 million. However, if full remediation proceeds, the growing Macquarie Harbour-based aquaculture industry may contribute an extra $8 million a year to the local economy. If even half the tourists visiting Strahan stay one additional day it will generate another $9 million yearly through tourism. Importantly, site remediation would enhance Tasmania's 'clean green' image and send a message to local, national and international mining and environmental communities that Tasmania is serious about the environmental impacts of mining. Implementing remediation plans is a major step in fulfilling Australia's international responsibility to protect, conserve and preserve World Heritage Areas for future generations.
In implementing the recommended remediation strategy, the Tasmanian Government and CMT must negotiate an agreement which will promote remediation, recognise CMT's right to mineral access and permit third party involvement if required. It must provide a legal, logistical and financial framework so remediation proceeds and funding options at the Commonwealth, State and local level should not be limited to government sources. Given the longevity and severity of the acid drainage-related environmental issues and the effort and money invested in the MLRRDP and other studies, the community has a strong expectation from that effective action will occur. There is no putting Mt Lyell back in the 'too hard basket'.
