Soil washing, a method of cleaning contaminated land, is still relatively rare in the UK. Now two jobs are happening at once. Christina Taylor finds out why.
Last summer the cost of dumping hazardous waste quadrupled following introductions of the second round of the European Union's Landfill Directive. The legislation slashed the number of landfill sites licensed to take hazardous waste from 240 to 12. Wales, southern and south-east England were left without a single such site.
New waste acceptance criteria (WAC) introduced last month now oblige waste producers to pre-treat hazardous waste before it can be landfilled, and require waste to be strictly classified, tightening the screws still further.
The shift has skewed the waste management market heavily in favour of remediation and firms offering specialist on site treatments are gearing up for a boom. Soil washing jobs have been few and far between since the first was carried out in 1998, but now contractor Land & Water is cleaning heavy metals excavated from a disused shipyard at Brightlingsea, Essex, while Morrison is tackling coal tars on a former gasworks at High Wycombe, Buckinghamshire.
"We're seeing a lot of eagerness from clients - developers and the like - to spend more time and money to minimise hazardous waste production and looking at options on treatment of contaminated waste insitu," notes Arup senior environmental consultant, Chris Barrett.
The growing market is driving down costs. "Soil washing is now viable for 3,000-4,000 tonnes of material, as opposed to 20,000 tonnes before the Landfill Directive came in," confirms director of specialist remediation firm DEC, Guy Pompfrey. "The whole of the soil treatment industry is growing." His firm has ordered a new soil washing plant in response to rising demand.
Land & Water Remediation contracts manager Bill Gush estimates that, on his firm's Brightlingsea job, soil washing is working out up to 75% cheaper - £20-£25/t - than dig and dump.
This is notwithstanding complicated plant licensing systems and hurdles thrown up by environmental regulators: Contractors wishing to use soil treatments on site have to apply for a separate license for each process they are using, and these licenses have to be re-granted for each project.
Meanwhile, "under present waste management regulations certain soils are defined as hazardous waste. Even if these soils are remediated you are not often allowed to put them back into the ground, even if the soil around it is dirtier," fumes remediation consultant Mike Summersgill. "We've got a ludicrous situation."
The problem stems from the classification of waste as all material that is excavated for remediation. Even when contaminants have been removed, the soil is still legally waste. This means either that it must be removed to a landfill, or that the development site must gain an Environment Agency exemption - a process snarled in bureaucratic red tape. Both the High Wycombe and Brightlingsea projects have negotiated the Agency's complicated application procedure.
But there is good news. From October, the Agency's complex and cumbersome mobile plant licensing system will be simplified. Contractors will in future have to apply for just one license per piece of plant, which will be valid for multiple projects.
CASE STUDY: Brightlingsea, Essex
With a target of 100% reuse of contaminated materials, contractor Land & Water has set the bar high for its remediation of material excavated at a disused shipyard at Brightlingsea, Essex. Developer Hampstead Homes is to build new apartments, a carpark and a marina around the existing docks.
The £25m scheme involves excavating 20,000m³ of material, 12,000m³ of which is contaminated with lead, zinc, copper and fuel. Soil washing is being used so the ground can be reused on site for the creation of inter-tidal marshes to replace those lost to sea level rise and changing land uses. Much of the material will be placed below the high water mark, requiring it to be squeaky clean.
The end product of soil washing is a "cake" of concentrated contaminants mixed with a small quantity of uncleanable material. Cement is mixed with the cake to form solid blocks from which the nasties cannot escape. These are being used for landscaping above the high tidemark.
The Environment Agency has insisted that quality assurance analysis is carried out for every 500m³ of material reused, says Land & Water director James Maclean. "It's been quite onerous," he admits, "but we have effectively provided complete traceability of all the materials throughout the process." |
