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CIVIL REs'uRCEs, LLC <br /> ENGINEERS & PLANNERS <br /> August 20, 2025 RECEIVED <br /> Colorado Division of Reclamation and Mining Safety AUG 2 8 2025 <br /> Mr. Patrick Lennberg <br /> 1313 Sherman Street, Room 215 D%VIS10N 01= Ri_Cf�A�1' <br /> Denver, CO 80203 MINING ANp AFTE;Y Ac10r <br /> RE: Technical Revision 3—Monarch DENM Mine(Permit M-2022-009),Weld County, Colorado <br /> Dear Mr. Lennberg: <br /> Monarch Mountain Minerals and Aggregates, LLC (MMMA) requests a Technical Revision 3 (TR-03) to Permit M-2022- <br /> 009 to revise the mining plan and reclamation schedule. <br /> Background <br /> The Monarch DENM Mine was initially approved to be mined starting in the southernmost cell (Cell 1) and working north <br /> towards the plant ending with Cell 4. The phasing of the groundwater mitigation structures was modeled to align with this <br /> schedule. Specifically, no mitigation structures would be constructed prior to construction of the Cell 2B slurry wall. <br /> Proposed Changes to the Mine Plan <br /> MMMA proposes to alter the mine phasing to start with Cell 4 which is the northernmost cell closest to the plant. Cell 4 <br /> will be dry mined above the groundwater table until the slurry wall has been constructed at which time the cell will be <br /> dewatered. After Cell 4, mining will progress to Cell 1 after which the original mining sequence will be utilized. The Cell 4 <br /> slurry wall curtain area is approximately 397,320 square feet or 128,020 square feet more than the currently bonded Cell <br /> 1. <br /> The Cell 4 slurry wall is approximately 3,100 feet north of the southern property line and more than 3,600 feet from the <br /> nearest upgradient below grade structure, the Graybill property basement. Due to the distance from the slurry wall to the <br /> nearest upgradient below grade structure, it is not anticipated that construction of this slurry wall prior to construction of <br /> the proposed mitigation structures will have a negative effect on the surrounding property owners. <br /> The MODFLOW groundwater model for the Site was updated to include a model run with only the Cell 4 slurry wall <br /> constructed at the Site in addition to the Sweet Valley slurry walls that were constructed in the past year.The mounding <br /> caused by the slurry wall was greatest directly upgradient from the slurry wall at PZ-09 which showed a computed rise of <br /> 2.3 feet. PZ-25,which is approximately 2,000 feet upgradient of the slurry wall showed a rise of approximately 0.6 feet. <br /> This level of rise is less than the proposed cut off for mitigation outlined in the Monitoring and Mitigation Plan. See the <br /> below changes from baseline in the computed groundwater elevations with the inclusion of Cell 4 and the Sweet Valley <br /> site. <br /> 8308 COLORADO BLVD •SUITE 200• FIRESTONE, CO 80504 • PHONE: 303.833.1416 <br />