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CIVIL RES'~URCES,LLC <br />ENGINEERS 6 PLANNERS <br />January 5, 2006 <br />Mr. Jeff Gregg, Resources Manager <br />Hall-Irwin Corporation <br />301 Centennial Drive <br />Milliken, Colorado 80543 <br />Re: Stability Analysis for Parker/Dersham Sand and Gravel Resource <br />Dear Mr. Gregg <br />This letter has been prepared to address the Mine 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 <br />Parker/Dersham aggregate mine. This letter describes the project and slope stability calculations carried out 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 approximately on-half mile from the South Platte River. The site is within parts of east one-half of <br />Section 36, Township 1 North, Range 67 West of the 6~h Principal Meridian. The site is generally bounded on the <br />west by Weld County Road (WCR) 23.5, the north by WCR 23.75, on the south by Baseline Roatl (168x' Ave) antl <br />on the east by the existing Baseline Resource aggregate mine owned by Hall-Irwin. The project is located in Weld <br />County, Colorado, as shown on Figure 1. <br />Approximately three to four feet of overburden is underlain by a relatively deep alluvial aggregate deposit. The aggregate <br />will likely be transported via conveyor to an existing processing plant located to the north on the existing Hall-Irwin site. <br />Hall-Irwin plans to dewater and dry-mine Phase 1 and 2 at a 0.5:1 (horizontal to vertical) slope. Phase 3 will be mined <br />after constructing a perimeter soil-bentonite slurry wall that will tie into the existing slurry wall. Phase 3 will mine the <br />highwal! to a slope no steeper than 3:1 (horizontal to vertical) final grade, as indicated in the DMG permit application. <br />This report lists minimum safe setbacks for mining from structures within 200 feel of the permitted mining boundary <br />based on stability calculations. Actual setbacks maybe greater due to permit limitations, zoning requirements, <br />construction issues, agreements with owners, extent of economically mineable aggregate, or other issues. <br />GEOLOGY <br />The site is located approximately 30 miles east of the foothills of the Colorado Front Range on the western flank of the <br />Denver Structural Basin. The basin is a downwarp of sedimentary strata that trends north-northwest, parallel to the <br />mountain front. In the project area, the sedimentary beds dip gently eastward coward the axis of the basin east of the <br />site. Based on regional geologic mapping (Colton,1978), the near surface bedrock in the project area is the Paleocene <br />and Upper Cretaceous Denver and Arapahoe Formations. The bedrock is ovedain by upper Pleistocene and Holocene <br />(Quaternary age) gravel deposits and eolian (wind blown) overburden soils. The gravel deposits exist primarily within the <br />Broadway Alluvium deposit. The bedrock unit consists mainly of claystone and may contain lenses of siltstone and <br />sandstone. <br />457 OAK STREET, SUITE 2OJ ~ P, O. BOX 6H^ 1 FREDERICK, CO BO53D ~ (303) 833-1 47 6 ~ 1303) 833-28 SO -FAX <br />