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May 31, 2018 <br /> Mr. Mark Johnson, Compliance Manager <br /> Burnco Colorado, LLC <br /> 301 Centennial Drive <br /> Milliken, Colorado 80543 <br /> Re: Stability Analysis for the Inouye Gravel 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 Inouye <br /> Gravel Mine located at and in the vicinity of 12210 Weld County Road (WCR) 14.5 in Weld County, Colorado. This letter <br /> describes the project and slope stability analyses utilized to evaluate the minimum distance between the edge of mining <br /> and adjacent structures to avoid damage to the structure. <br /> The site is located on the south side of WCR 14.5, west of the South Platte River. More specifically,the site is within <br /> parts of Section 31, Township 2 North, Range 66 West; and Section 36, Township 2 North, Range 67 West of the 6th <br /> Principal Meridian. The mine is in an area of irrigated agricultural land with common oil and gas wells and related <br /> infrastructure and is bound by Weld County Road (WCR) 14.5 on the north; the South Platte River on the east; City of <br /> Fort Lupton waste water ponds and irrigated cropland on the south, and greenhouses on the west. The mine and vicinity <br /> are shown on Figure 1. <br /> The site will be mined in three cells located on the southwest, northwest and the northeast parts of the site. Oil and gas <br /> wells and facilities separate the southwest and northwest cells. The Lupton Bottom Ditch separates the northwest and <br /> northeast cells. The northeast and northwest cells will be lined with soil-bentonite slurry walls and will be reclaimed as <br /> below grade reservoirs. The southwest cell will receive wash fines from the processing of mined sand and 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 Laramie or the Denver and Arapahoe Formations(Colton, (1978) <br /> maps the Denver and Arapahoe Formations as undifferentiated). Colton (1978)describes the Laramie as mostly <br /> claystone, shale, sandy shale, and lenticular sandstone. The Lower Laramie is described as sandstone, sandy shale, <br /> and claystone with several coal beds. Colton (1978)describes the Denver and Arapahoe Formations as claystone and <br /> siltstone interbedded with tuffaceous sandstone and conglomerate. The regional mapping indicates the bedrock is <br /> overlain by the Piney Creek Alluvium. Colton (1978)describes the Piney Creek as sandy and gravelly alluvium in which <br /> the upper part is characterized by a weakly developed brown soil. <br />