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III IIIIIIIIIIIIIIII <br />STATE OF COLvivlvU <br />t DIVISION OF MINERALS AND GEOLOGY <br />Ueparlmcnl ui NaWral Resources <br />I l l 4 tihwmdn SL, Koum ? I S <br />Denver, Colorado H0203 <br />f'hune I SD}) fS66-356' <br />rAX: LP111 n i?-ri I UL <br />December 22, 1997 <br />Mr. J.E. Stover <br />1.E. Stover & Associates <br />2768 Compass Drive, Suite 101 <br />Grand Junction, CO 81506 <br />RE: Bowie No. l Mine (C-81-038) <br />TR-28; Post Mine Topography <br />Dear Mr. Stover, <br />~~~ <br />DEPARTMENT OF <br />NATURAL <br />RESOURCES <br />R~,y Rnmrr <br />f~OYPrnO~ <br />tames 5 Lw hhead <br />E.ecwi.r DIrrUOr <br />ntchael B. Lonq <br />Division Director <br />The Division received your letter dated October 16, 1997 regarding technical revision 28 (TR- <br />28). A majority of the questions have been adequately addressed, but the Division has one issue <br />that needs to be resolved prior to the approval of the revision; <br />Bowie proposes to retain mine terraces and benches that are over 100-feet in width. The <br />Division is required to make specific findings under Rule 4.14.2(2)(a) granting a variance from <br />over 20-feet in width. The variance is based on the stability of the terraces, erosional control or <br />roads included in the post mining topography. The Division has specific questions related to <br />stability, erosional control and roads for all of the terraces and benches greater than 20-feet; <br />1 a. Geohydro Consultants conducted the original stability analysis on the post-mining cross- <br />sections based on a 2h:1 v slopes. The Division needs to determine that the terrace <br />benches greater than 20 feet are necessary for stability. It should be noted that on many <br />of the terrace slopes and reclaimed highwalls, the slopes can be reduced to something less <br />than 2h:ly. Has Bowie examined the stability of slopes less than 2h:ly and in a different <br />configuration to determine if the slopes will be more stable? The Division believes that <br />a slope.of 3h:1 v or less will ultimately be more stable, less erosive and will be quicker to <br />revegetate. Bowie should reevaluate the terrace slopes at 3h:ly or Less to ensure greater <br />stability of the out slopes and to provide a more sturdy surface for revegetation. <br />I b. Bowie provided the Division with a demonstration that terrace benches will improve the <br />watershed lands within the permit area as defined under Rule 2.06.5(2)(d). Bowie has <br />demonstrated that terraces will reduce the amount of total suspended solids (TSS) al}d the <br />total volume of tlows from the permit area. The Division remains unclear 13ow a 100-toot <br />