Coal Action Scotland briefing
The environmental impacts of open cast mining
Open cast mining is distinct from other forms of mining, due to that fact that it does not require extractive methods that include tunnelling into the earth, but instead occurs at the soil surface. As a result, the environmental impacts associated with this practice are slightly different to those that may be associated with other types of mining.
Impacts of open cast mining
- Destruction of the topographical landscape
- Degradation of ecological communities
- Degradation of water quality
- Destruction of agricultural and forest lands
- Noise pollution
- Air quality
- Sedimentation and erosion
- Land subsidence
- Vibration from blasting and air blasts
- Old mines often converted into landfills
Coal is normally extracted from surface mines using heavy equipment such as draglines, trucks, shovels and excavator machinery. Surface vegetation is eliminated as a first step in the mining process and wildlife is displaced [Coal mining, 2008]. The use of heavy machinery creates roads which leads to soil compaction and encourages soil erosion. Dust from coal haul roads, topsoil stockpiles, and coal extraction also causes significant degradation to air quality, particularly in areas of low rainfall and high winds. [Sengupta, 1993] One study found that 7.8 tonnes of dust were generated a day due to topsoil removal and the extraction of coal, while wind erosion added a further 1.6 t of dust per day to this figure.
Blasting is one of the main contributors to dust production [Ghose & Majee, 1998.]. Apart from destroying local biodiversity, the erosion associated with this practice can lead to the transport of sediment to surface waters. Mining pits also collect water from rainfall and surface runoff, which then becomes heavily sedimented. The chemical composition of the water often changes due to higher concentrations of sulphur, soluble salts and/or contact with oxidised pyretic materials, which can lead to increased acidity. The water is typically pumped out of the pit straight on to the surrounding land [Sengupta, 1993].
Waste piles created during the mining process can also contribute sediment to streams, as leached water containing toxic trace elements enters water ways. The soil profile is generally totally destroyed during the process, upsetting micro organisms which inhabit it and perturbing natural nutrient cycles [Coal mining, 2008]. The ‘spoil’ (left over unwanted soil) created during the mining process is often dumped or buried leading to acidification of the area due to its high sulphur content [Sengupta, 1993] These processes are often refereed to as ‘Acid mine drainage’, which occurs naturally within some environments due to rock weathering processes, but is exaggerated by industrial practices [Coal mining, 2008].
If mining takes place below the water table then drainage can result in a lowering of the water table as well as land subsidence. This places considerable strain on ground layer vegetation as well as surrounding communities of people. Open cast coal mining of this type leaves large areas of land devoid of the ecological communities that once occupied them. The land use potential is usually significantly reduced, as soil, air and water properties are degraded beyond short term repair [Sengupta, 1993].
Ecological Impact Assessment
An Environmental Impact Assessment (EIA) is designed to identify the potential environmental effects of a development proposal. Its purpose is to ‘prevent, reduce or offset’ any projected detrimental impacts. The environmental study typically includes data collection and species identification, and is the first stage of the assessment. The findings from this are reported in an environmental statement (ES) which is submitted at the same time as the planning application. The planning authority considers the ES (along with other things such as public consultations) in their final decision of whether or not the project can go ahead.
An EIA may or may not be required depending on whether the type of project falls under Schedule 1 or Schedule 2. An EIA is always required for a Schedule 1 project, but it is only required for a Schedule 2 project if it is thought it will have significant environmental effects. Open-cast mining, underground mining and quarries come under the ‘extractive industry’ and are deemed schedule 2 projects. The Scottish Government state that as far as schedule 2 projects are concerned ‘the overwhelming majority of development projects however, normal planning powers are perfectly adequate to gain environmental information and EIA is not required’ [The Scottish Government Publications, 1999.]
Sengupta, M (1993) Environmental Impacts of Mining: Monitoring, Restoration, and Control. CRC Press.
The Scottish Government Publications, 1999. [Accessed on the 09/10/08] Available from: http://www.scotland.gov.uk/Publications/1999/10/pan58-root/pan58
Ghose, M.K and Majee, S.R (1998) Assessment of dust generation due to opencast coal mining – An Indian case study. Centre of Mining Environment, Indian School of Mines, Dhanbad – 826004, India
Coal mining, 2008 [Acessed on the 09/10/08] Available from: http://en.wikipedia.org/wiki/Coal_mining#Environmental_impacts