Modeling the Impact of Cracking in Low Permeability Layers in a Groundwater Contamination Source Zone on Dissolved Contaminant Fate and Transport
2012
Sievers, Katherine W
The storage and transport of a dense non-aqueous phase liquid (DNAPL) was evaluated using a numerical model. Many DNAPLs are used as solvents by the DoD and industry. The improper disposal and handling of these chemicals has led to long term contamination of groundwater. When spilled, a DNAPL will pool atop low permeability layers and slowly dissolve creating a contaminant plume. The dissolved contaminant within a low permeability layer serves as long-term sources of contamination once the source is removed. In this study, cracks are hypothesized to exist in the low permeability layers, allowing for enhanced transport. A numerical model is employed using a dual domain construct (high and low permeability layers) to investigate the impact of cracking on DNAPL and CAH movement. Three scenarios were modeled to evaluate the impact of cracks: (1) CAH diffusion into an uncracked low permeability clay layer; (2) CAH advection-dispersion into cracks, and (3) separate phase DNAPL movement into the cracks. This study found cracking will cause an increase in transport and storage of TCE into low permeability layers, and that this increased transport will sustain down gradient concentrations for decades. Further, DNAPL phase TCE within cracks can significantly contribute to down gradient concentrations.
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