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sPr" m 148 VoMM GEOTECHNICAL STABILITY EXHIBIT(CONT) Page 2 lake it tends to fan out so the underwater slope is 5 : 1 or less In the worst case scenario where the 14 foot tall backfill highwall failed and sloughed off at rate of 5 : 1 the slope failure would still be 157 feet from the closest structure and the safety factor is 3 .24 : 1. This shows, that should any backfill slope fail, the impacts would not affect the closest structure and therefore cannot affect structures outside the limits of the backfilling area. Calculations In the past, Mr. Alan Sorenson reviewed Slope Stability Report prepared for the mine in Colorado and he suggested a simple methodology using the angles of the slopes in question to determine the Safety Factors. The material in use to backfill is an unconsolidated dirt that has a fairly fine structure. This, along with the lower part of the fill being in water, suggests that the potential to sough off to a shallower rate then sand and gravel prompted using a friction angle (4120) of 11 .31° (5 : 1) . Since backfilling began there have been no observations of bank sloughing on the back filled area. The closest point the fenceline is to the backfill face is 227 feet and the slope angle from the toe of the slope to the fence is 3 . 53° (0) Using this information the safety factors for the slope was calculated using the 11 . 31° as the friction angle. The Safety Factor is calculated using the formula FS = TancD =Tan0, where 0 is the slope angle from the toe of the slope to the closest structure (permit line) . SLOPE EVALUATED CALCULATED FACTOR OF SAFETY FOR SLOPE ANGLE NATURAL SLOPE ANGLE 0=11.31° PROPOSED FILLING SLOPE 63.5° 0.1 ('/:1) SLOPE FROM TOE TO 3.530(1) 3.24 CLOSEST STRUCTURE 3.25° angle is calculated using 14 feet slope height and 227 feet horizontal distance from the toe of the fill face to the permit line .