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V06U <br /> r'�l�N011�tl�� <br /> January 24 2020 <br /> Mr.Mark Johnson <br /> Burnco Concrete and Aggregate <br /> 301 Centennial Drive <br /> Milliken,CO 80543 Vogl Amendment to Shores <br /> Re: Stability Analysis for the WGravel Mine <br /> Dear Mr.Johnson: <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 Vogl 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 west and north of the intersection of Weld County Roads 11 '%and 26, immediately north of the Town <br /> of Firestone,Colorado. More specifically,the mine is within parts of Section 1,Township 2 North, Range 68 West and <br /> Section 36,Township 3 North,Range 68 West of the 6t"Principal Meridian. The site is 200 feet south of the Saint Vrain <br /> River at its closest point. Land uses in the area include agricultural,oil and gas production, active gravel mines,gravel <br /> mines reclaimed as below grade reservoirs,and residential housing. The mine plan is shown on Figure 1. <br /> The site will be mined in four cells referred to as Cell 1,Cell 2a,Cell 2b,and Cell 3. The Cells 2a and 3 will be lined with <br /> soil-bentonite slurry walls and will be reclaimed as below grade reservoirs. Cells 1 and 2b will be unlined and will receive <br /> wash fines from the processing of mined sand and gravel. The unlined cells(Cells 1 and 2b)will be mined at a slope of <br /> 2 horizontal to 1 vertical(21­1:1V). The lined cells(Cells 2a and 3)will be mined at a slope 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 17 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 the Upper Transition Member of the Pierre Shale with the Fox Hills Sandstone <br /> mapped just to the east. Colton(1978)describes the Upper Transition Member as friable sandstone containing sandy <br /> shale and large calcareous sandstone concretions. Colton(1978)describes the Fox Hills Sandstone as cross bedded <br /> sandstone that grades downward to a fine grained silty sandstone interbedded with gray fissle shale. The regional <br /> mapping indicates the bedrock is overlain by the Post Piney Creek and Piney Creek Alluviums.The Piney Creek is <br /> mapped over the area of Cell 1 and parts of Cells 2a and 3. The Post Piney Creek is mapped at parts of Cells 2a and 3 <br /> and all of Cell 2b. Colton(1978)describes these alluvial deposits as sandy to gravelly alluvium. <br /> GEOTECHNICAL CONDITIONS <br /> Based on the site investigations,the natural site stratigraphy generally consists of three main units: 1)Overburden <br />