Superfund Research Program
Factors Controlling the Environmental Mobility, Microbial Transformation and Toxicity of Mixed Non-Aqueous Phase Liquids and Exposed Soils/Sediments
Project Leader: Walter J. Weber (University of Michigan)
Grant Number: P42ES004911
Funding Period: 1995 - 2006
Final Progress Reports
Year: 2004 1999
Theoretical and modeling studies for the prediction of nonaqueous phase liquid (NAPL) organic contaminant entrapment and dissolution have largely assumed that aquifer materials are preferentially water-wet. Many natural systems, however, exhibit fractional wettability (both water- and NAPL-wet solids), as a consequence of spatial and temporal variations in fluid and soil properties. In this project period, a numerical simulator was developed and applied to data derived previously in a series of NAPL dissolution column experiments. Modeling results revealed that dissolution mass transfer coefficient correlations from the literature were unable to accurately predict dissolution of entrapped PCE in fractional wettability media. Low and persistent concentration tailing behavior, observed after recovery of the separate phase PCE, was adequately modeled by incorporation of rate limited desorption. Two alternative models for dissolution mass transfer were developed. The first incorporated a two-parameter power function expression for the lumped mass transfer coefficient. This model was successfully fit to the laboratory data, and correlations were developed for the fitted mass transfer model parameters, as a function of wettability and grain size distribution characteristics. Because of the semi-empirical nature of this modeling approach, its predictive ability for other NAPL/porous media systems was rather limited. Thus, a more fundamental modeling approach was also investigated. In this second approach, the lumped mass transfer coefficient was successfully represented using independent estimates of the film mass transfer coefficient and the NAPL-water interfacial area. Results from numerical experiments indicate that both the magnitude and spatial distribution of wettability can significantly influence PCE dissolution behavior and remediation time field scales.