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CIVIL RESURCES, LLC <br /> ENGINEERS & PLANNERS <br /> October 29, 2025 <br /> Colorado Division of Reclamation and Mining Safety <br /> Mr. Patrick Wenberg <br /> 1313 Sherman Street, Room 215 <br /> Denver, CO 80203 <br /> RE: Technical Revision 09—Pond 2(Stage 6)&Pond 3(Stage 5) Interior Reclamation Slopes <br /> Holton Mine (Permit M-2008-082),Weld County, Colorado <br /> Dear Mr.Wenberg: <br /> Ready Mixed Concrete Company, Inc. (RMCC), a subsidiary of Brannan Sand & Gravel Company (BSG), requests a <br /> Technical Revision 09 (TR09) to allow modification of the interior slopes of the remaining storage facilities within the <br /> mine boundary.A site location map is provided on Figure 1. <br /> Background <br /> The approved reclamation plan associated with the DRMS mining permit M-2008-082 (commonly Holton Mine) and <br /> Technical Revision 07 (TR07) incorporated flood control spillways on Ponds 1, 2, 3, and 4 in areas where flooding from <br /> either the South Platte River(SPR) and Big Dry Creek are most likely. In addition to the spillways, Pond 1 was approved <br /> to be mined at a 1:1 temporary slope and reclaimed at a 4:1 finished slope using compacted clay material. Ponds 2, 3 <br /> and 4 were approved to be mined at a 1:1 slope and reclaimed at a minimum of 4:1 finished slope where the spillways <br /> are located and mined to a 3:1 slope and reclaimed at a finished 3:1 slope in all non-spillway areas. <br /> Proposed Revisions to the Mining and Reclamation Plans <br /> This Technical Revision 9(TR-09) proposes the following modifications to the approved Reclamation Plan: <br /> • Pond 2& 3 Flood Event(May 2023):The Holton Mine was damaged by severe flooding in May 2023 causing a <br /> breach of the Big Dry Creek and damage to the Pond 3 bentonite slurry wall. Approximately 625 linear feet(LF) <br /> of the slurry wall was eroded causing an influx of river water, groundwater and overburden material south of the <br /> mine boundary. This event also caused damage to the previously mined side slopes that were reclaimed at a <br /> 3:1 slope as approved in the reclamation plan. Due to high costs for slurry wall repair and extent of the damage, <br /> the alternative repair option was to construct a compacted clay liner in place of the damaged slopes similar to <br /> the interior slope reclamation approved for Pond 1 (TR07). Proposed flood protection measures for Ponds 2 <br /> and 3 include: <br /> o Flood control spillways (approved in TR-07) <br /> o Interior slope reclamation with compacted clay material at a 4:1 finished slope. The compacted clay is <br /> erosion resistant and will help maintain the integrity of the interior slopes in future storm events since <br /> portions of Ponds 2 and 3 are in the floodway. <br /> o The final bottom grading of the reservoir also includes "stilling pools" that connect the bottom of each <br /> spillway to retain flood water and protect the toe of the slopes from being eroded during the initial <br /> flooding inflow. <br /> • Compacted Clay Slope Reclamation:After the flood damage in 2023, it was determined that the location of the <br /> reservoirs make them susceptible to future flooding. As part of the final site reclamation plan, the proposed <br /> interior slopes of Ponds 2 & 3 be mined at a 1:1 slope and be reclaimed with compacted clay material at a 4:1 <br /> finished slope. Previously, the approved reclamation plan included this design for the finished slope in the <br /> 8308 COLORADO BLVD SUITE 200• FIRESTONE, COLORADO 80504 • PHONE: 303.833.1416 <br />