Pore Scale Determination of the Rate of NAPL Dissolution or Volatilization

EPA Grant Number: R826268
Title: Pore Scale Determination of the Rate of NAPL Dissolution or Volatilization
Investigators: Keller, Arturo A.
Institution: University of California - Santa Barbara
EPA Project Officer: Lasat, Mitch
Project Period: October 1, 1997 through September 30, 1999
Project Amount: $133,179
RFA: Exploratory Research - Physics (1997) RFA Text |  Recipients Lists
Research Category: Water , Land and Waste Management , Air , Engineering and Environmental Chemistry

Description:

To design a remediation scheme, it is important to understand the physicochemical processes that govern inter-phase mass transfer of NAPLs in the subsurface, both in the unsaturated and water-saturated regions. The rate at which NAPLs dissolve or volatilize in large part determines the time required to clean up a contaminated site. Non-equilibrium conditions are most important during remediation, when the rate of inter-phase mass transfer can significantly limit the effectiveness of any treatment scheme. The most important parameter for determining the rate of inter-phase mass transfer is the interfacial contact area, ac, which up to now has proven impossible to measure experimentally. The existing empirical correlations available for calculating the inter-phase mass transfer coefficient, kp, have used 'surrogates' for the interfacial contact area. The objective of this project is to experimentally observe the dissolution and volatilization processes at the pore scale as a function of saturation and pore space geometry for various NAPLs, and then to determine how kp is functionally related to the observed ac and how this correlates with NAPL saturation, Sn. The hypothesis is that the relationship between ac and Sn varies with time, is non-linear, but can be expressed as a power function. A field-measurable value (Sn) can then be used to estimate kp, for applications in a modeling framework.

Approach:

A micromodel setup will be used, which allows the observation of the mass transfer processes within a controlled pore scale geometry, with a known fluid (water or vapor) flow rate. The images are captured dynamically through a video camera for numerical processing of the digitized images to determine both Sn and ac as a function of time. The outlet concentration of dissolved or volatilized NAPL in the flowing phase is measured using GC/MS. This information allows the experimental determination of the mass transfer coefficient, kp, as a function of ac or Sn.

Expected Results:

This project will provide a basic understanding of the inter-phase mass transfer processes for dissolution and volatilization. The current conceptual model for these processes has been lacking concrete experimental observation of the interfacial contact area, actual NAPL saturation and their relationship. The results of the experimental work will also provide a correlation between Sn and kp, which is a critical parameter for simulating remediation of NAPL contaminated sites. These results will have significant and immediate application in the design of remediation strategies, by providing (1) a clear understanding of the physical limitations to faster inter-phase mass transfer and (2) an observational and conceptual basis for relating the inter-phase mass transfer coefficient to NAPL phase saturation.

Supplemental Keywords:

groundwater, chemical transport, mass transfer, NAPL, VOC, remediation, environmental chemistry and physics, engineering., Scientific Discipline, Water, Waste, Environmental Chemistry, Physics, Remediation, Engineering, Chemistry, & Physics, Environmental Engineering, Groundwater remediation, chemical composition, chemical transport modeling, mass transfer, chemical kinetics, environmental contaminants, dissolution, pore scale determination, groundwater contamination, NAPLs

Relevant Websites:

http://www.bren.ucsb.edu/~keller/default.html#Projects

Progress and Final Reports:

  • 1998
  • Final Report