The process of acquiring mine closure permitting is normally a long and exhaustive process that involves complex analyses and dealings with the relevant authorities and affected parties. It is best to plan mine development and operational strategies with closure objectives in mind from the feasibility phase onwards. However, mining operations are dynamic and operational strategies and practices often change during the life of mine, necessitating mine closure planning during the late phases of the life of mine.
From a water perspective, these plans would take into consideration:
- Long-term water qualities;
- Potential for Acid Mine Drainage conditions to develop;
- Decant potential and volume, and
- Decant qualities amongst others.
Because there are many variables to be taken into account, not least of which is long term cost of the closure programme, several different approaches to achieve mine closure can be considered. Each of these different approaches usually has different technical requirements which can influence capital outlay and the long-term maintenance costs.
Future Flow GPMS has been involved in a number of closure scenario assessment studies. These studies usually quantify long term groundwater characteristics mentioned above, thereby providing input into the initial closure planning. We use numerical flow modelling to quantify decant potential and volumes. And we use chemical and geochemical (ABA and leach testing) analysis results to determine water and decant quality and AMD potential.
Once we identify and quantify the parameters that will play a significant role in the post- operational environment, we can suggest different management strategies . These are evaluated for effectiveness and the optimum closure plan is compiled. These closure plans often involve:
- Removal or reduction of the potential pollution sources;
- Passive treatment systems such as final voids or evaporation dams;
- Interception trenches to control shallow seepage of pollution away from point sources on surface; and
- Active water treatment plants.
From a groundwater, and to a lesser degree surface water perspective, the different closure plans can be evaluated using 3-D numerical groundwater and contaminant transport modelling. Based on the simulation results, the optimum and most cost effective water management strategy can be identified.
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