VLEACH models liquid advection, gas diffusion, and
three-phase equilibration in the vadose zone.
Current limitations include constant cell dimensions and
homogeneous soil properties throughout the profile.
Advection solution is time-centered (Crank-Nicholson), space-upward.
Diffusion solution is backward-difference (fully-implicit), space-centered.
Simultaneous equations are solved in matrix form using the Thomas algorithm.
Chemical and soil input parameters
* Chemical Parameters:
* KOC : Organic carbon distribution coefficient (ml/g)
* KH : Henry's constant (dimensionless)
* CMAX : Aqueous solubility (mg/l)
* DAIR : Free air diffusion coefficient (m2/d)
* Polygon-specific parameters:
* TITLE : Description of polygon
* AREA : Area of polygon (sq. ft.)
* DELZ : Vertical spacing of cells (ft)
* Q : Groundwater recharge rate (ft/yr)
* RHOB : Dry bulk density of soil (g/ml)
* POR : Total effective porosity of soil (dimensionless)
* THETA : Volumetric water content of soil (dimensionless)
* FOC : Organic carbon content of soil (dimensionless)
* CINF : Concentration of solute in infiltrating water (mg/l)
* CATM : Concentration of solute in atmosphere (
* CGW : Lower b'dry condition for gas diffusion:
* CGW < 0., water table is impermeable to gas diffusion
* CGW >= 0., fixed concentration at water table, (mg/l)
* NCELL : Number of vertical cells