Final Report: Simulation of Three-Dimensional Transport of Hazardous Chemicals in Heterogeneous Soil Cores Using X-ray Computed Tomography

EPA Grant Number: R825549C023
Subproject: this is subproject number 023 , established and managed by the Center Director under grant R825549
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: HSRC (1989) - Great Plains/Rocky Mountain HSRC
Center Director: Erickson, Larry E.
Title: Simulation of Three-Dimensional Transport of Hazardous Chemicals in Heterogeneous Soil Cores Using X-ray Computed Tomography
Investigators: Peyton, Lee , Anderson, Stephen H.
Institution: University of Missouri - Columbia
EPA Project Officer: Hahn, Intaek
Project Period: February 1, 1990 through September 1, 1992
Project Amount: Refer to main center abstract for funding details.
RFA: Hazardous Substance Research Centers - HSRC (1989) RFA Text |  Recipients Lists
Research Category: Analysis/Treatment of Contaminated Soil , Land and Waste Management

Objective:

1. Quantify the spatial distribution of bulk density, porosity, velocity and dispersivity on a macropore scale in undisturbed soil cores using X-ray computed tomography.

2. Numerically simulate conservative (nonadsorbed) chemical transport using velocities and dispersivities quantified by X-ray computed tomography. Test the simulation against experimental measurements.

3. Numerically simulate nonconservative (adsorbed) chemical transport using velocities and dispersivities quantified by X-ray computed tomography and using adsorption isotherm coefficients from the literature. Test the simulation against experimental measurements.

Summary/Accomplishments (Outputs/Outcomes):

In heterogeneous porous media, it is not uncommon for hydraulic conductivity to vary by orders of magnitude over small distances which makes modeling groundwater flow and chemical transport very challenging. In this study, x-ray computed tomography (CT) was used to nondestructively measure small-scale porosity and chemical concentration in undisturbed field cores. A three-dimensional mathematical model was developed to estimate the parameters of the groundwater contaminant transport model from CT measurement and to predict small-scale organic chemical concentration in soil cores.

Three undisturbed soil cores taken from a field near Columbia, Missouri, were collected in a plexiglass cylinder which was 7.8-cm-diameter by 6.8-cm-long. The soil texture was silt loam. Breakthrough experiments were conducted using potassium iodide followed by 2-chlorophenol. Potassium iodide was chosen as a tracer because it is non-adsorbing and nonreactive, and it can be measured by x-ray CT. The organic chemical tracer 2-chlorophenol was chosen because it is a common groundwater contaminant

Each soil core was saturated with a background solution of dilute calcium chloride and magnesium chloride and placed in the CT unit with its longitudinal axis oriented horizontally and perpendicular to the scan plane. The pixel size was 2 mm by 2 mm and the scan slice thickness was 8 mm. After a steady-state flow rate was achieved, the soil cores were scanned to obtain initial data. Then, a steady-state inflow of a 1% (by weight) solution of potassium iodide was initiated. The soil cores were repeatedly scanned throughout the entire length of the cores until a steady-state concentration of potassium iodide was detected at the outflow. The effluent samples were collected and the outflow rate from the soil cores was measured during the breakthrough experiment. At the end of this first experiment, the flow of potassium iodide solution into the soil cores was stopped, and the soil cores were flushed with the background solution until zero concentration of potassium iodide was reached at the outflow. Then, another breakthrough experiment in the same soil cores using 50 mg/I 2-chlorophenol solution as the tracer was conducted under the same flow condition but without CT scanning.

A computer program was written to compute porosity and relative concentration of the solute for each 2 mm by 2 mm by 8 mm cell using the CT measured data by the following equations:

F(i,j,k) = CTNSW(i,j,k) - CTNSWC (i,j,k)
CTNW(i,j,k) - CTNWC(i,j,k)

C*(i,j,k,t) = CTN(i,j,k,t) - CTN(i,j,k,t=0)
CTN(i,j,k,t=T) - CTN(i,j,k,t=0)

where F is porosity; i, j and k are the position indices for the volume elements; CTNSW is the
CT number for soil solids saturated with water, CTNSWC is the CT number for soil solids saturated with chemical solute; CTNW is the CT number for water; CTNWC is the CT number for the chemical solute; C* is the relative concentration of the chemical solute; t is the time since beginning of the breakthrough experiment; CTN is CT number, and T is the time at the end of the breakthrough experiment.

After the 2-chlorophenol experiment, the soil cores were weighed, and the soil was oven dried to determine the degree of saturation and the mean porosity. The mean pore-water velocity for the entire soil core was computed as the total volumetric outflow rate divided by the cross-sectional area and mean porosity of the soil core.

The three-dimensional, saturated, steady groundwater flow equation along with Darcy's law was applied to estimate the velocity in each volume element in the soil cores using the finite-element method. The hydraulic conductivity of each volume element in this numerical solution was calculated from the CT-measured porosity of each volume element. Six empirical equations were employed to calculate hydraulic conductivity from the CT measured porosity. They were the Hazen equation, Kozeny-Carman equation, Kruger equation, Slichter equation, Terzaghi equation and Zunker equation. These equations relate hydraulic conductivity to porosity, effective grain diameter and empirical coefficients.

A finite-element model was developed to numerically solve the three-dimensional solute transport equation using the volume element velocities determined from the previous solution to the flow equation to predict potassium iodide and 2-chlorophenol transport in soil cores.

The model predictions using six empirical equations were compared with the CT measured concentrations, and the results from the Kozeny-Carman equation produced the best agreement. Also compared were the resulting relative frequency distributions for porosity, pore water velocity and hydraulic conductivity within each core. It shows that the mean CT-measured porosity was within 8% of the lab-measured value, mean model predicted hydraulic conductivity was within 5% of the lab-measured value and mean model predicted pore water velocity was within 1% of the lab-measured value. This approach quantifies the spatial variation of transport parameters on a macropore scale rather than on a core-averaged scale. Thus, the influence of macropore-scale heterogeneities on solute transport can be incorporated into field-scale transport models using the approach developed in this research project.

The results have been presented at professional meetings and communicated to others who have expressed interest in the research.


Journal Articles on this Report : 2 Displayed | Download in RIS Format

Other subproject views: All 12 publications 2 publications in selected types All 2 journal articles
Other center views: All 904 publications 230 publications in selected types All 182 journal articles
Type Citation Sub Project Document Sources
Journal Article Anderson SH, Peyton RL, Wigger JW, Gantzer CJ. Influence of aggregate size on solute transport as measured using computed tomography. Geoderma 1992;53(3-4):387-398. R825549C023 (Final)
not available
Journal Article Peyton RL, Haeffner BA, Anderson SH, Gantzer CJ. Applying X-ray ct to measure macropore diameters in undisturbed soil cores. Geoderma 1992;53(3-4):329-340. R825549C023 (Final)
not available

Supplemental Keywords:

x-ray computed tomography, heterogeneous media, soil, porosity., Scientific Discipline, Waste, Ecosystem Protection/Environmental Exposure & Risk, Environmental Chemistry, Geochemistry, Contaminated Sediments, Analytical Chemistry, Fate & Transport, Ecology and Ecosystems, fate and transport, X-ray computed tomography, contaminant transport, contaminated sediment, hazardous waste, hazardous organic substances, bioremediation of soils, chemical kinetics, groundwater contamination, three dimensional model

Relevant Websites:

http://www.engg.ksu.edu/HSRC Exit

Progress and Final Reports:

Original Abstract
  • 1990
  • 1991

  • Main Center Abstract and Reports:

    R825549    HSRC (1989) - Great Plains/Rocky Mountain HSRC

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R825549C006 Fate of Trichloroethylene (TCE) in Plant/Soil Systems
    R825549C007 Experimental Study of Stabilization/Solidification of Hazardous Wastes
    R825549C008 Modeling Dissolved Oxygen, Nitrate and Pesticide Contamination in the Subsurface Environment
    R825549C009 Vadose Zone Decontamination by Air Venting
    R825549C010 Thermochemical Treatment of Hazardous Wastes
    R825549C011 Development, Characterization and Evaluation of Adsorbent Regeneration Processes for Treament of Hazardous Waste
    R825549C012 Computer Method to Estimate Safe Level Water Quality Concentrations for Organic Chemicals
    R825549C013 Removal of Nitrogenous Pesticides from Rural Well-Water Supplies by Enzymatic Ozonation Process
    R825549C014 The Characterization and Treatment of Hazardous Materials from Metal/Mineral Processing Wastes
    R825549C015 Adsorption of Hazardous Substances onto Soil Constituents
    R825549C016 Reclamation of Metal and Mining Contaminated Superfund Sites using Sewage Sludge/Fly Ash Amendment
    R825549C017 Metal Recovery and Reuse Using an Integrated Vermiculite Ion Exchange - Acid Recovery System
    R825549C018 Removal of Heavy Metals from Hazardous Wastes by Protein Complexation for their Ultimate Recovery and Reuse
    R825549C019 Development of In-situ Biodegradation Technology
    R825549C020 Migration and Biodegradation of Pentachlorophenol in Soil Environment
    R825549C021 Deep-Rooted Poplar Trees as an Innovative Treatment Technology for Pesticide and Toxic Organics Removal from Soil and Groundwater
    R825549C022 In-situ Soil and Aquifer Decontaminaiton using Hydrogen Peroxide and Fenton's Reagent
    R825549C023 Simulation of Three-Dimensional Transport of Hazardous Chemicals in Heterogeneous Soil Cores Using X-ray Computed Tomography
    R825549C024 The Response of Natural Groundwater Bacteria to Groundwater Contamination by Gasoline in a Karst Region
    R825549C025 An Electrochemical Method for Acid Mine Drainage Remediation and Metals Recovery
    R825549C026 Sulfide Size and Morphology Identificaiton for Remediation of Acid Producing Mine Wastes
    R825549C027 Heavy Metals Removal from Dilute Aqueous Solutions using Biopolymers
    R825549C028 Neutron Activation Analysis for Heavy Metal Contaminants in the Environment
    R825549C029 Reducing Heavy Metal Availability to Perennial Grasses and Row-Crops Grown on Contaminated Soils and Mine Spoils
    R825549C030 Alachlor and Atrazine Losses from Runoff and Erosion in the Blue River Basin
    R825549C031 Biodetoxification of Mixed Solid and Hazardous Wastes by Staged Anaerobic Fermentation Conducted at Separate Redox and pH Environments
    R825549C032 Time Dependent Movement of Dioxin and Related Compounds in Soil
    R825549C033 Impact of Soil Microflora on Revegetation Efforts in Southeast Kansas
    R825549C034 Modeling the use of Plants in Remediation of Soil and Groundwater Contaminated by Hazardous Organic Substances
    R825549C035 Development of Electrochemical Processes for Improved Treatment of Lead Wastes
    R825549C036 Innovative Treatment and Bank Stabilization of Metals-Contaminated Soils and Tailings along Whitewood Creek, South Dakota
    R825549C037 Formation and Transformation of Pesticide Degradation Products Under Various Electron Acceptor Conditions
    R825549C038 The Effect of Redox Conditions on Transformations of Carbon Tetrachloride
    R825549C039 Remediation of Soil Contaminated with an Organic Phase
    R825549C040 Intelligent Process Design and Control for the Minimization of Waste Production and Treatment of Hazardous Waste
    R825549C041 Heavy Metals Removal from Contaminated Water Solutions
    R825549C042 Metals Soil Pollution and Vegetative Remediation
    R825549C043 Fate and Transport of Munitions Residues in Contaminated Soil
    R825549C044 The Role of Metallic Iron in the Biotransformation of Chlorinated Xenobiotics
    R825549C045 Use of Vegetation to Enhance Bioremediation of Surface Soils Contaminated with Pesticide Wastes
    R825549C046 Fate and Transport of Heavy Metals and Radionuclides in Soil: The Impacts of Vegetation
    R825549C047 Vegetative Interceptor Zones for Containment of Heavy Metal Pollutants
    R825549C048 Acid-Producing Metalliferous Waste Reclamation by Material Reprocessing and Vegetative Stabilization
    R825549C049 Laboratory and Field Evaluation of Upward Mobilization and Photodegradation of Polychlorinated Dibenzo-P-Dioxins and Furans in Soil
    R825549C050 Evaluation of Biosparging Performance and Process Fundamentals for Site Remediation
    R825549C051 Field Scale Bioremediation: Relationship of Parent Compound Disappearance to Humification, Mineralization, Leaching, Volatilization of Transformaiton Intermediates
    R825549C052 Chelating Extraction of Heavy Metals from Contaminated Soils
    R825549C053 Application of Anaerobic and Multiple-Electron-Acceptor Bioremediation to Chlorinated Aliphatic Subsurface Contamination
    R825549C054 Application of PGNAA Remote Sensing Methods to Real-Time, Non-Intrusive Determination of Contaminant Profiles in Soils
    R825549C055 Design and Development of an Innovative Industrial Scale Process to Economically Treat Waste Zinc Residues
    R825549C056 Remediation of Soils Contaminated with Wood-Treatment Chemicals (PCP and Creosote)
    R825549C057 Effects of Surfactants on the Bioavailability and Biodegradation of Contaminants in Soils
    R825549C058 Contaminant Binding to the Humin Fraction of Soil Organic Matter
    R825549C059 Identifying Ground-Water Threats from Improperly Abandoned Boreholes
    R825549C060 Uptake of BTEX Compounds by Hybrid Poplar Trees in Hazardous Waste Remediation
    R825549C061 Biofilm Barriers for Waste Containment
    R825549C062 Plant Assisted Remediation of Soil and Groundwater Contaminated by Hazardous Organic Substances: Experimental and Modeling Studies
    R825549C063 Extension of Laboratory Validated Treatment and Remediation Technologies to Field Problems in Aquifer Soil and Water Contamination by Organic Waste Chemicals