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<br />III IIIIIIIIIIIIIIII <br />5731 State Highway 13 <br />Meeker, Colorado 81641 <br />(303) 824-4451 <br />May 10, 1993 <br />Mr. Steve Wathen <br />Reclamation Specialist <br />Colorado Division of Minerals and Geology <br />215 Centennial Building <br />1313 Sherman Street <br />Denver, Colorado 80203 <br />Re: Colowyo Mine, Permit C-81-019 <br />Auger Mining (TR-21) Response to PAR <br />Dear Mr. Wathen: <br />~~rJ~1~c0 <br />MPV 11 ~gg3 <br />~ ~,»en)9 <br />1 t'1R~~iJG <br />D.~~y~0n u <br />Attached for the Division's information is a report title <br />"Colowyo Auger Mining Implementation, Technical Summary Report" by <br />Norwest Mine Service, Inc., May 4, 1993. The report provides <br />technical engineering information regarding Colowyo's auger mining <br />proposal. We believe the report includes the material necessary to <br />resolve the Division's remaining issues as outlined in the March <br />26, 1993 Preliminary Adequacy Review (PAR). <br />In particular, the remaining issues can be found in the <br />following locations in the report and are addressed as follows: <br />Subsidence - Section 4.0, page 16, states "The support webs are <br />designed for zero yielding, which will prevent surface subsidence. <br />The only surface effect of auger mining may be due to a very minute <br />amount of elastic deformation of support webs. Maximum, cumulative <br />vertical deformation of the support webs is estimated to be about <br />0.4 in at the C seam level, but the FE model indicates that only <br />about 0.1 in of this deformation will be transmitted to the <br />surface. <br />Hydrologic Impact of Auger Mining - Section 5.0, page 24, concludes <br />that "It is anticipated that the impact of auger excavations on the <br />groundwater regime will be negligible. If percolating groundwater <br />(from specific precipitation events or snow melt) is intercepted by <br />the auger excavations, there will be no flow from the openings, due <br />to the down-dip inclination of the holes". <br />Potential for Spontaneous Combustion or Coal Strength Reduction Due <br />to Drving - Section 6.0, page 24, summarizes the limited potential <br />for fires due to the lower rank of the coal and the limited amount <br />of time that the auger openings will be exposed to the atmosphere. <br />Regarding reduction in strength due to air-drying the report states <br />"The support webs have been designed with an adequate factor of <br />