Chemical clues found for methane leaks caused by fracking

Methane can seep from underground deposits into people’s well water through leaks occurring naturally or those caused by nearby hydraulic fracturing, or fracking, operations. Such leaks are a concern because methane is a greenhouse gas and because it can build up and cause explosions. Now researchers report chemical signatures indicative of methane leaks tied to fracking in the Marcellus Shale, a rich gas deposit in the Appalachian Basin (Proc. Natl. Acad. Sci. USA 2018, DOI: 10.1073/pnas.1809013115).

For six years, Pennsylvania State University geochemist Susan Brantley has been studying the water chemistry and geology at Sugar Run, outside Hughesville, Pa. The area has a high density of shale gas wells that were drilled between 2008 and 2012, and researchers including Brantley have reported methane leaking into the region’s potable water supply. But there is natural background leakage in the area, so it has been difficult to connect the presence of methane in the water with hydraulic fracturing.

By sampling ground and surface water, the Penn State researchers found a chemical signature to make the connection. They observed that levels of dissolved iron and sulfate were elevated in water samples containing high levels of methane from areas with fracking operations. But samples with methane present from nonfracking areas had normal iron and sulfate levels.

Methane does not have any direct health effects, but downstream chemical changes might, Brantley says. Microbes feed on the hydrocarbon, creating a reducing water chemistry that can dissolve metals and release sulfates. Brantley says homeowners concerned about fracking’s effects on their water quality could look for these chemical signatures in a typical analysis of their well water.

David Dzombak, who studies water quality at Carnegie Mellon University, is impressed by the environmental forensic analysis. But he says to truly understand the impact of fracking on ground and surface water, government, industry, and scientists need to work together on prospective studies throughout the life cycle of a well.