2008-04-30_REPORT - M1973021 (3)

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O TETRA TECM The original North Quarry Reservoir Plan was included in the fifth amendment to permit M-1973- 021. The reservoir plan defines a high water line between elevations 6020 and 6080 with a bottom at elevation 5770. The reservoir was designed below the 6455 elevation and, therefore, was planned to have 80 feet highwalls and 40 feet benches (Figure 1) Quarry development is controlled by a default slope of 1:1 (H:V) unless a geotechnical evaluation of the rock being mined indicates competent rock that can be mined at a steeper slope. The 80 feet highwalls with 40 feet benches required geotechnical evaluation clearance to be developed per the mine permit. GEOTECHNICAL EVALUATIONDATA In accordance with an agreement with the Colorado State Division of Reclamation and Mining Safety (DBMS), AI contracts a geotechnical evaluation to be performed every year. This geotechnical report is prepared as an addendum to the Morrison Quarry Annual Report submitted every year to the DBMS. The report contains rock mechanics data based on field observations and measurements of the rock being mined at the quarry. The data in the report is used to define the rock mass as either "competent" or "poor". Competent implies minimal stability issues are present in the rock mass and allows the default slope to be steeper than 1:1. Poor indicates a potential for rock mass instability through features such as faults, shear zones, or unfavorable foliation and/or joint combinations and may allow the default slope to be steeper than 1:1, however, typically the default slope value is retained in these areas. 2001 GEOTECHNICAL ADDENDUM The 2001 geotechnical addendum indicates mining in the North Quarry was completed on the north and east sections of benches to approximately elevation 6,595. The mine slopes were recorded as 60 feet highwalls with 40 to 70 feet benches. The rock described in the report was granitic gneiss with mafic and felsic intrusions (felsic dikes and pegmatites). Joints in the rock mass were described as closed with slight to moderately weathered surfaces and spacing of approximately Y2 to 2 feet. Foliation orientations vary greatly due to the folding of the rock with an average dip to the west. The rock mass was defined as primarily competent with the following exceptions defined as poor: • A shear zone, 6 feet wide, dipping 50-60 degrees SE • A wedge failure, 20 feet wide • A shear zone, 2-10 feet wide • A shear zone, undulating and continuous • An intrusive dike, 6 feet wide -2-