Theoretical Evaluation of the Interfacial Area between Two Fluids in Soil

EPA Grant Number: R827116
Title: Theoretical Evaluation of the Interfacial Area between Two Fluids in Soil
Investigators: Bryant, Steven
Institution: The University of Texas at Austin
EPA Project Officer: Lasat, Mitch
Project Period: October 1, 1998 through September 30, 2001 (Extended to November 30, 2002)
Project Amount: $246,378
RFA: Exploratory Research - Physics (1998) RFA Text |  Recipients Lists
Research Category: Land and Waste Management , Air , Engineering and Environmental Chemistry

Description:

Nonaqueous phase liquids (NAPLs) are among the primary sources of contamination of groundwater. The overall rate of mass transfer of a chemical species between a NAPL and an aqueous phase is a critical parameter in assessing risk from a given contaminant source, in designing remediation strategies, and in interpreting results from allied technologies such as interwell partitioning tracer tests used to assess the volume of NAPL in place. The rate of mass transfer depends upon the thermodynamic driving force and the area of the interface between the phases. The interfacial area depends very strongly upon the geometry of the pore space of the host soil or rock and is consequently very difficult to measure directly. This project will develop a novel mathematical modeling technique to predict the interfacial area from first principles.

Approach:

The configuration of fluid phases in a porous medium, and hence the interfacial area, is governed by the pressure difference between the phases and by the geometry of the pore space. In naturally occurring granular porous media the locations of the grains are random, and consequently the pore space is highly irregular. This is the principal obstacle in obtaining quantitative predictions of interfacial area. The proposed research overcomes this obstacle by using a physically representative and geometrically determinate porous medium: the random, dense packing of equal spheres described by Finney. This packing, and numerical modifications of it, have proven to be excellent models of the pore structure in well-sorted sands and sandstones, permitting quantitative a priori predictions of transport properties and capillary phenomena. Previous research has yielded techniques for uniquely locating pore throats and pore bodies in the packing, for extracting network representations of the pore space and for simulating both drainage and imbibition in these networks. These simulations provided only approximate phase volumes. We propose to refine these techniques to provide more accurate phase volumes and to compute for the first time interfacial areas. This will be done by computing the local configuration of the phases on a pore-by-pore basis; this is feasible because the global capillary pressure is known at any time during imbibition/drainage and the geometry of every pore is known. The predictions can be validated by measurements from a recently published technique employing interfacial tracers.

Expected Results:

Based on the success of previous applications that used physically representative model porous media, this research should yield quantitative predictions of interfacial surface area in simple granular porous media. The results will be presented as functions of the phase volume fractions for both drainage and imbibition. The fundamental understanding obtained from these predictions will serve as a guide to evaluating laboratory and field data. In particular, it will be possible to extract the intrinsic mass transfer coefficient from the lumped mass transfer coefficient which is typically obtained from column experiments, and this will greatly enhance the ability to extrapolate laboratory data to field applications. Predictive models of fluid interfacial area in porous media will also enhance the predictive capability of existing models of subsurface multiphase transport, which often do not account for variation in interfacial area. Improved transport models will yield more reliable assessments of contamination risks and remediation strategies for NAPL sites.

Publications and Presentations:

Publications have been submitted on this project: View all 15 publications for this project

Journal Articles:

Journal Articles have been submitted on this project: View all 5 journal articles for this project

Supplemental Keywords:

network modeling, porous media, multiphase flow, remediation, chemical transport, RFA, Scientific Discipline, Air, Toxics, Waste, Physics, Mathematics, HAPS, Chemistry, chemical mixtures, Groundwater remediation, Engineering, Chemistry, & Physics, fate and transport, soil , porus media, NAPL, chemical transport modeling, interfacial phenomena, mass transfer, interwall partitioning tracer tests, groundwater contamination, mathematical formulations, NAPLs

Relevant Websites:

http://www.ticam.utexas.edu/CSM/EPA/area/index.html
http://www.ticam.utexas.edu/CSM/EPA/connectivity/index.html
http://www.ticam.utexas.edu/CSM/EPA/critcurv/index.html

Progress and Final Reports:

  • 1999 Progress Report
  • 2000 Progress Report
  • 2001 Progress Report
  • 2002
  • Final Report