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Mountain Coal Company West Elk Micro Post Office Box 591 Somerset, Cokxaoo 81434 Telephone 970 929,5015 Fex 970 929.55.% April 18, 1997 l RF(`FI~f~D Mr. Michael Boulay AI'tC ~ 1 ~88~ Colorado Division of Ivtmerals and Geology 1313 Sherman Street, Room 215 Denver, CO 80203 Biwieien m nwieimro ~ mnelHpr RE: Technical Revision No. 79; West Elk Mine; Permit No. C-80-007 Dear Mr. Boulay: III IIIIIIIIIIIII III 999 Mountain Coal Company (MCC) has reviewed the Division's adequacy review letter for the above referenced technical revision, and per our meeting on April 15, 1997 presents the following responses and additional information. Cultural and Historic Resource Information Subsequent to the cultural and historical resource survey performed by WESTEC in 1995, another survey was conducted in September 1996 following the guidelines of the U.S. Forest Service. This second survey covers the area to be affected by the RPE. The results of that survey were submitted to CDMG with Permit Revision No. 7. No sites eligible for nomination to the National Register of Historic Places were identified in the survey. Ground Water Information 2. MCC has reviewed the RPE design drawings in relation to the peak groundwater levels that have been measured since January 1996. This data is contained in Appendix I. MCC's findings show that the maximum groundwater elevation at LRP-4, which is located within the footprint of the RPE, was approximately elevation 6081, or about 15 feet below ground surface elevation 6096 and represents about 2.76 feet of rise over the annual hydrologic cycle (refer to Appendix I and the Phase 1D cross section). At LRP-1, which is outside the western edge of Phase 1D, the highest measured groundwater depth was approximately 27 feet below ground surface. A worst case scenario would be to double the maximum observed groundwater rise of 2.76 feet at LRP-4, as it is located near the low point of the RPE footprint, and there would be over 10 feet of elevation difference between the maximum groundwater level and the bottom of the RPE liner. The lowest elevation of the liner in all other areas of the RPE is at elevation 6110, which provides up to l4 feet of