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7 K <br /> <br />Barr Engineering Company <br />4700 West 77th Street • Minneapolis, MN 55435-4803 <br />Phone: 952-832-2600 • Fax: 952-832-2601 • www.barr.com An EEO Employer <br />Minneapolis, MN • Hibbing, MN • Duluth, MN • Ann Arbor, MI • Jefferson City, MO <br />Memorandum <br />To: Phil Schmidt <br />From: Philip B. Solseng, P.E. <br />Subject: Monument Dam stability <br />Date: 18 March, 2008 <br />Project: Monument Dam interim stability review <br />c: Jed Greenwood, Ivan Contreras <br />This memorandum presents the stability of Monument Dam as of February 2008. The Monument Dam <br />was essentially completed in January 2008 but the final review and formal approvals cannot be completed <br />until summer of 2008 because of snow cover and because the final inspection will not be conducted until <br />the end of summer, when the reservoir empties.. The stability of the dam was computed with the proposed <br />modifications performed. The following are the results of the stability analyses for Cross Section C which <br />was considered to be the critical cross section: <br />1. Seismic Acceleration (g) from mine-induced seismic activity: Factor of Safety=1.27 <br />2. Seismic Acceleration (g) from natural earthquake activity: Factor of Safety= 1.0 <br />The seismic analyses were the critical analyses for stability and governed the dam modifications <br />performed. Prior to the improvements to the dam, the factor of safety for a natural earthquake activity was <br />less than 1.0. The size and geometry of the downstream buttress was established based on the seismic <br />analyses from a natural earthquake, where a factor of safety of 1.0 is considered acceptable. The final <br />analyses and documentation report will be prepared and submitted after the dam has been inspected and <br />reviewed in the summer of 2008 <br />As shown by the factors of safety above, the mine induced seismic activity has a higher factor of safety <br />than a natural earthquake. Before modifications were made to the dam, mining induced seismic activity <br />was highly unlikely to cause impacts to the dam. With the modifications made, mine induced seismic <br />activity has a factor of safety much greater than required. As a result, seismic impacts from mining on <br />Monument Dam have been resolved. <br />Philip B. Solseng, P.E. <br />Vice President, Barr <br />X tj?G,s <br />% <br />0 N ? <br />YVW <br />e <br />aS>?;JAL. ?isl1/.