An Assessment of the Rate Limited Liquid-Liquid Interphase Mass Transfer in DNAPL Source-Zones: Modeling Techniques and Applications in Site Characterization.
Abstract: Remediation of
dense nonaqueous phase liquids (DNAPLs) remains an important challenge for the
environmental engineering community. Many characterization and remediation technologies
rely on the mass transfer of solutes between the aqueous and DNAPL phases. Therefore,
accurate description of the solute mass transfer rate is essential to the design and
implementation of these applicat... read moreions. This research focused on modeling studies to
quantify rate-limited interphase mass transfer between liquid-liquid phases within DNAPL
source zones in laboratory and field-scale applications. Numerical modeling of
experimental data from laboratory scale column experiments indicated that intra-NAPL
diffusion offered negligible resistance to interphase mass transfer. Thus, a linear
driving force approximation of aqueous phase diffusion adequately described interphase
partitioning within homogeneous source zones. The effect of source zone heterogeneities
on the effective mass transfer rate coefficient was explored through a series of 2D
simulations. A predictive model for the upscaled mass transfer coefficient was developed
and verified. The immobile phase spreading in the vertical direction, Reynolds number,
pool fraction, and the effective organic phase saturation were identified as the
parameters controlling partitioning rates. 3D field scale simulation of push-pull tracer
tests was used to investigate the hypothesis that solute partitioning in heterogeneous
source zones could be effectively described using the rate-limited model developed here,
in contrast to the current practice based on a local equilibrium assumption. For the
examples considered herein, the upscaled model was capable of estimating the overall
NAPL saturation with less than three percent error, but not the pool fraction or the
vertical spreading of NAPL. Results of this research may be used to estimate the mass
exchange rate between the separate liquid phases in heterogeneous porous media and
improve our understanding of the transport of partitioning solutes in DNAPL source
zones. The models developed in this research, based on rate-limited partitioning as
opposed to the current approach of using local equilibrium models, provide more precise
methods to analyze field scale partitioning tracer tests. Partitioning tracer tests in
conjunction with other site characterization methods provide techniques to quantity the
presence and distribution of NAPL in the subsurface. Future research in this area should
focus on diversifying and increasing number of 3D simulations over a broader range of
parameter values, i.e. saturation and mass distribution metrics, to further explore the
predictive potential of the developed model for estimating spatial distribution of the
Thesis (Ph.D.)--Tufts University, 2013.
Submitted to the Dept. of Civil Engineering.
Advisor: Linda Abriola.
Committee: John Christ, Eric Miller, Kurt Pennell, and Andrew Ramsburg.
Keywords: Environmental engineering, Hydrologic sciences, and Geology.read less