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Balaz & Associates <br />New Coal Waste Pile and Haul Road Project, Sanborn Creek Mine, Somerset, CO <br />June l8, 1997 Page 4 <br />fragmrnts and the downward sloping alignment oC much of the stratification indicates the majority of material <br />encountered in the upper portion of the exploration pit was deposited by natuca! processes. <br />As was discussed during the 8-28-96 site visit by personnel oCLincoln DeVore, Balaz ~ Associates and Division <br />oCMinaals & Geologyv, the surface oCthe Rollins Sandstone does indeed Call very rapidly in this gully. It 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 sedimrnt 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 Cect below the bast oC the <br />scdimrnt pond wall Cooting. These native soils which arc 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 density (ASTM D-1557), which is believed sufficirnt to obtain a minimum Soil <br />Cocfficimt of Prnncabilih• of I.Ox 10'' cm/sa.. The replaced soils should be processed, placed and compacted <br />in accordance.vith the rewmmendations contained in our report Cor the Haul Road Slope Stability, 2-20.97. <br />It is rewmmrnded that in no instance should any fmal compacted fill lift be greater than 8 inches. <br />After the native soils have been replaced and compacted as structural fill, the wall footing can be Cormed and <br />concrete placed and a protective layer in the pond layer consisting oCcobblcs and rocks should be placed over <br />the structural fill. This protective layer should be a minimum oC 16 inches in thickness. These cobbles and rocks <br />may contain carieble amounts of fines and will serve as a base of the pond to aid equipmrnt operators during <br />removal oCsedimrnt. <br />It is believed that all pertinent points have been addressed. ICany further questions arise regarding this project <br />or if we can be of any further assistanee,~ease do not hesitate to contact this ot~ice at any time. <br />Respectfully Submitted, ~0~~_'„~w. <br />LfNCOLN DeVORE, <br />b-ld- <br />bv: <br />EngineedWestem <br />LD Job No.: 86097-2697-J <br /> <br />