Mining is the process or business of extraction or removal of valuable minerals, ores or other geological materials from the earth. There are different types of mining depending upon the techniques employed in the extraction of minerals. Each type has a bearing on varying environmental concerns related to biodiversity, air, water and land. It can be broadly classified into two—surface and under-ground mining.
It is a form of mining in which the surface soil and rocks (termed as overburden) covering the mineral deposits are removed. This method is ideal when the coal seams or mineral deposits are closer to the surface.
Environmental problems associated with surface mining
Surface mining is highly destructive to the ecosystem, but it is preferred by most industries due to lower labour requirements and higher yields, especially coal, as compared to underground mining.
Destruction of landscape and biodiversity: Surface mining requires clearing of large forest areas and agricultural land. This leads to various ecological disturbances such as reduction in forest cover, loss of wildlife habitat and erosion of the topsoil. The Coal Vision 2025 by the Ministry of Coal, Government of India estimated that the requirement of forest land for mining would increase more than three-fold from the current 22,000 ha to 73,000 ha since much of the coal resources to be exploited in future are located in forests (Singh, 2008). The Korba coalfield in Chhattisgarh, for example, has seen a tremendous change in land cover/land use. According to the Amnesty International Report 2016, more than 397 hectares of forest land in the region have been destroyed. As far as impacts of mining on biodiversity are concerned, about 11 per cent of the Singrauli coalfield overlaps the Sanjay Dubri National Park and the Guru Ghasidas National Park, which are important habitats for tigers, jeopardising their movement (Spandana, 2016).
Barren land: The damaged and contaminated land left behind after mining, stays barren for a long period of time. The reclamation and rehabilitation processes of these lands are slow and cost intensive.
Disfiguring and contamination of water bodies: The eroded topsoil is washed out easily by rains. The sediments not only disfigure the river channels and streams, they lead to deleterious alteration of the river ecosystem and subsequent downstream flooding. Acid mine drainage is another common threat from mining processes as sulphides are exposed to water and air. It alleviates the pH of water bodies which devastates streams, rivers and various aquatic life forms for many years.
The rate at which rivers in Jharkhand are degrading is a striking example of river pollution in India due to mining activities. Research says that about 130 million litres of industrial effluents and about 45 tonnes of fine coal from one coal washery are discharged in the Damodar River every day. The Karo River in West Singhbhum is also reported to be highly polluted with red oxides from iron ore mines of Naomundi, Gua and Chiria. Another major river in this area, the Subernarekha is also highly contaminated with heavy metals and toxic radioactive wastes from TISCO, Jamshedpur, HCL Ghatsila and Uranium Corporation of India Limited at Jaduguda (Priyadarshini, 2017).
Deterioration of air quality: Huge amount of air pollutants—particulate matters, carbon dioxide, carbon monoxide, sulphur dioxide and methane are produced from mining areas. Surface mining is known to have a greater impact in polluting the air as it operates in the open and can spread over large areas. Dhanbad in Jharkhand is one such place where open cast mining has had serious impact on its air quality. In recent years, air pollutants such as oxides of sulphur and nitrogen, PM2.5, PM10 and trace metals like lead, arsenic and nickel have been observed in Dhanbad, which are much higher than India’s air quality standards (Kundu and Pal, 2015).
Underground mining is undertaken when the ore or mineral resources are too deep to efficiently mine from the surface. It is a method of mining in which overlying rocks are left untouched and the required mineral deposits are removed through shafts or tunnels. Two methods of underground mining are room and pillar and long wall.
How underground mining affects the environment
There are huge environmental impacts associated with underground mining. Unlike surface mining its impact is mainly felt on land conformation as it requires deep drilling and removal of huge chunks of earth materials.
Land subsidence: It is the collapse of earth into underground mines. It occurs due to compression and pressure change pertaining to excessive removal of water, oil or mineral resources from beneath the ground where the resources are located. It can cause structural damages to services and buildings, fracturing and altering the drainage pattern of groundwater from shallow aquifers. It also leads to surface water diversion, reducing water supply to streams and lakes etc. (IESC, 2014).
Underground coal fire: Coal seam burning aids air pollution by releasing smoke laden toxic gases. India is said to have world’s greatest concentration of coal fires (Greenpeace, 2016). Jharia coalfield which has been burning for more than a century is an explicit example. Bharat Coking Coal Limited (BCCL) estimates that about 37 million tonnes have been already burnt by coal seam fires since they overtook the coal fields. Moreover, out of 80 identified fires only 10 have been successfully extinguished till date (Bavashi, 2017).
Coal mine methane: Coal mines release methane which is a potential green house gas. About 6 per cent of methane emissions come from coal mining (Greenpeace, 2016).
Impacts on water resources: Underground mining also lowers the groundwater level around the mines since vast quantities of groundwater is pumped out in order to remove the coal from the mines. This affects water availability in the vicinity of the mining area.
Exposure of geologically toxic elements and minerals: Underground mining exposes huge amount of earth materials and rocks. They possess a significant risk of contamination from heavy metals and geologically derived toxic minerals to nearby ground and surface water sources.
The environmental impacts caused by mining cannot be remediated immediately. However, mining locations should be carefully checked and monitored. Moreover, sustainable mining practices and novel technologies could reduce the environmental repercussions caused by mining operations. The implementation of proper waste management strategies would decrease the rate of air, water and soil pollution from mining activities. Most importantly, rehabilitation and effective biological reclamation of mined areas can minimise the ecological impacts of mining.