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As discussed, it is assumed that the foundation material <br />will be significantly stronger than the pile itself. The critical <br />failure areas would therefore occur within the spoil pile and would <br />not pass through the consolidated foundation strata. To assure <br />this, the pile was not be placed on the terrace fan, or the <br />undifferentiated surficial material. In addition, all topsoil and <br />shallow colluvium and soil cover was removed from beneath the waste <br />area, and the surface proof rolled, prior to the placement of the <br />pile. If the depths of the colluvium become excessive, then <br />additional studies should be conducted to estimate its behavior, <br />and determine what effects, if any, this layer would have on the <br />overall stability of the pile. <br />As presented, the pile appears to be stable, even in the <br />unlikely event that a water table surface does develop within the <br />spoil. However, there is a potential that excessive water <br />pressures could develop along the interface of the pile and the <br />foundation strata if springs developed within the channel. The <br />potential for this to occur can best be detrmined by observations <br />of the area over time. If this condition exists, a free draining <br />underdrain would need to be installed. The location of any spring <br />would determine the longitudinal extent of the required underdrain. <br />The results of this analysis indicates an adequate factor <br />• of safety against slope instability for the assumed material <br />properties, slope profile, and ground water conditions outlined in <br />this report. These results will be verified with the actual <br />behavioral characteristics of the waste material once it is <br />available for testing. <br />CTL/Thompson conducted a Supplemental Stability <br />Investigation of the RDA in 1995. The results of this <br />investigation are presented in the report located in Exhibit 30, <br />Geotechnical Study, Coal Processing Waste Bank. Compaction testing <br />in 1995 and 1996 also confirmed construction of the facility to <br />specifications. <br />• ~ ~~9 ~' <br />205E3. 626 2.05-43 revised 10/23/97 <br />