Contamination of the Don catchment came to light in 1991 after high levels of dioxins were found in cows' milk, crops and soils on farms surrounding the Coalite works. In 1996, the company was fined £150,000, with £300,000 in costs, for failing to use the "best practicable means" to abate emissions from its incinerator (ENDS Report 253, pp 48-49 ).
High dioxin levels were also found in sediments in the river Doe Lea, which received scrubber liquors from the incinerator. The National Rivers Authority (NRA) dropped plans to prosecute Coalite for polluting the river in favour of a civil claim to recover the cost of removing the contamination (ENDS Report 213, pp 5-6 ).
However, the NRA abandoned its clean-up plan in 1995 when a risk assessment concluded that most of the contamination had dispersed and that the cost of removing it would exceed the environmental benefits (ENDS Report 246, pp 11-12 ). Subsequent monitoring by the NRA and Environment Agency has found that the dioxins have spread downstream and are now found at significant levels in the rivers Rother and Don near Rotherham.
The issue has resurfaced because of complaints by barge operators of grounding in low flow conditions in the Don. British Waterways, which has a statutory duty to maintain navigation, told ENDS that it had come under "considerable pressure" to act, but faced a dilemma because of the high levels of dioxins in the sediment.
Agency samples of sediments from the Don at Rotherham found dioxin levels of 110-568ng/kg, expressed as the toxic equivalent (TEQ) of the most toxic dioxin, 2,3,7,8-TCDD. These are well below the record levels in the Doe Lea downstream of Coalite's works, but still far above typical values in urban or industrial rivers (ENDS Report 231, pp 9-10 ).
British Waterways has found dioxins at 212-987ngTEQ/kg, and estimates that some 30,000m3 of sediment containing more than 100ngTEQ/kg needs to be removed from the Don. This contamination precludes disposal of the dredgings to its own landfills because, in the absence of official guidance, it has adopted a policy of not accepting sediments with dioxin levels over 100ngTEQ/kg - the German standard for sludge disposal to agricultural land.
A report by British Waterways estimated that disposing of the dredgings to a commercial landfill would cost £1.0-4.5 million, with additional costs for transport. Other options include dumping sediments in the Humber estuary or at nearby weirs. However, the report recommended a trial of a new technique called water injection dredging (WID) which uses water jets to dislodge fine sediments and allow them to be washed downstream.
A WID trial on 2.5 kilometres of the Don at Rotherham was approved by the Agency and conducted over ten days in March. Research on the long-term impacts is continuing. The trial was timed to protect young fish which are most sensitive to high levels of suspended solids.
However, the local angling community complained that the fishery would be damaged. Richard Kirk, secretary of the Don Fisheries Consultative Association and a retired NRA officer, told ENDS: "What really concerned me is that they did it when fish are spawning...This has been done just for cheapness." He complained that the Agency should not have let the situation become so urgent that immediate flushing of the river was necessary, and that landfilling should not have been discounted on grounds of cost.
The row over dredging has again turned the spotlight on Coalite's potential liabilities. The Water Resources Act 1991 allows the Agency to remove contaminants from a watercourse and recover the costs from the polluter - but the power has never been used because of lack of funds.
An alternative was provided by the Environment Act 1995, which enables the Agency to serve a works notice on a person who "caused or knowingly permitted" contamination. These powers could be used to require Coalite to remove the sediments - but regulations to bring them into force have still not been made.
In June, Anglo United announced the sale of Coalite Chemicals and Coalite Smokeless Fuels for £24.3 million to Thomas Potts - a company unknown to several industry specialists approached by ENDS. Anglo United said later that the sale had hit an unforeseen problem. It is not clear whether potential liabilities for clean-up of the river were taken into account in the sale price.
British Waterways and the Agency accept the need to reconsider the earlier cost/benefit assessment. Mr Tate says that the Don is the "obvious place" to quantify or remove the contaminants because of its large reservoir of fine sediments. Access would be simpler than on the Doe Lea because barges could be used for transport - a factor which would significantly alter the risk assessment. The Agency hopes to submit a proposal for the reassessment when British Waterway's data collection is complete later this year.