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TIPTON AND KALMBACH, INC. ONE PAR1t CENT RP L.SUITE iapi 1519 nR<Pq HOE STREET GLINTON w. HEH RING. PR E51p ENT E. R. MIGHf LL. EXEC. VICE PRESIO ENT H. F. BiS NOP. ViGf PR ESiD ENT A J. DEVTSC H.TR E45U RER J. H. TURNER.SEGRET4RY DENV ER, COLORADO 80202 P..pNC bOJI 5T2-BOOS cgRLE g RTIP - DENVER TW%' B IO~BJI-2590 May 5, 1981 Mr. Richard Atkinson Colowyo Coal Company 5731 State Highway 13 Meeker, Colorado 81641 Subject: Stability of the Spoil Fill in Streeter Gulch Dear Mr. Atkinson: On 27 April 1981 and 30 April 1981, I met with representatives of Colowyo Coal Company to discuss your proposed change of the configuration of the spoi I fi I I in Streeter Gulch. On the afternoon of 30 April 1981, I accompanied representatives of Colowyo Coal Company (Messrs. McDonald, Brown and Atkinson) to the offices of the Office of Surface Mining where representatives of the Office of Surface Mining and the Mined Lond Reclamation Division were apprized of your proposed change. In this meeting, I stated that it was my opinion that the proposed change in configuration would have a minimal effect on the stability of the spoil fill. The purpose of this letter is to confirm this opinion. The configuration of the spoil fill as originally planned starts at a toe elevation of approximately 6588 feet and includes 30-foot wide benches at EI, 6700, EI. 6800, and EI. 6900. The slope between the benches is 3 horizontal on 1 vertical. The material to be placed above the bench at EI. 6900 was to be placed on a flatter slope to EI. 7100. The slope between EI. 6900 and El. 7100, when measured in a plane that is continuous with the 3:1 slope between EI. 6588 and EI. 6900, was to be approximately 6 horizontal on 1 vertical. The fill has been completed to this configuration from the toe to EI. 6900. It is our understanding that the proposed change in the configuration is between EI. 6900 and EI. 7300. For the purposes of the stability analysis, the slope between EI. 6900 and EI. 7300, when measured in a plane that is continuous with the 3:1 slope between EI. 6588 and EI. 6900, is to be approximately 3 horizontal to 1 vertical. After additional study, you may determine that some additional berms are to be added which would tend to slightly flatten the slope. The stability of the spoi I fi I I in Streeter Gulch is the subject of reports prepared by W. A. Wahler 8, Associates, Golder Associates, Inc., CTL/Thompson, Inc., and Tipton and Kalmbach, Inc. The latest and most comprehensive investigation was prepared for the Office of Surface Mining by CTL/Thompson, Inc., and the results are shown in a report entitled,