Laserfiche WebLink
February 15, 2023 <br /> Mr. Phillip Courtney <br /> Land Manager West Division <br /> Martin Marietta Materials <br /> 1627 Cole Boulevard, Suite 200 <br /> Lakewood, CO 80401 <br /> Re: Martin Marietta,Thunderbird Gravel Mine, Geotechnical Stability Analysis <br /> Dear Mr. Courtney: <br /> This letter has been prepared to address the Mined Land Reclamation Board (MLRB)Construction Materials Rule 6, <br /> Section 4, Subsection 19, Exhibit S-Permanent Man-Made Structures (6.4.19, Exhibit S)for the proposed Thunderbird <br /> Gravel Mine. This letter describes the project and slope stability analyses utilized to evaluate the minimum distance <br /> between the edge of mining and adjacent structures to avoid damage to the structure. <br /> The site is located in the Arkansas River Valley, east of Pueblo, Colorado, along Baxter Road, approximately three <br /> quarters(3/4)of a mile south of U.S. Highway 50 in Pueblo County. More specifically, the site is within parts of Sections <br /> 31 and 32, Township 20 South, Range 63 West of the 6th Principal Meridian. The permit area is divided by the Excelsior <br /> Ditch. In addition, overhead transmission lines cross the site. <br /> Mining at the site will be occur in three (3) phases: <br /> • Phase 1: limited mining at the fresh water and siltation ponds on the west <br /> part of the site, south of the ditch; <br /> • Phase 2: mining of a cell east of the ditch and east of overhead <br /> transmission lines; and <br /> • Phase 3: mining of a cell east of the ditch and west of overhead <br /> transmission lines. <br /> Phase 1 will be wet mined with excavators to maximum depths of approximately 20 feet. The mine slope will at the 0.5 <br /> horizontal to 1 vertical (0.5h:1v). Final reclamation will be backfilling and reseeding. <br /> Phases 2 and 3 will be lined either with slurry walls or a combination of clay liners and slurry walls. These cells will be <br /> dry mined either with the liner in place or with conventional dewatering for areas that may be mined prior to lining. At the <br /> Phase 2 and 3 cells, mine highwalls will be approximately 0.5h:1v. Final reclamation will be lined water storage with <br /> compacted reclamation slopes of 3h:1v. <br /> Based on the stability analyses, this report indicates that the setbacks and perimeter slopes in the mining plan are <br /> sufficient to protect structures within 200 feet of the permitted mining boundary. Actual setbacks may be greater due to <br /> permit limitations, zoning requirements, construction issues, agreements with owners, and extent of economically <br /> mineable aggregate or other issues. <br /> GEOLOGY <br /> The Site is located approximately 35 miles east of the eastern flank of the Rocky Mountain Front Range. Younger <br /> sedimentary strata dip eastward off the Pre-Cambrian igneous and metamorphic rocks that form the core of the Front <br /> Range. <br /> Bedrock does not crop out at the site, however regional geologic mapping of the area(Tweto, 1979)indicates the near <br />