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December 2002 Seneca Coal Comparry * Seneca II W Mine Sedimentation Pond 077 Stability Anafynt ~ 2 <br />• strength and index classification lab results for the soils tested at Pond 10, Pond 14, and Pond 17 aze <br />included in Appendix A, and aze summarized on Table 1. <br />- - TABLE 1 <br />INDEX AND STRENGTH PROPERTIES OF SOILS FOR PONDS <br />SAMPLE ATTERBERG PARTICLE SIZE EFFECTIVE EFFECTIVE <br /> LIMITS DATA FRICTION ANGLE, COHESION, <br /> ILL - PI) (% passing No. ~' c' Ipso <br /> 200) <br />Pond 17 Embankment 40-17 90 - - <br />Fill <br />Pond 17 Foundation 28 - 10 59 - - <br />11 G) <br />Pond 14 Foundation 28 - 11 75 24.5 0 <br />Pond 10 Embankment 38 - 22 86 27.5 338 <br />Fill <br />The parameters described above were input into the SLOPE/W program to evaluate static stability of the <br />Pond 017 structure and are shown in [he attached progam printouts with associated results. <br />2.0 RESULTS <br />Using the described inputs, the stability analysis indicates a static FOS of 1.56 fot a downstream <br />slope, which meets the required FOS under applicable provisions of Rule 4.05.6(11)(k). The <br />SLOPE/W computer printouts, located in Appendix B, document all inputs and stability analysis <br />results. This stability analysis result is based on the assumption that construction practice employed <br />• for this embankment resulted in embankment material compaction of at least 95% Standard Prottor. <br />3.0 REFERENCES <br />Leidich, Tom (2002). Pond 017 As-Built Exhibit /3-9B, Seneca II W Permit. Prepared for Seneca Coal <br />Company. <br />Lou L. and Peng S.S. (June 1999). Integrated Approach for Predicting Mining Subsidence in Hilly <br />Terrain. Mining Engineering. p. 101. <br />Northwest Colorado Consultants (July, 1994). "Geotechnical Investigation, Haulroads Y-A & Y-B oral <br />Sedimentation Pond 010, Seneca II W Mine Area, Routt County, Colorado". Prepared for Seneca <br />Coal Company. <br />Northwest Colorado Consultants (August, 1996). "Geotechnical Investigation/Summary Report Pond 010 <br />Embankment -Permit C-94-082 Seneca I/ W Mine, Roun County, Colorado". Prepared for Seneca <br />Coal Company. <br />MWH, Ins 165 Sautb Union BaulenarA, Suite 410 * Lakemaod, Cokrado 80228 * (303J 763-5140 <br />J:\2470708 Seaera Cooi\PondrArbb\Ward~POND 77 Arbaitr S7ABIL17Y.dor <br />08/05/03 djm <br />