Laserfiche WebLink
tlLdlll~ lrlaOn tafa0ClaNa III IIIIIIIII IIII III <br />September 17. 1997 999 <br />Mr. Norm Every <br />Mountain Coal Company <br />West Elk Mine <br />P.0. Box 591 <br />Somerset. Colorado 84134 <br />RE: MCC LaadsGde Mitigation Rccommendarions <br />The following report summarizes the potential mitigation methods that could be used by <br />MCC on the active landslide to slow down the rate of movement to previous background <br />rates. This letter report will serve as a guide for MCC in making the financial decisions <br />needed for this site. <br />I.0 INTRODUCTION <br />A review of existing monitoring data over the last four years shows a disttubirtg pattern <br />/'1 Although the buttress that was constructed in the Spring of 1997 effectively cropped the <br />/`~y~ lartdslide in the ricinity of the screening plattt and thus is protecting these local critical <br />structures, an accelerating but not exponrntial acceleration is noted in the monitoring data <br />at other facilities starting in 1995 with large stuficial movements observed in 1997. <br />Utu current data shows the length of the landslide to be approximately 1000 feet in <br />length. Shear sveagth data of the native colluvial soils shows that total failure occurs <br />when the soil has strained to az little as 0.5% to an upper limit of t%. In other words, <br />when displacement of the monitoring mirrors that are installed on critical structures shows <br />anywhere from S to 10 feet of total movement, a potential major displacement of critical <br />structures is likely. The scarp. which grew extensively in 1997 to approximately halfway <br />down to the toe of the landslide, will continue to elongate in a north direction until it <br />reaches the toe of the slide. At this time, the landslide will release with horizontal <br />potential movement of 50 feet or more possible based on past landslide knowledge and <br />stability analyses. Obviously critical structure damage will occur in this event. <br />HLA has presented with this report polynomial cttrves that show total movement of the <br />lturdslide has reached 30 to az much az 70 percent of the allowable strain prior to tailure <br />C2~ azsuming movement began in 1992. Total failure of the upper portion of the slide is <br />J possible is 1998 while the lower portion may be delayed to possibly the yeaz 2000 if <br />normal climatic conditions occur. However the effects of a far wetter than norms[ <br />winter/spring az may be associated with the predicted "El Nino' event this winter may <br />have serious consequences to the operation az WEM. <br />This report will discuss information recently acquired concerning the character of the <br />existing landslide at the site of the ARCO/Mountain Coal Company West Elk Mine <br />Enq~nen~eq erne ASS Sown 700 Wae. Sw4'0J. Sail lw Cary. Uuh ]nm Rie°n0ec (901) J93~U] PscvmiK~. lEOp )63+16 <br />en.~romm~mai Semce] <br />