2009-06-18_PERMIT FILE - C1981018A (6)

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• One bore hole was drilled in each of the refuse subareas 1, 2, 3, 4, 5, 6, 7, and 9 near the point of maximum fill. See Map 76. Additional bore holes were drilled at the locations of sediment ponds RP-1, RP2-3, RP-3 and RP-4. Percolation tests were also conducted at the sediment pond locations. Laboratory strength tests were performed on samples which were taken from the test holes. Chemical analyses were performed on soil samples taken at the depths of the proposed nontoxic fill material. No ground water was found in any of the bore holes. The deepest hole drilled was RP 1 B (44 feet) which is near the lowest part of the area. A stability analysis of fills up to 100 feet high having 3h:1v and 5h:1v face slopes was pertormed using data obtained from the field investigation and assumed typical strength parameters for the coal refuse to verify that the proposed refuse banks will meet the requirement of Section 4.10.4(2) to have a safety factor of 1.5. The coal refuse strength parameters were based on published data and tests of coal samples taken during coal sampling drilling for the Deserado Mine. Similar analysis were pertormed for fills having 4h:1v using the actual design parameters determined from the refuse in place. The results of the Geotechnical Investigation are included in Illustration 21 and the results of the chemical analyses are included in Section II.I -Illustration D. • Map 82 presents calculations on the amount of topsoil to be stripped from Sub-Areas 1 to 4 plus the associated sediment ponds. The tables presented on Map 82 show that Sub-Area 1 and Pond RP-1 involve a total disturbance of 14.07 acres. Further, the calculations show that an average thickness of 1.51 feet of topsoil was stripped from Sub-Area 1 and Pond RP-1. Illustration D of the Soils Report contained in the permit application gives Selenium values at depth for core holes R-1 to R-7 The selenium values reported by Agricultural Consultants, Inc. appeared to be high. The lack of observed selenium efion and animals was deemed to be evidence that selenium was not present in levels to be harmful or to require special handling procedures. In the spring of 1981, split samples were sent to Inter-Mountain Laboratories for analysis. The samples were dried, sieved using -20 mesh, extracted in a steam bath, filtered and analyzed by the gaseous hydride method and atomic absorption spectrophotometry. The resultant selenium values ranged from undetectable to 0.022 ppm., well below the 2 ppm. standard. Therefore, there are no selenium problems expected at the refuse disposal area. The waste fills were designed by, and the construction was certified by a qualified engineer registered in the State of Colorado. Waste banks #1 has a face slope of Sh:1v. Subsequent waste banks will have final face slopes of • 4h:1v or gentler. The gentle slope was selected to provide positive stability, minimize potential Mid-Term Review 2002 (8!2002) V-13