Date of Award

3-11-2011

Document Type

Thesis

Degree Name

Master of Science in Environmental Engineering and Science

Department

Department of Systems Engineering and Management

First Advisor

Mark N. Goltz, PhD.

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.

AFIT Designator

AFIT-GES-ENV-11-M02

DTIC Accession Number

ADA544034

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