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September 29, 2023 <br /> Mr. Chris Oestreich <br /> Operations Manager-Aggregates <br /> Bumco Colorado, LLC <br /> 10100 Dallas Street <br /> Henderson, Colorado 80640 <br /> Re: Stability Analysis, L.G. Everist Conveyor, Inouye Gravel Mine <br /> Dear Mr. Oestreich: <br /> This letter has been prepared to update 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 Inouye Gravel Mine <br /> located at and in the vicinity of 12210 Weld County Road (WCR) 14.5 in Weld County, Colorado. Specifically,this letter <br /> has been prepared to address the stability of a conveyor to be constructed through the northwest-mine cell. The <br /> conveyor will be owned and operated by L.G. Everist. This letter follows previous stability analyses summarized in our <br /> letter of May 2018. <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 6t' <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 slung 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 summarized in this and the May 2018 reports,the setbacks and perimeter slopes in the <br /> mining plan are sufficient to protect structures within 200 feet of the permitted mining boundary. Actual setbacks may be <br /> greater due to permit limitations,zoning requirements, construction issues,agreements with owners,and extent of <br /> economically 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 />