Untreated Sediment Research Articles

Stabilization of contaminated canal sediments

ABSTRACT Morocco has valuable assets in marine seaboards and resources. The Mediterranean coasts do more than attracting tourists. That is why it is imperative to reconcile economic development with the quality of the environment. The industrial area in Tangier (Morocco), situated in the south-east area of the city, is a primary source of sediment pollution in the canal which runs through the area and discharges into the sea. This paper studies the contaminated and untreated sediments from that canal. A physical, chemical, mineral and environmental characterization was made to evaluate its possible use as sand for mortar. The replacement of sand by sediment indeed reduces the mechanical strengths. The chemical analysis of leachates after leaching test yet show a certain stabilization of pollutants, specially heavy metals in the cementitious matrix.

Precipitation of arsenic under sulfate reducing conditions and subsequent leaching under aerobic conditions

The stability of As precipitates formed by microbial SO4 reduction was examined via leaching of precipitate-laden sediments with aerobic groundwater. Sediment and groundwater collected from an As-contaminated aquifer were used to construct the flow-through columns utilized to demonstrate precipitate formation and stability. For 4 months, indigenous SO4-reducing bacteria in these columns were stimulated with injections of lactate, ethanol, FeCl2, (NH4)3PO4 and SO42-. Analyses, including 35S autoradiography, sequential extraction, SEM and XANES, of one of the columns revealed elevated As and 35S sulfide concentrations, and microcrystalline overgrowths comprised of FeAsS, AsS, S and phosphates restricted to “black” zones that had formed within the sediment. Two columns were then treated with a H2O2/K2HPO4 solution in order to produce Fe phosphate coatings that would theoretically protect sulfides from subsequent oxidation. Sediment from an untreated and a treated column were also packed into smaller syringe columns to record As depletion during aerobic leaching. Aerobic, As-bearing natural groundwater and artificial, As-free groundwater were passed through both untreated and treated columns and syringe columns for 4 months during which the As release rate from the columns and the removal of As from the syringe columns was observed. The As release rate from the untreated column and the rate of As removal from the syringe columns of untreated sediment correlated well and both indicated overall leaching of ∼2% of the microbially precipitated As-bearing sulfide. The As release rate from the treated sediments was 3–4 times greater than that of the untreated sediments, contrary to expectations that treatment would minimize As release. Sequential extraction, SEM and XANES analyses of the untreated column after aerobic leaching revealed that a significant portion of the remaining As was arsenate associated with Fe3+ hydroxides. A reactive transport model, which incorporated the oxidative dissolution of Fe and As sulfides and the adsorption of arsenate to Fe3+ hydroxides, reproduced the timing of As and sulfate release from this column and indicated that the release rate was limited by the O2 flux and Fe sulfide abundance. Scaling down the laboratory flow rate to that of the groundwater at a local field site suggests that microbially precipitated FeAsS produced in this manner should be stable over a decadal time scale.

Assessment of field‐related influences on polychlorinated biphenyl exposures and sorbent amendment using polychaete bioassays and passive sampler measurements

Field-related influences on polychlorinated biphenyl (PCB) exposure were evaluated by employing caged deposit-feeders, Neanthes arenaceodentata, along with polyoxymethylene (POM) samplers using parallel in situ and ex situ bioassays with homogenized untreated or activated carbon (AC) amended sediment. The AC amendment achieved a remedial efficiency in reducing bioaccumulation by 90% in the laboratory and by 44% in the field transplants. In situ measurements showed that PCB uptake by POM samplers was greater for POM placed in the surface sediment compared with the underlying AC amendment, suggesting that tidal exchange of surrounding material with similar PCB availability as untreated sediment was redeposited in the cages. Polychlorinated biphenyls bioaccumulation with caged polychaetes from untreated sediment was half as large under field conditions compared with laboratory conditions. A biodynamic model was used to confirm and quantify the different processes that could have influenced these results. Three factors appeared most influential in the bioassays: AC amendment significantly reduces bioavailability under laboratory and field conditions; sediment deposition within test cages in the field partially masks the remedial benefit of underlying AC-amended sediment; and deposit-feeders exhibit less PCB uptake from untreated sediment when feeding is reduced. Ex situ and in situ experiments inevitably show some differences that are associated with measurement methods and effects of the environment. Parallel ex situ and in situ bioassays, passive sampler measurements, and quantifying important processes with a model can tease apart these field influences.

Influence of iron redox transformations on plutonium sorption to sediments

AbstractPlutonium subsurface mobility is primarily controlled by its oxidation state, which in turn is loosely coupled to the oxidation state of iron in the system. Experiments were conducted to examine the effect of sediment iron mineral composition and oxidation state on plutonium sorption and reduction. A pH 6.3 vadose zone sediment containing iron oxides and iron-containing phyllosilicates was treated with various complexants (ammonium oxalate) and reductants (hydroxylamine hydrochloride and dithionite-citrate-bicarbonate (DCB)) to selectively leach and/or reduce iron oxide and phyllosilicate/clay Fe(III).57Fe-Mössbauer spectroscopy was used to identify initial iron mineral composition of the sediment and monitor dissolution and reduction of iron oxides and reduction of phyllosilicate Fe(III).57Fe-Mössbauer spectroscopy showed that the Fe-mineral composition of the untreated sediment is: 25–30% hematite, 60–65% small-particle/Al-goethite, and <10% Fe(III) in phyllosilicate; there was no detectable Fe(II). Upon reduction with a strong chemical reductant (dithionite-citrate-bicarbonate buffer), much of the hematite and goethite was removed. Partial reduction of phyllosilicate Fe(III) was evident in the sediments subjected to DCB treatment. Sorption of Pu(V) was monitored over one week for the untreated and each of five treated sediment fractions. Plutonium oxidation state speciation in the aqueous and solid phases was monitored using solvent extraction, coprecipitation, and XANES. The rate of sorption appears to correlate with the fraction of Fe(II) in the sediment (untreated or treated). Pu(V) was the only oxidation state measured in the aqueous phase, irrespective of treatment, whereas Pu(IV) and much smaller amounts of Pu(V) and Pu(VI) were measured in the solid phase. Surface-mediated reduction of Pu(V) to Pu(IV) occurred in treated and untreated sediment samples; Pu(V) remained on untreated sediment surface for two days before reducing to Pu(IV). Similar to the sorption kinetics, the reduction rate appears to be correlated with sediment Fe(II) concentration. The correlation between Fe(II) concentrations and Pu(V) reduction demonstrates the potential impact of changing iron mineralogy on plutonium subsurface transport through redox transition areas. These findings should influence the conceptual models of long-term stewardship of Pu contaminated sites that have fluctuating redox conditions, such as vadose zones or riparian zones.

Normalizing XRF-scanner data: A cautionary note on the interpretation of high-resolution records from organic-rich lakes

X-ray fluorescence (XRF) scanning of unlithified, untreated sediment cores is becoming an increasingly common method used to obtain paleoproxy data from lake records. XRF-scanning is fast and delivers high-resolution records of relative variations in the elemental composition of the sediment. However, lake sediments display extreme variations in their organic matter content, which can vary from just a few percent to well over 50%. As XRF scanners are largely insensitive to organic material in the sediment, increasing levels of organic material effectively dilute those components that can be measured, such as the lithogenic material (the closed-sum effect). Consequently, in sediments with large variations in organic material, the measured variations in an element will to a large extent mirror the changes in organic material. It is therefore necessary to normalize the elements in the lithogenic component of the sediment against a conservative element to allow changes in the input of the elements to be addressed. In this study we show that Al, which is the lightest element that can be measured using the Itrax XRF-scanner, can be used to effectively normalize the elements of the lithogenic fraction of the sediment against variations in organic content. We also show that care must be taken when choosing resolution and exposure time to ensure optimal output from the measurements.

Trends in PAH and black carbon source and abundance in a tropical mangrove system and possible association with bioavailability

The presence of black carbon (BC) and its interaction with polycyclic aromatic hydrocarbons (PAHs) in mangrove sediments were studied for the first time. The study included an oil contaminated mangrove and two other sites of different character. BC content ranged from 0.03% to 0.47% (dry weight sediment), reaching a maximum of 9% of the total organic carbon. Cluster analysis indicated strong BC and high molecular weight (HMW) PAH association but no relationship was found between BC and alkylated PAHs. The ratio C 4Ph/BaP was used to verify differences in the mobility of alkylated and HMW PAHs along a core from the oil contaminated site. Results for the solid–water coefficient of distribution ( K d in l kg −1) for pyrene were similar using untreated sediment samples (log K d 4.66 ± 0.03) and chemo-thermal oxidation (CTO) residues (log K d 4.39 ± 0.03), confirming the importance of BC in the partitioning of PAHs. However, the resulting BC-normalized distribution coefficients (log K BC 7.1–7.4 μg kg BC - 1 ) were greater than published values, probably because of the presence of other hydrophobic phases in the refractory organic matter pool. In addition, BC normalization of pyrene concentration in mangrove crabs reduced the variability in calculated bioaccumulation factors vs. organic carbon-normalized concentrations for the sites. The evidence agrees with the general view of BC particles controlling the fate of PAHs in sediments, but also points out the necessity for studying the process in further detail when considering organic matter-rich mangrove sediments.

Chemical Lake Restoration Products: Sediment Stability and Phosphorus Dynamics

Laboratory experiments with sediments from three shallow Danish lakes were conducted to evaluate the effects of chemical lake restoration products during resuspension. Phosphorus (P) removal, sediment stability, sediment consolidation and color reduction were studied over time. The investigated products were aluminum (Al), Phoslock (a commercial bentonite product coated with lanthanum) and a combination of Al covered with bentonite (Al/Ben). All treatments effectively reduced the P concentration in the water. However, the treatments containing Al reduced the P concentration immediately after resuspension, whereas Phoslock required several days after resuspension to reduce the P concentration. Especially Phoslock, but also Al/Ben, increased the sediment stability threshold by 265% and 101%, respectively, whereas Al had no stabilizing effect. The fresh Al floc was resuspended 5x easier than untreated sediment. The largest consolidation of the sediment occurred with addition of Phoslock, followed by Al/Ben, while Al alone had no effect. Enhanced consolidation may be of importance for macrophyte colonisation of organic sediment. Phoslock improved the light climate moderately by removing color, whereas Al was very effective in removing color. Ben/Al showed intermediate effects on color reduction. These findings are important when decisions are made on restoration method for a specific lake, which may be more or less wind exposed.

Effect of sodium dithionite on the surface composition of iron‐containing aquifer sediment

AbstractAES, XPS and SIMS analyses were used to characterize the surface of Pantex aquifer sediment under pretreatment conditions previously shown to activate the sediment for remediation of the explosives‐contaminated aquifer. The untreated sediment contains detectable concentrations of iron, but the composition is heterogeneous and the nature of the iron at the surface is poorly defined. Treatment with dithionite (Na2S2O4) produced Fe3O4‐like material, as evidenced by characteristic Fe 2p XPS structure. Sediment treated with buffered dithionite (pH = 8.8) shows a higher Fe2+/Fe3+ ratio and retains strongly adsorbed FeS‐like surface species even after copious washing with deionized water. The negative SIMS data indicate that, in the absence of the K2CO3 buffer, the dithionite treatment places relatively little sulfur onto the surface, but requires the higher buffered pH to form sulfide and sulfates. Detection of Fe3O4 and FeS on the sediment surface after dithionite treatment supports the effectiveness of this treatment in remediating contaminated aquifer sediment. SIMS and XPS indicate that treating with buffered dithionite also results in some loss of iron from the sediment surface. Copyright © 2009 John Wiley & Sons, Ltd.

Impact of Pyrolysis Treatment on Heavy Metals in Sediment

This paper describes a laboratory study that examined the effect of pyrolysis treatment on the behavior of Hg, Cr, Zn, Pb, Cu and Cd in a stream sediment. The influences of pyrolysis on the evaporation, sequential extraction and leaching behavior of these metals were investigated. Cr, Zn, Pb and Cu were retained quantitively in the solid residue at temperatures up to 800°C while mercury and cadmium were completely or partially evaporated. The metal form distribution in the sludge samples was determined by the sequential extraction procedure. The procedure revealed that as a consequence of pyrolysis, the metals were more strongly fixed in the treated sediment, as could be seen by the decrease with temperature of the first two sequential-extracted fractions and increase of the residue fraction. The leaching results showed that the quantities of the studied metals leached in the two pyrolysis samples were lower than those in the untreated sediment. The amounts of metals leached from the pyrolysis residues correlated significantly with the first extracted fraction (exchangeable fraction).

Resuspension behaviour of aluminium treated lake sediments: effects of ageing and pH

Lake restoration with aluminium (Al) has been widely used in shallow lakes, but it is unknown how ageing of the Al floc affect resuspension behaviour, sediment stability and entrainment of Al and phosphorus (P). High primary production in shallow lakes can lead to high pH in the water column with a potential release of Al and P during resuspension events. A laboratory resuspension experiment at defined hydrodynamic conditions using a calibrated erosion chamber was performed with intact sediment cores (with intact vs. disturbed biofilm on the surface) from previously Al-treated shallow Lake Mollen, NE Germany. Newly applied Al reduced surface sediment stability, but ageing led to the same stability as untreated sediment within 2 months with an intact biofilm and within 4 months with a disturbed biofilm. Dissolved Al increased markedly at resuspension after 2 days and 2 weeks of ageing and with elevated pH (9–11) in the water. The Al floc were redissolved and dissolved Al increased with elevated pH and shear velocity. Dissolved P concentration was constantly low due to excess binding capacity of the Al floc. In conclusion, Al application to shallow lakes prone to resuspension and with a high production must be done in periods with less resuspension risk to allow 2–4 months time for floc stabilization. Otherwise, possible resuspension and high(er) pH may lead to elevated concentrations of dissolved Al in the water column.

Lake sediment treatment with aluminum, iron, calcium and nitrate additives to reduce phosphorus release

Treatment of lake sediments with salts is a promising approach for preventing phosphorus release from sediments. Five 35-d treatments of undisturbed sediment cores in the East Lake, Wuhan, China were applied under anoxic conditions: nothing added (control), Al2(SO4)3 added, FeCl3 added, CaCl2 added, and NaNO3 added. To identify changes in the P binding sites in the sediment caused by the treatments, different P binding forms were extracted from the sediment before and after the treatments. We found that the mean P release rates for anoxic treatments with Al2(SO4)3, FeCl3, CaCl2 and NaNO3 were −0.6, 0.03, 0.6 and 2.6 mg/(m2·d), respectively, while the P release rate with no additives was 7.3 mg/(m2·d). In suboxic conditions, the concentration of total phosphorus (TPaverage 657 mg/kg) in sediment was much lower than that of untreated sediment (TPaverage 688 mg/kg) and treatments with salts (TP(Al2(SO4)3) 793 mg/kg, TP(FeCl3) 781 mg/kg, TP(NaNO3) 802 mg/kg, TP(CaCl2) 747 mg/kg). We also found that adding CaCl2 prevented P release because of apatite formation and because PCa (Ca bound P) increased at the sediment surface. Addition of Fe3+ and NO3− to the sediment increased the amounts of PFe, Mn (Redox-sensitive P, mostly Fe and Mn compounds), since iron oxide has the ability to combine P. Addition of Al2(SO4)3 increased the fraction of PAl, Fe (P bound to metal oxides (Al, Fe)) and decreased the P and Fe in the water above the anoxic sediment, showing the greater ability of Al in binding P. The results showed that Al2(SO4)3, FeCl3, CaCl2 and NaNO3 all had an effect in controlling phosphorus release. The effect was related to the forms of phosphorus existing in the sediment before treatment and the forms resulting after adding the four reagents. The combination of Al3+ or Fe3+ with NO3− promises to be a reasonable chemical treatment for increasing the P retention capacity of sediments in eutrophic lakes. If chemical treatment is combined with bioremediation, the aim of environmental repair may be achieved.

In-situ stabilization of Pb, Zn, Cu, Cd and Ni in the multi-contaminated sediments with ferrihydrite and apatite composite additives

Three additives were evaluated for their effectiveness in the attenuation of Pb 2+, Zn 2+, Cu 2+, Cd 2+, Ni 2+ in contaminated sediments. Apatite, ferrihydrite and their composite were applied to the sediments. For the remediation, BCR, SEM/AVS and TCLP were adopted as the evaluating method and comparison of their results were used for the first time to test in-situ stabilization effect. The results showed that after 5 months composite treatment, more than 70% Pb 2+, 40% Zn 2+, 90% Cu 2+, 50% Cd 2+ and 80% Ni 2+ was immobilized in oxidizable and residual phases, respectively. Compared to untreated sediment, Pb 2+, Zn 2+, Cu 2+, Cd 2+ in residual fraction increased 20%, 10%, 10%, 10% with composite treatment after 5 months, respectively. ΣSEM/AVS ratio declined from 12.6 to 9.3, in addition, composite treatments reduced the leaching of Pb 2+ and Zn 2+ from 10.6 mg L −1and 42.5 mg L −1to 5.4 mg L −1 and 24.1 mg L −1 in the sediment by TCLP evaluation. Meanwhile, apatite and ferrihydrite composite additives lowered the bioavailability and toxicity of sediments as well. Ferrihydrite had a positive effect in controlling the bioavailability and toxicity of heavy metals because it effectively retarded the oxidation of AVS in sediment.

Evaluation of Bioaerosol Components, Generation Factors, and Airborne Transport Associated with Lime Treatment of Contaminated Sediment

Lime treatment has been used in contaminated sediment management activities for many purposes such as dewatering, improvement of physical properties, and reducing contaminant mobility. Exothermic volatilization of volatile organic compounds from lime-treated sediment is well known, but potential aerosolization of bioaerosol components has not been evaluated. A physical model of a contaminated sediment treatment and airborne transport process and an experimental protocol were developed to identify specific bioaerosol components (bacteria, fungi, cell structural components, and particles) that may be aerosolized and transported. Key reaction variables (amount of lime addition, rate of lime addition, mixing energy supplied) that may affect the aerosolization of bioaerosol components were evaluated. Lime treatment of a sediment contaminated with heavy metals, petroleum-based organics, and microorganisms increased the sediment pH and solids content. Lime treatment reduced the number of water-extractable bacteria and fungi in the sediment from approximately 106 colony-forming units (CFU) · mL-1 to less than the detection limit of 103 CFU • mL-1. This reduction was seen immediately for bacteria and within 21 days for fungi. Lime treatment immediately reduced the amount of endotoxin in the sediment, but the effects of lime treatment on β-D-glucan could not be determined. The temperature of the treated sediment was linearly related to the amount of lime added within the range of 0–25%. Bacteria were aerosolized during the treatment trials, but there was no culturable evidence of aerosolization of fungi, most likely because of either their particular growth stage or relatively larger particle size that reduced their aerosolization potential and their collection into the impingers. Nonbiological particles, endotoxin, and β-D-glucan were not detected in air samples during the treatment trials. The amount of lime added to the reaction beaker and the relative amount of mixing energy supplied to the reaction significantly affected the aerosolization ratio of bacteria (amount of aerosolized bacteria divided by the amount of bacteria in untreated sediment) from the reaction beaker. The rate of lime addition did not significantly affect the aerosolization ratio of bacteria. The aerosolization results suggest that exposure to bacteria is possible with sediment treatment activities, but the hazard level could not be determined because speciation of the aerosolized bacteria for pathogen identification was not performed, and health and safety standards and criteria for bioaerosol components have not been developed. Quantitative scaling analysis and whether the system represents actual environmental conditions were not studied.

The effect of activated carbon on partitioning, desorption, and biouptake of native polychlorinated biphenyls in four freshwater sediments

The present study evaluated the effect of activated carbon amendment in four freshwater sediments from the Great Lakes (North America) areas of concern with a wide range of sediment geochemical characteristics (0.83-5.1% total organic carbon) and polychlorinated biphenyl (PCB) concentrations (0.33-84.7 microg/g). The work focused on understanding the impact of activated carbon amendment on PCB aqueous partitioning, PCB desorption characteristics, and PCB biouptake in a freshwater oligochaete (Lumbriculus variegatus). The results showed that PCB aqueous equilibrium concentrations, rapid desorption fractions, and biouptake by the oligochaete were reduced after activated carbon amendment. Addition of activated carbon at a dose of 0.5-fold native organic carbon reduced PCB bioaccumulation by 42% for Niagara River sediment, 85% for Grasse River sediment, 74% for Milwaukee River sediment 1, and 70% for Milwaukee River sediment 2. A linear relationship was observed between log biota-sediment accumulation factor and the first 6-h desorption fractions for each PCB homologue for treated and untreated sediments. Water-lipid bioconcentration factors for PCB congeners were largely conserved after amendment with activated carbon. Our present results suggest that at steady state, changes in the aqueous PCB concentrations can be used to predict changes in PCB bioaccumulation in deposit-feeding organisms. Thus, use of advanced pore-water measurement techniques, such as solid-phase extraction passive samplers, may be suitable for long-term monitoring of treatment performance.

Measuring and modeling reduction of DDT availability to the water column and mussels following activated carbon amendment of contaminated sediment

A 28-day accumulation study demonstrated the use of mussel uptake, passive samplers, and biodynamic modeling to measure the reduction of dichlorodiphenyltrichloroethane (DDT) availability in the water column after the addition of activated carbon to contaminated sediment. Sediment collected from Lauritzen Channel, Richmond, California (16.5 mg total DDT/kg) was mixed with either virgin activated carbon or a reactivated carbon for one month, after which a 28-day laboratory exposure study was completed. Mussels ( Mytilus edulis) suspended above activated carbon-treated sediment accumulated significantly less total DDT in soft tissue, 91% and 84% for virgin and reactivated carbon, respectively, as compared to untreated sediment. Mussel tissue concentrations correlated to concentrations in semipermeable membrane devices (SPMDs) and polyethylene devices (PEDs) suspended over the same sediments. A biodynamic model that incorporated DDT water concentrations, either analytically measured or estimated from PED uptake, described mussel accumulation over time. Thus, passive samplers in combination with biodynamic modeling may provide an important screening tool for assessment of filter-feeding uptake and ecological risk to water-dwelling organisms exposed to aqueous phase hydrophobic organic contaminants.

New cell extraction procedure applied to deep subsurface sediments

A new method is presented for the separation of cells from a marine sediment matrix. Different methods and reagents were tested for detaching microbial cells from sediment particles; the highest yields were achieved in a solution of EDTA, Tween 80, sodium‐pyrophosphate, and methanol plus gentle ultrasonic treatment, followed by density centrifugation through a cushion of Nycodenz. If present, carbonates were dissolved before extraction. Comparison with untreated sediments and pure cultures verified that this technique minimizes cell lysis. The new procedure was tested on seafloor sediment from several locations and water depths (<1 to >4000 m) and subseafloor sediment from the Arctic Ocean (IODP Expedition 302). Cell extraction efficiency was relatively high (65% to 100%) and consistent for each sediment type, with significantly (P < 0.01) lower variability of counts of separated cells compared with conventional counts on slurried sediments. Concentrating cells before enumeration allows for a much lower minimum detection limit and lower uncertainty than the conventional approach of simply slurrying sediment. Resolving relatively small differences in the distribution of microorganisms will allow for comparisons to other parameters (porewater chemistry, lithology, etc). Additionally, this method has potential for the use of molecular techniques that were previously difficult owing to coelution of interfering compounds from the sediment matrix.

Effects of gamma-sterilization on the physico-chemical properties of natural sediments

Batch U(VI) sorption/reduction experiments were completed on sterilized and non-sterilized sediment samples to elucidate biological and geochemical reduction mechanisms. Results from X-ray absorption near-edge structure (XANES) spectroscopy revealed that γ-sterilized sediments were actually better sorbents of U(VI), despite the absence of any measurable biological activity. These results indicate that γ-irradiation induced significant physico-chemical changes in the sediment which is contrary to numerous other studies identifying γ-sterilization as an effective and minimally invasive technique. To identify the extent and method of alteration of the soil as a result of γ-sterilization, untreated soil samples, physically separated size fractions, and chemically extracted fractions of the soil were analyzed pre- and post-sterilization. The effects of sterilization on mineralogy, pH, natural organic matter (NOM), cation exchange capacity (CEC), and iron oxidation state were determined. Results indicated that major mineralogy of the clay and whole sediment samples was unchanged. Sediment pH decreased only slightly with γ-irradiation; however, irradiation produced a significant decrease in CEC of the untreated sediments and affected both the organic and inorganic fractions. Mössbauer spectra of non-sterile and γ-sterilized sediments measured more reduced iron present in γ-sterilized sediments compared to non-sterile samples. Our results suggest that sterilization by γ-irradiation induced iron reduction that may have increased the sorption and/or reduction of U(VI) onto these sediments. However, Mössbauer and batch sorption data are somewhat contradictory, the former indicates that the iron oxide or iron hydroxide minerals are more significantly reduced while the later indicates that reduced clay minerals account for greater sorption of U(VI).

Cement Deep Soil Mixing (CDSM) for Solidification of Soft Estuarine Sediments

A preliminary study was conducted to determine the potential for cement deep soil mixing (CDSM) technology as a method for in-situ solidification of contaminated river and estuarine sediments. The study was conducted in Newark Bay, near the mouth of the Passaic River, New Jersey. The primary objective of the study was to evaluate the viability of CDSM for the in-situ S/S with a focus on: 1) determining the correct mix of the cement slurry, which provides rapid stabilization of the sediment matrix, 2) potential resuspension of solids during CSDM operations, 3) the effects of high organic content on the solidification process, and 4) the feasibility of using conventional dredging/extraction methods once the sediments have been stabilized and allowed to cure. The results of the study show CDSM slurry mixtures, as low as 7% in cement content, result in significant solidification and strength gain of in-situ sediments under ambient conditions. In sediments with very high organic contents (> 20%), the slurry mix would need to be adjusted to account for retardation effects of organics on cement hydration. Sediment resuspension during application was shown to be minimal at a distance of as little as 75 feet from the mixing head. Strength gains were considerable, effectively consolidating the sediment particles in a secure matrix, but not so high as to preclude extraction of solidified sediments with conventional dredging equipment. Dredged solidified sediment exhibited characteristics of a stiff glacial clay, and as such was easier to handle and transport than untreated dredged sediments. This technique has high potential to be used as an interim remedial measure prior to either extraction and decontamination/disposal or proper capping.

PCB Bioavailability Control in Lumbriculus Variegatus through Different Modes of Activated Carbon Addition to Sediments

PCB bioavailability to a freshwater oligochaete (Lumbriculus variegatus) was studied using sediments from a PCB-impacted river that was treated with different modes of granular activated carbon (GAC) addition. For sedimenttreated with 2.6% GAC and mixed for 2 min prior to L. variegatus addition, the reduction in total PCB biouptake was 70% for 75-300 microm size carbon, and 92% for the 45-180 microm size carbon. For the case where the GAC was placed as a thin layer on top of the sediments without mixing, the reduction in total PCB uptake was 70%. PCB biouptake kinetics study using treated and untreated sediment showed that the maximum PCB uptake in tissue was achieved at 28 days and decreased after that time. Although the absolute uptake of PCB changed over time, the percent reduction in total PCB uptake upon GAC amendment remained constant after the first few days. Our results indicated that PCB bioavailability was reduced upon the addition and little or no mixing of GAC into sediments. PCB aqueous equilibrium concentration and desorption rates were greatly reduced after GAC amendment, indicating reductions in the two primary mechanisms of PCB bioavailability in sediments: chemical activity and chemical accessibility.

Field methods for amending marine sediment with activated carbon and assessing treatment effectiveness

Previous laboratory studies have shown reductions in PCB bioavailability for sediments amended with activated carbon (AC). Here we report results on a preliminary pilot-scale study to assess challenges in scaling-up for field deployment and monitoring. The goals of the preliminary pilot-scale study at Hunters Point Shipyard (San Francisco, USA) were to (1) test the capabilities of a large-scale mixing device for incorporating AC into sediment, (2) develop and evaluate our field assessment techniques, and (3) compare reductions in PCB bioavailability found in the laboratory with well-mixed systems to those observed in the field with one-time-mixed systems. In this study we successfully used a large-scale device to mix 500kg of AC into a 34.4m(2) plot to a depth of 1ft, a depth that includes the majority of the biologically active zone. Our results indicate that after 7 months of AC-sediment contact in the field, the 28-day PCB bioaccumulation for the bent-nosed clam, Macoma nasuta, field-deployed to this AC-amended sediment was approximately half of the bioaccumulation resulting from exposure to untreated sediment. Similar PCB bioaccumulation reductions were found in laboratory bioassays conducted on both the bivalve, M. nasuta and the estuarine amphipod, Leptocheirus plumulosus, using sediment collected from the treated and untreated field plots one year after the AC amendment occurred. To further understand the long-term effectiveness of AC as an in situ treatment strategy for PCB-contaminated sediments under field conditions, a 3-year comprehensive study is currently underway at Hunters Point that will compare the effectiveness of two large-scale mixing devices and include both unmixed and mixed-only control plots.