A large illegal landfill site near Londonderry costs the Stormont department hundreds of thousands of pounds every year, BBC News NI has learned.
It is estimated that more than one million tonnes of waste were illegally dumped at the Mobuoy site before its closure in 2013.
The Northern Ireland Environment Agency (NIEA) spent £1.2 million managing the public health risk from the contaminated site between 2013 and 2018.
But officials have not yet decided the best options for making the site safe.
One MLA described the costs as “astronomical”.
The Mobouy landfill site is located next to the River Faughan which supplies a significant portion of Derry’s drinking water.
But Northern Ireland Water (NIW) and the Department of Agriculture, Environment and Rural Affairs (Daera) both told BBC News NI that no breaches in water quality have occurred since the scale came to light of illegal dumping.
Daera described the water as “safe.”
In 2018, NIEA took responsibility for managing pollution risk and developed cleanup plans.
BBC News NI can reveal that Mobouy’s site has since cost more than £3 million.
This includes:
The work undertaken by the project team includes extensive environmental monitoring of the site, maintaining site access and safety, and working with agencies on remediation options.
Daera said investigations of the site indicate that up to 1.16 million tonnes of waste could be buried there, including a mix of construction and demolition materials, metal and household waste.
There are also thousands of liters of contaminated water and problems with landfill gas at the site, according to a 2017 Daera report.
In 2020, then-environment minister Edwin Poots ruled out a public inquiry into Mobouy. He said his aim was to implement the recommendations of an independent review of the waste sector.
The Mills report, commissioned after the landfill was discovered, found it was “on a scale never before seen” in Northern Ireland.
In March 2023, a team of consultants appointed by the NIEA recommended several options for making the site safe.
These included excavating and removing some waste and biocovering large parts of the site to contain further pollution risk.
SDLP MP Mark H. Durkan, Stormont’s former environment minister, said it was unlikely a business case could be approved without a Stormont executive in place.
There has been no executive in place at Stormont since February 2022.
“When we look at all the proposals, the costs are astronomical. This is a problem that requires a cross-departmental effort to solve.
“We need full executive approval for something of this magnitude. I don’t know how far we are from having that approval required, but I also don’t know how far we are from having an executive.”
“It won’t 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 wouldn’t be surprised if 10 years from now we’re still sitting here arguing about how much waste there is and how big the risk is,” he said.
“The problem is that the longer it goes without any cleanup, the greater the risk it continues to pose.”
Daera confirmed that a business case will need to be approved by Stormont before any such work can begin.
The overall cost could run into tens of millions of pounds.
A Daera spokesperson said the work was expected to take several years to complete, adding: “The size and complexity of the Mobuoy waste site means its cleanup will not be a quick fix.”
In September 2022 two men pleaded guilty to a series of charges related to unauthorized waste disposal.