Groundwater Contamination

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95067/1/eost7969.pd

Self-adaptive hierarchic finite element solution of the one-dimensional unsaturated flow equation

The advantages associated with the use of self-adaptive methods for the solution of problems which require the prediction of a frontal position in time are well known. In this paper a self-adaptive finite element solution for the non-linear unsaturated flow equation is developed using hierarchic p -version enrichment of the interpolating space. Additional computational advantages are demonstrated for an iteration scheme in which iterations after enrichment are performed only over a subdomain. Numerical solutions are presented for a one-dimensional infiltration scenario.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50201/1/1650100302_ftp.pd

Dense nonaqueous phase liquid (DNAPL) source zone characterization: Influence of hydraulic property correlation on predictions of DNAPL infiltration and entrapment

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95335/1/wrcr9623.pd

IAHS/AGU symposium on groundwater contamination

Papers presented at a two-day jointly sponsored IAHS/AGU symposium on groundwater contamination are briefly summarized. This international symposium was held 11–12 May, 1989, in Baltimore, Maryland. Presentations encompassed recent research developments in three general areas: abiotic and biotic processes governing contaminant transport; aquifer rehabilitation; and the influence of agricultural practices and nonpoint sources on aquifer quality. Contributions offered an interesting mixture of theoretical, mathematical, laboratory, and field studies. In the first session, transport processes explored ranged from dispersion and fingering to nonequilibrium sorption, metals complexation, and bacteria migration. The use of optimization modeling in the design of remediation strategies was the focus of another session. Here theoretical studies were presented alongside case histories of aquifer rehabilitation. In a final session, a number of models for agricultural management were described. These presentations were complemented by case studies of actual aquifer degradation resulting from land-use and management practices.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46767/1/254_2005_Article_BF01701696.pd

Predicting DNAPL entrapment and recovery: the influence of hydraulic property correlation

The influence of aquifer property correlation on multiphase fluid migration, entrapment and recovery was explored by incorporating correlated and uncorrelated porosity, permeability, and capillary pressure-saturation (P c -Sat) parameter fields in a cross-sectional numerical multiphase flow model. Comparison of two-dimensional entrapped organic saturation distributions for a simulated tetrachloroethylene (PCE) spill in ensembles of aquifer realizations suggests that the degree of spatial correlation in P c -Sat parameters exerts a controlling influence on dense nonaqueous phase liquid (DNAPL) spreading and redistribution in saturated aquifers. The predicted evolution of DNAPL source zones and resultant remediation efficiency under surfactant enhanced aquifer remediation (SEAR) also appear to be strongly influenced by the spatial correlation of aquifer parameters and multiphase flow constitutive relationships. Results for a limited number of realizations selected from each ensemble showed that removal of 60% to 99% of entrapped PCE could reduce dissolved contaminant concentration and mass flux by approximately two orders of magnitude under natural gradient conditions. Aqueous phase contaminant mass flux did not vary uniformly as a function of % DNAPL removed, however, and notable differences in behavior were observed for models incorporating correlated versus uncorrelated P c -Sat and permeability fields. Although these results must be confirmed through analysis of additional realizations, it is likely that similar or larger differences between correlated and uncorrelated system behavior will be observed in aquifers with greater spatially variability than that of the nonuniform, homogeneous sand aquifer studied here.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47837/1/477_2003_Article_162.pd

On the explicit incorporation of surface effects into the multiphase mixture balance laws

Interfacial conditions for multiphase flows are formulated on the microscale to include the possibility of surface effects. These conditions are then averaged to obtain macroscopic continuum equations which may be used in describing multiphase flows. A transformation is presented whereby the resultant macroscopic equations can be rewritten in a form identical to that which has been developed previously for a multiphase system not influenced by interfacial effects. This transformation is shown to have an impact on the forms of the intraphase stress tensor and heat flux vector in addition to the interphase stress and heat flux terms. Inclusion of interfacial effects is demonstrated to be essential to the proper understanding of phase interaction.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25521/1/0000062.pd

An iterative compositional model for subsurface multiphase flow

The governing equations describing multiphase flow with multicomponent solute transport may be cast in a number of forms. While mathematically equivalent, the numerical models based on each formulation differ in flexibility and efficiency. The set-iterative compositional formulation, a mathematical formulation that separates the solution of the phase-balance equations from the species balance is described herein. A mathematical model based on this formulation describes the flow of two mobile phases. Each phase may transport multiple chemical components. Mass exchange between phases is expressed by a linear kinetic equation. The numerical model based on the set-iterative compositional formulation is shown to model non-equilibrium phase partitioning, to provide a flexible framework that may be applied to organic mixtures with differing numbers of components and to yield a more efficient solution in comparison with models arising from standard compositional formulations.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31668/1/0000604.pd

Surfactant enhanced remediation of soil columns contaminated by residual tetrachloroethylene

The ability of aqueous surfactant solutions to recover tetrachloroethylene (PCE) entrapped in Ottawa sand was evaluated in four column experiments. Residual PCE was emplaced by injecting 14C-labeled PCE into water-saturated soil columns and displacing the free product with water. Miscible displacement experiments were conducted before and after PCE entrapment to determine the influence of residual PCE on column dispersivities. The first two column studies involved the injection of a 4% solution of polyoxyethylene (POE) (20) sorbitan monooleate, resulting in the removal of 90% and 97% of the residual PCE from 20-30- and 40-120-mesh Ottawa sand, respectively. Although micellar solubilization of PCE was the primary mode of recovery in these experiments, this process was shown to be rate-limited based on: (a) the disparity between initial steady-state concentrations of PCE in the column effluent and equilibrium values measured in batch experiments; and (b) the increase in effluent concentrations of PCE following periods of flow interruption. In the latter two experiments, surfactant solutions containing mixtures of sodium sulfosuccinates removed >99% of the residual PCE from soil columns packed with 40-270-mesh Ottawa sand. Approximately 80% of the PCE was mobilized as a separate organic liquid after lushing with -1) are not required to achieve significant PCE mobilization when buoyancy forces are important. The potential for displacement of dense nonaqueousphase liquids as a separate organic phase should, therefore, be evaluated during the selection of surfactant formulations for aquifer remediation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31591/1/0000520.pd

Phenomenological models for transient NAPL-water mass-transfer processes

A phenomenological model for transient NAPL dissolution, referred to as the "sphere" model, is developed. In this model, the mass-transfer coefficient and specific surface areas are quantified independently. The unique aspect of this work is the assumption that the complex distribution of NAPL blob shapes and sizes can be represented by a set of spheres with a range of diameters. The sphere diameter distributions are determined through the entrapment, polymerization and characterization of styrene blobs in sandy media. Mass-transfer coefficients are estimated from experimental measurements of the dissolution of naphthalene emplaced as solid spheres within sandy media.The phenomenological model describing NAPL dissolution rates is incorporated into a solute transport equation and solved with a numerical simulator. Simulations show that the sphere model can be calibrated to experimental NAPL dissolution data from column studies presented previously. The inclusion of a range of sphere sizes resulted in a model which represents experimental data better than a model based on mono-size spheres. The sphere model also adequately predicts dissolution for NAPL's with a range of solubilities provided the NAPL blob size distributions can be adequately estimated.The primary limitation of the sphere model is the qiantity of input data required to describe the distribution of effective sphere sizes. While these data requirements are extensive, the ability to define the NAPL blob distribution within the model makes the sphere model much more versatile for extrapolation to heterogeneous systems than other available dissolution models.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31587/1/0000516.pd