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• North Refuse Collection Ditch. The north refuse collection ditch extends along the northern toe of the refuse storage pile. This ditch collects all surface drainage flowing off the north slope of the pile, in addition to flow contributions from the west collection ditch, and conveys it to Sediment Pond 4. The north collection ditch is divided into three (3) sections as shown on Figure 3, Refuse Disposal Area Drainage Plan. Each section has the same channel slope but different channel configuration. Section A is designed as a trapezoidal channel with a 5-foot bottom width and 2H:1V sideslopes. The channel section extends approximately 750 feet at a 3.6 percent slope. The design velocity is 4.8 fps, therefore, vegetative erosion protection is adequate for this section. Section B is designed as a trapezoidal channel with an 8-foot bottom width and 2H:1V sideslopes. The channel section extends for approximately 340 feet at a 3.6 percent slope. The design velocity is 5.0 fps, therefore, • vegetative lining provides effective erosion protection for this section. Section C is designed as a trapezoidal channel with a 2-foot bottom width and 2H:1V sideslopes. The channel section extends approximately 420 feet at a 3.6 percent slope. The calculated velocity (6.2 fps) exceeds 5.0 feet per second, therefore, rock riprap (D~, = 8 inches) is installed in Section C to prevent erosion. The riprap is placed to an approximate depth of 18 inches along the channel bottom and sideslopes. Appropriate bedding material was placed as a base for the riprap. Design details for each channel section are summarized in Figure 5, Refuse Collection Ditches - Design Detail. Refer to Table 11, Refuse Collection Ditches, 100-Year, 24-Hour Hydrograph Analysis, at the end of this section, for computer printouts. South Refuse Collection Ditch. The south refuse collection ditch extends around the southwest corner of the refuse storage pile and along its • southern toe. This ditch collects surface drainage flowing off the southern slope of the pile and runoff from a small undisturbed area southwest of the pile, and routes it to the east to Sedimentation Pond 4. ll7