It is "extremely unlikely" that ground water supplies would be polluted by methane as a result of controversial "fracking" for shale gas, UK geologists said today.
And although the process, which uses high-pressure liquid pumped deep underground to fracture shale rock and release gas, caused two earthquakes in Lancashire last year, they were too small to cause damage, they said.
Campaigners have called for a moratorium on fracking in the UK in the face of the earthquakes and amid fears it could lead to pollution of drinking water by methane gas or chemicals in the liquid used in the process.
Fracking has proved controversial in the US, where shale gas is already being exploited on a large scale and where footage has been captured of people able to set fire to the water coming out of their taps as a result of gas contamination.
But Professor Mike Stephenson, of the British Geological Survey, said most geologists thought it was a "pretty safe activity" and the risks associated with it were low.
He said the distance between groundwater supplies around 40-50 metres below the surface and the deep sources of gas in the shale a mile or two underground, made it unlikely methane would leak into water as a result of fracking.
"Most geologists are pretty convinced that it is extremely unlikely contamination would occur," he said.
There was no evidence in peer-reviewed literature of pollution of water by methane as a result of fracking, he said, adding that the presence of the gas in US water supplies was likely to be natural.
But a survey was currently being conducted in the UK, to establish a baseline of any gas naturally found in groundwater before drilling took place.
"If you don't know what the baseline is, you don't know if people are running a tight ship. There's natural methane in groundwater and you have to distinguish between what's there already and what might have leaked in."
He said two cases of methane pollution of water in the US, neither of which were due to fracking for shale gas, were the result of mismanagement.
The UK has one of the strictest regulatory regimes in the world, he added.
Fracking by energy company Cuadrilla was halted in the Blackpool area last year, after two small quakes in the area which the geologists are certain were caused by fracking.
Although they were felt by around 50 people in the area, they were too small to cause any damage.
Professor Peter Styles, of Keele University, said the rock in the UK was not strong enough to transmit the energy to cause larger earthquakes from one to two miles underground, where fracking occurs.
But he said it was important to have effective seismic monitoring of sites from day one, if companies including Cuadrilla apply for licences to drill elsewhere in the UK such as Sussex.
The company had no monitoring of seismic activity in place in Lancashire when it began fracking, with the British Geological Survey picking up the first quake and putting in instruments on the site which registered the second tremor.
But it has pledged it will employ monitoring and a "traffic light" system which will halt fracking before seismic activity can build up to a similar quake in the future.
Cuadrilla has estimated the resource in the area could be as much as 200 trillion cubic feet.
The estimate by the British Geological Survey is much smaller, at just four trillion cubic feet in Lancashire, and work is currently under way to assess the extent of the shale gas resource.
However it may prove cheaper for the UK to import gas from abroad than develop shale gas domestically.
Jenny Banks, energy and climate change policy officer at environmental charity WWF-UK, said: "Although it's good news that these geologists think that the risk of water contamination from fracking is low, the very limited existing peer-reviewed evidence suggests that failure of the well casing itself, not the actual fracking, is more likely to be a cause of contamination.
"However, WWF's main concern is that shale gas adds to existing known fossil fuel reserves and so burning is another threat to the aim of keeping global climate change below 2C.
"It's not just us saying this either; the International Energy Agency warned last year that without a real push for clean energy, we'll face a 'lock-in' to high-carbon infrastructure.
"They also warned specifically that a global dash for gas to meet our energy needs resulting from shale could push global temperatures up to a potentially catastrophic 3.5C.
"Ultimately, if we're serious about tackling climate change, we need to make sure gas doesn't displace truly low-carbon forms of energy such as renewables, and start thinking about just leaving fossil fuels in the ground."
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