Methane concentrations in streams reveal gas leak discharges in regions of oil, gas, and coal development

As natural gas has grown in importance as a global energy source, leakage of methane (CH₄) from wells has sometimes been noted. Leakage of this greenhouse gas is important because it affects groundwater quality and, when emitted to the atmosphere, climate. We hypothesized that streams might be most contaminated by CH₄ in the northern Appalachian Basin in regions with the longest history of hydrocarbon extraction activities. To test this, we searched for CH₄-contaminated streams in the basin. Methane concentrations ([CH₄]) for 529 stream sites are reported in New York, West Virginia and (mostly) Pennsylvania. Despite targeting contaminated areas, the median [CH₄], 1.1 μg/L, was lower than a recently identified threshold indicating potential contamination, 4.0 μg/L. [CH₄] values were higher in a few streams because they receive high-[CH₄] groundwaters, often from upwelling seeps. By analogy to the more commonly observed type of groundwater seep known as abandoned mine drainage (AMD), we introduce the term, “gas leak discharge” (GLD) for these waters where they are not associated with coal mines. GLD and AMD, observed in all parts of the study area, are both CH₄-rich. Surprisingly, the region of oldest and most productive oil/gas development did not show the highest median for stream [CH₄]. Instead, the median was statistically highest where dense coal mining was accompanied by conventional and unconventional oil and gas development, emphasizing the importance of CH₄ contamination from coal mines into streams.