When Groundwater Changes: Why Scientific Testing Must Come Before Source Attribution
When a private water well begins to smell unusual, appear discolored, bubble, or otherwise change, landowners understandably want answers—especially when oil and gas activity is occurring nearby. But determining whether groundwater has been affected, and identifying the source of any contamination, is rarely as simple as testing for one compound or measuring the distance to the nearest well pad.
A peer-reviewed study co-authored by Medusa Analytical partners Dr. Zacariah Hildenbrand and Dr. Kevin Schug examined this challenge across four major shale energy regions in the United States. Published in Science of the Total Environment, the research evaluated 36 private water wells associated with 19 anecdotal claims of groundwater contamination in the Barnett, Eagle Ford, Haynesville, and Marcellus shale regions.
The findings demonstrate why groundwater investigations require a careful, weight-of-evidence approach: only five of the 36 sampled wells showed potential evidence of contamination related to unconventional oil and gas development. At the same time, testing revealed other water-quality abnormalities that landowners did not know were present and that were likely unrelated to nearby development.
In other words, a concern may be genuine even when the suspected source is not.
What the Researchers Examined
The participating landowners reported concerns ranging from gastrointestinal discomfort and skin irritation to odors, bubbling water, and water that could allegedly be ignited. Rather than assuming that nearby unconventional development was either responsible or uninvolved, the researchers used progressively more advanced analyses based on the evidence observed at each site.
The testing included:
Basic field measurements, including pH, conductivity, total dissolved solids, salinity, dissolved oxygen, temperature, and oxidation-reduction potential;
Analysis of metals, anions, volatile organic compounds, semi-volatile organic compounds, total organic carbon, and total nitrogen;
Measurement of methane and other natural-gas constituents; and
Where warranted, isotopic and noble-gas analyses designed to help distinguish microbial gas from deeper thermogenic gas and evaluate possible migration pathways.
Importantly, the analytical laboratories involved were not given the details of the landowners’ concerns until after testing was completed. This blinded approach helped reduce the risk that expectations about a site would influence the interpretation of its results.
Detecting Methane Is Not the Same as Identifying Its Source
One of the clearest lessons from the study is that the presence of methane does not, by itself, prove that a nearby oil or gas operation caused contamination.
Methane in groundwater can be biogenic—produced by microbial activity—or thermogenic, originating from deeper geological formations. Even when thermogenic gas is detected, additional testing may be needed to determine the formation from which it came and the pathway by which it entered an aquifer.
For example, several wells in Gonzales County, Texas, contained substantial dissolved methane. One sample contained methane above the 28 milligrams-per-liter action threshold cited in the study, creating a potentially significant explosion hazard. Yet compositional and isotopic evidence indicated that the gas was likely microbial rather than the result of nearby hydrocarbon extraction.
The distinction matters. The hazard may still require immediate attention, but an effective response depends on correctly identifying both the contaminant and its origin.
Source Attribution Requires Multiple Lines of Evidence
The study’s examination of southern Parker County, Texas, illustrates the complexity of point source attribution. Groundwater in the area may interact with more than one gas-bearing formation, including the Barnett Shale and the shallower Strawn formation. Methane concentration or conventional isotope measurements alone could not definitively distinguish between those potential sources.
The researchers therefore incorporated noble-gas tracers. Because noble gases are chemically inert and respond predictably to subsurface transport processes, they can help scientists evaluate where gas originated and how it migrated. The combined evidence pointed to the Strawn formation as the source of gas found in the shallow groundwater, while also suggesting that more than one migration pathway may have been involved.
This is why a simple proximity analysis—such as comparing methane levels with distance from the nearest production well—may be insufficient in a geologically complex area. Reliable attribution may require water chemistry, hydrocarbon composition, isotopic signatures, noble-gas data, well-construction information, local geology, and changes over time to be considered together.
Abnormal Water Quality Does Not Always Point to Industrial Activity
Several wells in the study contained elevated total dissolved solids, chloride, arsenic, iron, or other metals. Those findings were important, but they did not automatically establish an industrial source.
In some locations, naturally occurring geology offered a more plausible explanation. In another case, elevated metals in an older well may have reflected deteriorating or corroded plumbing. The study also found that unusual odors or visible effervescence did not necessarily correspond with volatile organic contaminants.
These examples underscore a critical principle in environmental forensics: detecting an abnormality is only the beginning of the investigation. The next questions are what caused it, when it occurred, how it traveled, and whether the available evidence can reliably connect it to a particular activity or responsible party.
Why Timing and Sampling Methods Matter
Groundwater is not static. Contaminants may dilute, oxidize, volatilize, migrate, or be degraded by microorganisms. A single sample collected long after a reported event may therefore provide an incomplete picture.
Sampling technique can also affect the result. Dissolved gas may escape almost immediately when water is collected through an open system, potentially causing methane concentrations to be underestimated. Proper well purging, stabilization of field measurements, quality-control samples, suitable containers, and closed-loop collection methods may all be necessary to produce defensible data.
Where conditions are changing or a suspected source remains active, repeated sampling over time can be far more informative than a one-time snapshot. Baseline testing conducted before nearby industrial activity begins can be especially valuable because it provides a point of comparison if water quality later changes.
Concern Is a Starting Point—not a Scientific Conclusion
The study did not attempt to calculate the overall rate of groundwater contamination in shale regions, and its authors cautioned against making broad regional conclusions from the limited, opportunistically selected sample set. Instead, the research demonstrated how reports from landowners can be evaluated through an organized scientific process.
Community observations remain essential. Residents are often the first to notice changes in taste, odor, appearance, air quality, animal health, or well performance. Those observations can help identify where investigation is needed. But conclusions about contamination and responsibility should be reserved until representative samples have been analyzed by a qualified laboratory and the results have been evaluated in their full environmental and geological context.
For landowners, attorneys, regulators, and industry stakeholders, the takeaway is straightforward: good environmental forensics neither dismisses a concern nor assumes its cause. It follows the evidence.
How Medusa Analytical Can Help
Medusa Analytical applies advanced analytical chemistry and a weight-of-evidence framework to questions involving groundwater contamination, subsurface brine migration,oil and gas operations, industrial releases, and environmental point source attribution. Our experts can assist with sampling strategy, laboratory-data review, identification of analytical gaps, interpretation of chemical and isotopic evidence, and the communication of complex findings in litigation and regulatory matters.
If a groundwater result raises more questions than it answers, the appropriate next step is not speculation—it is a scientifically defensible investigation.
Research discussed: Hildenbrand, Z. L., Carlton, D. D. Jr., Wicker, A. P., Habib, S., Stigler Granados, P., & Schug, K. A. (2020). “Characterizing anecdotal claims of groundwater contamination in shale energy basins.” Science of the Total Environment, 713, 136618. https://doi.org/10.1016/j.scitotenv.2020.136618