2002 Progress Report: Contaminant Release During Removal and ResuspensionEPA Grant Number: R828773C004
Subproject: this is subproject number 004 , 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: Contaminant Release During Removal and Resuspension
Investigators: Tomson, Mason B. , Hughes, Joseph B , Thibodeaux, Louis J. , Valsaraj, Kalliat T. , Apitz, S.
Current Investigators: Tomson, Mason B. , Thibodeaux, Louis J. , Kan, Amy T. , Valsaraj, Kalliat T.
Institution: Rice University , Louisiana State University - Baton Rouge
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 , Nanotechnology , Land and Waste Management
Louisiana State University Portion
The objective of this portion of this research project is the development of a theoretical thermodynamic/transport kinetic model for organic and metal desorption from resuspended bed-sediment particles.
Rice University Portion
The objective of this portion of the research project is to understand the dynamics and fate of heavy metals during resuspension events. Five specific objectives are to:
· Test the hypothesis that sorption and desorption of heavy metals from natural sediments are not the reverse of each other (i.e., sorption/desorption of toxic metals exhibits hysteresis).
· Test the hypothesis that although there are a number of unique combinations of sediments, it is possible to identify a few key parameters that can be used to predict heavy metal release, thereby allowing the potential for ecological exposure.
· Simulate resuspension events in the laboratory, study the kinetics of heavy metal release during resuspension, and identify key parameters controlling contaminant transportation.
· Study rate processes; heavy-metal release is multiphasic, with one set of process controlling the early resuspension and a different set of processes important at times in excess of a few hours.
· Understand that particle fines are released upon initial resuspension. These fines do not resettle rapidly, yet they contain the heavy metal load on a mg/g basis. These fines will facilitate the migration of many of the most dangerous heavy metals. Furthermore, these fines will impact the existing organisms.
Lastly, we also will investigate the possibility to identify a potential remediation plan that can be used to prevent heavy metals release during resuspension events and dredging. Attention has been and will continue to be focused on the impacts of resuspension on fines versus settleable particles and short versus long timeframes.
Louisiana State University Portion
Inevitably, some bed-residing particles are resuspended in the water column during all remediation activities. These activities include monitored natural recovery, capping, dredging, and in situ treatment process. Ex situ treatment processes via bioremediation also involve slurries of particles in aqueous biological cultures. Sorbtive release and mass transfer of chemicals from the particles to the adjacent aqueous phase is the common process in the above situations, and oftentimes becomes the rate-limiting process. The goal of this research project is to develop a practical, theory-based chemodynamics algorithm for the particle-to-aqueous release process.
The main objective of this research project is to develop a mathematical model based on a Laviosier species mass balance describing organic chemical release process from the particle phase to water. In the published literature, there exists much information about the desorption thermodynamics of organic chemicals sorbed onto soil and sediment. Correspondingly, there exists much kinetic data on the biotreatment of sediment particle originating organic chemicals. The bioremediation kinetic data are conventionally represented by the "hockey-stick" empirical model because the graphical data typically appears in the shape of a hockey stick. The empirical model is for the fraction chemical remaining on the solid F; it is:
where L and T are the initial loosely bound and tightly bound fractions, kl and kt are the corresponding kinetic parameters for the respective fractions, and t is time. The negative sign in the equation signifies the process is desorption.
The use of the terms "loosely bound" and "tightly bound" have been adopted to describe the chemical adsorbate association with the corresponding adsorbent sites within the solid matrix. Alternative names for the loosely bound are "quick release" or "labile fraction." Those for the tightly bound are "desorption resistant", "slow release," and "non-labile". In a theoretically sound robust kinetic model, the rate parameters kl and kt should be direction independent, and they should apply for desorption as well as adsorption. The physiochemical nature of the adsorbent sites within particles has been variously described based on chemical evidence of thermodynamic association and spectroscopic physical evidence. These descriptors are summarized in Table 1.
|Investigator Group||Model Name||Tightly Bound Sites||Loosely Bound Sites|
|Tomson and Kan||Biphasic||Solute conformational rearrangement (CR) SOM||Non-CR of SOM|
|Weber, et al.||DR Model*||Hard carbon OM "condensed glass"||Soft carbon OM "amorphous glass"|
|Pignatelo, et al.||Dual-Mode||Glassy SOM, rigid condensed structure||Rubbery SOM, flexible expanded structure|
|Luthy, et al.||Surface Ads.||"Black" particles coal derived, wooden like||"Silica" particles inorganic content|
*Distributed Reactivity includes exposed mineral surfaces as a third site for adsorption.
We have developed a theoretical mathematical model and have conducted preliminary testing against sets of existing bioremediation data for general congruence. The sets include polycyclic aromatic hydrocarbons (PAHs) and chlorinated solvents.
Theoretical Model Structure. Soil and sediment grains have adsorptive patches within and on their outer surfaces. Two types of adsorptive compartments are assumed to exist within these patches. They are denoted as for those sites which possess loose chemical bonding characteristics and t for those which possess tight chemical bonding characteristics, of the adsorbate molecules or inorganic species. Figure 1 illustrates the two compartments associated with the solid particle phase as a patch of adsorbent material on the surface and in the internal matrix of the porous solid particle. If it is assumed that chemical equilibrium exists between the compartments of the sediment solid matrix and the tightly bound fraction, TO is expressed by:
where Kdt and Kdl are the respective partition coefficients for the tightly and loosely bound compartments. The loosely bound fraction is LO =1-TO. It is likely that such a fractional distribution exists at equilibrium within the bed sediment layer prior to its disturbance. There is evidence that chemical species move from particle to particle within beds. Jackman, et al., (Journal of Hazardous Materials 2001) report on laboratory studies of cobalt desorption from small sediment particles with subsequent sorption onto larger ones. Stream water solutions containing 1 ng/L to 1,000 mg/L cobalt were exposed to small (1.0 to 1.2 mm) particles for 6 hour to 14 days. They were rinsed and placed together in water with larger (3.4 to 4.0 mm) particles from Little Lost Man Creek. Desorption was much lower than adsorption, and it was found that interparticle migration of metal cations proceeds at significant rates.
The chemical release pathways are illustrated in the patch detail of Figure 1. Pathways a and b illustrate the movement of the adsorbate from the tightly (t) and loosely () bound compartments of the adsorbent patches to the aqueous phase. Internal pathways c and d move the adsorbate between the t and compartments similar to the movement process between sediment particles. The detail portion of Figure 1 gives general pathway arrangement that is inclusive of the five patch types illustrated for the single particle. We used a lumped parameter model; the chemical content of each compartment was assumed to be uniform. Adsorbate desorption from the solid phase within the compartment followed by diffusion through water-filled pore spaces is the assumed release mechanism. An effective diffusion coefficient, Dv, diffusion path length, d, and interfacial mass-transfer area, av, quantify the transport character of each compartment pathway. Four kinetic parameters, ka, kb, kc, and kd, are required; each have the general form:
Each kinetic parameter consists of a transport group divided by a thermodynamic group. The two groups are shown in brackets in Equation 3. Pp is particle density. The kinetic parameters have inverse time dimensions.
Lavoisier species mass balances on the two compartments yield the second order differential equation that describes the decrease of the adsorbate content in the loosely bound compartment with time, L:
This linear ordinary differential equation (ODE) has an analytical solution with the form shown in Equation 1. In the case where only pathways a and b are not zero:
This is the parallel pathway case; see Figure 1. In this case, L = LO and T = TO. For the other patch arrangements shown in Figure 1 with internal pathways, such a simple result is not possible. In those cases, the four parameters in the two-exponent model of Equation 1, kl and kt, L, and T, are complex functions of the individual pathway kinetic parameters plus TO and LO.
Some preliminary conclusions can be drawn based on the above parallel pathways, tightly/loosely bound compartment model:
· A two-exponent theoretical model result was obtained, which is consistent with the empirical one used by numerous investigators to correlate the desorption kinetics of organic chemicals.
· The kinetic parameters in the empirical model, kl and kt, are the ratios of well-known basic transport and thermodynamic parameters.
· The observed smaller numerical value of kl compared to kl is due to kdt being larger than kdr. If the transport groups are similar in magnitude, equations 5a and 5b show this behavior pattern of kl and kt.
Other combinations of internal and external pathways are shown in Figure 1. There can be two other arrangements besides parallel desorption from disconnected internal compartments: series and parallel-series. In the series case, the tightly bound compartment is completely surrounded by the loosely bound one. The parallel-series, the most general case, is shown in the detail of Figure 1.
Rice University Portion
In resuspension of contaminated sediments, heavy metals such as Pb, Cd, Cu, and As, represent several special challenges and will be the focus of this Hazardous Substance Research Center (HSRC) research. For example, DiGiano, et al., observed that the dredging elutriate test (DRET) protocol corresponds reasonably well to field-dredge tests for polychlorinated biphenyl (PCBs) and probably for other organic contaminants during dredging, but not for the heavy metals. This notion further was explained by Myers, et al. During resuspension, the largest physical-chemical effect with respect to heavy metal sorption is the change in redox of the freshly disturbed sediments. At the point of dredging, the sediments are suspended in the river bottom and there is an immediate increase in solid surface area and a corresponding immediate change in the physical chemical parameters that characterize the water. Following these immediate changes, there will be several timescales that are applicable: (1) the slower redox processes; (2) the desorption kinetics; and (3) the relative rates of redeposition of the sediment particles. The objective of this research project is to understand the dynamics and kinetics of heavy metal release processes and to derive methods to reduce heavy metal release during dredging and resuspension.
Adsorption and Desorption Experiments. Studies of the adsorption/desorption of Cd, Pb, and Zn by Utica and Lula sediments were conducted in batch experiments and the reversibility of Cd, Pb, and Zn adsorption on these sediments were investigated by comparing observed desorption isotherms and edges to their respective adsorption isotherms and edges. We transferred Cd, Pb, and Zn solutions (40 mL) at various concentration levels (15-500 µM) to 50-mL plastic tubes and 1 g of dry Utica sediment was added. The sediment-water mixtures were sealed and placed on a slowly rotating rack that provided gentle (40 rpm) end-over-end mixing during the reaction period. At the end of each experiment, we centrifuged the reaction tubes and we withdrew the supernatant solutions with a syringe. We filtered them through 0.2 µm Nalgene syringe filters (SFCA). We acidified the filtered samples with 1 percent nitric acid analyzed for solution metal concentrations. We conducted desorption experiments in two different ways: (1) by replacing 30 mL supernatant with background electrolyte solution; and (2) by lowering the solution pH. Desorption experiments also were conducted by replacing supernatant solutions with EDTA-containing electrolyte solution to investigate the desorption mechanisms. The effect of the washing procedure (removing colloidal materials) on heavy metal adsorption reversibility has been studied by prewashing the sediments before initiating adsorption and subsequent desorption experiments.
Sediment Analysis. For the determination of heavy metal binding, we used a modification of the sequential extraction method of Tessier, et al. (1979). We determined the fraction of each metal in each sediment fraction (exchangeable, carbonates, iron and manganese oxides, and organic matter and pyrite). We determined reactive metal concentrations following a 24-hour extraction in 1N HCl at a solid/solution ratio of 1:50 (Huerta-Diaz and Morse, 1990). We determined the acid volatile sulfide (AVS) and simultaneously extracted metal (SEM) concentrations following the method of Simpson (2001). We also determined total organic and inorganic carbon by combustion and coulometric titration. Pore water and suspended particulate matter from Trepengier sediment also was analyzed for heavy metal concentration. The heavy metal in suspended particulate matter was collected on a preweight filter paper (0.45 µm) and extracted with 1 N HCl for 24 hours to obtain the reactive metal concentration.
Resuspension Experiments. We conducted resuspension experiments on Trepangier Bayou and Lake Charles sediments at various particle concentrations (20 and 40 g/L). We collected Trepangier Bayou sediment in the summer of 2002, and kept it frozen to maintain its anoxic character. We collected Lake Charles sediment in 1995, and kept it refrigerated until now. We resuspended these two sediments in aerated 0.01 M NaCl solution by an overhead propeller stirrer at room temperature. We monitored the experiments for 1 to 4 weeks. We measured the solution pH and Eh regularly during the experiments. Water samples were collected as a function of time (15, 30 minutes followed by 1, 3, 5, 24, and 72 hours) and episodically over the next few weeks (1, 2, 3, and 4 weeks) for the determination of the concentration of 25 inorganic compounds including Fe, Mn, Al, Ca, Mg, Zn, Pb, Cd, Cu, As, P, Cr, and S. In subsequent samplings, we took the samples from the supernatant solution (~ 20 mL) and we replaced the amount of solution withdrawn by an equivalent volume of 0.01 M NaCl solution to maintain a constant solid/solution ratio. The stirrer was stopped for 2 to 3 minutes prior to sampling to allow solids to settle. We measured dissolved heavy metal and the inorganic compound concentrations by either inductively coupled plasma-optical emission spectroscopy (ICP-OES) (major elements) or inductively coupled plasma-mass spectrometry (ICP-MS) (trace elements).
We used two methods to prevent heavy metal release, CaCO3 addition for pH control, and polymer addition for fines control. Resuspension experiments also were conducted on the Trepangier sediment with the addition of CaCO3 (12 percent).
The Effect of Polyacrylic Acid (PAA) on Heavy Metal Dsorption From Natural Sediments. We used Utica and Trepangier Bayou sediments as sorbents in these desorption experiments. Adsorption experiments were initiated by adding ~10 mL of Cd stock solution (2.5mM) into 20 g of sediments in a 100-mL plastic bottle. We shook the bottle by hand to mix the solution and sediment and left it overnight to reach adsorption equilibrium. At the end of adsorption, we transferred 2 g of slurry into 50-mL plastic bottles. We added different amounts of a polyacrylate stock solution (450,000 MW, 9.47 g/L, pH 7.3) into each bottle and left overnight. To begin the desorption experiment, we added 40 mL of electrolyte solution to each bottle, and we tumbled the bottles at 30 rpm for 24 hours. The polylacrylate concentrations of the solutions were 23, 115, 227, 1,137, and 1,867 mg/L, respectively. At the end of each experiment, we centrifuged reaction tubes and we filtered and analysed the supernatant solutions for solution metal and polyacrylate concentrations.
Rice University Portion
The percent adsorption of Cd, Zn, and Pb on Utica sediment after desorption by lowering the solution pH are shown in Figure 2. The extent of metal desorption is minimum at high pH, and it increases significantly with decreasing solution pH. The desorption edges of Cd, Zn, and Pb are almost identical to their respective adsorption edges, suggesting that heavy metal adsorption on Utica sediment is completely reversible. In addition, more than 90 percent of adsorbed Cd and Pb are released from Utica and Lula sediment after four successive desorption steps with 200 µM EDTA solution, suggesting that Cd and Pb are readily desorbable from both sediments.
Figure 2. Percent Adsorption of Cd, Pb, and Zn on Utica Sediment (25 g/L) in 0.01 M NaNO3 + 0.01 M NaN3 Solution as a Function of pH After Desorption by Lowering Solution pH (o). (a) Cd on Utica at (Cd)init = 100 µM; (b) Zn on Utica at (Zn)init = 100 µM; (c) Pb on Utica at (Pb)init = 360 µM. For comparison, Cd, Pb, and Zn adsorption edges also are present as solid circles.
We conducted adsorption/desorption experiments with Cd on "washed" Utica and Lula sediments following the same procedure as the "unwashed" sediments, where the "washed" sediments were washed several times before the initiation of adsorption experiment to remove the suspended colloidal matter. The amount of Cd sorbed by "washed" sediments is higher than that observed on unwashed Utica at pH 4-7 (see Figure 2). With each additional sediment washing, higher Cd adsorption is observed. The lower adsorption of Cd on "unwashed" sediments may be explained by the presence of colloidal materials in the sediments. We observed apparent unconformity of adsorption and desorption isotherms by the replaced supernatant method. However, the agreement between adsorption and desorption isotherms has been improved significantly after washing sediments several times (see Figure 3), indicating the important role that colloidal materials play on heavy metals mobility in sediments.
Impact of Dredging of Anaerobic Sediments. Figure 2a shows the change of solution pH and redox potential during the resuspension of 40 g/L anaerobic sediment from Trepangier Bayou. SEM/AVS of this sediment is about 0.04, indicating that it is a safe sediment according to the standards proposed by the U.S. Environmental Protection Agency (EPA) for five metals (Cu, Cd, Ni, Pb, and Zn). Nevertheless, after exposing the anoxic suspension to atmosphere for 4 weeks, redox potential increases constantly from about -240 to +560 mV and the solution pH decreases from 7.3 to 1.8. The dramatic decrease of the solution pH is mainly due to the oxidation of sulfide, and it increases the mobility of heavy metals. As shown in Table 2a, metal concentrations in the solution increase up to 200-fold. After 5 days of resuspension, the water became highly contaminated with respect to Cd, Pb, Zn, Cu, and As (76, 447, 17, 300, 301, 14 µg/L, respectively). However, the short-term release of both Fe and heavy metal in a few hours have a different release pattern when compared to the long-term release over weeks, indicating that different mechanisms affect heavy-metal release in a short versus a long time frame. For the resuspension experiment conducted on Trepangier sediment at 20 g/L, a similar trend was found, but heavy metals were not released to the same extent.
We conducted similar resuspension experiments on the Trepangier sediment with the addition of 12 percent CaCO3. As shown in Figure 2b and Figure 3, with the addition of the calcite, solution Eh and pH do not change as dramatically. The addition of calcite does not have a strong impact on the short-term heavy-metal release, yet has a large stabilization effect on sediment over the long term. Eh increased from about -255 to -97 mV, and the solution pH stays near neutral (7.1-7.5) during the resuspension for 8 days. In this case, heavy metal release to the overlying water is negligible (open symbols), while the release of heavy metal from the same sediment (filled symbols) could be several orders of magnitude higher without the amendment of calcite. For resuspension experiments conducted on Lake Charles sediments, little change in pH occurred and metals release was negligible, because sediments in Lake Charles are partially oxidized.
The Effect of Polyelectrolyte on Sediment Resuspension and Heavy Metal Desorption. Heavy metal release during dredging and resuspension is largely due to the resuspension of fine colloidal particles. The fine colloidal particles typically contain high surface area and heavy metal concentrations. Polyelectrolytes are widely used as flocculants in solid liquid separation and in the sludge dewatering process and as soil amendment in agriculture to improve the retention of nutrients. Polyelectrolyte also is a strong adsorbent for heavy metals. It is proposed that such polymers may be useful in dredging or capping to aid both the dewatering and settling of sediments and to slow the release of heavy metals. Preliminary data indicate that the polymer may have significant impact on the sedimentation and heavy metal desorption. However, the condition of polymer application needs to be carefully designed. For example, both the amount of polymer and aqueous pH will have a strong impact on the process. Solution pH is critical toward all four processes: (1) the amount of polyacrylate adsorption to sediments; (2) heavy metal complexation to polyacrylate; (3) heavy metal adsorption/desorption from sediment; and (4) heavy metal adsorption to surface-bound polyacrylate.
Figure 3. Comparison of pH, Eh, and Heavy-Metal Concentrations of a Trepengier Sediment Resuspension Experiment With 12 Percent (w/w) Calcite Added Versus the Control Trepengier Resuspension Experiment Where No Calcite Was Added. The filled symbols are data from Trepengier sediment and open symbols are from calcite amended Trepengier sediment.
|sampling time||pH||Eh (mV)||[Fe] (mg/L)||[Mn] (mg/L)||[Ca] (mg/L)||[Pb] (µg/L)||[Zn] (mg/L)||[Cd] (µg/L)||[S] (mg/L)||[As] (µg/L)||[Cu] (µg/L)||[Co] (µg/L)|
|S1||15 minute||7.33||-237||16.21||0.74||23.67||0.12||0.137||< D. L.||1.07||5.85||2.5||0.23|
|S3||3 hour||7.15||-187||5.18||0.46||17.43||1.08||0.0684||< D. L.||4.45||8.03||5.83||0.81|
|S4||6 hour||7.14||-182||4.1||0.4||40.82||0.97||0.0429||< D. L.||9.04||7.37||6.17||0.89|
|S5||24 hour||6.59||-88||7.5||1.84||127.55||0.82||0.0674||< D. L.||82.5||4.17||6.44||3.13|
|sampling time||pH||Eh (mV)||[Fe] (mg/L)||[Mn] (mg/L)||[Mg] (mg/L)||[Ca] (mg/L)||[Pb] (µg/L)||[Zn] (µg/L)||[Cd] (µg/L)||[Cu] (µg/L)||[Al] (µg/L)||[S] (mg/L)|
|S1||40 minute||7.33||-255||11.514||0.63731||14.342||25.755||2.02||< D. L.||< D. L.||< D. L.||5.05||1.1|
|S5||48 hour||7.13||-150||0.02323||1.9695||39.592||406.02||1.01||14.96||0.06||5.87||< D. L.||328|
|S6||72 hour||7.41||-95.5||0.00808||0.3131||40.703||471.67||< D. L.||48.59||0.14||5.21||< D. L.||372|
|S7||5 days||7.47||-65.6||0.01111||0.0101||38.784||482.78||< D. L.||84.3||0.09||6.92||< D. L.||388.8|
|S8||7 days||7.5||-85.8||0.018||0.004||38.3||497.9||< D. L.||63.94||0.15||8.5||< D. L.||394.9|
|S9||8 days||7.54||-97||0.011||0.004||37.4||492||6||71.67||0.193||9.08||< D. L.||N.A.|
Figure 4. Cd Desorption Concentrations From two Sediments in the Presence of Various Concentrations of Polyacrylate at pH 7.3, Where Plot A is From 0-220 mg/L Polymer and Plot B is from 0-1200 mg/L Polymer Concentrations.
For the Louisiana State University Portion, we will:
· Continue with the theoretical developments of the two-compartment model.
· Perform addition numerical simulations with the three compartment arrangements and explore the sensitivity of the F versus t behavior pattern with variations in particle size, compartment dimensions, porosity, surface areas and kd's.
· Select the simplest realistic model for use, correlating organic chemical desorption data sets selected from the literature to extract basic transport and thermodynamic parameters.
· Apply the two-compartment model to metal desorption when such data becomes available or appropriate sets are located in the literature.
For the Rice University Portion, we will:
· Conduct resuspension experiments on more fresh sediments with distinct variation in sediment character such as acid volatile sulfide (AVS), carbonate content, etc.
· Model the mobility of heavy-metal release during resuspension event using a few predominant mechanisms.
· Investigate the interactions between polymers and priority contaminants sediments (heavy metals and organic pollutants) and test the potential use of polymers to reduce the mobility of organic and inorganic pollutants during sediment resuspension events.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
|Other subproject views:||All 47 publications||14 publications in selected types||All 12 journal articles|
|Other center views:||All 279 publications||92 publications in selected types||All 63 journal articles|
||Chen W, Kan AT, Newell CJ, Moore E, Tomson MB. More realistic soil cleanup standards with dual-equilibrium desorption. Ground Water 2002;40(2):153-164.||
||Gao Y, Kan AT, Tomson MB. Critical evaluation of desorption phenomena of heavy metals from natural sediments. Environmental Science & Technology 2003;37(24):5566-5573.||
Supplemental Keywords:contaminated sediments, contaminated sediment, sediment resuspension, resuspension, dredge, storm events, atomic force microscopy, bioavailability, biodegradation, bioremediation of soils, contaminated soil, dewatering, dredged sediments, dredging, kinetics, microbial degradation, phytoremediation, labile fraction, nonlabile fraction, desorption kinetics, desorption, heavy metal, pH, redox potential, polymer, polycyclic aromatic hydrocarbon, PAH, polychlorinated biphenyl, PCB., RFA, Scientific Discipline, Waste, Water, Contaminated Sediments, Analytical Chemistry, Hazardous Waste, Hazardous, Environmental Engineering, dewatering, vegetative dewatering, dreging, microbial degradation, bioavailability, biodegradation, resuspension, contaminated sediment, contaminated soil, bioremediation of soils, kinetcs, phytoremediation, dredged sediments, bioremediation
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