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<br />Memo to Christine Johnston <br />MCC Upper Repuse Pile <br />page 3 <br />Page 10 <br />The text states; "Section 4.09.1 of the Regulations of the <br />Colorado Mined Land Reclamation Board for Coal Mining states <br />that excess spoil shall be placed to ensure a long-term static <br />safety factor of 1.5. To meet this requirement, a static <br />earthquake loading of 0.05 g has been applied during the <br />stability analysis." To avoid any confusion, the URP is a <br />coal mine waste bank. Underground development waste is no <br />longer categorized with excess spoil, but is now included <br />under the definition of coal mine waste. As such the URP is <br />subject to compliance with Rule 4.10, which includes <br />compliance with Rule 4.09 by reference, except when more <br />stringent requirements are imposed by Rule 4.10. Rule <br />4.10.4(2) requires all coal mine waste banks to achieve a <br />minimum static safety factor of 1.5. Further, Rule 4.10.4(3) <br />requires all coal mine waste banks to be compacted to a <br />minimum of 90 percent of the maximum dry density in lifts of <br />not more than 24 inches in thickness. <br />Impacts of Subsidence <br />The URP was originally included in the permit application by <br />revision in 1984. On page 35 of the 1984 permit revision <br />application, Anaconda stated: <br />"Effect of Mining on Refuse Pile Stability <br />The refuse pile will be located above the main entries <br />which must remain stable for the life of the mine. There <br />are no plans for secondary mining (pillar extraction <br />panels) near this part of the main entries. The <br />extraction of the primary mining will not induce any <br />subsidence. Therefore, underground extraction will have <br />no effect on the refuse disposal pile." <br />Subsequent modifications to the mine plan have resulted in <br />subsidence of the URP site. In fact, several subsidence <br />cracks have been documented within the proposed footprint of <br />the pile. <br />The application will have to discuss the implications of mine- <br />induced subsidence for the pile. These implications include <br />the implications for the strength of the overburden materials <br />upon which the pile will be founded. Will multi-seam mine- <br />induced subsidence effect the material strength of the <br />materials? Should these impacts be reflected in the material <br />strengths or failure modes addressed within the stability <br />analyses? These implications also include design <br />