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highwall mining experience at Colowyo Mine has shown weak mudstone roofs <br />tend to fall when exposed and soft floor conditions could hinder trafficability. <br />Please address whether you plan on leaving a four -inch coal roof /floor barrier <br />as recommended by AA when encountering weak mudstone to prevent roof <br />falls and any other issues that may occur. <br />Response: Colowyo is fully committed to follow all recommendations <br />presented in the AA Geotechnical Report (pages vi, 36, and 60) pertaining to <br />this matter. Colowyo will develop mine plans to leave 4 inches of roof coal, <br />and if soft floor conditions are encountered, Colowyo will leave a similar <br />amount of floor coal to increase trafficability. <br />5. According to AA, interburden thickness -to -lower seam mining height ratio <br />needs to be 2.0 or greater. Please discuss how you plan on highwall mining a <br />section of E and F Seams with an interburden thickness -to -lower seam mining <br />height less than 2.0 while maintaining a safety factor of at least 1.5. <br />Response: Colowyo will develop mine plans to appropriately adhere to the AA <br />recommendation of interburden thickness -to -lower seam mining height ratio <br />needing to be 2.0 or greater. Colowyo will ensure this by limiting mining <br />height (no more than 5.0 feet) and depth of penetration in the F seam (no <br />more than 1,100 feet) relative to the interburden thickness between E and F <br />Seams to obtain adherence to the 2.0 ratio and conformance with maintaining <br />a safety factor of at least 1.5. AA makes this same recommendation on page <br />60 under Multiple Seam Mining, which Colowyo will adhere to. <br />If you should have any additional questions or concerns, please feel free to <br />contact Tony Tennyson at (970) 824 -1232. <br />Sincerely, <br />��UZ� <br />Chris McCourt <br />Mine Manager <br />Enclosure <br />Cc: file CF 1.1.2.89 <br />A mining property of Western Fuels- Colorado, A Limited Liability Company <br />