2007-06-06_REVISION - C1996083 (2)

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D. Letter, dated March 27, 2006, from the Colorado Division of Water Resources (Denver). E. Letter, dated March 29, 2006, from the Colorado Historical Society. F. Letter, dated April 13, 2006, from the Board of Delta County Commissioners. G. Letter, dated May 1, 2006, from the Western Slope Environmental Resource Council. H. E-mail, dated May 2, 2006, from Colorado Division of Water Resources (Denver). 1. Letter, dated May 2, 2006, from the USDA-Forest Service. J. Letter, dated May 2, 2006, from the Terror Ditch and Reservoir Company (with attachments). K. Letter dated May 16, 2006 from Jason Ward of the Colorado Division of Water Resources The Division has received two adequacy review letters as responses to BRL 's submittal dated December 28, 2006 Both letters are attached. L. Letter dated February 22, 2007 from the USDA-Forest Service. M. Letter dated June 4, 2007 from Jason Ward of the Colorado Division of Water Resources. Division's Adequacy Review Letter Dated June 6.2006 The proposed seismic monitoring plan is in Exhibit 18 of the revised materials. We believe the design, methodology, hardware, and software are appropriate for the analysis required by the Division. While this Exhibit discusses the technical aspects of seismic monitoring, it does not clearly discuss the monitoring plan with regard to timing, implementation, and reporting to the Division. Ultimately, some sort ofthreshold event will need to be determined, and an analysis of how much ground motion is acceptable at Terror Creek Reservoir without creating instability is also necessary. Additional stations relative to the mine plan may be necessary to confirm ground motion at or near the reservoir. The site-specific known seismic events being presently collected from the current array should be used in any future analysis that is required by part S of stipulation no. 9. 33. Included with the revised materials in Permit Revision 10 is Volume 10, Geotechnical Studies, Bruce Park Dam. One part of this Volume is a report titled Geotechnical Evaluation of Mine-Induced Seismicity on Bruce Park Dam, GEI Consultants, Inc, June 2002, Project 99292 (GEI report). This report, and the analysis included, forms the basis for seven conclusions reached by GEI with regard to mining within 1300 feet of Terror Creek Reservoir (Bruce Park Dam). 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. 11