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To edit the general data for a model either select the General Data item from the Data Entry menu or click on the title of the model. The General Data form will be displayed.
This form can be used to edit the following data for the model:
Title: The title of the model is used to describe the model, and may be up to 255 characters long.
Number of Layers: The model or deposit is divided into layers where each layer has different parameters. The total number of layers is entered with this parameter.
Maximum Depth: This is the maximum depth of the model including the bottom boundary condition. It is used only for drawing purposes and will not affect the calculations within the model.
Darcy Velocity: The Darcy Velocity is defined as: va = n v where, n = the effective porosity, v = the seepage (groundwater) velocity. If zero is entered for the Darcy velocity the transport mechanism will be purely diffusive. When the Variable Properties or Passive Sink options have been selected the Darcy Velocity parameter is omitted, since it is entered in these options.
Laplace Transform Parameters: The solution of the contaminant migration equations involves the inversion of a Laplace Transform. In this inversion the accuracy depends upon four parameters: TAU, N, SIG, and RNU. The user may adopt the default values (TAU=7, SIG=0, N=20, and RNU=2) or specify other values. It has been found that a value of TAU between 7 and 10, and a value of SIG = 0 is satisfactory in most cases. The more critical parameters, RNU and N, typically yield accurate results when:
RNU = 0.1 (Layer Thickness) (Darcy Velocity) / Minimum Diffusion/Dispersion Coefficient
and
N = 10 * RNU if RNU is greater than 1.0.
These values of RNU and N will work extremely well but will often require more integration than is necessary. If the computation times seem excessive smaller values of RNU and N should be tried, and the accuracy of the results compared.
The program will detect grossly unreasonable results and automatically repeat the calculation with the values suggested above, in this circumstance the value of RNU is limited to 40.