oxymoron sediments

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Information about oxymoron sediments

Published on January 1, 2008

Author: Savina

Source: authorstream.com

Contaminated Sediment Management Still an Oxymoron?:  Contaminated Sediment Management Still an Oxymoron? Danny Reible Chevron Professor of Chemical Engineering Director, Hazardous Substance Research Center/S&SW Louisiana State University Baton Rouge, LA 70810 Outline:  Outline • Contaminated Sediments - What makes them so difficult? • How did we manage sediments in 1985-1990? • How do we do it now? • What do we know about contaminated sediment processes? - Dynamic sediment environments - Stable sediment environments - Bioavailability/bioaccumulation of contaminants So what are the options? • Contaminated Sediment Management - Still an Oxymoron? Hazardous Substance Research Center :  Hazardous Substance Research Center South and Southwest Established under CERCLA Mission Research and technology transfer Contaminated sediments and dredged material Unique regional (4&6) hazardous substance problems Contact info - Danny D. Reible, Louisiana State University Ph: 225-388- 6770 Email: reible@che.lsu.edu Web: www.hsrc.org LSU Rice Georgia Tech Research Theme Areas for HSRC/S&SW :  Research Theme Areas for HSRC/S&SW • Contaminant availability in sediments <Its not what we can measure, its what can receptors absorb? • Biotransformation processes of contaminants in sediments <Is recovery possible without the risk/expense of physicochemical treatment? • Science of risk management for sediments <How do we select and design appropriate technologies? • Unique regional hazardous substance issues <Are there regional problems that have been overlooked in the national debate? Key Research Contributions To-Date:  Key Research Contributions To-Date HSRC/S&SW • Availability <Developed promising approach to evaluate availability of nonpolar organics <Identified limitations of SEM/AVS ratio to define metals availability <Identified importance of volatile release from sediment/dredged materials • Biotransformation <Identified mechanism and limitations of phytoremediation of TNT <Developed a simple and inexpensive sediment biodegradation technology <Observed enhanced PAH degradation by common benthic organisms • Science of risk management <Helped develop contaminant loss criteria for technology selection <Defined a robust and relatively inexpensive in situ monitoring technology <Developed design guidance for in-situ and dredged material capping Contaminated Sediments :  Contaminated Sediments What makes them so difficult? • Reside in highly variable, dynamic systems <Normal variation in flows and storm events <Significant source of uncertainty • Large volume of sediment <Often greater than 1MM m3 <Average Superfund site involving ex situ treatment - <30,000 m3 • Large amounts of water <Hydraulic dredging generates at least 4 volumes water per volume sediment <Controls on environmental dredging often causing average solids content of dredged material to be 1-10% • Often marginal contamination with incomplete exposure pathways and uncertain risks to human and ecological health Contaminated Sediments :  Contaminated Sediments What makes them so important? • Historical sources of contamination largely controlled <Leaves legacy of contaminated sediments as important source <Continuing sources, however, limit potential cleanup • Lack of disposal options is a major impediment to harbor development <95% of shipping trade passes through dredged ports • Significant impediment to unrestricted usage of waterways <Fish advisories throughout Great Lakes and other areas • Widespread problem < Of 21,000 national sediment sampling stations (1996 Survey) 26% exhibit potential of adverse effects Additional 49% exhibiting intermediate probability of adverse effects < About 30% of Superfund sites involve contaminated sediments How did we manage sediments?:  How did we manage sediments? 1985-1990 • Assumed ex situ technological solutions available <Removal via dredging <Treatment or disposal onshore • Deferral of large, complicated sites <Hudson River <New Bedford Harbor <Fox River • Attempts to implement conceptual approach at Asmall@ sites < Bayou Bonfouca, Louisiana Bayou Bonfouca:  Bayou Bonfouca • Facility <Wood treating facility in operation since 1892 <Employed and released creosote <Adjacent to navigable bayou - Bonfouca • Bayou Bonfouca <150,000 - 170,000 cu yd of contaminated sediments <Surficial concentrations to 13,450 mg/kg total PAHs • Remediation <Removal of sediments in excess of 1300 mg/kg - mechanical excavator <Incineration of dredged material and burial of incinerator residual <Capping of residual contaminated sediments in bayou <Total Cost - $130 million How do we manage sediments now?:  How do we manage sediments now? • Increased reliance on predictive modeling of options <Need to understand natural fate and transport processes <Need to understand normal and episodic hydraulic state <Evaluation of management options requires sophisticated prognostic models • Increased reliance on in situ options <Monitored natural recovery <In-situ capping <Bioremediation and/or stabilization • Large, complicated sites still unresolved Contaminated Sediments:  Contaminated Sediments • Natural Recovery • Passive In-Situ Treatment or Containment • Removal and Upland Treatment or Containment • Removal and Subaqueous Treatment or Containment What are the Options? How do we choose among the options?:  How do we choose among the options? • Ultimate Goal - Reduction of Risk <Reduction or elimination of exposure and exposure pathways <Complications BHuman Risk - Selection and quantification of exposure pathways/effects? BEcological Risk - Pathways? Exposed Species? Effects? <Surrogate measures often used instead • Surrogate Goal - Mass Removal <Reduction in whole sediment concentration <Commonly used and just as commonly misses the mark! • Alternative Goals <Reduction in surface sediment concentration <Reduction in fish tissue levels <Reduction in water column levels <Reduction in integrated concentration/exposure/risk Natural Recovery of Contaminated Sediments:  Natural Recovery of Contaminated Sediments • When is it appropriate? <Large volumes of contaminated sediment with marginal level of contamination <Low energy, depositional environments <Dredging for navigation not required <Not a do-nothing proposition- entails monitoring and institutional controls <Not an ineffective approach chosen to minimize costs - may be best approach • Example - Kepone in James River <Expected to eliminate fish advisories faster than active remedial alternatives <Model employed to assess recovery <Recovery met targets - James River considered remediated • What are possible enhancements? <Sediment traps to enhance deposition <Particle broadcasting - artificially enhanced deposition <Source area removal - outfalls and sediment “hot spots” Passive In-Situ Containment or Treatment:  Passive In-Situ Containment or Treatment • What is it? <Enhanced biodegradation <In-situ solidification <Containment - capping • When is it appropriate? <When removal may result in unacceptable or increased risks <When hydraulic and other water body conditions are supportive <When navigation dredging is not required • What are the key assessment needs? <Evaluation of effectiveness/engineering feasibility of approach <Evaluation of long-term contaminant fate <Evaluation of armoring needed to maintain stability of sediments during treatment • Capping <May be used alone as containment or in combination with in-situ treatment to ensure containment during treatment In-Situ Treatment Options:  In-Situ Treatment Options • Enhance containment (capping) to provide time for treatment PEnhance natural adsorption and sequestration processes <Addition of adsorbents <Permeability controls <Enhance deposition to ensure clean surficial sediments • Enhance natural fate processes <Addition of reactants/catalysts BFerrous sulfate or iron addition for anaerobic degradation of chlorinated organics BOxygen sources for aerobic degradation <Capping to drive anaerobic conditions and (often) mobility reduction for metals • Active in-situ treatment <In-situ solidification technologies <In-situ reactor (e.g. auger/reactive hood technologies) Removal with Upland Treatment and Containment:  Removal with Upland Treatment and Containment • What is it? <Hydraulic or mechanical dredging <Generally requires temporary holding facility -confined disposal facility (CDF) <Upland landfill or treatment/destruction in incinerator, thermal desorber, biotreater, etc; • When is it appropriate? <Dredging required for navigation purposes <Dredging will not result in unacceptable or increased risks <Dredging can be accomplished with minimal generation of contaminated water <Upland treatment and containment options available and cost-effective • What are the key assessment needs? <Evaluation of contaminant losses during dredging and handling <Evaluation of ecological effects of sediment removal <Evaluation of solids content of produced dredged material Environmental Dredging :  Environmental Dredging A Double-Edged Sword? • Limited removal efficiency <Multiple passes, “overbite” generally required to meet removal targets <Removal hindered by debris or presence of bedrock or “hardpan” • Large quantities of potentially contaminated water generated <Environmental dredging conditions tends to increase produced water <Most environmental dredging operations achieve less than 10% solids produced • Contaminant losses during operation <Silt curtains limit impact of resuspended sediment, minimal impact on released contaminants <Efforts to reduce contaminant losses at point of dredging tend to slow operations and increase volumes of water produced <Losses to air, water from holding cell (confined disposal facility) Dredging - A Double-Edged Sword:  Dredging - A Double-Edged Sword Example of Exposure of Buried Contaminants PBulk of mass initially buried PDredging removes upper layers and significant contaminant mass <Sediment removed to layer 3 <Total removal 75% of contaminant PResult - Exposure doubled! <Concentration in surficial sediments BPre-dredging (layer 1) , C=10 BPost-dredging (layer 3), C=20 PCommon observation <historical contamination depositional environment <sufficient overbite impossible/undesirable Navigational Dredging:  Navigational Dredging Non-dredging options essentially unavailable Operational changes to allow non-removal options shouldn=t be be overlooked Because of lack of viable options, non-removal often default Forced to consider upland treatment or containment Return to subaqueous environment remains an option Level -bottom capping Return of contaminated dredged material to subaqueous environment Capping with clean sediment Confined aquatic disposal Preparation of subaqueous pit Return of contaminated dredged material to subaqueous pit Capping with clean sediment When are Natural Processes Important?:  When are Natural Processes Important? When natural recovery is the preferred option When removal approaches leave a residual When secondary areas of contamination are not actively remediated When upland treatment and disposal options leave a residual Conclusion Natural Recovery is a component of ALL sediment remediation options Pathways of Water-Column Exposure via Natural Processes:  Pathways of Water-Column Exposure via Natural Processes • Direct exposure due to resuspension of bottom sediment <Riverine systems and shallow water environments subject to storms <Water column tends to equilibrate with resuspended sediment <At sufficiently high sediment loads, water column approaches equilibration with bed sediment levels <Analogous to exposure during dredging events • Indirect exposure by contaminants moving into food chain <Contact of benthic organisms to contaminated sediment followed by predation by higher animals <Benthic organisms tend to equilibrate with the bed sediment <Basis for sediment quality criteria • Direct exposure due to contaminant release from stable sediments <Variety of natural processes result in contaminant migration to overlying water <Degree of equilibration of overlying water dependent upon rate of these processes • Natural recovery & in-situ remediation requires assessment / intervention to control these natural pathways Slide24:  Contaminant Processes at the Sediment-Water Interface Important Natural Processes :  Important Natural Processes • Diffusion <Ubiquitous but generally slow for sediment-associated contaminants • Advection <Defined by local groundwater gradients <In permeable beds also influenced by local pressure variations due to flow over uneven sediment bed <Also slowed by sorption to sediment • Sediment resuspension and deposition <Resuspension and scouring potentially dominate mechanism of movement of sediment-associated contaminants <Deposition enhances containment and natural recovery of surficial sediments • Bioturbation <Significant sediment reworking due to presence of benthic organisms <Tends to be most significant process for sediment-associated contaminants in stable sediments Slide26:  Table C-1 Sediment Processes & their Relationship to Sediment Environments Environment Environmental Characteristics Key Fate and Transport Processes Lacustrine Low energy environment Generally depositional environment Groundwater interaction decreasing away from shore Organic matter decreasing with distance from shore Often fine-grained sediment Sediment deposition Water-side mass transfer limitations Groundwater advection in near-shore area Bioturbation (especially in near-shore area) Diffusion in quiescent settings Metal sequestration Aerobic and anaerobic biotransformation of COCs Biotransformation of organic matter (e.g., gas formation) Riverine Low to high energy environment Depositional or erosional environment Potential for significant groundwater interaction Variable sediment characteristics (fine to coarse grained) Local and generalized groundwater advection Sediment deposition and resuspension Aerobic biotransformation processes in surficial sediments (potentially anaerobic at depth) Bioturbation Estuarine Generally low energy environment Generally depositional environment Generally fine-grained sediment Bioturbation Sediment deposition Water-side mass transfer limitations Aerobic and anaerobic biotransformation of COCs Biotransformation of organic matter (e.g., gas formation) Coastal Marine Relatively high energy environment, decreasing with depth and distance from shore Often coarse sediments Bioturbation Sediment erosion and deposition Localized advection processes Characterizing Natural Processes:  Characterizing Natural Processes Measurements Physical, chemical and biological characterization of sediments Vertical profiles of contaminants or tracers - average and episodic behavior Monitoring of tracers to indicate source of suspended sediment during storm events Comparison of contaminant fluxes from sediment to flux downriver Modeling Conceptual and/or mathematical modeling of sediment/contaminant dynamics Mass flows- tool for comparative assessment of potential exposure Excellent tool for examining uncertainty or spatial or temporal variability Dynamic Sediment Environments:  Dynamic Sediment Environments • Contaminant dynamics often defined by sediment dynamics <Contaminants strongly associated with fine particulate fraction <Contaminated areas generally net depositional environment <Sediments may still be subject to episodic erosional events • Response of cohesive sediments to high flow events? • Research <HSRC/S&SW Fundamentals of adhesion of clay particles (Amirtharajah and Sturm, GIT) Response of shallow estuarine sediments to storm events (Ferrel and Adams, LSU) < Wilbert Lick, UCSB Developed experimental protocol and modeling framework currently in wide use Significant Natural Processes Influencing Contaminant Fate:  Significant Natural Processes Influencing Contaminant Fate Sediment resuspension and erosion Sediment deposition Sediment suspended load transport Sediment bed load transport Analogous to resuspension and sediment transport during dredging operations Exposure defined by equilibrium with resuspended sediment Dynamic Sediment Environment K C + 1 W C = C sw S s S w Slide30:  Sediment Movement in Dynamic Environment Stable Sediment Environments:  Stable Sediment Environments • Associated with low flow environments • Contaminant dynamics controlled by <Water side mass transfer resistances <Sorption retarded diffusion/advection in pore water <Bioturbation - normal life cycle activities of benthic organisms <Contaminant availability • Bioturbation <Dominated by deposit feeders that ingest sediment <Increases sediment cycling to the surface- surface release of contaminants <Increases porewater irrigation of sediments <Increases oxygen transport into the sediments- enhancing biodegradation <Organism uptake contributes to transmission up food chain <90+% of measurements worldwide show biologically mixed zone <15 cm Bioturbation Enhanced Flux:  Bioturbation Enhanced Flux Sediment Age days W Pyrene mg/kg Bioturbation M- T Coeff . Limnodrilus 26,700 #/cm 2 0.48 mg/cm 2 Lumbriculus 26,700 #/cm 2 1.27 mg/cm 2 Bayou Manchac 30 74±9 0.42 0.46 60 65 ±6 0.29±0.13 0.35±0.06 University Lake 30 68±3 0.41 0.39 60 59±6 0.37±0.12 0.26±0.06 Slide34:  0% 20% 40% 60% 80% 100% 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Depth (mm) Moisture Content (%) Worm Control Slide35:  0 10 20 30 40 50 60 70 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Depth (mm) Pyrene (mg/kg dry) Worm Control Slide36:  Control Cells Flux 5% Degradation 43% Remaining 52% Flux 13% Remaining 15% Degradation 72% Worm Cells Slide37:  Table C-2 Summary of Characteristic Times of Sediment Fate and Transport Processes Process Characteristic Time Relationship Typical Range of Key Parameter Values Illustrative Value of Characteristic Time 1 Diffusion D R H 4 = eff f 2 2 diff p t R f > 1,000 (Hydrophobic organics) D eff ~ 10 -6 cm 2 /s 1,280 years Advection v R H = f adv t Groundwater velocity, v , widely variable 100 years Sediment Erosion U H = ero t Bed erosion rate, U, widely variable 10 years Bioturbation D H 4 = bio 2 2 bio p t 0.3 cm 2 /yr<D bio <30 cm 2 /yr 13 years Reaction k 1 = rxn fate t Reaction rate, k rxn , widely variable 100 years * Assumes a 10 cm thick surficial layer contaminated with a hydrophobic organic with an effective retardation factor of 1,000. A groundwater velocity of 1 meter/ yr, a bed erosion rate of 1 cm/ yr, an effective bioturbation diffusion coefficient of 3 cm 2 /yr and a reaction rate of 0.01 yr -1 are assumed for purposes of illustration. Contaminant Availability:  Contaminant Availability Metals availability Some success with AVS/SEM ratio > 1 indicates several important metals fixed in sulfide form and unavailable < 1 not a clear indicator Full description requires sophisticated metal speciation dynamics Hydrophobic organic availability Significant limitations shown for PAHs in soils (e.g. Martin Alexander) Significant sequestration in sediments containing soots Biphasic desorption rates and equilibrium commonly observed Linear, reversible compartment Nonlinear, desorption resistant compartment (Langmuir in shape) Biological Availability? Accessibility - Within biologically active zone? Availability - Sequestered or available to porewater? Assimilative Capacity - Can uptake occur? Slide39:  r2 = 0.9 Summary:  Summary Selection of remedial options should be based on risk, not aribtrary and simplistic measures such as contaminant mass Exposure requires Access Availability Assimilation capacity All remedial options entail exposure and risk Exposure and risks occur on different time scales and magnitudes Detailed assessment of each option required for valid comparison All remedial options have conditions under which they are appropriate Removal of contaminated sediments from subaqueous environment potentially costly and often not the best means of reducing risk Even dredged material may be best returned to subaqueous environment and capped to isolate from environment What has research contributed?:  What has research contributed? • Improved understanding of sediment fate and transport processes <Natural recovery/attenuation processes <Recovery of residuals remaining after active remediation <Recognition of fundamental stability of many contaminated sediments • Improved understanding of contaminant loss processes during application of remedial options <In situ options such as capping <Ex situ options involving dredging, pretreatment and ultimate treatment or disposal • Development of in-situ containment and remediation options <In-situ bioremediation <In-situ capping • Limited development of technological options for ex situ treatment and disposal Contaminated Sediment Management:  Contaminated Sediment Management Still an Oxymoron? • Improved understanding of what can and cannot be done • Increased reliance on quantitative tools for assessment and evaluation • Use of these tools growing but conflicts at major sites remain

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