Laserfiche WebLink
<br />CONCLUSIONS <br />I) Based on our recent, cursory observations made a[ the project site, it appears [hat all seventeen (l7) of the <br />existing sediment pond embankments are stable and we did not observe any signs of distress or slope <br />failures in any of the subject structures. <br />2) An individual slope stability analysis was conducted for five of the seventeen embankments. The analyses <br />were completed on the five largest embankment structures. The stability analyses were completed for all of <br />the embankments with Drainage Areas greater than 20 acres and with Total Storage Volumes greater than <br />2.0 acre-feet. Based on the analyses, it appears that the minimum theoretical Factor of Safety for each of <br />these embankments was over 13 for the maximum water level and with steady state seepage and static <br />loading conditions. At the assumed strength parameters for the embankment materials and underlying <br />natural soils, we have calculated that the factors of safety for these embankments range from 1.7 to 5.9. <br />PURPOSE AND SCOPE OF STUDY <br />This report presents [he results of a stability evaluation completed for the seventeen (17) existing sedimentation <br />pond embankments located at the Eagle Mine Complex in Moffat County. The subject mine complex is situated <br />along the east and west sides of Colorado State Highway l3 approximately 6 to 8 miles south of Craig, Colorado. <br />• Afield investigation was completed to visually evaluate [he conditions at each of the pond sites, as well as verify [he <br />dimensions and configurations of the existing embankments. Individual stability analyses were also completed on <br />six of the embankments to evaluate the minimum theoretical factors of safety against failure based on the ponds <br />being full and with steady state seepage and static loading conditions. <br />This report has been prepared to summarize our observations made at [he site and to present our conclusions based <br />on the stability analyses completed for the subject embankments. <br />EXISTING CONSTRUCTION/SITE CONDITIONS <br />To evaluate the existing construction and site conditions at each of the subject embankments we visited the subject <br />property on May 16, 2001 and met with Mr. Rick Mills of Twentymile Coal Company. We visually inspected all <br />seventeen (17) of the subject embankments to visually evaluate the site conditions at each of the sites and to verify <br />the conditions and actual as-built configurations of the subject embankments. [t should be noted that seven (7) of <br />the embankments range from 2 to 4 feet in height; four (4) of the embankments range from 5 to 9 feet in height and <br />six (6) of the embankments range from 10 to 1 l feet in height. Listed below are a summary of our observations and <br />measurements obtained for each of the embankments. <br />g 1~~ s.9 <br />3`~~ PondS-Pt <br />~' <br />• The embankments were in good condition. No signs of distress or movement in the downstream or upstream faces <br />of the embankments. Approximately 6 inches of standing water in base of pond. Crest width is 8'; embankment <br />height is approximately 4.5 ;downstream face at 2:1 (H: V) and upstream face at 3:1 (H:V) configurations. <br />Job Number: OI-4857 NWCC, Inc. Page I <br />