<< Click to Display Table of Contents >> Navigation:  Appendix A Examples > Example 12: POLLUTE vs. Analytical Solution > Description

The results obtained from POLLUTE are compared to those obtained by an analytical solution developed by Tang et al. (1981) for a single fracture system. A conservative contaminant is considered with a constant source concentration of 1. The fractures are 10 µm wide, have a groundwater (seepage) velocity along the fracture of 730 m/a, a dispersivity of zero, and a diffusion coefficient along the fractures of 0.077 m2/a. In this comparison the fracture spacing is 1 m. Because of the very low matrix diffusion coefficient there is no interaction between fractures over the time frame considered, thus the same result would be obtained if the fracture spacing were increased to 10 m. The Darcy velocity, which occurs along the fractures, can be calculated by multiplying the fractures per m times the fracture width times the seepage velocity:

 

va = 10x10-6 * 1 * 730 = 0.73x10-2

 

A porosity of 0.05 and tortuosity (the ratio of effective diffusion coefficient to the molecular diffusion coefficient in water) of 0.0000983 were assumed for the matrix material. The matrix diffusion coefficient is then given by multiplying the fracture diffusion coefficient and the tortuosity:

 

Dm = 0.077 * 0.0000983 = 7.5691x10-6

 

The following parameters are defined for this example: