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+ ~ TWBNTYM166 ~ COA6 COMPANY A Cyprus Amax Company iiiiiiiiiiiiiiiiiii Twentymile Coal Corporation 29515 Routt County Road # 27 Oak Creek, Colorado 80467 303-879-3800 May 31, 1995 4ECEIVED Mr. Kent Gorham JUN p ~ 1995 Environmental Protection Specialist Colorado Division of Minerals and Geology Division of Minerals & Geolo 1313 Sherman Street, Room 215 9Y Denver, Colorado 80203 RE: PERMIT C-82-056: TECHNICAL REVISION 95-19: SANDSTONE CLIFF MITIGATION PLAN Dear Mr. Gorham: In response to the second round of adequacy questions raised in your letter of May 4, Twentymile Coal Company (TCC) provides the following information for your review. Adequacy item responses are presented in the order comments were received and revised permit materials are included with this submittal as necessary. Comment 2.) The Table of Contents is still incorrect. Please correct and resubmit. Response 2.) The Table of Contents page vi has been corrected in accordance with this comment. Comment 3.) The intent of the original question was to have TCC identify for each zone the specific protection barrier to be constructed for each zone and provide cross-section and map information which corresponds to each barrier. The current map does not properly represent the disturbed area based on the text identifying the barrier to be constructed for each zone. Also, as per our phone conversation, it is my understanding that the information in Section 7 of Exhibit 7F was not meant to accurately depict the crossectional area of the tested barriers. It is my understanding that crossections are currently being developed for each barrier, which, when compared to Drawing 2, will match with the disturbed area shown on Drawing 2. If the disturbed area is shown as 100 feet on Drawing 2 then TCC will be held to this limit in the field. Please submit the appropriate information. Response 3.) Revised copies of the text pages (20, 21, 22, and 25) presented as Section 4 of Exhibit 7F are included with this submittal. Figures 4-1 and 4-2 in this section (pages 23 and 24) remain unchanged. The revised text in Section 4 specifies the protection barrier to be utilized in each zone (see page 25) and references Drawings 2, 3, and 4, and Appendices C and D for specific design and construction information as appropriate. Drawing 2 has been revised to reflect the maximum potential disturbed area associated with the project. TCC will limit disturbance to the areas depicted on this Drawing. Drawings 3 and 4 are newly submitted and depict plan views and cross-section location information for the selected mitigation measures to be implemented. The cross-section points depicted correspond to elevations presented in Appendix D Table 3. Appendix C is newly submitted and consists of revised CRSP Model simulations demonstrating the v- bottomed trench/berm configuration provides better pertormance than the flat-bottomed trench/berm configuration previously recommended for use in selected zones. Appendix C also provides a reevaluation of zone 9 section 1 utilizing revised slopes in the trench/berm at this location.