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EM 1110-1-4001 3 Jun 02 porosity of the soil in region J Si = water saturation in region J No = density of the solid matrix in region J R, = l+ S)01 + Ps j Kir (l_Of) (F-2) H(l—SJ)O) R, is the retardation factor for contaminant transport in the vapor phase and is analogous to the well- known retardation factor for contaminant transport in the liquid phase H is the dimensionless Henry's constant for the contaminant under investigation at the soil temperature Ka, is the distribution coefficient of contarmnants between the solid and liquid phases These parameters are described in more detail in Chapter 3 of the Manual This formulation assumes a NAPL is not present and surfaces of the soil grains are completely wetted by the pore water Removal of contaminants from the specified volume V during SVE or bioventmg occurs by two mayor mechanisms The first is by extracting the soil gases from the mobile regions and the second is degradation of the contaminants In addition,as the concentration is reduced in the mobile region, contaminants diffuse from the immobile region into the mobile region From a simple mass balance,the change in mass in the mobile fraction of the volume by these three mechanisms 1s described by dmn, dt -Q %-,,,n - "Ym Cw,m Sm 4�m fm V + a,01 (1 - SO f, V(Cv, - Cv m) (F-3) In the immobile region, the change in mass is governed by dm, dt - Y, Cw,1 Si 01 fi V - a 01 (1 - S,) f, V ( Cv, -Cv m) (F-4) where Q = volumetric extraction rate of soil gases t — time yj = degradation decay constant in region J Cc = first order mass transfer coefficient between the mobile and immobile regions The first term in equation (F-3)represents the removal by pumping and the second term accounts for in situ degradation The degradation is assumed to occur in the aqueous phase only The third term accounts for mass transfer from the immobile regions into the mobile regions The first term in equation (F-4) represents degradation in the pore water of the immobile region The second term couples the transfer from the immobile region to the contaminant concentration in the mobile region The transfer occurs only by diffusion in the vapor phase in this derivation,although equation (F-4)can be formulated to include liquid diffusion and advection if the water saturation is high in the immobile region F-4