טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentYaniv Sharon
SubjectAnalyzing Remediation Methods of Fractured Aquifer
Contaminated by NAPL (Non-Aqua Phase Liquids)
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Hillel Rubin
Full Thesis textFull thesis text - English Version


Abstract

This study concerns the development of modeling approach for simulating and evaluating entrapped light nonaqueous phase liquid (LNAPL), like kerosene, dissolution of the entrapped NAPL and transport of the organic solute in a fractured permeable aquifer. The term fractured permeable formations refers to an aquifer made of a formation composed of porous blocks of high permeability embedding fractures. LNAPL entrapment results due to artificial and seasonal fluctuations of the water table.

The objective of this study is to characterize and evaluate by theoretical means and laboratory experiments, the contamination and remediation of fractured permeable formations. In the framework of the research, two experimental setups were developed and constructed to synthesize the experimental results with the numerical modeling and simulations. One experimental setup is a physical model of a homogeneous aquifer. The second experimental setup is a physical aquifer model made of a fractured permeable formation.

            The conceptual basic model developed in this study is a two-dimensional (2-D) model of permeable blocks, embedding oblique equidistant fractures with constant aperture and orientation. The top layers of the aquifer are contaminated with completely stagnant entrapped LNAPL in the form of ganglia, which are surrounded by the mobile and immobile water phase. The numerical model consists of a finite difference grid composed of small squares and three major types of simulations have been performed:

Two major parameters control the LNAPL dissolution and the solute transport: (1) The dimensionless interphase mass transfer coefficient, and (2) The mobility number, which represents the ratio of the permeable block discharge to the fracture discharge.

Numerical simulations concerning high initial saturation of the entrapped LNAPL, have shown that during initial stages of the fractured permeable formations cleanup, the contaminant concentration increases, and later it decreases. This phenomenon originates from significant groundwater bypassing the LNAPL ganglia entrapped in the permeable blocks via the fracture network. This theoretical result is coherent with the experimental results obtained in this study.

The presence of fractures within the permeable formation may significantly change the characteristics of the LNAPL contaminated aquifer remediation. The fracture network and reduced porous block permeability and porosity by the entrapped LNAPL provide mechanisms for groundwater flow bypassing the entrapped LNAPL ganglia. The entrapped LNAPL dissolution is affected by the heterogeneity of the porous matrix, nonuniform distribution of the entrapped LNAPL saturation and different shapes of the entrapped LNAPL ganglia.