| Managing Mine Waste |
|
Managing mine waste is the most important challenge facing OTML. The major wastes are overburden or waste rock from the mine pit and tailings from the mill. OTML has undertaken more than 120 studies to assess options for managing the mine waste rock and tailings. The original Ok Tedi project was designed to include a large tailings dam on the Ok Ma. The foundations of the Ok Ma tailings dam were destroyed by a landslide in 1984, during construction of the dam. A small volume of tailings was retained in the Interim Tailings Scheme near the mill in the early years of operations. Since then, and with approval from the State, tailings have been discharged directly into the Ok Tedi and Fly River systems as an alternative tailings treatment was not feasible, given the unstable terrain, geological formations and very high rainfall of the region.  In the early 1990s, large areas of stressed vegetation and vegetation dieback became evident along the Ok Tedi. The cause was not initially apparent, but investigations subsequently determined that it was caused by increased flooding due to the build-up of mine-derived sediment in the bed of the river. Research into mine waste managementIn 1996, OTML set up the Mine Waste Management Project (MWMP). The project brought together international experts from a wide range of disciplines to undertake an extensive two-year study of the engineering, environmental, social and risk components involved in mitigating the environmental impacts of the mine waste. The MWMP also included a two-year, US$60 million, dredging trial in the lower Ok Tedi to investigate the effectiveness of dredging as a measure to reduce sediment build up in the river system. After reviewing a large number of mine waste management possibilities, four possible options to deal with mine waste issues at Ok Tedi were examined in detail in the MWMP:
The final Mine Waste Management Project Risk Assessment was completed and provided to the PNG government in August 1999. It concluded that the environmental effects of the mine were likely to expand significantly. It identified sedimentation, vegetation dieback, acid rock drainage, copper toxicity and fish biomass decreases as key environmental issues into the future. It concluded that none of the options examined offered a clear solution to the environmental and social impacts of the mine's operations.  The government requested its own consultant and the World Bank to review the Risk Assessment, and set up a task force to advise the government on its response to these findings. In January 2000, the World Bank reported that “from a purely environmental perspective, the risk assessment suggests that the Ok Tedi mine needs to be moving towards closure as soon as possible”, but that “immediate closure would appear to carry with it the worst social impact”. Sulphide mitigationThe high sulphide content of the Mount Fubilan ore body means that some potentially acid-forming mine wastes are generated. This potentially acid-forming material needs to be managed to minimise environmental impacts from “acid rock drainage” (ARD) where acidic water, with associated high metal content, is released to the environment. Active measures for managing ARD include adding additional limestone to waste rock at the mine to maintain acid neutralising capacity in the waste rock dumps. New information from Ok Tedi's environmental monitoring and research program shows that the impacts of sulphur and copper released to the river in the mine waste are going to be greater than previously thought. While there's nothing to suggest a risk of direct human impacts, there is an impact on the ecology of the river system, and the data indicate this impact will be long-lasting and will increase over time. On the basis of the current mine plan, sulphur in the ore will increase towards the end of mine life. Consequently, with sulphur and copper already impacting on the river ecosystem, OTML is investigating how these impacts can be most effectively minimised. OTML has been investigating a range of mine and mill improvements to reduce copper and sulphide minerals released to the river system. These include:
As a result of these investigations, OTML has constructed a tailings plant at the mine-site to remove the pyrite from the mine tailings, and a pipeline to storage dams in Bige. It is anticipated that this will come online in the third quarter of 2008. Dredging at BigeThe dredging of the Ok Tedi at Bige, the trial period of which was completed in 2002, is now continuing on a permanent basis. Currently around 15 million tonnes of sand is dredged from the lower Ok Tedi each year. Whilst dieback continues to be a ConsultationThe government and OTML undertook an extensive consultation process with local people in 2000 to inform them of the environmental predictions and to give them the opportunity to express their views on the future of the mine. The communities within the region affected by the mine — which include about 50,000 people — strongly endorsed the continued operation of the mine until planned closure. This community endorsement was formalised through a Mine Continuation Agreement process. Community consultation has been ongoing, to keep communities informed about environmental monitoring results and progress with development projects. In light of the increasing environmental impacts, formal discussions and negotiations with all communities across the impact area was undertaken in 2006 to review the compensation and benefits packages and re-set the balance of the competing environmental, social and economic issues. Other OTML initiatives relating to monitoring, reporting on and mitigating impacts of mine waste are discussed in Environment Monitoring and Reporting. |
significant problem in the Middle Fly extensive recovery of dieback-affected forest has accompanied this dredging in the lower Ok Tedi region.