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EM 1110-1-4001
<br /> 3 Jun 02
<br /> V, _ (1—fm)$,(1—S,)V
<br /> V. f m�.(1—S m)V
<br /> H(1—S,)
<br /> —b+ bz —4RmR,[r(O+Da)+Oct]
<br /> 2Rn,R,
<br /> —b— bz -4RmR,[F(O+(Da)+Oa]
<br /> r2 =
<br /> 2RmR,
<br /> b = R,n((x+r)+R,(O+(D(x)
<br /> Equations (F-20)and (F-21)are simple to use for matching contaminant extraction concentrations for a
<br /> given extraction history Early data may not fit well because the initial distribution of contaminants at
<br /> field sites is generally very different than the uniform,average concentration assumed by the theoretical
<br /> formulation However, after the initial sweep of the mobile soils,the concentration history is generally
<br /> . well-behaved and approaches an average concentration because of mechanical dispersion(i e , advective
<br /> mixing) The equations provide an accurate engineering model for predicting site behavior in the later
<br /> mass-transfer-limited phase if complicating factors do not exist(c g,NAPL)
<br /> Because of the volume averaging over each soil region,very few parameters appear in the equations
<br /> relative to the input required for detailed numerical modeling of an SVE system The input and/or fitting
<br /> variables are,
<br /> Soil Physical Properties 0,,,, 0„ Sm, S.
<br /> Site-Specific Contaminant Properties H, Rm, R„y,,,,y,
<br /> Initial Vapor Concentrations C,,,,o, CIO
<br /> Representative Contaminated Volume V(or V,,,)
<br /> Fraction of Soil Characterized as Mobile f,,,
<br /> Field-Scale Mass Transfer Coefficient a
<br /> This list of variables is very similar to the parameters used in two-region modeling of solute transport in
<br /> saturated systems (Griffioen et al , 1998) Average soil physical properties in each region such as
<br /> porosity and water saturation are usually available from independent measurements With these soil
<br /> physical properties and Henry's constant for the contaminant, the retardation coefficient in each region
<br /> can be estimated as described in Chapter 2 If degradation of the contaminant is considered significant,
<br /> the degradation coefficient could be estimated from the appearance of daughter compounds in the
<br /> extracted vapors, however, such an analysis is beyond the scope of this document By definition the
<br /> concentration in extracted vapors is equal to the concentration in the mobile soils Therefore, the
<br /> • measured extraction concentration at a specified start time to is the initial concentration in the mobile
<br /> F-13
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