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CIVIL RES-DURCES, LLC
<br /> ENGINEERS & 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 d scribes 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 4h-half mile from.the South Platte River The sf.e is Wit in;parts of east one-half of
<br /> Section 36, Township 1 Nortb, Range 67,West,of'the 61h PTrineiPU 11viefi�� 'n sites rs generally,bounded on the
<br /> west by Weld County;Road,(WCR) 23'5, the north by-6 R 23.7 ;on,the sou p by Baseline Fioady(168th Ave) and
<br /> nn the } hl o mn R' ingpo nllrn rrn } 'min num lJ II Ins' r� Y fl '� i5, +.,A IAI I,J
<br /> VII L,IV east �,�th�,.,Xistllly �:, sa,i,l,� I,�,,s�ul„e ayyrega�e,,.11lle V/Ylled y.,,-!a«-�I�Yin Tkiz pl,.�ac t Cateu in �Yel'
<br /> County, Colorado, as;showr, on P yur e
<br /> Approximately three'fo tour feet of overourdei is underlain py a reiatiVeiy deep alluvial aggregate peposit. The aggregate
<br /> will likely be transported via conveyor-ta an,existing procesSjn'g�plarit located to the north on tk e exjsfing Hal! Irwin site.
<br /> t �.
<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 6A9i ng slurry wall. Phase 3 will mine the
<br /> highwall 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 feet of the permitted mining boundary
<br /> based on stability calculations. Actual setbacks may be 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 toward 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 overlain 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 /> 451 OAK STREET, SUITE 209 0 P.O. BOX 6BO • FREDERICK, CO B0530 * (303) B33-1 41 6 0 (303) 633-2B5❑ - FAX
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