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LEACHATE GENERATION <br /> Leachate generation analyses were completed to evaluate the volume of leachate that may <br /> collect at the base of the planned Forward Landfill expansion area and to develop design <br /> criteria for sizing leachate collection and recovery system (LCRS) appurtenances. The <br /> LCRS calculations for the Forward Landfill development include calculations for LCRS <br /> lateral spacing based on infiltration modeling,pipe capacity based on anticipated <br /> tributary flows, and LCRS pipe wall thickness based on deflection analysis. The sections <br /> that follow present the background and results for the LCRS calculations. <br /> Leachate Generation Analyses <br /> Modeling of potential leachate generation within the planned vertical and horizontal <br /> landfill expansion was performed using the United States Army Corps of Engineers <br /> Waterways Experiment Station's Hydrologic Evaluation of Landfill Performance model <br /> (HELP V. 3.07,November 1997). This modeling simulated a refuse fill placed over the <br /> entire liner development system. Sample input and output files are included. The <br /> calculated rate of leachate generation and accumulation were the primary parameters <br /> used in designing the LCRS. <br /> Model Description and Setup <br /> HELP is a quasi-two-dimensional model that simulates moisture flux into and out of <br /> landfills. It has become the standard method for evaluating the potential performance of <br /> landfill liner and cover systems. The model calculates water balances in daily <br /> increments, and can provide output for daily,monthly, and annual values of precipitation, <br /> runoff, evapotranspiration, percolation, and lateral drainage. The calculations integrated <br /> the following user-selected variables: <br /> Input Parameters <br /> Parameter Selection Criterion <br /> Precipitation Daily values synthetically developed by <br /> HELP using average monthly rainfall data <br /> from weather station in Stockton, <br /> California, <br /> Evapotranspiration Default values for Sacramento, California. <br /> Runoff Runoff coefficient modified for"poor stand <br /> of grass." <br /> Soil and refuse moisture storage capacity Upper zone conservatively assumed to <br /> always be at field capacity. <br /> Root zone depth No vegetation included. <br /> Surface slope 3%surface gradient. <br /> Subsurface lateral drainage 2% gradient with LCRS pipe at 200-foot <br /> centers. <br /> Solar radiation Data for Fresno,California,synthetically <br /> modified by HELP for Stockton's latitude. <br />