Fracking should take place at least 600 m down from water supplies, according to a study.
A new study revealed the process, which uses high-pressure liquid pumped deep underground to split shale rock and release gas, caused fractures running upwards and downwards through the ground of up to 588 m from their source.
The research, published in the journal Marine and Petroleum Geology stated the chance of a fracture extending more than 600 m upwards was exceptionally low, and the probability of fractures of more than 350 m was 1 per cent.
Researchers said the study showed it was “incredibly unlikely” that fracking at depths of 2 km to 3 km below the surface would lead to the contamination of shallow aquifers which lie above the gas resources.
Shale gas extraction has been controversial in the US because of claims that cancer-causing compounds used in the process have polluted water supplies, and that the flammable methane gas itself can pollute drinking water.
But Prof Richard Davies, of Durham University, said it was more likely any contamination came from drilling down through rock containing methane and where the cement or steel well casing failed, rather than the separate fracking procedure carried out kilometres down where shale gas forms.