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TR-36_ RESPONSE TO CDM COMMENT OF MAR H 4 1996 <br />The Division has indicated two primary azeas of concern regazdmg TR-36: 1) Subsidence and 2) <br />Sealing of Coal Seams. Colowyo's response is as follows. <br />1. SUBSIDENCE <br />The Division speculates that the auger bores could coalesce at depth causing an increased chance of <br />subsidence ofthe West Prt F>71 Because of this concern the Division requested that monuments be placed on <br />the reclaimed surface. <br />Colowyo believes the Division's concerns aze not warranted for the following reasons and that our <br />proposal for subsidence monitoring of the rechtimed surface remains appropriate. <br />A) Our experience with Auger Area #1 showed that the auger bores aze controllable and their <br />parallel configuration can be maintained. Furthermore, since coalescing of bores would severely <br />reduce coal recovery, and the Contractor auger mining company is paid based on tons mined, there <br />is plenty of incentive to keep the bores under control <br />B) The coal recovery within the Auger Area #1 was in the range of 400 to 500 feet in depth. No <br />such coalescing at depth and loss of coal recovery was encountered. <br />C) If, for some reason, the bores are not "exactl}~' parallel, for every "thin" web, there will be <br />a corresponding "thick" web, thus, providing a compensating affect to maintain the design stability. <br />D) Curiously, the issue of establishing monuments on the reclaimed surface was also addressed <br />during the previous approval process for TR-21, Auger Mining #1. At that time Colowyo pointed <br />out that it would be impossinle to sepazate the effects of backfill spoil settlement from any effects of <br />subsidence due to auger mining. The Division concurred with our assertion and accepted our plan <br />to place perimeter markers (steel fence posts) azound that initial auger area. (A copy of the <br />Division's May 26, 1992 correspondence is included for your information.) <br />Colowyo has again proposed to place perimeter mazkers on the perimeter of Auger Area #2. <br />Given that the Division has previously concluded during the review of Auger Area #1 that <br />Colowyo's proposed method for monitoring the auger area would provide superior utility over <br />utilizing monuments, and that the Division's proposal `would not provide accurate information," <br />Colowyo believes our present proposal remains the most appropriate long term solution for <br />monitoring any surficial effects of auger mining. <br />2 SEAT ING COAL. SEAMS <br />Since the initial evah>ation of Colowyo's proposed West Pit Fill by CTI/fhompson in 1991, Colowyo <br />has conducted significant additional activities. We have completed additional exploration activities to more <br />accurately define the coal reserves in the West Pit and we have opened the initial West Pit box cut. Because <br />of these activities CTL/Ihompson now has additional geologic information at its disposal with which to draw <br />from when addressing the concerns expressed by the Division. Attached please find a letter from <br />CTL/Thompson addressing the Division's concerns specific to TR-36. <br />