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0 <br />The general dip of the bedrock in the West Pit area is on the order of 3 to 5 <br />degrees to the NNE. Localized undulations in the bedrock create localized variations <br />in the dip angle and direction. There are several existing slides of various sizes in <br />the general vicinity. The unfavorable dip direction, presence of low friction claystone <br />layers, and seepage in combination can create marginal to unstable conditions. At <br />this time evidence of significant bedrock movement or failure has not developed. <br />Alternatives to improve conditions are limfted. Measures to improve stabilty <br />condkions were performed in the spoil fill area and are planned in the existing pond <br />slide area. We do not believe a slide in the seepage area will affect tfie spoil fill and <br />removal of the slide mass will control possible effects on sediment pond operations. <br />We anticipate that excavation of the West Pit will cut off a significant recharge area <br />of the seeps. We do not believe additional investigation or stabilization efforts are <br />required at this time. <br />We recommend the following drainage improvements for the seepage areas. <br />The topsoil in the seep areas should be removed to expose the seep. A gravel drain <br />(2 inch, clean rock) should be installed and provided wkh a gravity outlet. A <br />conceptual detail of the proposed drain is shown on Fig. 2. The drain can be <br />installed at each significant seep location. <br />We do not believe monitoring of the seep areas to detect movement is <br />merited. If significant movement of bedrock occurs we believe it will be readily <br />apparent. <br />Spoil Fill Stability <br />During stripping operations and drain construction for the excess spoil fill, <br />seep areas were identified near the face of the fill and were provided with drains and <br />lateral connections to the main underdrain (Observations of Stripping Operations, <br />Job No. 21,952; letter dated July 30, 1994). An observation well will be installed on <br />the first bench of the fill and survey monuments installed. Quarterly monitoring of <br />these features is recommended. <br />Based on our field observations, we believe the construction of the excess <br />spoil fill has been in conformance with the design recommendations presented in our <br />Geotechnical Investigation, West Pit Excess Spoil Disposal Site (Job No. 16,516, <br />report dated March 1,1991). Seepage areas evident during stripping were provided <br />with drains and the main underdrain exceeds the length recommendations in our <br />previous report. At this time we have not observed conditions which we believe <br />compromise the stability of the fill. We believe the proposed montoring program is <br />adequate to detect water buildup near the face which could affect stability. <br />COLOWYO COAL COMPANY L P. <br />cnJr aa,ooi 3 <br />