|M.Sc Student||Sharon Yaniv|
|Subject||Simulation of the Reclamation of Aquifers|
Contaminated by NAPL
|Department||Department of Civil and Environmental Engineering||Supervisor||Full Professor Rubin Hillel|
This study concerns characteristics of entrapped non-aqueous phase liquid (NAPL) dissolution in a fractured permeable formation. The study takes into account the reduction of rates of interphase mass transfer during the process of entrapped NAPL dissolution, as well as the effect of increasing porosity and permeability of the porous blocks that is associated with that dissolution. It was found that according to some models, unless the NAPL saturation is very low, changes of the permeability of the porous blocks during the entrapped NAPL dissolution might lead to significant local variations in the preferential flow pattern (division of the total aquifer flow between the fracture segments and the porous blocks) in the fractured formation. The study incorporates reference to this phenomenon, and it includes the development and application of a simplified model for rate-limited NAPL dissolution in fractured permeable media. The focus of this work is to characterize processes controlling NAPL removal by long-term gradual dissolution. Two major parameters control this flow phenomenon, NAPL dissolution, and solute transport: (1) The dimensionless interphase mass transfer coefficient, and (2) The mobility number, which represents the ratio between the permeable block and fracture flow rates. Local values of these parameters are subject to changes during the NAPL dissolution process. Such changes are affected by the dependence of the porous block permeability on the residual saturation of the entrapped NAPL. Three different models of this dependence have been considered in this study: 1) No effect of the entrapped NAPL on the porous block permeability( no K effect), 2) Moderate effect of the entrapped NAPL on the porous block permeability (Corey’s model), and 3) Significant effect of the entrapped NAPL on the porous block permeability (Parker’s model). The study indicates that the rate of reclamation of the formation by the pump-and-treat arrangement can be characterized according to the initial value of the dimensionless interphase mass transfer coefficient in the contaminated portion of the domain, and the value of the mobility number in regions of the domain that are free of entrapped NAPL. The effect of permeability changes during the reclamation process depends on the type of model describing the dependence of the porous block permeability. Generally, significant differences take place between the reclamation features of porous media represented by the three models considered in this study.
The calculations of this study imply that ‘depending on the type of model characterizing the dependence of the porous block permeability on the residual saturation of the entrapped NAPL, pump-and-treat reclamation of an aquifer might be extremely difficult. Therefore, various types of treatment technologies, and possibly combinations of such technologies should be applied to enhance the reclamation process taking place in a fractured porous formation, which is contaminated by entrapped NAPL.