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'~ becember 1986 12 863-2052 The Williams Fork units sampled during the recent field investi- gation are typical of the sandstone, siltstone, and claystone sequence present above the Wadge and Wolf Creek seams. The sandstones encountered in the five borings are typically fine grained, strong, moderately to slightly weathered, and are often cemented with calcite. The claystones encountered are more highly weathered and are poorly indurated relative to the sand- stone. However, no low shear-strength claystone samples which would potentially affect foundation stability were obtained from the five borings. The siltstones encountered are moderately indurated relative to the sandstone and claystone. Discontinui- ties observed in the rock units sampled are not considered sig- nificant in terms of their impact upon foundation stability. The only known fault within the mining area strikes approximately perpendicular to the toe of the spoil structure (Figure 2). It is unlikely that this or any other faulting would influence the stability of the excess spoil. 4.3 Soil Conditions Reconnaissance of the excess spoil area indicates that minor surficial slumps are present in colluvial soils in the vicinity of B-1 (Figure 2). No other areas of slope instability were observed by aerial photo and field reconnaissance of the excess spoil area. Both slumps shown on Figure 2 are apparently shallow- seated features which have developed in loose slope-wash mate- rials which mantle the Williams Fork bedrock in this area. The surficial slump located in the drainage west of B-1 is associated with a seep near the center of the drainage. Since all topsoil and subsoil will be stripped in the excess spoil structure foundation areas prior to mining, existing soil conditions are of limited importance for the stability of the excess spoil struc- ture. Golder Associates