2008-06-12_REVISION - C1996083 - Laserfiche WebLink

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Resources (DWR), dated June 11, 2003, in which additional information was requested concerning the landslide immediately adjacent to the Bruce Park main dam. A copy of this letter is attached. Please submit these data and report, per the recommendations described in the DWR letter of June 11, 2003, as part of the adequacy review for PR-10. The Division has no further concerns. The May 12, 2008 submittal contained a geotechnical monitoring plan in Exhibit 20 of Volume IIIA. 32. The Division has received one comment letter from the USDA-Forest Service, dated April 18, 2008, which is attached. The Division anticipates receiving a comment letter from the Colorado Division of Water Resources, which will be forwarded to BRL when it is received. 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 of threshold 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 5 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 clarify 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 10