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GEOTECHNICAL STABILITY EXHIBIT <br />There are a number of structures within two hundred feet of the permit boundary of Tomichi Pit. <br />A minimum fifty foot buffer will be maintained from the permit boundary line to all excavations. <br />All reclaimed areas will be restored to relatively flat (5 -15 %) slopes except for the side slopes. <br />The sidelopes will be mined to 3H:1 V down to a foot below water level, then 2H:1 V to the pit <br />bottom. The slopes will then be backfilled to a minimum configuration of 3H:1 V down to ten <br />feet below the water level, then 2H:1 V to the lake bottom. Backfilling to gentler slopes will <br />occur in some areas to produce an organic lake shore appearance. <br />Design factors <br />The designed slopes at the Tomichi Pit were evaluated using Bishop's Method of slices in a <br />slope stability software program. Three scenarios will be evaluated: <br />1. Figure GS -1 table standards for the gravel (GP) and backfill (SM) materials, with <br />compaction of the backfill at 95% of maximum dry density <br />2. Reduction of the cohesion value for SM to zero. <br />3. Reduction of the cohesion value for SM to zero, and a backfill compaction of 75% of <br />maximum dry density <br />Each of these scenarios uses the slopes proposed in the permit: mining to 3H:1 V slopes down to <br />two feet below the water line, and then 2H:1 V slopes, with backfilling extending the 3H:1 V <br />slope down to 10 feet below the water line, and then 211:1 V slopes to the bottom. All three <br />scenarios can be seen on Figure GS -2. <br />The backfill material will consist of overburden and screening fines, and therefore is considered <br />to be an SM class material. A Buckhorn Geotech report is attached to this exhibit showing the <br />classification of the gravel material as GP. See Figure GS -1 for the material class descriptions. <br />Backfill final placement will be by dozer, and therefore compaction can be assumed to be well <br />over 75% of maximum dry density. To achieve sufficient compaction, backfill will be placed in <br />12 inch or lower lifts and driven over with a dozer. In the event of a planar failure along the <br />plane between the backfill and the native gravel material, there is no risk of damage to the <br />Tomichi Pit, December 2013 GS -1 <br />