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7.'~' -_ <br />• <br />III IIIIIIIIIIIIIIII <br />999 <br />=; SubTerra, Inc. <br />Mr. Karl Koehler <br />Twentymile Coal Company <br />Cyprus-Amax Coal <br />29515 Routt County Road #27 <br />Oak Creek, CO 80467 <br />Re: Rockfall Hazards Mitigation Project <br />Mining Engineering <br />Civil and Mining Rock Mechanics <br />Mine Subsidence <br />Solid Waste Disposal <br />Tunnel Engineering <br />Concrete/Shotcrete Technology <br />Construction Bid Documents <br />27 December, 1995 <br />Dear Karl: <br />We have examined the as-built drawings prepared by Epp and Associates (PLS) and the soils <br />reports prepared by Northwest Colorado Consultants in determining overall compliance of the as- <br />built twentymile, rockfall hazards mitigation project with the design prepared by SubTerra, Inc. <br />Compliance is summarized as follows: <br />1. 225 nuclear density tests were pertormed by NCC (see Attachmed tables). Approximately 7 <br />tests were below the specified requirement of 95% of maximum standard Proctor density. <br />Each of the tested areas was reworked and retested. All retested areas passed the density <br />standard. <br />2. Drainage modifications were made at the westem end of the easternmost trench berm <br />combination. These changes will not alter the effective pertormance of the barrier. <br />3. Modifications were made to the drainage break at Section J of the westem trench/beret <br />combination. The predicted pertormance at this modified section was evaluated in our letter of <br />October 31, 1995 (attached). Additional, recommended, remedial construction has been <br />implemented. <br />4. The as-built survey prepared by Epp and Associates indicates that, with the very minor <br />changes noted above, the trench/benn has been constructed as designed. <br />If you have any further questions, please contact me at (206)-827-8003. <br />Yours Sincerely <br />Chris D. Breeds, P.E. <br />President <br /> <br />