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Ms. Catherine Robertson <br />Mazch 20, 2008 <br />Page 5 <br />significant surface impacts are very likely including surface cracks that will <br />intercept any water flow, both sheet flow and channeIized flow, including Big Salt <br />Wadi a perennial stream (as indicated in Appendix C Subsidence). Where hard <br />sandstone or other brittle rocks aze present at the surface, ground cracking in this <br />scenario is likely to be extensive. <br />In addition, back stowing entries is not common practice and if discussed as a <br />necessary measure, the applicant will have to demonstrate that this can be <br />accomplished during routine mining operations. This subsidence control <br />mea:3ure will need to be included in our DBMS permit application. <br />The DRMS believes that the 200 foot "minimum overburden depth" is too <br />liber~aI to prevent undesirable impacts. Given the thickness of the coal to be <br />minE:d and the subsequent subsidence of 6-9 feet, we believe that the impacts <br />described on page C-4 of the PDEIS are likely, but they may be understated. <br />Otherwise we concur with the subsidence estimates and the methods used to <br />calculate subsidence. <br />Please feel free to contact me if you have any questions regarding our review of the Red <br />Cliff Mine F'DEIS. <br />Sincerely, <br />/~'1;~/~ I? ~3 <br />Michael P. I3oulay <br />Environmental Protection Specialist <br />C: Sandy Brown, Dan Mathews, and Kent Gorham/DRMS <br />Glenn Wallace/BLM <br />