|
|
|
|
|
Continuity of concentration and flux is assumed at the boundary between layers. If a fractured layer is in contact with an unfractured layer, it is assumed that all fluid flow is transported along the fractures that intersect the unfractured layers (i.e., it is equivalent to having a very thin sand layer between unfractured and fractured layers).
In a fractured model the program can consider advective-dispersive transport along the fractures coupled with diffusion into the matrix on either side of the fracture. However, if the Darcy velocity is zero, or small, then the transport mechanism will be essentially diffusive through the matrix, the fractures will have no effect and should not be considered in modelling the migration of contaminants. Users planning to model migration in fractured media are warned that they should first see Rowe and Booker, 1990, 1991a, 1991b, and Rowe et al, 2004 for a discussion of modelling of fractured systems.
The following information about the fractures in each dimension can be specified on the Fracture tab:
Fracture Spacing: The spacing of fractures is the distance between fractures in each dimension.
Fracture Opening Size: The fracture opening size is the width of the gap between the fracture walls.
Number to sum: This is the number of terms to sum in the evaluation of the advective-dispersive equation for contaminant migration [Rowe and Booker, 1990, 1991a, 1991b]. For blocks where the fracture spacing is of the same order in all directions, 8 to 10 terms is usually adequate.
As the aspect ratio (horizontal spacing/vertical spacing or vertical spacing/vertical spacing) increases more terms are required in the summation. When the aspect ratio is large, the problem can usually be reduced to a lower order (eg. from 3D to 2D or 2D to 1D). For example, if the spacing between fractures in one vertical direction is 50 units, and in the other vertical and horizontal directions is 2 units. The widely spaced fractures can be ignored and the problem reduced to a 2D problem [Rowe and Booker, 1990].
In addition the following can be specified for the fractures:
Dispersion coefficient: This is the dispersion coefficient along the fracture. For a more complete description of dispersion coefficient see the Diffusion/ Dispersion Coefficient for a layer.
Distribution coefficient: This is the distribution coefficient along the fracture as defined by Freeze and Cherry (1979). This is often assumed to be zero.
After the data for the layer is entered, the user can go to the next layer by selecting the Next button, go back to the previous layer by selecting the Previous button, go to the first layer using the First button, or go to the last layer using the Last button. When the data for all the layers has been edited, the user can save the information by selecting the OK button.