REP46333

• Permit No: M1973021
• IBM Index Class Name: Report
• Doc Date: 4/10/2007
• Doc Name: Geotechnical Addendum
• From: Tetra Tech
• To: DRMS
• Media Type: D
• Archive: No

The baseline rock conditions described in Amendment 3 to Mining Permit M-1973-021 are
"competent" for granite or biotite gneiss and "poor" for shear zones or highly to extremely
weathered zones that have the potential to decrease the stability of the slope. The conditions
observed in highwalls mined in 2006 in the North Quaay indicate that the rock is predominantly
"competent" with localized areas of "poor". Further, no features were observed that are anticipated
to cause large block size failures, rather the projected failures are estimated to be raveling of
smaller blocks in localized areas. These localized failures are not anticipated to extend further than
the bench width.
5.0
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 '/~ 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 southeast section of the Quarry did not exhibit any instability or
large erosional features.
Mining in the Notch Quarry in 2006 appeared to adhere to the mine plan and expanded the quarry
area towards the east highwall and south highwall mining limits. 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 granitic gneiss with the
following exceptions:
• Lower highwall station 0+35 to 0+50 consisted of a bowl shaped failure of weathered
granitic gneiss.
• Lower highwall station 0+75 to 1+35 consisted of highly weathered biotite gneiss and
biotite schist.
• Upper highwall station 3+00 to 4+50 contained a shear zone consisting of slightly
weathered biotite gneiss.
The combination of the moderately dipping foliation and various joint set orientations creates the
potential for continued localized areas of instability and block raveling in the future. The sections
of poor rock observed in the 2006 mined areas in the North Quarry are localized areas and
instability arising from these features is anticipated to be contained on bench surfaces. Based on
our observations, these conditions encountered are anticipated to remain relatively minor, with the
overall slope conditions considered stable, and warrant only operational considerations.
F:U919_038~Annual_Repott_2006~Annual_Report_2006.doc - 5 - Apnl 2007