2006-05-31_REVISION - M1978056 (12)

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z slope StaWftty Analysts Varra Gravel operation - Durham Pit Greeley. Colorado Page 2 the dewatering operation. The regional site location is depicted. on Figure 1. Site conditions are depicted on Figure 2. Site g oloration and Laboratory Testins? The bank between the Durham gravel operation and Poudre River is approximately 5100 feet in length. The unsaturated bank width varies between 40 feet in the western portion of the study area to In excess of 200 feet in the eastern portion of the study area. The river side bank height generally varies between 12 and 20 feet. The maximum vertical relief on the pit side of the bank is on the order of 50 feet, based in information provided by Anderson Consulting Engineers, Inc. The embankment was inspected on April 12, 2006, and no apparent signs of failure such as tension cracks or raveling were observed. Soil conditions within the bank were evaluated by drilling six soil borings with a truck mounted hollow stem auger rig. The depth of the borings varied between 20 and 50 feet below grade. Representative soil samples were obtained by advancing a fiao-inch outside diameter split barrel sampler ahead of the auger bit. Details of each boring log are presented in Appendix A. Soil descriptions of cores obtained from within the embankment were recorded during drilling activities. In general, soil conditions consist of up to five feet of fill which is underlain by alluvial deposits of well graded sand and gravel. Bedrock, which consists of a dense, dark gray shale (Pierre Shale) underlies the sand and gravel, deposits. The depth to water within the bank varied between 4 and 22 feet below grade. The boring locations are depicted on Figure 2. Overview of Stability Analyses Soil samples obtained from borings B-3, B-4, and B-5 were submitted to CTL Thompson of Fort Collins, Colorado and tested to determine the following properties: >water content;