More than 500 tonnes of hazardous waste was dumped at a quarry in north Louth following an illegal diesel washing operation, it has emerged.

The amount of toxic sludge discovered at the Cavan Hill site is more than 100 times greater than the average sized recovery of hazardous diesel residue, according to the local authority.

The residue is typically left behind by illegal diesel washing operations.

The council has advertised for contractors to clean up the dump, which includes soil treatment and remediation, indicating that some or all the toxic sludge was buried.

RTÉ News understands issues relating to the incident are currently under investigation by the Director of Public Prosecutions.

The council discovered the illegal dump two years ago in a high-profile operation.

However, details of the amount of hazardous waste on the site have only now emerged.

According to figures provided by the local authority to RTÉ News, the amount of toxic sludge dumped on the site was roughly equal to the volume of hazardous diesel waste which the local authority would typically encounter over one calendar year.

No immediate risk to public health

The director of water and environmental services at Louth County Council said that the quantity of hazardous diesel sludge was "huge."

Speaking on RTÉ’s News at One, Frank Pentony said that the cost of removing the toxic sludge from the quarry would run to several hundred thousand euro.

He said there was no immediate risk to public health. A number of nearby residential properties were upstream from the site, Mr Pentony said.

Aside from the Cavan Hill site, this year so far the council has found 400 tonnes of toxic sludge relating to washed diesel operations in 67 separate incidents.

The council discovered around 600 tonnes in 2012, a spokesman told RTÉ News.

Most toxic diesel residue is not buried and most discoveries relate to the roadside dumping of Intermediate Bulk Containers (IBCs) - each containing around 1,000 litres of toxic sludge.

Each incident of dumping varies from 1,000 litres to 40,000 litres.

The recent average dumping have been in the order of 4,000 litres per incident, the council spokesman said.

Because of its proximity to the border region, Louth County Council experiences a disproportionate problem with dumped diesel residue than other counties in the republic, according to the Environmental Protection Agency.

The EPA said it did not have specific figures on the range or size of toxic sludge finds arising from illegal diesel laundering, making it difficult to place the discovery at Cavan Hill in a broader national context.

In addition to the 500 tonnes of toxic sludge there is another 1,100 of unauthorised infill material on the site - believed to be a mixture of building material and rubbish - which the council said needs to be cleared away.

The office of the DPP declined to comment.