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CIVIL RESURCES, 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;jia;:l'ett describes the project and slope stability calculations carried out to evaluate <br /> the minimum distance betwghliti45edge of mining and adjacent structures to avoid damage to the structure. <br /> f •Rig .�...'Y�.-,v( .`, <br /> tjL'1.S� .o, 4P <br /> fief 3y. �� <br /> The site is located approximately o 1 half mile,fro►�,the"eduth Platte River. =¢a 't A`f i •arts of east one-half of <br /> Section 36,Towrrsl 1p�1 North,' ange 6 'r West:of�the 6thRiar q a Y i fla;yst "`'.3 bounded on the <br /> g+o-9 v.,. alt-` tai .K.,west by Weld , ounty�Road,(WCR) ;5,the north byvWCR 2 ,Kigg - so oId( t°©�o,4168th Ave)and <br /> on the east b '" l t n me I r:y t( e k i g ppurce aggregate"rrtine owned • 1-lrw prsal, 4.1.1o.cated in Weld <br /> County,Colorado,� ;shown,on figure t-.=.. , . <br /> Approximately threeetosfou:eot>or.overbureen•)rs rid`er`tain by. iativei ee aiiut>>.re a o 'a i T <br /> ��, �:.� ,�., ,��,� ��.. a x g � t. he aggregate <br /> will likely be transported"'"via`1co tr tpaq e • t1.sE a --s ) plant locateed -Y.rth on is g Hall-Irwin site. <br /> Hall-Irwin plans to dewater and dry-mine Phase 1 and 2 at a 0.5:1 (horizontal to v- ,ie {} o ie. Phase 3 will be mined <br /> after constructing a perimeter soil-bentonite slurry wall that will tie into-the-0g' s urry 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 • P.O. Box 680 • FREDERICK, CO 00530 • (303) 833-1 41 6 • (303) 833-2850 - FAX <br />