As we discussed earlier, transport of a contaminant is controlled by advection, but also is impacted by mechanical dispersion and/or molecular diffusion. In some cases, biogeochemical processes might be important, for example, reactive decay or sorption to soils and other solids.
In MAGNET, you can assign dispersity and diffusion coefficients or biogeochemical properties within the Aquifer Attributes tab of the Domain Attributes menu (Conceptual Model Tools, then DomainAttr). Note that you can also specify these parameters using zone features, but the applied properties only apply with that zone.
We will assign a longitudinal (i.e., along the pathline of the fluid flow) dispersivity coefficient of 7m in this example (see Figure 65). Longitudinal dispersivity coefficient typically can vary from 5 to 100m. Dispersion acts to dilute solutes in groundwater and lower their concentrations and is a result of mixing of contaminated fluid with uncontaminated fluid in the porous media. Click SAVE to close the Domain Attributes menu and preserve the changes.
Figure 65: Using the Domain Attributes menu (Aquifer Attributes tab) for assigning a longitudinal dispersivity coefficient