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Mining Methods and Slope Stability Evaluation for Expanded Development of the Walstrum Aggregate Quarry_ <br /> 1.0 INTRODUCTION <br /> Albert Frei & Sons (AFS) is currently operating the Walstrum quarry in the Clear Creek County <br /> of Colorado. AFS has recently applied for rezoning and planned development amendments that <br /> will add about 166 acres of land to their long-range mining plan. A map showing the proposed <br /> mining expansion boundaries is shown in Figure 1.1. <br /> As is customary, various government agencies review development plan changes to ensure they <br /> are safe, environmentally responsible and in compliance with all regulatory rules. During the <br /> course of these reviews, Clear Creek County -- with input from the Colorado Geological Survey <br /> and State Division of Minerals & Geology -- has expressed concerns about the stability of new <br /> rock slopes planned for the quarry expansion. The County has specifically requested that a <br /> Geotechnical Stability Report be prepared that addresses the safety of new rock slopes that will be <br /> steeper than 3:1 (horizontal:vertical). For the planned expansion work, the requested evaluation <br /> would include walls extending to the eastern boundary of the quarry, slopes adjacent to a new <br /> access corridor, and potentially the final slopes against a buffer ridge that will remain to shield the <br /> quarry from Interstate Highway 70 and U.S. Highway 6. <br /> In response to this request, AFS has retained REVEY Associates, Inc. (RAI), an independent <br /> mining and blasting engineering services company, to evaluate and recommend measures that can <br /> be applied to maximize the safe development of temporary rock benches and the long-term <br /> stability of final rock slopes. <br /> On September 24, 2001, Gordon F. Revey of RAI -- the report's author — visited the Walstrum <br /> Quarry site. During that visit, the conditions of existing rock slopes were examined and proposed <br /> expansion areas were inspected. The quarry was again visited on February I and 5, 2002, at which <br /> time site-specific measurements were made to confirm the structural geology of the pit walls. <br /> Since that time, the author has analyzed the field data and evaluated practical methods that can be <br /> used to ensure the stability of future rock slopes planned for the Walstrum Quarry. This report <br /> contains the findings and recommendations that have resulted from this evaluation. <br /> REVEY Associates,Inc. Page 1 of 14 October,2001 <br />