2008-03-05_REVISION - M1997054 (23)

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Introduction Front Range Aggregates, LLC proposes to mine the property located in Township 18 South, Range 72 West of the 6a' Prime Meridian, Fremont County, Colorado. The property is bounded by the Arkansas River on the south and land owned by the Bureau of Land Management on the ' north. The proposed mining operation will extract gravel reserves near the Tallahassee Creek. A slope stability analysis was performed to analyze safe mining and reclamation conditions. This ' report contains an overview of geotechnical results and methodology used in the analysis of the proposed liner and shell material placed against the mining slopes. t Overview The Division of Reclamation, Mining, and Safety mining plan proposes that the sand and gravel pit will be mined in one large cell. During mining the highwall will be mined at a near vertical slope a cross section is included showing the mining section. The reclamation plan proposes the future use for this property to be a lined water storage reservoir. The reservoir will cover an estimated 93.5 surface acres when full. Actual surface area will depend on the final configuration of the reservoir after reclamation is complete. The mined slope will be reclaimed with a zoned embankment constructed from on-site materials. A 15-ft wide clay liner will be constructed from clay bedrock materials against the 0.5H:1 V mining highwall. A shell consisting of granite fines will be placed on the liner to create the final 3H:1 V slopes. An exhibit illustrating a typical maximum cross section is included. Geotechnical Data A preliminary geotechnical investigation has been performed by J. A. Cesare and Associates, Inc. JAC estimated soil strength parameters based on their field exploration. The soil strength parameters were provided to Applegate Group, Inc. by JAC for use in this slope stability analysis. The JAC tests provided specific values for soil densities and material classifications. For the sand and gravel material, the JAC reports provided soil classification only. The Design of Small Dams book was used to establish densities for the SP-SM sand and gravel, and the value ranges for cohesion and friction angle based on all soil classifications. The values were used in a sensitivity analysis to determine conservative, worst-case scenarios. Table 1 represents a summary of the soil strength parameters that were used in this stability analysis. Table 1. Soil Properties Description Max Dry Density (pcf) Saturated Density (pef) Cohesion (psi) Internal Friction Angle Granite Fines 137.7 142.4 0-100 30-35 Clay Liner 124.0 128.0 100-1225 28-38 Bedrock 130.0 133.0 100-1225 28-38 Native Sand and Gravel 135.0 141.0 0-100 -30