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<br />~muuinimiiiii <br />CTL/THOMPSON, INC. <br />CONSULTING GEOTECHNICAL AND MATERIALS ENGINEERS <br />RECEfVED <br />May 5, 1995 JUN 2 6 1995 <br />Colowyo Coal Company L.P. <br />5731 State Highway 13 Division of Minerals s Geology <br />Meeker, Colorado 81641 <br />Attention: Mr. Jim Kiger <br />Subject: Landslide South of West Pit Pond <br />Vicinity of West Pit Excess Spoil Disposal Area <br />Colowyo Coal Mine <br />Moffat County, Colorado <br />Job No. 23,001 <br />Gentlemen: <br />At your request, our Mr. Gray visited the West Pit Pond on April 12, 1995 to <br />observe the slump movement which had occurred a few weeks previous to our visit. The <br />movement consisted of a slide located at the south side of the West Pit Pond, west of the <br />toe of the West Pit Excess Spoil Disposal Site (Fig. 1). The purpose of our visit was to <br />help evaluate conditions which may have contributed to the slide, determine if the slide <br />affected the stability of the sedimentation pond embankment, and to formulate repair <br />recommendations. We previously observed conditions near the toe of the excess spoil <br />pile during initial stripping and drain installation, which documented two small slides to <br />the southeast of the current area of concern (Job No. 21,952, letter dated July 30, 1994). <br />This letter summarizes our observations of the current slide, opinions regarding possible <br />causes and recommendations for repair. <br />SITE CONDITIONS <br />The approximate location of the slide is shown on Fig. 1. A photograph of the <br />slide is reproduced on Fig. 2. The slide is located at the south side of the detention pond <br />at the base of a slope in an area where topsoil was stockpiled. The depth of topsoil is <br />estimated to be about 1 to 6 feet in the slide area. The direction of slide movement was <br />to the north. The slide appeared to be a lateral and downward movement with little <br />rotation with a near vertical head scarp. Near the head of the slide, a "slickensided" <br />claystone surface was visible at the base of the slide mass. The claystone dip direction <br />corresponded with the slide direction. <br />Several seeps and small soil slumps have occurred in the natural slope to the east <br />of the slide. This portion of the slope had previously been stripped to bedrock to <br />facilitate lateral drain construction to the West Pit underdrain, and topsoil placed to an <br />approximate depth of 18 to 24 inches. The slumps were relatively shallow and appeared <br />to involve movement of shallow surficial soils and re-placed topsoil. <br />1971 WEST 12TH AVENUE DENVER, COLORADO 8020a (303)8250777 <br />