A tsunami of pollution from an alleged illegal dump could hit the river Faughan if the winter is particularly wet.
The stark warning about waste at Campsie on the outskirts of Londonderry which was uncovered as one of the biggest allegedly illegal dumps in Europe last year will have a huge detrimental impact not just on the environment but also on human health.
The head of waste management at Northern Ireland Environmental Agency, Mark Livingstone, said that despite 1.5 million litres of contaminated fluid being removed already, a wet winter could spell disaster.
A considerable clean-up of the site at a cost of £800,000 has already begun, which along with the contaminated fluid, netted 4,786 tonnes of waste and 2,458 tyres.
NIEA is currently at the site where a risk assessment project at a cost of £350,000 is under way which is looking at the long and short-term risks from the illegal waste dump. Mr Livingstone said that while there was potential for serious environmental damage, including a risk to human health, the situation was under control.
He said: "At the minute there is no real evidence that the Faughan is being polluted and we have so far been quite successful in that. But the problem is there is seepage into the ground and certain pollutants have been detected in streams nearby.
"The weather is dry now but the problem is we need to get this solved by the winter when it rains, that's when there will be further leacheat problems which will further impact on the river.
"This is putrifying waste, dead animals and old black bin waste and if this isn't cleaned up the environmental impact will be huge in terms of human health and in terms of environmental health but so far we have been keeping a lid on it and it is controlled."
Gerry Quinn, secretary of the Faughan Anglers, said the DoE must prepare for a worst case scenario. He added: "We have urged the DoE to err on the side of caution and assume the worst and get ready for it.
"We already know that there is sewage fungi evident in the preferred pathways for the leachate which is coming from a site the size of a lake.
"Along with the fears that a wet winter will see this flooding down into the Faughan there is the fear of the amount of seepage and the damage that is doing right now."
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A huge illegal waste dump was allegedly found at Campsie Sand and Gravel and City Waste sites, near the Faughan. Environment Minister Mark H Durkan has said that both City Industrial Waste Ltd and Campsie Sand and Gravel Ltd have made no effort to comply with notices issued by Environmental Crime Unit on June 5, 2013. A file has been submitted to the Public Prosecution Service.