Laserfiche WebLink
December 30, 2021 <br /> Mr. Drew Damiano <br /> Red Tierra Equities <br /> 8301 East Prentice Ave.,#120 <br /> Greenwood Village, CO 80111 <br /> Re: Stability Analysis for the Section 20 Gravel Mine <br /> Dear Mr. Damiano: <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 Section 20 <br /> Gravel Mine located northeast of the intersection of State Highway 60 and Weld County Road 42 in Weld County, <br /> Colorado. 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 approximately'/of a mile west of the town of Gilcrest. More specifically,the site occupies nearly all <br /> of Section 20,Township 4 North, Range 66 West of the 611 Principal Meridian. The mine is in an area of irrigated <br /> agricultural land with common oil and gas wells and related infrastructure and is bound by Weld County Road (WCR)42 <br /> on the south, State Highway 60 on the west,WCR 44 on the north,and WCR 29 on the east. <br /> The mine will consist of eight(8)cells. One(1)of the cells will be wet mined at a mine slope of 2 horizontal to 1 vertical <br /> (2h:1v)and backfilled with the silt byproduct of the wash plant operation. The other seven (7)cells will be lined with <br /> slurry walls and will be dry mined at slopes of 1.5h:1. <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 21 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 beneath the site is most likely the Laramie Formation. 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. The regional mapping indicates the bedrock is overlain by the Broadway Alluvium. <br /> Colton (1978)describes the Broadway as sand and gravel deposited by the South Platte River and its tributaries that is <br /> terraced typically lying about 40 feet above major streams. Along the South Platte River,the Broadway is typically on <br /> the order of 35 feet thick but can range up to 125 feet thick. <br /> GEOTECHNICAL CONDITIONS <br /> Based on the site investigations,the natural site stratigraphy generally consists of four main units: 1)Overburden: <br /> generally consisting of near surface fine to medium grained sand locally grading to silty or clayey sand; 2) Sand and <br /> Gravel:alluvial deposits that underlie the overburden and overlie the bedrock; 3)Mud Lens: silty to clayey sand <br />