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

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• The foundation materials for all the ponds are classified as silty clay loams and characterized (by the NRCS) as having low strengths and being prone to erosion and piping. Natural material subject to seepage forces, such as the downstream side of semi-in situ ponds, is protected from piping by toe drains or liners if required. In addition, anti-seep collars are provided along the primary spillway conduits extending through the dam embankments. These collars have been designed using methods contained in the EPA publication EPA-625.3-76-006, "Erosion and Sediment Control". Soil surrounding all spillway conduits is carefully compacted to further reduce seepage through the embankments. All pond embankments are constructed of clean cohesive fill material which has a liquid limit between 30 and 50, a plasticity index between 10 and 25, and containing at least 70% passing the U.S. No. 200 sieve. Toe drains are constructed of free draining granular material meeting the requirements of ASTM C-33 Concrete sand. The "D" Portal Area sedimentation pond DP-1 has a toe drain. The entire pond is lined with a one foot thick layer of cohesive material meeting the same requirements as the embankment material. The liner and the face of the dam is covered with a 6 inch layer of compacted gravel which protects the liner during sediment cleanout operations. Seepage along the Scullion Gufch diversion culvert beneath sedimentation pond DP-1 is prevented by backfilling along the culvert with cohesive material and by anti-seep collars on the culvert. See Illustration 20. Geotechniral Investigation Report. V.B.5 Waste Banks Design The material to be disposed of in the Refuse Disposal Area will consist of a mixture of coal processing waste (coal and rock fines) and coarse rock fragments (see Table V-1 for chemical analysis of the waste material). The portion of the processing waste that is coal fines is expected to be less than 20 percent by weight. These fnes will contribute to the stability of the fill material by aiding in a more dense compaction of the material. The coal is low in sulfur content thus the fill material will be nonacidic in composition. The coal waste disposal embankments are located in watershed areas which do not have average profile gradients in excess of 10 degrees and, except for isolated rock outcrops, do not have side slopes in excess of 20 degrees. These embankments are not, therefore, classified as either valley-fills or head-of-hollow fills. They are constructed to meet specific requirements in Section 4.09.1 and 4.10 for these types of fills with the exception of the deletion of the rock underdrains. A subsurtace investigation of the Refuse Disposal Area was completed during late 1980. The investigation was conducted to verify that any groundwater present is deep enough that it will not infiltrate into the coal refuse, to show that the foundation soils will remain stable under the weight of the refuse banks, and to verify that the soils proposed to be used as nontoxic fill are adequate for this purpose. Mid-Term Review 2002 (8/2002) V-12