As immiscible organic contaminants migrate through the
subsurface environment, a significant portion of non-aqueous
phase liquids (NAPL's) is trapped by capillary forces and
remains in the subsurface as immobile blobs or ganglia.
Residual saturations of NAPL on the order of 5-30 percent have
been observed in saturated subsurface systems. The NAPL can
partition into the aqueous phase and serve as a long-term
source of groundwater contamination. NAPL-aqueous mass
transfer rates impact the distribution and the rate of
movement of the contaminant within the subsurface. The mass
transfer coefficient is a function of many variables including
aqueous phase velocity and NAPL-aqueous interfacial area.
A one-dimensional column apparatus and experimental
procedure was developed to study the nature of mass transfer
between the aqueous phase (water), and a non-aqueous phase
liquid (NAPL) in porous media. The NAPLs used in the
experiments were composed of soluble and insoluble (inert)
compounds. These experiments were designed to investigate the
aqueous mass transfer of benzene, toluene, ethylbenzene, and
xylene from and inert compound (soltrol or hexadecane).
The results of this research indicate that the rate of
NAPL-aqueous interphase mass transfer increases as a function
of increasing aqueous phase velocity and percent NAPL
saturation. Miller's equation was used to compare the model
performance. Comparison of the experimental K values obtained
by the literature was performed. The results indicated a
satisfactory model performance.
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