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Seepage along the Scullion Gulch diversion culvert beneath sedimentation pond DP-1 is prevented <br />by backfilling along the culvert with cohesive material and by anti-seep collars on the culvert. See <br />Illustration 20. Geotechnical Investigation Report. <br />V.B.5 Waste Banks Design The material to be disposed of in the Refuse Disposal Area will <br />consist of a mixture of coal processing waste (coal and rock fines) and coarse rock fragments (see <br />Table V-1 for chemical analysis of the waste material). The portion of the processing waste that is <br />coal fines is expected to be less than 20 percent by weight. These fines will contribute to the <br />stability of the fill material by aiding in a more dense compaction of the material. The coal is low in <br />sulfur content thus the fill material will be nonacidic in composition. <br />The coal waste disposal embankments are located in watershed areas which do not have average <br />profile gradients in excess of 10 degrees and, except for isolated rock outcrops, do not have side <br />slopes in excess of 20 degrees. These embankments are not, therefore, classified as either <br />valley-fills or head-of-hollow fills. They are constructed to meet specific requirements in Section <br />4.09.1 and 4.10 for these types of fills with the exception of the deletion of the rock underdrains. <br />A subsurface investigation of the Refuse Disposal Area was completed during late 1980. The <br />investigation was conducted to verify that any groundwater present is deep enough that it will not <br />infiltrate into the coal refuse, to show that the foundation soils will remain stable under the weight of <br />the refuse banks, and to verify that the soils proposed to be used as nontoxic fill are adequate for <br />this purpose. <br />One bore hole was drilled in each of the refuse subareas 1, 2, 3, 4, 5, 6, 7, and 9 near the point of <br />maximum fill. See Map 76, Additional bore holes were drilled at the locations of sediment ponds <br />RP-1, RP2-3, RP-3 and RP-4. Percolation tests were also conducted at the sediment pond <br />locations. Laboratory strength tests were performed on samples which were taken from the test <br />holes. Chemical analyses were performed on soil samples taken at the depths of the proposed <br />nontoxic fill material. <br />No ground water was found in any of the bore holes. The deepest hole drilled was RP 1 B (44 feet) <br />which is near the lowest part of the area. <br />A stability analysis of fills up to 100 feet high having 3h:1v and 5h:1v face slopes was performed <br />using data obtained from the field investigation and assumed typical strength parameters for the <br />coal refuse to verify that the proposed refuse banks will meet the requirement of Section 4.10.4(2) <br />to have a safety factor of 1.5. The coal refuse strength parameters were based on published data <br />• and tests of coal samples taken during coal sampling drilling for the Deserado Mine. Similar <br />(Permit Renewal #3, 8199) V-14 <br />