A large illegal dump near Londonderry is costing a Stormont department hundreds of thousands of pounds annually, BBC News NI has learned.
It is estimated more than one million tonnes of waste was illegally dumped on the Mobuoy site before it shut in 2013.
The Northern Ireland Environment Agency (NIEA) spent £1.2m managing the risk to public health from the contaminated site between 2013 and 2018.
But officials have still not decided the best options to make the site safe.
An MLA has described the costs as “astronomical”.
The Mobouy dump is beside the River Faughan which supplies a significant proportion of Derry’s drinking water.
But Northern Ireland Water (NIW) and the Department of Agriculture, Environment and Rural Affairs (Daera) have both told BBC News NI there have been no breaches in water quality since the scale of the illegal dumping came to light.
Daera described the water as “safe”.
In 2018, NIEA took over responsibility for managing the pollution risk and came up with plans for remediation.
BBC News NI can reveal that since then, the Mobouy site has cost more than £3m.
Work undertaken by the project team includes extensive environmental monitoring of the site, maintaining site access and security, and working with agencies on remediation options.
Daera said surveys of the site indicated that up to 1.16m tonnes of waste could be buried there – including a mixture of construction and demolition material, metallic and domestic waste.
There are also thousands of gallons of contaminated water on the site and issues with landfill gas, according a Daera report in 2017.
In 2020, the then-environment minister Edwin Poots ruled out a public inquiry into Mobouy. He said his focus was on implementing the recommendations of an independent review of the waste sector.
The Mills Report, commissioned after the dump was discovered, found it was “on a scale not previously encountered” in Northern Ireland.
In March 2023, a team of consultants appointed by the NIEA recommended several options to make the site safe.
These included digging up and removing some of the waste and biologically capping large parts of the site to contain a further risk of pollution.
SDLP MLA Mark H Durkan – a former Stormont environment minister – said it was unlikely a business case could be signed off without a Stormont Executive in place.
There has been no functioning executive at Stormont since February 2022.
“When we look at all the proposals, the costs are astronomical. This is something that needs a cross-departmental commitment to resolving it.
“We need full executive approval for something of this scale. I don’t know how far we are from approval from being required, but nor do I know how far we are away from having an executive.”
‘It will not be a quick fix’
Dean Blackwood, director of the River Faughan Anglers and co-founder of the campaign group Environmental Gathering, said the group first raised environmental concerns about Mobouy in 2008.
“We would not be surprised if we are still sitting here in 10 years’ time arguing about how much waste is in there and how big of a risk it is,” he said.
“The problem is that the longer it sits there without remediation the bigger the risk it continues to pose.”
Daera has confirmed that a business case will have to be approved by Stormont before any such work can begin.
The overall cost is likely to run into tens of millions of pounds.
A Daera spokesperson said the work is expected to take a number of years to complete, adding: “The size and complexity of the Mobuoy waste site means that its remediation will not be a quick fix.”
In September 2022, two men pleaded guilty to a string of charges linked to the unauthorised disposal of waste.