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' SECTIONTWO seeaal~e Analysis "base case" material properties were applied to the model and the steady state plu•eatic ' surface corresponding to tho ultimate embankment height was estimated. 5. A transient seepage analysis was performed for the ultimate height case. The "base case" ' conductivity of the tailing sands was also conservatively increased by 1 order of magnitude, as was done for the existing height case. The phreatic surface at the end of six w~;eks was evaluated for the elevated pond. ' 6. The transient seepage analysis was continued for the post-closure embankment conditions to evaluate the gradual lowering of the elevated phreatic surface after the pond has been drawn down. We assumed the decant pond was completely drained for the post-closure conditions. ' 2.3 SEEPAGE MODEL AND ASSUMPTIONS ' The seepage analyses were performed using the finite element softwaze program SEEP/W, version 4.22, developed by Geo-Slope. ' Cross Section Geometry The same embankment study section (Section 8), as presented in our April 2000 report, was used ' and updated by raising the embankment slope 4H:1 V (horizontal:vertical) to the cun•t:nt crest elevation of 8810 feet. The following three components of the model cross-section Here kept the same, as described in our Apri12000 report. • The internal geometry of the study section was not changed, but was extended to ~:onform with the current embankment height. ' • A sand beach width of 1,000 feet with a 1 percent inwazd slope was maintained frir the normal operating pond conditions. ' • The natural ground profile beneath the tailing dam was assumed to be at about EI, 8600 feet. For the ultimate height case, the cross-section geometry of the raised embankment wt~s estimated by raising the crest of the existing embankment geometry to El. 8900 feet on a 4H:1 V slope. The t sand beach width for the raised section was estimated to be 1,000 feet A beach width of 100 feet was assumed at the conclusion of the PMP event with the elevated ' decant pond for both the existing and ultimate height conditions. Calibrated Material Properties ' The seepage model was initially configured using a "best estimate" of the material conductivity values, based on the laboratory tests performed for our report, dated April 2000, and our ' experience with other tailing dams of this type. These conductivity values were adju:;ted from initial estimates to calibrate the model such that the computed phreatic surface closely matched the observed piezometer readings. Piezometers A-8, B-8, C-8, D-8, and E-8, located along study ' Section 8, were used in the calibration process by using the highest recorded measurements that were provided by Climax for the period from January 2000 through November 2000. The calibrated material conductivity values aze summarized in Table 1. *~` N:NROJEGTS6819610_HENDERSON MILL_BNiG~SUB 008.0 VROJ DELNVI#11lL RJ.D0~1't4JUL-01~~ 2-2 1 v-r+