Transcript No Slide Title

Contaminated Land
1. Full-Scale Remediation Technologies
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Engineering Methods
Solidification and Stabilisation
Biological
Physical
Chemical
Thermal
Engineering Methods
Excavation and Landfill
– Incomplete solution,
– Landfill often pollutes (gas and leachate)
– Relatively cheap, low risk
• On-site Disposal
– Landfill area created on part of the site
• Planning Consent
– Transport costs reduced
• Restructuring
– Excavation and grading of contaminated soil
– Mixing of heavily and lightly contaminated fractions
– Restructured Fill Material
– contaminant concentrations reduced below SGV
Engineering Methods
Use of Covers
• Provides containment
• improves structural and engineering properties
• sustains vegetation
• only useful above a water table
• if Contaminant migration understood
Covers Comprise
• top/sub-soil
• low water-permeability layer
• break layer
– coarse granular, low capiliarity (avoids soil suction)
• specific layers
– bio-, chemical, gas venting, drainage, filter
• Contaminated layer
COVERS
Engineering Methods
In-Ground Barriers (Vertical / Horizontal)
(grouting and membranes)
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Displacement Systems
– Sheet Steel Piling
– Vibrated Beam Wall
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Excavated Barriers
– Secant Piling Wall
– Shallow cut-off Walls or Slurry Trench Walls ( may
include membrane)
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Injected Barriers
– Chemical Grouting
– Jet Grouting
– Auger mixing
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Others
– Electro-kinetic barriers, Ground Freezing
Engineering Methods
Grouting Materials
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PFA / Cement
Cements
Cement / Clay
Cement / Bentonite
Bentonite / Cement
Bentonite / Chemical
Silicates
Phenolic Resin
lignins
Acrylamides
Aminoplasts
Polyurethane
GROUTING, BARRIERS
Engineering Methods
Hydraulic Measures
• Containment
– temporary method (rapid implementation )
• Free Product Recovery
– depression of groundwater (cone)
– induced gradient
• Reversal of Groundwater Vertical Flow
– contaminated water diverted from entering sensitive strata
• Funnel and Gate / Reactive Barriers
– (see later)
CONTAINMENT
Solidification & Stabilisation
Overview and Principles
Solidification and Stabilisation Technologies
Ex Situ
1. Cement and Pozzolanic Based Systems
1b. Lime Based Systems
2. Vitrification
In Situ
3. Cement and Pozzolanic Based Systems
4. Vitrification
Examples
Solidification & Stabilisation
Overview and Principles
Stabilisation
• Chemical fixation of soluble components
– metal sulphides and hydroxides
• Accessibility is reduced, gives reduced Toxicity
Solidification
• Formation of a monolithic mass (good mechanical strength)
• Entrapment and occlusion
• Low-permeability (non-leachable)
Vitrification
• Formation of Glass-like solids
• Metals immobilised
Solidification & Stabilisation
Overview and Principles
Long Term Stability
• breakdown due to action of:
– acids, freeze-thaw, oxidation
Physical Characteristics
• Better (reduced) Leachability and Mobility
• Volume increase
• Improved handling (vs. sludges)
• Improved mechanical properties (loads)
• Soil Structure and fertility
– severe adverse effects
Solidification & Stabilisation
Ex Situ Technologies
1. Cement and Pozzolan- Based Systems
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Mixture selection (Laboratory)
Excavation
1. Mixing in Processing Plant (cf. concrete batch plant)
2. Direct Mixing (construction equipment)
Fill with stabilised material
• significant volume increase
• Chemical Basis
– Portland Cement
• physical entrapment
• Insoluble metal hydroxides
– Pozzolans (e.g. PFA)
• Silicates and Aluminates form Ca silicate gel with CaO
• Binders
– Organophilic clay
– asphalt (bitumen) emulsions
Solidification & Stabilisation
Ex Situ Technologies
1b. Lime Based Systems
• For soils containing Pozzolan-like materials
• Based on hydration of Lime
CaO + H2O --> Ca(OH)2 + heat
• Calcium hydroxide Encapsulates Contaminant
• Subsequent Reaction with Carbon dioxide in air
– Solid carbonate coating
• Pretreatment of Hydrophobic contaminants
– stearic acid reagent
Solidification & Stabilisation
Ex Situ Technologies
Time
– Intensive (days - weeks)
Costs (Ex situ)
– S/Stabilisation
£60 per m3
Resources
– high for Plant
– high for manpower
Application Range
– Inorganics (metals, non-metals, cyanides)
– asbestos
– PCB, PAH
– Oil
Solidification & Stabilisation
Ex Situ Technologies
2. Vitrification
• Hot-Top Glass Furnace
– 1500C for 10 hours
– lime, alumina and sand additions
• Air Emission Control
– volatiles
• Soil Pretreatment
– washing to reduce treated volume
– max 10% soil organic matter
• Glass Frit
– composition 40% CaO, 27% SiO2, 14% Al2O3, 10% Waste
• Plasma-Arc Furnace
– 2-Stage
• Plasma Furnace (melt)
• Combustion Furnace ( oxidation of organics)
Solidification & Stabilisation
Ex Situ Technologies
Time
– Intensive (hours - days)
Costs (Ex situ)
– Vitrification
> £500 per tonne
Resources
– very high power consumption
– manpower - excavation, transport, process
– Plant - excavation and furnace
Application Range
• Primary
– metals
– asbestos
• Secondary
– all organic contaminants
• oxidised, pyrolysed, or treated in gas emission
Solidification & Stabilisation
In Situ Technologies
3. Cement and Pozzolan-Based Systems
Batch mixing Plant
– process additives prepared for injection
Soil Mixing Equipment
• Soilcrete jet grouting
• Auger Mixing Equipment (Secant Piling)
– Multiple Auger (15RPM)
– Enclosed Shallow Mixing Auger (dry reagents)
• Overlap of columns to cover site
Geo Con Multi-auger
Solidification & Stabilisation
In Situ Technologies
Time
– Intensive (but slow)
Costs (In situ)
– Solidification/Stabilisation £25 - 45 per m3 (surface mix)
£110 – 170 per m3 (deep auger)
Resources
– Plant - reagent mixing and auger
Application Range
– Inorganics (metals, non-metals, cyanides)
– asbestos
– PCB, PAH
– Oil (Direct Chemical Reaction (DCR) method (hydrophobic
submicron CaO particles)
Solidification & Stabilisation
In Situ Technologies
4. Vitrification (ISV)
(currently pre-commercial)
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Demonstration Process
Electrode heating 1600C - 2000C
Molten zone expands downwards
Organics oxidised
hood collects gas emissions
Long cooling periods
Soil volume reduction
Costs and availability
– Geosafe Corp
– Minimum £100K
Example Solidification & Stabilisation
• Site
– Former Scrap-yard
• Contamination
– cadmium, zinc, lead
– PCB
• Remediation Method
– Ex situ Solidification & Stabilisation
(Cement, PFA, proprietary reagent)
• Performance
– 99% reduction of leachable contaminant levels
• Time
– 28 days
• Cost
– £50 per tonne
Solidification & Stabilisation
Example Vitrification
• Site
– Naval Dockyard, Chatham
• Contamination
– Asbestos
– Lead, arsenic, mercury
• Remediation Method
– Ex situ Vitrification
(pretreatment, grading, barge shipment)
• Performance
– > 95% reduction of leachable metals
– asbestos completely immobilised
• Time
– months (240 tonnes/d)
• Cost
– estimated. > £500 per tonne