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NEW, TETRA TECH RMC <br /> March 21,2003 <br /> Mr. Jeff Gregg <br /> Hall-Irwin Corporation <br /> P.O. Box 2150 <br /> Greeley,Colorado 80632 <br /> Re: Hall4rwin Corporation,Nissen Farms,Weld County,Colorado,Stability <br /> Analysis as Required by the Division of Minerals and Geology for Permanent <br /> Structures Within 200 Feet of the Mined Area;Tetra Tech RMC <br /> Job No.80-0636.141.00 <br /> Dear Mr.Gregg: <br /> This letter has been prepared to address Mine Land Reclamation Board(MLRB)Construction <br /> Materials Rule 6,Section 4,Subsection 19,Exhibit S-Permanent Man-Made Structures(6.4.19, <br /> Exhibit S)for the proposed Nissen Farms aggregate mine. <br /> The proposed mine will occupy 89 acres in the South Half of Section 12,Township 5 North,Range <br /> 65 West of the 6th Principal Meridian in Weld County,Colorado. The site is in the alluvial valley of <br /> the South Platte River near its confluence with the Cache la Poudre River. The South Platte River <br /> meanders around the west and north sides of the proposed mine. Weld County Road 58 is south of <br /> the mine. Land use in the area is mostly agricultural and rural residential. Numerous gas wells are <br /> also present in the area. <br /> The Mining Plan(attached for reference) for the project is to mine the site in a total of six phases <br /> ranging from approximately 5.9 to 21.3 acres in size. A slurry wall will be constructed around the <br /> mine perimeter. The mine will be reclaimed as three ponds,all within the slurry wall perimeter. <br /> Certain interior parts of the mine will not be mined in order to leave access for vehicles and pipelines <br /> to site gas wells and tank batteries. For our analyses,we have assumed that the mine highwalls on <br /> the perimeter of each pond will be vertical. Actual highwalls will likely be less than,but near <br /> vertical. Overburden stockpiles may be placed 10 feet from the perimeter of the mined areas. <br /> GEOLOGIC STRATA <br /> The mine site is located in the alluvial valley of the South Platte River. Geologic mapping at the site <br /> (Smith, et al., 1972)' indicates the mine is on the recent alluvial terrace of the South Platte River. <br /> ' Smith,Schneider,and Petri, 1967,"Groundwater,South Platte River Basin,"USGS Water Supply Paper <br /> 1658. <br /> 1900 S.Sunset Street Surte I-F,Longmont,CO 80501 <br /> Tel 303.772.5282 Fax 303.665.6959 <br /> www.ttrmc com <br />