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6fiibit 60C <br />Subsidence Evaluation and 2004 Geologic Hazard Field Observations <br />West Flatiron Lease Area <br /> <br />• <br />for the U.S. Bureau of 1~Imes (Engineers International) indicated that surface crack depth rarely is <br />greater than 50 feel Cracks will also be less extensive or terminate where shale and claystone <br />layers are presert. <br />Based on annual field subsidence observations in the Apache Rocks and Box Canyon mining <br />areas by the author, the maximum crack depth is estimated to be considerably less than the 50- to <br />100-foot calculated range. The maximum crack depth in bedrock in the West Flatiron Lease area <br />is estimated to be 1) 5 to 20 feet in terrain sloping less than, or equal to, 30 percent, and 2) 10 to <br />35 feet in terrain sloping more than 30 percent (Table 1). <br />831-032.650 Wright Wafer Etgineers, Inc Page 16 <br />November 2004 <br />