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~__- ~- ~.. INTRODUCTION This report summarizes construction observation results for the on-site and laboratory quality assurance testing conducted during the construction of the Nissen Farm Resource slurry wall. Information contained within this report was collected as part of the construction related engineering services that were provided by Tetra Tech RMC throughout the slurry wall construction. The slurry wall was constructed by Hall-Irwin Construction. Aggregate mining is planned on the site. Upon completion of the mining operations, the site will be used as a water storage reservoir. Construction of the Nissen Farm Resource slurry wall began in early January 2004. The construction consisted of lining a proposed gravel pit with approximately 9,500 feet ofsoil-bentonite slurry. The goal of the slurry wall liner is to minimize hydraulic interaction between the proposed gravel pit and the surrounding alluvium. The reduction in hydraulic interaction will aid mining efficiency in two ways: 1; reducing dewatering requirements during mining operations, and 2) by reducing draw down effects on any neighboring water wells. Upon completion of the mining activities, the final goal of the slurry wall construction is to provide a primary low permeability liner for a below grade water storage reservoir. The slurry wall was constmcted using a design build approach. The scope of Tetra Tech RMC's work during construction included on-site quality control and observation of the slurry wall conshuction. The scope of our work did not include groundwater monitoring or future reservoir design. Hall-Irwin Construction supplied labor, equipment, and materials to construct the slurry wall. PROJECT DESCRIPTION - The project site is located in Weld County, Colorado, west of Greeley and just east and south of the South Platte River. The site is more particularly described as located in Section 12, Township 5 North, Range 65 West of the 6th Principal Meridian, as shown on Figure 1. The site is bound by Weld County Road 58 on the south and the South Platte River on the west and north. The eastern boundary is the east section line of Section 12. The site is approximately 2,000 feet wide from north to south and 4,000 feet tong from east to west. The project area is located approximately 25 miles east of the eastern flank of the Rocky Mountain Front Range. Regional geologic mapping of the area (Colton, 1978)[ indicates the near surface bedrock at the site is the Laramie Formation. This formation is comprised primarily of claystones, siltstones, and sandstones. Bedrock at the site is overlain by alluvium regionally mapped as the Post-Piney Creek Alluvium. The natural site stratigraphy generally consists of three main units: 1) clayey sand and sandy clay overburden, 2) sand and gravel alluvial deposits, and 3) claystone and sandstone bedrock. Locally, sandy clay "mud" lenses are present in the alluvial deposits. Colton, R.B., 1978, "Geologic eLfap ojthe Boulder, Fort Collins, Greeley Area, Front Range Urban Corridor, Colorado," U.S. Geological Survey Map I-855G. - 1 - November 2004 F:W6J6 16TCOHtrvction Rcpon4YU,cn Fina Canswnov Rcpartdac