A NETWORK of gas and water mains are to be left running underneath Edinburgh's tram rails despite fears that a major leak would cause chaos.
A number of pipes are to be diverted before the tram line is built, but project chiefs have adopted a strategy - described as "high-risk" - which will see many of them left in place.
The decision has been taken despite officials being warned it could lead to major disruption to services.
The plan, which would save millions of pounds, was originally drawn up when the trams were set to run in a loop around the city centre. That meant trams could continue serving all stations in the event of a blockage on the line.
But TIE - the council-owned firm behind the plans - has decided to stick with the plan after rising costs forced it to shelve the loop in favour of a single line from Leith's Western Harbour to Edinburgh Airport. The firm said a risk assessment was being carried out into which pipes could be left in position. Officials are also using a newly developed technique for laying the tracks which would allow workmen access for emergency repairs without stopping trams running.
But a senior industry insider said TIE officials knew their strategy was "high-risk". The source said it would be impossible to continue running trams over pipes in the event of a major gas or water leak. "TIE adopted a high-risk strategy, that would leave as many utility works in situ as possible," the source said.
"With a loop, and two tracks in each direction, the network could deal with any problems.
"But the decision to have just one line from Leith to the airport will store up problems. If there's a burst pipe in Constitution Street, where there are a lot of gas mains, trams would be trapped between there and Ocean Terminal."
SNP Lothians MSP Kenny MacAskill said the concerns about potential disruption confirmed his belief the scheme was off track.
He said: "This grand plan is unravelling. It has seen public money wasted and public funds continue to be wasted. The time has come to call a halt."
The first phase of construction work, scheduled for next January, involves moving most major water mains and gas pipes from directly underneath the track. This is designed to prevent pipe problems impacting on the tram service.
It is believed large numbers of pipes are likely to be left running beneath the tram lines on Constitution Street and York Place.
A TIE spokeswoman said some pipes would be left underground and a risk assessment is being carried out to determine which need to be moved.
"The tram project is a complex scheme, and yes, issues have arisen in developing the project," the spokeswoman added. "Every large project has to overcome problems, be they technical, financial or administrative.
"We work with a large team of consultants, who assist TIE in dealing with issues, and many problems have already been resolved. It is better to address problems now, rather than years down the line."