1997 Conference Proceedings

Mathematical Modeling of Surfactant-Enhanced Mobilization and Kinetic Dissolution of DNAPLs in Soil Columns

M. D. White, M. Oostrom
Pacific Northwest National Laboratory, Richland, Washington

Proceedings of Seventeenth Annual American Geophysical Union Hydrology Days, Fort Collins, CO

Abstract

A mathematical model for surfactant-enhanced mobilization of dense-nonaqueous-phase liquids (DNAPLs) is developed and combined with previously developed models for kinetic dissolution to systematically investigate the processes of surfactant-enhanced aquifer remediation (SEAR). The model couples four nonlinear mass balance conservation equations (i.e., water, DNAPL-phase organic, aqueous-phase organic, and aqueous-phase surfactant) that incorporate aqueous- and NAPL-phase migration and transport of aqueous-phase dissolved surfactant and organics. Sorption of surfactant is assumed to conform to a Langmuir isotherm model, whereas organic sorption is modeled using a linear isotherm with a soil-organic content dependent retardation coefficient. Rate-limited solubilization of the organic into the aqueous phase is represented by a linear driving force expression, dependent on the surfactant-enhanced equilibrium concentration. Surfactant-enhanced mobilization of the fluid phases is incorporated using surfactant concentration dependent interfacial tension lowering and scaled relative permeability-saturation-capillary pressure relations. These mechanistic models are implemented into an integrated-volume finite-difference solver for flow and transport through variably saturated geologic media. Simulations of one-dimensional soil columns are executed to investigate the combined processes of surfactant-enhanced dissolution and mobilization. The appropriateness of assuming an immobile DNAPL phase during the application of surfactant-flushing type aquifer remediation techniques is the subject of the investigation. Sensitivity analyses will be used to investigate the influence of interfacial tension on the mobilization of the fluid phases. Subsequent investigations will completely address the surfactant-enhanced remediation process from initial DNAPL infiltration, redistribution, and entrapment to surfactant dissolution and mobilization of free and entrapped DNAPL.

Physical Modeling of Multifluid Behavior in Porous Media

M. Oostrom¹, C. Hofstee², R.J. Lenhard³, R.C. Walker², J.H. Dane², M. D. White<sup>1

1</sup>Pacific Northwest National Laboratory, Richland, Washington
²Department of Agronomy and Soils, Auburn University, AL
³Department of Soil and Water Sciences, Sultan Qaboos University, Sultanate of Oman

Proceedings of Seventeenth Annual American Geophysical Union Hydrology Days, Fort Collins, CO

Abstract

Nonaqueous-phase liquids (NAPLs), such as solvents and hydrocarbon fuels, are found in the subsurface at many sites. Investigations have involved numerical as well as experimental studies. The lack of quantitative experimental data, especially on constitutive relations between fluid saturation, capillary pressure, and relative permeability, has hampered the testing and evaluation of numerical models. In this paper, an overview will be given of several quantitative, intermediate-scale multifluid experiments in porous media that have been conducted at Auburn University and at the Pacific Northwest National Laboratory. Some objectives of the experimental studies were to:

• generate data sets for testing numerical simulators,
• test and evaluate the ability of commonly used constitutive relations to predict infiltration and redistribution of NAPLs in variably saturated porous media,
• study the application of the scaling concepts for nonspreading liquids,
• investigate the behavior of NAPL vapors in the vadose zone,
• study two- and three- phase multifluid hysteresis
• evaluate remediation techniques such as Surfactant Enhanced Aquifer Remediation (SEAR)