Natural gas is widely hailed as a “clean” fuel because when burned it produces much lower levels of conventional air pollutants and carbon dioxide than oil or coal. And in contrast to nuclear power plants — which generate electricity without producing any carbon dioxide or conventional air pollutants — gas-fired electric plants can be built much more quickly and at lower costs.
But natural gas is stirring controversy because of an increasingly popular method of extracting it from deep inside the earth. Called hydraulic fracturing, or “fracking,” the approach involves pumping millions of gallons of water and chemicals under high pressure into rock formations to crack them open and let gas flow upward.
Many landowners complain that fracking is polluting drinking water supplies with chemical additives and flammable methane, the main component of natural gas. Drillers add many types of chemicals to fracking water to help dissolve rock, reduce friction or for other purposes. And when fracking fluids flow to the surface, they can carry dissolved metals and salts from underground.
Fracking has been in use since 1947, but only recently have energy developers combined it with another technique — horizontal drilling — to extract vast quantities of natural gas trapped in underground shale formations. Horizontal drilling allows developers to drill thousands of feet into the earth, then turn the drill sideways to penetrate gas formations trapped tightly between rock layers.
Between 2000 and 2006, production from shale gas formations grew at an average rate of 17 percent annually. Then, as methods improved, production surged, rising at an average yearly rate of 48 percent through 2010. The natural gas industry estimates that fracking and horizontal drilling have increased available domestic supplies from about 60 years' worth to at least 100 years' supply at current levels of production.
Yet fracking has stirred alarm in localities where it is being used. Controversy has been most intense in states located over the Marcellus Shale, an immense formation of gas-rich sedimentary rock that stretches from upstate New York through parts of Pennsylvania, Ohio and West Virginia.
In Pennsylvania alone, more than 2,400 gas wells were drilled in 2006-2010 using either fracking or conventional methods. State officials welcomed the economic activity, but media investigations documented widespread problems, including spills of contaminated wastewater and pollution escaping into drinking water. The documentary film “Gasland” showed homeowners lighting their tap water on fire to demonstrate how much methane it contained.
Tap water containing methane gas is ignited in the documentary film “Gasland.” (Gaslandthemovie.com)
The natural gas industry, which issued a detailed rebuttal of charges in “Gasland,” argues that fracking takes place at levels well below the water table and does not threaten human health or the environment. “No allegations of fracking contaminating drinking water have been proven,” says Bruce Vincent, chair of the Independent Petroleum Association of America. He argues that the flammable tap water shown in “Gasland” was caused by naturally occurring methane.
“Fracking has moved into areas that aren't used to gas development, which is raising concern from local communities,” Vincent says. “Our industry needs to get out and do a better job of educating and communicating so that people understand how the process works and see the economic benefits.”
Just this month, however, four Duke University scientists published the first peer-reviewed study linking fracking to contaminated drinking water. The researchers sampled 68 wells near gas-production sites in Pennsylvania and New York and found that water from wells within one kilometer of drilling had much higher levels of dissolved methane than water from wells farther away. The methane's chemical signature was consistent with gas from nearby wells and underground shale formations. The scientists did not find evidence that fracking fluids were contaminating groundwater.
The gas industry argued that the study lacked “key data that would be needed to validate its conclusions,” but federal regulators are stepping up oversight of fracking. Currently the process is almost entirely regulated at the state level, but the Environmental Protection Agency is reviewing the drilling method's impacts on drinking water. In April Robert Perciasepe, EPA deputy administrator, accused companies that had injected fracking fluids containing diesel fuel underground without permits of violating the Safe Drinking Water Act, which limits underground injection of fluids. Fracking is exempt from federal regulation under the act except for one additive — diesel fuel, which contains several toxic compounds.
And this month Energy Secretary Steven Chu created another expert panel to review impacts from fracking and recommend ways to make the process cleaner and safer, with initial recommendations due by August.
— Jennifer Weeks