New York Paper - Run-off and Mine Draining (with Discussion)

The eleven mines of the United States Coal and Coke Co. in the Pocahontas coal field are situated in McDowell County, W. Va., which is a mountainous region. The valleys rarely exceed 200 ft. (60 m.) in width, the hillsides slope from 25°to 33°, and the tops, from 600 to 900 ft. above the valleys, carry practically no level land. At least 80 per cent. of the area is covered with timber. All the workings are drift mines; and while the average grades of the seams worked are ample for drainage, local dips and swamps necessitate the use of a large number of local pumps or of numerous drainage ditches to keep the mines free from water during heavy rains. The water handled in any mine is not great, compared with the coal output, and usually causes little trouble except during extremely wet periods. In new workings, the water encountered, except in rare cases, is trifling; it is only after rib drawing has started and the surface has been broken that water troubles begin. The strata overlying the coal are sandstone, shales, and slates; as the soil is thin and sandy, it does not tend to puddle and stop the cracks, which remain open for a long time. As mining progresses and the robbed area increases, the broken area becomes larger, increasing the openings into the mined territory. The cover over the robbed portions of the mines varies from 30 to 750 ft. (9 to 228 m.). When the ground is saturated, considerable water finds its way into the mines the day after a heavy rainfall and for three or four days it tends to fill the low places, wash the tracks, etc. and unless from three to four times as many pumps are installed as are normally needed, considerable output is lost. In most cases the water will flow from the mines, and the obvious solution is to provide drainage ditches of ample size to carry the maximum flow expected, so that the inflow will have no opportunity to flood the working places. Laying out the drainage headings on the proper average grades was an easy matter but where blasting was necessary to provide uniform grades, as was frequently the case, it was important that the maximum flow to be expected and the size of ditches to be provided should be known so that only rock work necessary to provide proper drainage