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Unconventional oil and gas (UOG) extraction, which includes processes such as horizontal drilling and hydraulic fracturing, has created major positive geopolitical and economic advantages for the United States.
Unconventional oil and gas (UOG) extraction, which includes processes such as horizontal drilling and hydraulic fracturing, has created major positive geopolitical and economic advantages for the United States. It is also a process that has generated extremely polarizing views regarding its provenance for, on one hand, providing abundant (and perhaps, cleaner) sources of energy, and on the other, its potentially deleterious effects on the environment. The past year or two have seen a large increase in research activity associated with studies to better assess the latter. This is good, as it is an area of study that has been sorely lacking. In 2011, some colleagues approached me about conducting some studies to investigate the potential impact of UOG extraction on private well water quality in North Texas. Here, we sit on the Barnett Shale, the birthplace of many of the commonly used unconventional extraction techniques, and one of the major producing shale plays for natural gas in the country. With some initial literature searching, our team found that virtually no work had been performed to assess groundwater quality in proximity to natural gas extraction in the United States, much less (that is, none!) in the Barnett Shale area. With an initial report from Rob Jackson’s group out of Duke (he is now at Stanford) on water contamination by methane in the Marcellus Shale (the Pennsylvania area) (1), a newly released list of voluntarily provided hydraulic fracturing fluid ingredients published by Congress (2), and a handful of EPA methods to be used for guidance, we set out to collect samples and develop a comprehensive set of analytical techniques that could be used to measure virtually every type of chemical entity you might expect to find in groundwater if contamination in one form or another were present.
One of our initial reasons for undertaking this study in 2011, besides the general lack of scientific data to date, was the fact that the quality of private well water is not systematically monitored by the government, unless it serves a significant number of people. In North Texas, you do not have go far to find suburban and urban settings where the use of well water is the norm. We set out to collect water samples from 100 private wells. This is quite an undertaking in its own right. Not only does someone have to literally go from door to door to request access to water well sites (we also recruited participants using press releases), the water needs to be collected in different ways depending on the type of analysis desired. For example, for metals analysis, the sample should be filtered and acidified with nitric acid. For volatile and semivolatile organics, it is necessary to collect samples with minimal headspace, get them into refrigeration, and complete the analysis within two weeks of collection. For organic ions (inorganic ions can also be measured on these samples), we add a few drops of a bactericidal agent. We also refrigerate these samples and perform their analysis within two weeks. Every manner of blanks must be considered. We take multiple field blanks. These are prepared by depositing bottled water into high-purity, opaque polypropylene sample containers, and then a number of them are taken into the field. Some are simply opened and closed again, and others are left sealed. The blanks are analyzed together with the real samples. We also have such blanks in our laboratory refrigerators (and separate refrigerators dedicated solely to water samples) to evaluate any potential for contamination during storage. All of this represents an enormous amount of thought, coordination, and effort, even before we begin the instrumental analysis process.
We have constantly refined our methods and workflows. Since we began work in the area, and when we reported our initial work on the first 100 water wells in 2013 (3), we were already well on our way to collecting and analyzing what now is approximately 800 more water well samples from multiple locations in Texas. Because no standard methods (for example, from ASTM or EPA) were available for simultaneous detection of the myriad chemicals that we might like to check, we collated and integrated parts of different standard methods from various sources to ensure that we were following best practices and generating reliable data. For example, from work I have done previously consulting on analysis of data and methods associated with court cases on blood alcohol determination, we developed our analytical sequences for gas chromatography–mass spectrometry (GC–MS) and headspace GC to include a series of blanks and quality control checks to validate the results (for example, assess carry-over and the viability of calibration curves) obtained for each batch of samples analyzed.
Results from our initial study primarily centered on the detection of elevated levels of arsenic and strontium in a significant fraction (one-third) of the samples we collected. Importantly, the exceedances were found to be for wells <2 km from unconventional natural gas extraction sites. Although Texas waters naturally contain measurable levels of arsenic, historical records available to us did not show any anomalous elevations in times before significant unconventional drilling in the region. We posited a variety of possible explanations for our findings, including the possibility for indirect effects from hydraulic fracturing, such as increases in pH and seismic activity, leading to the resolubilization of scale in pipes that may have accumulated such species. We did not regard our findings to provide a conclusive link between groundwater contamination and UOG extraction, but rather used our work to suggest that more in-depth work and additional studies were needed. By this time, we were using inductively coupled plasma–mass spectrometry (ICP-MS) for metals analysis. We had further developed combined targeted and untargeted headspace GC and GC–MS to monitor volatile and semivolatile organic compounds. Although we also found significant hits for ethanol and methanol in our initial set of 100 well water samples, no correlation could be found for these values with respect to their levels and distance to the nearest gas extraction well.
To follow up on our first study, we began two additional larger-scale efforts. While I am not at liberty to discuss the results of these efforts at this time (manuscripts are in preparation and results will be made public following their peer review and acceptance for publication), these provided an opportunity for a more detailed look at the issue. Simultaneously, we continued to refine and add analytical techniques to expand the range of chemical species we could monitor. We added a broader screen of metal compounds using inductively coupled plasma–optical emission spectrophotometry (ICP-OES). We began making total carbon and nitrogen measurements in the laboratory to complement our data set of bulk water quality measurements taken in the field during sample collection (pH, salinity, dissolved oxygen, specific conductance, and so forth). We further teamed with the group of Prof. Sandy Dasgupta (his labs are just next to mine in our department at U.T. Arlington), to perform the measurement of organic and inorganic ions using ion chromatography (IC). While our current methods are validated and operational, we continue to explore additional analytical techniques, such as liquid chromatography – mass spectrometry, to investigate the presence of any unanticipated contaminants. Even while some lists of hydraulic fracturing chemicals have been disclosed, individual operator’s recipes are still proprietary, so some potential target compounds for monitoring are not known. Further complicating the myriad chemical species to monitor is that flow-back or produced water, which returns to the surface after hydraulic fracturing, contains a mixture of both fracturing chemicals and subsurface brines. Because proper disposal of this produced water is also an important component of UOG exploration, the potential for spills or improper handling of this waste could result in the introduction of contaminants into aquifers. For those interested in learning more about what might be contained in such mixtures (and the unconventional drilling process, in general), the independent web source FracFocus (www.fracfocus.org) is an excellent resource.
Overviewing our more recent investigations, in West Texas we were able to collect a set of samples from water wells in an area where no significant UOG extraction had yet occurred, but for which this activity was soon planned. Thus, when the drilling activity began, we were able to initiate a time-course study. We were able to collect matched samples sets before, during, and after UOG extraction commenced. Such a study on this scale has never been reported, and the results are expected to provide valuable new insight overall, but especially related to the potential environmental impact of UOG exploration in the Cline Shale. Further, we have completed the collection and analysis of a 550 well water sample set in and around the Barnett Shale. With our expanded repertoire of methods, we have been able to assemble an impressive database of water quality measures, and this study, also the largest ever initiated in the world on this topic, will provide a more comprehensive look on the impact in North Texas compared to our initial study.
The fact that I cannot report the results of these larger studies makes this article rather anticlimactic for you, the reader. Five years ago, I would never have guessed that such a significant portion of our research effort would be focused on environmental monitoring. Over the past several years, we have strived to maintain a purely neutral, objective, and scientific view of this effort. Importantly, we have initiated several collaborations in the past year that are focused on the development of new water and wastewater remediation strategies. From a research standpoint, these collaborations have expanded our interest into the development and evaluation of new materials for passive filtration and active degradation of undesirable chemical constituents. This work clearly brings to bear our expertise in MS to help understand the mechanisms, limits, and efficiencies of these technologies. In the end, for a group that was more focused on trace bioanalysis from biological fluids before this environmental endeavor, I have new appreciation for the complexity of natural waters as a matrix. It is my hope, and that of our team, that our efforts to objectively evaluate the potential impact of UOG processes on water quality, coupled with our desire to develop new technologies and methods that can help make the process cleaner and more efficient, will be met with a positive response. Certainly more such efforts by other groups are needed so that a more informed dialogue can ensue. Those interested in more information about our analytical work are welcome to contact me with questions. We are also awaiting the publication of a book chapter submission that discusses our analytical methods and their context in greater detail (4).
(1) S.G. Osborn, A. Vengosh, N.R. Warner, and R.B. Jackson, Proc. Natl. Acad. Sci. USA108(20), 8172–8176 (2011).
(2) US House of Representatives Committee on Energy and Commerce Chemicals used in hydraulic fracturing. United States House of Representatives Committee on Energy and Commerce, Washington DC, 2011, http://democrats.energycommerce.house.gov/sites/ default/files/documents/Hydraulic-Fracturing-Chemicals-2011-4-18. pdf.
(3) B.E. Fontenot, L.R. Hunt, Z.L. Hildenbrand, D.D. Carlton Jr., H. Oka, J.L. Walton, D. Hopkins, A. Osorio, B. Bjorndal, Q. Hu, and K.A. Schug, Environ. Sci. Technol.47, 10032–10040 (2013).
(4) D.D. Carlton Jr., Z.L. Hildenbrand, B.E. Fontenot, and K.A. Schug, “Addressing Concerns About Impacts from Unconventional Drilling Using Advanced Analytical Chemistry,” in Hydraulic Fracturing Impacts and Technologies: A Multi-Disciplinary Perspective, V. Uddameri, A. Morse, and K. Tindle, Eds. (Taylor & Francis/CRC Press., publication expected May 2015).
Previous blog entries from Kevin Schug: