“Common Challenges Encountered On Sediment Remediation Projects
– with Lessons Learned”
“Common Challenges Encountered On Sediment Remediation Projects
– with Lessons Learned”
August 2008August 2008
George L. Hicks, V.P. Market Segment DirectorSediment Management
CH2M HILL
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Common challenges (and decisions) on sediment remediation projects - including “lessons learned”:
•Dredging and Dewatering •Subaqueous Capping•In-Situ Monitored Natural Attenuation •Making Disposal vs. Beneficial Re-Use Decisions•Balancing Remediation Costs with Risk Reduction
AGENDAAGENDA
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Start by Evaluating the Appropriate Technologies:
• Dredging• Water depths, currents & tidal fluctuations• Production Rates (Cys/hr; 24/7, etc.)• Sediment Characteristics
• Dewatering• Dredge Productivity Rates• Available Laydown Area for Dewatering Technology• Available Schedule Duration (limited dredge “windows”)
• Water Treatment• Discharge Criteria (NPDES; Pre-treatment for POTW, etc.)• Re-circulation to dredge prism area
• Transport and Disposal• Hazardous; Non-hazardous; Beneficial Reuse
Dredging and DewateringDredging and Dewatering
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Select Dredging Method for Site-Specific Conditions & Regulatory Acceptability
Reference: EPA/OSRTI Sediment Remedies: Dredging – Technical Considerations for Evaluation and Implementation - Michael R. Palermo, PhD
Dredging and DewateringDredging and Dewatering
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Select Dewatering Method Based on Site-Specific Conditions and Regulatory Conditions
• Passive dewatering– Lagoon– Confined disposal facility (includes final disposal)
• Active dewatering– Mechanical dewatering (e.g., filter and belt presses, centrifuges )– Geotextile tubes
• May need amendments to increase strength and % solids for disposal
Geotextile TubesFilter Presses
Dredging and DewateringDredging and Dewatering
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Plate & Frame Filter Press Operations: Fox River – “Phase I”
Hydraulic Auger Cutter Head Dredge 1,500 – 3,000 GPM @ 5-15% solids
20,000 Gal V-Bottom Screw Auger Tank w/Hydocyclones, Coarse & Fine Liner Motion
Shaker Screens
10 – 18,000 Gal. Agitated Mix Tanks
Filter Press Fast Feed Pumps10 - Plate & Frame Filter Presses (219 ft3 each)
Dewatered PCB Sediment & Filter Cake for Off-site Regulated Disposal
Equalization/Filtration ModuTank – 75,000 Gals. Sand Media Filters & Granular Activated Carbon Contactors
Multiplex Bag Filter Unit
Magnetic Flow Meter
Treated Water Discharge Return
to Fox River
Dredging and Dewatering; ExampleDredging and Dewatering; Example
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Dredging and Dewatering; ExampleDredging and Dewatering; Example
Ashtabula River Dredging ProjectWorld’s Largest Geotextile Dewatering Tube Pyramid
14 acres, 50’ deep containing 505,000 Cys of PCB Sediments in 457 tubes – 75’ – 90’ circumference – 100’
to 375’ long
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When Selecting Environmental Dredging and Dewatering Technologies - Evaluate Total Project Costs!
• Investigations, lab, pilot tests, and engineering studies• Administrative—cost, schedule, work plans• Mobilization and demobilization• Shore facilities—docks, roads, storage, processing• Silt containment and turbidity mitigation• Water treatment and air pollution control• Solid waste treatment and disposal• Sampling, monitoring, and regulatory compliance • Health and safety• Dredging equipment and operations
Dredging and Dewatering – Lessons LearnedDredging and Dewatering – Lessons Learned
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• Imperative that the production rates from the dredge matches thethroughput capabilities of the dewatering (and water treatment) process. Ideally both the dredging and dewatering are controlled by one contractor to eliminate the “blame game” for poor production rates.
• With hydraulic dredging a sophisticated mass flow / polymer delivery system is needed due to the variability of sediment characteristics across most sites. The optimum operating point is a constantly shifting target as the dredging operation proceeds.
• Unexpected debris can make startup and shakedown all the more difficult. On past projects, we have encountered materials that include; animal hides and carcasses, scrap metal and auto parts,heavy equipment tires, sunken timbers, and treated utility poles.
Dredging and Dewatering – Lessons LearnedDredging and Dewatering – Lessons Learned
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•Advantages-Quickly reduces exposure
-Risks during capping can be less then those during dredging
-Easier to implement than dredging
-Residual risk (after capping) can be less than after dredging alone
-Can be utilized where debris is present
-Cost Effective
•Disadvantages-Contaminants remain in the aquatic environment
-Water depth is reduced
-Potential erosion
-Long-term monitoring and maintenance is required
-Institutional controls are required
Subaqueous CappingSubaqueous Capping
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Many Issues Must Be Considered for an Effective Cap
Factors that must be evaluated during the feasibility study and design stages. Early identification of data needs is essential to cost-effective
project execution and successful remedy negotiations.
Subaqueous CappingSubaqueous Capping
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Subaqueous Capping; ExampleSubaqueous Capping; Example
Cap Material Placement at
Fox River OU1
2” Core Sample
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Subaqueous Capping – Lessons LearnedSubaqueous Capping – Lessons Learned
Requirements for Capping
•Level bottom slopes•Stable Sediment•Mild water currents•Water deep enough for cap and navigation•Not susceptible to ice scour and flooding•No obstructions or structures•Groundwater and/or NAPL discharge is low•Use restrictions can be implemented and enforced to protect cap•Suitable capping material is readily available•Sediment bearing capacity is great enough to support cap
St. Louis River Interlake Duluth Tar Site
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Permitting Requirements Can be Extensive
Subaqueous Capping – Lessons LearnedSubaqueous Capping – Lessons Learned
•Federal Regulations-Section 404 Clean Water Act (33 U.S.C. 1344)
-Section 10 of the Rivers and Harbor Act of 1899 (33 U.S.C. 403)
•State and/or Local Regulations-Inland Lakes and Streams
-Wetlands Protection
-Great Lakes Submerged Lands
-Water Resources Protection
-Floodplain Regulations/Protection
-Sand Dunes Protection and Management
-Shoreland Protection and Management
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In-Situ Monitored Natural AttenuationIn-Situ Monitored Natural Attenuation
• USEPA recognizes Monitored Natural Attenuation (MNR) as an effective and permanent remedy
• MNR should be considered initially for all sediment sites• Minimizes ecological impacts associated with remedy implementation • Cost-effectively reduces risk by incorporating natural processes into
remedy decision making • The impulse to remove contaminated sediments from the environment
does not always reflect proper environmental stewardship and risk management
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In-Situ Monitored Natural AttenuationIn-Situ Monitored Natural Attenuation
Monitored Natural Recovery (MNR) involves leaving contaminated sediment in place and allowing ongoing aquatic, sedimentary, and biological processes to reduce the bioavailability of the contaminants in order to protect receptors
NRC, 1997. Contaminated Sediments in Ports and Waterways
MNR…uses known, ongoing, naturally occurring processes to contain, destroy, or otherwise reduce the bioavailability or toxicity of contaminants in sediment.
MNR…includes…monitoring to assess whether risk is being reduced as expected.
USEPA, 2005. Contaminated Sediment Remediation Guidance for Hazardous Waste Sites
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In-Situ Monitored Natural AttenuationIn-Situ Monitored Natural Attenuation
• Biological (or chemical) oxidation/reduction• Sorption and sequestration • Geochemical precipitation (metals)
Contaminant weathering, transformation and risk attenuation
• Source control• Sediment deposition and burial • Consolidation • Benthic mixing processes
Containment and dilution through natural sedimentation
Long-term monitoring and ecological recovery
Modeling to predict long-term recovery
Sediment stability / resuspension
MNR Approach Lines of Evidence
• Demonstrate achievement of remedial objectives• Demonstrate long-term recovery processes• Demonstrate long-term ecological recovery
• Hydrodynamic models • 1-D sediment modeling • Complex chemical transport modeling
• Desorption or dissolution • Hydrodynamic studies • Sediment critical shear strength• Modeling
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Monitored Natural Recovery - Lessons LearnedMonitored Natural Recovery - Lessons Learned
Remedy Comparison• Compare MNR with capping and dredging
– What is a “reasonable time frame” for MNR? – Compare to the realistic time tables for dredging and/or capping to be
fully implemented– When are risk-levels acceptable for MNR?– Balancing costs: Is it worth accelerating MNR?
• When Should I Consider/Use MNR?– Natural processes are always ongoing– Maximize MNR to reduce negative impacts of more aggressive
remedies– Make sure remedies complement MNR processes– Integrate MNR with other remedies– Monitor to reduce uncertainty
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Sand[>.0625 mm]
Clay[<.0039 mm]
Silt[>.0039 mm][<.0625 mm]
Clean3
Contaminated2
•Manufactured Soil•Aggregate•Intermediate Landfill Cover•Ocean Disposal•Beach Nourishment1
•Habitat Restoration/Creation•Upland Fill•Highway Construction
•Manufactured Soil•Ocean Disposal•Landfill Final Cap•Landfill Liner•Upland Fill•Nearshore Fill •Brownfield Cover•Habitat Restoration/Creation•Highway Construction
•Upland Fill•Brownfield Cover•Habitat Restoration/Creation•Nearshore Fill•Manufactured Soil•Highway Construction
•Intermediate Landfill Cover•Confined Aquatic Disposal•Confined Upland Disposal•Upland Fill•Nearshore Fill (with Capping)
•Confined Aquatic Disposal•Confined Upland Disposal•Nearshore Fill (with Capping)•Landfill Cap (with Clean Cover)•Brownfield Cap (with Clean Cover)•Mine Reclamation
•Confined Aquatic Disposal•Confined Upland Disposal•Nearshore Fill (with Capping)•Landfill Intermediate Cover•Mine Reclamation•Brownfield Cap (with Clean Cover)•Decontamination and Disposal
What Happens to Our Dredged Material?
1 75% Sand; grainsize distribution must be equivalent to existing conditions2 Uses assume no decontamination3 Uses assume clean or decontaminated
Certain chemical constituents may preclude sediments from beneficial reuse applications
Making Disposal vs. Beneficial Re-Use DecisionsMaking Disposal vs. Beneficial Re-Use Decisions
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• Develop sampling and testing protocols for dredging projects and dredged material management consistent with potential upland end uses.
• Identify potential impacts to the environment and public health.
• Determine cost-benefit ratios• Regulate and manage proposed
activities to minimize adverse impacts.• Monitor and establish protocol for
potential adverse impacts.
Beneficial Reuse - Lessons Learned
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Balancing Remediation Costs with Risk ReductionBalancing Remediation Costs with Risk Reduction
BioturbationResuspension/TransportDepositionAdvectionDiffusion
Humans
Biota(e.g., invertebrates)
Historical Filling inYosemite Creek AreaHistorical Filling in
Yosemite Creek Area
Transport viaHistorical SloughTransport via
Historical Slough
GroundwaterDischarge/
Tidal Pumping
GroundwaterDischarge/
Tidal Pumping
ShorelineErosion/Runoff
ShorelineErosion/Runoff
SedimentSediment
Surface WaterSurface Water
IngestionIngestion
Upper Trophic Level Receptors(e.g., sport fish, piscivorous birds,invertebrate-eating birds, seals)
Direct ContactDirect Contact
Historical Parcel EFilling/Disposal Activities
Historical Parcel EFilling/Disposal Activities
Major pathway
Minor pathway
Active Source
IngestionIngestion
BioturbationResuspension/TransportDepositionAdvectionDiffusion
Humans
Biota(e.g., invertebrates)
Biota(e.g., invertebrates)
Historical Filling inYosemite Creek AreaHistorical Filling in
Yosemite Creek Area
Transport viaHistorical SloughTransport via
Historical Slough
GroundwaterDischarge/
Tidal Pumping
GroundwaterDischarge/
Tidal Pumping
ShorelineErosion/Runoff
ShorelineErosion/Runoff
SedimentSediment
Surface WaterSurface Water
IngestionIngestion
Upper Trophic Level Receptors(e.g., sport fish, piscivorous birds,invertebrate-eating birds, seals)
Upper Trophic Level Receptors(e.g., sport fish, piscivorous birds,invertebrate-eating birds, seals)
Direct ContactDirect Contact
Historical Parcel EFilling/Disposal Activities
Historical Parcel EFilling/Disposal Activities
Major pathway
Minor pathway
Active Source
Major pathway
Minor pathway
Active Source
IngestionIngestion
Onshore Filling/Disposal
Activities
Historical Filling in Adjacent Tributary
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Net Environmental Benefit Analysis (NEBA) for Site Remedy ConsiderationNet Environmental Benefit Analysis (NEBA) for Site Remedy Consideration
Net Environmental Benefit Analysis (NEBA) Defined: A Risk-Benefit Analysis Applied to Environmental Management Options• Analytical framework to quantify and compare the ecosystem service benefits
and/or losses associated with an environmental management option (e.g., remedial action)
• Uses formally quantified values to help identify the break-point between remedial alternatives
• Supports feasibility studies and decision-making • Demonstrate and maximize potential benefits
Origin: Oil Spill Response • Evaluation of tradeoffs associated with response actions
Prince William Sound Exxon Valdez
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When to Consider Net Environmental Benefit Analysis (NEBA) for Site Remedy Consideration When to Consider Net Environmental Benefit Analysis (NEBA) for Site Remedy Consideration
Balance of risks and benefits of remediation are ambiguous
• Site retains significant ecological value• Remediation will cause environmental damage creating NRD Liability?• Ecological risks are small, uncertain, or limited• Remediation or restoration may fail or not truly change risk scenario• Costs appear disproportionate to changes in the risk scenario
There are no unacceptable human health risks
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• QUESTIONS?
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George L. Hicks, V.P.Market Segment DirectorSediment ManagementCH2M HILL8501 W. Higgins, Suite 300Chicago, Illinois 60631-2801Mobile 812-946-1669www.ch2mhill.com
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