2002 Progress Report: In-Situ Containment and Treatment of Contaminated Sediments: Engineering Cap Integrity and ReactivityEPA Grant Number: R828773C002
Subproject: this is subproject number 002 , established and managed by the Center Director under grant R828773
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: HSRC (2001) - South and Southwest HSRC
Center Director: Reible, Danny D.
Title: In-Situ Containment and Treatment of Contaminated Sediments: Engineering Cap Integrity and Reactivity
Investigators: Wiesner, Mark R. , Hughes, Joseph B , Valsaraj, Kalliat T. , Edge, Billy
Current Investigators: Wiesner, Mark R. , Hughes, Joseph B , Willson, Clinton S. , Valsaraj, Kalliat T. , Edge, Billy
Institution: Rice University , Texas A & M University , Louisiana State University - Baton Rouge
Current Institution: Rice University , Georgia Institute of Technology , Louisiana State University - Baton Rouge , Texas A & M University
EPA Project Officer: Lasat, Mitch
Project Period: October 1, 2001 through September 30, 2006 (Extended to September 30, 2007)
Project Period Covered by this Report: October 1, 2001 through September 30, 2002
Project Amount: Refer to main center abstract for funding details.
RFA: Hazardous Substance Research Centers - HSRC (2001) Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management
This research project is divided into two categories: the Rice University and Louisiana State University Portion, and the Texas A&M University Portion.
Rice University and Louisiana State University Portion. The overall objective of this portion of the research project is to develop "second-generation" sediment caps with specific chemical transport characteristics and built-in sustainable reactivity. The specific objectives of the research project are to: (1) determine how post-placement processes such as consolidation, deposition, and colloidal transport impact cap function, and how to control cap stability and permeability; (2) determine the long-term variability of caps subject to the dynamic processes identified above and to strong episodic storm events; and (3) develop innovative approaches to be used during cap placement to achieve desired reactivity and transport characteristics.
Because of the cost of dredging, and concerns in the management of dredge spoils, it is imperative that in situ solutions be developed from the management and treatment of contaminated sediments. Capping, the placement of a clean layer of sediment over the contaminated bed, is an attractive solution in many cases, as it is effective in rapidly isolating contaminants from benthic organisms, and can improve sediment stability. However, there are concerns regarding the long-term effectiveness of caps as a result of storm events or other phenomena that may compromise the cap integrity. The need to develop innovative approaches to manage and treat contaminated sediments in situ is the impetus for this research project. Successful implementation of a cap will require that depositional processes used in cap placement be tailored so that the desired cap characteristics are achieved. Research also is necessary to understand and predict the stability of these cap characteristics in the case of a major resuspension event. Our studies also focus on the development of sediment caps, where the contaminant destruction is achieved during the transport through the cap. The net effect will be the ability to reduce contaminant flux to the water column and allow for natural recovery of the sediment. To accomplish these objectives, it must be possible to engineer the cap for specific chemical transport characteristics, and to incorporate sustainable reactive processes (biotic and abiotic). These studies will form the basis for larger-scale second-generation caps.
Texas A & M University Portion. The overall objective of this portion of the research project is to establish a basis for directly estimating the effects of dynamic events (storms) that will affect the net circulation in coastal waters. The study will define the circulation pattern using a baroclinic solution of a three-dimensional hydrodynamic model.
A practical use of this research is to develop a model of the long-term stability of the capping sediments, as well as the likelihood of non-scouring existing contaminated sediments at or near the top of the benthic layer. The cap may well be stable in daily currents and waves, but it is possible that the cap may be scoured during significant dynamic events such as tropical storms.
Under vertically stratified conditions, a depth-averaged model approach is not adequate to resolve the vertical velocity and salinity distribution. Most of the applied models have not included baroclinic effects. For three-dimensional models, baroclinic terms will more suitably explain the variability of vertical current shear. The determination of baroclinic flow is important because it may cause convergence zone, where the converging pressure gradients drive internal circulation pattern into a common point. Convergence zone represents location where substances tend to remain for a longer period and may accumulate, allowing increased concentrations and flocculation to develop in the water column.
The magnitude of bottom stress also is related to the baroclinic term associated with the vertical current shear. It is presumed that this term affects the magnitude of bottom shear stress. In stratified water, the inclusion of baroclinic terms may better describe resuspension of sediment and the life cycle of capped sediments.
Issues relevant to any cap design are the morphology and deposition of cap materials and the long-term viability of the cap towards scouring and dynamic events. Microscopic aspects of cap morphology and long-term viability are integral to the construction of any second-generation cap. Therefore, studies should be conducted towards proposing an overall strategy of cap placement and stability. These studies provide the necessary framework for designing laboratory experiments toward the construction of second-generation caps. Thus, there is a great deal of integration between the tasks to be performed. The studies can be divided into three areas of parallel experiments: (1) the role of depositional processes on cap permeability and morphology; (2) effects of significant event dynamics on cap stability and integrity; and (3) studies directed towards second-generation caps that focus on polyaromatic hydrocarbon (PAH) transport and degradation in caps. In all cases, experimental and computational elements are required to achieve our project goals.
System scale modeling is performed using the extended three-dimensional version of Advanced CIRCulation (ADCIRC) hydrodynamic circulation model that includes both two-dimensional depth-integrated and three-dimensional solutions. The detailed explanations of the model are given in Luettich, et al., 1992; Luettich, et al., 1994; Luettich and Westerink, 2001; and Pandoe and Edge, 2002.
The model solves the free surface displacement, current velocity, salinity, temperature, and density distributions. The most recent developed model allows baroclinic forcing term to be included in the momentum equations. Therefore, in the stratified waters, the three-dimensional flow can be well estimated. A summary of governing equations of three-dimensional circulation is given below.
Momentum equations in the longitudinal and lateral directions:
where u and v are depth-dependent horizontal velocity, is vertical velocity and is the coordinate system, is a free surface elevation, ps(x,y,z) is a time-averaged pressure, f is the Coriolis force, mi is a horizontal momentum diffusion, zi is a combined viscous and turbulent Reynolds stress, and o represents reference sea water density. The terms bx and by are baroclinic pressure gradients. Robertson, et al., 2001, applied normalized density to reduce the truncation error in the computation of baroclinic pressure gradient. Therefore, the normalized baroclinic forcing terms in ADCIRC can be represented as:
|= baroclinic x - forcing||(5a)|
|= baroclinic y - forcing||(5b)|
where is a free surface elevation, C is depth-dependent concentration (i.e., salinity, temperature, or sediment). E and D are the source and sink terms for erosion and deposition, respectively.
Rice University and Louisiana State University
Sediment Cap Formation and Evaluation. A custom made plexiglas sedimentation/diffusion column was designed and built based on an existing packed bed column to study transport properties of in situ deposited sediment caps. In parallel with these sedimentation/diffusion experiments, simple diffusion tests were performed using a modified Louisiana State University diffusion cell. Modifications allowed for a wider range of experimental conditions such as: (1) higher closed-circuit cross-flows; (2) liquid-phase bottom compartment simulating contaminated sediment; (3) pump pulse dumping section at the entrance; and (4) sampling ports to monitor contaminant depletion in the contaminated sediment. A series of deposition experiments, as well as non-reactive and reactive tracer diffusion tests, was performed for caps of different compositions. The performances of clay loam, sand, and clay/cement composite caps were studied and compared. To compute corresponding transport characteristics, a finite-differences numerical model of tracer diffusion in the above geometries was developed and applied. Based on results of non-reactive tracer diffusion tests, it was demonstrated that higher shear strength clay/cement composite caps with less than 10 percent cement content are characterized by permeability higher than that of clay or sandy caps. Diffusion coefficients of dichlorophenol in sediment caps of different compositions (clay loam, sand, and clay/cement composite) also were determined.
Applicability of environmental scanning electron microscopy (ESEM) for the study of in situ hydration of cements and cement-clay composites was demonstrated. For ESEM studies, specimens do not have to be coated, which makes the examination of wet and vapor-producing samples in their native state possible. Adequate pump-down procedure needed to keep water-saturated vapor above the sample throughout the chamber evacuation was established. Hydration conditions (temperature and pressure) in the ESEM chamber were identified and a dynamic hydration/dehydration study was performed. Presence of clay minerals was found to significantly alter the processes of cement hydration and strength development.
Methodology for the resin impregnation of 100 percent water-saturated low permeability sediment caps for the subsequent thin-sectioning and morphological study was established. Two types of low-viscosity embedding media were evaluated. Although embedding with both epoxy resin- and glycol methacrylate (GMA)-based agents allowed for the preparation of high quality thin sections, GMA was found to be especially effective for the impregnation of hard-to-infiltrate samples. Polarizing light microscopy and SEM with a secondary electron detector negatively biased for the selective detection of backscattered electrons, employed for thin section imaging.
Parallel message passing interface (MPI) implementation of the Lattice Gas Automata (LGA) model was developed and the model's almost perfect scalability was demonstrated. Based on the observed scaling, we concluded that the presented model was amenable to parallelization. The main reason to prefer this approach to more traditional approaches is the ability of LGA models to deal with fractal boundaries, which are typical for such porous media as soils, and are responsible for the anomalous transport in such media. In addition, the LGA method naturally allows for simultaneous consideration of processes of formation of, and transport in, porous media. Further extensions of this model, such as its application to the studies of contaminant reaction/diffusion in porous media, will increase the amount of computations per communication event, and will only improve scalability.
Figure 1. Comparison of Current Velocity and Salinity Distribution Between With (top) and Without (bottom) Baroclinic Terms Along the Idealized Rectangular Basin
During the research project period we: (1) designed a sedimentation/diffusion column and modified existing diffusion cells to study transport properties of in situ deposited sediment caps; (2) developed a numerical model of tracer diffusion in the above geometries; (3) carried out non-reactive tracer tests to determine the permeability of sediment caps of different compositions (clay loam, sand, and clay/cement composite); (4) determined the diffusion coefficients of dichlorophenol in sediment caps of different compositions (clay loam, sand, and clay/cement composite); (5) showed that clay/cement composite caps with less than 10 percent cement content are characterized by higher shear strength and permeability than clay or sandy caps; (6) demonstrated the applicability of ESEM for the study of in situ hydration of cements and cement-clay composites (presence of clay minerals was found to significantly alter the processes of cement hydration and strength development); (7) innovated the methodology for the resin impregnation of 100 percent water-saturated sediment caps for the subsequent thin-sectioning and morphological study; and (8) developed parallel MPI implementation of THE LGA diffusion model and demonstrated the model's almost perfect scalability.
Modeling Contaminant Transport and Fate. The general equations governing the fate and transport of contaminants in the sediment and the cap layer are shown in Equation 6 and 7, respectively.
Analytical solutions for the system of equations shown above exist when k1 and k1 are equal and constant with respect to time. The solution for contaminant flux at the cap-water interface is shown by Equation 8.
where I0 (n) and N (n) are the initialization and normalization integrals shown by Equations 9 and 10.
This case was adopted as a simplified first step in the process of the transport model development. In a test case shown in Figure 2, the effect of a non-reactive and a reactive cap on surface fluxes are plotted. The first order degradation rate constant was assumed to be 0.007 d-1.
Figure 2. Test Case Simulation of Contaminant Fate and Transport in the Presence of a Reactive Cap
In the presence of an adsorptive non-reactive cap, the contaminant flux is reduced several orders of magnitude as compared to that from an uncapped sediment. In the presence of a reactive cap, the surface flux is further reduced. This study illustrates the potential of a reactive cap using a basic simplified model. The input to this model is comprised of estimated physical parameters such as cap and sediment porosity, bulk density, cap thickness, fractional organic carbon, sediment concentration, effective diffusivity, retardation factors, initial porewater concentration, and cap-water interfacial mass transfer coefficient.
System Scale Modeling. Up to this point, the model development was extended for a three-dimensional description of salinity, temperature, and density in the flowing stratified fluid. It is important that the model represent a wide range of possible stratified situations. Various idealized rectangular basins were developed corresponding to different initial and boundary conditions. The inclusion of the baroclinic term governs important flow pattern associated with density currents, where the layer stratifications are well defined. The effect of density (i.e., salinity and temperature) variations gives a measure on stability indicated by the Richardson Number that represents a relative importance between dynamic and density effects. Most flows in estuaries are turbulent. Turbulence occurrence will tend to mix the fluid, where the light fluid is mixed up and the heavier fluid mixed down. To illustrate the effect of the baroclinic term, Figure 1 describes the three-dimensional flow pattern of salinity with and without baroclinic terms in an idealized rectangular basin.
Luettich Jr RA, Westerink JJ, Scheffner NW. ADCIRC: an advanced three-dimensional circulation model for shelves, coasts, and estuaries. U.S. Army Corps of Engineers, Report 1, Technical Report DRP-92-6, Dredging Research Program, Washington DC, 1992.
Luettich Jr RA, Hu S, Westerink JJ. Development of the direct stress solution technique for three-dimensional hydrodynamic models using finite element. International Journal of Numerical Methods in Fluids 1994;19:295-319.
Luettich Jr RA, Westerink JJ. Formulation and numerical implementation of the 3D ADCIRC finite element model version 36.01, 2001.
Pandoe W, Edge BL. Three-dimensional hydrodynamic model, study cases for quarter annular and idealized ship channel problems. Journal of Water Way, Port, Coastal, and Ocean Engineering (submitted, 2002).
Robertson R, Padman L, Levine MD. A correction of the baroclinic pressure gradient term in the Princeton ocean model. Journal of Atmospheric and Oceanic Technology 2001;18(6):1068-1075.
Future activities are to make further progress in cap formation and evaluation and to: (1) perform further deposition and diffusion experiments with three other contaminants: pentachlorophenol, naphthalene, and cyclotrimethylenetrinitramine (RDX); (2) carry out an ESEM study of the hydration of 100 percent water saturated clay/cement composite over time scales from minutes to months for various cement contents, and correlate these observations with shear strength measurements of the composites; (3) study heavy metal transport through cement/clay composite caps; (4) perform an ESEM/energy dispersive x-ray analysis (EDAX) study of cement/clay hydrating composites to obtain semi-quantitative morphology and elemental (cement phases, clay minerals) composition data; (5) extend the LGA diffusion model to the simulation of diffusion/reaction in porous media; (6) apply the model to porosity patterns derived by thin-sectioning of actual caps, and compare model results with experimentally determined macroscopic transport parameters; and (7) continue transport and fate modeling.
One of the assumptions in the model development described above is that the degradation is assumed in both the cap and the sediment layers and the absence of the effect of oxygen transfer into the cap. The oxygen transfer can be described by Equation 11.
where raer, the rate of aerobic degradation is dependent on the contaminant concentration. This introduces a coupling of Equation 11 with Equation 6 and 7. A numerical algorithm currently is being developed to accommodate the effects of variable rate constants in the cap and sediment layers and the effect of oxygen transfer into the cap. The following stages planned for the next year of transport model development include: (1) developing a numerical algorithm using Formula Translation/Translater (FORTRAN) and the calibration of the model using the analytical solution presented in Figure 1; (2) incorporating different rate constants for the cap and the sediment (i.e., ki k2 ); (3) developing a numerical algorithm for the coupled solution of the oxygen transport and contaminant transport equations; (4) calibrating transport equations with experimental data; and (5) following the accomplishment of these tasks. The data from the cap integrity models developed at Rice and Texas A & M universities will be used to predict contaminant fate and transport in the reactive cap layer.
System Scale Modeling. The next phase of model development is to include the mechanics of the source and sink terms for the transport of suspended particles. It will be applied to any specific problem to identify the scour potential of a sediment or capping material. The effect of baroclinic term in the sediment transport is very important in stratified waters. Specific efforts are required to assess the stability, consistency, and accuracy of the model. Then, the model would be applicable to an estuarine zone, and should be verified for specific instances.
Texas A & M University Portion. The next phase of development of the model is to include the mechanics of the source and sink terms for the transport of suspended particles. It will be applied to any specific problem to identify the scour potential of a sediment or capping material. The effect of baroclinic term in the sediment transport is very important in stratified waters. Specific efforts are required to assess the stability, consistency, and accuracy of the model. Then, the model would be applicable to an estuarine zone, and should be verified for specific instances.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
|Other subproject views:||All 20 publications||8 publications in selected types||All 8 journal articles|
|Other center views:||All 279 publications||92 publications in selected types||All 63 journal articles|
||Pandoe WW, Edge BL. Three-dimensional hydrodynamic model, study cases for quarter annular and idealized ship channel problems. Ocean Engineering 2003;30(9):1117-1135.||
||Tarabara VV, Pierrisnard F, Parron C, Bottero J-Y, Wiesner MR. Morphology of deposits formed from chemically heterogeneous suspensions: application to membrane filtration. Journal of Colloid and Interface Science 2002;256(2):367-377.||
Supplemental Keywords:enhanced natural recovery, reactive barrier, confined aquatic disposal, reaction, diffusion, porous media, environmental cement, three-dimensional hydrodynamic model, resuspension, sediment transport, deposition, sediment capping, reactive caps, mathematical model., RFA, Scientific Discipline, Waste, Water, Contaminated Sediments, Remediation, Environmental Chemistry, Analytical Chemistry, Hazardous Waste, Ecology and Ecosystems, Engineering, Hazardous, Environmental Engineering, contaminant transport, fate and transport , in situ remediation, contaminant dynamics, sediment caps, computer models, contaminated sediment, kinetic studies, contaminated soil, computer modeling, contaminant transport model, treatment, kinetic models, contaminant management
Progress and Final Reports:Original Abstract
Main Center Abstract and Reports:R828773 HSRC (2001) - 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).
R828773C001 Bioturbation and Bioavailability of Residual, Desorption-Resistant Contaminants
R828773C002 In-Situ Containment and Treatment of Contaminated Sediments: Engineering Cap Integrity and Reactivity
R828773C003 Phytoremediation in Wetlands and CDFs
R828773C004 Contaminant Release During Removal and Resuspension
R828773C005 HSRC Technology Transfer, Training, and Outreach