2007-06-06_REVISION - C1996083 (2)

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27. In reviewing the information on Map 14B, Map 27 and the "Station Locations " figure on the second page of the Exhibit 18 report, it appears that the closest that longwall mining will get to a seismometer is 4500 feet by the end of 2006. Assuming that PR-10 is approved by the end of 2006, please explain how BRL intends to show that seismic events recorded at a seismometer that is no closer than 4500 feet away from the generating longwall mining event can be used to predict the seismic effect on the Bruce Park Dam from events that are generated by longwall mining that will be 2500 feet away from the Bruce Park Dam. In the submittal dated December 28, 2006, BRL stated that a site-specific attenuation relationship will be developed to determine the effects at varying distances from a seismic source. BRL further stated that this process is routinely used by seismologists to determine ground motion at a site from a distant earthquake. However, since BRL is proposing to mine within 1390 feet of the Bruce Park Dam, the Division requests that BRL obtain seismic data generated by mining events that are about 1390 feet from a seismic receiving station. In their letter dated February 22, 2007, the USDA-Forest Service is requesting that, when mining approaches seismic station FGH, additional seismic data recording and analyses be made and compared to current modeling. The Division agrees with this approach. Please submit an analysis of the seismic data obtained when mining gets to within about 1390 feet of seismic station FGH. If the analysis does not confirm the current seismic modeling approved in PR-10, appropriate changes to the modeling will need to be made. 28. Since the Hughes cabin is mentioned in Section 2.05.6(6)(a)(ii)(A) on revised permitpage 2.05-103, please include a discussion of the cabin in Section 2.05.6(6)(b)(i)(C) and describe any potential effects, if any, on it from subsidence. The Division has no further concerns. A discussion was added to page 2.05-107 of the December 28, 2006 submittal. 29. In PR-10, BRL is proposing to longwall undermine Dove Gulch and Dove Cave. The Division's regulations do not necessarily prohibit these actions, although certain protection or mitigation measures may be needed. However, the stipulations on Federal Coal Lease COC 61209 mayprohibit such actions. If the USDA-Forest Service does not approve the proposed actions, then BRL does not have the right to enter and longwall undermine those two areas. In this case, the Division would not be able to approve PR-10 as written. The Division will need documentation that the USDA-Forest Service approves of these changes. In a letter dated February 22, 2007 to the Division, and included in this adequacy review letter, the USDA-FS is approving the undermining of Dove Gulch and Dove Cave with conditions. Please respond to the permit text changes requested by the USDA-FS in their February 22, 2007 letter. 30. On revised page 2.05-110, the last sentence reads in part "...subsidence does affect... ". This should be revised to state "subsidence does not affect... ". The Division has no further concerns. The sentence in question was moved to page 2.05-111 and this page was revised in the December 28, 2006 submittal. 9