Porosity, Dispersivity, and Contaminant Transport in Groundwater

Porosity (n) and Dispersivity (D) were modeled in relation to Solute Transport Time (t) in a saturated, homogeneous, isotropic, unconfined aquifer using the MOC model. It was noted that n and D have an important influence on solute transport time t in groundwater, with a consistently strong and direct relationship between n, D, and t. In the case of porosity, the relationship was found to be directly related to t when other aquifer properties remained unchanged. This was also mathematically argued using a form of the flow equation put forward by Henry Darcy (1856). Dispersivity on the other hand had somehow the same relationship with solute transport time t as porosity, but with much less effect. That is, higher dispersions lead to longer solute transport time within the aquifer system. This was because as the individual solute particles set off from the average seepage velocity, they traversed through longer distances due to tortuosity, mechanical mixing, diffusion, and microscopic heterogeneity latent in the porous media. Also when n and D were co- treated over t, n was noted to be dominant over D with regard t. This follows that the effect of porosity on solute transport time far out shadowed that of dispersivity. Stated in other words, the dispersivity of a substance in any porous medium is to a large extent a function of the porosity of that medium.