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In Pennsylvania, fracking discharges were banned in 2011, but traces prior to the ban are still visible in aquatic environments.
Frack the environment
Hydraulic fracturing (or hydraulic fracturing) is a process by which oil companies can recover otherwise inaccessible reserves. shale gas. As its name indicates, it is to use a mixture of water and chemicals (called fracturing fluid) under high pressure to create a fracture system allowing the gas to Escape to the surface, where he can be captured.
Illustration of hydraulic fracturing and related activities. Image credits: US Environmental Protection Agency.
Fracturing is controversial for a number of reasons. It uses massive amounts of water, it seems to cause an increase in seismicity and, of course, leaks. Creating a system of cracks a few kilometers underground is a challenge, but it is much more difficult to ensure that the system is waterproof and does not allow leaks. Naturally, many people fear that the fracturing fluid or the gas itself will leak to the surface, infiltrating into the soil and water reserves – which has already been observed in some wells.
But the disposal of used fracturing water is also a major problem with lasting consequences.
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"Freshwater pollution is a major concern for ecological and human health," said David Gillikin, professor of geology at Union College and co-author of a new study. "It is important to find ways to retroactively document this pollution in order to shed light on what is happening in our waterways."
In their new article, Gillikin and his collaborators report the discovery of high concentrations of strontium, an element associated with oil and gas sewage, in the shells of freshwater mussels downstream of the disposal sites. fracking wastewater.
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Image credits: Engbretson Eric, USFWS.
In a way, freshwater mussels look a bit like trees: they can provide a lot of information about the environmental quality of the water in which they live, just as tree rings provide information on past climate events. Because they feed by filtering water, the mussels retain a trace of the water quality of the past, which can be studied.
"Freshwater mussels filter the water and when they develop a hard shell, the shell material registers some of the quality of the water over time," he said. Nathaniel Warner, assistant professor of environmental engineering at Penn State. "Like tree rings, you can count the seasons and years in their shells and have a good idea of the quality and chemical composition of the water for specific periods of time."
After use, the fracturing fluid is treated and cleaned – but this process is not perfect. In 2011, biologists found that despite this treatment, water and sediment downstream of the fracking wastewater disposal sites still contained disturbing amounts of fracking chemicals. The water was contaminated and had, in turn, affected the aquatic life, causing considerable damage. After this was revealed, Pennsylvania banned all fracking wastewater treatment facilities from releasing water into the ecosystem. But the effect of water released before the ban is still not clear.
To shed light on this project, researchers have collected freshwater mussels from the Alleghany River, both upstream and downstream of a sewage disposal facility in Warren, in Pennsylvania. They also collected mussels in two other rivers – Juniata and Delaware – for which no history of oil and gas spills had been reported for comparison purposes.
In particular, they examined isotopes of strontium, which in this context can be used as a smoking gun for sewage fracturing. They also analyzed the isotope of oxygen to identify the year and the season. Unsurprisingly, they found high concentrations of strontium in the shells of freshwater mussels collected downstream of the facility, while all others showed no significant elevation. But all did not go as planned.
Despite the 2011 ban, strontium levels did not immediately drop. Instead, it took a while before the decrease was visible, and the decrease was quite slow. This suggests that even in years when fracking water has not been returned to the ecosystem, the effects are still visible.
"We know that the development of Marcellus has affected downstream sediments for tens of kilometers," Warner said. "And it seems like it could still be affected for a long time. The short time frame in which we authorized the release of this waste could leave a long legacy. "
Given the extent of modern fracturing, this is of particular concern. According to the US Department of Energy, 95% of new wells drilled today are hydraulically fractured.
"Wells get bigger, they use more water, they produce more wastewater, and that water has to go somewhere," Warner said. "Making the right choices to manage this water will be vital."
This study then shows that even a few years of process could have long-term negative consequences. This also suggests that freshwater mussels can be used to investigate potential infiltration at oil sites, as conventional oil drilling can also cause a similar type of pollution.
Journal Reference: Thomas J. Geeza, David P. Gillikin, Bonnie McDevitt, Katherine Van Sice and Nathaniel R. Warner. Accumulation of metals in Marcellus oil and gas sewage in freshwater mussel shells. Science and technology of the environment2018; 52 (18): 10883 DOI: 10.1021 / acs.is.8b02727
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