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<br /> <br />' [n addition, mining has generally continued in a sequence of 40 ft [0 80 ft vertical highwalls <br /> with benches equal to or greater than 40 to 80 ft wide and, Locally, as wide as 100 ft creating <br />' stable interim highwall slope angles. Mining interim 80 ft maximum vertical highwalls with <br />benches equal to or greater than 80 ft wide was done in 1998 to develop the North Quarry <br /> and to tie-in [o older benches established under the original mine plan. As [Wining progressed <br /> to tie-in with existing benches a[ the wes[ end of the North Quarry benches and highwalls <br />' were tapered to smaller widths and heights as necessary. Current mining of 40 ft highwalls <br /> progressing in a westerly direction has improved interim stability conditions. <br />' Due to the geome[ry of the Curren[ mining configuration with respec[ to the final proposed <br /> mine buildout, none of the 1998 highwalls in the North Quarry are expected to be fully <br /> developed final quarry highwalls. About 200 linear ft of two 40 ft to 60 ft highwalls near the <br />' north-central part of the North Quarry between approximately El. 6,760 ft and EI.6,860 ft are <br /> approaching final highwall locations near the haul road that runs inside the Limits of Mining. <br /> Because no final highwalls were established in the North Quarry in 1998, detailed <br />' geotechnical evaluations were not necessary and were not performed. Both Haley & Aldrich <br /> and CAMAS made observations, however, to assess highwall stability and sttfery, <br /> respectively. <br />1 <br /> <br /> <br />1 <br /> <br />1 <br /> <br />1 <br />LJ <br />1 <br /> <br />' G:~PROIECfS"_0200 Morrison Qrazry\OpHArvwal ftepon Geornhnrcal Adtlrndum11998\9Hrpi markup dce Page 4 <br />