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SENT SY: GREVSTONE ENVIRONMENTAL; <br />August 26, 2003 <br />Mr. John W. Rozelle <br />Land Manager <br />Lafarge West, Inc. <br />1400 W. 64`" Avenue <br />P. O. Box 21588 <br />Denver CO 80221-0588 <br />303 6B9 0194; AUG-27-03 4:18PM; PAGE 2!3 <br />i r F <br />~' <br />Re: Slope Stability Analysis for RivQr Valley Resource <br />Dear John: <br />You requested Greystone to analyze s~dpe stabil~y in response to Rule 6.4.19 <br />(EXHIBIT S -Permanent Man-Made 5tructure~) of your 112 Construction <br />Materials Permit. This rule requires La>`arge to provide an appropriate <br />engineering evaluation that demonstrates that miffing can occur within 200 feet of <br />"significant, valuable, or man-made stlvt[ures" without damage to the structure. <br />The purpose of this study is to demonstrate that mining can occur Closer than <br />200 feet of a structure without damage to the structure from slope failure. <br />Greystone completed its analysis of the stability df the proposed excavation of <br />0.5H:1.0 V slopes at depths ranging from 2G feet to 30 feet. The ground is <br />assumed to be unsaturated as a result!of dewateAing ahead of mining. Once <br />mining is completed, slopes are generally constructed to 3.OH:1.OV before <br />dewatering is discontinued and slopes are allowed to develop a piezometric <br />surface. The analysis was conducted using typica9 and normal physical <br />properties for sand and gravel pit slopes;- no site specific samples and <br />laboratory analyses were available. <br />Based on the information provided by Lafarge, conservative material parameters <br />were assumed for the excavated slopes, as listediin the following table: <br />Representative.MateriallAnalysis parameters <br />Sail Material ! Sand end ravel mix <br />Moist Soil Densit 130 I er cubic foot <br />Internal Friction An lei; 3p de rees i <br />Cohesion i 0 Ib r s uare foot <br />5231 SJUIh Quehet Str<el • CrXenw~ud ~'ili~Ge, Ccluradn $Ol l! <br />Phune (.i03) b5(I 0930 ~ Fux (303) 921-929$ <br />Nrb Site' www~,Y+cYStone-coaa,Irmtts.eum •Ib-maiL greysc~e(~groYerone-:nnm"mu-com <br />