Final Report: An Investigation of Chemical Transport from Contaminated Sediments through Porous Containment Structures

EPA Grant Number: R825513C008
Subproject: this is subproject number 008 , established and managed by the Center Director under grant R825513
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: HSRC (1989) - South and Southwest HSRC
Center Director: Reible, Danny D.
Title: An Investigation of Chemical Transport from Contaminated Sediments through Porous Containment Structures
Investigators: Reible, Danny D. , Thibodeaux, Louis J. , Valsaraj, Kalliat T.
Institution: Louisiana State University - Baton Rouge
EPA Project Officer: Hahn, Intaek
Project Period: January 1, 1992 through January 1, 1995
Project Amount: Refer to main center abstract for funding details.
RFA: Hazardous Substance Research Centers - HSRC (1989) RFA Text |  Recipients Lists
Research Category: Hazardous Substance Research Centers , Land and Waste Management


The focus of this study was to provide a better basis for the estimation of contaminant release rates from in-water and near shore confined disposal facilities (CDF) which have been and are used for the disposal of contaminated dredged material. This focus can be clarified through the three main objectives for this study: 1) development of an analytical capability for chemical and dissolved organic carbon measurement; 2) development of a column for sediment leaching experiments; and 3) the numerical simulation of the significance of in-dike transport processes. Contaminant transport as a dissolved phase, colloidally bound phase and particulate bound phase were to be considered. These processes were to be investigated experimentally using model sediment and dike materials as well as representative CDF construction and fill material. Further information on the objectives of this study are outlined below.

Experimental Evaluation of Transport and Dispersion
This work was done in thin layer, large diameter polycarbonate columns. The primary advantage of this column design is large column diameter and short length which maximizes the volumetric flowrate of water through the sample. This is especially important to minimize experiment length for very low permeability samples.

Develop Conceptual/Mathematical Models
Three sets of experiments allowed testing and development of conceptual and mathematical models of seepage in a porous dike structure as a result of water level transients. Both existing sophisticated numerical transient porous media flow models (Tracy, 1973; Barends et al., 1983; Voss, 1984; Black and Craig, 1989) as well as simpler models (Martin et al., 1988; Martin and McCutcheon, 1989)were considered for comparison to the collected data.

Summary/Accomplishments (Outputs/Outcomes):

Experimental Evaluation of Transport and Dispersion
The columns selected and designed were based on a review of the available column types by Myers e al. (1991). The purpose of the column is to collect fundamental sorption, desorption and leaching rate data on sediment and confined disposal facility dike materials. The media will be either sediment or CDF construction material or a combination of the two. Media used was characterized as to its physical parameters, such as sand, silt, clay and organic content and size classification. Equilibrium partitioning of the contaminants of interest was determined by batch testing

In all experiments, chemical analysis of inoculated chemical compounds was done via solid phase extraction and high performance liquid chromatography. Particulate analysis was done via gravimetric and turbidometric methods. Analysis in the presence of dissolved organic carbon (i.e. the colloidal fraction) was also done by solid phase extraction. Determination of the dissolved organic carbon was performed via a total organic carbon analyzer.

Develop Conceptual/Mathematical Models of Transient Water Level Changes and Dike Hydraulics and Transport
A two dimensional finite element model was developed to evaluate free surface unsaturated flow in a CDF dike wall. A finite element convection-dispersion transport model was also developed to use the predicted flow field for purposes of predicting chemical movement. Linear, reversible partitioning between water and the sediments are assumed in the model.

This work focused on the evaluation of the importance of seepage as a hydrophobic contaminant release mechanism in CDFs. It was found that the transport of pyrene, a polynuclear aromatic hydrocarbon (PAH), through a sediment column was enhanced in the presence of a synthetic colloidal carrier. Degradation studies on PAHs in different natural colloidal systems, however, indicated fast degradation rates of these compounds. Even though colloidal carriers that can increase the seepage rates of PAHs in CDFs are present in the seepage water, at high degradation rates, contaminant spreading via this mechanism may not be significant. In the natural environment, diverse populations of microorganisms which can degrade or catalyze the breakdown of PAHs are abundant.

A sediment column cell representing the CDF dike wall was developed. The seepage flow under saturated conditions was depicted by pumping the feed water vertically upward through the interstices of the porous material. Realistic values for the column characteristics such as porosity, bulk density, particle density and dispersivity were obtained by measuring in situ. Based on the good reproducibility of the experimental results, the physical modeling scheme adapted provided a consistent means of studying the effect of colloidal matter on the seepage rates of hydrophobic contaminants through soil/sediment media.

In the pyrene transport simulation experiments, a synthetic colloid was employed while attempts to find potential sources of natural DOC water were conducted.

Colloidal Studies - PS706 Colloid
The transport parameters and sorption properties of the synthetic colloid were experimentally determined. It was shown that the adsorption/desorption of PS706 colloid was reversible. From the colloid breakthrough data, the colloid sediment-water partition coefficient of 4.0 L/kg was obtained by applying three different methods.

Colloidal Studies - Natural DOC
Collection and concentration methods for DOC did not yield sufficient quantities of high DOC water. However, the possibility of using unconcentrated water from a local surface water source, Bayou Manchac (BM), was pursued. BM water was characterized in terms of its absorbance, DOC content (15-20 mg/L), and sorption behavior. The adsorption curve indicated that the organic carbon of BM DOC water may be associated mainly in two colloidal size fractions. Furthermore, BM DOC appeared to exhibit a higher retardation to the sediment phase than the synthetic colloid, although partial breakthrough was readily observed.

The use of BM DOC as a potential colloidal feedstock was problematic. The problem encountered was mainly the lack of stability of the PAHs which was attributed to contaminant degradation in the DOC laden water. It was observed that light had no effect on the degradation rate. In addition, tests conducted to determine if significant stabilization of the PAHs-colloid system could be gained by periodic addition of 0.0002% sodium azide did not yield positive results. Further degradation studies were conducted and decay rate constants were measured by assuming first order kinetics. A first order model adequately fit the biodegradation rate data.

Pyrene Transport
Pyrene was highly retarded in the sediment column. In the presence of PS706 colloid (3.5 and 20 mg/L,) however, significant breakthrough was observed indicating that colloidal matter facilitated the transport of pyrene through the porous material. The CAD model satisfactorily predicted the transport of pyrene in the aqueous phase, however, an exponential decay term accounting for the first order degradation of pyrene had to be included to obtain acceptable fits of the experimental data. In the presence of PS706 colloid, the CAD model including the exponential decay term for degradation was also applicable to the transport of the aqueous fraction of pyrene reversibly sorbed to the colloids. The pyrene fraction associated with the colloids sorbed to the sediment column was modeled by assuming that this material was in equilibrium with the feed concentration. Due to the fast degradation of dibenzofuran and phenanthrene, no significant transport data were gathered.

The results of the colloid and PAHs transport and degradation studies implied that PAHs in the mobile water phase are relatively unstable in the presence of natural colloidal material. Due to the short lifetime of even mid-range PAHs (e.g. pyrene) in DOC-laden waters, these compounds would not be expected to leach from a CDF in significant quantities.

Modeling was undertaken employing conditions appropriate for a relatively porous CDF, the Chicago CDF. For the particular conditions of the Chicago CDF, the estimated evaporation rate of water-side mass transfer resistance controlled contaminants is approximately the same as the maximum rate of contaminant transport via seepage through the dike walls. Since the Chicago CDF is one of the more porous CDFs and thus exchanges water more readily with adjacent waters, the conclusion is that vaporization of volatile compounds is likely to be more important than dike wall seepage as a contaminant loss mechanism from most confined disposal facilities. The dike wall can also serve to attenuate the contaminant seepage by sorption or biodegradation while neither process serves to slow evaporation. Further, the estimate of volatile losses neglects evaporation from exposed dredged material in the CDF. Thibodeaux (1989) predicted that freshly exposed dredged material would result in the greatest contaminant evaporation.

Based upon the above, seepage is unlikely to be a significant contaminant loss mechanism through most CDFs. Even in the case of the relatively porous Chicago CDF, it was expected that vaporization of organic compounds is of equal or more importance.

It should be recognized, however, that non-volatile compounds such as many of the heavy metals will not evaporate and dike seepage may remain an important loss mechanism for these contaminants in a confined disposal facility. In addition, volatile losses, while potentially greater than seepage losses, may have a lesser impact due to dilution in the atmosphere. Seepage losses will have a direct impact on the ecology of the adjacent water body and the ability of that water body to dilute the contaminants released via seepage may be limited.

Summary of Results:

  • Demonstration of rapid degradation of refractory PAHs in the presence of natural colloids
  • Identification of volatilization as a likely more important loss mechanism than seepage from most CDFs
  • Demonstration of colloidal enhancement of transport of PAHs in sediment although colloidal enhancement was insufficient to overcome the enhanced degradation rate of PAHs and the potentially more important vaporization loss mechanism from a CDF.

  • Journal Articles on this Report : 5 Displayed | Download in RIS Format

    Other subproject views: All 15 publications 6 publications in selected types All 5 journal articles
    Other center views: All 392 publications 154 publications in selected types All 106 journal articles
    Type Citation Sub Project Document Sources
    Journal Article Sojitra I, Valsaraj KT, Reible DD, Thibodeaux LJ. Transport of hydrophobic organics by colloids through porous media. 1. Experimental results. Colloids and Surfaces - A Physicochemical and Engineering Aspects 1995;94(2-3):197-211. R825513C008 (Final)
    not available
    Journal Article Sojitra I, Valsaraj KT, Reible DD, Thibodeaux LJ. Transport of HOCs by colloids through porous media. 2. Commercial humic acid micromolecules and PAHs. Colloids and Surfaces A - Physicochemical and Engineering Aspects 1996;110(2):141-157. R825513C008 (Final)
    not available
    Journal Article Thibodeaux LJ, Valsaraj KT, Reible DD. Associations between polychlorinated biphenyls and suspended solids in natural waters: An evaluation of the HOC uptake rate by particles. Water Science and Technology 1993;28(8-9):215-221. R825513C008 (Final)
    not available
    Journal Article Valsaraj KT, Verma S, Sojitra I, Reible DD, Thibodeaux LJ. Diffusive transport of organic colloids from sediment beds. Journal of Environmental Engineering 1993;122(8):722-729. R825513C008 (Final)
    not available
    Journal Article Valsaraj KT, Thoma GJ, Porter CL, Reible DD, Thibodeaux LJ. Transport of dissolved organic carbon-derived natural colloids from bed sediments to overlying water: Laboratory simulations. Water Science and Technology 1993;28(8-9):139-147. R825513C008 (Final)
    not available

    Supplemental Keywords:

    contaminant release, volatilization, and colloids., RFA, Scientific Discipline, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Chemical Engineering, Contaminated Sediments, Environmental Chemistry, Fate & Transport, Analytical Chemistry, Hazardous Waste, Ecology and Ecosystems, Hazardous, Environmental Engineering, environmental technology, sediment treatment, hazardous waste management, hazardous waste treatment, risk assessment, fate and transport, mathematical model, contaminated marine sediment, soil and groundwater remediation, biodegradation, contaminated sediment, kinetics, confined disposal facilities, chemical contaminants, contaminated soil, bioremediation of soils, marine sediments, remediation, chemical kinetics, hydrology, biotransformation, currents, anaerobic biotransformation, extraction of metals, technology transfer, heavy metals, bioremediation, aquifer fate and treatment, technical outreach

    Progress and Final Reports:

    Original Abstract
  • 1992
  • 1993

  • Main Center Abstract and Reports:

    R825513    HSRC (1989) - South and Southwest HSRC

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R825513C001 Sediment Resuspension and Contaminant Transport in an Estuary.
    R825513C002 Contaminant Transport Across Cohesive Sediment Interfaces.
    R825513C003 Mobilization and Fate of Inorganic Contaminant due to Resuspension of Cohesive Sediment.
    R825513C004 Source Identification, Transformation, and Transport Processes of N-, O- and S- Containing Organic Chemicals in Wetland and Upland Sediments.
    R825513C005 Mobility and Transport of Radium from Sediment and Waste Pits.
    R825513C006 Anaerobic Biodegradation of 2,4,6-Trinitrotoluene and Other Nitroaromatic Compounds by Clostridium Acetobutylicum.
    R825513C007 Investigation on the Fate and Biotransformation of Hexachlorobutadiene and Chlorobenzenes in a Sediment-Water Estuarine System
    R825513C008 An Investigation of Chemical Transport from Contaminated Sediments through Porous Containment Structures
    R825513C009 Evaluation of Placement and Effectiveness of Sediment Caps
    R825513C010 Coupled Biological and Physicochemical Bed-Sediment Processes
    R825513C011 Pollutant Fluxes to Aquatic Systems via Coupled Biological and Physicochemical Bed-Sediment Processes
    R825513C012 Controls on Metals Partitioning in Contaminated Sediments
    R825513C013 Phytoremediation of TNT Contaminated Soil and Groundwaters
    R825513C014 Sediment-Based Remediation of Hazardous Substances at a Contaminated Military Base
    R825513C015 Effect of Natural Dynamic Changes on Pollutant-Sediment Interaction
    R825513C016 Desorption of Nonpolar Organic Pollutants from Historically Contaminated Sediments and Dredged Materials
    R825513C017 Modeling Air Emissions of Organic Compounds from Contaminated Sediments and Dredged Materials title change in last year to "Long-term Release of Pollutants from Contaminated Sediment Dredged Material"
    R825513C018 Development of an Integrated Optic Interferometer for In-Situ Monitoring of Volatile Hydrocarbons
    R825513C019 Bioremediation of Contaminated Sediments and Dredged Material
    R825513C020 Bioremediation of Sediments Contaminated with Polyaromatic Hydrocarbons
    R825513C021 Role of Particles in Mobilizing Hazardous Chemicals in Urban Runoff
    R825513C022 Particle Transport and Deposit Morphology at the Sediment/Water Interface
    R825513C023 Uptake of Metal Ions from Aqueous Solutions by Sediments
    R825513C024 Bioavailability of Desorption Resistant Hydrocarbons in Sediment-Water Systems.
    R825513C025 Interactive Roles of Microbial and Spartina Populations in Mercury Methylation Processes in Bioremediation of Contaminated Sediments in Salt-Marsh Systems
    R825513C026 Evaluation of Physical-Chemical Methods for Rapid Assessment of the Bioavailability of Moderately Polar Compounds in Sediments
    R825513C027 Freshwater Bioturbators in Riverine Sediments as Enhancers of Contaminant Release
    R825513C028 Characterization of Laguna Madre Contaminated Sediments.
    R825513C029 The Role of Competitive Adsorption of Suspended Sediments in Determining Partitioning and Colloidal Stability.
    R825513C030 Remediation of TNT-Contaminated Soil by Cyanobacterial Mat.
    R825513C031 Experimental and Detailed Mathematical Modeling of Diffusion of Contaminants in Fluids
    R825513C033 Application of Biotechnology in Bioremediation of Contaminated Sediments
    R825513C034 Characterization of PAH's Degrading Bacteria in Coastal Sediments
    R825513C035 Dynamic Aspects of Metal Speciation in the Miami River Sediments in Relation to Particle Size Distribution of Chemical Heterogeneity