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Methane threat to drinking water

May 9, 2011 By Sid Perkins This article courtesy of Nature News.

Fracturing rock to extract natural gas boosts methane in nearby water wells.

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A controversial method of extracting natural gas from shale rock formations significantly increases methane concentrations in drinking water taken from wells nearby, suggests the latest study by US environmental scientists. The findings come just as a moratorium on the practice in one US state is due to expire, and are likely to stoke the public debate.

Injecting large quantities of water and other fluids to fracture deep rock formations to liberate the methane within — a practice called hydraulic fracturing, or fracking — has become economically viable only in the past decade or so. In that short time, it has gained popularity with natural-gas producers: in one county in Pennsylvania alone, approvals for fracking permits increased 27-fold between 2007 and 2009.

According to the US Energy Information Administration, in 2009, 63 billion cubic metres of gas were produced from deep shale formations. That had doubled by 2010, and by 2035 fracking is projected to account for some 47% of US gas production.

Contamination concern

However, many homeowners in areas where fracking is common say the practice has tainted their drinking water, either with methane or with the waste water that is produced by the process. Research published in the Proceedings of the National Academy of Sciences1 today will give them further ammunition.

Robert Jackson, a biogeochemist at Duke University in Durham, North Carolina, and his colleagues measured the methane concentrations in 60 drinking-water wells in northeastern Pennsylvania and nearby areas of New York state. Dissolved methane concentrations in water from the 34 wells located more than 1 kilometre from fracking operations averaged about 1.1 milligrams of dissolved methane per litre. But in water taken from 26 wells within 1 km of one or more fracking operations, methane concentrations averaged 19.2 mg l–1. Isotopic analyses of the carbon in that methane shows that the gas has the same signature as that being recovered from deep underground by fracking operations.

Although methane concentrations in drinking water aren't regulated, says Jackson, the gas readily comes out of solution and is an asphyxiation and explosion hazard. The US Department of the Interior recommends mitigating methane levels in water if concentrations reach 10–28 mg l–1.

"We don't know the precise mechanism of how the gas is getting into the wells," says Jackson. The team suspects that the gas is leaking from the pipes that bring methane to the surface, or is escaping the deep layers of fractured rock — either through fissures generated during the fracking process or through abandoned water or gas wells.

Fracking under scrutiny

This study is the first to look at the extent of water contamination from fracking in a comprehensive, objective way, says Robert Howarth, a biogeochemist at Cornell University in Ithaca, New York. "Data clearly show that water wells within 1 kilometre of active gas wells have a high probability of being contaminated with methane," he notes. This contamination, he contends, shows the need to reassess the use of the technology.

Late last year, David Paterson, then-governor of New York state, instituted a temporary moratorium on fracking operations that drill wells horizontally and inject more than 300,000 litres of fluid. Once the ban expires on 30 June, the state's environmental conservation department will release the results of a study on the risks of fracking to air and water quality.

With the public debate set to ramp up in New York state and elsewhere in the coming months, the report by Jackson and his team "couldn't come at a more timely moment", says William Schlesinger, a biogeochemist at the Cary Institute of Ecosystem Studies in Millbrook, New York. "It's a nice piece of work, and it's too visible to overlook."


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