'Unstable' water supply to 150,000 homes

MORE THAN 150,000 homes in Dublin and Wicklow could be left without guaranteed drinking water “for years” if an unstable 19th century water tunnel collapses, Dublin City Council has said.

The Vartry water tunnel, which runs through the Wicklow Mountains, “could suffer a partial or total collapse at any point in time”, the council said.

However, it said it would not be in a position to build a replacement tunnel until 2013 – if Government finances are available at that time.

The 4km tunnel was constructed in the 1860s.

It was designed to bring drinking water to Dublin through a rock-lined passage bored through the Wicklow Mountains.

Its daily flow of 80 million litres represents about 20 per cent of the total of the water supply to the greater Dublin area.

Failure of the tunnel would lead to the loss of water supply to vast areas of south Dublin–north Wicklow.

The council said much of this area cannot be serviced, even on a temporary basis, by any alternative Dublin supply source.

Investigations undertaken within the past two years by external consultants on behalf of the city council uncovered a fault line in the rock which could collapse at any time.

“The good news is that it has been there for 140 years; the bad news is that if it does collapse it would cause huge disruption and significant supply problems for an extended time,” said Tom Leahy, executive manager with the council.

Mr Leahy added that Dublin City Council wanted to build a 1 km “bypass pipe” parallel to the existing pipe.

He claimed more exploration was needed before the cost was determined, but he said it was likely to be in the region of €10 million to € 20 million.

“Unfortunately, as with any capital project, and particularly in the current difficult times, it is a question of when funding will be made available by central government,” he said. “We are hopeful, but 2013 is probably the earliest it could be done.”

The construction work could be done over an 18-month period and would cause no disruption to residents, Mr Leahy said.

“Nobody will even notice it’s there.”

The Vartry system, including the tunnel and the treatment plant, is the only source of supply to north Wicklow, as well as being the primary source of supply for a considerable portion of the administrative areas of Dún Laoghaire-Rathdown County Council and Dublin City Council.

A report contained in the council’s budget for 2011 states: “Studies have indicated that this rock-lined tunnel is not stable and could suffer a partial or total collapse at any point in time.”

It adds: “Any failure of this rock-lined tunnel would deprive over 150,000 customers of guaranteed availability of drinking water for months or years.”