2006-12-19_REVISION - M2001107 - Laserfiche WebLink

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I -INTRODUCTION Northern Colorado Constructors, Inc. (NCCI) currently operates the NCCI Pit #1 aggregate mine located in the !Northeast'/. of Section 24, Township 2 North, Range 67 West, Sixth P.M. in Weld County. The property is bounded by private property on the west and north, WCR 25 on the east, and WCR 18 on the south. United States Highway 85 is approximately one half mile east of the subject property. The mining operation will extract gravel reserves from locations adjacent to man-made structures. The rules and regulations of the Division of Reclamation, Mining and Safety (DRMS) require that any mining within a setback of 200 feet of a man-made structure show through engineering analysis that the proposed mining will not cause damage to these structures. The accepted method of demonstrating this is through a slope stability analysis. This report contains an overview of the prior geotechnicai investigation results by Terracon and the methodology used in the analysis of the mining slopes and their estimated affects on all man- made structures. Recommendations regarding acceptable setbacks from man-made structures have also been included. II -OVERVIEW NCCI plans to mine the property in one contiguous cell. The future use for this property is expected to be a lined water storage reservoir. The mined slopes will be reclaimed with a 3h:1v embankment constructed from clay shale and overburden. Concurrent reclamation is planned such that the reclaimed embankment will be constructed as the mining progresses. The reservoir cell will cover an estimated 55 surface acres when full. Actual surface area will depend on the final configuration of the reservoir after reclamation is complete. III - GEOTECHNICAL DATA A preliminary geotechnical investigation and subsequent liner evaluation have been performed by Terracon. J&T Consulting, Inc. (JT) estimated soil strength parameters based on the information from the Terracon report and liner evaluation, which was provided to JT by NCCI, and other stability analyses that have been performed on gravel mining operations along the front range. Table 1 represents a summary of the soil strength parameters that were used in this stability analysis. Table 1 -Soil Proaerties Description Max dry density c Saturated Density c Cohesion s Internal Friction An le Overburden 110 131 150 22 Sand and Gravel 110 131 0 35 Weathered Bedrock 125 141 100 18 Stable Bedrock 125 141 2000 20 NCCI Pit #1 Slope Stability Malysis Page 1