The LCGC Blog: The Analytical Arsenal for Point Source Attribution


This blog is a collaboration between LCGC and the American Chemical Society Analytical Division Subdivision on Chromatography and Separations Chemistry.

The past year has been a remarkable ride for the oil and gas industry, and for the entire energy sector in general. Extreme volatility in commodity pricing, an oil contango, and an apparent paradigm shift away from fossil fuel-powered vehicles—thanks to Tesla—has all been “par for the course” in the past 12 months. Fortunately, the petroleum industry appears to be making significant strides to improve the environmental stewardship and operational efficiency of energy production by implementing new technologies and capitalizing on previously wasted resources like produced water and flare gas. Nonetheless, many questions still remain about the management of aging or even abandoned infrastructure because abandoned production wells provide a potential for undocumented contamination events. More specifically, how can we monitor the environmental impacts of these neglected sites, and will these impacted sites grow in magnitude over time? To answer these questions, we must first understand what is required to perform such analyses.

Having contributed to numerous high-profile litigations involving alleged oil and gas-related contamination, we never cease to be amazed at how intricate and idiosyncratic these cases can be. A thorough account of historical events and the chronology of nearby anthropogenic activities is certainly helpful, but this information does not tell us about the extent of the problem from an environmental or ecological perspective; and it generally doesn’t provide enough resolution to successful identify the point source. For this latter function, we turn to analytical chemistry to help guide us towards a successful outcome, a process known as point source attribution.

In many cases, a relatively straightforward analysis of the environment can provide sufficient insight into the extent of environmental damage from a specific source (1). In the case of alleged groundwater contamination, using ion chromatography and inductively coupled plasma–mass spectrometry (ICP-MS), we can characterize various brine elements (chloride and bromide) and pertinent metal ions species, respectively, to better under the extent of fluid migration from flowback and produced water. Concurrently, gas and liquid chromatography–mass spectrometry (GC–MS and LC–MS) can be utilized to characterize the presence of volatile and semi-volatile organic compounds, which collectively can be representative of chemical additives used in the energy production process (that is, hydraulic fracturing) and be a reflection of other natural gas constituents ( C1-C5 hydrocarbon gases) being present. In the event that natural gas is present, as may be evidenced by a strong sulfur-bearing aroma or water effervescence, the characterization of methane, ethane, and propane, and their respective carbon isotopes, can provide insight into the origin of the rogue gas and help differentiate between naturally occurring biogenic (microbial) gas and thermogenic gas that may have made its way into the water via anthropogenic activities.

This is where things get very interesting. In numerous cases, we have seen that the isotopic signature of the rogue natural gas in a water source is a match with the equivalent signature collected from a nearby production well. Case closed, right? Not exactly. In some instances, there may also be a naturally occurring source of shallow gas that is not economically viable to extract, and that has a comparable isotopic signature to the two other thermogenic gases. In situations like these, higher-resolution analytical tools are required to parse out the differences. For example, the relatively recent emergence of noble gas and noble gas isotopic analyses has allowed investigators the opportunity to better perform point source attribution, and simultaneously characterize the migration pathway from the contamination source to the contamination site (2,3). Because noble gases are chemically inert and are not subject to oxidation and microbial degradation, they are ideal tracer elements that can be used to better understand subsurface fluid and gas migration. Using the aforementioned case with three matching methane isotope signatures, the characterization of noble gas analytes allowed us to differentiate water wells that had been inadvertently drilled directly into the intermediate gas layer from those that has been impacted by the activities of a nearby production well (4).

Another tool that is adding a lot of value to environmental investigations, particularly groundwater and surface water analyses, is matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). This particular tool has made a tremendous impact in the clinical setting as a way to screen through a large library of bacterial species that can have deleterious effects to susceptible or immune-compromised patients. MALDI-TOF-MS is now making a big splash in the environmental realm with the ability to screen samples for the presence of thousands of different microbes (5). Our research across Texas using MALDI-TOF-MS has demonstrated the value of comprehensive microbial analyses as a way to characterize bacterial ecology, which can be representative of the current contamination state (6,7). And although the aforementioned noble gas analyses are arguably the most powerful weapon in the environmental arsenal, MALDI-TOF-MS microbial analysis is much more rapid (<48 h) and can detect various indicator species that can suggest the presence or absence of atypical environmental conditions. For example, the detection of extremophilic or halophilic species that are not native to typical, healthy groundwater conditions can be indicative of a much larger problem that may warrant further investigation.

Unconventional oil and gas extraction is a multi-faceted landscape. From assessment of air, soil, and water quality to oilfield wastewater treatment and re-use, there are many places where both routine and advanced chemical analysis can provide insight. Even as some favor the rapid transition to renewable energy resources, the extraction and use of fossil fuels will continue as a pertinent piece of the energy supply puzzle for the foreseeable future. We will continue to be faced with situations where environmental forensics and point source attribution are needed to understand the cause of various contamination events. Even if fossil fuel extraction declines significantly over the next 20 years, we will still be left with the need to ensure abandoned well sites are properly closed and pose no threat to the environment. We have the technology and the know-how, but of course, there are still real limits in the research that can be performed with limited to no investment in such studies from traditional funding agencies.


  1. I.C. Santos, Z.L. Hildenbrand, K.A.Schug, Anal. Chem. 91, 689–703 (2019).
  2. T.H. Darrah, A. Vengosh, R.B.Jackson, N.R. Warner, and R.J. Poreda, Proceedings of the National Academy of Sciences, 111(39), 14076–14081 (2014).
  3. C.J.Whyte, A. Vengosh, N.R. Warner, R.B. Jackson, K. Muehlenbachs, F.W. Schwartz, andT.H. Darrah, Sci. Total Environ., 780, 146555 (2021).
  4. Z.L. Hildenbrand, D.D Carlton Jr., A.P. Wicker, S. Habib, P. Stigler-Granados, K.A. Schug, Sci. Tot. Environ. 713, 136618 (2020).
  5. I.C. Santos, Z.L. Hildenbrand, K.A. Schug, Analyst, 141, 2827–2837 (2016).
  6. M.S. Martin, I.C. Santos, D.D. Carlton Jr., P. Stigler-Granados, Z.L. Hildenbrand, K.A. Schug, Sci. Tot. Environ. , 622–623, 1562–1571 (2018).
  7. I.C. Santos, M.S. Martin, M.L. Reyes, D.D. Carlton Jr., P. Stigler-Granados, M.A. Valerio, K.W. Whitworth, Z.L. Hildenbrand, K.A. Schug, Sci. Tot. Environ.618, 165–173 (2018).

Zacariah L. Hildenbrand is a partner of Medusa Analytical. He sits on the scientific advisory board of the Collaborative Laboratories for Environmental Analysis and Remediation (CLEAR), is a director of the Curtis Mathes Corporation (OTC:TLED) and is a research professor at the University of Texas at El Paso. Hildenbrand’s research has produced more than 60 peer-reviewed scientific journal articles and textbook chapters. He is regarded as an expert in point source attribution and has participated in some of the highest profile oil and gas contamination cases across the United States. Hildenbrand has also provided consultation for several private-sector clients on various water-treatment and hydrocarbon-capturing technologies.

Kevin A. Schug is a Full Professor and Shimadzu Distinguished Professor of Analytical Chemistry in the Department of Chemistry & Biochemistry at The University of Texas (UT) at Arlington. He joined the faculty at UT Arlington in 2005 after completing a Ph.D. in Chemistry at Virginia Tech under the direction of Prof. Harold M. McNair and a post-doctoral fellowship at the University of Vienna under Prof. Wolfgang Lindner. Research in the Schug group spans fundamental and applied areas of separation science and mass spectrometry. Schug was named the LCGC Emerging Leader in Chromatography in 2009 and the 2012 American Chemical Society Division of Analytical Chemistry Young Investigator in Separation Science. He is a fellow of both the U.T. Arlington and U.T. System-Wide Academies of Distinguished Teachers.

This blog is a collaboration between LCGC and the American Chemical Society Analytical Division Subdivision on Chromatography and Separations Chemistry (ACS AD SCSC). The goals of the subdivision include

  • promoting chromatography and separations chemistry
  • organizing and sponsoring symposia on topics of interest to separations chemists
  • developing activities to promote the growth of separations science
  • increasing the professional status and the contacts between separations scientists.

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