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