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June 9, 2021 <br /> Mr. Joe Lamanna <br /> Ready Mixed Concrete Company <br /> 11778 Highway 52 <br /> Fort Lupton, CO 80621 <br /> Re: Stability Analysis for the Nix Gravel Mine <br /> Dear Mr. Lamanna: <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 Nix Gravel <br /> Mine located in Weld County, Colorado. This letter describes the project and slope stability analyses utilized to evaluate <br /> the minimum distance between the edge of mining and adjacent structures to avoid damage to the structure. <br /> The site is located at the southwest corner of the intersection of State Highway 66 and Weld County Road 19, <br /> approximately 3.3 miles west of the town of Platteville, Colorado. More specifically,the mine is within part of Section 28, <br /> Township 3 North, Range 67 West of the 61h Principal Meridian. The site is 0.6 miles east of the Saint Vrain River in an <br /> area of agricultural land with common oil and gas wells and related infrastructure. The mine plan is shown on Figure 1. <br /> The site will be mined in three areas located on the southwest(Freshwater and Silt Ponds, Cell 1),south central (Cell 2) <br /> and the northeast(Cell 3)parts of the site. The Cells 2 and 3 will be lined with soil-bentonite slurry walls and will be <br /> reclaimed as below grade reservoirs. The silt pond will receive wash fines from the processing of mined sand and <br /> gravel. <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 20 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 into the Denver Structural Basin. The Denver Basin is an asymmetrical downwarp of sedimentary strata with a <br /> steeply dipping west limb and a gently dipping east limb. <br /> Bedrock does not crop out at the site, however regional geologic mapping of the area(Colton, 1978) indicates the near <br /> surface bedrock at the site is most likely either the Fox Hills Sandstone and/or the Laramie Formation. Colton (1978) <br /> describes the Fox Hills Sandstone as cross bedded sandstone that grades downward to a fine grained silty sandstone <br /> interbedded with gray fissle shale. Colton (1978)describes the Laramie as mostly claystone,shale,sandy shale, and <br /> lenticular sandstone with common coal beds in its lower section. The regional mapping indicates the bedrock is overlain <br /> by the Piney Creek and Broadway Alluviums.The Piney Creek is mapped over most of the site. The Broadway is <br /> mapped on the southeast part of the site. Colton (1978)describes these alluvial deposits as sandy to gravelly alluvium. <br /> The Piney Creek Alluvium is usually covered in flood waters. The Broadway Alluvium forms the adjacent higher terrace <br /> that is typically 20 to 40 feet above major streams. <br /> GEOTECHNICAL CONDITIONS <br /> Based on the site investigations,the natural site stratigraphy generally consists of three main units: 1)Overburden <br />