2008-04-30_REPORT - M1973021 (3)

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low probability of wedge or toppling failures. Markland orientation data also indicates a low • probability of plane failure; the plane failures are most probable on the foliation surface when • it dips out of the highwall face at greater than approximately 38 degrees. These results are similar to previous geotechnical addendum data. Therefore projected failures are estimated to be limited to raveling of smaller blocks in localized areas. These localized failures are not • anticipated to extend further than the bench width. It is likely that active mining in the North Quarry expansion will be completed in 2008. As such, AI requested a summary of the mining activity and conditions for the North Quarry for . future reference and inclusion in the Annual Report. This report is dated February 7, 2008 and contains survey data from September, 2007 (The approximate quarry bottom was lowered another 40 feet after this survey was completed as reflected in this geotechnical addendum). . This mining summary is included in Appendix B. The highwall conditions observed for the South Quarry for 2007 indicate that the rock is • predominantly "competent". Although the rock is moderately to highly weathered, joint orientations are primarily favorable to the highwall development orientation and joint • roughness and persistence is generally favorable to retain blocks in place. Further, no features were observed that are anticipated to be detrimental to slope stability. Markland orientation • data indicates very low probability of plane or wedge failure. Markland orientation data ld f h , ie e indicates a slight potential for toppling failure which concurs with observations from t however, blocks are typically small and in most cases are held in place due to the rough, wavy • nature of the foliation joint surface. Therefore projected failures are estimated to be limited to • raveling or toppling of smaller blocks in localized areas. These localized failures are not ns ti id l i . o era cons ona anticipated to cause any problems beyond operat . 5.0 CONCL IISIONS The observed condition of the slopes within the Central Quarry appears to be stable. • Observations of the Central Quarry include: • No large scale failures in the past year. • Minor accumulations of small rocks (up to 1 '/2 feet diameter) on bench surfaces. • • Nearly all material was contained on the adjacent bench surfaces with very little evidence of the material proceeding down slope to subsequent benches or into the • water storage reservoir. • The stabilized slope in the northeast section of the Quarry did not exhibit any instability or large erosional features. Mining in the North Quarry in 2007 appeared to adhere to the mine plan and extended the • quarry depth by approximately 40 feet (1 bench). This bench contains further rock to be mined towards the east side of the quarry. Current mine slopes are being excavated to approximately • the default slope configuration utilizing 1~:1 highwall height to bench width. Rock observed in the highwalls was predominantly competent granite or biotite gneiss with the following • exceptions: • Bench D stations 1+90 to 2+OS consisted of a shear zone of weathered biotite gneiss. • Bench D stations 4+10 to 5+60 consisted of biotite gneiss and biotite schist shear zone. -7- • F:\3919_038 W nnual_Report_2007\Gcotcch_Addcndum_2007W nnual_RcpoR_2007_Gcotcch.doc Apri 12008