THE PROPOSED subsea tunnel for one of the last sections of the Corrib gas high-pressure pipeline would be the longest of its kind in western Europe, Shell consultants have confirmed.
The company has also told An Bord Pleanála that there was “no guarantee” that the route structure under the Sruwaddacon estuary would be used to carry pipelines from other offshore energy finds, or that the life of the Ballinaboy terminal would be extended.
A Shell consultancy team was responding to questions on design, stability and safety issues posed by An Bord Pleanála consultant and former British Gas engineer Nigel Wright at yesterday’s oral hearing in Belmullet, Co Mayo.
The 4.9km tunnel proposed for Sruwaddacon estuary, a special area of conservation, is almost a kilometre longer than the longest western European gas pipeline tunnel in the Netherlands, Mr Wright was told.
When asked what “problems” might have been experienced in constructing the Dutch tunnel, the Shell team told An Bord Pleanála’s consultant that it had been a “very smooth process” and it was “absolutely feasible” to bore such a structure. Mr Wright queried why there was so little information in the developers’ environmental impact statement (EIS) on the route and on stress analysis. Shell’s team replied that stress analysis was an “ongoing process”.
“Here we have the longest [gas pipeline] tunnel in Europe” and it was still in the “design process”, Mr Wright observed. Shell is undertaking borehole drilling in the estuary under licence from the Minister for the Environment.
Shell’s senior counsel Esmonde Keane said that the developers had no difficulty in providing information on initial stress tests, and explained that the assessment was protracted as a “very high standard” was being applied.
Mr Wright also asked the developers how they now proposed to reduce pressure of raw gas in the pipeline when they had stated at last year’s initial oral hearing that this was not possible.
Shell Corrib gas project deputy director Gerry Costello said studies had been carried out in response to the board’s concerns about hazard distance from housing.
Results showed that maximum allowable operating pressures could be set at 150 barg and 100 barg respectively for the offshore and onshore sections – “significantly less than the maximum pressure of 144 barg recommended by [Government consultants] Advantica in 2006”, Mr Costello said.
During the 2009 hearing, Shell consultants had acknowledged that residents would have just 30 seconds to escape from thermal radiation caused by a rupture in the pipeline if gas was at full pressure, and houses within 230m could “burn spontaneously”.
The new proposed route is 4m outside this zone, being at least 234m from existing dwellings according to the company.
Mr Wright referred to technical issues he had raised last year which, he said, had been “dismissed” by the developers in their new EIS.
Correcting Mr Wright on one point, Shell corrosion specialist Dr Steve Paterson said he had not “dismissed anything” but had included it in the appendix.
“Perhaps ‘dismissed’ is a shortened version for not including it in the quantified risk assessment,” Mr Wright responded. Mr Wright also queried plans to deal with possible build-up of natural gas hydrates, which can plug or block a pipeline. Dr Paterson said that one was “more likely to be hit by a meteorite” than to have this occur.
“I think I read this morning that a meteorite fell in Tipperary,” Mr Wright responded.