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RECEIVED <br /> Int TETRA TECH FEB 1 1 2026, <br /> DIVISION OF RECLAMATION <br /> MINING AND SAFETY <br /> February 6,2026 <br /> Patrick Lennberg <br /> Division of Reclamation,Mining and Safety <br /> 1313 Sherman Street,Room 215 <br /> Denver,CO 80203 <br /> RE: Transmittal of Engineering Evaluation for Distel Succession <br /> Longmont Distel Operation(M-1989-029) <br /> Dear Mr. Lennberg: <br /> Amrize West Central Inc. (Amrize) asked Tetra Tech to review the current Distel site conditions to satisfy the <br /> engineering evaluation requirements regarding potential effects to structures from Amrize's plans for <br /> additional work. Pursuant to DRMS rule 6.3.12/6.4.19,Amrize sent out Structure Agreements to the structure <br /> owners;many of the agreements were not returned.Where such an agreement cannot be reached, DRMS <br /> rules require the applicant to provide an appropriate engineering evaluation that demonstrates that such <br /> structure shall not be damaged by activities occurring at the mining operation.This letter serves as the <br /> required engineering evaluation demonstrating no adverse effects to structures identified in the area from the <br /> planned site operations. <br /> Tetra Tech reviewed high-resolution drone aerial imagery,drone LiDAR topography,Google Earth imagery, <br /> and other information from Amrize to identify the locations of pits and confirm the locations of structures <br /> with a focus on those structures closest to the existing pits.All material extraction areas within the Distel <br /> DRMS permit boundary have been mined and reclaimed except for the area near the south-central part of the <br /> site where there are several remaining pits that will be reclaimed.Attached Figure 1 shows the locations of the <br /> existing pits along with a listing of owners of structures adjacent to the mine permit area including owner <br /> addresses,names of structures,and nearest distance to existing pit. As shown,the only structure within 200 <br /> feet of the pits is a fenceline immediately east of the easternmost pit. <br /> This pit,along with the other remaining pits,were mined more than 10 years ago and have existing vegetated <br /> slopes. No further development of pits is planned for the site.The only remaining earthwork operations to be <br /> completed within the Distel permit area will involve backfilling the existing pits and completing reclamation <br /> and revegetation on the final surface areas. <br /> These operations will substantially increase stability of the area.With the pits no longer present,stability risks <br /> (from the pits)to structures within 200 feet of the pits would be eliminated. Prior to backfilling the pits,the <br /> fenceline immediately east of the pit would be the only structure to evaluate regarding pit stability.The <br /> attached Figure 2 shows a typical section for the east slope of this pit,with the pit slope at approximately 2.4:1 <br /> (42%slope) and top of berm at 10 feet above the toe of the slope on the pit side and 6.8 feet above the toe of <br /> slope on the opposite side(outside)of the berm-for a net slope height of 3.2 feet.This short slope height, <br /> along with the distance separating the pit from the fenceline,would result in no adverse effects expected from <br /> the pit to the fenceline(see location of hypothetical 3:1 slope away from the fenceline on Figure 2). <br /> In summary,based on observed stability of the dormant pits and greater than 200-foot distance between the <br /> pits and structures,except for the eastern fenceline,and the plan to backfill these pits as part of the <br /> reclamation program thus eliminating the slopes,it is expected that remaining operations will not cause <br /> damage to the identified structures. <br /> TETRA TECH page 1 of 2 <br />