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Field Findines The inspectors (Ron Sassaman and Kent Gorham) concluded that both fill structures were in compliance with the permit. (For details, see the narrative to the OSM inspection report, signed by Ron Sassaman on 6/19/97.) Because both fill structures are still being built, it is dif£tcult to assess present stability; i.e., if a problem develops during construction, the mine operator takes the steps necessary to correct the problem. The measures taken to stabilize t}te RDA downdrains by regrading and adding rock gabions are examples of the improvements being taken to stabilize the structure. Although there was no evidence of massive impending failure of either fill structure, l have the following concerns regarding long-term stability: Development Waste Pile: The DWP is located in the Stonewall Valley flood plain. The Purgatoire River that flows through Stonewall Valley ltas been straightened by the mine operator to facilitate mining operations. Based on the flow pattern in relatively undisturbed areas, the river has a natural tendency to _ meander. Because the DWP structure is located inuncdiately adjacent to the river and the fill ~ slope next to the river appears to be susceptible to erosion--especially during major runoff events--it is conceivable that stream flow could erode the fill eventually to the point of structural failure. During the field review, Kent Gorham pointed out that the lower fill section was put in place perhaps 17 years ago and therefore should not be evaluated as part of the oversight review. in response, I explained that the old fill is serving as the foundation fur the new fill; in which case, no new fill should be added to the old fill unless it has been determined that the old fill will be stable under desigtt conditions. The reasons why the DWP fill was located in this area is not clear. Locating the fill in a flood plain does not appear to satisfy the requirement of reestablishing the approximate original contours (AOC). Variances to AOC cannot be approved unless the mine operator demonstrates that the reclaimed land configuration will be wittpatible with the post-mine land use, which is a flood plain. Ignoring AOC considerations, even excess spoil must be placed so that it is compatible with the surroundings. Furthermore, the final configuration must minimize erosion; yet, the DWP could have been graded at much flatter slopes. For shat matter, it is not clear why the coal waste was not disposed of in the RDA facility, thereby eliminating potential impacts on the flood plain altogethc(l Refuse Disposal Area: Conditions exist that require attention at this disposal site. Runoff on the terraces are not draining properly to the side drains. Some water is flowing down the terrace slopes, while at other areas on the terraces water is being trapped in depressions. Side downdrains have required considerable maintenance to control erosion; the present erosion-control measures appear inadequate to ensure long-term stability. The terrace slopes have areas where reestablishment of vegetation is not progressing well because the topsoil is slipping down hill. 'l'he runoffthat is flowing down the valley fill from undisturbed areas above the RDA and discharge from the top of the fill structure are causing excessive erosion. (No certified designs were found in the permit for either fill structure.) 5 iZ ='90I81E86 -W S 0 gtnn ttt ~a-uz-i .t^ i~~ac