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a 24 hour 100 year event. The runoff coefficient used was 0. 6. <br /> Slope protection and erosion control are accomplished by vegetating <br /> and keeping side slopes at or below a maximum of 3 : 1. The 3 : 1 <br /> slopes are located along the perimeter of the landfilled area. The <br /> top landfill surface final cover slopes will be 3-6% to prevent <br /> drainage slope reversal from landfill settlement. The 3-6% slopes <br /> will also keep sheet flow on the landfill surface at minimal <br /> eroding velocities. <br /> The entire final site face will be vegetated with drought resistant <br /> grass to provide a low maintenance form of erosion control. The <br /> grass will be fertilized as needed and it will not require <br /> irrigation other than natural rainfall. <br /> 10.0 LEACHATE CONTROL <br /> In some areas of the United States, where precipitation is high or <br /> when cover on landfills is poor, rain may infiltrate through the <br /> landfill cover soil and percolate into the waste fill. Leachate is <br /> produced when the infiltration of water into the landfill exceeds <br /> the moisture-holding capacity of the wastes. <br /> Leachate control will be provided by properly constructing the <br /> final cover to meet all state and federal regulations in force at <br /> the time it is to be constructed. In general, the final cover <br /> will be designed to promote maximum runoff without causing erosion, <br /> and thereby reduce the amount of moisture which might otherwise <br /> infiltrate/percolate down into the waste. The average annual <br /> precipitation at the Foothill Sanitary Landfill site is <br /> approximately 17.5 inches (See Figure 5, Isohyetal Map for San <br /> Joaquin County) . Moisture is not expected to percolate into the <br /> waste. It is expected that moisture falling on the site will be <br /> balanced by surface runoff, evapotranspiration, soil moisture <br /> storage of the vegetative layer, and/or runoff on the clay barrier <br /> layer. The vegetative cover will be fertilized, as necessary, and <br /> seeded with moderately rooted, erosion-resistant vegetation native <br /> to the surrounding area. <br /> 10. 1 BASE LINER AND LEACHATE CONTROL FACILITIES <br /> Future modules will have a composite base liner meeting the <br /> requirements of new state regulations( Chapter 15, Article 5) . <br /> These new state regulations allow for engineered alternatives to <br /> the prescriptive design standard specified in federal regulations <br /> (Subtitle D) . The liner to be installed is not specified here <br /> because alternatives to the prescriptive standard will be proposed <br /> for approval prior to module construction. However, a general base <br /> liner cross section detail is shown on Figure 10. A Leachate <br /> Collection and Removal System (LCRS) will be installed in all <br /> modules constructed in accordance with the new state regulations. <br /> 26 <br />