2015-10-06_PERMIT FILE - M2015017

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COLORADO Divisior, of Reclan-taticn, Minino an6 Safety 5,i S I -n Start Prx,in Z15 Laen r . CU &0203 Date: October 6, 2015 To: Michael Cunningham; Division of Reclamation, Mining & Safety From: Peter Hays; Division of Reclamation, Mining & Safety Re: Second Review of Engineering Analysis, JRS Mining LLC, Sullivan Aggregate Pit, File No. M-2015-017 The Division of Reclamation, Mining and Safety (Division/DRMS) staff has reviewed the engineering analysis included with the Sullivan Aggregate Pit 112c permit application and the stability analysis submittals dated October 2 and 5, 2015 in response to the Division's adequacy letter. The following list describes the information used by the Division as presented in the permit application to evaluate slope stability for the proposed site. • The maximum mining slope will be 2.5H:1V • The depth to bedrock is expected to be 25 to 60 feet from the surface • The mining excavation will extend to bedrock, or to the limit imposed by the mining slopes, or to 2 feet above groundwater level whichever is encountered first • A minimum offset distance of 30 feet from the permit boundary to the edge of the excavation limit will be established and identified with survey stakes placed at a minimum interval of 150 feet • An offset distance of 20 feet on both sides of the Platte City Placer Ditch will be established • Pre -mining topography will be restored to the approximate pre -mining contour or a minimum 3H:1V slope will be constructed with overburden material during final reclamation • The pre -law highwall at the sluice area will be backfilled at a minimum 3H:1V slope • Soils on the site are classified by the Applicant as well -cemented 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 31 degrees and a 21 degree slope angle, a 1.56 factor of safety was calculated • Stability analysis models were submitted by the Applicant for two (2) critical cross- section (B -B' and E -E') as indicated on the Exhibit C-3 (A coz 1313 Sherman Street, Room 215, Denver, CO 80203 P 303.866.3567 F 303.832.8106 http://mining.state.co.us John W. Hickentooper, Governor I Mike King, Executive Director I Virginia Brannon, Director