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!t~ <br />Western Associated Coal Corp. OcLuber 2Z, 1781 Page 2 <br />Dur recommendation is LhaL the drainnyc trench be installed at <br />such a location that with a cJcpih of :,ppruximatcly six feet <br />maximum, the drain line would intercept the interface between <br />the original hillside and the new fill s]ope. If the drain line <br />is located in this position, it vrill intercept any seepage flows <br />between the fill and the original slope Lhat would be Lending <br />to cause sliding, instability, and consolidation of the fill <br />material. Details of the design trench, the six inch perforated <br />pipe to be installed in the bottom of Lhe trench, and backfill <br />are shown on the enclosed drawing. <br />We recommend that, inaccordance a+iCh your Application C-U47-81 <br />for the Blue Ribbon Coal 14ine, you perform a ycoLechnical <br />investigation of the bench area. The investiyation should furnish <br />us with the location ^nd depth of Lhe fill material, Lhe interface <br />between the fill material and Lhe original elope, a stability <br />safety factor for this slope, and .information for designing the <br />filter material around the six inch pipe. AfCer receipt of Lhe <br />geotechnical information, we will conipleLe the design of the <br />drainage system trench as discussed herein. We cJo not recumrnend <br />construction of tl~e drainage i:rencli until after completion <br />of the geotechnical analysis. It .is uur understanding that this <br />analysis will be complete and the information should be <br />available by mid December, 1981, <br />If you have any guestiuns reilarding tho rr.coinmendcd work, pleose <br />call Lhis office. <br />~.~~~--E <br />E. LeRoy 81ack <br />ELB/ab ~ <br />enclosures <br />