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<br /> <br />STATE III IIIIIIIII I III III <br />999 <br />OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />DeWrlmeN of N,lWral Resources <br />1 313 Sherman SL, Room ? 15 <br />Denver, Colorado A0203 <br />DIVISION o F <br />Phune: (303) A66-}567 MINERAL S <br />FAX. (30}) 832-8106 $c <br /> GEOLOGY <br />Memo to TR-33 tile, Empire Mines (Permit C-S1-044) MENINGMSAFEOTY <br />~ <br />~ <br />From: Tom Kaldenbach <br />~ Bill Ovens <br /> Govc~nor <br /> <br />Date: September 7, 2001 Greg E. N'alcher <br />Execnlrve Dneclnr <br /> Michael R. Lung <br />Re: Review of operator's submittal received 8/02/01 o'vi,i°" °.re"°` <br />The submittal adequately addresses the following comments from the Division's Midterm review <br />letter: 2, 8b, 8c. and 8d. <br />The submittal does not contain responses to the following comments: 1, 3, 4, 5, 6, 7, and. <br />Responses will be requested in a follow-up adequacy letter. D' (~ ~ K tTK <br />Notes on comment 2 (demonstration of pond embankment safety factors) <br />1 reviewed the reasonableness of the parameters used in the SB slope runs and made the <br />following observations: <br />a) The runs using 1400 psf for cohesion seem of little value for demonstrating meeting <br />the minimum L3 safety factor because 1400 psf is an unreasonably high cohesion <br />value. <br />b) The runs using 100 psf for cohesion and angle of friction of 0, adequately <br />demonstrate the embankments have a minimum L3 safety factor because these <br />parameters seem reasonable. It seems likely the actual materials have greater strength <br />than these assumed parameters. <br />c) The back-calculated parameters seem to lend support to the 100 psf analysis. <br />d) The assumption that the soils are clays seems unreasonable, although the runs using <br />the conservative parameters (100 psf, 0 iaf), in effect, determine the safety factor for <br />a more reasonable mixed composition of sand, silt, and clay. <br />e) SB Slope runs were done for only the five largest ponds. These runs can reasonably <br />be expected to demonstrate the stability of the other, smaller ponds inasmuch as the <br />same strength parameters would be used their analyses. <br />'I ~ <br />