Every time we breathe, we inhale trace amounts of methane, one of the planet’s most powerful greenhouse gases.
Methane gas — which can be released both naturally and from man-made sources — is a primary component of the natural gas that fuels our kitchen stoves, heats our hot water, and powers the furnace that keeps our homes warm in the wintertime. However, when methane gas leaks into groundwater systems and into the atmosphere, it sparks environmental and climate change concerns. Underground methane can have negative impacts on drinking water quality, and contributes to greenhouse gas emissions if it escapes into the atmosphere.
Combined approaches yield unexpected results
A multidisciplinary team from the Department of Geoscience joined up with researchers from the University of Guelph and the University of British Columbia for an unprecedented look into how leaking methane acts in shallow groundwater. The study was published last week in Nature Geoscience. Over an eight-month observation period, the team injected a controlled amount of methane gas into a shallow groundwater body at Canadian Forces Base Borden in Ontario, and followed its fate.
“To study how methane behaves in groundwater, we need to know in what direction it flows, how quickly it migrates, and how the gas reacts with water constituents, minerals and micro-organisms in the aquifer,” explains co-author Bernhard Mayer, a geochemist and professor.
Using sophisticated monitoring equipment and techniques, the team set out to track how far the gas moved, and how much of it leaked towards the atmosphere or was consumed by micro-organisms.
The team used ground-penetrating radar and chemical monitoring approaches, which allowed them to map how far the gas plume migrated in the subsurface. Their findings indicated that approximately half the methane went into the atmosphere, and half of it remained in the aquifer. Part of the methane persisted in the groundwater for more than the observation period, and travelled farther than the researchers had anticipated.
Kay Kuloyo, an Eyes High PhD student, worked with Marc Strous and postdoctoral scholar Emil Ruff to measure the impact that methane had on the micro-organisms in the groundwater. Their findings indicated that the micro-organisms responded to the presence of the methane, and seemed to be “getting ready” to consume the methane via a process called natural attenuation.
“Because these micro-organisms can consume methane, they can potentially be used as bioremediation agents. With high enough numbers of micro-organisms, and under the right conditions, they could do the job of removing the methane,” says Kuloyo, who notes that limited oxygen in the deeper parts of the investigated aquifer prevented the micro-organisms from carrying out their functions. “In the shallower parts of the aquifer, closer to the surface, the micro-organisms were more active and the numbers were higher,” he says.
“In the long run, the micro-organisms may do the job of removing the methane entirely for small methane leaks provided suitable geochemical conditions exist,” says Mayer.
Better monitoring of gas migration can help inform environmental policies
Knowing how methane behaves in groundwater is arguably of particular importance in Alberta, the backbone of Canada’s natural gas industry. Methane does occur naturally in many aquifers, but a potential culprit of methane contamination in groundwater is also leakage from energy wells drilled to produce natural gas and oil.
“Such leaks may occur especially along some older wells, where the sealing cement deteriorates or breaks down,” Mayer explains. “In these cases, there is potential for fugitive gas to migrate upward. Because gas is buoyant, it wants to come to the surface, which is one of the main reasons why methane may come to impact shallow groundwater.”
Fortunately, Mayer says, engineering solutions exist for re-sealing leaky wells, and the province is already working diligently to find out where the most significant issues occur.
“There’s lots of background natural methane in groundwater in the province, and it’s possible that the impacts of fugitive methane from leaky energy wells might be minimal,” adds co-author Cathy Ryan, also a professor in the Department of Geoscience.
“Understanding more about what we can interpret from surface and groundwater investigations about where fugitive gas leakage is happening might help improve the remediation success for these wells.”
The team’s findings provide important insight that will help other researchers and government bodies understand methane gas contamination of shallow groundwater.
Since the Alberta government has committed to reducing methane emissions into the atmosphere by 45 per cent by 2025, Mayer says the ability to better monitor gas migration is important. “Understanding methane emissions and differentiating natural from anthropogenic sources is an important ingredient in benchmarking our current emissions,” he explains.
Adds Kuloyo, “This is arguably the first time this kind of experiment has been carried out. We now have a better understanding of what actually happens, or what might happen, to methane in groundwater during a methane contamination event.”
The study was funded by an NSERC Strategic Project Grant.