Coal miners used to carry along a canary to warn them of methane gas in the mines. That's certainly an option for homeowners living near a gas well, but getting their water tested makes a lot more sense.
The amount of dissolved methane in the drinking water of homes located close to a shale gas well was six times higher than in homes farther away, according to a recent study in homes in Northeastern Pennsylvania near the Marcellus shale formation.
Drinking methane-containing water is not known to cause health problems, but dissolved methane will escape from the water and enter the air. If this happens in a poorly ventilated area, like a basement, the methane gas can ignite and cause an explosion.
Methane cannot be removed by common water treatment devices such as filters. Removing it usually requires aeration, mixing air into the water. This causes the methane to come out of solution and into the air, where it can be vented away.
Wells within one kilometer (5/8 of a mile) of a shale gas well contained six times more methane on average than wells further away did.
The Marcellus shale formation stretches from Ohio into several Eastern States. The Marcellus is currently the country's most productive natural gas field, with wells in Pennsylvania, Ohio and West Virginia.
To get at the gas trapped inside the rock, drillers crack it open by pumping in a high pressure mix of water, fine sand and chemicals, a process called hydraulic fracturing or fracking. Fracking is extremely controversial for several reasons, its potential for water pollution being chief among them.
The researchers looked at water from 141 drinking wells. Fully 82% had detectable levels of methane. Those within one kilometer (5/8 of a mile) of a shale gas well contained six times more methane on average than wells further away did.
While there's no federal limit for methane in water, the Department of the Interior recommends that owners of wells containing 28 milligrams per liter methane or more should take steps to remove it. The study found 12 such wells. Eleven of these were within one kilometer of an active shale gas well. The twelfth was 1.4 kilometers from an active well.
Ethane, another component of natural gas, was 23 times higher in the water of homes located less than one kilometer from a gas well.
The simplest explanations for the methane contamination are inadequate steel casing or cement seals around the gas wells. In 2011, Pennsylvania required that these be stronger than in the past, but older wells don't always meet the new standards. In 2010, the Pennsylvania Department of Environmental Protection issued 90 violations for faulty casing and cementing on 64 Marcellus shale gas wells; 119 similar violations were issued in 2011.
An article on the study appears in PNAS and is freely available.