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i ii iiiiiiiiiiiiiiii 999 STATE OF COLO Roy Romer, Gove DEPARTMENT OF NATURAL RESOURCES MINED LAND RECLAMATION DIVISION FRED R. BANTA, Director GATE: August 24, 1989 T0: Grassy Gap Mid-Term File FROM: Susan Mowry C~~~ RE: Pits 5 and 6 On July 19, 1989 I inspected the Grassy Gap mine site. Mr. John Elliot, geomorphologist with the U.S. Geological Survey, was able to meet me and inspect pits 5 and o with me. I had requested nis assistance in evaluating the reclaimed topograpny and stability of these two pit areas. Based on our discussion, I have come to the following conclusions: The reclaimed topography in pit 6 does meet AO C. Adjacent undisturbed slopes exnibit a similar oasic configuration. Tne pit was enclosed by a low wall and hign wall during the mining phase. Both the highwall and low wall have been completely backfilled. The vestiges of these confines are evident in the reclaimed pit area. All the backfill has been replaced within these confines. The coal seam removed was several feet thick. This void snould be compensated for by spoil swell fairly equally. There are two small depressions where water ponds within the reclaimed area out overall positive drainage has been estaolisned. For these reasons I believe the pit 6 reclaimed topography meets AO C. I do not believe that pit 5 reclaimed topography meets AO C. Several features currently exist in the reclaimed topography which I do not believe were pre-existing. Tnese features are as follows: an over steepened slope in the area of the reclaimed southwest highwall, a large flat area in the south central region of the reclaimed pit, an oversteepened slope immediately above the natural drainage along the north edge of the reclaimed pit, a road bisecting the nortneast and southwest portions, a nicx point along the south highwall (where the reclaimed slope dips then rises to meet the natural slope), and shifting of the ridge top location to the southeast. Currently 55-50% slopes are found at the top and base of the reclaimed area. These slopes are comparaole to pre-mining slopes which were 50-62%. The lengtn of these siopes is less in the post-mining topograpny, tnereby lending to the overall staoility of the site. The oversteepened slopes have been suoject to some rill erosion. Several rills were noted on born the slopes at the southwest and along the north. However, the worst is probably over and the "healing" process appears to have begun. Vegetation regrowth appears to be largely successful. This area is scheduled for vegetation sampling in late August. Overall the reconfigured pit appears stable. No tension cracks or slumps were noted on an.y of the siopes. 215 Centennial Building, 1313 Sherman Street Denver, Colorado 80203-2273 Tel. (303) 666-3567