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Contaminated Land

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

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Contaminated Land

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  1. Contaminated Land 1. Full-Scale Remediation Technologies Engineering Methods Solidification and Stabilisation Biological Physical Chemical Thermal

  2. 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

  3. 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

  4. COVERS

  5. 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

  6. Engineering Methods Grouting Materials • PFA / Cement • Cements • Cement / Clay • Cement / Bentonite • Bentonite / Cement • Bentonite / Chemical • Silicates • Phenolic Resin • lignins • Acrylamides • Aminoplasts • Polyurethane

  7. GROUTING, BARRIERS

  8. 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)

  9. CONTAINMENT

  10. 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

  11. 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

  12. 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

  13. 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

  14. Solidification & StabilisationEx 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

  15. Solidification & StabilisationEx 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

  16. Solidification & StabilisationEx 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)

  17. Solidification & StabilisationEx 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

  18. Solidification & StabilisationIn 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

  19. Geo Con Multi-auger

  20. Solidification & StabilisationIn 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)

  21. Solidification & StabilisationIn Situ Technologies 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

  22. 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

  23. 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

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