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<br /> <br />R. G. OTTO & ASSOCIATES <br /> <br />E~ <br />~~ <br /> <br />The waste rock is also very coarse material relative to the <br />natural soils that surround or underlay it. The pile is therefore <br />more permeable to water than the natural soils. Given the <br />elevation of the waste pile above the stream channel and the high <br />porosity of the pile relative to the native soils, it follows that <br />the only movement of water into the pile is by percolation from <br />the top. Ground water should not infiltrate the pile from the <br />bottom as a consequence of capillary draw. <br />There aze two sources of water for pezcolation, rainfall and <br />snow-melt. The pile presumably remains unsaturated because of the <br />high porosity of the waste rock. Excess moisture contained in the <br />pile travels downward due to gravity. Water percolating through <br />the pile to the interface between waste rock and the alluvium may <br />either continue to percolate into the alluvium or travel <br />horizontally downslope along the waste rock/alluvium interface to <br />the stream. The relative proportions that infiltrate the alluvium <br />or become suzface runoff depend upon the moisture contents in the <br />pile and alluvium, relative infiltration capacities and the <br />intensity/duration of the precipitation or snow-melt event. <br />Surface runoff will occur if (1? the rate at which the <br />precipitation infiltrates through the waste rock pile is greater <br />than the alluvium's saturated hydraulic conductivity and (2) the <br />duration of the percolation event exceeds the time required for <br />the soil surface to become saturated <br />Because the alluvium is <br />2~ <br />