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STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Depanmem of Natural Resources <br />1311 Sherman 51., Room 215 <br />Denver, Colorado 80203 <br />Phone: (3071 86G-7567 <br />FA%: (3071 8328106 <br />DATE: February 7, 1995 <br />TO: Christine Johnston <br />FROM: Jim Pendleton - <br />RE: Mt. Gunni n #1 - . 75 -Supplemental #2 <br />Lone Pine Coal Refuse Pile - <br />Material Strength Value Justififcation <br />(Permit No: C-80-007) <br />II~~~ <br />DEPARTMENT OF <br />NATURAL <br />RESOURCES <br />Roy Romer <br />Governor <br />lames 5 Lochhead <br />Exec Wive DueUOr <br />Michael B. Long <br />Drvrsion Dueclor <br />I have reviewed the second supplemental submittal by Kathy Welt of <br />Mountain Coal Company in response to my earlier request for <br />justification of the strength values used in analyzing the refuse <br />piles stability. You will recall that I asked for additional <br />information to support the consultant's choice of mechanical <br />strength parameters for the coal refuse. Kathy submitted a brief <br />explanation prepared by Charles C. Rehn, P.E. of Envirocon, Inc., <br />who prepared the earlier analysis. Mr. Rehn stated that the <br />material strength values were obtained from the testing performed <br />by the company in completing its evaluation for the Lower Refuse <br />Pile at the Mt. Gunnison No. 1 mine. Mr. Rehn observed that while <br />seven tests were performed in the earlier analysis of the lower <br />refuse pile, only one had a dry weight similar to that of the coal <br />derived from the Lone Pine Gulch portal. As additional supporting <br />evidence Mr. Rehn performed a sensitivity analysis of the pile <br />configuration. Each of the seven strength values was used to <br />complete the analysis. while the chosen strength values yielded <br />the highest slope static safety factor of 2.98, the lowest result <br />was 2.30, well in excess of the required factor of safety of 1.5. <br />In consideration of the information provided I recommend that you <br />consider my earlier condition to have been satisfied. <br />cc: David Berry <br />Doc: M:\COAL\JAP\MTGTR75.MEM <br />JP/JP <br />~ . <br />C <br />