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JCB Engineering, LLC <br />26 March 2004 <br />Page 3 <br />Each condition was evaluated for 1) any slope failure and 2) a failure that would potentially affect the pipeline. <br />Assumed soil conditions for the analysis were based on the Tetracon investigation and are shown in Figure 2. <br />The following table summarizes the analyses and results. Slope stability analyses output are included as <br />Appendix B. <br /> Minimum Calculated Factor Minimum Calculated Recommended <br />Analysis Conditions Soil of Safety for Any Slope Factor of Safety fora Minimal Factor of <br /> Parameters Failure (with the mode of failure affeMing the Safety <br /> failure given in parentheses} pipeline <br />Fully excavated Pit dewatered Drained Varies. See note below. 2.6 1.5 <br />pit <br />Reservoir rapid Reservoir emptied Undrained 1.7 3.4 1.2 <br />drawdown quickly, resulting in (for failure of the soil liner) <br /> excess pore water <br /> ressure <br />Note: [ucalized instabilities of the mined slope configuration in the sand and gravel can be expected due to the nature of mining and the materials. BeWUSe <br />of these instabilities, the overall slope angle of the excavation in which the sand and gravel is expelled to become inherently stable is (1.5:1). Based on this <br />slope angle, it can be expected that the slope will be unstable for up to 60 feet from the edge of the pit bottom (assuming a vertically mined highwall). <br />However, the pipeline is located no less than 156 feet from the edge of the pit bottom, and should riot be affected by localized instabilities. <br />Based On OUr SIopC Stability analySlS rCSUItS, the proposed eRC8yat10n Slope and reSerVO1C slope <br />conTigurations appear to be stable in terms of protecting the Town of Windsor's pipeline. <br />We appreciate the opportunity to provide engineering services on this project. Please call if you have any <br />questions or comments. <br />Sincerely yours, <br />~~ <br />Jay C. Davenport, P <br />Project Manager <br />38616 t .4/ ~ <br />Z6 n7r~O~~ %,~ <br />~',' Tracy J. 1 <br />•. <br />Sj~~,'~;'~G~ Principal <br />P.E. <br />Enclosures: <br />Figure 1 -Plan View of Proposed Final Slope Configuration <br />Figure Z -Profile View of Proposed Excavation and Reservoir <br />Appendix A - Terracon's Test Boring Reports and Laboratory Analysis Reports <br />Appendix B - SLOPE/W's Slope Stability Analysis Outputs <br />G:\PROJECTS\103070 Whiting Fdrm\R. Records and ComspondenceVt.l I Reports\Letter Report FMAL.doc <br />~~I,YMAN~ <br />(; HENN ~~ <br />~( ImC <br />