3.3 Underground mining
Underground mining operations have four significant environmental impacts — spoil heaps, methane build-up, subsidence and water pollution. Spoil heaps have always been the principal surface feature of underground mining operations. However, legislation and technical advances have brought improvements in modern mines, and the closure of many of the UK's older mines has often been followed by successful rehabilitation of mine sites and spoil heaps by landscaping and tree planting.
Coal seams naturally generate methane, and as this is an explosive gas, build-up in old mine workings has to be prevented by venting to the atmosphere. Such methane has been successfully used to generate saleable electricity or diverted into household gas supplies, which lessen its effect as a powerful greenhouse gas.