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Memo to Steve Shuey 3 July 31, 2003 <br />Gypsum Ranch Pit Permit No. M-1998-014 <br />Analysis 2 of the east profile considers the stability of a more deep-seated circulaz failure surface with the same <br />initiation and termination points as analysis 1. The resultant safety factor of 1.12 shows that shallow calving or <br />slab shaped failures are more likely to occur than deeper circular failures. This finding correlates with <br />observations made at the site. <br />Analysis 3 of the east profile considers the stability of adeep-seated circular failure surface that intersects a <br />substantial portion of the over burden stockpile. The safety factor of 1.34 indicates that adeep-seated failure <br />that would take out the stockpile at this location is unlikely to occur. <br />Analyses 4 and 5 of the east profile consider failure surfaces through the over burden stock-pile that initiate and <br />terminate at the same points as the analysis 3 failure surface, but are more slab shaped and shallower than in <br />analysis 3. The derived safety factors for these shallower surfaces aze 1.06 and 1.02 respectively, which <br />indicates a potential for slab shaped failure that would carry portions of the over burden stockpile into the Eagle <br />River. Three sets of back analyses were conducted for the analysis 5 failure surface. The results of these <br />analyses demonstrate: <br />• The in situ gravel deposit would need a friction angle of 62 degrees at zero cohesion in order to yield a <br />1.5 safety factor. <br />• The loose or sloughed gravel would need a friction angle of 53 degrees at zero cohesion in order to yield <br />a 1.5 safety factor and a friction angle of 44 degrees to yields a 1.25 safety factor. <br />It is not reasonable to assume that these materials will be able to provide these very high shear strengths to resist <br />failure in the long term, particularly if triggering actions, as were discussed above, were to occur at this location. <br />In summary, the DMG's analyses combined with observations at the site and with the stability analyses supplied <br />in the original permit application, lead to the conclusion that the escarpment along which the over burden <br />stockpile was placed is potentially unstable. As a result the Operator must move the stockpile to a stable, <br />approved location within the permit area. The concrete rubble that is south of the stockpile at some locations <br />must also be moved. The DMG could entertain a proposal from the Operator to leave potions of the stockpile in <br />place if the Operator can demonstrate stability in locations where the stockpile is set back farther from the cliff <br />or locations where the cliff is not as severe as it is at the east and west profiles. <br />The DMG Office of Mined Land Reclamation does not regulate safety issues at mine sites. However, given the <br />results of the stability analyses described in this memo and attachments, the Operator is advised to develop an <br />earth moving plan that will protect men and machinery from the potential for a slope failure during the <br />movement of the over burden stockpile. <br />attachment(s) <br />cc: Carl Mount, DMG (via email and w/o attachments) <br />c:\acsU4y Documents\gypsum ranch.doc <br />