2015-03-03_PERMIT FILE - M2014070

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A7COLORADO Division of Reclamation, Mining and Safety Department of Natural Resources 1313 Sherman Street, Room 215 Denver, CO 80203 Date: March 3, 2015 To: Eric Scott, Division of Reclamation, Mining & Safety From: Peter Hays, Division of Reclamation, Mining & Safety Re: Review of Slope Stability Analysis, VESCO Consulting Services, LLC, GoodMiller #2 Pit, File No. M- 2014 -070 The Division of Reclamation, Mining and Safety (Division) staff has reviewed the stability analysis included with the GoodMiller #2 permit application. The following list describes the information used by the Division as presented in the permit application geotechnical stability exhibit to evaluate slope stability for the site. Please review the list and confirm the list is accurate. • A minimum 20 foot buffer will be maintained from the permit boundary line to all excavations. • The side slopes will be mined at a 1.5H:1V and reclaimed at 3H:1V. • The maximum depth excavated will be 40 feet. • No laboratory strength tests were performed on soils at the site. • The soil strength parameters used were based on typical values for anticipated soils. • Soils on the site are classified as GC (clayey gravels, poorly graded gravel- sand - clay). • An analysis was performed using the formula; Factor of Safety (FOS) = Tangent of Internal Angle of Friction / Tangent of Actual Angle of Failure Surface. Using a friction angle of 34 degrees and a 21 degree slope angle, a 1.7 factor of safety was calculated. • Groundwater was not accounted for in the stability analysis. • The closest structure to the mine excavation limit is a power line 20 feet from the excavation limit. The following information is required by the Division to continue the stability analysis review. of cow. 1313 Sherman Street, Room 215, Denver, CO 80203 P 303.866.3567 F 303.832.8106 http: / /mining.state.co.us t- John W. Hickenlooper, Governor I Mike King, Executive Director I Virginia Brannon, Director * 1g76'.*