REP26199 - Laserfiche WebLink

Home Browse Search

iii iiiiiiiiiiiiiii STATE OF COLORADO DIVISION OF MINERALS AND GEOLOGY Department of Nalu rat Resources 1313 Sherman 51., Ruom 27 5 Denver, Colurado 80203 Phone: (3031 R6(> 3567 FA%:13031832-A106 DATE: September 6, 1995 TO: Susan Burgmaier FROM: Jim Pendleton RE: Edna Mine~Clos3lre~- Moffat Area Stability t No: C-80-001) ~~~~~~~ DEPARTMENT OF NATURAL RESOURCES lames 5. Luchhead Executive Dueclor Roy Romer Governor Muhael 8. Long Division Director In August, before lead on the Edna permit transferred to you, Kent Gorham forwarded a memo regarding the potential stability of the Moffat Area to my attention. The plan will be terminated prematurely, resulting in a configuration different from that originally approved. I have completed a review of the issue. In 1990, as a portion of the Moffat Area permit revision adequacy response, we required Edna to analyze the stability of the proposed outside the box cut spoil pile adjoining the Moffat Area. I was concerned because of the history of reclaimed (Center Ridge) and unmined (West Ridge) slope failures at the Edna Mine. Edna completed a stability analysis (Section 3.4 of Permit Revision application), which we subsequently reviewed and accepted. I have revisited the stability analyses, examined the air photos and monitoring well records forwarded by Kent, and revisited my earlier adequacy memos regarding this concern. Earlier stability analyses completed on the Center Ridge reclaimed area landslide, and the Moffat Area both indicate that if an artesian head does not develop beneath the parting separating the Lower Wadge and the Wadge seams, the backfilled spoil slope should be stable. In order to verify that the permit projections regarding phreatic surface within the bedrock and the spoil were accurate, the Division required the installation of several additional monitoring wells. Prior to the cessation of mining in late 1994 the Wadge well appears to show no effect from the approach of the advancing pit. The Lower Wadge well showed more variation, with a general decline and stabilization since 1990 at an elevation approximately 10 feet below its original equilibrium elevation. Since cessation both wells have rebounded, the Wadge well approximately 5 feet and the Lower Wadge well approximately 14 feet. However, this spring and summer were unusually wet in Northwest Colorado. A spoil spring has developed and continuously flowed at the low point in the low wall of the Moffat area pit, to the south of the current pit location.