The mining company responsible for a spate of sinkholes in Co Monaghan wants a sixfold increase in the amount of sulphate it is allowed to discharge into a local river.
Gypsum mining firm Gyproc is being prosecuted by the Environmental Protection Agency (EPA) for breaches of its sulphate discharge licence since the 2018 underground flooding incident that sparked a series of ground collapses.
But the company says it can no longer work within the constraints of that licence, and it has applied to the EPA to have the limits increased.
The request has raised concerns within the EPA and Irish Water. The local river, the Bursk, flows into the Lagan River which becomes the Glyde River which supplies drinking water to Tallanstown in neighbouring Co Louth.
Inland Fisheries Ireland has also said it is "very concerned" about the impact on fish life.
Gyproc has provided reports to show that by the time the water reaches the drinking water abstraction point, sulphate levels reduce to within current permissible levels.
It also says there is minimal effect on freshwater algae and an "absence of significant acute toxicity to freshwater fish or crustaceans".
The EPA said it was not in a position to make a decision yet. "The agency is currently awaiting additional information from the applicant in relation to this application," it said.
Gyproc's existing licence lets it discharge sulphate into the Bursk at a maximum rate of 200mg per litre. It wants to have the limit raised to 1,250mg per litre, saying the higher levels will occur only at certain times, and will not be year-round.
Sulphate occurs naturally in the ground where Gyproc mines and is discharged when the company pumps out water that accumulates in the underground chambers of its Drummond mine.
The amount of water and sulphate pumped out into the Bursk has risen sharply since the mine flooded in June 2018.
Initially, the flood water was pumped into the adjacent spent Drumgossat mine but that had to stop in September 2018 after the water undermined support pillars and parts of the mine ceiling collapsed, destroying Magheracloone GAA's playing fields and clubhouse as well as a community centre above. A series of smaller collapses has occurred in surrounding areas since.
Water with high sulphate levels has an odour, is unsuitable for livestock to drink, is damaging to freshwater plant and animal life and can cause diarrhoea in humans if it gets into drinking supplies.
Separately, it has emerged that Gyproc was reprimanded after failing to report a discharge of reddish-brown coloured water into a local stream on Christmas Day last.
EPA inspectors who visited the scene two weeks later following complaints by members of the public found a pump had tripped during heavy rain, causing an overflow of sediment-laden water from a storage lagoon.
The EPA recorded five compliance issues, including failure to notify the agency of the incident as soon as practicable; failure to produce evidence that testing of the discharged water had taken place; and failure to show evidence that daily visual inspections at discharge sites were being carried out as required.
The breaches come at a time when the company is preparing to submit a planning application for a new open-cast mine close to its existing operations.
Gyproc said in a statement that the issues over Christmas had been "resolved promptly with no impact to the area".
In relation to its discharge licence application, it said: "A review of Gyproc's industrial emissions licence relating to its mining activities is currently under way and we look forward to its conclusion."
The company added that land and road monitoring agreed after the ground collapses was continuing.
"The monitoring programme is important to ensure ongoing safety and we hope it provides reassurance to the community that our focus on the mine workings has not been diluted even during this unprecedented Covid-19 pandemic," it said.