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struction, the berm will be continued to the nearest point of exit from the site. For Modules 7 through 11, the perimeter berm will also be constructed one module ahead of the fill module. When construction of the perimeter berm interferes with any major natural drainage channels entering the site, the remainder of the perimeter berm will be constructed and joined with the berm adjacent to Module 1. The discharge of sediment -laden runoff will be controlled by silt fences during the excavation, preparation, and operation phases. The silt fences will be constructed parallel to all drainage ditches and swales to control sediment at the source and limit the volume of flow passing through any one section of fence. A series of straw -bale dikes will be constructed approximately every 150 feet along the down - gradient silt fences to limit downgradient flow of sediment -laden wa- ter. Final cover and vegetation will be placed as soon as possible after each module is brought to final grade. Vegetative growth will reduce sheet flow run-off, limiting erosion and movement of sediment. 4.5 LEACHATE CONTROL In some areas of the United States, where precipitation is high or when cover on landfills is poor, rain may infiltrate through the land- fill cover soil and percolate into the waste fill. Leachate is pro- duced when the infiltration of water into the landfill exceeds the moisture -holding capacity of the wastes. When the absorptive capacity of the refuse is exceeded, leachate (water containing soluble sub- stances) is generated. To evaluate leachate produced when precipitation infiltrates into landfills, the U.S. Environmental Protection Aqency (EPA) uses the water -balance method developed by C.W. Thornthwaite. Thig method is based on the relationship between precipitation, surface runoff, evap- otranspiration, and soil -moisture storage. Using this method, the PJ9 9390209A.00D 16