2008-08-01_REVISION - C1996083 (3)

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Conclusion I b states "The yield acceleration needs to be greater than the applied acceleration for significant deformations to occur. " Figure 3.4 shows a yield acceleration much greater than the average maximum acceleration at all depths. Therefore, it seems that significant deformations are likely. Please clam or correct this important conclusion as necessary. The Division has no further concerns. In the December 28, 2006 submittal, page 19 of the referenced report was revised accordingly 34. Concerns addressed in the SEO June 11, 2003 letter with respect to the landslide stability analysis should be addressed prior to longwall mining within a one-mile radius of the dam. Apparently, Jim Stover has indicated that this information will be submitted later this year (2006). The Division has no further concerns. Exhibit 20 of Volume IIIA, provided in the May 12, 2008 submittal, addressed the remaining concerns. 35. Confirmation is needed that actual seismic events experienced now and in the future are within the range of events used in the modeling and prediction of impacts (or lack of impact) to the dam. Bowie should determine a seismic "threshold event" that would trigger more detailed monitoring and analysis of the dam should this threshold event occur as a result of mining. No data has been submitted at this time. However, again, Jim Stover has apparently indicated that actually seismic data will be submitted later this year. It should be noted that other information seems to indicate that between September 1, 2004 and November 18, 2004, Bowie experienced mine induced seismic events of 3.2 M, 3.3 M, and 3.5 M. The GEI analysis included one event of 4.2 and a combination ofsmaller events, the largest of which was 2.5 M. It may be important to re-evaluate the previous analysis with larger events more indicative of actual conditions. Bowie should submit actual data recorded since seismic stations were brought on-line for review in conjunction with this revision. The Division has no further concerns. The seismic monitoring plan that was provided in Exhibit 18 of Volume IIIA of the May 12, 2008 submittal was reviewed and is acceptable. 36. The Division does not concur with conclusion #7 of the June 2002, GEI report that's states "additional monitoring of the dam and saddle dam... is not required to address risks associated with mine-induced seismicity. " The Division concurs with the SEO that seismic monitoring is required at the Bruce Park Dam as mining moves inside a one-mile radius of the dam. Without actual monitoring data to compare to pre-mining analysis and conclusions reached, we cannot evaluate the adequacy of any seismic monitoring plan at this time. Bowie should submit actual data along with permit text clearly stating a seismic monitoring plan for the Bruce Park Dam. It is the Division's understanding that the Division of Water Resources will review and comment on BRL's monitoring program for the Bruce Park Dam, saddle dam and Bruce Park landslide. When the Division receives this letter from the Division of Water Resources, it will be forwarded to BRL. 12