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With the ever increasing aim for the concept of sustainability within the mining industry, the adoption of planned rehabilitation and closure of mines needs to be implemented. The implementation of mechanisms to successfully rehabilitate and decommission mines must meet legislative, community, industry and stakeholder expectations about the long term and environmental and cultural criteria relevant to the local area (Farrel 1998).
Due to the magnitude and complexity of modern mine sites, a multitude of differing but interlinked hazards and consequences can occur during operation and rehabilitation. However due to economic and time constraints, not all of these potential ecological threats can be assessed and mitigated extensively. This is why formal risk assessment techniques and cost effectiveness analysis tools are used to identify and prioritise the major issues that have the potential to cause the biggest detrimental impact to the rehabilitation objectives (McCarthy and Purtill 1998).
Environmental Risk Assessments (ERA) depict a scientific based analysis of the incremental probabilities of harm occurring to the natural environment (Masters 1998). This involves the examination of mining operations, practices and processes and their potential impact on surrounding ecosystems. The aim of this project is to apply a systematic approach to the degradation of the quality and quantity of surface water and groundwater will be considered, due to the magnitude of the cumulative impacts of mining operations on waterways.
By introducing water standards to the appreciation of uncertainty, a risk assessment tool for ranking the rehabilitation options of water quality and quantity will be developed. This will be achieved through the application of engineering judgement the potential uncertainties of the risks identified in the Fault/Event tree. The cost effectiveness of the surface and ground water rehabilitation will then be developed and applied in accordance to the risk assessment model to give an indication of the economic limitations. The application of this cost-effectiveness analysis is only indicative of the final economic costs of the proposed rehabilitation strategies. Due to the variation in the value of industrial progression and environmental conservation, a complete cost-benefit analysis was not carried out.
This project will therefore develop a multi-disciplinary and risk assessment based methodology of selecting the most sustainable and economically advantageous process for rehabilitating any potential damage to surface and ground water supplies.
Environmental Risk in Coal Mine Rehabilitation
[whats been done/introduced over the history of realising that mining kills s/w and g/w]
[for the purpose of this project, what is required for a mine site to be successfully relinquished in terms of groundwater and surface water requirements?
The main ecologically degrading characteristics of contaminated minewater include acidity, ferris precipitates, trace metals and turbidity (14.26
The risk assessment tool within this project is based on a comprehensive analysis of the risk context and specific hazards regarding the failure to decommission an open cut coal mine based on surface and ground water conditions. The completion of this task requires an understanding of the cumulative effects of open cut coal mining projects, and the impact these have on achieving sustainable mine closure.
water treatment is unique dependent upon
establish and maintain procedures to identify key aspects of the organizationâ€™s activities, products or services that could impact the environment and analyze, assess and manage the risk of such impacts
A risk analysis and assessment should identify and prioritize the significant environmental aspects and risks (those which could cause significant impacts to the environment), taking into account the scale of the impact, probability of occurrence and duration of the impact
Of the range of potential environmental risks caused by mining, stakeholder expectations and statutory compliance rank the monitoring, verification and protection of water resources amongst the highest priorities (8.11). The financial cost of water treatment is also a major consideration for establishing and maintaining an environmentally and economically sustainable mine closure. This includes finding a sustainable water source and treating it to a level suitable for specific uses within the mining operation. It also includes optimising and sustaining the treatment of water wastes (14.19).
Degradation of water quality is due to contaminated mine water generated when rock containing sulphidic minerals is exposed to water and oxygen, resulting in the production of acidity and elevated conditions of metals and sulphate in the water. The nature of the formation of coal deposits mean that contaminated mine water is a virtually ubiquitous problem as the extraction process causes the disturbance and exposure of rock surface and thus sulphidic minerals to the air (15). Contamination can also occur from an external source of hydrocarbons or any other chemical source that has not been sufficiently remediated from mining operations.
The steps in risk management outlined by the Australian Standard on Risk Management (AS/NZS 4360, 1999) were followed to develop the risk assessment tool for this project, this includes the initial identification of the strategic, organisation and context of the risk management situation.
The risks to surface and groundwater sources during the rehabilitation and post-closure processes were then identified in order to be successfully managed. There are a broad range of systematic, formal and informal risk assessment methodologies utilised throughout the engineering industry. A fault tree analysis (FTA) was chosen for this project as broad range of primary sources needed to be identified and their interaction monitored in order to identify the failure causes of mine water depletion. A fault tree analysis can be described as a technique for graphically depicting interaction of failures and other events within the system (16).
The process systematically analyses the logical structure of the possible causes and contributory factors leading to the depletion of surface or groundwater quality or quantities through the inclusion of semi-quantitative inputs which are used to define the likelihood and consequence ratings using descriptions that relate to the abovementioned four point severity scales. This facilitates the understanding of the possible causes, estimation of the likelihood of occurrence and identification of options for treatment (16).
Although the risk analysis is a scientific method of confronting and expressing uncertainty in predicting the future risks, this methodology is not enough to guarantee an effective mitigation or management procedure is applied to the risk and resulting environmental disturbance (20).Risk assessments are only the first step in a risk management process. In order to successfully manage environmental risks to decommissioning objectives and water sources, risk management strategies must be planned and adopted from the early life of the mine (8.7).
However the risk assessment developed cannot be unanimously applied to each and every open cut coal mining operation throughout Australia. The structure and functionability of each coal mine operation is different, and each continuously changing mine footprint will heavily influence the decommissioning and future ecological benefit of the closed and rehabilitated mine (13). This complex factor is outside the scope of the risk assessment, but must be incorporated to produce an effective strategy to ensure the quality and quantity of surface and ground water systems is maintained.
A third parameter should also be considered when assessing environmental risks to coal mine rehabilitation. Risk proximity, such as when the risk is likely to occur, is an important factor due to the longevity of mine operations and the direct impact the mine footprint has on the ability to rehabilitate surface and groundwater. Certain risk mitigation needs to be planned and employed well before the risk develops or eventuates.
The risk assessment undertaken in this project is a comparative tool for quantifying the potential damages to surface and groundwater conditions. However due to economic and time constraints, not all of these potential risks can be assessed and mitigated extensively. In the industrial corporation of coaling mining, environmental management systems require the ability to demonstrate that the targets can be achieved effectively and at the lowest possible cost (22). This is why economic analysis tools are used in conjunction with risk assessments in order to set priorities by comparing the cost with the major issues that have the potential to cause the biggest detrimental impact to the rehabilitation objectives (McCarthy and Purtill 1998).
Rather than measuring impacts and dealing with remediation of mine impacted water, companies should aim for environmental performance that excels beyond the legislative requirements and fully explore the technological advances available to minimising any adverse impacts on surface or ground water supplies. This includes integrating different mining and industrial disciplines and focus of planning and prevention, rather than remediation (3).