PNAS: Fracking Contaminates Groundwater
Many people have been pushing natural gas as the fuel of the future. Less polluting than oil or coal, the only thing holding gas back has been supply, causing a scramble for new gas fields using the latest drilling techniques. The conclusion of a new study, published in the Proceedings of the National Academy of Sciences, is that drilling for natural gas in shale formations, using the process known as fracking, has seriously contaminated shallow groundwater supplies beneath Pennsylvania. Duke University scientists sampled well water across 175 kilometers of far northeast Pennsylvania centered on the town of Dimock, made famous by the film Gasland. The analysis does not indicate how pervasive such contamination might be.
Directional drilling and hydraulic-fracturing technologies are dramatically increasing natural-gas extraction. The drilling technique called fracking has been used across the wide areas of the Northeast United States, Texas, Arkansas and other states where drilling for shale gas has been booming in recent years. Along with the drilling boom has come controversies over radiation in drinking water and man-made earthquakes. But perhaps the most persistent complaints from residents near the new gas wells are claims that their groundwater supply has been contaminated by high levels of methane, in some cases to the point where tap water can be set on fire. This problem has spawned protests in many areas and led to the controversial film Gasland. Of course may in the gas industry consider Gasland anti-drilling propaganda.
A typical fracking well site.
Unfortunately, to date there has been little in the way of unbiased, scientific studies of the groundwater contamination problem. Now, a new study in PNAS says that the rumors are true, at least in areas of Pennsylvania. Environmental scientist Robert Jackson of Duke University and three colleagues sampled well water across 175 kilometers of far northeast Pennsylvania centered on the town of Dimock, location of the Gasland film. A few samples were also taken in an area 75 kilometers from Pennsylvania in adjacent New York. Geologist Stephen Osborn was lead author of the paper describing the study's results. Here is the description from the paper's abstract:
In aquifers overlying the Marcellus and Utica shale formations of northeastern Pennsylvania and upstate New York, we document systematic evidence for methane contamination of drinking water associated with shale-gas extraction. In active gas-extraction areas (one or more gas wells within 1 km), average and maximum methane concentrations in drinking-water wells increased with proximity to the nearest gas well and were 19.2 and 64 mg CH4 L-1 (n = 26), a potential explosion hazard; in contrast, dissolved methane samples in neighboring nonextraction sites (no gas wells within 1 km) within similar geologic formations and hydrogeologic regimes averaged only 1.1 mg L-1 (P < 0.05; n = 34). Average δ13C-CH4 values of dissolved methane in shallow groundwater were significantly less negative for active than for nonactive sites (-37 ± 7‰ and -54 ± 11‰, respectively; P < 0.0001). These δ13C-CH4 data, coupled with the ratios of methane-to-higher-chain hydrocarbons, and δ2H-CH4 values, are consistent with deeper thermogenic methane sources such as the Marcellus and Utica shales at the active sites and matched gas geochemistry from gas wells nearby.
The δ13C-CH4 and δ2H-CH4 values and the ratio of methane to higher-chain hydrocarbons (ethane, propane, and butane) can typically be used to tell the difference between shallower, biologically derived methane and methane from deeper gas reservoirs. For example, methane from decomposing plant matter contains higher levels of carbon 14 than methane that has been sequestered deep in the ground for long periods of time. The researchers used these isotope fingerprints to identify the source of the contamination.
Analyses of 60 wells showed methane contamination near active gas wells and the authors concluded that the methane was, indeed, coming from the deep shale formations. Most wells 1 kilometer or less from a gas well produced water with 19 to 64 parts per million methane. That’s at or above the “action level” of federal safety guidelines for methane, which are high enough to displace airborne oxygen and cause asphyxiation. In contrast, almost all water wells more than a kilometer from an active gas well had only a few parts per million methane in their water.
Map of drilling operations and well-water sampling locations
In some cases, the levels were in the flammable range. “I watched one homeowner light his water on fire,” Jackson said, in an article in ScienceNow. It was the image of a flaming faucet that captured the media's attention and led to Gasland's Academy Award nomination for best documentary. But is this an isolated case, blown out of proportion for heightened impact? Not according to the report in PNAS.
After considering several different possible sources and mechanisms for the methane, the report authors had this to say: “Overall, the combined gas and formation-water results indicate that thermogenic gas from thermally mature organic matter of Middle Devonian and older depositional ages is the most likely source of the high methane concentrations observed in the shallow water wells from active extraction sites.” In other words, the contamination is coming from deep shale gas deposits, clearly pointing the smoking gun at fracking wells in the area.
The clearest indication may be a diagram, taken from the report, which shows the correlation between distance from gas wells and the concentration of methane in the groundwater. Both active and inactive well sites are shown. Methane from sources such as the Marcellus and Utica shales was found at the active sites and matched gas geochemistry from gas wells nearby. In contrast, lower-concentration samples from shallow groundwater at nonactive sites had isotopic signatures reflecting a more biogenic or mixed biogenic/thermogenic methane source.
Methane concentrations vs distance to the nearest gas well.
There was some good news regarding possible groundwater contamination from the fracking fluids themselves. “We found no evidence for contamination of drinking-water samples with deep saline brines or fracturing fluids,” the authors state. “We conclude that greater stewardship, data, and—possibly—regulation are needed to ensure the sustainable future of shale-gas extraction and to improve public confidence in its use.”
As an outgrowth of their study, the Duke scientists have issued a white paper where they summarize the situation this way:
Natural gas has been used as a domestic and industrial fuel source for over a century. It contains more energy per pound than coal. When burned, it produces almost none of the mercury, sulfur dioxide, and particulates that burning coal produces, nor does it require destructive mountain‐top mining and other approaches inherent in coal production. As a cleaner source of energy, and as a bridge to a carbon constrained future, natural gas has many desirable qualities. Despite these benefits, more research is needed to assess the mechanisms of water contamination and possible methane losses to the atmosphere.
As usual, there are at least two sides to this story. Fracking, as natural gas-advocate T. Boone Pickens pointed out on the “Daily Show," has been going on in gas and oil fields for more than 50 years with few problems. America's Natural Gas Alliance (ANGA) Executive Vice President Tom Amontree has called the nomination of the film “Gasland” for an Oscar in the documentary category “a deeply disappointing development” given that key scenes in the film have been widely documented to be myths.
“Contrary to the film's claims, natural gas development can and does exist in harmony with our environment, and it can play a central role in improving our nation's air quality and solving our energy challenges,” Amontree said in a statement on the drilling industry site Rigzone.com.
Dr. Charles Groat, Director of the Energy and Earth Resources Graduate Program, University of Texas said, “Drilling for natural gas in itself doesn't pose a threat to air and water quality, if it's done properly. There are thick shale sequences, for example in upstate New York, that have been bubbling gas for millions of years, and it does get into water. It's there naturally. Methane moving around in the natural environment is not an unusual occurrence.” This, of course, doesn't mean that drilling into and fracturing the rock of such formations will not add to methane migration into groundwater.
Each shale formation has its own distinct geologic setting that could be crucial to the release of gas during drilling and fracking. In response to the rising furor, US Energy Secretary Steven Chu announced on 5 May the formation of a blue-ribbon panel to recommend ways to improve the safety and environmental performance of shale gas fracking. Any immediate recommendations are due in 90 days but this will undoubtedly lead to more government regulation and more drilling delays.
Natural gas, the energy source for (some of) the future.
The cold hard reality is that the US and the world need more energy. Gas is not perfect, but as a bridge to more permanent solutions it is much cleaner than the alternatives. Given the economics of the situation, more gas wells will be sunk in America and elsewhere, and the latest drilling techniques will be employed. Horizontal wells, which may extend two miles from the well pad, are estimated to be 2‐3 times more productive than conventional vertical wells, and see an even greater increase in production from hydraulic fracturing. The alternative to fracking is to drill more wells in an area, a solution that is often economically or geographically prohibitive.
No form of energy is without its price—damage the land digging it out, pollute the air burning it, dump toxic waste into rivers and streams from the leftover ash, or harming wildlife directly—there is a downside to everything. In this case, there are possible problems with moving too fast, acting in haste during the fracking process. These problems can be addressed, but in a clear headed, unemotional way. In short, it is time to act like adults with regard to energy policy. Despite sneers from greens and liberals, we have indeed entered the age of “drill, baby drill.” We just need to make sure we do so safely and responsibly.
Be safe, enjoy the interglacial and stay skeptical.