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Mr. Lee Sampson <br />September 22, 2022 <br />Page 7 <br /> <br />Agapito Associates, Inc. <br />Furthermore, observations5 of water draining through waste dumps at other surface coal mines <br />indicate that blockage by sediment does not occur in a free-draining dump. Provided that adequate <br />entrance capacity is constructed, flow-through drains should therefore be suitable for permanent <br />abandonment. Moreover, a rock drain developed through segregation of relatively well graded <br />waste rock (as in this case) is also naturally filtered through the segregation process4. A filter zone <br />should only be placed on top of the rock drain in the cases where the waste rock is expected to be <br />poor quality, or where the dump heights are less than that required for natural segregation4. <br /> <br />Considering the favorable quality of the spoil material, particularly the height of the dump pile and <br />the well graded nature of the material in conjunction with previous research and studies conducted <br />elsewhere and at the mine, it is Agapito’s view that the spoil end dumped in Little Collom Draw <br />will permit a free-draining environment. <br /> <br />Additionally, the well graded nature of the overlying spoil should prohibit excessive infiltration of <br />fines into the underlying cobbles and boulders, which could otherwise result in plugging of the <br />rock drain. Therefore, it is Agapito’s conlcusion that a manufactured filter fabric is not required to <br />mainitain a free-draining environment in the Little Collom Draw valley fill. <br /> <br />If you have any questions, please feel free to contact me. <br /> <br />Sincerely, <br /> <br />Ry Stone, CPEng. <br />Senior Associate <br /> <br />RS:kah <br />Transmitted in PDF format via email to lsampson@tristate.org <br /> <br /> <br />5 Nichols, R.S. and A.L. Rutledge (1982), “Water Drainage Through Waste Dumps at Fording Coal Ltd.,” CIM <br />Bulletin, 75(44):74–77.