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March 7998 Slump Investigation and Mitigation Report • Page 1 <br />1.0 INTRODUCTION <br />This report summarizes the results of an investigation of, and development of mitigation <br />measures for, the slump located in the southern portion of [he reclaimed Hayden Gulch Coal <br />Mine south of Hayden, Colorado. This investigation was performed in accordance with the <br />Work Plan (TerraMatrix/Montgomery Watson, 1997) submitted to the Colorado Division of <br />Minerals and Geology (CDMG) in August 1997. The purpose of the investigation was to: <br />• Determine the most likely cause of the slump; <br />• Evaluate groundwater conditions within the slump vicinity; <br />• Delineate the boundaries and monitor potential future movement of the slump; <br />• Evaluate the effectiveness of the French drain installed just above the slump; and, <br />• Develop additional mitigative measures to stabilize the slump. <br />In order to accomplish these objectives Montgomery Watson Americas, Inc. (dba TerraMatrix <br />[MWAll performed the scope of work summarized in the following sections. The area <br />disturbed by this investigation was not more than approximately one-quarter acre and included <br />tire tracks and small areas denuded of vegetation, such as at piezometer heads and an excavaced <br />and backfilled area. The original topography was not altered. Exhibit I-I, Slump Mitigation <br />Map, delineates the slurnp and shows the location of existing piezometers and drainage <br />structures, and the proposed new drainage structures discussed in Sections 7.0 and 8.0. <br />Montgomery Watson Americas "P.O. Box 774018 "Steamboat Springs, Colorado "80477 ~970f 879-6260 <br />~': ~[n~51.mR Mm,won ~fl.mp Rrpon <br />V}f/9~Jv <br />