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TABLE 2-SOILS ENGINEERING PROPERTIES USED FOR MODELING Soil Properties Alternative Final Cover Mixture at 10% Compacted Relative Density 90% Sat.Permeability cm/sec)(degraded on-site soils) 3.30 x 10'6 Optimum Moisture Content 16.8 Dry Density(PCF) 99.5 Liquid Limit NA Plasticity Index NA <#200 Sieve 76 <5 Micron % 30 U.S.C.S.Classification CL Remolded Bulk Dry Density( /cm) 1.56 Campbell's A Coefficient -4.89 Campbell's B Coefficient 8.403 4.2.4 CLIMATIC CONDITIONS Precipitation - Another critical element in modeling cover performance using LEACHM involves identification of total daily precipitation, as well as the time and rate of water application. For each rain event, LEACHM calculates the maximum time period allowed for infiltration as the specified quantity of water to be applied divided by the application rate. Water, which has not entered the soil profile at the end of the application period, is assigned to an excess runoff term and included in the mass balance calculations. The matric potential of the soil and the unsaturated hydraulic conductivity of the soil thus limit infiltration into the profile at the time of water application. In other words, infiltration is limited by the ability of the soil to take water. Since positive drainage will always be maintained on the landfill surface, no ponding of rain or irrigation waters was included in the analyses. The enclosed analyses of a non-prescriptive cover at the FSL were performed utilizing precipitation data recorded at the Western Regional Climate Center's Stockton Station for the years 1993-2002. The magnitude and duration of the rainfall events were estimated in a fashion believed to conservatively represent typical anticipated application. This included defining the time of day for water application to be 0.4 days (9:36 am) and a water application rate of 60 mm/day. Evapotranspiration- LEACHM requires mean weekly pan evaporation data from which daily potential evapotranspiration(DPET) is calculated as one-seventh of the weekly total pan evaporation. Daily potential transpiration is calculated by multiplying the DPET by a crop cover fraction. Daily potential evaporation is then calculated as the difference between DPET and potential transpiration. For modeling purposes, LEACHM assumes that evapotranspiration starts at 0.3 days (7:12 a.m.) and ends 12 hours later at 0.8 day (7:12 p.m.). During this period, potential evapotranspiration is varied sinusoidally with -5- C:\2005-0082\FOR WARD/ForwordCOVER.DOC\7/13/2005 Geologic Associates