Marcellus Air Emissions: Closest to the Wells See Steep Increases

  • A Chevron rig in Lawrence County, Pa. Shale gas emissions bring new sources of pollution to rural areas. Photo: Reid R. Frazier


February 23, 2013

The state’s first-ever tally of air pollution from the fracking boom shows shale gas activity comprises a fraction of the overall pollution in the state. But the state’s new figures also show that the industry has brought pollution to areas that were largely free of it.

Over 6,400 wells have been drilled in the Marcellus shale in Pennsyvlania.

Among the largest emissions from the shale industry are Nitrogen Oxides and Volatile Organic Compounds. In the presence of sunlight, NOx and VOCs form ground-level ozone, which can exacerbate asthma and respiratory conditions. The Pittsburgh area currently exceeds federal ozone limits.

The state’s emission inventory found that shale was responsible for 8.6 percent of Nitrogen Oxides (NOx), and 13.8 percent of Volatile Organic Compounds (VOCs) from stationary sources. These don’t take into account the state’s transportation sector – cars and trucks – which are a major source of emissions.

Overall, the picture for air in the state is improving, the DEP’s numbers show. Thanks in part to stricter emissions regulations, and a conversion in electric generation from coal to natural gas, overall pollution from power plants is declining. NOx and VOCs declined nearly 20 percent each from 2008 to 2011, while Sulfur Dioxide emissions plummeted from 865,000 tons to 353,000 tons.

“The data show that emissions from drilling represent a small fraction of air pollution in the state, which has gone down considerably since shale gas development began in earnest several years ago,” DEP Secretary Mike Krancer said.

The gas industry has greatly increased the output from the Marcellus shale through hydraulic fracturing, or fracking. The technique involves injecting water, sand and chemicals into tight, gas-rich rock, to release natural gas. Natural gas is mostly methane, which is non-toxic, but it's a potent greenhouse gas.

Natural gas also contains VOCs and hazardous air pollutants, like benzene and formaldehyde, which are known carcinogens. Those gases can escape at the well or in leaky pipeline valves. But the biggest source of emissions from the industry, according to the state figures, are compressor stations. These stations clean the gas of impurities and pressurize it for transport to consumers. These stations are full of pumps, valves, flanges, and seals that can leak or periodically vent VOCs into the atmosphere. And combustion that takes place at compressor stations in engines contribute to Nitrogen Oxides.

“The most significant emissions and the ones that are going to be the longest-term are the ones that are going to be associated with the compressor stations,” said Aimee Curtright, a scientist at the Rand Corporation. Curtright wrote a study that found the air emissions from shale gas would cost the state between $7 and $32 million a year, mainly from increased impacts on public health. Curtright said that on balance, the shale gas emissions were manageable.

"In the grand scheme of things we're not talking about a huge additional contribution to our air pollution problems in the state."

The DEP’s data show that drilling has brought large emissions to rural counties that previously had very little. Bradford County, for instance, had emissions of 261 tons of NOx in 2010, according to DEP's air emissions inventory for that year. But in 2011, emissions of NOx from the shale gas industry climbed to 2,621 tons.

Joe Osborne, of the Group Against Smog and Pollution, says that for people close to the wells, the largest concern is not so much ozone precursors, but hazardous air pollutants.

“These are pollutants that are often carcinogenic or neurotoxic, cause reproductive problems, things like benzene or hexane or toluene. If you’re living very near a source these pollutants can potentially be present in concentrations that can cause a health effect just based on ambient air exposure.”

In Washington County, for instance, shale gas drilling released three tons of benzene in 2011, according to the DEP inventory. According to the state’s own data from 2010, there were only .3 tons of benzene released in the county the year before.

The DEP conducted an ambient air study in Washington County in 2010, and found the levels of air pollution to be under levels "that would likely trigger air-related health issues." It is also conducting a year-long ambient air quality study in Washington County. That study is expected to wrap up this year.