Coal mines and mining 153 Environmental aspects 133 History 99 Coal 80 Water resources development 69 Pollution 64 Industrial arts 57 more ... Flood control 53 Study and teaching (Secondary) 52 Roads 47 Water 46 Coal mine accidents 43 Water-supply 38 Cooking 37 Floods 36 Railroads 35 Bridges 32 Environmental impact statements 32 Petroleum 31 Strip mining 31 Geology 30 Air 28 Mines and mineral resources 28 Watershed management 27 Natural gas 25 Highway planning 24 Cooking, American 23 Mountaintop removal mining 23 Covered bridges 21 Mineral industries 21 less ...