A simplified model for transport in aquifers

Chemicals that are dissolved in groundwater flow along with the slow-moving water as it makes its way through the complex pores of the aquifer; during this process they are dispersed in different directions. The rate of dispersion depends on the porous structure and the fluid speed. Many groundwater aquifers have a natural layered structure; here this is used to advantage by discretizing them into almost horizontal layers, where each may have different matrix properties such as thickness, permeability, dispersivity, porosity, etc. The mean dynamic pressure (or mean hydraulic head) may be assumed constant vertically at each horizontal point if it is not in the vicinity of a well or where there is very small vertical flow. In the vicinity of recharge or pumping wells, the mean dynamic pressures or hydraulic heads for each sub-layer of the aquifer may be allowed to have different values for each different sub-layer. Steady-state fluid flow is considered here, in both confined and phreatic (unconfined) aquifers for illustration