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STATE OF COLOI~DO <br />DIVISION OF.NINERALS AND GEOLOGY <br />Oeaartmenr or Natural Resources <br />I l i l 5herma~ it.. Room ' l i ` <br />Denver. Colorado 30707 D i v l S i 0 .~ O <br />Phone: GOlI 356-7567 MINERAL S <br />FAX: 13071 91J~9105 & <br />GEOLOGY <br />0.3ClAMATIpN <br />MINI,V G•SAFET~ <br />DATE: December 26, ?000 e... o..Ms <br />C°"x°or <br />TO: Tom Schreiner """""` °ireCpf <br />,ni~,ael 3. ~°°y <br />0~"~v~°n Oirec:°r <br />I-ROivC Allen Sorenson I <br />J <br />RE: Stability Analysis, Hall-Irwin Corporation. <br />Yorth La Poudre Resource, File Yo. ~I-?000-1-t-t <br />I have revie`xed [he st3bili~! 1na1`~sis provided wi[h :he above rePe:enced acolicauon. The closest <br />structure to the proposed near ve^.IC31 pi[ wails is 1 Sinclair gis 2ioe!ine. The lpelicatlon s;,ecities 1 <br />mining setbac'.< of ~0 feet from the pipeline. The aoolica[ion SJnher states tha[ the pit depth will <br />gene: ally not exceed 30 feet. Typically, any ;Wining setbac': m an alluvial grlve! pit that is equal to or <br />greater than two-times the maximum pit depth :nay be cons.dered a safe, conservative. and pn:dent <br />protection measure. Also, the Ap°licant provided limit equilibrum stabiiiry analyses ;neiding 1 slope <br />stability safety tac:or of l.d for the gas pipeline. Although 1 do not necessarly ag-ee that :he shear <br />strength for :he claysrone bedroc!c input :O Che 1na1V525 IS suc:C:enC1V COnSe.^~aCive °OC 1 C:.C:Cal C:OSS <br />sec::on of :he proposed slope. the .applicant's demenscadon is addiuona! evidence that the proposed ~0 <br />foot setbacl [or the pipeline is satisfac:ors. (I[ is the Dtvision's experience tha[ residual strength <br />weathered shale or claysrone at :he roe of a pit wall may be the weak lave: that causes slumping or slope <br />failure: residual strength weathered shale may be modeled using c=0 and ~_! 1 degrees). <br />In summari, the Division can approve the mining se:bac!ts proposed in the application. The Aoplicanl <br />should commit to martin; the underground utilities and establishing the setbac!c lines on the ground <br />prior to mining. Of greater concern than the setback distances, is the potential fer the lateral berm that <br />will suppott the Sinclair pipeline following minim to be washed ou[ during a flood. Toe Applicant <br />must provide a design for the Division's review and approval thaz will demonstrate and ensure <br />equalization of hydrostatic pressure between the two mining pods.during a flood. This design must be <br />approved prior to consideration of the tecl~amation permit application for approval. <br />°:lwmdows~person°M°nh la poudrc.doc <br />