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<br />wssTexn <br />FI;EIS-UTAH <br />rnc. <br />A SuW'idiarv <br />of <br />Wialenr £ueG <br />Awcia(iors, Irsr. <br />Mr. Dan Mathews <br />Division of Minerals and Geology <br />2148 Broadway, #C-5 <br />Grand Junction, CO 81503 <br />R~~~~~D <br />~~~, , ~~:,19°.16 . <br />k~W1t~ Sept. 9, 1996 <br />Qi1Ast';~~CdiOn <br />ILE: Geotechnical investigation of RP-4 Sediment Pond Embankment <br />Dear Mr. Mathews: <br />~I I I I~ I I~ ~ I~ ~~~~ ~I~ <br />999 <br />Enclosed with this letter is a report of geotechnical investigations conducted by Lincoln DeVore, <br />Inc. of Grand Junction, Colorado. The report titled "Subsurface Soils Exploration, Deserado Coal <br />Mine, Itangely, Colorado" and dated 8/20/96 provides a reasonable conclusion for the cracking <br />observed in the ItP-4 sediment pond embankment derived from scientific experimentation and <br />experience working with similar soils. <br />Lincoln DeVore concludes that the cracking was caused by the swelling of expansive soils <br />beneath the embankment. These sods have become progressively wet over the years from water <br />contained in the sediment pond migrating downward into the native soils below the pond. This <br />wetting of the native soils have caused a "slightly upwazd bowed appearance" and "has been <br />manifested within the embankment as a tension crack." My interpretation of this description is <br />sketched in figure 1. <br />Most importantly the report concludes that there is no obvious cause for the cracking within the <br />embankment itself and that no unstable zones or strata could be identified. The only warning <br />gven in the report referred to the possibility of "piping" that could occur "if the sediment pond <br />contained a relatively large head of water for extended periods." Because we are required to <br />maintain room for the storage of a ten yeaz precipitation event the pond must dewatered when it <br />contains an excessive amount of water. Thus, proper compliance with the mining permit <br />precludes the storage of large amounts of water and therefore should prevent any destabilization <br />from piping within the embankment. The report concludes that the soil has probably reached <br />saturation and that further movement is unlikely. <br />lkserado Aline <br />P.O. Box 1061 <br />Rangely, Colorado 81648 <br />Telephone 303/675 8431 <br />Teleropier 303/615-52?9 <br />