Hydrofracking and Drinking Water Contamination?
Crossposted with National Geographic’s Great Energy Challenge Blog.
A smoking gun in the form of methane isotopes links the two.
Shale Gas: Game Changer or Potential Problem?
The abundant, cleaner-burning fossil fuel known as shale gas has been hailed as a bridge fuel that’ll allow the transition from coal to a renewable-fueled future. Not only that, drilling for shale gas has propped up economies in some of the country’s down-and-out regions.
But its pursuit has led some to cry foul, thanks to the process by which the stuff is extracted — horizontal drilling and hydraulic fracturing (which cracks the rock through high-pressure injections of a mix of water, sand, and chemicals). Homeowners living near hydrofracturing sites have complained of contaminated drinking-water wells. The plight of these folks was dramatically captured in the Oscar-nominated documentary Gasland as flowing tap water touched by a lit cigarette lighter burst into a blue flame.
An investigative series by the New York Times examined the potential for serious pollution to streams, rivers, and lakes from the improper disposal of chemical-laden fracking fluids and the wastewater (a k a “produced water”).
But gas industry reps have largely dismissed these concerns with claims that:
- The methane in homeowners’ wells is nothing more than naturally-occurring methane that has been there for centuries and is unrelated to drilling activities; and
- The idea that fracking fluids injected at roughly 1,000-2,000 meters below the surface would migrate up into shallow groundwater aquifers makes no geologic sense.
Duke Researchers Dig Into the Issues
Into this fray stepped a team of Duke researchers led by Nicholas School postdoc Stephen Osborn. The scientists collected and analyzed water samples from 68 private groundwater wells (some near active drilling sites, some not) across five counties in northeastern Pennsylvania and New York.
The results [pdf], which the scientists have been sitting on for months awaiting publication in the Proceedings of the National Academy of Sciences, have now been made public and they’re already stirring controversy. (See examples here and here. One critique went so far as to accuse the authors of having “known anti-gas special interests.” Knowing these guys, I found that to be in the clutching-for-straws category.)
The good news? The researchers found no evidence of contamination from chemicals contained in fracking fluids and produced water.
The bad news? The “results show evidence for methane contamination of shallow drinking-water systems in at least three areas of the region and suggest important environmental risks accompanying shale-gas exploration worldwide.”
OK, so they found methane in well water, industry experts may say, but how do you know if it has anything to do with our drilling operations?
That’s a fair question, and Osborn and colleagues have two lines of evidence.
1. The spatial distribution of the contamination.
The authors found lots more methane contamination in wells near fracking sites than in wells far from the sites. They report:
“Methane concentrations were detected generally in 51 of 60 drinking-water wells (85%) across the region, regardless of gas industry operations, but concentrations were substantially higher closer to natural-gas wells. Methane concentrations were 17-times higher on average … in shallow wells from active drilling and extraction areas than in wells from nonactive areas.”
The fact that methane spikes in the vicinity of shale gas wells implies, but does not prove, that the mining activity is causing the increased methane levels.
2. The isotopes tell the story.
Remember isotopes from chemistry class? All atoms have protons and neutrons. The number of protons determines what kind of element it is. For example, any atom with six protons is carbon (C). But an element can have different numbers of neutrons and these are known as different isotopes of the same element. For example, carbon with six neutrons (called C-12) and carbon with seven neutrons (C-13) are two carbon isotopes.
The cool thing about isotopes? Their abundance in a given chemical can vary depending on how the chemical is produced. So scientists can use isotopic labels to identify the chemical’s origins.
That’s exactly what Osborn et al did to determine the source of methane in the wells. And lo and behold they found:
- that the methane composition in the most contaminated wells was consistent with thermogenic methane (methane formed at high temperatures deep underground),
- that the methane in a subset of water samples from Pennsylvania’s Susquehanna County isotopically matched methane from nearby gas wells, but
- that outside the one-kilometer zone of active drilling, the isotopic fingerprint was significantly different, representing a mixture of both shallow natural biogenic and deeper thermogenic methane.
Whence the Methane?
Without more study there’s no way to know how the methane is getting into those wells. One possibility advanced by the authors is leakage from the vertical well casings. If so, that’s pretty good news for industry. Fixing this would simply require better casing-installation techniques.
The authors acknowledge theirs is a preliminary study. One deficit is the before-drilling snapshot to go along with their after-drilling snapshot. This lack leaves some room for doubt. One could hypothesize that there’s something unique to areas with better shale-gas prospects