Deep/Underground coal mines

• METHANE: As the name suggests, mining goes deep underground where there are often higher concentrations of methane that are stored there under the pressure of the rocks and soil above it. Excavation allows that methane to escape (fugitive methane emissions) into our atmosphere. Methane is a potent greenhouse gas. Even after coal mining has finished, deep coal mines can continue leaking methane gas for decades, driving climate chaos and posing dangers to the public of explosion and suffocation near to shafts. Internationally, there is growing awareness of this issue and attempts to monitor and control leakage, but progress is slow. An estimated 40 million tonnes of methane leaked from coal mines in 2024.
• SURFACE STABILITY: When mining stops so does pumping water out to keep the mines dry. As the water slowly fills the mine from surrounding soil up to the water table, it can -along with time - it can cause the collapse of the pillars left in underground mining to hold up the roof of underground tunnels. This can then create 'sink holes' on the surface, and subsidence for houses built above tunnels. With the location of earlier mining works often undocumented, it is not always possible to assess the risks.
• WATER POLLUTION: When deep mines close, pumping out the water is stopped and the water levels rebound up to the 'water-table'. As water fills the mining tunnels and shafts, it reacts with minerals like pyrite, creating acidic, iron-rich water which can kill aquatic live if it enters rivers as well as pollute drinking water. At a number of mines around the UK, the Mining Remediation Authority pumps up mine water to clean it, then return it to the mine.
• UNCOVERED MINE SHAFTS: known as 'adits', these are vertical or near vertical shafts that can go down a long way - originally used with a lift system to lower miners to the right levels to dig horizonal tunnels along coal seams. As records have been lost or were never created for the earlier coal mines, not all the adits are known. This presents a falling danger for walkers or explorers. If you see an uncovered adit, please report it to the Mining Remediation Authority.

Opencast coal mines

• SOIL DEGRADATION: Unlike deep coal mines, opencast coal mines strip away large areas of vegetation, top soil, sub-soil, rocks, and non-target coal (called 'overburden') to get at the target coal beneath it. UK planning policy now requires mining companies to store these different layers separately and avoid compaction so they can be replaced like a lasagne after coal mining ceases. In reality, though, they are often mixed and compacted, drastically reducing their fertility and the viability of agriculture or nature return for decades. Over 70% of mined land globally suffers from soil degradation.
• FLOODED VOIDS: Opencast coal mining creates bowl-like voids in the earth with a track spiralling down around the edge of the void for HGVs to access the sides and bottom and carry the 'overburden' and coal out of the void. These voids can be huge. It is a conditional of planning permission for an opencast coal mine that once mining ends, the company refills the void with the 'overburden' they removed, leaving a level surface. However, the coal has been carried away and burned so additional "soil-forming material" would be needed to refill the void completely. This can be expensive, along with moving millions of cubic metres of overburden from where it has been dumped back into the void. This part of restoration alone can cost up to £100 million. As mining has finished by this point, there is no further profit to be made and the incentive for mining companies to evade delivering on their agreement keep that money means a degraded landscape and voids and are more often left behind to slowly flood from ground water and rain. Although these are euphemistically called 'lakes' by mining companies, these unplanned and huge bodies of water represent a flood worry for nearby communites and can be a hazard for swimmers as the water is very deep and cold. Due to the exposed coal face, some water bodies also test for hightened levels of metal pollutants.
• NOISE AND DUST: As the name indicates, opencast coal mines are open to the air and wind. Where explosive 'blasting' methods are used to expose coal seams, the sound and shockwaves isn't shielded by the surrounding ground as it is in underground mines. Dust from blasting and from HGV movements can be carried significant distances by the wind. Together, these activities can severely impact nearby residents. Where the dust is from the coal, it can also carry heavy metals that pose a health risk, particularly to asthma sufferers.

Both

• COAL TIPS: often referred to as coal tips for deep mines and overburden mounds for opencast coal mines, they are similar in composition and risks. These tips are where everything is dumped that is between the mining company and the target coal - vegetation, top soil, sub-soil, rocks, and non-target coal. These tips can be colossal in size, and some earlier ones have now settled and revegetated to such a degree that it is unrecognisable as a tip. However, both new and old tips suffer long-term stability risks, particularly as rainfall increases with climate change. The last tragedy to occur from coal tip was the Aberfan disaster of 1966, where coal tip became unstable during heavy rain and slipped down a valley into a school, killing 144 children and teachers. However, since 2020 there have been two near misses, also in South Wales. In wales, there is a new multi-million pound scheme to monitor tips for slippage and carry out stabilisation works if needed, to avoid further slips that could end in tragedy.