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• <br />3.2 Far-Field Horizontal Stress <br />The USBM researchers measured the far-field horizontal stress in the Bowie No. 1 mine <br />using the overcoring technique in roof rocks. These measurements were obtained at two <br />locations at the Orchard Valley Mine (Bickel 1993). More recently, another <br />measurement was completed in the Bowie No 2 mine using the same technique. Both sets <br />of measurements are consistent and reliable and thus provide a good estimate of far-field <br />horizontal stress in the vicinity of the Terror Creek. Table 1 provides a summary of these <br />measurements. <br />Table 1 -Far-field measured horizontal stress in the BRL properties. <br />Site Depth of cover, Max stress (P), psi Min stress (Q), Orientation of <br /> ft psi P <br />1 (Orchard 340 1,100 240 N 69° E <br />Valley) <br />2 (Orchard 1625 1,630 480 N 83° E <br />Valley) <br />3 (D Seam, 1,000 1,330 245 N 85° W <br />Bowie No. 2) <br />Overall trend N 80° to 90° E <br /> <br />Regional measurements show excess horizontal stress in the Somerset Coal Field along <br />the regional structural trend (N 74° to 80° E). Horizontal stress is only gravity induced <br />along the secondary direction (N 10° W). The excess stress is moderate, but increases <br />with depth (table 1). The far-field horizontal stress is very anisotropic in this basin. The <br />ratio of maximum to minimum secondary principal horizontal stress (P/Q ratio) is <br />approximately 4 to 6 (Maleki and others 1997). The orientation of maximum principal <br />stress is consistent, trending east-west near BRL properties. It is possible that some stress <br />reorientation may be found near stream valleys. <br />To estimate premining horizontal stress at the Terror Creek, we have utilized the existing <br />measurements of shallow cover conditions at site 1 while accounting for variations in <br />0 topography using the results of measurements and modeling by the USBM (Molinda and <br />Maleki Technologies, Inc. Page 12