A series of local and bench scale laboratory experiments and bench and field
scale numerical simulations were conducted to develop a better understanding of the
interrelationship between nonwetting phase (NWP) source zones and downgradient
aqueous phase concentrations in saturated porous media contaminated by immiscible
organic liquids. Specific emphasis was placed on the factors governing the rate of
NWP source zone evolution and the factors governing the rate of mass transfer from
the NWP to the aqueous phase. Hysteretic NWP relative permeability-saturation (krN-SW) relationships were
measured at the local scale for six sands to examine the relationship between krN-SW
functions and porous media type. Parameterization of the measured constitutive
relationships revealed a strong correlation between mean grain diameter and the
maximum value of NWP relative permeability. The measured krN-SW
relationships, were validated through a bench scale experiment involving the
infiltration, redistribution, and immobilisation of NWP in an initially water saturated
heterogeneous porous medium. This match of simulation to experiment represents the
first validation of a multiphase flow model for transient, fixed volume NWP releases.
Multiphase flow simulations of the bench scale experiment were only able to
reproduce the experimental observations, in both time and space, when the measured
krN-SW relationships were employed. Two-dimensional field scale simulations of a fixed volume NWP release into a
heterogeneous aquifer demonstrate the influence of spatially variable krN-S
relationships correlated to porous media type. Both the volume of the NWP invaded
porous media, and the length of time during which NWP is migrating, will be under
predicted if variable (correlated) kr,N is not accounted for in the numerical model
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formulation. This under prediction is exacerbated as the mean intrinsic permeability
of the release location decreases.
A new, thermodynamically-based interfacial area (IFA) model was developed
for use in the single-boundary layer expression of mass transfer as an alternative to
existing empirical correlation expressions. The IFA model considers consistency and
continuity of constitutive relationships, energy losses, effective specific interfacial
area for mass transfer, and dissolution of residual NWP. A bench scale experiment
involving the release and dissolution of a transient NWP source zone in
heterogeneous porous media was conducted to evaluate the appropriateness of the
developed IFA model when utilised to predict NWP dissolution rates. Comparison of
measured downgradient dissolved phase concentrations and source zone NWP
saturations in time and space with those from numerical simulations of the experiment
reveal that the proposed IFA model is superior to both a local equilibrium assumption
and existing empirical correlation expressions. This represents the first mass transfer
model validated for the dissolution of a complex NWP source zone. Twodimensional
simulations at the field scale of multiphase flow and dissolution suggest
that employing existing mass transfer expressions instead of the IFA model lead to
incorrect predictions of the life spans of NWP source zones, downgradient dissolved
phase concentrations, and the rate of mass flux through a downgradient boundary.
The practical implication of this research is that accurate numerical predictions
of the evolution of a transient NWP source in porous media require consideration of
krN-S relationships and NWP / aqueous phase IFA, as these factors dictate the rates of
the key subsurface contaminant processes of migration and dissolution, respectively
