Since the late 1980's, dense non-aqueous phase liquids (DNAPLs) have been identified as an important class of groundwater contaminants due their low aqueous solubilities and even lower drinking water standards; together these properties enable a relatively small volume of a DNAPL to contaminate a large volume of groundwater.; The goal of this research was to develop a conceptual model for the dissolution of entrapped, single-component DNAPLs in variable aperture fractures, and to use this conceptual model in conjunction with results from physical model experiments to develop an empirical model describing the inter-phase mass transfer process.; To develop the conceptual model for dissolution, a transparent cast of a variable-aperture fracture was fabricated and used to visualize two-phase flow and DNAPL entrapment. The visualization experiments involved releasing a DNAPL into the fracture cast at a constant capillary pressure.; The visualization experiments demonstrated several dynamic two-phase flow processes including: the hindrance of non-wetting fluids from entering larger aperture regions due to intervening smaller aperture regions; and the pinching off of a non-wetting fluid due to a decrease in capillary pressure upon encountering a larger aperture region.; The effluent concentration profiles generated from the dissolution experiments exhibited three distinct stages of dissolution: the initial pseudo-steady stage, the transient stage, and the tailing stage. Between 15 and 60% of the initial mass trapped within the fracture was removed over the course of each experiment, the majority of which was removed during the initial pseudo-steady stage. The mass removal rate began to decrease at the onset of the transient stage, and continued to decrease until it reached near zero at the start of the tailing stage.; The empirical model correlates the Sherwood number to dimensionless numbers representing the aqueous phase flow rate, the aperture field characteristics, the initial DNAPL saturation, and the transient DNAPL saturation. The model fits the data well, with all coefficients being highly significant, and a coefficient of determination of 0.88. The empirical model was successful in predicting the effluent concentration profile from two dissolution experiments not used in the model development. (Abstract shortened by UMI.)
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