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100 to 1000 time larger than that of the waste material. This indicates that the <br />water will move much faster through the dram than through the pile. Because of <br />this fact and the relative steep slope of the valley floor (drain slope) compared to <br />the pile surface, each zone drains approximately independently, in time, of the <br />others. This is the routing effect and means that only a portion of the pile will be <br />contributing flow to the drain during any given time interval of the design event. <br />Physical Properties <br />geometry valley slope = 0.1265 <br />pile face slope = 0.4000 <br />pile top slope = 0.0100 <br />pile length = 1600 ft <br />Average pile dimensions for five equal length segments (ft) <br />(bottom of pile upvalley to top of pile -~) <br />length 320 320 320 320 320 <br />width 320 500 420 380 200 <br />thickness 44 131 102 65 27 <br />hydraulic hydraulic conductivity, K <br />gravel (drain fill) material <br />range of Ku = 0.0010 ft/s to 0.1024 ft/s <br />average Ku = 0.0132 ft/s <br />waste rock material <br />Kw = 1.086 x 10~ ft/s <br />• hydrologic gross infiltration rate = 50% of long term precipitation <br />precipitation -mean max. month = 6.38 in. (period of record) <br />note: hydraulic conductivities and the infiltration are coarse estimates based on <br />reported text book values for similar materials. <br />After balancing the estimated inflow to the drain with the flow capacity of the <br />drain and adding a safety factor a size was estimated. It is reasonable to assume <br />that the drain size should decrease as you move upvalley and have less volume <br />and surface area contributing to it. <br />The lower portion (approximately 400 ft.) will be serviced by the existing drain <br />constructed for the original waste pile. The new drain was designed in three <br />sections of 400 feet. <br />Underdrain Size <br />Reach Length (ft. bottom to top) Drain size (width x depth in ft) <br />1 0 to 400 existing 3x3, square <br />2 400 to 800 7x4, rectangular <br />3 .800 to 1200 5x4, rectangular <br />4 1200 to 1600 3x3, rectangular <br />The new portion of the drain should be connected to the existing drain at its <br />terminus. Because the existing drain is not sized to handle all flow generated <br />above it an 8" drain pipe (schedule 40 pvc in bedding) should be connected at <br />January 1998 <br />