British Coal subsidiary CPL closed its Avenue coking works near Chesterfield in 1992. It was already clear that the giant effluent lagoons were causing contamination of underground mine workings and that the site was also the source of tar residues in the nearby river Rother (ENDS Report 209, pp 7-8 ).
The works, which opened in 1956, processed some 500,000 tonnes of coal per year to make smokeless fuel, benzole, tar and sulphuric acid.
In 1999 - the year the EU landfill Directive was adopted - East Midlands Development Agency began drawing up a long-term strategy to redevelop the site for uses including recreation, light industry and housing. Initially, it feared that as much as 2.7 million cubic metres of contaminated material would require treatment or off-site disposal - but after site investigation and risk assessment the volume was whittled down to 650,000m3.
To minimise off-site disposal, EMDA has supported technology demonstrations involving soil washing, bioremediation and stabilisation, and has now identified treatment solutions for almost two-thirds of the soil.
The rest of the material - slurry from the effluent lagoons - is more problematic. Containing some 18% total organic carbon, the slurry is in clear breach of the EU waste acceptance criteria (WAC) for landfill sites.
EMDA's preferred solution is to find a treatment option which avoids the need for off-site disposal. However, with the landfill Directive clock ticking, it submitted a planning application in March for works involving off-site disposal.
EMDA has also put out a tender for landfill contracts but has so far found it difficult to get a clear response from waste management companies. Most landfill sites will have to stop taking hazardous waste from July 2004, and in the face of regulatory uncertainty the industry has been slow to work up strategies for investment in new capacity for hazardous waste treatment and landfill (see pp 30-33 ).
"Nobody can give us a reliable price," says Phil Reeve, EMDA engineering manager.
If it went ahead, the campaign to remove the 230,000m3 of slurry would span nine months - rushed through ahead of EMDA's preferred schedule in order to meet the July 2005 deadline. The material would be blended with cement to improve handling and transported in 180 lorry loads per day - causing difficulties with the local community - unless a landfill with railhead facilities can be identified.
However, EMDA is simultaneously working up an option for on-site treatment by low temperature thermal desorption - a technology rarely used in the UK but which is well established in the US and northern Europe.
At one point EMDA was close to abandoning efforts to test the technology. The Environment Agency initially refused authorisation for a 300-tonne batch to be shipped to a plant operated by SITA and the dredging firm DANI in Rotterdam. Its grounds were that the UK has a general prohibition on exports of waste for disposal.
EMDA even offered to repatriate the consignment following treatment, but the Agency still would not give the go-ahead. The eventual solution, following 18 months of negotiation, was to reuse the treated material in the Netherlands, thereby getting round the ban on exports for "disposal". Even this option was viewed sceptically by the Agency to begin with - on the grounds that the exercise could not be justified economically and therefore amounted to "sham disposal".
Mr Reeve says that the Rotterdam trial appears to have been successful, creating a material that would be fit for reuse on site. A full report on the trial is awaited, after which a second 500 tonne batch will be dispatched to another plant in Ghent, Belgium, operated by Jan De Nul, another dredging business.
Mr Reeve puts the likely costs of thermal desorption in excess of £20 million - close to the likely costs of off-site disposal. However, it remains early days as it will be necessary to find a contractor to build a treatment plant at the Avenue site. It could well take three years to treat all the slurry, after which the plant would have to be dismantled.
The timing leaves EMDA with a nail-biting dilemma. The landfill Directive deadline means that, if EMDA opts for thermal desorption, there will be no possibility of falling back on landfill disposal should any problems emerge as the work proceeds.
Addressing a seminar in Birmingham organised by the Environmental Industries Commission in April, Mr Reeve was highly critical of the landfill Directive implementation strategy. "A huge stone is being thrown into the pond but nobody knows the extent of the ripples," he said.
"We are having huge problems in delivering this project because of the landfill Directive. There's every prospect of us declaring we cannot remediate this site." Mr Reeve also had harsh words for the Environment Agency, which he said should adopt a more enabling approach, including help with filling the technology gap that land remediation businesses are facing.
Illustrating how little the remediation sector had until recently been engaged with debate on the landfill Directive, Mr Reeve explained that the Directive's impact on the Avenue project only came to light in the past year.
Among the challenges facing EMDA is that it must make a convincing case to funding bodies. It hopes to put forward a remediation strategy by the end of May - but there are significant uncertainties over the costs of both landfill and thermal desorption.
Mr Reeve said that EMDA might end up with no alternative but to scale down its ambitions for the site - and invite the local authority to make a determination under the contaminated land regime.
If all goes to plan, however, the full project will involve excavation of a large section of the river valley followed by back filling with clean material. A plume of dense non-aqueous phase liquids identified at up to 80 metres depth and some 500 metres from the site will remain in the minor aquifer. But the re-engineering will at least remove the sources nearer to ground level which are responsible for the river pollution.
The final bill is expected to exceed £100 million, of which £23 million has already been spent on site investigation, plant dismantling and technology demonstrations. The work is being funded jointly by the Government's regeneration agency, English Partnerships, and the Department of Trade and Industry in its role as successor to the nationalised British Coal.