Assessment of Partitioning Tracers for Estimation of DNAPL Source Zone Architecture.
Abstract: It is
estimated that 15,000 to 25,000 sites across the United States are impacted by dense
nonaqueous phase liquid (DNAPL) contamination. The difficulties in cleaning up and
closing out these sites have prompted many to consider the potential benefits of partial
removal of the source mass. Mathematical models developed to assess these benefits often
employ metrics of the spatial ... read moredistribution of DNAPL mass within the source. This spatial
distribution is termed the DNAPL architecture. Interestingly, there are currently no
field methods available for characterization of the DNAPL architecture. Thus, the
overall objective of this research was to develop a framework for assessing the
local-scale DNAPL architecture using partitioning tracers in push-pull tests. The
central hypothesis of the research is that differences in the mass transfer kinetics
between high and low saturation areas will permit estimation the mass fraction of DNAPL
present in pools (i.e., pool fraction). This hypothesis was tested using laboratory
experiments and mathematical modeling. Liquid-liquid-equilibrium experiments and
subsequent thermodynamic modeling were employed to assess the phase behavior of
partitioning of three representative alcohol tracers (1-pentanol, 1-hexanol, and
2-octanol) with a model DNAPL (trichloroethene), and determine the range of
concentrations over which partitioning may be assumed linear. Results from 1-D column
experiments and 2-D aquifer cell experiments indicate that tracer transport in systems
comprised of TCE-DNAPL can be described with linear driving force models that employ
mass transfer coefficients developed for the dissolution of pure-component DNAPLs.
Push-pull tests conducted in heterogeneous source zones created within 2-D aquifer cells
indicate that partitioning tracers can describe DNAPL architecture, but not the pool
fraction metric. Tests in these heterogeneous source zones also indicate that
differences in push-pull test breakthrough curves are not dominated by mass transfer
kinetics between high and low saturation areas. Instead, simulations conducted in
several, simplified source zones suggest push-pull tracer tests are strongly affected by
the amount of the vertical domain that contains DNAPL and the distance from the well to
the DNAPL mass. Results of this research indicate that push-pull tests may be useful
within a larger characterization framework to help resolve local-scale architecture,
thereby improving predictions of contaminant plume response to various level of
treatment within the source. It is recommended that future work focus on 3-D simulations
to explore the influence of radially distributed DNAPL on the ability of the push-pull
test to estimate the vertical extent of the DNAPL and distance from the well to the
Thesis (Ph.D.)--Tufts University, 2012.
Submitted to the Dept. of Civil Engineering.
Advisor: Andrew Ramsburg.
Committee: Linda Abriola, John Christ, Grant Garven, and Kurt Pennell.
Keyword: Environmental engineering.read less
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