Coal minesites can have significant effects on local environments. In addition to the physical disruption of land forms and ecosystems, mining can also leave behind a legacy of secondary detrimental effects due to leaching of acid and trace elements from discarded materials. A new report from the IEA Clean Coal Centre looks at the remediation of both underground and opencast minesites, covering reclamation methods, back-filling issues, drainage and restoration. Examples of national variations in the applicable legislation and in the definition of rehabilitation are compared.
The changing importance of reclamation
Removing coal from the ground is impossible without causing disruption to surrounding land and ecosystems. This disruption is commonly greater in surface mining than in underground mining. In the past, the only concern was the efficient production of coal and the detrimental effect on the environment was often ignored. However, times have changed and now mining operations in most regions of the world are legally required to ensure that the minesite be returned to a minimum standard.
In regions such as the EU, North America, Australia and New Zealand, mining permits will only be granted if a full mine plan is provided, covering the cradle-to-grave lifetime of the mine. This must take into consideration the surrounding environment (land, soil, water, ecosystems) and also the local heritage and community. In some cases, mining bonds must be set aside to cover the costs of reclamation and these will not be released until the minesite has been closed, reclaimed and restored to minimum standards.
In some cases, minesites have been abandoned for so long that the ownership is either not known or no longer valid. In these situations, countries must set up their own remediation plans and funding organisations to bring brownfield sites back to being useful and beneficial to the local communities.
Mining activities and water
Where possible, existing rivers or streams should be redirected past the minesite during operation. The re-landscaping of areas as a result of the removal of topsoils and coal affects the natural flow of water through the region. In most countries, water and water quality are protected by law and so care must be taken to ensure that no contamination leaks from the mine workings. Water that accumulates through mining activities can become acidified (acid mine drainage – AMD) through the release of sulfur and trace elements from newly exposed rocks and soil. This water must be treated and cleaned before it can be returned into natural watercourses. AMD can be treated with chemicals or specially selected bacteria and this type of approach is commonly used while the mine is still in operation. More gentle, passive treatments can be used for long-term neutralisation of AMD following mine closure. When abandoned mines are being back-filled, the use of naturally alkaline materials such as FGD (flue gas desulphurisation) gypsum and FBC (fluidised bed combustion) ash from coal combustion can be extremely beneficial and cost effective. In countries such as South Africa, which are prone to water shortages, the water produced and collected during mining activities can be treated and provided to the local community.
Following opencast lignite mining, which requires removal of large areas of topsoil followed by the coal or lignite, the final landscape can be significantly topographically lower than was originally the case. Opencast sites are therefore prone to flooding. Rather than let this happen, many sites allow controlled flooding to turn flat, mined-land into new water features. Minimum levels of safety and water quality have to be met and the flooding of some areas can take decades. However, these new water features are often regarded as positively beneficial to some communities, for example some previously dry landscapes in Germany are now the sites of new lakes and water parks for the benefit of locals and tourists.
The first issue that must be dealt with following mine closure is to ensure that the land is safe and not likely to sink, subside or collapse. Once the site is structurally sound, the site can be returned to its approximate original contouring. However, this may not be possible at all sites and some may actually benefit for a modification of the landscape to suit a new purpose.
Impact on local animals and local communities
In addition to taking into account the potential negative effects on the environment, mine activities must also consider disruption to local animals and local communities. This may involve the temporary removal of endangered species to safe areas before their return when mining is complete. Sites of important cultural heritage should be avoided but, in some cases, buildings have been removed and then either rebuilt or replaced upon closure of the mine. For this approach to be appropriate, community involvement from the very beginning of the mining process is required. Most mining activities cannot commence until local communities and business have been advised of the proposed mine plans and all concerns have been addressed.
A change in ethos
In recent years, in many areas of the world, the whole ethos of mine reclamation has moved from simply cleaning up the land and leaving it safe to moving towards making the site better than before and leaving a useful and valuable legacy for future generations. In most cases, previously mined lands are turned over to agriculture or forestry, depending on the local community requirements and desires. However, successful projects have also created new recreational ground, shopping centres, theatres and even world-class land art.
Dr Lesley Sloss is the principal environmental consultant at at the IEA Clean Coal Centre. Their full report is available from the IEA Clean Coal Centre Bookshop.
Read the article online at: https://www.oilfieldtechnology.com/drilling-and-production/06042013/coal_minesite_reclamation_iea_clean_coal_centre-192/