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u <br />• <br />Halaz k A~aoci.ates <br />New Coal Baste Pile Project, Sanborn Creek Mine, Somerset, CO <br />Febr+tary 5, 1991 Page 3 <br />Ttte actvnL s~_:rfacP of the weathered Rollins ~ sandstone erosional <br />surface mad be smooth enough in this Lower area that another <br />keywa}-, paced 50 to i5 feet upslope may be desirable. <br />Slone S abilit~• of Coal Waste pile: The presence of <br />the Rollins sandstone extending further up the bane area of the <br />coal waste pile changes some of the assumptions for the slope <br />stability anal}•sis performed by Westec. The pile toe area will <br />require at. least one and possibly two keyways for stability, The <br />rat.hter deep Bested failure surface generated in the comp~.rter <br />3na1}sis La- wastes will probably not occur, as the somewhat <br />weaker sil'sLone, claystone, shale and thin coal sediments of the <br />Huwie Pieiubrr, will nut be enccuntered as close to the pile toe as <br />vrigittal].~• anLi.c.ipaLed. IL is believed that with the construc- <br />±ion of the ~e}•ways at I.he toe sera, t}te slope stability of this <br />Dual a~ast.~• pile will be sir}nificantly enhanced o~•er that origi- <br />nall; anticipated by the Westec study. <br />IL is Uelirved Lhal all perlirrettt poi:tts have been addressed. If <br />an}• farther questions arise regarding Lhis project or if we can <br />be of any further.assistance, please du not }tesitate to contact <br />this office at any time. <br />Respectfuil}~ Submitted, ~~0;+,'.••~~y: <br />LINCOLN DeVORE, Inc. <br />30590 <br />b~: Edward M. Morris PE ~ <br />.Engineer/Western Slope <br />LD Job Nu.: 85688-J <br />• <br />