REP22705 - Laserfiche WebLink

Home Browse Search

1 This report summarizes construction observations and results of the on-site and laboratory quality assurance testing at the La Poudre Pit slurry wall. Informadion contained within this report was collected in conjunction with the construction related engineering services that were provided by Rocky Mountain Consultants, Inc. (RMQ throughout the slurry wall construction. Construction began on the slurry wall lining project at the La Poudre Pit in September, 1997, and consisted of lining a working gravel pit with approximately 9,500 feet of slurry wall. The goal of the slurry wall liner is to minimize hydraulic interaction between the pond storage area and the surrounding alluvium. The reduction in hydraulic interaction will aid mining efficiency in two ways: 1) by reducing dewatering requirements during mining operations, and 2) by reducing drawdown effects on neighboring wells. Upon completion of the mining activities, the final goal of the slurry wall construction is to surround the reclaimed pit and provide a low permeability liner for a below grade water storage reservoir. The slurry wall was constructed using adesign/build approach. The scope of our work during construction included on-site quality control testing and observation of the slurry wall construction. The scope of our work did not include groundwater monitoring or reservoir design. Hall-Irwin Construction supplied labor, equipment, and materials to construct the slurry wall. The work was performed under a contract with the Central Colorado Water Conservancy District (CCWCD). CCWCD will make use of the reservoir storage to supplement their existing water delivery/storage system. PROTECT DESCRIPTION The site is owned by Hall-Irwin Construction and is located in Section 19, Township 6 North, Range 67 West of the 6th Principal Meridian in Weld County, Colorado, as shown on Figure 1. The project area is located south of Highway 392, east of Weld County Road 13, and north of the ' Cache la Poudre River. Regional geologic mapping (Hershey and Schneider, 1972) indicates bedrock in the area strikes to the northwest with dips to the southeast in the range of one to five degrees. The site is underlain by a thick sequence of sedimentary strata. Regional mapping indicates near surface bedrock at the site is the upper unit of the Pierre Shale shown as the Pierre Transition Zone. Regionally, the Pierre Transition Zone has been described by Hershey and Schneider (1972) as containing interbedded sandstone and shale. Bedrock at the site is overlain by unconsolidated Quaternary Alluvial deposits, regionally mapped as the Post-Piney Creek Alluvium. ' -1-