Diffusional Rate Limitations in Heterogeneous Porous Media: Model Structure, Scale, and Geologic CharacterizationEPA Grant Number: R824768
Title: Diffusional Rate Limitations in Heterogeneous Porous Media: Model Structure, Scale, and Geologic Characterization
Investigators: Freyberg, David L. , Roberts, Paul V.
Institution: Stanford University
EPA Project Officer: Hiscock, Michael
Project Period: November 1, 1995 through October 1, 1998
Project Amount: $198,000
RFA: Water and Watersheds (1995) Recipients Lists
Research Category: Water and Watersheds , Water
Description:This project aims to elucidate the nature and significance of diffusional rate limitations during solute transport in saturated, heterogeneous porous media, with a view to evaluating the role of diffusional limitations in contaminant remediation. The research is considering the relative importance of diffusional rate limitations manifested over a range of spatial scales, from the grain scale up to regional scales, within the context of a numerical transport model that accounts for advection, dispersion, and sorption. Along with multi-scale diffusion submodel development, the project is addressing: (1) the interactions between geologic structure, heterogeneity, upscaling, and diffusional transport process representation; (2) physically-based aggregation schemes that are consistent with different model formulations of transport processes; and (3) the increase in size and complexity of heterogeneities that are likely to be encountered with increasing size of an aquifer domain under analysis.
This aspect of the investigation is using a quasi-deterministic approach that postulates a set of realistic scenarios for heterogeneity based on physically-founded consideration of geologic depositional processes. Using a non-dimensional form of the transport model, dimensionless groups incorporating space and time scales will be identified that quantify the relative importance of the diffusional rate limitations in terms of influence on contaminant transport. Sensitivity analyses will be conducted to differentiate between: (1) situations in which diffusional rate limitations are important and need to be accounted for, and (2) circumstances where such rate limitations are negligible. As a preliminary test of the modeling methodology, site characterization data from the well-documented Borden transport experiment will be utilized.
The results from this research will contribute to fundamental understanding of the impact of heterogeneities at differing scales on solute transport in groundwater, under the influence of diffusionally controlled slow release from zones of low permeability, with applications to contaminant remediation design, site characterization, and the interpretation of field monitoring and laboratory experimental data.