Water is leaking into Dublin Port Tunnel at the rate of half a litre a second - but there is no cause for alarm, Dublin City Council has insisted.
The leak, the third identified in 18 months, is located on a crossover point between the twin tunnels at an area below Marino Park in north Dublin.
The volume of water approximates to an average household tap being left on full. It was discovered during an inspection two weeks ago.
According to Dublin City Council, the section of the tunnel crossover should have had walls of pumped concrete 400mm (15.7 ins) thick. However, it appears that hollows developed in the concrete when it was being pumped, leading to a thickness of just 300mm in some parts.
Water from fissures in the rock face built up behind the wall and was identified as a problem over a four square metre section.
When the defective section of concrete was removed, the bare rock carrying water was exposed, causing increased leaking.
Dublin Port Tunnel is in parts 30m below the water table. It is constructed as a twin bore, each being 4.5km long.
While each bore is cut by a drilling machine, the crossover points are blasted through and the rock face lined.
Although the city council said the issue was routine and was detected as part of the quality control process, the senior engineer in charge of the project, Tim Brick, said he would have preferred if the contractor "had got it right initially". He said leaks were a regular feature of tunnels.
"There isn't a tunnel in the world that doesn't leak. It can be disconcerting to a layperson but it is not a show-stopper."
Mr Brick said the tunnel was "still on target" to open by next May, when it will provide an eight-minute link between the Dublin port and the M50.
Repair work will be carried out over the next two weeks by contractors working for the main contractor, the Nishimatsu Mowlem Irishenco consortium.
Mr Brick told The Irish Times yesterday that the repairs would be carried out at the contractor's expense. However this could not be confirmed by the consortium's London-based press spokesman of Mowlem, Tim Needham,
While Mr Needham confirmed that "a small leak" had been detected and would be repaired, he said the cost of the repair was "a contractual matter and we have never commented on a contractual matter".
The Nishimatsu Mowlem Irishenco consortium is in dispute with the city council over the cost of the tunnel. Currently running at about €750 million, the tunnel is already some €200 million more expensive than was originally planned.
Fine Gael's transport spokeswoman Olivia Mitchell insisted yesterday that the final cost of the tunnel would be more then €1.3 billion - a figure she said was €750 million over budget.
She said the project was "the biggest disappointment since the Titanic . . . and to add insult to injury, it has now sprung a leak", she concluded.
