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• Balaz & Associates New Coal Waste Pile and Haul Road Project, Sanborn Creek Mine, Somerset, CO June 18, 1997 Page 3 It is possible that the quality of borrow materials may be such that a Geogrid material will have to be either partially or completely substituted for the geotextile fabric. To make this detetmittation, either a lazge number of exploration pits and additional laboratory testing will be required or changes will possibly be made during actual wnswction. The fill section at station 27+00 will probably require mechanically reinforced earth in the rntire fill. Evrn though this slope is somewhat Flatter than the section at station 8+00, it is anticipated the materials used Cor construction in this arcs may contain a significantly higher amount of sill and clay Ernes end the anticipated wlluvial soils at the bast and toe area will control the design. The use of mechanically stabilized soils ' forces' the projocted failure surfaces back toward or into the more wmpetrnt Bowie Member. It is anticipated the more clsn• wltuvial soil will be used to conswct this fill. The `external wck loading' creates potential failure near the upper fill face, which can be resisted by the mechanically stabilized earth. Thc surface exposures of sandstone and siltstone are expressed on the topogaphy map as relatively steep slopes, ~~ttich were initially avoided for the road alignmrnt. ARer wnsidcration of the increased amounts of sandstone and siltstone beds in these areas, it is believed the majority oC the cut slopes can be steepened to between 1:2 (H:V) to 1:4 (H:V) without sacrificing the integrity of these cut slopes. These cut slopes will have to be carefully • observed during the wnswction process to determine if any additional stabilization techniques, such as benching, (latter slopes, rock buttress/MSE walls or tie-backs in the worse case are required. Item l8_ Location and Type of Fill Slopes LinwlnDeVareandBalaz&Associatesheve jointly developed shcet OXWVF• I G to indicate typical cut and fill sections, slope stabilization and anticipated stationing along the proposed toads for revicty, bidding and wnswction purposes. Actual field wnditions may require modifications of this plan. Ilcm 24. Scdimcnt Pond Edward M. Moms. PE, of Linwln DcVorc was present, during the excavation of an exploration trench within the proposed sediment pond on 9-1 G-9G. IL was our understanding that as this exploration trrnch was being logged by personnel oC WESTEC, and that a log of the soil profile and rewmnrcrrdations Cor the wnswction of the sediment pond would be Corthwming Crom WESTEC. Following is our description of this exploration pit. Personnel of Lincoln DcVorc did not obtain any samples for testing and the following descriptions will be based on visual logging only. Thc exploration pit ryas situated near the in-flow point oC the sediment pons, as indicated on the attached drawing. This drawing is based upon the Plan of the Scdimcnt Pond as depicted on the Plan OXWVF-03. prepared by Balaz & Associates. Thc total trench was approximately 50 fat long, including minor probing at the upstrcarn side. near the visible outcrop oC the Rollins Sandstone. At the lower, southern end of the trench, the native debris fan/colluvial material .vas cnwuntcrcd at a total depth of IS fact and the Rollins Sandstone surface had fallen bclrnv the maximum reach of the backhce bucket. At approximately 10 fat below the ground surface, some iron/stcel debris ryas encountered, indicating the original ground surface may have been approximatch 10 feet bclrnv the presrnt ground surface. It is believed that some of the 'recent' fill in this gully is related to construction oC the Railroad embankment. At a depth of 6 to 7 feet below the prcsrnt ground . surface, a cm rcek}• zone was enwuntered, which does not appear to be man-made fill but appeared to be part of natural deposits of alluvium and wiluvium The type of stratif ication, the orientation of the rock and boulder