Modeling Enhanced Storage of Groundwater Contaminants due to the Presence of Cracks in Low Permeability Zones Underlying Contaminant Source Areas
Abstract
Throughout DoD, chlorinated aliphatic hydrocarbons (CAHs), a type of Dense Non-Aqueous Phase Liquid (DNAPL), have been frequently used. In the subsurface, spilled DNAPLs may pool atop low permeability clay layers. In this study a numerical model is constructed using the Groundwater Modeling System to assess how cracks in the clay, either pre-existing or the result of DNAPL-clay interactions, might impact a dissolved CAH plume generated by the DNAPL source. The conceptual model posits a DNAPL source in a high permeability sand aquifer sitting atop a low permeability clay layer. The model assumes dissolved CAH generated by the DNAPL is transported by advection, dispersion, and sorption in the sand. These transport processes are coupled to processes in the clay. In the clay, dissolved CAH is transported by diffusion. However, due to cracks in the clay; "enhanced diffusion" of dissolved CAH by advection may also occur. Advective transport in the cracks coupled to diffusive transport in the clay matrix is simulated using a dual domain model. Modeling indicates that as cracking increases, mass of contaminant in the clay increases. This leads to higher concentrations of contaminant "back diffusing" out of the clay and higher downgradient concentrations long after source removal.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 2011
- Accession Number
- ADA544034
Entities
People
- Jeremy M. Miniter
Organizations
- Air Force Institute of Technology