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<br /> <br />Balaz & Associates <br />New Coal Waste Pile and Haul Road Project, Sanborn Creek Mine, Somerset, CO <br />June 18, 1997 Page 4 <br />Fiagmrnts and the do~m~vard sloping alignment of much of the sVatification indicates the majority of material <br />encountered in the upper portion of the exploration pit was deposited by natural processes. <br />As was discussed during the 8-28-96 site visit by personnel oC Lincoln DeVore, Balaz & Associates and Division <br />oC Minerals & Geology, the surface of the Rollins Sandstone does indeed fall very rapidly in this gully. Il is not <br />practical nor feasible, as related to the stability of the existing railroad embankment, to excavate down to the <br />Rollins Sandstone to place the sediment pond wall directly upon the sandstone. <br />It is proposed to over excavate these soils in the pond and wall area a minimum of 3 Ccet below the bast oC the <br />sedimrnt pond wall footing. These native soils which are excavated should be sorted to remove all rocks larger <br />than 6 inches in diameter and recompacted back into place beneath the pond and the pond wall to a minimum <br />of 90% of the maximum dcnsih• (ASTM D-1557), which is believed sufficient to obtain a minimum Soil <br />Cocfficirnt of Permeabilit}~ of I.Ox 10' cm/sec.. The replaced soils should be processed, placed and compacted <br />in accordance with the recommendations contained in our report Cor the Haul Road Slope Stability, 2-20-97. <br />It is recommended that in no instance should any fmal compacted fill IiII be greater than 8 inches. <br />After the native soils have been replaced and compacted as structural GII, the wall footing can be formed and <br />concrete placed and a protective layer in the pond la}•cr consisting of cobbles and rocks should be placed over <br />the structural fill. This protective layer should be a minimum of 16 inches in thickness. These cobbles and rocks <br />may contain variable amounts oC fines and will serve as a base of the pond to aid equipment operators during <br />removal of sediment. <br />It is believed that all pertinent points have been addressed. ICany further questions arise regarding this project <br />or if we can be o(any further assistance, glease do not hesitate to contact this otTice at any time. <br />~ ~PGp REGisr~, <br />Respectfully Submitted, gyp; ; ao M. Maq,'~'Fo <br />°'~P 91 <br />LINCOLN DeVORE, In !„°, 10 <br />6 -la - <br />bv: <br />Engincer/Westem <br />LD Job No.: 86097-2697-J <br />