Contaminated Land 1. Full-Scale Remediation Technologies Engineering Methods Solidification and...

Contaminated Land

1. Full-Scale Remediation Technologies

• 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)

• Displacement Systems– Sheet Steel Piling– Vibrated Beam Wall

• Excavated Barriers– Secant Piling Wall – Shallow cut-off Walls or Slurry Trench Walls ( may

include membrane)• Injected Barriers

– Chemical Grouting– Jet Grouting– Auger mixing

• Others– Electro-kinetic barriers, Ground Freezing

Engineering Methods

Grouting Materials• 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 TechnologiesEx Situ

1. Cement and Pozzolanic Based Systems1b. Lime Based Systems

2. Vitrification

In Situ3. 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 & StabilisationEx Situ Technologies

1. Cement and Pozzolan- Based Systems– 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


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


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


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


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)


4. Vitrification (ISV) (currently pre-commercial)

• 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 & StabilisationExample 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

Contaminated Land 1. Full-Scale Remediation Technologies Engineering Methods Solidification and...

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