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PROM MYERS DSGN ENG~MINES GROUP INC PHONE NQ. 702?332413 No~•. 20 1??7 06:37AM P3 etc. ). When active they tend to mask the presence of the other failure planes and dominate the measured displacements B type planes tend to have more moderate displacement rates and aze also intermittent but remain active over longer periods of nme that can extrnd well into the dryer periods ofthe year. C type planes tend to have the lowest displacement rates and represent a steady, virtually ever present creep throughout the fandsiide mass that is independent of the periods of high moisture. The measured surface displacements represent the cumulative displacement on all of the f3ilttte planes present at a given monitoring station. Therefore, in order to assign displacemrni rates to the individual planes, a correction must be applied to remove the backzround displacement on the slowest plane to provide the best estimate of the actual displacemem rate on the next fastest plane. All of the dispiacemrnt rates depicted in the figures accompanying this letter have bern corrected m this manna. There arc any number of methods for predicting time to catastrophic failure from Surface displacement data, all of which attempt to "linearize" the data for the purpose of making futtue predictions. The two methods selected for use with the data at the West Elk site arc Inverse Velocity and Logarithmic Displacemem Velocity. Inverse Velocity tends to be best in the Lur stages of acceleration just weeks prior to a potential macro failure while the Logarithmic Displacement Velocity method tends to be better (i.e., more consistent and stable) for long range projections of dme to failtue. Review of the post-RCC buttress monitoring data indicates that movement on the A and B planes was effectively arrested by the buttress at monitoring sites 13, 14, l5, and 22. Movement on plane A only was arrested at monitoring sites 5, 10, 11, 23, 24, 29, and 3l. Movements on plane A were impacted but not arrested at monitoring sites 4, 25, and 28. The remaining monitoring sites cotttinuc to displace with minima! impact from the RCC buttress. Review of the figure showtng Inverse velocity for A plants only shows numerous stations with predicted time to failure (i.c., interception of the inverse velocity = 0 line) in the spring- stttrtmer and fall of 1997. However, all of these were effectively arrested by the RCC buttress with the exception of 28 which was impacted (slowed) but not arrested. There are two additional stations of conccm on this figure which are station 27 with a projected failure date of March 1998, and station 16 with a projected failure date of January 1999. However, the Logarithmic Displacement Velocity plot for A planes only would project failure data of October 1998 gad June 1998 for stanons 27 and 28