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1] GeoSyntec Consultants 3.4.4 Drainage and Erosion Control (D) drainage and erosion control systems pursuant to §21150, A drainage plan was developed for the proposed WMU B final grading plan as shown on Figure 3-1. Drainage features were designed to transmit surface water run-off from the 100 -year, 24-hour storm per Table 4-1 of Title 27, CCR for Class III MSW landfills. The goal of the plan was to prevent ponding and to prevent soil erosion due to high run-off velocities per §20365, Title 27 CCR. Supporting calculations for the drainage plan are found in Appendix F. Surface water on the WMU B top deck will be directed toward perimeter ditches along the crest, which will drain toward flared end sections leading into drainage pipes. The top deck will have a minimum, initial grade of 5% toward the perimeter ditches. Surface water on the sideslopes will drain downslope toward grass lined, v -ditches (18 -inches deep with 2H:1 V side slopes) running along benches or the toe of slope. The benches and v -ditches will have a minimum, initial grade of 2%. Surface water in the grass lined, v -ditches will drain toward flared end sections leading into drainage pipes. The 18 -inch downdrain pipes on the south slope of the WMU B closure area will drain into a 24 -inch, perimeter drainage pipe. This perimeter drainage pipe will drain at a 0.5% slope toward the north sedimentation basin as shown on Figure 2-3. The 18 -inch downdrain pipes on the north slope will drain into existing drainage ditches on the east and west perimeter of the WMU A final cover. Flow velocities from these pipes will be reduced with drainage -tees and rock energy dissipaters. The 12 -inch downdrain pipe on the east slope will drain into a 12 -inch perimeter drainage pipe. This smaller diameter drainage pipe will drain into the larger diameter perimeter pipe at a 0.25% slope. The top and side slopes of each phase will be hydroseeded with a drought -tolerant grass mixture to inhibit erosion (see Section 3.4.2.2). An organic binding agent will be applied to the seed mix to prevent seed loss by runoff during the first several rainstorms prior to germination. This vegetative system has been used successfully on the WMU A final cover. The establishment of this vegetative cover will be consistent with the proposed post -closure landfill use which is non -irrigated, open space. J.\ALLIED\FORWARD\CLASUREPLAN\REPORT 3-13 99.11.30 0