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3. Cover thickness—In accordance with WDR, Item C.8, the partial cover will be placed <br /> and compacted to 85 percent relative density, at minimum thicknesses of: <br /> • 3-feet for slopes 511:1 V or flatter <br /> • 2-feet for slopes 511:1 V or steeper <br /> ' 4. Soil Gradation— Native soil will be selected for high content of"fines". The native soil <br /> at the Foothill Landfill tends to contain pebbles,which provide a shielding effect against <br /> ' erosion. The cover material will be consistent with the several cover systems that could <br /> be applied, including the prescriptive cover and an evapo-transporative cover(not yet <br /> approved). <br /> 5. Vegetation—Vegetation will be established by hydroseeding or placing seed and root- <br /> laden soil scraped from the surrounding pasture adjacent to the landfill. <br /> ' 6. Slope Stabili —The overall slope stability of Module"I" for interim and final slopes <br /> configurations will be presented in a slope stability report appended to the "Cover and <br /> ' Drainage Plan". Based on slope stability work done during the design of Module 1, <br /> stability of the refuse fill and partial soil cover at 3H:1 V or flatter slopes should be <br /> adequate for both static and seismic conditions that could occur, even during wet weather <br /> intervals. <br /> Drainage Facilities <br /> The drainage facilities for all modules will include 15-to 20-foot-wide benches with drainage <br /> ditches, inlets, and overside drains. The benches will be constructed during waste filling at <br /> approximate elevations of 300, 350, and 400 feet MSL with 1 to 3 percent longitudinal gradients <br /> for drainage to standard flared inlets. Corrugated underdrains and overside drainage pipes, or <br /> ' equivalent,will be used to intercept bench flows and discharge this run-off into the perimeter <br /> drainage facilities. <br /> ' Drainage analyses will be performed to assess stormwater flows and compute the size of <br /> drainage facilities for all modules. This calculation will utilize procedures in the County of <br /> San Joaquin Hydrology Manual or other generally accepted design methods. In addition to <br /> sizing for the 100-year 24-hour storm event, design criteria include: <br /> 1. Rational Method-The rational method from the County Hydrology Manual will be used <br /> ' to determine if drainage facilities should be designed for a storm which will provide peak <br /> flows greater than the regulatory required 100-year, 24-hour storm event. The Rational <br /> Method considers: <br /> ' - The run-off coefficient, C. This is dependent on surface slopes, soil infiltration <br /> potential,vegetal cover, and the potential for"storage", or ponding will be selected <br /> ' using Caltrans' Highway Design Manual. A high value of 0.6 will be assigned for <br /> module calculations. <br /> October 28,2003 3 Foothill Sanitary Landfill <br /> Partial Cover Workplan Public Works/Solid Waste <br />