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TATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY / <br />Department of Natural Resources <br />1313 Sherman St., Room 215 <br />Denver, Colorado 80203 <br />Phone: (303) 866-3567 <br />FA%: (303) 832-8106 <br />DATE: May 17, 2005 <br />TO: Vince Mathews, CG <br />~ <br />FROM: / <br />Allen Sorenson `~ <br />COLORADO <br />D !VISION O F <br />MIN SRALS <br />GEOLOGY <br />IIECLAN ATION•NINING <br />SAf ETT•SeIENCE <br />glll DWenS <br />Governor <br />Russell George <br />Executive Director <br />Ronald W. Gttany <br />Division Director <br />Natural Resource Trustee <br />a~ <br />RE: Seismicity in the Williams Fork Valley, Henderson Mill, DMG Permit No. M-1977-342 <br />Please find enclosed a copy of the 1995 report titled "Probabilistic Seismic Hazard Analysis of the <br />Henderson Tailing Dam." This report contains probabilistic peak accelerations of 0.12 g for a 500 year <br />return period event and 0.19 g for a 1000 year return period. The Division of Minerals and Geology uses <br />these peak accelerations to evaluate the stability of the Henderson Mill Tailing Impoundment under <br />earthquake shaking. Do the on-going CGS investigations of the Williams Fork and associated faults give <br />any indication that other criteria would be more appropriate for evaluating the impoundment? <br />enclosure(s) <br />cc: Ron Cattany, DMG (via email, w/o enclosures) <br />Hany Posey, DMG (via email, w/o enclosures) <br />Carl Mount, DMG (via email, w/o enclosures) <br />c:\Documents and SettingsWCSVNy Documents\henderson CGS review of seismiciry.doc <br />Office of Office of Colorado <br />Mined Land Reclamation Active and Inactive Mines Geological Survey <br />