BASFORD GAS WORKS REMEDIATION USING SOIL WASHING TECHNOLOGY

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BASFORD GAS WORKSREMEDIATION USINGSOIL
WASHING TECHNOLOGY
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History of Basford Gas Works

• 2.5 miles north-east Nottingham city centre
• Flood plain River Leen
• Operational 1854 1972
• Valuable by-products
• Decommissioned 1972
• 1995 1997 site investigations
• Major Contaminants
• Granular soil soil washing

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Objectives of Remediation Project

• Acceptable contamination levels
• Selective excavation
• Soil washing
• Minimise landfill
• Re-use clean soil
• Minimise local disruption
• Minimise environmental impact

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Project Processes

• Preliminary investigation
• Identify need for remediation
• Test suitability of soil washing
• Detailed site investigation
• Full scale remediation
• Performance assessment

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Soil Washing - Process

• Remove debris
• Mix with water
• Particle size separation
• - Contaminants bind to small particles
• - Small particles bind to larger particles
• - Washing processes separate small from large
• Gravity separation
• - Removes high or low specific gravity particles
  e.g. heavy metal containing compounds
• Attrition scrubbing
• - Removes surface contaminant from coarse
  particles
• Sequential washing

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Soil Washing - Applicability

• Originally developed to remove PAHs and PCP
• Also applies to - Fuels
• - Pesticides
• - Various industrial
  chemicals
• - Metals
• Removes a wide range of organic and inorganic
  contaminants from coarse grained soils

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Soil Washing as a solution at Basford Gasworks

• Efficient technique for contaminant types (mainly
  hydrocarbons) and soil
• Waste minimisation technique, reduced lorry
  movement offsite (23,000 to 8,000 movements)
• 14,500 movements saved compared to traditional
  dig and dump
• Significant recovered quantities of ash clinker
  (steel and breezeblock manufacturing) using soil
  washing

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Efficiency of Soil Washing

• 80.5 of input recovered as clean for re-use
• That unclean usually contained high coarse
  organic content within gravel fraction
• Most contaminants located in filter-cake - the
  higher the input contaminant concentration the
  more effectively it is washed
• 15,000t of excavated contaminated soil blended
  with filter-cake to stabilize it

Soil Washing Plant
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Material Processing

• 161,650 tonnes of material supplied
• Processing rate of 370t of clean output/day
• 125,761t of clean material (sand gravel
  fractions) and 32,240t of filter cake
• 76 excavation was re-used (compared to 11 for
  traditional methods)
• Site restored to original ground levels (/-
  0.3m) with the addition of 81,402t clean fill

Clean soil from Washing Plant
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Alternative Solutions

• No recommended alternatives
• Dig and dump would have been cheaper did not
  meet the requirements
• (Cost of soil washing was 21.11/t)
• Selective excavation (low cost, low technology)
  was also used in conjunction with soil washing
  (higher cost, higher technology)

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Summary

• Only solution to fulfil all objectives
• Showed that soil washing was effective on a
  variety of contaminants
• Reduced volumes transported offsite
• Minimised disruption to local community
• Significant quantities of recycled materials
• 30 less energy compared to road haulage
• 200,000t of contaminated material excavated, this
  represents a substantial saving in landfill void
  space
• Better results as voluntary project