lecture19

lecture19 - Lecture 19 Landfill hydrology Landfill...

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Lecture 19 Landfill hydrology
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Landfill hydrology Transpiration Interception Evaporation Interception Snow Evaporation Snow Accumulation Snow Melt Runoff Rainfall/Snowfall Plant Growth Infiltration Lateral Drainage Depth of Head Barrier Soil Percolation Water Pathways Adapted from: Peyton, R. L. and P. R. Schroeder. "Water Balance for Landfills." Geotechnical Practice for Waste Disposal . Edited by D. E. Daniel. New York: Chapman & Hall, 1993. Vertical Percolation Soil Evaporation
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Water balance during active filling L = P + S – E –WA L = leachate P = precipitation S = liquid squeezed from solid waste E = evaporation WA = water adsorbed into solid waste
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Water balance after closure L = P + SM – RO – ET – DS – Q – WA + ME P = precipitation SM = snowmelt infiltration RO = runoff ET = evapotranspiration DS = soil moisture storage Q = lateral drainage in cap drainage layer WA = water adsorbed into solid waste ME = moisture extraction from waste
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ME term - Moisture extraction Moisture extraction occurs via landfill gas collection system Enhanced by heat in landfill 27 to 52ºC; 80 to 125ºF Every million m 3 of gas extracted includes 6.7 to 81 m 3 of condensate
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Soil moisture Soil moisture varies between: Saturation – 100% of pore space filled by water If allowed to drain by gravity field capacity Typically reached in about 2 days Evapotranspiration can remove additional water wilting point Duplicated in lab with suction of 25 atmospheres Difference between field capacity and wilting point is available water
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Soil moisture vs. time ~2 days saturation field capacity wilting point soil moisture content available water With ET Without ET time
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Soil moisture replenishment Soil still dry below wetting front Soil now wetted to field capacity Rainfall Wetting front Dry soil – Initially at wilting point
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Soil moisture replenishment Depth of soil determines how much rainfall is needed to bring soil to field capacity throughout soil column In dry climates, there is never enough rainfall to wet entire soil column and there is never ground-water recharge
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Typical soil properties Soil Saturation (porosity) Field capacity Wilting point Sand 0.39 0.09 0.05 Sandy loam 0.40 0.18 0.06 Loam 0.43 0.24 0.12 Clay 0.42 0.40 0.20 MSW 0.67 0.29 0.08 All properties are expressed as fractions of bulk volume.
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Typical soil properties Loam is a term from soil science to describe soils that contain a mix of clay, silt, and sand Ce nt im et er s Pe r 10 0 cm So il De pt h rc en t, Vo lu me Sand Fine sand Sandy loam Loam W i l t n g P o Available Water F e d C a p c y Clay loam Clay 0 8 16 Silt loam 24 32 0 8 16 24 32 Adapted from: Foth, H. D. Fundamentals of Soil Science. 8th ed. New York: John Wiley & Sons, 1990.
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Soil moisture vs. time Soil moisture content constantly fluctuates: Increased by rainfall Decreased by ET Soil moisture has great influence on ground-water recharge
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Annual water-table cycle 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month Precipitation (inches) 16.5 17 17.5 18 18.5 19 19.5 20 20.5 Depth to ground water (feet) Precipitation (inches) Depth to water table (ft)
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