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Fall 2008 Subsidence and Geologic Field Observations <br />Box Canyon, Apache Rocks, and South of Divide Mining Areas <br />• For dialnostiC purposes. the largest difference hct\1CC11 subsidence cracks and Construction <br />cracks is that the construction cracks: 1) have a less regular pattern. 2) are related to the material <br />they occur in. and 3) lack any spatial relationship to the lonpull mining geometry. <br />At; <br />? r <br />1 <br />J <br />11 <br />Figure 2. This cutbank in bedrock is located above mined Longwall Panel 17 in an excavation <br />area at well site MDW 17-02. Cracks on either side of the dominant, irregular crack (right middle) <br />are natural or the result of construction. The most prominent irregular crack has an estimated 75 <br />percent likelihood of being mine related. <br />2.3 Desiccation Cracks <br />Desiccation cracks tend to occur in cla\stones and siltstones of the Mesaverde and Wasatch <br />Formations in the West Flk Mine area ?khere the rocks are 1ycathered to clays and silts (Figure 1). <br />The process of desiccation involves the shrinking of previously \vetted clays and silts during the <br />di-vino process. <br />831-032 790 Wright Water Engineers, Inc. <br />December 2008