By Clare Davidson
Business reporter, BBC News, Neath Valley, Wales
The project is tipped to use 242,000 tonnes of steel
Black and yellow pipes, large enough to sit in, snake their way over the brow of a hill, before winding far into the distance.
The scale of the project is striking, with its swathe of cleared land and mounds of earth.
Running from Milford Haven to near Swansea, the first section in what is expected to become the UK's largest gas pipeline is nearing completion.
Most people do not think too much about where the gas they use to heat their houses and boil their eggs comes from.
This massive engineering project in Wales should give them pause for thought.
If the National Grid - which operates the UK's energy infrastructure - gets the go-ahead for the second phase of the project, then this same pipeline, destined ultimately for England, will cut through the Brecon Beacons National Park.
A designated area of Outstanding Natural Beauty, the park has made it clear it is opposed to the idea and says that according to European Union rules a more thorough survey of the environmental impact is needed.
"We are fearful a good job will not be done, because the timeframe to build the pipeline is so tight," says Paul Sinnadurai, the Park's ecologist.
One of the biggest fears for the Park is that business interests will overpower environmental concerns, especially after a period of public consultation was delayed by a month, increasing time pressures even further.
The pipeline, expected to meet around 20% of the UK's energy needs, will link LNG (liquefied natural gas) terminals in Milford Haven, West Wales, to the national network in Swansea and ultimately Gloucester.
The whole project is forecast to cost £750m ($1.4bn) and National Grid is contractually obliged to start delivering gas in October 2007. It aims to start building the second section - 115 miles long - in early 2007.
If it fails to meet the timetable, it could incur up to £36m in fines by September 2008, imposed by energy regulator Ofgem. The penalty would start at £2m for the first month and increase incrementally.
In addition, National Grid would have to compensate the energy firms - Exxon, Qatar Petroleum, BP and Petronas - for their inability to import LNG.
The National Grid said it is working hard to balance the UK's energy needs with environmental concerns and points out that the pipeline will run underground so it will not be visible.
It also said that its construction methods take great environmental care, adding that each layer of soil removed is labelled and set aside so that it can be put back in its original order.
National Grid highlights its systematic methodology
Next to the pipeline trench, neat piles of clearly labelled earth are visible.
"After we tell you all the environment issues you'd be amazed we can build a pipeline," said National Grid project engineer Nigel Bevan said.
The Park's ecologist are still not convinced and argue that the Brecon Beacons fragile upland habitats could take much longer to recover from the pipeline construction than other regions.
They also argue that the Park has unique geological characteristics, with special UNESCO status.
Neil Crumpton of Friends of the Earth Wales, said that even though the Department of Trade and Industry still has to approve the second section of pipeline construction, it seems to be a fait accompli.
Despite the environmental worries, the gas pipeline could provide a welcome boost to the region's economy, according to Minister for Economic Development and Transport for Wales Andrew Davies.
Firms that in the past have been deterred from setting up in West Wales by the huge costs of transporting energy will now have it on their doorstep, he
The Brecon Beacons National Park questions the long term benefits
National Grid also emphasised the economic benefits of such an undertaking, saying that more than 1,000 people will work on the project.
While the Park does not object to the first section of pipeline, it questions how vital it will be to Wales's national interests and points out that many of the new jobs will be temporary with as many as 40% filled by outsiders.
Critics also argue that pipeline projects like the one in Wales fail to address longer term issues such as diminishing energy supplies and global warming.
For example, the pipeline's current LNG supplies, from nations including Qatar and Malaysia, are forecast to end in 25 years and there are no guarantees as to where the replacement gas will come from.
Matter of principle
Regardless of the arguments, the final say on where the pipeline can be routed, rests in Westminster, with the DTI.
With security of supply an increasing concern, the UK government has every incentive to get the pipeline finished soon and the Park fears that if it gives the second-half of the project the green light, this could set a dangerous precedent.
Once the DTI gives consent to build, landowners will be compensated for any loss of income during the period of construction and any party that opposes the plan faces compulsory purchase by National Grid.
For Mr Wade of the Environment Agency Wales, the question is a simple one.
"In the final issue, this is a matter of principle and policy," he said. "Should such developments be allowed within national parks?"