Environmental impacts of coal mining and associated wastes: a geochemical perspective

Abstract

Abstract Ever since the commencement of industrial-scale coal mining (in northeast England around 1600), substantial environmental impacts have been recorded as arising from both the mined voids and from the wastes left behind at the surface. In the early days of coal mining, complaints about such impacts were strident, as the newly established industry adversely affected long-established agricultural interests. When the coal trade had come to dominate regional economies in mining districts, its negative impacts came to be accepted as a necessary byproduct of the generation of coal-based wealth. It has only been since large-scale mine closures began to take place in the major coal-mining economies of the developed world during the last few decades that the negative impacts of coal mining have once more been deemed unacceptable. The environmental impacts arising from coal mining activities are fundamentally attributable to the exposure of reduced earth materials (especially coal, pyrite, siderite, and ankerite) to the oxidizing power of the Earth’s atmosphere. The consequences range from the spontaneous combustion of coal to the release of acidic waters from pyrite oxidation. A typology of the known impacts arising from mine voids and wastes in coal mining districts has been developed, which recognizes many subcategories of impacts under five major headings: air pollution, fire hazards, ground deformation, water pollution, and water resource depletion. A robust understanding of geochemical processes is key to understanding how these impacts arise, and to developing sustainable mitigation strategies. The application of the newly developed typology is illustrated using the case of the Shilbottle Coalfield (Northumberland, UK). Although few demonstrable impacts have arisen in the categories of air pollution, fire hazards, or ground deformation, major problems of water pollution have required both preventative and remedial interventions. For the flooded underground voids, these took the form of a pump-and-treat system, whereas emissions of leachates from surface spoil heaps have necessitated the installation of an innovative ‘hybrid’ passive treatment system, comprising a permeable reactive barrier, oxidation ponds, and a wetland. Inverse geochemical modelling has clarified the linkages between the various types of water encountered in the coalfield, providing a baseline geochemical understanding upon which future investigations of remedial system sustainability can be based.