Abstract
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.
Highlights
A common water quality impact related to shale gas development is contamination by fugitive migration of natural gas (e.g., Brantley et al, 2014; Cahill et al, 2017; Hammond et al, 2020; USA Environmental Protection Agency (US EPA), 2016; Vengosh et al, 2014; Wen et al, 2017, 2016)
Natural gas leakage is problematic when CH4 escapes to the atmosphere, as this greenhouse gas has a warming potential 84 times that of carbon dioxide on a 20-year timescale (Myhre et al, 2013)
Hydrocarbon Development in Pennsylvania We focused on Pennsylvania (PA), the center of the current Marcellus shale development boom, because it has a long history of conventional hydrocarbon development
Summary
A common water quality impact related to shale gas development is contamination by fugitive migration of natural gas (e.g., Brantley et al, 2014; Cahill et al, 2017; Hammond et al, 2020; US EPA, 2016; Vengosh et al, 2014; Wen et al, 2017, 2016). The extent and impact of methane leakage is unknown even though more than 4 million oil and gas wells have been drilled worldwide since the mid-1800s (Davies et al, 2014). To explore the impacts from leaking methane into water resources, we measured hydrochemistry of streams and seeps in the northern Appalachian Basin where the earliest commercial oil well was drilled in 1859 and drilling continues today into both conventional and unconventional (shale) reservoirs (PA DEP, 2018b). We hypothesized that streams might be most contaminated by CH4 in the region with the longest history of hydrocarbon extraction activities
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