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Title: MULTI-REGION REACTIVE TRANSPORT DUE TO STRONG ANISOTROPY IN UNSATURATED SOILS WITH EVOLVING SCALES OF HETEROGENEITY

Abstract

At Hanford, the prediction of field-scale flow and transport in the vadose zone beneath tank farms and other waste-management facilities provide as good example of the limitations of current conceptualizations. Contaminant plumes in Hanford's vadose zone typically show extensive lateral spreading with splitting along flow paths and multiple zones of high-contaminant concentrations, even in sediments that appear homogeneous and isotropic at the regional scale. Because of the limited success in predicting current contaminant distributions using existing conceptual models and approaches to parameterization, there is some uncertainty about predictions of future transport behavior. This is mostly because current parameter upscaling procedures result in overly smoothed descriptions of the hydraulic functions that cause many of the important details (e.g. extreme water and solute flux, anisotropy), known to be caused by finescale heterogeneity, to be ignored.

Authors:
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA; Lehigh University, Bethlehem, PA
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
893181
Report Number(s):
EMSP-86952-2005
R&D Project: EMSP 86952; TRN: US200625%%127
DOE Contract Number:
FG07-02ER63512
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; 58 GEOSCIENCES; ANISOTROPY; FORECASTING; HYDRAULICS; PLUMES; SEDIMENTS; SOILS; SOLUTES; STORAGE FACILITIES; TRANSPORT; WASTE MANAGEMENT; WATER

Citation Formats

Ward, Andy. MULTI-REGION REACTIVE TRANSPORT DUE TO STRONG ANISOTROPY IN UNSATURATED SOILS WITH EVOLVING SCALES OF HETEROGENEITY. United States: N. p., 2005. Web. doi:10.2172/893181.
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Ward, Andy. MULTI-REGION REACTIVE TRANSPORT DUE TO STRONG ANISOTROPY IN UNSATURATED SOILS WITH EVOLVING SCALES OF HETEROGENEITY. United States. doi:10.2172/893181.
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Ward, Andy. Wed . "MULTI-REGION REACTIVE TRANSPORT DUE TO STRONG ANISOTROPY IN UNSATURATED SOILS WITH EVOLVING SCALES OF HETEROGENEITY". United States. doi:10.2172/893181. https://www.osti.gov/servlets/purl/893181.
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@article{osti_893181,
title = {MULTI-REGION REACTIVE TRANSPORT DUE TO STRONG ANISOTROPY IN UNSATURATED SOILS WITH EVOLVING SCALES OF HETEROGENEITY},
author = {Ward, Andy},
abstractNote = {At Hanford, the prediction of field-scale flow and transport in the vadose zone beneath tank farms and other waste-management facilities provide as good example of the limitations of current conceptualizations. Contaminant plumes in Hanford's vadose zone typically show extensive lateral spreading with splitting along flow paths and multiple zones of high-contaminant concentrations, even in sediments that appear homogeneous and isotropic at the regional scale. Because of the limited success in predicting current contaminant distributions using existing conceptual models and approaches to parameterization, there is some uncertainty about predictions of future transport behavior. This is mostly because current parameter upscaling procedures result in overly smoothed descriptions of the hydraulic functions that cause many of the important details (e.g. extreme water and solute flux, anisotropy), known to be caused by finescale heterogeneity, to be ignored.},
doi = {10.2172/893181},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Wed Jun 01 00:00:00 EDT 2005},
month = {Wed Jun 01 00:00:00 EDT 2005}
}
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DOI:  10.2172/893181
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  • Current conceptualizations of state-dependent anisotropy have failed to describe field observations, and the importance of multi-region flow in strongly anisotropic soils appears to be unrecognized. It is hypothesized that under the typical conditions of arid waste sites, when strong heterogeneity is predicted, the first order small anisotropy analysis is not rigorously applicable, and non-equilibrium mass transfer governs transport. Inter-region mass transfer is dominated by local velocity variations rather than diffusion, and access to reactive sites becomes limited. Accurate representation therefore requires an analysis to transport over evolving scales of heterogeneity and complexities to account for the interacting physical and chemicalmore » processes governing sorption in anisotropic media. In order to address these issues an integrated laboratory, field-modeling study with the following objectives is proposed. (1) Determine the scale of applicability and the limitations of th e small perturbation (stochastic) approach for predicting flow and transport at arid sites with strong heterogeneity. (2) Develop an appropriately rigorous averaging approach to better quantify local scale behavior in anisotropic soils. (3) Investigate precisely a range of macroscopic flow regimes, measure accurately their three-dimensional average properties, and develop a multi-region transfer method to bridge the gap between pore-scale fluid migration and macro-scale displacement behavior under strong anisotropy. To accomplish the stated goals and objectives, the project is investigating transport processes over evolving scales of heterogeneity and complexities using three essential components of subsurface science identified here as three unique tasks. Task 1--Controlled Laboratory Studies. Task 2--Controlled Field Experiments. Task 3--Numerical Simulations Task 1 has been divided into two activities: (1) an investigation of pore-scale processes and (2) an investigation of intermediate-scale processes. Researchers at Lehigh University are focusing on part 2 of Task 1 that involves the use of a research centrifuge.« less

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    This project is testing the hypothesis that sedimentary lithofacies determine the geochemical and physical hydrologic properties that control reactive solute transport (Figure 1). We are testing that hypothesis for one site, a portion of the saturated zone at the Hanford Site (Ringold Formation), and for a model solute, carbon tetrachloride (CT). The representative geochemical and physical aquifer properties selected for quantification in the proposed project are the properties that control CT transport: hydraulic conductivity (K) and reactivity (sorption distribution coefficient, Kd, and anaerobic transformation rate constant, kn). We are combining observations at outcrop analog sites (to measure lithofacies dimensions andmore » statistical relations) with measurements from archived and fresh core samples (for geochemical experiments and to provide additional constraint to the stratigraphic model) from the Ringold Formation to place local-scale lithofacies successions, and their distinct hydrologic property distributions, into the basinal context, thus allowing us to estimate the spatial distributions of properties that control reactive solute transport in the subsurface.« less

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