BASFORD GAS WORKS REMEDIATION USING SOIL WASHING TECHNOLOGY

History of Basford Gas Works 2.5 miles north-east Nottingham city centre Flood plain River Leen Operational 1854 – 1972 Valuable by-products Decommissioned – 1997 site investigations Major Contaminants Granular soil – soil washing

Objectives of Remediation Project Acceptable contamination levels Selective excavation Soil washing Minimise landfill Re-use clean soil Minimise local disruption Minimise environmental impact

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

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

Soil Washing - Applicability Originally developed to remove PAH’s and PCP Also applies to: - Fuels - Pesticides - Various industrial chemicals - Metals Removes a wide range of organic and inorganic contaminants from coarse grained soils

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

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

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

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)

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