(AP) -- Exploratory work to extract gas by hydraulic fracturing in England should be allowed to resume even though the technique has caused earth tremors, a report commissioned by the government said Tuesday.
Cuadrilla Resources is using the technique, commonly called fracking, at a prospecting site in northwestern England.
The consultants' report, which reviewed earlier reports by the company, recommends that fracking should be halted temporarily if there is a tremor greater than magnitude 0.5 on the Richter scale. Cuadrilla has said that is acceptable.
On April 1 and May 27 last year, tremors of magnitudes 2.3 and 1.5 caused alarm in northwestern England but didn't cause structural damage. Cuadrilla's work was halted after the second tremor was linked to fracking.
The government will announce its decision following a six-week consultation period.
"If shale gas is to be part of the U.K.'s energy mix we need to have a good understanding of its potential environmental impacts and what can be done to mitigate those impacts," said David MacKay, chief scientific adviser at the Department of Energy and Climate Change.
"This comprehensive independent review of Cuadrilla's evidence suggests a set of robust measures to make sure future seismic risks are minimized, not just at this location but at any other potential sites across the U.K.," MacKay said.
Hydraulic fracturing involves pumping water, sand and chemicals under pressure into wells to open cracks which release gas. Cuadrilla has reported 50 fracking-induced tremors at its drilling site, including the two that were felt by people living nearby and several 0.5 magnitude events.
Cuadrilla estimates that the Bowland Basin prospect site in Lancashire contains as much as 200 trillion cubic feet of gas. Even a fraction of that represents a significant energy resource.
"We are pleased that the experts have come to a clear conclusion that it is safe to allow us to resume hydraulic fracturing, following the procedures outlined in the review," Mark Miller, chief executive of Cuadrilla.
Andy Atkins, executive director of Friends of the Earth, said the environmental group's concerns include potential air and water pollution as well as tremors.
"There should be a full scientific assessment of all the impacts of fracking," Atkins said. "A short consultation on one of the problems is completely inadequate."
In the United states, shale gas released by fracking has risen from 8 percent of total natural gas output in 2007 to nearly 30 percent in last year, according to the Energy Information Administration. Consumers have benefited, through lower home-heating and electric bills, but fracking still faces strong opposition.
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