Laserfiche WebLink
The Division has no further concerns. In the December 28, 2006 submittal, page 19 of the referenced <br />report was revised accordingly <br />34. Concerns addressed in the SEO June 11, 2003 letter with respect to the landslide stability analysis <br />should be addressed prior to longwall mining within a one-mile radius of the dam. Apparently, Jim <br />Stover has indicated that this information will be submitted later this year (2006). <br />As mentioned in comment number 31 B above, in a submittal dated November 14, 2006, BRL <br />provided a report by Yeh and Associates entitled "Final Geotechnical Investigation and Evaluation <br />Report - Bruce Park Landslide". The Colorado Division of Water Resources has reviewed this report <br />and their comment letter is attached. <br />35. Confirmation is needed that actual seismic events experienced now and in the future are within the <br />range of events used in the modeling and prediction of impacts (or lack of impact) to the dam. Bowie <br />should determine a seismic "threshold event" that would trigger more detailed monitoring and <br />analysis of the dam should this threshold event occur as a result of mining. No data has been <br />submitted at this time. However, again, Jim Stover has apparently indicated that actually seismic <br />data will be submitted later this year. It should be noted that other information seems to indicate that <br />between September], 2004 and November 18, 2004, Bowie experienced mine induced seismic events <br />of 3.2 M, 3.3 M, and 3.5 M. The GEI analysis included one event of 4.2 and a combination ofsmaller <br />events, the largest of which was 2.5 M. It may be important to re-evaluate the previous analysis with <br />larger events more indicative of actual conditions. Bowie should submit actual data recorded since <br />seismic stations were brought on-line for review in conjunction with this revision. <br />BRL responded in their December 28, 2006 submittal that the seismic monitoring plan was provided <br />in Exhibit 18 of Volume IIIA. As mentioned in comment number 31 A above, the Division is <br />requesting that the GEI report "Geotechnical Evaluation of Mine Induced Seismicity on Bruce Park <br />Dam" be updated with a site-specific seismic signal. In comment number 26 above, the Division is <br />also requesting certain changes to the format of the seismic monitoring report. <br />In a letter attached to this adequacy review letter, the Colorado Division of Water Resources is <br />requesting additional information concerning a threshold monitoring program for the landslide that is <br />adjacent to the Bruce Park Dam. The Division and the USDA-Forest Service, as stated in their letter <br />dated February 22, 2007, also have concerns with the monitoring plan as to timing, implementation <br />and reporting to the Division. Ultimately, there needs to be some sort of threshold event that will need <br />to be determined, and an analysis of how much ground motion is acceptable at the Bruce Park Dam <br />and adjacent landslide without creating instability. Please provide a threshold monitoring program, as <br />described in the Division of Water Resources letter, for both the Bruce Park Dam and the adjacent <br />landslide. <br />36. The Division does not concur with conclusion #7 of the June 2002, GEI report that's states <br />"additional monitoring of the dam and saddle dam ... is not required to address risks associated with <br />mine-induced seismicity. " The Division concurs with the SEO that seismic monitoring is required at <br />the Bruce Park Dam as mining moves inside a one-mile radius of the dam. Without actual monitoring <br />data to compare to pre-mining analysis and conclusions reached, we cannot evaluate the adequacy of <br />12