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Ralaz R, Associates • .`lew r.oal wasr.e Pile Project., Sanborn Creek Mine, Somerset, CO Fel,rnarv 5, 1997 Page 2 ~I r•. Rill Balaz, PE, }ias reworked the road alignments to fit the slopes as a refinement of the oz•iginal, preliminary road plan. T:~c relative amounte of cut and fill have changed somewhat and the heights of most of the cuts and. Pills has been decreased. Specific road sections will be analyzed for slope failure as a part of the final report. Sediment Collection Pond: The proposed sedi- ment eollec.tion pond, at the toe oP the proposed new wacee pile, is ylaced in a ancient nlluvial/colluvisl filled gully. The closer t}ze actual embankment is toward the railroad right-of-way, the deeper t}ie gulf- becomes, exceeding 16 feet in the explora- tion pit, excavated to observe the soil Yill, as witnessed b}• versorrnel ~f ~~estec and Lineoln DeVore. Providing proper benring and att.aclrinent. Lc; I.}rc sandsto:e Tully sides for the embankment is not judged Lo Le a significant problem, however, some soil con- solidation end probable 'piping' of the soil by water movement under the embankment must be anLic:ipaled. It is possible to over' excavate the soils in the e~nbanl.nrent and pond area and recompact Lhem to achieve soil of low to very low pez•meability. It must be emphasized ttrat if the over excavation and r•ecompaction is not • done properly and completely, piping and some soil subsidence may still occur. 7t. is recommended this area be over excavated a minimum of 2 feet and the soils properly wetted and recompacted beneath the embank- ment anti the pond ax•ea. Due to the presence of significant amounts of cobble and boulder sized roclt fragments, achieving propaz• and .complete compaction may be somewhat difficult. There- fore, it is recommended that a geosynthetic liner (for example, Hypalonl b? rrtili2ed as the primary pond seal. Protection of this liner will probably require 1 to 2 feet of a soil top cover- ing of t}re liner. goal 1:asCe Piie oe A:•ea: 1'he exploration pit for the proposed sediment pond also indicated the sandstone oP the 'Rollins' Sandstone is quite competent in this area brrt, the Lap oC 1. },e sancist.one unit appears to be 20 to 30 feet higher in elevation than anticipated in the WESTEC Report. The toe area of t}re coal waste pile will be placed or. a downhill sloping surface of t'ne Rollins sandstone. It is recommended the Rollins ~anclstone he excavated in the *_oe area, a minimum of 3 Peet deep t.+~ F feet. wide, across tF,e bottom and sides oP the toe area. This excavated keyway will have to be discontinuous at the lowest Uo:•tion of tl,e toe area, where the t,nderdrain at the base of the coal waste pile passes througtr the toe and Snto the sediment pond area. F..xc-avation of this keyway may require minor amounts of hlact.ing.