2010-10-22_REVISION - M2008017 (4)

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INTRODUCTION Broken Arrow Investments, LLC proposes to mine the property located in the Northeast '/ of Section 4, Township 5 North, Range 65 West, Sixth P.M. in Weld County. The property is bounded by Balsam Avenue on the west, adjacent to an Aggregate Industries minin operation, and private property on the north, south, and east. State Highway 263 (8t Street) is less than a quarter of a mile south of the subject property. The proposed 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 200 foot setback of a man-made structure show thorough engineering analysis that the proposed mining will not cause damage. The accepted method of demonstrating this is through a slope stability analysis. This report contains an overview of the prior geotechnical investigation results by Terracon and Two Rivers Testing, 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. OVERVIEW The revised DRMS mining plan proposes that the property will be mined in 5 phases. The first phase, Phase 1A-1C, will mine to a depth of approximately 6 feet, staying above groundwater, and using 3H:1V slopes from the final mining limit as approved in the current permit. The reclamation plan in the current permit, Exhibits E and F, show the future use for this property to be a slurry wall lined water storage reservoir. Subsequent phases, Phases 2 through 5, will be initially wet mined to an interim mining limit, using vertical slopes, and then, once the proposed slurry wall is installed and the pit is dewatered, mined at 3H:1 V slopes to the final mining limit. Concurrent reclamation is planned such that the reclamation embankment will be constructed as the mining progresses. The reservoir will cover an estimated 30 surface acres when full. Actual surface area will depend on the final configuration of the reservoir after reclamation is complete. GEOTECHNICAL DATA Preliminary geotechnical investigations have been performed by Terracon and Two Rivers Testing. J&T Consulting, Inc. (JT) estimated soil strength parameters based on the information from the geotechnical investigations, which were provided to JT by Broken Arrow Investments, LLC, and other stability analyses that have been performed on gravel mining operations along the front range. Table 1, on the following page, represents a summary of the soil strength parameters that were used in this stability analysis. Broken Arrow Investments, LLC - Derr Pit - M-2008-17 J&T Consulting, Inc. Technical Revision No. 1- Slope Stability Analysis aPage 1