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Apn! 2002 Senera Coa! Compmry * Senem II W Mine Sedimema6on Pond 076A Design Stability Analyri.r ~ 2 <br /> <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 /> (LL - PI) (% passing No. ~' c (psQ <br /> 200 <br />Pond 016 Foundation 49 - 20 96 29.9 0 <br />Pond 016 37 - 22 83 - - <br />Embankment Fill <br />Pond 010 38 - 22 86 27.5 338 <br />Embankment Fill <br />2.0 RESULTS <br />Using the described inputs, the stability analysis indicates a static FOS of 1.5 for a downstream slope, <br />which meets the required FOS under applicable provisions of Rules 4.05.9 (6) and 4.05.9 (8) (b). 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% Standazd Proctor. <br />3.0 RECOMMENDATIONS <br />In order to achieve the design pazameters, it is recommended that the following procedures be <br />utilized in the construction of the sedimentation pond embankments: <br />• 1) Upon Bearing topsoil and construction of the embankment keyway, have a <br />Registered Engineer (or a qualified person under the supervision of a Registered <br />Engineer) verify the subgrade (foundation) material classification in association with <br />this stability analysis. <br />2) Given the location of the dam, the height of the dam (greater than 15 feet) and a <br />FOS of 1.5; prior to construction, soil samples should be collected from the borrow <br />azeas and tested to verify the borrow material/embankment fill strength parameters <br />used in association with this stability report. <br />3) Construct embankment in maximum 1-foot horizontal lifts. <br />4) Compact each individual lift to 95% of standazd proctor using available equipment. <br />5) Maintain slopes no steeper than 3H:1V. <br />4.0 REFERENCES <br />Montgomery Watson Hazza (December 2001). Pond 016A Design. Attachment 13-SB, Seneca 1l W <br />Permit. Prepazed for Seneca Coal Company. <br />Northwest Colorado Consultants (July, 1994). "Geotechnical Investigation, Haulroads Y-A & Y-B and <br />Sedimentation Pond 010, Seneca ]I W Mine Area, Routt County, Colorado". Prepared for Seneca <br />Coal Company. <br />Northwest Colorado Consultants (August, 1996}. "Geotechnical Investigation/Summary Report Pond OIO <br />Embankment -Permit C-94-082 Seneca 11 W Mine, Routt County, Colorado". Prepared for Seneca <br />Coa] Company. <br />Momtgomcry Wa[ran Har{a, 0765 South Union B°ule°a>~ .faire 410 *]vkewa°d, Colorado 80228 * (303) 763-5740 <br />J:\2J70108 Senem Cea7~PA,03\Pand76REV\Wad~POND 16A De.rtgn STABIIII'Y nervpa,dda <br />W/17/02 dlin <br />