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<br />~~~G L~~tv~c{r ~:;c ;ysscc;.a-.s <br />MAY 13 7993 <br />April 26, 1993 <br />Joe Dudash <br />Mined Land Reclamation Division <br />1313 Sherman Street 2nd Floor <br />Denver, Colorado 80202 Re <br />Dear Joe: <br />J'~9 U njli VI nniiGirl: u .]GUIUy~' <br />iii iiiiiiiiiiiu iii <br />999 <br />t oa3 Cuun a!acc <br />o C'IC JC~ <br />- .tln~-':n 4fiC7 <br />_C.i~ri~9-cC3_ <br />Sediment Pond Certification <br />at the Rimrock Mine. <br />Upon hearing that the previous certification was still lacking <br />some information, this final revised certification document has <br />been prepared. I must provide comments regarding the two main <br />issues lacking in the certification: 1) the height of the dam <br />measured from the bottom of the original ground at the dam <br />location to the bottom of the emergency spillway was measured to <br />be slightly less than 10.0 feet, therefore no compliance with the <br />State Engineer's requirements or C.R.S. 37-87-105 was necessary <br />to be discussed, and 2) the fact that the compaction testing was <br />successful and that the pond slopes were reconstructed at 2.5:i <br />was the basis for my statement in the earlier certification that <br />the embankment was sound and met prudent engineering design. To <br />me, it was understood that the dam met the 1.3 slope stability <br />safety factor. With the compaction evidence and the mild slopes, <br />my experience in slope stability allows me to state that it would <br />be unlikely if a detailed slope stability analysis revealed a <br />factor of safety less than ''<.0. <br />1 am a certified professional engineer in the State of Colorado <br />with experience in the Eastern and Western United States in the <br />design, construction and operation of sediment ponds, mine <br />hydrology systems and slope stability of embankments. <br />Site inspections were conducted on December 7 and 22, 1992. A <br />final inspection was conducted on Aoril 22, 1993. Inspections and <br />measurements were conducted by myself and Mark Kerr. A precision <br />eye level, stadia rod and measuring tape were used to verify <br />elevations, slopes and dimensions. Additional work has been <br />comoleted so that the pond slopes are totalling 5:1 at any point <br />along the dam. Compaction tests have been made on the embankment <br />by a geotechnical firm from Pueblo. The results of the tests are <br />enclosed. <br />Sincserel you s_, <br />GregJ'~ew~.P.E. <br />Greg Lewicki and Associates <br />