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Coal Company. Since it was not apparent which cross-section was <br />• the most critical one to be used in the stability analysis, both <br />proposed cross-sections were analyzed. The foundation conditions <br />for the proposed refuse piles were based on the subsurface soil <br />borings which were performed in September 1984 by Rocky Mountain <br />Geotechnical. The appropriate thickness of alluvium and location <br />of the bedrock strata were plotted on the model at each of the <br />test borings and linear interpelation was used between these <br />points. <br />6.4 PHREATIC SURFACE <br />The position of the phreatic sucface within the pile is very <br />critical to the stability analysis. The piezometers at the site <br />• indicated that a dry condition now exists at the proposed site. <br />The field investigation did not indicate any areas of seepage <br />along the face of the existing slope, nor any observed water in <br />the foundation borings. Therefore, the only water which can <br />enter the refuse pile itself will be strictly from precipitation <br />events which will occur over the site. A diversion berm located <br />along the upper reaches of the coal refuse piles will divert <br />stream and surface runoff away from the waste piles. <br />Even if the annual precipitation of approximately 10.5 inches <br />occurs instantaneously, and assuming the pile could not drain, a <br />maximum groundwater mound approximately 10 feet high could occur. <br />• This groundwater mound assumes water could not drain into this <br />foundation and the coal waste material has a specific yield of <br />0.10 which is typical of silts and fine sands. <br />11 <br />