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'L <br /> <br />i • iii iiiiiiiiiiiuiii <br />999 <br />STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Department n( Natural Resources <br />1 313 Sherman 51., Ruom ?15 <br />Denver, Colorado 80203 <br />Phone: 1303) 866-3567 <br />FA%:13031 832-8106 <br />DATE: July 26, 1995 <br />TO: Berhan Keffelew <br />FROM: Jim Pendleton <br />RE: CRESSON MI T ical Spec Revision <br />Carlton Tai s Lift Thickness Increase <br />(Permit No: M-80-244) <br />I~~~~ <br />DEPARTMENT OF <br />NATURAL <br />RESOURCES <br />Roy Romer <br />Governor <br />lames 5. Lochhead <br />Erecuuve Director <br />Michael B. Long <br />Division Director <br />In response to your request, I have reviewed John Hardaway's <br />supplemental submittal in response to my earlier adequacy comments. <br />Briefly summarized, this Cripple Creek & Victor Gold (CC&VG) <br />revision application requested an increase in relocated Carlton <br />Mill Tailings placement lift thickness specification from a maximum <br />of 18 inches to 7 feet. The revision application stated that the <br />structural stability of the relocated Carlton Tailings material is <br />not of importance, because it will be covered with waste rock and <br />be buttressed by the relocated Highway embankment. I responded <br />that the structural character of foundational materials is <br />important for any large earthen structure. In the short term the <br />Carlton Tailings materials will not be buttressed. Further, I also <br />intended to express a longer term concern, noting that a failure of <br />this low strength foundational material beneath the final Arequa <br />Gulch excess overburden fill and adjoining superimposed structure <br />might compromise the hydrology control structures located above the <br />relocated highway embankment. <br />Short Term Scenario <br />John Hardaway has submitted a supplemental response including a <br />reevaluation of the stability of the relocated Carlton Mill <br />Tailings. This stability analysis is limited to my short term <br />concern, in that it evaluates the stability of a zoned relocated <br />Carlton Mill Tailings fill, buttressed by a waste rock embankment. <br />Golder theorizes that conservatively weak properties for the <br />Carlton Mill Tailings are achieved by modeling the fill assuming <br />the traditional "p = 0" assumption, with an assumed cohesion of 300 <br />psf. This case is normally assumed to represent a fast loading <br />situation in which the material is unable to drain, resulting in a <br />plastic mode of material performance. This represents but one <br />possible scenario for the relocated Carlton Mill Tailings fill. <br />