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irrigation. Their solutions can be used to evaluate the impact of rainfall on subsurface FIGURE G-1
<br /> moisture conditions. The drainage of soil by gravity following infiltration of one
<br /> centimeter of water for two soil types,sand and silt,is shown in Figure 1. The figure Soil or.ln.So cry..(Gordn•r at.1.,1570)
<br /> demonstrates that these two soil types drain within approximately five days.
<br /> Additionally,Sisson et al.(1980)derived a one-dimensional unsaturated flow equation au
<br /> by assuming a unit gradient approximation. The estimation of the rate of drainage for a
<br /> silty sand is shown in Figure 2. The figure shows that silty sand drains within about five g a.0
<br /> days,agreeing with the approximations by Gardner et al.(1970). !
<br /> REFERENCES a� 4
<br /> SILT `f
<br /> Auer, L.H., N.D.Rosenberg,K.H.Birdsell,and E.M.Whitney. 1986. The Effects of
<br /> Barometric Pumping on Contaminant Transport. Journal of Contaminant Hydrology,v.
<br /> 24,p.145-166. SAND
<br /> a ¢ • a m ': u
<br /> Clements,W.E.,and M.Wilkening. 1974. Atmospheric Pressure Effects on 222Rn Ti-le•yal
<br /> Transport across the Earth-Air Interface. Journal of Geophysical Research,v.79,n.33, „w ,<
<br /> p.5025-5029.
<br /> Eberling,B.,F.Larsen,S.Christensen,and D. Postma. 1998. Gas Transport in a Soil drainage curves where gravity predominates as derived from Gardner et al.(1970).
<br /> ur
<br /> sata
<br /> Confined Unsaturated Zone during Atmospheric Pressure Cycles. Water Resources The figure denotes two scenarios,silt and sand,where the initial unsaturated hydraulic
<br /> Research, nv. at a 2855-2862. conductivity within the infiltration zone is 1 centimeter per day and 1000 centimeters per
<br /> p. day,respectively. An instantaneous infiltration of one centimeter is assumed in the
<br /> Gardner,W.R.,D.Hillel,and Y.Benyamini. 1970. Post-Irrigation of Soil Water,1. evaluation. The figure demonstrates that drainage to asymptotic moisture conditions
<br /> Redistribution. Water Resources Research,v.6,n.3, 851—861. occurs within about five days for these two soil types.
<br /> Kienbusch,M.,and D.Ranum. 1986. Validation of Flux Chamber Emission `
<br /> ,�. NL,FIGURE G-2
<br /> Measurements on a Soil Surface. Draft Report to EPA-EMSL,Las Vegas,under EPA
<br /> Contract No.68-02-3849,Work Assignment 69,June 1986. 0 .............._8o°.°ri _p'rvq_� �0°�"� 1°80t.
<br /> Nilson,R.H., E.W.Peterson,K.H.Lie,N.R.Burkhard,and J.R.Hearst. 1991. zo
<br /> Atmospheric Pumping:A Mechanism Causing Vertical Transport of Contaminated r +o
<br /> Gases through Fractured Permeable Media. Journal of Geophysical Research,v.B13, *; 80 aLnswO -..
<br /> o
<br /> p.21,933-21,948, ; _D25
<br /> so 5
<br /> Massmann,J.,and D.F.Farrier. 1992. Effects of Atmospheric Pressures on Gas R 10D -p
<br /> Transport in the Vadose Zone. Water Resources Research,v.28,n.3,p.777-791. E '20
<br /> '1a
<br /> Radian Corporation. 1984. Soil Gas Sampling Techniques of Chemicals for Exposure
<br /> Assessment—Data Volume. Report to EPA-EMSL,Las Vegas under EPA Contract No. ' 0.10 0.20 a]a 0.+0 ow
<br /> 68-02-3513,Work Assignment 32,March 1984. w�»w.aaoaa M+•,0
<br /> Sisson,J. B.,A.H.Ferguson,and T.Th.van Genuchten. Simple Method for Predicting
<br /> Drainage from Field Plots. Soil Science Society of America Journal,v.44,p.1147— Soil drainage curves as derived from Sisson et al.(1980)where a unit gradient is
<br /> 1152. assumed. The figure denotes one scenario,silty sand,where the initial unsaturated
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