shale gasShould the shale gas revolution be feared or cheered?

The boom in shale gas production currently reshaping North American energy markets has a mixed environmental record. Cheap natural gas is forcing the closure of dozens of America's dirtiest coal plants and driving U.S. carbon dioxide emissions to new lows, giving some environmentalists cause for celebration. At the same time, the controversial hydraulic fracturing method used to unlock shale gas resources consumes vast amounts of water and raises new fears over the potential for water contamination.

A typical hydraulic fracturing operation involves pumping millions of gallons of water, sand, and a cocktail of proprietary chemicals – ranging from the mundane, such as salt and citric acid, to toxic and carcinogenic substances, including benzene, formaldehyde, and lead – all carried at pressures up to 15,000 pounds per square inch through a well drilled horizontally into shale rock formations as deep as 10,000 feet below the surface. The high pressures force open dozens of fissures that then become propped open by sand and other materials carried in the fracking fluid. After the fluid is pumped back to the surface, natural gas once trapped in the shale can flow freely, pumped through the fissures and back up the well by the natural pressure created by the thousands of feet of rock sitting above.

This fracking process raises a number of environmental risks. Improperly drilled wells or faulty well casings can leak fracking fluids, associated chemicals, or methane gas into nearby aquifers and water wells. To date, these kinds of failures have been relatively rare, but the Environmental Protection Agency has investigated at least two cases of probable drinking water contamination near fracked wells in Pavillion, Wyoming and Susquehanna County, Pennsylvania.

The larger environmental challenge centers on the safe disposal of the billions of gallons of used fracking fluid produced at natural gas wells annually. Of the five to ten million gallons of water used in a typical frack job, about 20 percent will flow back to the surface. This flowback water contains both the original cocktail of fracking chemicals as well as minerals, heavy metals, and radioactive radon gas dissolved from the rock formations.

Most wastewater treatment facilities are ill-equipped to handle flowback water. Instead, drillers typically hire hundreds of trucks to carry the water away to be injected into wells and stored deep underground. "There’s a lot of cost and collateral damage from that trucking process," says Warren Sumner, CEO of Omni Water Solutions, an Austin, Texas company that has developed a system to recycle flowback water. Recycling waste water may go a long way towards mollifying environmental concerns over fracking and could mean reduced costs for drilling companies and the local communities who host them. "The volume of trucking is enormous and the wear and tear on the roads is large," explains Sumner. "Everyone would like to reduce that.”

Yet while fracking raises new risks for gas field communities, cheap gas is in the process of driving Old King Coal out of electricity markets, leading to cleaner air and lower CO2 emissions. Coal-fired power generation fell by 12.5 percent in 2012, with rising output at natural gas-fired plants displacing coal megawatt-hour for megawatt-hour. Coal's share of electricity production has plummeted from 50 percent in 2008 to under 38 percent last year, helping drive down U.S. CO2 emissions to the lowest levels in 20 years.

A one-two punch of cheap gas and tightening pollution regulations is also driving the planned closure of at least 175 coal-fired generators by 2016, representing 8.5 percent of the U.S. coal fleet. One third of those plants are expected to shut down this year alone, making 2012 the biggest year for coal plant retirements in the nation’s history. Among the planned closures are some of the nation's oldest and dirtiest power plants. Their permanent retirement will mean cleaner skies and will prevent hundreds of premature deaths annually, according to research from the Clean Air Task Force.

While this reduced air pollution is an unmitigated good, the long-term climate benefits of this historic coal-to-gas shift hinge on the ability to control the amount of methane leaking from gas wells and pipelines. Burning natural gas emits about half as much carbon per kilowatt-hour as coal, but methane leakage can undermine this climate savings. Pound for pound, the climate warming impact of methane is 72 times more potent than CO2 over a 20-year time frame and more than 20 times more potent over a 100-year period.

“If methane leakage is too high, it negates all the climate benefits of shifting from coal [power plants] to gas,” explains Fred Krupp, Executive Director of the Environmental Defense Fund. EDF is now leading a national effort to assess the rate at which methane leaks from natural gas wells and pipelines and is working to identify and promulgate industry-wide best practices to stop leaks. According to Krupp, their initial research indicates that “65 percent of leaks come from just 10 percent of wells," meaning that controlling a few bad actors may be the key to realizing the full climate benefits of shale gas. In the end, "we can solve this,” concludes Krupp.