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Volume IIIA, Tab 21 <br />• A Determination of Angle of Draw <br />D-seam Longwall Mining <br />Bowie Resources, LLC <br />Summary <br />Bowie Resources, LLC, (BRL) has monitored subsidence resulting from longwall mining <br />in the D-seam at the Bowie No. 2 Mine since 1999. The results of analysis of this data <br />indicate the draw angle varied from 10 degrees to 22 degrees with an average angle of <br />draw (draw angle) of 16 degrees. <br />Scope of Study <br />The study was designed to summarize, analyze and review the available data from the <br />BRL subsidence monitoring program at the Bowie No. 2 Mine. The data set represents <br />monitoring data obtained between 1999 and August of 2005 for the east mining district <br />and from 2002 for the southwest mining district (Figure 1). The analysis represents pre- <br />and post-mining data for the D-seam longwall panels. <br />Data <br />The data base used in this study consisted of approximately 740 subsidence data points <br />collected over a six-year period from 164 subsidence monitoring points. Data were <br />collected using a global positioning satellite survey system. Accuracy of this survey <br />• methodology is approximately ±0.15ft. Monitoring frequency varied from annual to <br />semi-annual based on mining activity and surface accessibility. Winter snows and spring <br />mud make surface access and subsidence monitoring difficult to impossible. <br />The subsidence data are collected from a network of subsidence monitoring points <br />installed over the east and southwest mining districts of the BRL D-seam mine workings. <br />These workings include mains, a continuous mine pillar section, gateroads, longwall <br />panels and areas well outside the expected subsidence zone. <br />Analysis Methodology <br />All the available subsidence data was compiled along with mining face positions for each <br />survey date. These data were then organized by subsidence monitoring point into lines of <br />data generally transverse to the long axes of the longwall panels. A review of the data <br />indicated that six of these lines could be used to calculate a draw angle from longwall <br />mining of a specific panel. The data from these monitoring points were such that all the <br />measured subsidence each monitoring point could be attributed only to mining of a single <br />longwall panel. Other data represented points where the timing of mining and monitoring <br />were such that each point was subject to subsidence from both the initial panel as well as <br />the adjacent panel. <br />The total measured subsidence for each point was plotted on a graph as illustrated in <br />Figure 2 for analysis line A-A'. The location of the edge of the underground longwall <br />panel was plotted to scale and the angle between the point of zero subsidence and the <br />• edge of the longwall panel was calculated. This arrangement is illustrated in Figure 2. <br />P12- 10 <br />? PP?2aU?? <br />112 y /a a