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Model Description and Setup <br /> HELP is aa uasi-two-dimensional model that simulates moisture flux into and out <br /> of landfills. It has become the standard method for evaluating the potential <br /> performance of landfill liner and cover systems. The model calculates water <br /> balances in daily increments, and can provide output for daily, monthly, and <br /> annual values for precipitation, run-off, evapotranspiration, percolation, and <br /> lateral drainage. The calculations integrated the following user selected <br /> variables: <br /> Input Parameters <br /> Parameter Selection Criteria <br /> Precipitation Synthetically developed by HELP using <br /> average monthly rainfall data for Stockton, <br /> California. <br /> Evapotranspiration Default values for Sacramento, California. <br /> Run-off Runoff coefficient modified for "poor stand <br /> ofgrass", but not transpiration. <br /> Soil and refuse moisture storage capacity Upper zone always at Field Capacity <br /> Root zone depth No vegetation included. <br /> Surface sloe 3% surface gradient. <br /> Subsurface lateral drainage 2% gradient with LCRS pipe at 200-foot <br /> centers. <br /> Solar radiation Data for Fresno, California data synthetically <br /> modified by HELP for Stockton's longitude <br /> and latitude. <br /> With the exception of the iterative moisture contents described below, all soil <br /> and refuse parameters used in modeling the Forward Landfill LCRS are default <br /> values selected from the HELP program as typical for municipal solid waste <br /> landfills. Weather data was synthetically generated by the program for the <br /> Stockton area and corrected for the latitude of the Forward Landfill facility, <br /> yielding an average annual rainfall total of approximately 15.5 inches. <br /> As a conservative measure, the HELP modeling that was completed for the <br /> project anticipated that the subgrade (liner) gradient beneath all development <br /> areas would be 2%, and that yearly thickness of refuse would no greater than 10 <br /> feet. While wastes that are initially placed in landfills are typically dry, with a <br /> moisture content that is well below their field capacity (moisture holding <br /> capacity), for the Forward Landfill leachate generation analyses, as a conservative <br /> Forward landfill JTD 5-22 <br /> L\Allied\2000.193\ReportsUTD-PC PC MP702:Sec-5-0:5/24/02 <br /> Revision 1:07/16/02 <br /> BRYAN A.STIRRAT S ASSOCIATES <br />