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COLORADO <br /> jig <br /> oul..-.00 Division of R eclamation, <br /> " Mining and Safety <br /> Department of Natural Resources <br /> 1313 Sherman St. Room 215 <br /> Denver, CO 80203 <br /> May 7,2020 <br /> JC York <br /> J&T Consulting <br /> 305 Denver Ave STE D <br /> Ft Lupton CO 80621 <br /> RE: File M2008-017; Derr Pit; Technical Revision 04 (TR04) —Benching for Slurry Wall, <br /> Modification to Phase 5a Mining Plan, and Modified Grading Plan for Eastern <br /> Disturbed Area; Adequacy Review 1 <br /> Mr. York: <br /> The Division of Reclamation, Mining and Safety received Technical Revision 04 on May 5, <br /> 2020. The decision date for this revision has been set for June 4, 2020. Please be advised <br /> that if you are unable to satisfactorily address any concerns identified in this review before <br /> the decision date, it will be your responsibility to request an extension of the review period. <br /> If there are outstanding issues that have not been adequately addressed prior to the end of the <br /> review period, and no extension has been requested, the Division must deny this revision. <br /> DRMS has completed the initial adequacy review of TR04. As with most revisions, there are <br /> items that will require clarification of the existing information or submittal of additional <br /> information. The TR as submitted addresses three proposed modifications to the existing <br /> approved permit for this site: utilization of temporary benching to install the slurry wall <br /> surrounding Phases 1-4; increasing the allowed depth of mining in Phase 5a, and regrading of <br /> the disturbed area between Phases 1 and 2 and Phase 7. Supporting maps and stability <br /> analysis have been provided for the proposed changes. <br /> With respect to the installation of temporary benches to allow installation of the slurry wall <br /> surrounding Phases 1-4. DRMS approves this modification as proposed. <br /> With respect to increasing the depth of mining allowed within Phase 5a, DRMS approves this <br /> modification as proposed—with the understanding that all setbacks from existing structures <br /> will be observed and maintained unless new agreements are obtained and provided to <br /> DRMS; mining of the exterior slopes will take place at a 3:1 slope; and groundwater will not <br /> be exposed prior to installation of the slurry wall. <br /> ti <br /> of'�olp <br /> 01 <br /> 1313 Sherman St. Room 215 Denver, CO 80203 P(303)866-3567 F(303)832-8106 https://colorado.gov/drms <br /> Jared Polis, Governor I Dan Gibbs, Executive Director Virginia Brannon, Director * _ <br /> 18?6 <br />