Laserfiche WebLink
• <br />UI\'UIO.\' OF .~[WERALS AND GEOLOGY <br />Drp.nB~,mn: ,n ~\'dlur,ll k~:.uuro_t <br />I'll { Sh~_r:oan SI , Huunt ] 15 <br />Uru•. ~.:. C~n~ ~i.vlu :fn_0 1 <br />F:~\ t.u 1. Z~J ~liI IIL <br />DATE: <br />TO: <br />FROM <br />RE: <br />III IIIIIIIIIIIII III A 5~ag j~~ <br />STATF. OF COLOIZP~DO <br /> <br />April 23. 1999 / _ ,p G,~~ /" <br />Tom Schreiner /G`'OT _ <br />Allen Sorenson <br />„ I;IUN of <br />l1~tINERALS <br />GEOLOGY <br />a E C L .1 H A i I n N <br />MININ ~~$A FE TY <br /> <br />Grcc E. ~.~~alch~~r <br />Ea•cmi.p Dnr¢;or <br />.,,<S.,~I a. Low;; <br />Mining Setbacks for the Protection of Structures, CAMAS Colorado, Inc., o"~,~~~„ oar?Unr <br />Cooley Reservoir and Fulton Wildlife Area, File No. M-99-03•I <br />The above referenced permit application states the applicant's intention to mine within 200 feet of <br />certain manmade structures. The applicant has provided slope stability analyses to demonstrate that <br />these structures will not be damaged by potential land sliding into the proposed pit. The purpose of this <br />memo is to describe the results of the Division's review of the stability analyses, and to provide a <br />tabulation of the type of additional information chat will be required to approve mining within the 200 <br />foot setback established in the Construction Materials Act at 34-32.x-11~(4)(e1. C.R.S. <br />1. Public Service Comoanv Towers <br />The applicant proposes a ~0-foot setback for the line of electrical transmission towers that bisect the <br />site. However, the applicant indicates that the minimum setback will be closer to 8~ feet due to the <br />current configuration of the easement boundary and the location of the towers within the easement. The <br />statemen[ that the actual minimum setback would be 85 feet appears to conflict with the discussion in <br />the stability analyses indicating that mining would occur within the easement. The applicant should <br />address this apparent conflict. <br />The enclosed stability analysis prepared by the Division, using the applicants proposed critical cross <br />section, soil strength values, and minimum safely factor of 1.~, demonstrates that a slope failure could <br />occur to within 13 feet of one of the towers. A second analysis was conducted on an approximation of <br />the slope configuration that would result from the initial failure in order to analyze the potential for a <br />progressive failure. The progressive failure analysis demonstrates that a failure surface with a safety <br />factor below the established minimum of l.~ will develop subsequen[ to the initial failure and will <br />intersect the transmission tower location. Based on these analyses, the Division cannot approve mining <br />to a ~0-foot setback from the towers. <br />In order to establish an acceptable mining setback relative to the towers the applicant ma}' either: <br />al Commit to a 200-foot setback. <br />b) Conduct a ~eotechnical evaluation to determine the actual soil conditions present at the si[e and <br />input the values established through the evaluation into an updated stabiltt}' analysis. If the <br />