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CTL/THOMPSON, INC. CONSULTING GEOTECHNICAL AND MATERIALS ENGINEERS September 25, 1981 Colowyo Coal Company 5731 State Highway 31 Meeker, Colorado 81641 Attention: t•1r. Rich Atkinson Subject: Monitor Well Installation and Stability Considerations Streeter Canyon Fill Near Meeker, Colorado Job No. 7245 Gentlemen: The purpose of this letter is to provide supplemental information on ground water levels and stability for the subject fill. The data serves as an addendum to our original slope stability analysis re- ported in our Job No. 7245 dated May 18, 1981. In May of 1981, three permanent ground water monitor wells were in- stalled at the subject site. Wells MW-1 and MW-2 were located on the 6,900 level. The third well (MW-3) was drilled at the toe of the slope at an elevation of 6,586 ft. The approximate locations of the wells are shown on Fig. 1. Due to difficult drilling in spoil, wells MW-1 and MW-2 were installed using a Becker Hammer Drill. The hole is advanced using a percussion drilling technique capable of providing 8,000 ft-lbs of energy per square inch. A turbo assist increases the energy to 9,500 ft-lbs. In the course of drilling MW-1, a moist zone was encountered at a depth of 118 feet, approximately the 6,800 level. Well MW-2 was drilled to 119 feet to monitor a potential perched water table condition. Monitor well MW-3 was drilled using conventional auger drilling .techniques and a CME-45 drill rig. The total depth of the hole was 70 feet; however, the monitor well was installed only to 35 feet below grade. Drill logs for each of the wells are presented in Appendix A. Subsequent to the installation, Colowyo Coal Co. personnel have been monitoring water levels within the wells. Table I presents dates and depth to ground water information. Based upon this data, it appears the overall fill is relatively dry. A perched water table may be forming at the 6,800 level. Data suggest a phreatic surface approxi- mately 8 feet above the bench. The moist zone is probably due to water being trapped above the low permeability compacted layer formed during construction. Ground water at the toe of the fill varied from 3 to 4 feet below grade and seems to correlate with the water level in Good Spring Creek. 1971 WEST 12TH AVENUE DENVER, COLORAD080204 (303) 825-0777