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n u Memo to Tony Waldron Bowie No. 2 Geotechnical Adequacy page 6 extracted thickness of 12 feet results in a projected maximum vertical subsidence of 0.69 x 0.56 x 12.0 feet = 4.6 feet, which is also significantly larger than the 3.5 feet maximum vertical subsidence projected by the preparer of Exhibit 15. The subsidence projections of Exhibit 15 and the appropriate maps will have to be revised accordingly. The preparer relates a selection of local observations in projecting an anticipated angle of draw for delineating areas to be effected by subsidence. The conclusion reached is the assumption of a 25° angle of draw for projection of subsidence boundaries. Experience at mines such as the York Canyon has concluded that draw angles can be effected by overlying surface slope. In general the angle of draw increases in the direction down topography slope, resulting in larger angles of draw downslope. However, experience at mines such as the Mt. Gunnison No. 1 and the Bear No. 3 suggest that 25° should be appropriate at the Bowie No. 2 mine. Subsequent inspection in the shallow overburden, near subcrop areas of the mine should verify the propriety of this assumption. 1.5 BREAK ANGLES The preparer states that the break angle "approximately corresponds to the cracks and fractures present at the ground surface due to subsidence." I believe it would be more appropriate, when generalizing, to assume that the break angle corresponds to the location of maximum residual cracking and fracturing present at the ground surface. It is not the only location in which cracking and fracturing would be expected to occur. Transient cracking will be expected throughout the panel and adjacent areas as the strain wave propagates behind the retreat line. The preparer further assumed a vertical break line for this study. Particularly in the case of the near subcrop, steep surface gradient areas, this assumption may be unfounded. A broad area should be thoroughly inspected for the development of surface cracking following the initiation of mining. 1.6 ZONES OF POTENTIAL FRACTURING The preparer states that the risk of surface fracturing will decrease as mining depth increases. This generally correct, except in the instances where mining encounters a significant discontinuity, such as a fault. As mentioned earlier, significant differential offset and resultant fracturing can occur rapidly above such a ground mass discontinuity. The preparer relates the unusually large surface cracking observed above the 1st West and 2nd West panels of the Bowie #1 mine. This area has been hypothesized to have undergone a general cantilevered failure of the outcrop barrier and remnant inter-panel