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iiiiiiiiiiiiiiiiiii I , 999 ' CTL/THOMPSON, INC. IL F.~.r•I JI CONSULTING GEOTECHNICAL AND MATERIALS ENGINEERS July 30, 1994 Colowyo Coal Company L. P. 5731 State Highway 13 Meeker, Colorado 81641 Attention: Mr. Jim Kiger Mr. Steve Hinkemeyer Subject: Observation of Stripping Operations West Pit Excess Spoil Disposal Site Colowyo Coal Mine Moffat County, Colorado Job No. 21,952 Gentlemen: At your request, our Mr. Gray visited the West Pit Excess disposal site on June 29, 1994 to observe conditions after stripping of topsoil. The purpose of our visit was to inspect conditions near the toe of the proposed fill and provide opinions and recommendations regarding seeps and soil slides found in this area. We previously performed a Geotechnical Investigation for the design of the spoil pile, (Job No. 16,516, dated March 1, 1991). This letter summarizes our observations and recommendations. Figure 1 shows the general configuration of the spoil pile. We understand the toe has been moved to the south from the location shown on Fig. 1 to provide room for surface water detention facilities. You reported that a soil slide was sound at Location A on Fig. 1 during stripping of the area. The slide was relatively shallow and the disturbed soils had been removed by the time of our visit. A seep was found at the base of the slide area and the slope had been excavated to expose the seep. The seepage water appeared to be exiting from a sandstone layer. A drainage Swale had been excavated from the seep area to the detention pond. Large boulders had been placed in the Swale and crushed rock was placed at the tace of the seep and over the boulders. We understand considerable crushed rock will be placed (cross-section area over 100 square feet) to restore grades and allow construction traffic. The amount of gravel is judged to be more than adequate to drain the seep. - We obtained a sample of the crushed rock from the stockpile at the crushing operation (referred to as 2-inch crushed rock at your site) and performed gradation testing, the results are shown on Fig. 2. The material has less than 6 percent fines (passing the No. 200 sieve) and is considered an acceptable drain rock. Another slide mass was reported at•Location B, Fig. 1. We observed the area, but due to the disturbance from stripping is was difficult to determine the overall extent of the slide mass. We recommended the slope be cut back along the suspected slide area and observed to confirm and determine the presence of a slide or seepage. We recommend removal of all unstable overburden or bedrock material in the slide area and to provide °7! :'/EST i2TH A`IENUE DENVER. COLORADO 80204 1303)8250777