Accounting for Mass Transfer Kinetics when Modeling the Impact of Low Permeability Layers in a Groundwater Source Zone on Dissolved Contaminant Fate and Transport.

摘要

In this study, the subsurface storage and transport of a Dense Non- Aqueous Phase Liquid (DNAPL) was studied using a numerical model. Recent studies have found evidence that cracks can exist in low permeability layers within aquifers, and that a significant mass of DNAPL can be stored within those cracks. In this research, we simulate the effect of DNAPL in the low permeability cracks on contaminant plume evolution and persistence. A key parameter governing fate is the rate of DNAPL dissolution. In this study, we model the dissolution rate as both a constant and as a function of time, using parameters applicable to a real world site. We find that when the dissolution rate varies with time, significantly more DNAPL persists in the low permeability zone and downgradient plume concentrations remain higher for longer than when the rate is modeled as constant. Furthermore, we found that DNAPL and plume persistence are very dependent on the parameters used to simulate source dissolution, which further depend on both DNAPL source and site characteristics, pointing to the need for good source zone characterization.