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South Permit Boundary PROJECT NO. 24004 <br />Bowie #2 Mine <br />Paonia, Colorado <br />PURPOSE AND SCOPE OF STUDY <br />This report presents the results of the rockfall hazard evaluation study pertormed <br />for the south permit area at the Bowie #2 Mine near Paonia, Colorado. The <br />study area included the south facing slope between Terror Creek and the current <br />Bowie #2 Mine access road. An earlier study by Yeh and Associates, Inc., dated <br />November 20, 2003, evaluated the rockfall potential on the east-facing slope <br />above the mine facilities. This second study was conducted for the purpose of <br />evaluating the potential impacts from rockfall hazards on the slope above the <br />south permit boundary. A mined-out seam of coal below the subject slope will be <br />collapsed in the spring of 2004. Subsidence of the ground surface is expected to <br />occur over several weeks or longer. Portions of the subject slope are within the <br />projected draw angle of the subsidence and may produce rockfall. Other potential <br />source areas within the permit boundary are outside of the projected draw angle <br />but have been considered because of the uncertain level of ground vibration <br />• likely to be caused by the subsidence event. While some subjective evaluation of <br />potential source areas was necessary to establish likely rock trajectories, the <br />primary focus of this study_was to evaluate whether statistically probable <br />trajectories would extend outside of the permit boundaries, and if so, to evaluate <br />potential hazards created by these trajectories. <br />Our evaluation is based on geologic reconnaissance, asite visit and computer <br />simulation of potential rockfall events. Mapping was conducted to obtain <br />information on the existing conditions and slope configuration. The information <br />obtained was analyzed to evaluate the potential rock trajectories. This report has <br />been prepared to summarize the data obtained during the study and to present <br />our conclusions and recommendations concerning rockfall hazards. The study <br />was conducted in accordance with our proposal dated January 28, 2004. <br />• <br />