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-3- <br />• Potential Sources of Ground I.7ater Poll <br />l The potential sources of pollutants at an open pit, western <br /> coal mine have been categorized by Everett (1979) in a report <br />` on a five-year study to assess the impact on ground water qua- <br />l lity of coal strip mining in the cJest. Contamination may <br /> result from: 1) runoff weathering coal and overburden in place <br /> as they are exposed to the elements during Stripping; 2) water <br /> percolation through coal stockpiles; 3) crater percolation <br /> through coal waste, in the overburden or partings where removal <br />_ of the coal was economically infeasible; 4) water percolation <br />I through overburden and fill materials; 5) water percolation <br /> through top soil storage piles; 6) runoff grater from roads; <br />( 7) runoff water that stands in the pit; and S) over-irriga- <br /> tion of reclaimed areas. <br />~. These eight general sources of pollutants do not contribute <br /> equally to pollution of ground water. Surface runoff flooding <br />~• over newly exposed coal will, theoretically, be affected by the <br /> coal. This effect, however, depends upon contact of rooter with <br /> the coal, such as during a rain or snowmelt season, at_ other <br /> times this source of pollutants is inactive, However, though <br />i acid drainage from surface mines is an important problem in the <br />lrr east, it is not a major problem in most western coal mines. <br />{ This is due in a large part to the lose sulfur content of western <br />L coals. The coals being mined at Colowyo have sulfur percentages <br />f that range from 0.33 to 0.57, averaging 0.40 per cent (Final EIS, <br />(_ Northwest Coal, 1976). rTater percolation through coal stockpiles <br /> is also a discontinuous source of pollutants during rainfall or <br /> snoormelt that may percolate through the material dissolving a <br /> 'variety of pollutants. Fla ter percolating through coal waste <br /> which has been separated from the overburden and stored separately <br /> is a distinct problem from percolation through coal stockpiles. <br /> Coal, as the product of the mine, is handled carefully. It is <br />. exposed to a minimum amount of weathering and a minimum amount <br />f <br />C.. <br />fF ' Leonard Rice Consulting Water Engineers.lnc <br />f <br />