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(a) provide a design, including maps and cross-sections, for the excess spoil facility; (b) identify all sources of ground water, including anticipated drainage from the backfilled mining pits, which may potentially impact the excess spoil disposal facility; (c) provide a detailed plan addressing the placement of permanent excess spoil in a manner which will achieve a long-term static safety factor of 1.5; (d) provide plans for the construction of at least three (3) underdrains at the excess spoil facility; and (e) using the materials submitted in subparagraphs (a) through (d) above, provide a geotechnical stability analysis of the excess spoil disposal facility. Such analysis must demonstrate that a long-term static safety factor of 1.5 will be achieved. Within the final cut areas of the Moffat Area, the final pit will occur where the coal seam outcrops or in an area where up to 20 feet of overburden exists. The final pit will be filled by grading the spoil towards the final cut, and in the case where a highwall exists, the highwall will also be graded towards the final cut. The applicant analyzed the worst-case for each of these situations. Where the final pit daylights at the outcrop, the ground elevation will be decreased up to 30 feet at the ridge top. However, due to the slope of the hillside, positive drainage will still occur (Exhibits 3.4-3 and 3.4-4 ). In the other situation, the ground elevation will be reduced approximately 15 feet and a large flat area approximately 100 feet along the slope in some areas will be created. Because this is located at the ridge top, drainage will not be problem. In the West Ridge Area, the applicant submitted a volumetric analysis for the final cut to determine if sufficient material was available to fill the cut. The Division concurs with the operator's estimation that the material available is sufficient. The operator has proposed a postinining topography with steepened convex slopes located near the bottom of the reclaimed hillslope (Exhibit 3.4-4, Typical cross-sections A and B). This slope shape has been shown in the literature to be susceptible to erosion. Some reclaimed areas at the Edna Mine have been subject to a recurring erosion problem, which, on the basis of field observation, appear associated with a slope convexity. Until now, the operator has been unable to control this erosion. The susceptibility of the hillslope to erosion could be reduced by eliminating the slope convexity from the foot of the slope. The Act requires that overburden be shaped and graded in such a way as to prevent erosion. The material could be moved further upslope as a convexity near the crest of a hillslope is less erosive, or disposed of in a permanent overburden stockpile. In order to achieve compliance with the requirements of the Act, the following stipulation is required: -39- January 13, 1988